Research On Crashworthiness Optimization And Software Development Using Equivalent Static Loads Method

The collision safety is one of the most important vehicle performances in which the crashworthiness occupies an important place.As a result,it is of great significance to reduce the weight of the vehicle under the premise of ensuring the safety of the car.Due to the fact that the crash problem is a kind of dynamic time domain problem consist of geometric,material and boundary conditions nonlinearities,so it is very difficult to apply the traditional methods in the nonlinear problems when we use the method based on gradient optimization to optimize the crash problems because structural nonlinear optimization gradient calculation is very complex.Equivalent Static Load Method(ESLM)converts the transient optimization nonlinear problems to static multi load cases optimization problems and the optimality of the solution in mathematics has been proved.In order to realize the application in the collision safety of the car,the work I have done is as follows:First of all,I have done some research on the theory of the ESLM including the definition,basic idea and the optimization process.Aim at the crashworthiness problem of the structural crushing and intrusion amount of the automobile,the ESLM based on the displacement of the key time point is proposed.On account of the so many time steps of dynamic analysis,it will cost a lot of time if we calculate the ESLs of all the time point.This method only needs to calculate the ESL corresponding to the max displacement response point which is used as the external loads to do the optimization.As a result,this method can tremendously reduce the calculation time of the ESLs.The optimization based on ESLM includes the dynamic analysis of the structure part and the static optimization part.Considering that we add the ESLs of the dynamic load case when we do the static optimization,the joint optimization of dynamic and static can be realized.Therefore,the dynamic-static joint optimization methods based on the ESLM of displacement is proposed and the optimization process of the dynamic-static has been designed.A kind of sheet-thickness size optimization software based on the ESLM of displacement is developed by Visual Basic.net,which can realize the ESLM optimization of all the time point or of all the time point or critical time point and the joint optimization of dynamic and static optimization.The software interface is so friendly that it is easy for users to operate,which shows a good man-machine interactive.Finally,three numerical examples are optimized based on the software we developed.The first numerical example is to optimize the crashworthiness of a simple front rail of top-hit.First,a kind of simple front rail of top-hit is designed.The samples are then prepared by the material of Q235.Then the impact tests of the sample are conducted.Then,an effective collision finite element model of the sample is established according to the size of sample and the boundary condition of the impact test.Finally,the ESLM of all time point and critical time point and genetic algorithm are used to optimize the crashworthiness of the simple front rail,and the results of optimization are compared and analyzed.From the optimization results we can see that the ESLM of critical time point can effectively deal with the large deformation collision optimization problem effectively and efficiently.The second example is to optimize the crashworthiness of front structure of a car.First,according to the regulations we establish an effective low-speed finite element model of front structure of a car.And then we use the software that we develop to optimize the low-speed crashworthiness of model.The third example is to optimize a simple front rail of top-hit under collision conditions condition and static bending condition.