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用氮化硼纳米管(BNNT)增强氮化硅(Si3N4)陶瓷制备了BNNT/Si3N4复合材料,利用三点弯曲强度及单边切口梁(SENB)法测定了BNNT/Si3N4复合材料的弯曲强度和断裂韧性。通过SEM观察了BNNT/Si3N4复合材料微观形貌。基于BNNT增强Si3N4陶瓷复合材料的裂纹扩展阻力计算公式,构建了BNNT对Si3N4陶瓷裂纹屏蔽区的裂纹扩展阻力的数学模型。用该模型的计算结果与Si3N4陶瓷的裂纹扩展阻力进行了对比。结果表明:BNNT/Si3N4复合材料的弯曲强度和断裂韧性明显高于Si3N4陶瓷,说明BNNT对Si3N4陶瓷的裂纹扩展有阻力作用,摩擦拔出是Si3N4陶瓷抗裂纹扩展能力提高的主要原因;BNNT对Si3N4陶瓷有明显的升值阻力曲线行为。通过有限元模拟裂纹尖端应力分布,发现BNNT使Si3N4陶瓷裂纹尖端的最大应力转移到纳米管上,而且BNNT降低了Si3N4陶瓷裂纹尖端的应力,对Si3N4陶瓷尖端的裂纹有屏蔽作用,从而提高了Si3N4陶瓷的裂纹扩展阻力。
The BNNT / Si3N4 composites were prepared by the addition of boron nitride nanotubes (BNNT) on Si3N4 ceramics. The flexural strength of BNNT / Si3N4 composites were measured by three-point bending strength and unilateral notched beam (SENB) Fracture toughness. The microstructure of BNNT / Si3N4 composite was observed by SEM. Based on the calculation formula of crack growth resistance of BNNT reinforced Si3N4 ceramic composites, a mathematical model of the crack growth resistance of BNNT to the cracked area of Si3N4 ceramics was constructed. The calculated results of this model are compared with the crack propagation resistance of Si3N4 ceramics. The results show that the flexural strength and fracture toughness of BNNT / Si3N4 composites are obviously higher than that of Si3N4 ceramics, which shows that BNNT has a resistance to the crack propagation of Si3N4 ceramics. Friction and pulling out are the main reasons for the improvement of crack growth resistance of Si3N4 ceramics. Ceramics have a clear appreciation of the resistance curve behavior. Through the finite element simulation of crack tip stress distribution, it is found that the BNNTs transfer the maximum stress of the Si3N4 ceramic tip to the nanotube, and the BNNT reduces the stress at the crack tip of Si3N4 ceramic and shields the crack tip of the Si3N4 ceramic, thus increasing the Si3N4 Ceramic crack propagation resistance.