G. Haugou

Material behaviour law identification for the various zones of the spot-weld under quasi-static loadings

The aim of this paper is to predict by FE simulation the non-linear behaviour and rupture of spot-welded assemblies subjected to quasi-static loadings and to show the feasibility of numerical works. The three material zones of the spot-weld (metal base, melted zone and heat affected zone) are analysed and studied on a metal sheet assembly structured 0.7/0.7mm Experimental works based on tensile-shear, cross-tensile and peeling tests are done, as well as a numerical sensitivity analysis on the three material zones. Different fracture modes are put into evidence. A methodology to identify the material behaviour law of the MB, HAZ and MZ is proposed. The rupture of the spot-welded structure is simulated with the help of the Gurson damage model. The damage parameters of the MB and HAZ are identified through an inverse method on the basis of tensile-shear and cross-tensile tests. The numerical/experimental comparison on the various applied quasi-static loadings validates this methodology.

Brittle Fracture: Experimental and Numerical Modeling Using Phase-Field Approach

Crack paths prediction is one of the most challenging of fracture mechanics. The difficulty in this seek is how to obtain numerical models able of predicting unknown crack paths. One of these models is called the phase-field approach. It represents cracks by means of an additional continuous field variable. This model approximates a sharp crack with a diffuse crack phase-field where a characteristic length regularizes the crack topology and a crack energy density describes the energy dissipated in order to break a brittle piece. This method avoids some of the drawbacks of a sharp interface description of cracks. The phase-field model for brittle fracture assumes quasi-static loading conditions. However, dynamic effects have a great impact on the crack growth in many practical applications. Therefore, this investigation presents an extension of the quasi-static phase-field model for the fracture to the dynamic case. Experiment tests will be presented in this work in order to study the efficiency and the robustly of phase-field approach for modeling brittle fracture and capturing complex crack topologies.

Characterization of a structural adhesive by Digital Image Correlation

In the recent years, structural bonding takes an important place in assemblies techniques used for the automotive design. The next step to optimize the use of adhesive in car structures is to realize accurate finite element simulations of behaviour until failure of bonded joints. These kinds of calculations are only possible if fine behaviour and failure models are provided into the finite element software. In these works, tests on bulk adhesive specimens are realized to characterize the mechanical properties. 2D and 3D Digital Image Correlation are used to investigate the behaviour and failure of the shear and tensile specimens.

Elasto-viscoplasticity behaviour of a structural adhesive under compression loadings

Improvement of automotives’ crashworthiness is of high interest for governments prior to objectives focused on the reduction of passengers’ injuries. In these recent years, steel industries have studied the dynamic behaviour of tapered side rails so as to increase the capacities of energy absorption combined with light-weight aspects. On the basis of the global mass’ reduction of cars, bonded techniques have been tested with respect to the reduction of the mass/energy’s ratio. In this study, a test programme has been performed on a structural adhesive under a very large range of strain rates, thus [0.1;5000] /s. For that, a split Hopkinson bars device made of PA66 has been used so as to access to materials responses in the upper domain of strain rates, thus [500;5000] /s. To complete the expected domain of strain rates, compression tests have been done using a high-speed hydraulic machine on the same geometry from 0.1 up to 50 /s. A special mould has been machined and 2 sheets have prepared (thickness: 4 and 6 mm) in order to consider the effect of the pressure during the curing process. Water jet technique has been used to extract cylindrical samples from the sheet with accurate dimensions.