Structure Simulation Of Car Body Considering Formability Effects

With the amount of global auto product increasing rapidly,the three themes,safety of product,energy consumption and environment contamination become research focus,which have to be concerned and solved in the automotive engineering industry.Lighting product weight in design,which not only help to reduce fuel consumption and save energy,but also let out less exhaust.Car body is one of three assemblies(engine,chassis and body) which takes 40-60 percent of the whole vehicle weight.So,it is significant and practical to lighten structure weight in car body design.Modern CAE technology is an important approach to implement lighting design,its accuracy and reliability is the key to realize the design.Structure component and exterior panel of auto body especially car body are formed by cold forming,which will induce thickness variation,cause residual strain,residual stress etc.These effects will influence stiffness,strength,vibration performance and fatigue durability of car body and parts,but the general simulation ignores them.So,prior to structure analysis of car body,it is necessary to carry out parts pre-analysis for forming process.Then,taking these formability effects into structure simulation and fatigue life analysis,so that more valid and practical simulation results can be taken,these results can provide amount of accuracy data to car body structure weight-light design and optimization.Using one-step inverse forming finite element method,adopting automobile panel forming software KMAS owned by research group,program component for considering formability effects are programmed based on COMX.Integrating the one-step forming analysis into structure simulation is performed.Taking the body in white and front rail as simulation example,and then simulate them by MSC.Nastran software based on one-step inverse forming method.The effects of element nodal thickness and element effective plastic strain for structure are mainly researched.It is noted from the simulation results that the structure simulation method with forming effects is necessary to be carried out,especially the effective plastic strain effects obviously in nonlinear problems.Fatigue durability analysis,as an important aspect of CAE,we take frontal Suspension Tower as example in this paper,the effect of nodal thickness variation and residual strain on fatigue properties is investigated,Local stress-strain approach is used to predict fatigue life, then biaxial correction is performed to the part's uniaxial fatigue.Based on the result of simulation,effect of forming process on crack initiation analysis of car component is analyzed in quantity.