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Demands are increasing for the reduction of vehicle weight to enhance automobile fuel efficiency and driving performance, with the use of aluminum alloys expected to help. High-strength aluminum alloys (6xxx series, 7xxx series) are called for to enhance crash safety performance, and the prediction of material fracture is a key factor in the application of these alloys. This research presents a FEM model that can predict both tensile fracture and bending fracture when large deformations occur in the extrusion direction of high-strength aluminum alloy extrusion. The fracture characteristics of high-strength aluminum alloy extrusion were obtained by tensile and bending tests, and the factors governing ductile performance were clarified. Fracture was defined in the FEM model using the Cockcroft-Latham ductile fracture model.

This report describes the mechanical properties, formability, weldability, and collision deformation performance of the new 980 MPa-grade steel sheet used in the front side frame of an automobile’s body framework. In order to determine the material properties of the 980 MPa-grade steel sheet needed for use in the front side frame, the study used special bending tests to find the threshold values at which cracking occurred during collision deformation. It was found that these special bending characteristics correspond closely to hole-expansion properties and it is necessary to increase hole-expansion properties of the new 980 MPa-grade steel sheet. The new 980 MPa-grade steel sheet with high hole-expansion properties has an enhanced forming limit curve compared to conventional 980 MPa-grade steel sheet, and can be formed to the shape of the front side frame. In collapse tests simulating collision deformation, the steel sheets demonstrated the necessary performance without cracking.

Mechanical properties, formability and crash worthiness of a new sheet steel having an ultrafine grained (UFG) multi-phase (MP) microstructure are shown. The fabricated UFG-MP steel showed significant work hardening caused by deformation induced martensitic transformation of retained austenite, which resulted in a combination of high strength and large tensile elongation. It was confirmed by dynamic collapse test and FEM simulation that the large work hardenability of the UFG-MP steel promoted compact mode collapse that improved the absorbed energy.