An Investigation on Spot Weld Modelling for Crash Simulation with LS-DYNA
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.
Investigation of Spot Weld Behavior Using Detailed Modeling Technique
Summary: The development of suitable and robust simplified spot weld m odels for full vehicle crash simulation meets one of the major demands of the development process regarding efficient and appropriate full car crash models. Normally a high number of experiments are required to derive and validate accordant material and failure parameters for each material and gage combinations. Concerning systematical investigations, the effort for manufacturing and testing c an increase immoderately. In this paper, we describe a method to reduce the effort of characterizing the joint failure by using a highly detailed simulation model. Different loading conditions and geometrical aspects can be analyzed by using this model in combination with the Gurson’s materia l model as an appropriate visco-plastic material model which includes already a damage formulation. Especially the experimental investigation of strain rate effects at higher velocities of joints is quit e sophisticated due to dynamic effects of the test arrangement ‐ the magnitudes are often overlaid by oscillations. Using the simulation to evaluate the behavior of a spot weld allows to study and predict the strain rate effect for higher velocities. As a second point, we use the detailed model for a systematic analysis to determine the effect of the sheet thickness with respect to the failure parameters. The influe nce of imperfections which occurs due to the production process can be eliminated, so that a self-contai ned approach can be obtained.
Measuring Sheet Resistances of Dielectrics Using Co‐Planar Hydrogel Electrochemical Cells with Practical Applications to Characterize the Protective Quality of Paints on Sculptures
Electrical properties of thin dielectric films at the solid-liquid phase boundary are an important performance characteristic of many devices, coatings and sensors. In this paper, co-polymeric hydrogels of polyacrylic acid co-sulfonic acid, swollen with a salt solution to act as the solid electrolyte, were used to assess interfaces using electrochemical impedance spectroscopy (EIS) in a co-planar geometry. Silane-modified glasses were characterized by the co-planar hydrogel EIS cell and found to be distinguishable based on their surface monolayer chemistry. EIS measurements were also made on primed and painted metal substrates, using both test panels and an outdoor sculpture, Tony Smith's Stinger. The panels were then exposed to accelerated and outdoor weathering and showed degradation on the surface paint layers, which was observable electrochemically using EIS and confirmed visually by SEM. Electrochemical spectral features were compared between data from a standard paint-test cell versus this co-planar hydrogel cell; both cell types were able to measure coating capacitance, providing useful information about the condition of the bulk coating. Yet, sheet resistance (Rs) was a spectral feature seen only by the co-planar hydrogel cell. Thus, it can be concluded that the use of such co-planar hydrogel cells can provide an earlier warning sign to coating degradation and such cells provide a new type of spectral information that is not assessable by the standard geometry.