In this paper, dissimilar aluminum (Al) and copper (Cu) metals were joined together using ultrasonic metal welding (USMW), a solid-state welding technology. From the perspective of increasing the base metal welding contact area, the Cu/Al mating surface was innovatively prepared and ultrasonically welded. A comprehensive analysis was carried out on the forming quality, welding process temperature, interface structure, and mechanical properties of the welded joint. Defect-free and squeezed welds were successfully achieved by machining novel patterns especially C4-2. The results indicated that the reference joint can withstand higher loads, but its failure mode is very unstable. Failure may occur at welded interface and on the aluminum plate which is not good for actual production applications. Welded strength of reference joint was 4493 N, and the welded strength of C4-2 joint was 3691 N. However, microscopic analysis discovered that the welded joint internal morphology in C4-2 was more stable and hardest. C4-2 joint has successfully achieved higher tensile strength and stability under failure displacement of 38% which is higher than C4-1 joint. All welded joint failures occurred on aluminum plate, indicating that the joint strength is higher than that of bottom plate. This is attributed to unique structural design of chiseled joint and lesser thickness. SEM–EDS results investigated that the C4-2 joint can transfer more energy to area under welding head which provides welded joint with robust diffusion capacity. The transition layer has a higher thickness while the energy transferred to area away from welding head was smaller. Thickness of transition layer is significantly reduced and reference joint has similar diffusion characteristics. Conversely, the thickness of the transition layer at the corresponding position is smaller than that of pattern morphology. This is due to overall smaller thickness of the pattern joint which is more conducive to the transfer of welding energy. The surface-conformed approach and comprehensive temperature analysis provide a new understanding of USMW in dissimilar welded metals. © The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature 2024.

Ultrasonic wire welding is considered a method of choice for creating reliable interconnects in electronics industry including aerospace, batteries and electric vehicles. In this paper, ultrasonic welding tests between EVR252 copper wire and substrate are carried out. Novel pattern morphologies are machined on substrates to explore its influence on mechanical properties of welded joint. Patterns are divided into three different categories e.g., original surface, vertical and horizontal shapes. Cracks, microstructure strength and tensile properties of welded joint are studied and its joining mechanism is analysed. Compared with the reference substrate (S1), the welded joint performance of the longitudinal patterns (S2, S3, S4) has been improved, among which the longitudinal pattern (S4) has the most significant improvement (+ 15%). Likewise, the performance of transverse pattern (S5) welded joints is relatively poor (− 16%). The microstructural analysis using SEM has revealed predominant joint strength on Cu wire surface while maintaining rock-like and compact properties of S4 substrate. Upper side of wire-harness compactness is frequently observed due to vertical direction of patterns on substrate and also increases the strength of welded joint. Values of failure load, failure displacement and failure energy absorption were increased by 7.9%, 72% and 35% for S2, 6.1%, 75% and 42% for S3 and 15%, 87% and 113% for S4 compared to S1. Failure modes of welded joints are mainly characterized into: 1-poor ductility or rupture (no deformation) failure in vertical 3-line pattern joints 2-cylindrical deep holes failure in vertical 3-line zigzag pattern joints and 3-bulging effect failure in horizontal 3-line zigzag pattern joints. Point and line scans EDS measurement were performed to investigate weaker and stable trends of different locations in welded joints. In S4 substrate, 17.9% carbon content at the position of welded joint was investigated, leading to content of less oxides and fraction impurities. However, S1 weld zone contains 38.7% carbon content which can weaken welded joint and reduce durability. Graphical Abstract: (Figure presented.). © The Author(s) under exclusive licence to The Korean Institute of Metals and Materials 2024.

Ultrasonic metal welding machines are suitable for various complex applications (e.g., battery tabs) through unique mechanical design, special pressure application methods and high-precision welding. This work reports the weldability, forming quality and fractographic analysis of copper multilayered welded joints which were studied by SEM-EDS characterization, micro-hardness testing and tensile testing based on ultrasonic double roller welding (UDRW). Three groups of process parameters (A, B and C) were established to investigate the performance, production quality and welded joint surface interconnections. The tensile testing results of sample under parameter 3 in group A [S-P3(A)] indicate the maximum tensile strength of 69.859 N in T-peel test while the average tensile strength has increased by 58.525 N due to rise in welding time from 2 sec to 5 sec. The results analysis indicates that welding quality features in S-P3(A) joints under 4 bar, 100 mm/s, 45 % have been exploited. The over-welded zone was transformed into good-welded zone. The micro-cracks, fatigue stations and peeling texture in multilayers were reduced. It was found that when the welding energy was 10000 J then the tearing edges and interlayers cracks were minimized while keeping the other parameters constant. Moreover, when the amplitude increased up to 50 %, then numerous micro-cracks and micro-fissure stations were created, which leads to the occurrence of fracture in multi-layer welded joint. The EDS study investigated that the complex features are formed at the interface junction of sample 3 S3(A) in multilayer welds. The complex multilayer microstructures can induce and produce unique hardness properties for battery manufacturing. It leads to high quality and durable welds. Eventually, it is experimentally demonstrated that robust 40 layer welded joints can be obtained by the UDRW process. Data availability: The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request. © 2024 The Authors

With the increased focus on reducing carbon emissions in the automotive industry, more advanced materials are introduced to reduce the vehicle weight, and more complex component geometries are designed to both satisfy customer demands and to optimize the vehicle aerodynamically. With the increase in component complexity, the strain paths produced during the forming operation of car body components often display a highly non-linear behavior which makes the task of failure prediction during the manufacturing feasibility studies more difficult. Therefore, CAE engineers need better capabilities to predict failure induced by strain path nonlinearity. This study proposes a new tool designed for creating bi-linear strain paths, by performing a pre-strain of a sheet large enough to cut out Nakajima specimens to perform the post-straining in any direction. From five pre-straining tests the tool present a stable pre-straining operation with a uniform strain field in a radius of 100 [mm] from the centre, corresponding to the region of interest of a Nakajima specimen. From the five pre-strained samples, different Nakajima specimens are cut transverse and longitudinal to the rolling direction and a failure prediction approach in an alternative, path independent evaluation space was used to predict the onset of necking with promising results.

With the increased demand for application of sustainable materials and lightweight structures, the sheet metal forming industry is forced to push existing materials to the limits. One area where this is particular difficult is when it comes to assessing the formability limit for sheet edges. For decades, the ISO-16630 Hole Expansion Test (HET) has been the industry standard for expressing the edge formability of sheet metals through the Hole Expansion Ratio (HER). However, in recent years, this test has been criticized for its high scatter in results for repeated experiments. This scatter has been suspected to be caused by the operator-reliant post-processing of the test, or variations in the cutting conditions for the different test specimens. This study investigates the impact of shifting the evaluation point of the test from the through-thickness crack to the onset of surface failure on the reported scatter, as well as performs inverse modeling of the Hole Expansion Test to obtain an edge limit strain value.

