基于微观力学的复合材料低速冲击损伤演化及剩余疲劳寿命预测

The quantity of the ultra high-strength carbon fiber reinforced polymer (CFRP) composites used in the new developed aircraft is an important indication of the advanced degree of the structure. Whether the CFRP can be used extensively depends on the reliability and durabity of this kind of material. The CFRP laminates are susceptible to various damage, especially the low-velocity impact damage. The failure modes of CFRP laminates may initiate from either fiber, or matrix, or interface. After crack initiation, the damage evolution and residual strength and life of the composite structure are difficult to be evaluated. For the composite materials，the fiber strengths are influenced greatly by the the matrix. For the composite strutures for the long time service, the effect of viscoelasticity of the matrix resin on the composite material should be taken into account.For the the composite struture under fatigue loading, both the cycle number and the loading time should be considered. The conventional design theory faces challenge coming from above phenomena. The project applicant proposed new design theory about fatigue life of CFRP based on the theory of micro-mechanics of failure(J COMPOS MATER,2008), which provided a new methodology for the design of residual fatigue strength and life of CFRP. In this project, the theory of micro-mechanics of impact failure will be developed for the important and complicate low-velocity impact damage analysis, including the failure mechanisms of the CFRP laminate under impact loading, characterization of the impact strengths of the constituents and interface, and the design theory based on the micro-mechanics of failure will be established for the damage analysis for the composite structure under low-velocity impact loading, and for the evaluation of the residual fatigue strength and life after impact loading.

超轻高强碳纤维增强高分子复合材料的用量已成为飞机先进性的一个重要标志。复合材料使用可靠性和安全性是复合材料能否大量使用的关键。复合材料容易受到各类损伤，尤其是各种低能量物体的冲击，失效模式复杂，有可能是纤维、基体、或者界面；结构受初步损伤以后，损伤扩展较难判断，剩余疲劳寿命估算困难；纤维强度受基体性能的影响非常大，基体的粘弹性决定了复合材料性能也是粘弹性的，疲劳失效不但要考虑疲劳次数的影响，而且应考虑疲劳加载时间的影响。以上问题对传统复合材料疲劳强度设计理论提出了新的挑战。课题申请人提出了基于组分微观力学失效机理的复合材料疲劳强度表征和寿命设计理论,为复合材料疲劳强度理论和试验研究提供了一个新思路。本项目研究冲击状态下微观力学失效理论，对复合材料层合板结构的低速冲击损伤机理进行分析，对组分和界面的冲击强度进行表征，建立基于组分微观力学失效机理的结构冲击损伤、冲击后剩余疲劳寿命评价的方法。

超轻高强碳纤维增强高分子复合材料的用量已成为飞机先进性的一个重要标志。复合材料使用可靠性和安全性是复合材料能否大量使用的关键。复合材料容易受到各类损伤，尤其是各种低能量物体的冲击，失效模式复杂，有可能是纤维、基体、或者界面；结构受初步损伤以后，损伤扩展较难判断。本课题构建了一套微观力学失效（MMF）分析模型，该方法能够深入到纤维和基体内部的不同区域，实现对纤维和基体组分的失效位置及失效模式的精确分析，构建了一套非交互式组分失效判据，能够显著提高微观失效分析的计算效率。基于连续介质损伤力学构建了针对不同失效模式的材料性能退化模型，实现了对碳纤维增强复合材料的渐进损伤分析。采用双线性内聚力模型实现对分层损伤起始及扩展的分析。利用非线性-MMF方法对复合材料多向层合板螺栓结构静载拉伸，疲劳拉伸的强度及失效机制进行了分析。同时利用非线性-MMF方法对分别含间隙和预紧力的准各向同性多向层合板螺栓结构静载拉伸，疲劳拉伸的强度及失效机制进行了分析后与不含间隙和预紧力的情况进行对比。通过层间断裂韧性试验，确定了内聚力模型的关键参数。基于MMF理论，研究了相同冲击能量下不同铺层顺序、相同铺层顺序时不同铺层能量下的复合材料层合板的结构响应，面内及层间损伤失效行为。构建了冲击后碳纤维复合材料层合板的压缩模型，基于MMF理论分析了冲击损伤复合板在压缩载荷下的逐步失效行为，确定了影响冲击后压缩强度的关键因素，为复合材料层合板的材料及铺层设计提供思路。对ASTM D7137标准压缩夹具进行了改进，实现了对薄板复合材料层合板的剩余压缩强度的试验分析，验证了本研究所提出的模型的准确性。相关成果已经发表在《Composite Structures》等SCI期刊上。