Study On Toughness Damage Model Of Hot Stamping Parts For Mechanical Properties Gradient Distribution

Automotive lightweight technology is an important way to save energy and reduce carbon emissions.High strength boron steel can reduce weight by changing the thickness of the plate.Boron steel parts can be used in automotive B-pillar,but the material is not easy to deformation due to its high strength.Hot stamping technology can change this problem.Considering car safety performance,gradient property is applied to boron steel material.The principle is to increase the plasticity of parts and transform the impact energy.Damage and fracture study of gradient materials is of great practical significance for the design of automotive parts.The purpose of this paper is study how to get gradient materials and further study the damage and fracture of materials.In order to obtain a series of materials with gradient properties,a set of temperature-controllable mold was designed in this paper.The mold temperature was set to25°C~500°C.First,the blank is placed in a heating furnace for full austenitizing,then rapidly placed on the mold for stamping and cooling,and a series of gradient properties are obtained by changing the mold temperature.Through the hardness measurement,five representative materials were selected as the subject of this study.The metallographic analysis was used to determine the material structure.Finally,a quasi-static tensile test and numerical simulation were used to study the damage model of the materials.In order to study the damage and fracture properties of five materials,four tensile specimens were designed under different stress states.Standard tensile tests is used to obtain true stress-true plastic curves to study the flow stress model.The flow stress model is the basis for studying damage and fracture.In this paper,five flow stress models are selected for thisstudy.The model parameters were studied by three methods,and the model parameters were obtained by modeFRONTIER software through reverse optimization method.By comparing the force-displacement curves of the circular hole and the groove tensile test and simulation,Voce + Voce model can be simultaneously applied to the five materials.In order to further study the damage fracture of five kinds of materials,GTN and Johnson-Cook models were selected.Among them,the GTN model is used to simulate the hole and groove tensile test,Johnson-Cook model is used to simulate the pure shear tensile test.Based on the above research results,taking into account the influence of mold temperature on the damage model,the relationship between the damage parameters and the mold temperature was established by empirical formula,and this damage model was used to predict the gradient distribution performance of automotive parts.