An area in the automotive industry that receives a lot of attention today is the introduction of lighter and more advanced material grades in order to reduce carbon emissions, both during production and through reduced fuel consumption. As the complexity of the introduced materials and component geometries increases, so does the need for more complex failure prediction approaches. A proposed path-independent failure criterion, based on a transformation of the limit curve into an alternative evaluation space, is investigated. Initially, the yield criterion used for this transformation of the limit curve was investigated. Here it was determined that the criterion for the transformation could not be decoupled from the material model used for the simulation. Subsequently, the approach using the transformed limit curve was tested on an industrial case from Volvo Cars, but a successful failure prediction was not obtained. © 2022 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

As new and more advanced sheet metal materials are introduced to the market, more accurate techniques for determination of failure limits are needed. One area that needs attention is edge formability, where the ISO-16630 standardized Hole Expansion Test currently is used to express this through the Hole Expansion Ratio. Over the years, this standard has been criticized for producing a large scatter in repeated tests. This paper investigates a new setup for the Hole Expansion Test which introduces draw beads into the setup to ensure sufficient restraining of the specimen during the test in an effort to reduced the scatter. In total 62 tests of a DP800 steel alloy were executed, but a large scatter in the results were still seen. It was therefore concluded that a lack of restraining force in the Hole Expansion Test was not the primary cause of the reported scatter seen in other tests.

In this paper, we present an investigation of ultrasonic welding performance for 25 mm2 copper wire and T2 copper plate across various welding parameters using orthogonal experimentation. The objective of this work was to explore the influence of operational parameters on the resulting welds. A comprehensive study of the mechanical properties and microstructure of the copper wire-to-copper plate joint was carried out using a series of sophisticated instruments. It includes a universal tensile machine, resistance measuring equipment, SEM, EDS and temperature measuring tool. This multifaceted approach enabled a detailed analysis of the joint's integral features and properties. This provides further insight into its performance and durability. Findings indicate that welding pressure has the most significant effect on welded joints. The optimal combination of parameters is achieved with the welding energy set at 6000 J, the welding amplitude at 85% and the welding pressure at 260 kPa. In different sets of welding parameters, joint strength is positively related to welding parameters and increases with increasing welding parameters. Joint resistance decreases with increasing joint tensile load and conductivity can be used to evaluate ultrasonic welding. It has been found that the development of the welded joint is achieved gradually in a direction moving inwards from the welding tool head, exhibiting a methodical forming process. Three distinct failure modes are observed in welded joints such as joint pullout, joint tearing and busbar breakage. The peak temperature during the welding process was recorded at 373 °C which indicates that the ultrasonic welding is a solid state connection. © The Author(s), under exclusive licence to Korean Society for Precision Engineering 2024.

The ultrasonic metal welding technology is widely promoted as a new connection approach in the field of current energy vehicle wiring harness connection. In the present investigation, low-temperature mechanical properties of slotted and normal terminals were studied. The EVR 25 mm2 copper wires are selected for welding using ultrasonic wire harness welding with two different structures of T2 copper terminals. Then, a more stable joint structure under the same welding parameters is investigated through tensile tests at − 30 °C and 25 °C. The results showed that the ST joint has higher static mechanical properties than the NT joint at 25 °C and the peak load of the joint is increased. In addition, the results investigated that the performance and welded interface texture of ST joints is reliable than NT joints under 25 °C, the maximum joint load is increased by 12.93% under − 30 °C, the joint energy absorption is increased by 87.58%, and ST joint stability is better and safer in actual production applications. At the same welding parameters, the ST joints have less neck contraction at 25 °C and the ligamentous sockets are smaller and densely welded surfaces. The failures of ST joints and NT joints are investigated under the same welding parameters. The energy loss during the ST joint welding process is smaller and the welding effect is better and advantageous. The SEM findings showed that the failure of the ST joint and the NT joint is different and the tensile strength of the ST joint is greater under the same low-temperature conditions. © International Institute of Welding 2024.

Self-piercing riveting process is a new connection technology with excellent performance, green, and high efficiency. It can realize the connection of the similar, different, and multi-layer light alloy sheet materials and is widely used in new energy vehicles and other fields. Furthermore, it is becoming one of the critical technologies for achieving a lightweight body. However, because the self-piercing riveting joint is a typical tight connection component, fretting damage is prone to occur under the action of alternating stress or vibration, resulting in premature joint fatigue failure. This paper uses 5A06 aluminum alloy sheet material to carry out self-piercing riveting and ultrasonic self-piercing riveting composite connection tests under different ultrasonic welding tool heads. Based on the tensile-shear and electron microscope tests, the effect of ultrasonic vibration on the static properties of 5A06 aluminum alloy self-piercing riveted joints was studied. The results show that: ultrasonic vibration can effectively improve the static properties of self-piercing riveted joints; the ultrasonic metal welding will form a solid phase of welding between the sheets during the composite self-piercing riveting, which is the fundamental reason for improving the mechanical properties of the combined joint; the area of ultrasonic metal welding joints affects the mechanical properties of self-piercing riveted joints; the degree of ultrasonic solid-phase welding is higher when the welding area is more extensive; ultrasonic welding will increase the temperature of the rivet, which will affect the stability of the joints to a certain extent. © 2023 Harbin Institute of Technology. All rights reserved.

Packages are the means of preservation, distribution and convenience of use for food, medicine and other consumer products. The introduction of a new package-opening technique for a better opening experience requires additional prototype development and physical testing. In order for the design process to be more rapid and robust, finite element (FE) simulations are widely used in packaging industries to compliment and reduce the amount of physical testing.

The goal of this work is to develop some building blocks for complete package-opening FE-simulation. To begin with, the study focuses on mechanical testing of packaging materials’ fracture and delamination; especially shear fracture. Use of tools like digital image correlation (DIC) and scanning electron microscope (SEM) greatly aided to the strain measuring technique and observation of fractured and delaminated surfaces respectively.

A modified shear test specimen for polymer sheet testing was developed and its geometry was optimized by FE-simulation. A geometry correction factor of shear fracture toughness for the proposed specimen was derived based on linear elastic fracture mechanics (LEFM). It was found that the specimen ligament length should vary between twice the thickness and half the ligament width of the modified shear specimen to measure the essential work of fracture.

