The welding of dissimilar metallic assemblies produced by high-velocity impact occurs at high strain rates (i.e., impact velocities) and various dynamic collapsing angles. However, the quality of the resulting weld surface depends on several parameters, one of which is the jet formation and particle cloud formation upon impact. This phenomenon arises from intense heat and pressure upon impact, playing a decisive role in determining the resulting weld quality. Here, the jet formation of such welds is described, providing new insights into the understanding of cold-welding methods. Jet formation plays a key role in generating the necessary conditions required to weld two dissimilar metal surfaces. Copper (Cu) and aluminum (Al) samples were subjected to high strain-rate loading using the single-stage gas gun available at ID19 beamline (ESRF, France) coupled with ultrafast synchrotron X-ray radiography in order to investigate, in situ, the production, propagation, and evolution of jets upon impact of dissimilar metals. Several impact conditions (impact angle and material configuration) were investigated at an approximate impact velocity of 500 m/s. The results reveal that the jet size, speed, and morphology evolve differently as a function of the initial impact conditions. These results demonstrate, for the first time, a direct in situ investigation of jet dynamics and weld quality in impact welding of dissimilar metallic materials.

Energy absorption capabilities are critical to the performance of structures in fast dynamic applications, such as crash and impact. This study experimentally investigated the influence of wall thickness on the compressive properties of a conventional body-centred cubic (BCC) lattice design. The structures were additively manufactured from aluminium alloy, AlSi10Mg, and heat-treated to increase ductility. Three wall thicknesses were investigated: 0.5 mm, 1.0 mm, and 1.5 mm, as well as no wall, with two relative densities for the BCC structure: 20% and 30%. This aimed to quantify their structural response in terms of apparent stress and strain, potential dynamic enhancement and specific energy absorption (SEA) capacities. The collapse mechanisms and plastic buckling wavelength of the deformed structures were examined, along with the effect of relative density, loading rate and heat treatment. It was found that the addition of the 0.5 mm wall increased the energy absorption qualities of the BCC structure for both relative densities. The lattice controlled the response mechanism similar to that of a bending-dominated structure. A dynamic enhancement was found for the BCC structure with 30% density and 1.0 mm wall thickness, with the lattice controlling the response mechanism under dynamic loading conditions. When considering an equivalent densification strain, the heat-treated and as-built structures with 0.5 mm wall thickness showed similar SEA and plateau stress responses for both relative densities. The findings of this study can be utilised to identify optimal wall thicknesses for various loading conditions in safety-critical impact applications.

The relative comparison in terms of energy absorption efficiency for a set of 4 structures made of various Triply Periodic Minimal Surfaces (TPMS) topologies is experimentally investigated. These TPMS structures are printed by Selective Laser Melting AM process using 316L SS. The study is carried out in consideration of the effect of parameters such as relative density, compressive loading directions and loading rates, number of unit cells for Diamond and Gyroids TPMS both declined for Sheet and Skeletal topologies. The objective is to quantify their structural responses in terms of apparent stress and strain, dynamic enhancement and Specific Energy Absorbed (SEA) and to evaluate their structural integrity in terms of collapse stability. The results reveal that the Sheet pattern of TPMS structures with its constant wall thickness and uniform geometry exhibits better energy absorption capabilities than the Skeletal pattern. The Diamond family shows greater interest rather than the Gyroid family only in the case of the Sheet pattern. The increase in relative density from 20 to 30 % is characterised by improved manufacturing quality, an increase in energy absorption capacity and more homogeneous progressive deformations during compression. On the whole, the set of TPMS geometries exhibits energy absorption capacities prior to those of other conventional cellular materials currently used for impact engineering applications. Finally, in a first approach, an original design methodology using charts can be developed to establish a link between the energy absorption capabilities and the design geometric parameters of TPMS structures.

