J积分法研究温度对Al⁃PTFE反应材料断裂韧性的影响

Effect of Temperature on the Fracture Toughness of Al⁃PTFE Reactive Material by J⁃integral Method

为探究聚四氟乙烯(PTFE)的温度引发相变特性对铝‑聚四氟乙烯(Al‑PTFE)反应材料断裂韧性的影响,通过开展准静态拉伸实验和断裂韧性实验,使用ASTM E1820单试样法中的归一化数据简化技术,对Al‑PTFE的弹塑性断裂韧性进行J积分分析,结合试样断面微观形貌分析,明确了温度对Al‑PTFE断裂韧性的影响。结果表明:随着温度的升高,Al‑PTFE反应材料强度降低,断裂韧性增大,屈服强度和断裂韧性在跨越相变温度后呈现明显的突跃变化,裂纹扩展模式由脆性断裂转变为延性断裂。当PTFE处于结晶相Ⅱ状态时,能够拉伸形成的PTFE纤丝较少,而当温度升高,PTFE晶相向Ⅳ和Ⅰ状态转变时,稳定成形的PTFE纤丝能够通过局部塑性变形有效耗散外部能量,并依托缠绕桥接使裂纹尖端发生钝化,阻止裂纹扩展,从而提高材料断裂韧性。

To investigate the influence of temperature‑induced phase transition of polytetrafluoroethylene(PTFE)on the fracture toughness of Al‑PTFE reactive material,the quasi‑static tensile test and fracture toughness test were performed,and the normalization data reduction technique with single specimen in ASTM E1820 was applied for analyzing the elastic‑plastic fracture toughness of Al‑PTFE by J‑integral method.Combined with the microstructures analysis of the fracture surface,the effect of temperature on the fracture toughness of Al‑PTFE was revealed.The results show that the strength of Al‑PTFE reactive material decreases with the increase of temperature,while the fracture toughness increases.Moreover,the yield strength and fracture toughness of this material change obviously after crossing the phase transition temperature.The crack propagation pattern changes from brittle fracture to ductile fracture.Furthermore,when PTFE is in phaseⅡ,less PTFE fibrils can be formed by stretching.However,increasing temperature can lead to the transform of the crystal phase for PTFE to phaseⅣandⅠ.Besides,the stable formed PTFE fibrils can effectively dissipate the external energy in the form of local plastic deformation.The crack tip is passivated by winding bridging,so as to prevent the crack propagation and improve the fracture toughness of this material.