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This article covers an application of third-generation advanced high-strength steel (3GAHSS) grades to vehicle lightweight body structure development. Design optimization of a vehicle body structure using a multi-scale material model is discussed. The steps in the design optimization and results are presented. Results show a 30% mass reduction potential over a baseline mid-size sedan body side structure with the use of 3GAHSS.

This paper presents development of a multi-scale material model for a 980 MPa grade transformation induced plasticity (TRIP) steel, subject to a two-step quenching and partitioning heat treatment (QP980), based on integrated computational materials engineering principles (ICME Model). The model combines micro-scale material properties defined by the crystal plasticity theory with the macro-scale mechanical properties, such as flow curves under different loading paths. For an initial microstructure the flow curves of each of the constituent phases (ferrite, austenite, martensite) are computed based on the crystal plasticity theory and the crystal orientation distribution function. Phase properties are then used as an input to a state variable model that computes macro-scale flow curves while accounting for hardening caused by austenite transformation into martensite under different straining paths.

The ability to quickly design new vehicles with optimal crashworthiness has long been a goal of automotive manufacturers and Tier 1 suppliers alike. This paper takes steps towards that goal by automating manual design iterations. The crashworthiness of an instrument panel was optimized using LS-OPT. In one design experiment, optimizing the gauges of non-styled parts in the instrument panel reduced the simulated force in a Bendix test setup by around 30%. In a second design experiment, optimizing the shape of non-styled parts in the instrument panel with a parametric preprocessor enhanced the simulated crashworthiness by around 20%. In a third design experiment, the design space was increased and an additional 7% improvement in simulated crashworthiness was found. The designs were generated several times faster and were less expensive to evaluate than with previous manual methods.