While structural ceramics usually display a brittle mechanical behavior, their composites may show nonlinearities, mostly due to microcracking. Herein, the stiffness evolution of a sandwich-like laminate of an Al₂O₃−15%vol. ZrO₂ matrix reinforced with Nextel 610 fibers is studied as a function of number of cycles N in tension. The stiffness of the composite degrades with increasing N, indicating microcracking. However, synchrotron X-ray refraction radiography shows that the internal specific surface of such cracks varies differently. A modeling strategy is developed for the calculation of the equivalent stiffness of mixtures (first the matrix and then the sandwich), based on the Voigt and Reuß schemes. The Bruno–Kachanov model is then used to estimate the initial microcrack density in the matrix (due to the thermal expansion mismatch) and the amount of microcracking increase upon cyclic loading. The stiffness in the composite degrades dramatically already after 20 000 cycles but then remains nearly constant. The combination of mechanical testing, quantitative imaging analysis, and modeling provides insights into the damage mechanisms acting: microcrack propagation is more active than microcrack initiation upon cyclic loading, but the second also occurs. This scenario is similar but not equal to previous results on porous and microcracked ceramics.

中文翻译：

---

循环加载后全氧化物陶瓷基复合材料的损伤演变

虽然结构陶瓷通常表现出易碎的机械行为，但它们的复合材料可能表现出非线性，主要是由于微裂纹。_{在此，Al 2} O ₃ -15%vol的夹层状层压板的刚度演变。研究了用 Nextel 610 纤维增强的ZrO ₂基体作为拉伸循环数N的函数。复合材料的刚度随着N的增加而降低，表示微裂纹。然而，同步加速器 X 射线折射射线照相显示，此类裂纹的内部比表面变化不同。基于 Voigt 和 Reuß 方案，开发了一种用于计算混合物（首先是基体，然后是三明治）的等效刚度的建模策略。然后使用 Bruno-Kachanov 模型来估计基体中的初始微裂纹密度（由于热膨胀失配）和循环加载时微裂纹的增加量。复合材料的刚度在 20 000 次循环后已经显着降低，但随后几乎保持不变。机械测试、定量成像分析和建模的结合提供了对损伤机制的深入了解：微裂纹扩展比循环加载时微裂纹萌生更活跃，但第二个也会发生。这种情况类似于但不等于先前在多孔和微裂纹陶瓷上的结果。