Thin-flexible laminate of low-density polyethylene (LDPE) and aluminium (Al) is another key packaging material addressed in this study. The continuum and fracture testing of individual layers provided the base information and input for FE-modelling. The FE-simulation material parameters were calibrated from the physical test response through inverse analysis. Identification process of the laminate interface fracture energy (G_c) from peel tests was studied experimentally and theoretically. A successful FE-simulation optimization framework using artificial neural network and genetic algorithm was developed for the calibration of G_c. To address the challenge in quantifying shear G_c of laminate with very thin substrates, a convenient test technique was proposed. In a separate case, the tearing response of LDPE/PET (polyethylene terephthalate) laminate was studied to examine crack propagation, crack path deviation and delamination of the laminate in mode III fracture. Several tear EWF evaluation theories were proposed along with a cyclic tear test method.

Packages are the means of preservation, distribution and convenience of use for food, medicine and other consumer products. Package opening is becoming complicated in many cases because of cutting cost in design and production of opening techniques. Introduction of new package opening technique, material or geometry for better opening experience, forces new design measurements which require a large number of prototype developments and physical testing. In order to achieve more rapid and accurate design, Finite Element Method (FEM) Simulations are widely used in packaging industries to compliment and reduce the number of physical testing.

The goal of this work is to develop the building blocks towards complete package opening simulation. The study focuses on testing and simulation of shear fracture and shear delamination of packaging materials. A modified shear test specimen was developed and optimized by finite element simulation. Test method was validated for High-density polyethylene (HDPE) and Polypropylene (PP). The developed method has been accepted by international standards organization ASTM. Based on linear elastic fracture mechanics, a geometry correction factor of shear fracture toughness for the proposed specimen was derived. The study concluded that, for ease of opening, HDPE is a more favorable material for screw caps than PP. When performing the experiment with the shear specimen to find essential work of fracture, the ligament length should be varied between twice of the thickness and half of the width of the specimen ligament.

Multi-layered thin laminate of Low-density polyethylene (LDPE) and aluminum (Al), also known as Al/LDPE laminate, is another key object addressed in this study. Continuum and fracture testing of individual layers provided the base information and input for numerical modeling. The propagation of an interfacial pre-crack in lamination in Al-LDPE laminate was simulated using several numerical techniques available in the commercial FEM solver ABAQUS, and it was concluded that using the combination of VCCT technique to model the interfacial delamination and coupled elasto-plastic damage constitutive for Al and LDPE substrates can describe interfacial delamination and failure due to necking. It was also concluded that the delamination mode in a pre-crack tip is influenced by the ratio of fracture energy release rate of mode I and II. To address the challenge in quantifying shear energy release rate of laminate with very thin substrate, a convenient test technique is proposed. Additionally, scanning electron microscopic study provided useful information on fractured and delaminated surfaces and provided evidence that strengthened the conclusions of this work.

The proposed test methods in this work will be crucial to measure the shear mechanical properties in bulk material and thin substrates. Laminates of Al and LDPE or similar material can be studied using the developed simulation technique which can be effectively used for decision support in early package development.

Large displacement peel was studied for cases where a compliant substrate leads to a large value of the root rotation. An existing simplified beam model to calculate the peel fracture energy was modified to allow for a kinematic hardening beam model of the foil. The steady-state peel force and the root rotation were used as input data to the resulting analytical beam model. Test results from the literature were analysed. A more elaborate finite element model was also studied, using cohesive elements for the interface layer between the foil and the substrate. The cohesive zone parameters used were the fracture energy, the cohesive strength and a shape parameter. An optimization scheme for the cohesive zone parameters was developed and optimized against experimental steady-state peel force and root rotation. The optimization scheme was effective to characterize the cohesive parameters. The method yields similar values of fracture energy for the two peel angles, with the one for 180degree being slightly higher than for 90degree. The difference in fracture energies for different peel angles suggests that the fracture energy can be mode dependent.

Thin laminates of Aluminum (Al) and Low Density Polyethylene (LDPE) is an essential constituent of food packages where these two substrates are bonded together with a thin layer of LDPE acting as adhesive. Noticeably, Al is a low ductile/quasi brittle material whereas, LDPE is highly ductile.  The mechanism of delamination and strength of bond between the interfaces dictates the continuum and damage behaviour of this composite. However, measuring the shear delamination is challenging as conventional test methods have limitations when the substrates are very thin. This study explains a method that uses uniaxial tensile testing on the pre-cracked specimen of this composite to find energy dissipation due to shear delamination and successfully use it in Finite Element Simulation in Abaqus. The delamination was observed in a narrow strip region close to fracture surfaces and measured with special visualization aid. Similar response was found in FEM simulation. Scanning Electron Microscopic (SEM) study of delaminated interface confirms the domination of shearing. In a cohesive zone modelling in Finite Element Simulation software, the shear delamination energy was used as input parameter along with an arbitrary bi-linear cohesive law. The substrates’ constitutive response was modelled considering non linear plasticity and softening. Finally proposed delamination energy separation method was validated with comparison between the physical tests and FEM simulations.

This research has investigated the essential work of fracture (EWF) from trouser tear test of polyethylene terephthalate (PET), low-density polyethylene (LDPE) films and their corresponding laminate using a convenient cyclic tear test method. Propagation of tear crack in these thermoplastics deflects from the initial crack path due to the material anisotropy. An improvement to a two-zone tear model for determining tear EWF was proposed for LDPE-like materials. Energy dissipation due to non-uniform bending of the trouser-legs was determined to be significant in EWF calculation of tearing and this was therefore considered in this study. To measure the tear EWF in laminates, contribution from delamination energy dissipation was accounted for.

This paper focuses on information-driven engineering, where information is gathered by means of innovation for people and by the people. This case study was carried out on innovation of a manual wheelchair. Through active participation of person with disability (direct users) and their carers (indirect user), knowledge awareness of the early design was increased. Computer aided engineering tools were used for the development of virtual prototype (VP) and after further feedback from direct and indirect users design was adjusted. Additionally, Physical prototype was built to practically demonstrate the new features to users and finally the prototype was readjusted to bridge user requirement even more. This innovation process identifies additional improvement aspects and contributes beyond fundamental personal needs and increases well being.

The aim of this work is to evaluate the effect of different specimen dimension and crack length on the mechanical properties of HDPE (High Density Polyethylene) which is often used in the packaging industry. In the experimental part, two main specimens are chosen. One is dog-bone shaped tensile specimen for finding the tensile material properties. The other one is modified shear specimen for studying the shear damage. A corresponding numerical simulation is done by applying a commercial Finite Element Analysis (FEA) program ABAQUS. In addition, the microscopic analysis was performed to observe the fracture surface of specimen after the test with scanning electron microscope (SEM). A series of experiments and simulation were processed and results show that fracture initiation and propagation behavior in the shear specimen is sensitive to the size of the pre-crack (notch) and shear strain at failure.

