Simulation Analysis Of Layered Expansion Of Composite Materials For Vehicles Based On Trilinear Cohesive Model

With the rapid development of China’s auto industry,vehicle lightweighting,as an important measure for energy conservation and emission reduction,has been paid more and more attention by the auto industry.Due to its superior performance,carbon fiber material has become one of the most effective ways for automobile manufacturers to achieve lightweight.As carbon fiber parts of the automobile have been subjected to various shocks and vibrations during the whole service process,the stress situation is very complex.Generally,carbon fiber laminates are made of carbon fiber prepregs with anisotropic properties,so the interlaminar properties of carbon fiber laminates become the key to determine the overall performance of carbon fiber parts.Therefore,the most common failure mode of carbon fiber laminates is delamination failure,i.e.interlayer debonding.As the type Ⅰ fracture toughness of carbon fiber laminates is smaller than that of types II and III,the delamination damage of carbon fiber laminates is often dominated by type Ⅰ delamination,and the damage caused by type Ⅰ delamination is the largest.Therefore,this paper focused on the type Ⅰ delamination growth damage of carbon fiber laminates.In this paper,the the effects of the layup sequence and specimen thickness on the fracture toughness of carbon fiber laminates were studied by combining experiments and digital simulation analysis with the aim of type Ⅰ delamination expansion damage of carbon fiber laminates.In terms of experiments,firstly,the T300/EPW epoxy resin-based unidirectional carbon fiber prepreg provided by Shandong Guangwei Company was used to make the laminate DCB specimens with four layup sequences and two thicknesses;And then,the DCB specimen of the laminate was stretched by a universal mechanical testing machine.The stable fracture toughness,the initial fracture toughness and the length of the fiber briging region were obtained via calculating the type Ⅰ fracture toughness by the modified beam theory method.Finally,the fiber bridging stress distribution and the maximum fiber bridging stress were obtained by fitting the fracture toughness R curve.In terms of simulation,firstly,the bilinear cohesion model was used to establish the finite element model of the DCB specimen without fiber bridge.The influence of cohesion parameters and viscosity coefficient on the simulation results was discussed.And then a trilinear cohesion model was built by stacking two bilinear cohesion models.And the UMAT subroutine for the secondary deveilopment was developed in the commercial software ABAQUS.The numerical simulation operation of the type Ⅰ layered expansion of the DCB specimen of the laminate considering the influence of fiber bridging was carried out;By comparing with the experimental results and the simulation results of the bilinear cohesion model,the effectiveness and superiority of the trilinear cohesion model were verified.The experimental results show that the initial fracture toughness of the unidirectional laminate and the multidirectional laminate are basically equal,but the stable fracture toughness of the multidirectional laminate is greater than that of the unidirectional laminate.The fiber bridging area of unidirectional laminates is longer than that of multidirectional laminates.The thickness of the specimen has no obvious effect on the initial fracture toughness.However,the stable fracture toughness of the36-layer laminate is greater than that of the 48-layer laminate under the same layup sequence.The simulation results show that the trilinear cohesion model constructed by the bilinear cohesion model can describe the fiber bridging phenomenon effectively.For the type Ⅰ layer damage gowth of unidirectional laminate,both the bilinear cohesion model and the trilinear cohesion model show higher simulation accuracy,and the calculation result of the trilinear cohesion model is more accurate;For the type Ⅰ layered damage growth of multi-directional laminates,the numerical simulation results of the bilinear cohesion model have large errors,but the numerical simulation results of the trilinear cohesion model are basically consistent with the experimental results.The investigation of the effects of layering sequence and thickness on the type Ⅰ fracture toughness and fiber bridging stress distribution of carbon fiber laminates in this paper has a positive significance for improving the type Ⅰ fracture toughness and strength of carbon fiber laminates used in vehicle.The trilinear cohesion model constructed by superimposing the bilinear cohesion model can provide referenced model and theoretical guidance for the numerical simulation of the carbon fiber laminate type Ⅰ layer damage growth.