Influence of forming processes on crashworthiness of automotive components

Vehicle mass reduction has been a constant design challenge since the origin of automobile engineering. The challenge target, that was initially devoted to obviate low engine power, has nowadays shifted to the reduction of fuel consumption and of pollutant emissions. Research aimed at preserving energy resources started to take off seriously in the seventies of the last century, in the wake of the first oil crisis. This goal remains valid today, and has been strongly reinforced through the Kyoto protocol (1992) and through the Paris climate conference agreement in December 2015. On this occasion, the reduction of CO2 emissions, joined with other environmental sustainability objectives, has been targeted in a bid to counter the greenhouse effect. The need to reduce automotive weight in order to comply to the stricter regulations coupled with the challenge to achieve improved passive safety standard forced the automakers to look for advanced materials with improved mechanical characteristics. The advanced high strength steels (AHSS) are innovative steels that are able to satisfy this automotive engineering need thanks to their improved performances from the mechanical and the production point of view. In fact, their peculiar microstructures allow these steels to reach high strength levels while still maintaining a decent manufacturability. The main advantage of these materials compared to other lightweight materials is that automotive components made in AHSS have no need for new manufacturing and assembly technologies. Thus, their use has considerably increased in the last decade and the forecast is a further increase in the next one. The production process definition and simulation of AHSS components, aimed to reach a satisfactory compliance with design specifications, is a challenging task for automotive engineers. Due to their advanced material characteristics, the stamping simulation parameters used for common steels are often not sufficient to predict the springback of AHSS stamped components with an adequate accuracy. The AHSS materials are subject to higher material characteristics modifications during the stamping processes in comparison to common steels, because of their advanced mechanical characteristics and in particular because of their strain hardening characteristics. The crashworthiness could be affected by the production process parameters, especially concerning advanced high strength steel components. The main target of this Ph.D. dissertation is to examine subjects related to lightweight in the automotive design and specifically the use of advanced high strength steel, analyzing their production process problematics and their production processes influence on the vehicle crashworthiness.