Shear fracture toughness is an important material behavior that needs to be determined and considered in many industrial fields. At the same time, shear testing is one of the complex material testing areas where available methods are few, often need special arrangements, and most of the methods do not strictly satisfy the definition of pure shear. In this study, a modified shear test specimen was proposed to measure the shear fracture toughness by uniaxial loading in a tensile testing machine. High density polyethylene (HDPE) was used as test material for the experiments. The specimen was created in order to suit the most common used tensile test machine. The specimen was then optimized by using finite element analysis (FEA) to find the geometry and the size of the pre-notch to avoid the mixed mode loading and minimize effects of normal stresses. For the specimen in discussion, an upper and lower limit of usable ligament length can be found. A method for determining the fracture toughness was discussed according to the essential work of fracture. Finally, an example of a special application of the proposed specimen was presented where the variation of shear strength of controlled delamination material (CDM) was measured.

This study analyses the tensile mechanical behaviour and deformation of neck i.e localization initiation, propagation and fracture of injection-moulded polymer composed of high-density polyethylene (HDPE) as a function of initial stress triaxiality. Three different specimen geometries namely i) Simple tension, ii) Plane strain and iii) Shear specimens were punched from injection-moulded HDPE plates and tested experimentally in uniaxial tension to introduce different stress triaxialities. These specimen geometries used are standard for the material characterization of sheet metals. However, for plate polymer materials such specimen geometries have not comprehensively been studied earlier. Standard shear specimen geometry has been further optimized in this work using finite element models to restrict unwanted out-of-plane deformations arising at large deformation. The digital image correlation (DIC) technique is used to acquire the full field deformation and in particular the localized strains in the neck region of the specimens. Based on the major-minor strain paths from DIC-measurements stress triaxiality has been calculated. It is challenging to follow the stochastic pattern at larger local strain in DIC and hence the strain at failure has been measured using orthogonal grid lines on the specimen surface. Finally, strains at neck-initiation and failure at three different stress triaxialities are reported for injection-moulded HDPE in two material orientations. It is observed that within the elastic limit the stress triaxialities obtained from the experimental tests were close to the ideal values found in the literature and neck-initiation strain is strongly dependent on the stress triaxiality. However, as neck initiates and propagates, the triaxialities for all geometries shift closer to the measured value in a simple tension specimen i.e. 0.33 limiting the effect of the initial triaxiality on failure strain.

Thin laminates of Aluminum (Al) foil and Low Density Polyethylene (LDPE) film are essential constituents of food packages where these two substrates are bonded together with a thin layer of LDPE acting as adhesive. Noticeably, Al is a low ductile/quasi brittle material, whereas LDPE is highly ductile. The mechanism of delamination and strength of bond between the interfaces dictates the continuum and damage behavior of this composite. However, measuring the shear delamination properties is challenging as conventional test methods have limitations when the substrates are very thin and flexible. This study explains a tentative method that uses uniaxial tensile testing on the pre-cracked specimen of this composite to find energy dissipation due to shear delamination and successfully uses it in Finite Element Simulation in Abaqus. The delamination was observed in a narrow strip-like region close to fracture surfaces and measured with special visualization aid. A similar response was found in FEM simulation. Scanning Electron Microscopic (SEM) study of delaminated interface confirms the delamination to be shear in nature. In a cohesive zone modeling in Abaqus, the measured shear delamination energy was used as input parameter along with an arbitrary bi-linear cohesive law for validation of the experimental measurement.

Shear fracture toughness is an important material behavior that needs to be determined and considered in many industrial fields. At the same time, shear testing is one of the complex material testing areas where available methods are few and often need special arrangements. In this study, a modified shear test specimen was proposed to measure the shear fracture toughness by uniaxial loading in a tensile testing machine. High Density Polyethylene (HDPE) was used as test material for the experiments. The specimen was created in order to suit the most common used tensile test machine. The specimen was than optimized by using Finite Element Analysis (FEA) to find the geometry and the size of the pre-crack to avoid the mixed mode loading and minimize effect of normal stresses. For the specimen in discussion, an upper and lower limit of useable ligament length can be found. Finally, a method for determining the fracture toughness was discussed according to essential work of fracture.

Shear testing is one of the most complex testing areas where available methods and specimen geometries are different from each other. Therefore, a modified shear test specimen (MSTS) combining the simple uniaxial test with a zone of interest (ZOI) is tested which gives almost the pure shear. In this study, material parameters of polypropylene (PP) and high density polyethylene (HDPE) are first measured by tensile tests with a dogbone shaped specimen. These parameters are then used as an input for the finite element analysis. Secondly, a specially designed specimen (MSTS) is used to perform the shear stress tests in a tensile testing machine to get the results in terms of forces and extension, crack initiation etc. Scanning Electron Microscopy (SEM) is also performed on the shear fracture surface to find material behavior. These experiments are then simulated by finite element method and compared with the experimental results in order to confirm the simulation model. Shear stress state is inspected to find the usability of the proposed shear specimen. Finally, a geometry correction factor can be established for these two materials in this specific loading and geometry with notch using Linear Elastic Fracture Mechanics (LEFM). By these results, strain energy of shear failure and stress intensity factor (SIF) of shear of these two polymers are discussed in the special application of the screw cap opening of the medical or food packages with a temper evidence safety solution.

Stress relaxation of high-density polyethylene is addressed both experimentally and theoretically. Two types of stress relaxation testing are carried out: uniaxial tensile testing at constant test specimen length and compression testing of a 3D structure producing inhomogeneous deformation fields and relaxation. A constitutive model for isotropic, semi-crystalline polymers is also proposed. The model has the ability to model stress relaxation at different time scales. The developed model was implemented as a user subroutine in Abaqus (UMAT). The implicit integration scheme including an algorithmic tangent modulus is described in detail. The material model is calibrated by use of the uniaxial tensile tests, and the model is then validated by simulating the compression tests of the 3D structure. The model is able to describe the uniaxial tension tests well, and the comparison between the simulations and experimental testing of the 3D structure shows very good agreement. © 2024, The Author(s).

5A06 aluminum alloy and TA1 titanium alloy were selected for the connection tests of flow drill screw, ultrasonic clinch and ultrasonic self-piercing riveting. The influence of plate overlap methods on mechanical properties of each group of joints was studied by static tensile tests. The results show that the mechanical properties of the flow drill screw joints and the ultrasonic self-piercing riveted joints are significantly improved when the soft plate is on top during the riveting process. The plate overlap method has little effect on the ultrasonic clinch joint. Flow drill screw joints have the best cushioning and shock absorption performance, but the stability is poor, and it is more limited when applied to body structures. Ultrasonic clinch joints have low cost and simple process, but poor shear resistance and are not suitable for body structures subjected to high stress. Compared with the other two connection methods, the ultrasonic self-piercing riveted connection has the best stability, the best tensile resistance and shear stiffness, and is suitable for much of the structure in lightweight field of automobile body. © 2023 Beijing Res. Inst. of Mechanical and Elec. Technology. All rights reserved.

