Hertzian-crack suppression in ceramics with elastic-modulus-graded surfaces
Hertzian-crack suppression in ceramics with elastic-modulus-graded surfaces
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DOI：
10.1111/j.1151-2916.1998.tb02625.x
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发表时间：
1998-09-01
影响因子：
3.9
通讯作者：
Suresh, S
中科院分区：
文献类型：
--
作者：
Jitcharoen, J;Padture, NP;Suresh, S
在梯度氧化铝-玻璃复合材料中进行了赫兹(球形)压痕实验，其杨氏模数随压痕表面下深度的增加而增加。采用一种用铝硅酸盐玻璃浸渍致密细晶氧化铝的原位加工方法来制备这种复合材料。利用这种技术，在玻璃和氧化铝的热膨胀系数和泊松比几乎相同的情况下，在大约2 mm的距离内引入了高达50%的单调、单向的杨氏模数变化。这样生产的宏观梯度弹性复合材料具有几乎全密度，在加工后基本上没有宏观的、长期的残余应力。压头下杨氏模数的单向变化完全抑制了赫兹锥形裂纹的形成。在没有这些弹性模数梯度的情况下，在大块玻璃和氧化铝中观察到了锥形裂纹的形成。此外，还对弹性梯度衬底上的球形压痕进行了有限元分析，以期对实验趋势有一个定量的了解。这一创新涉及到功能梯度表面及其原位加工，为提高各种陶瓷材料在广泛的工程应用中的某些接触损伤特性提供了新的可能性。此外，在功能梯度陶瓷中，这种抗接触损伤现象本质上是弹性的，因此在弹性极限内很可能不受机械疲劳的影响。
Hertzian (spherical) indentation experiments were carried out in a graded alumina-glass composite whose Young's modulus increased with depth beneath the indented surface. An in situ processing method involving impregnation of a dense, fine-grained alumina by an aluminosilicate glass was employed to fabricate such a composite. With this technique, a monotonic, unidirectional variation in Young's modulus of as much as 50% was introduced over a distance of approximately 2 mm, while keeping the coefficient of thermal expansion and the Poisson ratio for the glass and the alumina nearly the same. The macroscopically graded, elastic composite so produced with nearly full density has essentially no macroscopic, long-range residual stresses following processing. The unidirectional variation in Young's modulus under the indenter is shown to fully suppress the formation of Hertzian cone cracks. Without these elastic-modulus gradients, cone-crack formation was observed in bulk glass and alumina. Finite-element analyses of spherical indentation on elastically graded substrates were also performed to develop a quantitative understanding of the experimental trends, It is reasoned that the present innovations, involving functionally graded surfaces and their in situ processing, provide new possibilities for enhancing certain contact-damage resistance characteristics in various ceramic materials for a broad range of engineering applications. Furthermore, this contact-damage-resistance phenomenon in functionally graded ceramics is elastic in nature, and is, therefore, likely to be immune to mechanical fatigue within the elastic limit.