评价多孔Si3N4陶瓷断裂韧性的新方法——单向压缩试验

A Novel Method for Evaluating the Toughness of Porous Ceramics - Uniaxial Compression Testing

摘要:

人们常用单边梁切口法(SENB)评价多孔陶瓷的断裂韧性(K_1C),K_1C随孔隙率增加而不断下降,SENB测试结果表明多孔陶瓷中的微气孔、微裂纹不仅没有起到增韧作用阻止裂纹扩展,反而加速了扩展。而评价多孔陶瓷热震损伤抗力(R"""")时发现,多孔陶瓷R""""随孔隙率增加而增大,该理论表明气孔率增加阻止了裂纹扩展。很显然,采用SENB法测定的K_1C值与微裂纹增韧以及热震损伤理论相矛盾。多孔陶瓷的单向压缩试验表明,其σ-ε曲线可明显分为两部分,即弹性变形部分和非线性部分,非线性部分出现是由于众多微裂纹亚稳扩展所致,最终发生失稳断裂。用该法测出的断裂能,可量化微裂纹增韧效应,完善了多孔陶瓷断裂韧性的测试方法。

Abstract:

Traditionally, the fracture toughness (K_1C) of porous ceramics is evaluated by single edge notched beam method (SENB). For porous ceramics, the fracture toughness by SENB increases with decreasing porosity, it demonstrating that lower porosity improve the crack propagation resistance. However, previous experimental experience suggests that the thermal shock damage resistance (R"""") of porous ceramics will be increased with increasing porosity, it demonstrating that the high-porosity ceramics have the better capability to improve the crack propagation resistance in thermal shock situation. It is obvious that the SENB method is concluded to be in contradiction with the thermal shock damage theory. The uniaxial compression testing of porous ceramic indicating that the σ-ε curve can be divided into two parts, linear part and nonlinear part. Due to the metastable propagation of multi-micro-crack, the σ-ε curve displays nonlinear behavior. The fracture energy measured by uniaxial compression testing can be also used to characterize the quantity of mirco-crack-toughen effect, it can improve the test method of fracture toughness for porous ceramics.