Ultrasound welding technology is widely applied in the field of industrial manufacturing. In complex working conditions, various factors such as welding parameters, equipment conditions and operational techniques contribute to the formation of diverse and unpredictable line defects during the welding process. These defects exhibit characteristics such as varied shapes, random positions, and diverse types. Consequently, traditional defect surface detection methods face challenges in achieving efficient and accurate non-destructive testing. To achieve real-time detection of ultrasound welding defects efficiently, we have developed a lightweight network called the Lightweight Attention Detection Network (LAD-Net) based on an attention mechanism. Firstly, this work proposes a Deformable Convolution Feature Extraction Module (DCFE-Module) aimed at addressing the challenge of extracting features from welding defects characterized by variable shapes, random positions, and complex defect types. Additionally, to prevent the loss of critical defect features and enhance the network's capability for feature extraction and integration, this study designs a Lightweight Step Attention Mechanism Module (LSAM-Module) based on the proposed Step Attention Mechanism Convolution (SAM-Conv). Finally, by integrating the Efficient Multi-scale Attention (EMA) module and the Explicit Visual Center (EVC) module into the network, we address the issue of imbalance between global and local information processing, and promote the integration of key defect features. Qualitative and quantitative experimental results conducted on both ultrasound welding defect data and the publicly available NEU-DET dataset demonstrate that the proposed LAD-Net method achieves high performance. On our custom dataset, the F1 score and mAP@0.5 reached 0.954 and 94.2%, respectively. Furthermore, the method exhibits superior detection performance on the public dataset. © 2024 Elsevier B.V.

Self-piercing riveting (SPR) has been widely used in automobile body jointing. However, the riveting process is prone to various forming quality failures, such as empty riveting, repeated riveting, substrate cracking, and other riveting defects. This paper combines deep learning algorithms to achieve non-contact monitoring of SPR forming quality. And a lightweight convolutional neural network with higher accuracy and less computational effort is designed. The ablation and comparative experiments results show that the lightweight convolutional neural network proposed in this paper achieves improved accuracy and reduced computational complexity. Compared with the original algorithm, the algorithm's accuracy in this paper is increased by 4.5[Formula: see text], and the recall is increased by 1.4[Formula: see text]. In addition, the amount of redundant parameters is reduced by 86.5[Formula: see text], and the amount of computation is reduced by 47.33[Formula: see text]. This method can effectively overcome the limitations of low efficiency, high work intensity, and easy leakage of manual visual inspection methods and provide a more efficient solution for monitoring the quality of SPR forming quality. © 2023. The Author(s).

It is of great significance to identify all types of domestic garbage quickly and intelligently to improve people's quality of life. Based on the visual analysis of feature map changes in different neural networks, a Skip-YOLO model is proposed for real-life garbage detection, targeting the problem of recognizing garbage with similar features. First, the receptive field of the model is enlarged through the large-size convolution kernel which enhanced the shallow information of images. Second, the high-dimensional features of the garbage maps are extracted by dense convolutional blocks. The sensitivity of similar features in the same type of garbage increases by strengthening the sharing of shallow low semantics and deep high semantics information. Finally, multiscale high-dimensional feature maps are integrated and routed to the YOLO layer for predicting garbage type and location. The overall detection accuracy is increased by 22.5% and the average recall rate is increased by 18.6% comparing the experimental results with the YOLOv3 analysis. In qualitative comparison, it successfully detects domestic garbage in complex multi-scenes. In addition, this approach alleviates the overfitting problem of deep residual blocks. The application case of waste sorting production line is used to further highlight the model generalization performance of the method. © 2023, Springer Nature B.V.

In the industrial production process, unsupervised visual inspection methods have obvious advantages over supervised visual inspection methods due to the scarcity of defect samples, annotation costs and the uncertainty of defect generation. Currently, unsupervised defect detection and localization methods have demonstrated significant improvements in detection accuracy to find numerous applications in industrial inspection. Nonetheless, the complexity of these methods limits their practical application. In this paper, we integrate the FastFlow model plugin as a probability distribution by introducing a simpler and lightweight CNN pre-trained backbone. Concurrently, various training strategies are employed to optimize the 2D Flow module within the Lightweight unsupervised flow model (LightFlow). Notably, the number of model parameters in the LightFlow model is only 1/4 of the original model size of the typical Vision Transformer (ViT) model CaiT. Thereby, this offers heightened training efficiency and speed. Therefore, extensive experimental results on three challenging anomaly detection datasets (MVTec AD, VisA, and BTAD) using various CNN backbones and multiple current state-of-the-art vision algorithms demonstrate the effectiveness of our approach. Specifically, the existing method can achieve 99.1% and 95.2% image-level AUROC (area under the receiver operating characteristic) in MVTec AD and VisA, respectively. IEEE

Sheet metal forming (SMF) simulations are traditionally carried out with rigid active forming surfaces. This means that the elasticity and dynamics of presses and die structures are ignored. The only geometries of the tools included in the simulations are the active forming surfaces. One reason for this simplification is the large amount of computational power that is required to solve finite element (FE) models that incorporates elastic stamping dies. Another reason is the lack of die CAD models before the later stages of stamping projects. Research during the last couple of decades indicated potential large benefits when including elastic dies in SMF simulations. For example, for simulating die try-out or for Digital Twins of presses and dies. Even though the need and potential benefits of elastic dies in simulations are well known it is not yet implemented on a wide scale. The main obstacles have been lacking data on presses and dies, long simulation times, and no standardized implementation in SMF software. This paper presents an overview of existing methods for SMF simulations with elastic dies and discuss their respective benefits and drawbacks. The survey of methods shows that simulation models with elastic tools will be needed for detailed analyses of forming operations and also for purposes like digital twins. On the other hand, simplified and robust models can be developed for non-FEA users to carry out simple one-step compensation of tool surfaces for virtual spotting purposes. The most promising and versatile method from the literature is selected, modified, and demonstrated for industrial sized dies.

Previous research and experience points to many advantages if sheet metal forming is simulated with elastic dies. Some areas that are enabled by simulations with elastic dies are virtual spotting, improved digital twins, and improved production support. A promising method was selected from the literature, and after important modifications it is deemed to be fast and robust for simulating industrial sized dies. The method consists of meshing die solids with a coarse mesh to represent the structural behaviour of the die. The forming surfaces are then represented by a fine shell mesh connected to the solid mesh by tied contacts with an offset. With additional modifications to reduce solver time this yields a robust and flexible way of modelling sheet metal forming with elastic dies. There is an increase in preprocessing and simulation time compared to using rigid tools, but industrial dies can now be modeled within an hour and solved within a working day. It is also easy to update the model by replacing separate parts such as die solids or forming surfaces. One of the main criteria in favor of the selected approach is the realistic modeling of blankholder and cushion systems. In this paper simulations of three industrial cases are demonstrated: one case of virtual die spotting and two cases of production support. The three cases demonstrate the importance and potential of using elastic dies during virtual die tryout, production support, and for cases like digital twins and production control.

