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Fracture strain data provide essential information for material selection and serve as an important failure criterion in computer simulations of crash events. Traditionally, the fracture strain was measured by evaluating the thinning at fracture using tools such as a microscope or a point micrometer. In the recent decades, digital image correlation (DIC) has evolved as an advanced optical technique to record full-field strain history of materials during deformation. Using this technique, a complete set of the fracture strains (including major, minor, and thickness strains) can be approximated for the material. However, results directly obtained from the DIC can be dependent on the experiment setup and evaluation parameters, which potentially introduce errors to the reported values.

Motivated by a combination of increasing consumer demand for fuel efficient vehicles, more stringent greenhouse gas, and anticipated future Corporate Average Fuel Economy (CAFE) standards, automotive manufacturers are working to innovate in all areas of vehicle design to improve fuel efficiency. In addition to improving aerodynamics, enhancing internal combustion engines and transmission technologies, and developing alternative fuel vehicles, reducing vehicle weight by using lighter materials and/or higher strength materials has been identified as one of the strategies in future vehicle development. Weight reduction in vehicle components, subsystems and systems not only reduces the energy needed to overcome inertia forces but also triggers additional mass reduction elsewhere and enables mass reduction in full vehicle levels.

Advanced High Strength Steels (AHSS) have been implemented in the automotive industry to balance the requirements for vehicle crash safety, emissions, and fuel economy. With lower ductility compared to conventional steels, the fracture behavior of AHSS components has to be considered in vehicle crash simulations to achieve a reliable crashworthiness prediction. Without considering the fracture behavior, component fracture cannot be predicted and subsequently the crash energy absorbed by the fractured component can be over-estimated. In full vehicle simulations, failure to predict component fracture sometimes leads to less predicted intrusion. In this paper, the feasibility of using computer simulations in predicting fracture during crash deformation is studied.

Springback is a major concern in stamping of advanced high strength steels (AHSS). The existing computer simulation technology has difficulty predicting this phenomenon accurately even though it is well developed for formability simulations. Great efforts made in recent years to improve springback predictions have achieved noticeable progress in the computational capability and accuracy. In this work, springback simulation studies are conducted using FEA software LS-DYNA®. Various parametric sensitivity studies are carried out and key variables affecting the springback prediction accuracy are identified. Recently developed simulation technologies in LS-DYNA® are implemented including dynamic effect minimization, smooth tool contact and newly developed nonlinear isotropic/kinematic hardening material models. Case studies on lab-scale and full-scale industrial parts are provided and the predicted springback results are compared to the experimental data.

Advanced High Strength Steels (AHSS) along with innovative design and manufacturing processes are effective ways to improve crash energy management. Crash trigger hole is another technology which can been used on front rails for controlling crash buckling mode, avoiding crash mode instability and minimizing variations in crash mode due to imperfections in materials, part geometry, manufacturing, and assembly processes etc. In this study, prototyped crash columns with different trigger hole shapes, sizes and locations were physically tested in frontal crash impact tests. A corresponding crash computer simulation model was then created to perform the correlation study. The testing data, such as crash force-displacement curves and dynamic crash modes, were used to verify the FEA crash model and to study the trigger sensitivity and effects on front rail crash performance.

Advanced high strength steels (AHSS), such as dual phase (DP) and transformation induced plasticity (TRIP) steels, have been used successfully for making light weight vehicles and their usage is growing. Now, the automotive industry is expanding the use of AHSS to higher strength levels for further mass reduction. In a 2003 SAE paper, the material and formability characteristics for such steels were presented for steel grades of DP980, high yield type DP780 (780YM), low yield type DP780 (780YL), TRIP780, and TRIP590. In this study, experiments were conducted to assess the formability of these high strength steels using a T-channel, which incorporates several different forming modes in automotive stamping. The feasibility of computer simulation technology for the formability analyses of AHSS is also addressed.