Research On Design Of Engine Hood With Long Glass Fiber Reinforced Thermoplastics

With the rapid development of automobile industry,energy reduction and environmental pollution have become increasingly serious.The world’s major automobile manufacturers have started the research of new energy vehicles,in order to reduce the increasingly scarce energy use.In the design process of new energy vehicles,automotive lightweight design has become particularly important,"the concept of plastic steel" is increasingly recognized by the major automobile manufacturers.The research content of this paper is to replace the traditional steel materials by using the more lightweight,better performance long glass fiber reinforced thermoplastic composites.The specific research contents of this paper are as follows:In order to determine the constitutive model of LGFT material,the first is to test the mechanical properties of LGFT materials,including tensile test,bending performance test,impact performance test.Second,we establish material ST14 hood model,and carries on the finite element analysis,including analysis of torsional rigidity,the lateral stiffness,lock stiffness analysis and modal analysis.The analysis used to determine whether meet the principle of static analysis of engine hood.We also established a finite element model of the collision between the head type impactor and the engine cover model,and carried out the safety analysis of the pedestrian protection.Through the analysis,we found that the engine cover model of the steel plate material does not satisfy the evaluation criteria of pedestrian head injury,so it is necessary to improve the structure or choose other materials to replace the original steel material.Finally,considering the defects in the design of the original steel hood,we replaced the ST14 material with LGFT material by the principle of equal stiffness substitution.At the same time,we improved the engine cover of LGFT materials to find out the factors affecting the HIC value of the head.It is found that three main factors are the thickness of the front hatch cover,the thickness of the outer plate and the structure layout of the inner plate.We adopt orthogonal test,the optimal solution of the three factors to find out the optimal hood structure which satisfies pedestrian head injuries to evaluation standard and meet the design the required stiffness and first-order modal frequency.The results show that the optimal design of LGFT material engine cover structure can be obtained by using equal stiffness substitution method and orthogonal experiment method.The optimal solution is the outer plate thickness of 2.5mm,the inner plate thickness of 3mm,and the inner plate structure is convex.Under the same working conditions,the stiffness of the engine hood of LGFT materials is increased compared with that of steel material,and the first-order mode frequency is also increased by 6%.In terms of safety,the HIC values of the test points of the children’s head-type collision engine were reduced to a certain extent,and the HIC value of the C4C test point decreased by 46.3%.The research of this paper provides a reference for the design of the long glass fiber reinforced thermoplastic composite engine hood,which opens up a new way of thinking for the application of composite materials in automobile.