An experimental characterization of the mechanical properties in a low-density polyethylene (LDPE) film is performed in this article. Anisotropy in LDPE at different in-plane material orientations is measured from the stress–strain response and digital image correlation observations of the specimens under uniaxial tension. Finite element simulation of in-plane anisotropy of the material is carried out in Abaqus R2020 using available models like von Mises, Hill 48, Barlat Yld91, and Barlat Yld2004-18P. To express the mechanical behavior at larger strain, a suitable hardening extrapolation model is selected from a trial of several extrapolation models. To validate the simulation methods and the material characterization process, finite element simulation results such as force displacement and strain distribution are compared with the experimental data showing good agreement. Finally, a calibrated anisotropic yield model together with ductile failure criterion is shown to successfully simulate the response of precracked LDPE film under tension. Overall, this study provides valuable insights into the modeling of LDPE polymer films with and without cracks using different anisotropic yield functions and largely simplifies material characterization with some tradeoffs. Copyright © 2024 by ASTM International

In thin notched sheets under tensile loading, wrinkling appears on the sheet surface, specifically around the cracked area. This is due to local buckling and compression stresses near the crack surfaces. This study aims to numerically study the buckling behavior of a thin sheet with a central crack under tension. A numerical model of a notched sheet under tensile loading is developed using the finite element method, which considers both material and geometrical nonlinearity. To overcome the convergence problem caused by the small thickness-to-length/width ratio and to stimulate the buckling, an imperfection is defined as a small perturbation in the numerical model. Both elastic and elasto-plastic behavior are applied, and the influence of them is studied on the critical buckling stress and the post-buckling behavior of the notched sheet. Numerical results for both elastic and elasto-plastic behavior reflect that very small perturbations need more energy for the activation of buckling mode, and a higher buckling mode is predominant. The influences of different parameters, including Poisson’s ratio, yield limit, crack length-to-sheet-width ratio, and the sheet aspect ratio are also evaluated with a focus on the critical buckling stress and the buckling mode shape. With increase in Poisson’s ratio. First, the critical buckling stress reduces and then remains constant. A higher yield limit results in increases in the critical buckling stress, and no change in the buckling mode shape while adopting various crack length-to-sheet-width ratios, and the sheet aspect ratio changes the buckling mode shape.

Liquid food packages consist of various polymers films, which are bonded together with Aluminum foil (Al-foil) using adhesion or by direct heat. The main aim of this research was to define important material properties such as fracture toughness and some FE-simulation material model parameters such as damage initiation, damage evolution, and the adhesion between Al-foil and low-density polyethylene (LDPE) film. This investigation is based on both physical experiments and FE simulations in ABAQUS with and without initial cracks of different lengths for comparison purposes. The final FE model in ABAQUS was used to compare the numerical input parameters in an extensive study with the ambition to investigate the materials’ parameters in cases with or without adhesion between laminates. Finally, the relation between the theoretical and experimental results for Al-foil using linear elastic fracture mechanics and modified strip yield model were shown, and the fracture toughness was calculated for two different thicknesses of Al-foil. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

In sheet metal stamping, the occurrence of strain localization in a deformed sheet is considered a failure. As so, sheet metal's formability is conventionally evaluated using the Forming Limit Diagram (FLD), which separates the principal strain space into safety and unsafety regions by a Forming Limit Curve (FLC). This study presents an evaluation method for detecting strain localization based on Digital Image Correlation (DIC) during the experiment. The commercial DIC software ARAMIS is adopted to monitor the strain-field distribution on the deformed specimen's surface. A detailed analysis of the proposed method is presented considering Nakajima tests conducted for two automotive sheet metals: AA6016 and DP800. The identified FLC based on the proposed method is compared with that of well-established methods such as ISO 12004:2-2008 and time-dependent methods. For both investigated materials, the proposed method presents a lower FLC than the others.

This study presents a modeling approach for predicting strain localization during sheet metal stamping processes focused on automotive engineering applications. The so-called stretching-to-bending ratio, ρ, is proposed to characterize the loading conditions acting on an element during stamping processes. Then, localized strain or necking strain is suggested to be a function of ρ. Different stretch–bending tests with different tool radii, i.e., R3, R6, R10, and R50 are conducted for two automotive sheet metals, DP800 and AA6010, to identify their forming limits under combined stretch–bend loads. The calibrated necking limit curve of the AA6016 sheet is then employed in AutoForm R10 software to predict the necking and failure of a stamped panel. Agreement with the experimental observation of failure positions of the panel validates the usefulness of the proposed modeling approach in practice. © 2023 The Author(s)

This study presents a new criterion (MMFC2) for predicting the forming limit curve (FLC) of sheet metal. The strain path evolution of a critical element examined in a uniaxial tensile test is elaborated by incorporating the results of experimental measurement, finite element simulation, and theoretical prediction via the Modified Maximum Force Criterion (MMFC). A scaling factor is introduced to mimic the theoretical evaluation with the simulated one. It is believed that the rotation of the principal axes of the theoretically considering material point, which is initially co-axial with the external load coordinate, implicates the macro track of the strain path change. Furthermore, an optimal event of the second derivative of the axial rotations is proposed to indicate the strain localization and formulate the FLC. The performance of the proposed criterion is compared with that of the original MMFC in predicting the FLC of three automotive sheet metals, of which all related data were published in the Benchmark of Numisheet 2014 conference. The use of three different hardening laws and three yield functions is examined in the analogy. The comparison reveals that the results of MMFC2 are more sensitive to the employed constitutive model than that of MMFC. Furthermore, the proposed MMFC2 presents concordant results with the experimental data. Nakajima tests are conducted for CR4 mild steel sheets to validate the capacity of the proposed criterion. Well agreement between the experimentally measured data and theoretical prediction based on the Yld2k yield function verifies its usefulness in practice. © 2023 The Author(s)

A theoretical model for predicting the forming limit diagram of sheet metal, namedMMFC2, was recently proposed by the authors based on the modified maximum force criterion(MMFC). This study examines the application of MMFC2 for two automotive sheets, DP800 andAA6016, which are widely used in making car body parts. Uniaxial tensile and bulge tests areconducted to calibrate constitutive equations for modeling the tested materials. The developedmaterial models are employed into different frameworks such as MMFC, MMFC2, and Marciniak-Kuczynski (MK) models to forecast the forming limit curve (FLC) of the tested materials. Theirpredictions are validated by comparing with an experimental one obtained from a series ofNakajima tests. It is found that the derived results of MMFC2 are comparable to that of MK modeland agreed reasonably with experimental data. Less computational time is the major advantage ofMMFC2 against the MK model. (PDF) Prediction of forming limit diagram of automotive sheet metals using a new necking criterion.

