Development of mechanism-based models for resistance spot weld failure simulation of multi-material advanced high strength steel sheets 机翻标题: 暂无翻译,请尝试点击翻译按钮。

19. VDI-Kongress SIMVEC - Simulation und Erprobung in der Fahrzeugentwicklung: 20 und 21 November 2018, Baden-Baden, Germany
Daniel Dorribo
The automotive industry is constantly involved in the development of new projects aimed at reducing weight, and costs while improving passengers' safety. In order to achieve these increasing demands, the so-called Advanced High Strength Steels (AHSS) have been introduced in recent years, reducing the vehicle structure weight while even improving the crashworthiness. With the increase in the bearing capacity of crash relevant structural components due to the use of AHSS, the sheet metal joining techniques such as adhesive bonding and resistance spot welding (RSW) become critical. Frequently, full-vehicle crash finite element simulations are performed in order to develop the vehicle structure. In these simulations, spot welds fracture modeling is now of crucial importance. Simplified beam-like connection models are currently used to represent RSW joints response. The maximum bearing force of these models are fitted based on large experimental campaigns, considering all the main factors that have the highest influence on the fracture response of a welded joint. The objective of the present work were: (1) to develop a model that is able to partially replace the extensive experimental campaign in providing parameters for the crash simulation simplified spot weld models, and (2) to gain understanding of the spot weld joints failure response in order to improve the current simplified models. To achieve these objectives, a detailed spot weld model for the prediction of spot weld failure in joints in AHSS sheets is presented. The presented model includes a definition of the local material properties as well as the geometrical features of a spot weld. In addition, an industrially suited fracture criterion, i.e. robust and without a long-term calibration, is used for the prediction of the maximum force. For this purpose, an energetic fracture criterion based on the use of elastic-plastic fracture-mechanics well suited for the prediction of spot weld failure and corresponding joint bearing capacity. This fracture criterion is based on the J-integral that is evaluated at the weld notch and this value is compared with a material parameter, the fracture toughness, in order to obtain the joint maximum force. The presented detailed FE spot weld model is validated for joints of two typical steel grades of the AHSS family, a hot formed martensitic boron-alloyed steel (22MnB5) and a cold formed dual phase steel (CR700Y980-DP). The validation is performed comparing the maximum forces obtained with the finite element model and the results extracted from an extensive loading test experimental campaign, where the main factors that influence the spot weld fracture response are considered. The obtained simulated critical forces of the loading tests are in good agreement with the experimental ones in all tested configurations. The proposed procedure can be used to reduce the long-term characterization campaigns for new AHSS grades in the future.