针刺C/C复合材料面内拉伸强度预测

为研究针刺碳纤维增强碳基体复合材料(针刺C/C复合材料)面内拉伸强度与渐进损伤，建立了针刺C/C复合材料代表性体积单元有限元模型。模型包含无纬布层、网胎层、针刺纤维束、界面4类子区域，并考虑了孔隙的影响。采用基于应变的破坏准则及指数型损伤演化规律研究无纬布层及针刺纤维束损伤，采用弹塑性本构研究网胎层损伤，采用内聚力牵引分离定律和二次应力破坏准则分析界面损伤。通过两步法计算了孔隙对材料性能的折减效果，并得到上述4个子区域的力学性能，通过ABAQUS UMAT预测了材料的面内拉伸应力-应变曲线及各子区域损伤起始、演化与失效过程，非线性趋势及拉伸强度数值与试验数值吻合较好，验证了该模型有效性。 

Prediction of in-plane tensile strength of needle punched C/C composites

In order to study the in-plane tensile strength and the progressive damage behavior of needle punched carbon fiber reinforced carbon composites (needle punched C/C composites), a representative volume element finite element model of needle punched C/C composites was established. The model was divided into four sub-regions: non-woven cloth, short cut fiber felt, needling fibers and interface, and the effect of pores was estimated. Based on the failure criterion and exponential damage evolution law, the damage of the non-woven cloth and needling fibers was studied. The damage of the short cut fiber felt was defined by an elastic-plastic constitutive method. A cohesive force traction separation law and a quadratic nominal stress criterion were adopted at the interface. The negative influence of pores on mechanical properties of the material was considered by two steps. Then, mechanical properties of the four sub-regions were calculated. The in-plane tensile stress-strain curve of the material was predicted through ABAQUS UMAT subroutine, and the damage initiation, propagation and failure of the four sub-regions were simulated. The nonlinear trend and tensile strength agree well with experimentally measured data, which verifies the proposed model.