Defect inspection of the surface in ultrasonically welded wire terminations is an important inspection procedure to ensure welding quality. However, the detection task of ultrasonic welding defects based on deep learning still faces the challenges of low detection accuracy and slow inference speed. Therefore, to solve the above problems, we propose a fast and effective lightweight detection model based on You Only Look Once v8 (YOLOv8n), named LightYOLO. Specifically, first, to achieve fast feature extraction, a Two-Convolution module with FasterNet block and Efficient multi-scale attention (CTFE) structures is introduced in the backbone network. Secondly, Group-Shuffle Convolution (GSConv) is used to construct the feature fusion structure of the neck, which enhances the fusion efficiency of multi-level features. Finally, an auxiliary head training method is introduced to extract shallow details of the network. To verify the effectiveness of the proposed method, we constructed a surface defect data set of ultrasonic welding wire terminals and conducted a series of experiments. The results of experiments show that the precision of LightYOLO is 93.4%, which is 3.5% higher than YOLOv8n(89.9%). In addition, the model size was reduced to 1/2 of the baseline model. LightYOLO shows the potential for rapid detection on edge computing devices. The source code and dataset for our project is accessible at https://github.com/JianshuXu/LightYOLO. © 2024 The Authors

This paper conducts an investigation on the static mechanical properties and failure behavior of self-piercing riveted joints in aluminum alloy 5A06 after being subjected to the aging process. The study involves three distinct categories of joint specimens: original specimens, 1-year aged specimens and 1-year aged specimens that have been additionally heat-treated at 200 °C. The research findings affirm that strain aging is responsible for a reduction in the peak strength of the joints. Furthermore, the weakest failure chain within the self-piercing riveted joint shifts towards the upper sheet due to a more significant reduction in internal stress experienced by the upper plate. This leads to a failure model characterized by upper sheet pull-off. Through Weibull distribution analysis, it has been established that the 5 % lower limit value for the strength of the SPR joint experiences an 86 % decline following 1-year aging. In practical terms, this means that for a vehicle structure with 7000 riveting points will lose an overall structural strength equivalent to the initial strength of 1000 riveting points within one year. © 2024 Elsevier Ltd

In this study, laminated composites consisting of LDPE (Low Density Polyethylene), Al-foil (Aluminum foil)and an adhesive interface layer is focused. The defects like necking in LDPE, Al-foil layer and interfacial delaminationcan significantly impact the loading capacity of the laminated material. However, the influence mechanisms of thedefects are still unclear, and no appropriate research tool is available. Therefore, the FEM model based on alreadyavailable techniques in ABAQUS is developed in this work. The aim with the model is to create a robust numericalanalysis tool for further research work.In the modelling process, possibility of necking in substrates and interfacial delamination between material layers isconsidered. A coupled elasto-plasticity damage constitutive model, based on Hooke’s Law, the J2 yield criterion,isotropic hardening, associated flow-rule and ductile damage model, is formulated to demonstrate necking behaviorof substrates. In ABAQUS, three modelling techniques, namely VCCT, Cohesive Element, and XFEM, have been usedto simulate interfacial delamination. The simulation results are compared with the theoretical results.A uniaxial tension test consisting of a two material laminate is simulated by using these three modelling techniques.The special modelling skills for respective modelling techniques, element type, meshing technique of each model, arealso introduced. The comparison with the theoretical results shows necking in substrates and interfacial delaminationare also achieved in all three models as expected. Deformation results of the simulation are very close to that of thetheoretical analysis. Technique features of VCCT, Cohesive Element and XFEM in modelling of interfacialdelamination are analyzed and concluded. These three FEM models can all be utilized according to the requirementsof subsequent research.

In this study, laminated composites consisting of LDPE (Low Density Polyethylene), Al-foil (Aluminum foil) and an adhesive interface layer is focused. The defects like necking in LDPE, Al-foil layer and interfacial delamination can significantly impact the loading capacity of the laminated material. However, the influence mechanisms of the defects are still unclear, and no appropriate research tool is available. Therefore, the FEM model based on already available techniques in ABAQUS is developed in this work. The aim with the model is to create a robust numerical analysis tool for further research work.

In the modeling process, possibility of necking in substrates and interfacial delamination between material layers is considered. The constitutive material behaviour is elastic-plastic complemented with progressive damage, based on Hooke’s Law, the J2 yield criterion, isotropic hardening, associated flow-rule and ductile damage model are formulated to demonstrate necking behavior of substrates. In ABAQUS, three modeling techniques, namely VCCT, Cohesive Element, and XFEM, have been used to simulate interfacial delamination. The simulation results are compared with the theoretical results.

A uniaxial tension test consisting of a two material laminate is simulated by using these three modeling techniques. The special modelling skills for respective modeling techniques, element type, meshing technique of each model, are also introduced. The comparison with the theoretical results shows necking in substrates and interfacial delamination are also achieved in all three models as expected. Deformation results of the simulation are very close to that of the theoretical analysis. Technique features of VCCT, Cohesive Element and XFEM in modelling of interfacial delamination are analyzed and concluded. These three FEM models can all be utilized according to the requirements of subsequent research.

Efficient detection of defects in riveted joints during the self-piercing riveting (SPR) process will help improve riveting quality. Due to the complexity of SPR defects under actual working conditions, it is difficult for traditional visual technology to detect the forming quality of SPR joints effectively. To detect SPR defects and improve the efficiency of SPR joint forming quality, we proposed a defect detection model based on a multi-attention mechanism, named Multiple Attention Self-Piercing Riveting Network (MA-SPRNet), for the detection of SPR defects. Specifically, to alleviate problems such as unclear object features in complex environments, a multi-level fusion enhancement network (MFEN) is constructed. It fuses features into each level and improves the fusion effect by adding more levels of features. In addition, to alleviate the information redundancy generated during the feature fusion process, the triple attention module (TRAM) and the efficient multi-scale attention module (EMAM) were introduced to enhance the attention of the network to SPR defective. These modules are designed to refine the attention of the network, ensuring a more targeted analysis of riveting features. In addition, the Wise Intersection over Union (WIoU) loss function is introduced, aiming to guide the network to characterize features within the region of interest and to enhance the accurate positioning of riveting defects by the network. Finally, to verify the performance of the MA-SPRNet, an SPR defect dataset was constructed, and a series of experiments based on this dataset were conducted. The detection mAP0.5 of MA-SPRNet was 82.83%. The results of experiments show that MA-SPRNet effectively realizes the detection of riveted joint defects. © 2024 Elsevier Ltd

A wheelchair with a gear system was designed and analysed in order to find a good solution for people with wheelchair to move into the car. This gear system has been designed to be installed in the car and the whole wheelchair can be moved into the car automatically even with the people on it. The three dimensional design have been done in a CAD commercial program with this the solid mechanics analysis was also performed. Volvo XC 60 and V60 as well as a foldable wheelchair have been chosen in this work.

