Multiscale Progressive Damage Analysis Of 3d Basalt Fiber Composites With Pore Defects

Three dimensional basalt fiber composites have excellent mechanical properties,good environmental adaptability and low price.They have the potential to replace carbon fiber composites in aerospace,shipbuilding,automobile and other high-tech fields.However,in the manufacturing process of fiber-reinforced resin matrix composites,due to various factors,pore defects are inevitable.These pore sizes reach the micron level and are not visible to human eyes.The existence of initial pore defects will have a great impact on the mechanical properties of composites.In the previous numerical simulation of fiber composites,the influence of initial pore defects was not considered.In recent years,the literature begin to consider the initial pore defects in the simulation model,but the pores are often evenly distributed in the model,which does not accord with the characteristics of random distribution of pore defects.Research in this area is mostly focused on carbon fiber composites,less on basalt fiber composites.Composites have multi-scale characteristics.Multi-scale simulation method can consider the effects of micro damage and evolution on macro material properties and mechanical behavior.It is an important method and means of composite response analysis.Therefore,the multi-scale method is used to reveal the fracture failure mode of materials from the micro level.The finite element models with defects are established at the micro,micro and macro scales to reveal the influence of defects on the mechanical properties and damage failure mechanism of materials.In this paper,the micro composition of the composite material is obtained by means of micro CT scanning,the macro mechanical behavior of the material is interpreted from the micro and micro levels,and the damage of the material is predicted at multiple scales.The research results of this paper play a certain role in evaluating the influence of pore defects on the mechanical properties of three-dimensional basalt fiber composites,and further enrich the research of basalt fiber composites.The specific research contents are as follows:(1)The resin based three-dimensional basalt fiber composites were prepared,and the relevant macro mechanical property tests were carried out,including tensile,in-plane shear and three-point bending tests.The basic mechanical property parameters,fracture location,fracture direction and fracture strength were obtained.The initial void defect rate was obtained by micro CT scanning test.(2)At the micro scale,the micro void-model with spherical defects model and element-model with element defects of three-dimensional fiber composites are established.The differences between the two models in predicting the elastic properties of meso fiber bundles are compared and analyzed.The results show that the error range between them is 1%-4%,and the element defect construction method and approximate void defect construction method can be used for subsequent simplified calculation;The damage of micro cells under different load conditions is analyzed.The results show that under tensile load,the initial damage of the matrix will occur at the position with defects and large geometric transition area,and then the damage will expand to the position where the surface of the matrix is parallel to the loading direction;Under in-plane shear load,the overall mechanical properties of the matrix are relatively uniform,and the influence of defects on the damage of the matrix is limited;Under out of plane shear load,the interface between fiber and matrix will squeeze the fiber,the fiber interface tangent to the matrix will produce initial damage,and the matrix will be completely damaged at the diagonal of displacement.(3)The finite element model of meso unit cell defect is established by using the element-model with element defects construction method,the equivalent macro elastic modulus of meso unit cell is predicted,and the attenuation of the initial pore defect rate to the macro elastic modulus is quantified.The damage of meso unit cell under different load conditions is analyzed by element defect model.The results show that:With the increase of pore defect rate,the elastic modulus will gradually decline.When the defect rate increases from 0% to 5%,the shear modulus decreases to about 80%;The attenuation of tensile elastic modulus is about 90%.Under tensile load,the damage position is first at the fiber junction of warp and weft yarn and warp sewing yarn,and finally the warp and weft yarn will break;The fracture direction is about 45 ° in the shear direction of the matrix;Under out of plane shear load,the damage is distributed at the interface of fiber and the surface of matrix.(4)At the macro scale,multi crack inclusions are used to replace the initial defects,and the macro model of composite materials with multi crack inclusions is established,which is combined with the propagation finite element method to predict the crack propagation.Apply tensile,shear and three-point bending loads to simulate the final fracture.The results show that the fracture stress under the three loads is within the error range of 7%,and the fracture direction of the simulation model is consistent with that of the test sample.However,due to the existence of random defects,the fracture failure of the sample will occur at the place with high crack density,and the propagation direction will produce fracture phenomenon along the crack tip and parallel to the stress loading.