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Fatigue crack growth bridging mechanisms in titanium metal-matrix composites.

机译：钛金属基复合材料的疲劳裂纹扩展桥接机制。

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摘要

The bridging fatigue crack growth damage mechanisms in a unidirectional SiC/Ti MMC include matrix cracking, fiber/matrix interface debonding and sliding along bridging fibers and fracture of these fibers. The basic components of these mechanisms are examined in this program. The evolution characteristics of residual stresses indicated that extensive stress relaxation occurred in the Ti-alloy matrix phase of the composite following post-fabrication cool down to {dollar}rm 600spcirc C.{dollar} Parametric study on the SiC fiber coating materials showed that the effective residual stress component has an inverse relationship with the thickness of the composite reaction zone. The debonding shear strength of the composite is determined based on localized shear stress distribution along the fiber/matrix interface at the onset of debonding. The resulting shear strength is found to decrease from 221.2 MPa at ambient temperature to 138.6 MPa at {dollar}rm 650spcirc C.{dollar} An interphase debonding model, which combines fracture mechanics equations with finite element results on interphase shear stress and bridging fiber traction range, is proposed to establish a distribution of debonding lengths along a fiber-bridged matrix crack length. The longest debonding lengths in a SiC/Ti MMC was predicted along the first intact fiber at the crack mouth and the lengths decrease for fibers located closer to the crack tip. In addition, the debonding crack length increases with increasing temperature. The driving force for the interface debond crack, however, has an inverse relationship with the test temperature. The concurrent damage events of fiber stress evolution and continuous fiber strength degradation were postulated into a fiber fracture criterion to describe the fracture process of a bridging fiber. Although the strength properties of SiC SCS-6 fibers are found to be unaffected by test temperature of {dollar}rm 650spcirc C{dollar} and below, temperature influenced the fracture process of these fibers through the density of cracks in the outermost carbon-rich fiber coating. This fiber crack density has been correlated with the density of crack initiation sites observed in the interphase region along the reinforcing fibers in a SCS-6/Timetal-21S composite.
机译：单向SiC / Ti MMC中的桥接疲劳裂纹扩展损伤机理包括基体裂纹，纤维/基体界面脱粘，沿桥接纤维滑动以及这些纤维断裂。这些程序的基本组成部分将在此程序中进行检查。残余应力的演变特征表明，复合材料的钛合金基体相在制造后冷却至{rm} rm 600spcirc C后发生了广泛的应力松弛。对SiC纤维涂层材料的参数研究表明：有效残余应力分量与复合反应区的厚度成反比关系。复合材料的剥离粘合强度是根据剥离开始时沿纤维/基质界面的局部剪切应力分布确定的。发现所得的剪切强度从室温下的221.2 MPa降低到{rm} rm 650spcirc C时的138.6 MPa。为了建立沿纤维桥接基体裂纹长度的脱粘长度分布，提出了该范围。沿着裂纹口处的第一条完整纤维预测了SiC / Ti MMC中最长的脱胶长度，而靠近裂纹尖端的纤维的脱胶长度则减小。另外，脱粘裂纹的长度随着温度的升高而增加。但是，界面脱粘裂纹的驱动力与测试温度成反比关系。纤维应力演变和纤维强度持续下降的同时破坏事件被假定为纤维断裂准则，以描述桥接纤维的断裂过程。尽管发现SiC SCS-6纤维的强度特性不受650spcirc C {dollar}和更低温度的测试温度的影响，但温度通过最富碳层中的裂纹密度影响了这些纤维的断裂过程。纤维涂层。该纤维裂纹密度与在SCS-6 / Timetal-21S复合材料中沿着增强纤维在相间区域中观察到的裂纹萌生部位的密度相关。

著录项

  • 作者

    Tamin, Mohd Nasir.;

  • 作者单位

    University of Rhode Island.;

  • 授予单位 University of Rhode Island.;
  • 学科 Engineering Mechanical.; Engineering Metallurgy.; Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 1997
  • 页码 358 p.
  • 总页数 358
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 机械、仪表工业;冶金工业;工程材料学;
  • 关键词

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