Magnetic pulse welding (MPW) is a relatively new welding technique that has been gaining increasing attention from various industries. MPW allows for the welding of dissimilar materials, such as aluminum and copper, but with specific features at the interface. This study proposes the use of an original approach based on X-ray micro-computed tomography (XCT) to probe and analyze the surface interface between two dissimilar welded components. This method does not require the use of a peeling test to reveal the interface welding. XCT enables a global analysis of the interface and highlights specific features of MPW, such as vortexes and waves, from a new perspective involving metrics. Two vortex morphologies were observed at the interface and were described as standard or broken vortexes. They were classified based on their morphologies, sizes, and densities. Waves and vortexes were found to be inhomogeneous along the length and width of the welding direction at the interface, with sizes that could triple depending on the localization. The surfaces at the interface were numerically extracted and evaluated using roughness parameters. These values represent an increase in the average contact surface area of more than 26% between the two welded components. Vortex features obtained from the XCT analysis were similar to those observed on cross-sectional optical or electronic images, but containing lateral information (creation and collapsing) that are not available with standard cross-sectional images. These results demonstrate the material interlocking at the interface between the materials.

Magnetic Pulse Welding (MPW) is a high-velocity impact welding technique that allows the joining of dissimilar materials such as aluminium and copper. Welding should be produced under the appropriate conditions: impact velocity (200–500 m.s−1) and collision angle (10–30°). The formation mechanisms leading to the welding creation are not very clear. This work investigates the microstructure and hardness at the interface to understand these mechanisms. Al/Cu and Cu/Cu samples were formed with identical process parameters. They were first compared to the literature using Vickers microhardness. Obtained results are standard and correspond to previous studies. In a second step, a detailed characterization of the interface using nanoindentation and electron back-scattered diffraction (EBSD) methods is done. Different behaviors were found at the interface between Al/Cu and Cu/Cu. Al/Cu exhibited a thin layer of intermetallic compounds (IMC), increasing the hardness at the interface. This layer was composed of Al2Cu and Al4Cu9 compounds, as demonstrated by Energy Dispersive Spectroscopy (EDS) and X-ray Diffraction (XRD). Cu/Cu presented a dissimilar behavior at the interface. The flyer sheet shows an increase in hardness due to grains deformation and distortion. While, the base sheet manifested a decrease in hardness caused by dynamic recovery or recrystallization at the interface. In both cases, the samples were deformed and hardened due to the plastic deformation induced during impact. These results are complementary to previous studies. They provide new insights that could be used to improve our understanding of the mechanisms behind such high-velocity impact welding.

Magnetic Pulse Welding (MPW) is a method of growing interest allowing the joining of dissimilar materials such as aluminum and copper. The global mechanical properties of the joint are often evaluated with conventional tests, using the fully welded joint. However, these cannot elucidate the local mechanical properties of the joint or its interface when subjected to high strain rates loads. Cubic samples of Al/Cu have been designed and extracted from MPW joints, in order to locally characterize the mechanical properties. Samples were exposed to high strain-rate loading using the Split-Hopkinson Pressure Bar (SHPB) coupled to ultra-fast synchrotron X-ray radiography in order to investigate related failure processes in-situ. The measurements of the interface evolution were related to the macroscopic applied load. In addition, synchrotron microtomography was performed on the samples before mechanical deformation. Aside from the feasibility proof, this work provides, for the first time, the correlation of the interfacial opening evolution and the influence of pre-existing cracks of the weld. It is observed that, the pre-existing cracks at the interface correspond to the initiation sites of interfacial separation between the two dissimilar metals.

Magnetic Pulse Welding (MPW) facilitates the permanent joining of dissimilar metallic materials through the sudden impact generated by a magnetic pulsed field. The process can introduce distinct morphological features at the interface of bi-material joints, which subsequently affect the joint’s quality and durability. This article delves into the investigation and quantification of various interfacial morphologies in Aluminum/Copper and Aluminum/Steel joints, using high-energy phase-contrast synchrotron micro-tomography. Surface topography is extracted from 3D tomographic datasets between dissimilar materials, enabling a comprehensive comparison between different material pairings and various locations within the weld. The study analyses and compares the roughness parameters of these surfaces. Moreover, it describes the interface’s waves and vortexes through diverse morphological metrics, encompassing their shape and size. The results provide evidences that vortexes evolve in three dimensions, with lateral growth and collapse. The waves and vortexes shapes promote material interlocking, increasing the contact area between the dissimilar materials by up to 20%. The interface morphology of Al/Cu joints exhibits higher roughness and a greater number of vortexes compared to Al/Fe joints. Lastly, the findings reveal the presence of interface damage in the form of pre-existing discontinuities.

Additive Layer Manufacturing (ALM) processes like Selective Laser Melting (SLM) enable the conception of complex designs with a high precision and equal or enhanced mechanical properties compared to Conventionally Manufactured (CM) structures. Nevertheless, this process, which consists in melting metallic powders layer by layer with a laser beam, greatly influences the microstructure and therefore the mechanical properties. While some studies have considered the effects of the thickness and/or the building direction of 316L Stainless Steel (SS) specimens produced by SLM on the quasi-static mechanical behavior, the strain rate effect for crash or impact applications on these two parameters has not been fully investigated. To complete the actual knowledge, the present work proposes to analyze the mechanical behavior of 316L SS tensile specimens produced by SLM with different build orientations (0 degrees, 45 degrees and 90 degrees) and thicknesses (0.5, 0.75, 1 mm) and submitted to dynamic loadings at various strain rates up to 103 s-1. In addition, the microstructure and the fracture surfaces are analyzed to give a more detailed comprehension of the mechanical tests. It results that the SLM 316L SS achieves better Yield Stress (YS), similar Ultimate Tensile Stress (UTS) and equal or lower failure strain compared to the CM material. This is mainly a result of microstructure refinement. Anisotropy is observed at the macroscopic level with higher tensile stress and lower failure strain for horizontal specimens, which is explained by the different shapes, orientation and size of the grains at the microscopic level. The mechanical properties greatly decrease as the thickness reduces from 1 to 0.5 mm, by 14% for the YS and 16% for the UTS for a quasi-static loading. A minimum thickness of 0.75 mm is advised to at least recover the mechanical properties of the CM 316L SS. A positive strain rate sensitivity, higher than the CM material, is observed for all configurations, with the exception of 0.5 mm thickness. For strain rates ranging from to 10-3 to 103 s-1, there is an increase of 20% of the UTS. The material anisotropy is not affected by the strain rate sensitivity whereas the latter increases with the thickness.

To reduce the number of tests required to characterize anisotropic elastoplastic constitutive models, an approach is to design specimen geometries to diversify the stress states generated in a single test. The experiments are then processed using an inverse identification method based on full-field measurements to achieve the full potential of that specific test. Recent optimization methods were able to design complex specimens in which highly heterogeneous stress fields were generated. However, the specimen design is only assessed based on numerical simulations and does not consider the effect of the biases introduced by the full-field measurement method. The goal of this work is therefore to take into account some of the most frequently observed measurement biases in the specimen selection process. The proposed approach uses synthetic test images generated with numerical simulations. Four specimen geometries have been ranked based on two selection criteria. The first one is an indicator of the heterogeneity of the stress fields obtained by finite element simulations (unbiased data). The second one quantifies error for the identification procedure due to measurement biases. The two criteria provide different rankings for the set of specimens. It is concluded that the design with the most heterogeneous stress fields (first criterion) is not necessarily the more robust design in terms of measurement noise (second criterion), so the optimized geometry should be selected based on a compromise between these two criteria.

Purpose The purpose of this study is to develop an elasto-plastic multi-material shell model by which finite element analysis of laser welded joints is carried out at the interface of the heat-affected zone and base material. Design/methodology/approach The multi-material shell model is implemented on the simple cantilever and double cantilever welded plates to examine the efficiency of the developed model. Findings By reducing the computational time approximately 20 times with the developed model, the results obtained in the form of von Mises stress and equivalent plastic strain are found in good agreement as compared with the reference solid model. Originality/value The accurate and fast prediction of the stresses and strains in the laser welded joints, and the developed multi-material model is helpful to simulate complex industrial welded structures.

