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应用相变增韧、相变-晶须复合及相变-颗粒复合三种方式来改善氧化铝陶瓷的力学性能,研究了陶瓷基复合材料的疲劳特性。 在循环压缩载荷作用下,陶瓷材料的应力集中处(如缺口)会产生垂直于压应力轴的疲劳裂纹,随循环周次的增加,裂纹的扩展由快到慢,最终完全停止。循环压缩疲劳裂纹的形成机理是较大的应力集中使材料内出现以微裂纹为主要形式的不可逆损伤,在随后的卸载过程中,不可逆损伤区产生很高的残余拉应力,使疲劳裂纹形核并逐渐扩展。 陶瓷材料在四点弯曲循环载荷作用下,疲劳裂纹具有较长的亚临界扩展过程。裂纹护展速率与循环载荷的最大应力强度因子K_(max)及应力强度因子幅度△K都有关,且随载荷频率的降低及载荷波形由三角波变为正弦波,裂纹扩展速率增加。陶瓷材料四点弯曲疲劳裂纹的亚临界扩展是材料内损伤逐渐累积的结果。疲劳过程中材料通过形成微裂纹及裂纹分叉、克服增强物的阻碍及裂纹表面的桥接与互锁作用、产生裂尖微区内的塑性变形及部分稳定ZrO_2的相变等方式来消耗能量,在材料内造成以微裂纹为主要形式的微观损伤,从而弱化了材料,使疲劳裂纹得以亚临界扩展。 陶瓷材料在1050℃高温下的强度约为其室温强度的一半。陶瓷材料的高温循环疲劳是高温静载效应与循环载荷效应的迭加,1050℃下,循?
The mechanical properties of alumina ceramics were improved by phase change toughening, phase transformation - whisker recombination and phase transformation - particle composites. The fatigue properties of ceramic matrix composites were studied. Under the cyclic compressive load, the stress concentration points (such as notches) of the ceramic material will produce fatigue cracks perpendicular to the compressive stress axis. With the increase of the cyclic cycle, the crack propagation will increase from fast to slow, and finally stop completely. The formation mechanism of cyclic compression fatigue crack is that the larger stress concentration causes the irreversible damage in the material, which is the main form of microcracks. In the subsequent unloading process, the residual tensile stress in the irreversible damage area will be high and the fatigue crack nucleation And gradually expanded. Under the four-point bending cyclic loading, the fatigue crack has a longer subcritical expansion process. The crack propagation rate is related to the maximum stress intensity factor K max of the cyclic load and the amplitude Δ K of the stress intensity factor. The crack growth rate increases with the decrease of the load frequency and the change of the load waveform from the triangular wave to the sine wave. The subcritical expansion of a four-point bending fatigue crack in a ceramic material is a result of gradual accumulation of damage within the material. In the fatigue process, the material consumes energy through the formation of microcracks and crack bifurcations, overcoming the obstructions of reinforcements and bridging and interlocking on the crack surfaces, resulting in plastic deformation in the crack tip micro-zone and the phase transition of partially stabilized ZrO 2, In the material, microcracks are the main form of micro-damage, which weakens the material and makes the fatigue crack to subcritical expansion. The strength of a ceramic material at a high temperature of 1050 ° C is about half that of its room temperature. High temperature cyclic fatigue of ceramic materials is the superposition of static load effect and cyclic load effect at high temperature. Under 1050 ℃,