The present study investigates ultrasonic metal welding to manufacture 10 mm2 copper (Cu) wire joints with different core diameters. The primary purpose of this study is to explore the influence of wire core diameter on the performance of ultrasonic welded joints. Wire core diameter is positively correlated with the peeling resistance of the joint. Superior mechanical properties of the joint are achieved with an increased diameter of the wire core. The peeling strength of the welded joint of two wires with a wire core diameter of 0.25 mm reaches 306.8 N. Examining the welding temperature and assessing the joint's porosity reveals a significant impact of temperature on porosity. However, relying solely on porosity as a criterion for judging the overall forming quality of joints may be insufficient. Scanning electron microscope and energy-dispersive X-ray elemental analysis revealed that certain wires underwent plastic deformation at elevated temperatures without attaining atomic bonding. Additionally, the welded joint exhibits a compact structure externally and a more relaxed structure internally. The upper side of the joint in contact with the briquette and the lower side in contact with the welding head exhibit minimal gaps, while numerous gaps are evident in the middle of the joint. Furthermore, upon examining the fracture morphology, two distinct failure modes are identified at the joint surface of the conductor. The first involves the fracture of the wire core with a completely separated joint surface, resulting in poor mechanical properties of the joint. The second mode entails the ductile fracture of the wire core at the joint surface, indicating good mechanical properties of the joint.

Defect detection in Quick Response (QR) codes has important implications for downstream tasks. However, QR code defects include small objects and complex backgrounds, which makes their recognition effect poor. To address the above problems, we proposed a model based on YOLOv8, called YOLOv8-QR, to detect QR code defects. Specifically, first, the non-local attention (Non-local) module is introduced into the backbone of the YOLOv8 to enhance the interactive ability of the feature. The Non-local captures the correlation information of long-distance dependencies between features by calculating the attention weight between any positions. In addition, the contextual information required for representation learning of different defective objects is different. To extract multi-scale features, a Large Selective Kernel Network (LSKNet) was introduced. LSKNet dynamically adjusts the convolution receptive field of the neck fusion network and effectively uses the receptive field to capture the background information of different objects, thereby improving the representation ability of the model. To improve the defect detection accuracy of small objects in QR codes, the Normalized Gaussian Wasserstein Distance (NGWD) is introduced to replace the Intersection over Union (IoU) optimization function that is sensitive to the position deviation of objects and is not conducive to the regression of multi-scale objects. To verify the effectiveness of the model, the QR dataset was constructed and a series of experiments were conducted based on this dataset. The results show that the mAP50 and mAP50:95 of the YOLOv8-QR reach 95.5% and 65%, which are 3.8% and 2.3% higher than YOLOv8 respectively. The proposed YOLOv8-QR can better adapt to the needs of QR code defect detection in actual industrial environments. Our code is available at https://github.com/Code-of-Liujie/YOLOv8-QR.git. © 2024

The scanning electron microscope (SEM) is widely used in the analysis and research of materials, including fracture analysis, microstructure morphology, and nanomaterial analysis. With the rapid development of materials science and computer vision technology, the level of detection technology is constantly improving. In this paper, the deep learning method is used to intelligently identify microcracks in the microscopic morphology of SEM image. A deep learning model based on image level is selected to reduce the interference of other complex microscopic topography, and a detection method with dense continuous bounding boxes suitable for SEM images is proposed. The dense and continuous bounding boxes were used to obtain the local features of the cracks and rotating the bounding boxes to reduce the feature differences between the bounding boxes. Finally, the bounding boxes with filled regression were used to highlight the microcrack detection effect. The results show that the detection accuracy of our approach reached 71.12%, and the highest mIOU reached 64.13%. Also, microcracks in different magnifications and in different backgrounds were detected successfully.

In this work, similar (2A12) and dissimilar (6061) aluminum alloy sheets are validly joined using self-piercing rivet process. A quasi-static experiment is proposed to investigate the mechanical behaviors, failures mode, and mechanism of the different joints. Moreover, a method based on deep learning algorithm is anticipated to detect the appearance defects of the SPR welded joints. The results indicated that 2A12 joints of similar sheets contained the advantageous static strength and 6061 similar sheet joints had superior anti-vibration performance conducts. The joints with 6061-2A12 sheets introduced the most decent and comprehensive mechanical properties. The main failure mode of 2A12 similar sheet joints was substrate fracture. The performance of the substrate affects the failure mode of the joint and the plasticity of the substrate is better. When the time comes, the failure mode is mostly pull-off failure. Poor plasticity of the substrate can easily lead to substrate breakage. The reason for joint pull-off and button fall-off failure is that there is large plastic deformation in the lower plate of the joint and the mechanical internal locking structure is damaged. 2A12 substrate breakage belongs to a composite fracture that combines intergranular fracture and microvoid aggregation type fracture. The area of the 6061 substrate near the edge of the sample is shear fracture and the area near the center of the sample thickness is dominated by microvoid aggregation type normal fracture. The effectiveness of the method was verified by conducting a series of experiments and the detection accuracy of the method can reach about 90%. The detection speed was as high as 50 frames per second (FPS), which can effectively solve the problem that the rivet quality was difficult to monitor.

Ultrasonic welding has become a key joining approach in batteries and energy vehicles. This work reports the optimization in static property and stability of self-piercing riveting joints which is becoming the most versatile way to join microstructures. Tool heads of three different knurling profiles (e.g., A, B, and C) are used to perform ultrasonic composite with riveting. Based on tensile-shear tests, SEM, EDS, XRD, and Vickers microhardness analysis were conducted to investigate the comparative study of the fracture morphology, element distribution, phase structure, and hardness. The results indicated that all three types of knurling generate solid phase welding at the sheet joints. Thus, it improved the forming quality and mechanical properties of self-piercing riveting joints. The C-shaped welding tool head has advantageous effect on optimizing the mechanical properties of joints. Further, it enhanced the average peak load by 25.6%, the average failure displacement by 31.1%, and the average energy absorption by 88.8%. The microscopic results showed that a large amount of oxides are precipitated at the edge of welding joints when the B-shape knurling tool is used. The distribution of the hardness value of joints horizontal line is “M” shape. Besides, the coarse grains in the joint area and the interplanar space increase significantly after ultrasonic welding which softens the sheet. © 2023, The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature.