Multi material mix is a promising approach to reduce weight and the carbon footprint in automotive engineering at competitive costs. As a result, automotive industry is getting more venturous, expl...

Crash simulation of wood and composite wood for future automotive engineering

This paper presents an investigation on the modelling of flow-drill screw connections in thin-walled aluminium plates in large-scale finite element analyses using different macroscopic modelling techniques. Five models that were originally developed for adhesive bonds, spot welds and self-piercing rivet connections were examined. Two sets of experimental data were used, each with a different screw and material combination. Different trends were observed for the two sets, which challenged the flexibility of the models. The results indicated that a constraint-based model originally developed for self-piercing rivet connections was the best suited model. A two-step validation strategy was proposed and used for the present models.

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Macroscopic modelling of flow-drill screw connections in thin-walled aluminium structures

A cost and time effective process was developed to create spot weld failure parameters for crash models implemented in LS-DYNA. The process includes a design of experiment (DOE) approach for coordinating data collection, welding and testing, finite element modelling, statistical analysis, validation, and implementation. The DOE approach was used to coordinate testing of a reduced set of samples over a large range of material strengths and gauges. This testing included cross-tension, lap shea, and coach peel type evaluations. Computer models for each metal combination and sample geometry were developed to obtain normalised tensile, shear and bending stress at the incidence of weld failure. These normalised loads were then regressed to extend these results to all possible material combinations within the DOE space. These results were then used to estimate the spot weld failure parameters for all the stack-ups of interest. A set of multiweld T-section samples were then welded, physically tested and c...

Development of spot weld failure parameters for full vehicle crash modelling

This paper presents the construction and the validation of a volumic crash detailed model of different spotwelded coupons using the finite element method. The goal of this detailed model is to provide input data for the validation of a simplified model, which will be later on implemented in the complete car model. First, by studying a weld’s cross section, three different areas (spot weld, heat affected zone and basis material) have been identified and characterized using the Vickers hardness test. Moreover, the geometry of the specimen has been carefully analyzed to construct an accurate FE-model. To reflect the different mechanical properties of each zone, a simple method based on the extrapolation of the tensile strength from the Vickers hardness has been used. To compute the damage and the rupture inside the specimen, the Gurson material model implemented in the explicit time integration method “LS-DYNA3D” has been used. The global accuracy of the detailed model is checked by comparing the simulated and experimental force/displacement curves and the weld’s rupture mode under a quasi-static load case of 10 mm/min. This study shows that detailed models of shear-tension, lap-shear and coach-peel specimens are validated for a mild steel.

Detailed model of spot-welded joints to simulate the failure of car assemblies

On the shop floor, as in laboratories, destructive testing remains the main means of quality control of spot welds. After hand or mechanized weld destruction, the so-called “plug diameter” is measured and is usually considered a good indicator of the weld quality. However, it turns out that the “plug” failure of spot welds is far from being the rule. Moreover, fracture may occur in different zones of the weld, leading to very different meanings of the plug diameter. Therefore, the plug diameter is most of the time not well-correlated with the weld strength, which is the main value of the spot weld. Partial or full interfacial failures (through the weld nugget) exhibit equivalent mechanical strengths and therefore should not be rejected. Through this work, it is shown that the failure type depends on various parameters (nugget diameter, sheet thickness, loading mode, …), and consequently, it is not an intrinsic property of the steel grade. In this way, recommended quality criteria are based on weld strength, weld diameter (including the interfacial fracture area if any), or absorbed energy independently of failure occurrence. In addition, non-destructive techniques might be key investigation methods and have to be developed further.

An Investigation of Failure Types in High-Strength Steel Resistance Spot Welds

Because of weight reduction necessities, high-strength steels are more and more widely used in bodyin-white (BiW) structures in recent years. Concerning the behaviour of such structures during a car crash the joints between high-strength materials are seen as critical points. Therefore the properties of welded joints, especially the failure behaviour at high velocities have to be taken into consideration during the development phase. In this paper, we present an overview on the current activities at the DaimlerChrysler AG regarding investigations on spot weld failure behaviour. A suitable model that is able to represent the failure behaviour of spot welds in BiW structures and that is independent of mesh sensitivity has been developed. An elasto-plastic material model based on von Mises plasticity (MAT_100) has been further enhanced with a new failure criterion. The model has been implemented into LS-DYNA. The material as well as the failure behaviour is verified and calibrated through precision experiments conducted on specimen level and later validated on component level.

/pdf/an-investigation-on-spot-weld-modelling-for-crash-simulation-2t5rey0t43.pdf

F. Seeger

Papers

An Investigation on Spot Weld Modelling for Crash Simulation with LS-DYNA