The exploitation of field measurements with inverse identification methods may reduce the number of required tests to characterize complex material constitutive models, provided that the generated stress field is sensitive enough to the targeted material parameters. For anisotropic elastoplastic material, the objective is to generate various stress states in the specimen through a single test. In this study, the effect of Digital Image Correlation measurement biases on the selection of the most suitable specimen geometry for characterisation of a complex anisotropic plasticity criterion using a unique uniaxial tensile test is investigated. To this aim, finite element (FE) based synthetic images are generated and DIC is used on these images. The biases in DIC measurement result in biased stress states that may cause errors in identification results.

The Additive Layer Manufacturing (ALM) for metallic materials has grown in the past few years. However, this process influences the mechanical properties of the constitutive material and consequently those of the finished product. The influence of the thickness and the building direction of 316L Stainless Steel (SS) specimens produced by Selective Laser Melting (SLM) on the quasi-static mechanical behavior has already been reported. Considering the strain rate effect, it has been only studied for tensile properties of vertical specimens up to 102s–1. The aim of this work is to study the influence of the thickness and the building orientation at higher strain rates up to 101s–1 and up to 103s–1 for vertical specimens. Compared to conventional material, 316L SS SLM achieves equal and even better mechanical properties due to a refinement of the microstructure. Anisotropy is observed at the macroscopic level, which is explained by the microstructure with different shapes, orientation and size of grains. A minimum thickness of 0.75mm is recommended to recover the mechanical properties of the conventional 316L SS. A positive strain rate sensitivity is observed in every case. The material anisotropy and the thickness variation do not affect the strain rate sensitivity.

Microstructure characteristics and compressive property relationships of so-called harmonic (composed by fine and coarse grains) and conventional pure titanium (Ti) and Ti-6Al-4V alloy processed by powder metallurgy route are presented in the present work. Electron backscatter diffraction (EBSD) analysis was performed to characterize the as-processed microstructures. The harmonicity structure of selected samples is described, and relevant EBSD maps are presented. The bulk samples’ hardness is reported, along with compressive responses at quasi-static and intermediate strain rates, ranging from 0.005 s−1 to 16 s−1. The strain rate sensitivity of these metallic samples is discussed, and the benefits in terms of mechanical properties of the harmonic microstructures compared with the non-harmonic conventional ones are highlighted. Finally, a modified Johnson–Cook model was shown to predict fairly the experimental results.

The self piercing riveting (SPR) process is increasingly used in the automotive industry due to its ability to connect multi-materials for weight reduction considerations. The strength and failure of such multi-material assemblies need to be characterized and modelled for full-scale structural computations. An aluminum/PA66 composite 2-sheet SPR assembly is characterized in pure and mixed tensile/shear single connection Arcan experiments. The peak force and dissipated energy increase with the loading angle. Neither loading velocity sensitivity in the range 0.016mm/s - 100mm/s nor Pa66 composite fiber orientation sensitivity are observed. Some failure modes of aluminum-aluminum SPR are observed. Experiments are also carried out on a single hat component with multiple connections for two loading rates: 5mm/s and 1500 mm/s. The maximum forces and dissipated energies slightly increase at 1500mm/s. Both tensile and shear dominated mode mix ratio values are experienced by the connections. A 13 independent parameter SPR connector model is employed to model the metallic-composite SPR joint. It features three b-norm criteria employed for irreversible deformation, maximum force and failure. It can be generated by combining some elementary behaviors of the general connector model of Abaqus. The calibration procedure decouples the pure tensile/shear contributions from the mixed tensile/shear ones. The parameters are identified based on the Arcan tests and validated on the component experiments. The overall comparison between computations and experiments show satisfactory results.