Study On Key Techniques Of Safety Design For Automotive Side Impact

With the rapid development of the auto industry in our country, China has become the primary country for automobile production and sale, but traffic accidents and the resulting casualties and property losses also increased markedly as the increment of vehicle magnitude and driving speed at the same time. Especially the side collision keeping the highest accident rate, causing greater occupant injury since the region in vehicle body side has a weaker strength than other regions in vehicle compartment and lack of energy absorption devices, side impact safety design remains a difficult topic.Vehicle crash simulation is based on the finite element model, however, the increasing number of model elements requires for computing hardware and software to be enhanced, extend the computing time to solve the simulation accuracy and computational efficiency seems to be a pair of irreconcilable contradictions. How to make dialectical analysis for this issue, building crash models for different stages of development with different simulation accuracy and computational efficiency, to some extent, is of great significance; The real-world engineering problem of vehicle safety design involves in several uncertain factors such as impact velocity, impact location, material parameters, plate thickness, manufacturing factors, analysis model and the application environment of products, these uncertainties often lead to the design goals in a range of fluctuation. The quality of auto safety and cost of production also seems to be a pair of irreconcilable contradictions. How to make dialectical analysis for this issue, to some extent is of great significance.For the conflict of the simulation accuracy and computational efficiency in automotive side impact safety design process, the dissertation has developed side impact models for different stages with different simulation accuracy and computational efficiency; for the contradiction between design quality and design costs in automotive side impact safety design process, this dissertation has applied the method of quality engineering to make analysis in depth. The main innovative points of this dissertation are given as follows:(1) A FE model of moving deformable barrier (MDB) based on shell element is built by applying the shell element technology according to real structure of the honeycomb. For the situation of huge number of elements caused by shell element modeling as the same size of physics state, cell size and element size is enlarged by the identical scale. The out-of-plane compression simulation is executed to obtain the relationship between the thickness of shell elements comprising a honeycomb and compressive strength, a parameter study using a test piece is performed to achieve the compressive strength of the actual part. The air pressure effect is obtained from the results of punch tests by subtracting static punch test result from dynamic punch test result. Material failure is applied to simulate the failure phenomena of aluminum foil and the glue between the foil and the cover board during the crash. For the problem that one-dimensional beam element can not effectively simulate the torque problem of the spotweld, solid elements for spotweld are constructed to simulate the connection between the key parts of the side impact to impress the spotweld failure; For the problem of thickness change and resulting stress because of metal forming, the result of stamping-part thickness and the effective plastic strain is mapped to the collision model to simulate the stamping effects; For the problem of material strengthen of metal parts during high speed crush, Cowper-Symonds model is applied to express the strain rate effect.(2) In this paper,100DOE are conducted by Latin Hypercube experimental design in design of automotive side impact safety, the key response of vehicle structure and main response of dummy are extracted, the multiple linear regression model and the stepwise linear regression model are built between the response of vehicle structural as input parameters and the response of dummy as output parameters, and the equivalent relationship of the stepwise linear regression model is also built. The multiple linear regression model shows the relationship between dummy response and vehicle structural response comprehensively, while the stepwise linear regression model shows the relationship between dummy response and vehicle structural response which contributes significantly, and the equivalent relationship express it quantificationally, which provides reference for the automotive side impact design. The regression equation will be used to predict damage dummy value under the premise that side impact body structure response is known, and used to be the analysis standards for the simplified side impact model without the side impact dummy.(3) In the automotive concept design phase, we propose an establishing method of side impact simulation model composed of the mixing elements to simplify the finite element model based on the true mechanical properties (HD as an abbreviation). The HD model applies Hughes-Liu beam element (HL beam element) to simplify the thin-walled beams mainly exposed to bending loads in side impact; applies nonlinear spring elements to simplify the thin-walled beams mainly exposed to axial loads in side impact; applies plastic hinge spring elements to simplify the vehicle body joints; applies nonlinear spring elements to simplify the large sheet panels mainly exposed to shear loads such as floor; applies two-dimensional shell element to simulate large sheet panels under normal loads, and retains the main features of the contact surface; applies nonlinear spring elements to simplify the energy absorbing MDB blocks; applies mass distribution and moment of inertia to simplify other parts such chassis etc. HD model ensures the accuracy in engineering simultaneity greatly improves the computational efficiency.(4) Quality engineering method is proposed for the uncertainty in the field of engineering design, the method includes two steps:quality assessment and quality improvement. Quality assessment is achieved by the methods of Monte Carlo descriptive sampling; quality improvement is achieved by the methods of probabilistic optimization. Quality engineering method is used in lightweight design of automotive side impact safety, the approximate model of side impact is built by Latin Hypercube experimental design and Kriging model method. Deterministic optimization, reliability optimization and Six Sigma robust optimization are executed for the approximate model, the comparison of the optimal solutions and their quality is conducted for three methods. The results show that deterministic optimization algorithm tend to search for "peak" solutions while cannot ensure the quality of solutions; Reliability optimization and Six Sigma robust optimization tend to search for optimal solutions under the premise of guaranteeing quality.