On the effect of hydrostatic stress on fatigue crack propagation

被引：1

作者：

Andrianopoulos, Nikos P. ^{[1
]}

Pikrakis, Aggelos ^{[1
]}

机构：

[1] Department of Mechanics, National Technical University of Athens, Athens, Greece

来源：

International Journal of Structural Integrity | 2017年 / 8卷 / 02期

关键词：

Stress analysis - Digital storage - Constitutive equations - Fatigue crack propagation - Aluminum alloys - Brittle fracture - Numerical models - Continuum mechanics - Strain - Crack tips - Hydraulics;

D O I：

10.1108/IJSI-06-2016-0021

中图分类号：

学科分类号：

摘要：

Purpose: The purpose of this paper is to study mutual interaction between von Mises equivalent and hydrostatic stresses at the crack tip area of an elastoplastic material in order to obtain critical conditions for crack propagation under fatigue loading. Design/methodology/approach: A5083-H111 aluminum alloy is used to obtain a Chaboche-type constitutive equation, which is introduced in a commercial finite elements package to evaluate stress distribution at crack tip area. A simplified three-dimensional (generalized plane strain) grid is used, resulting in fast and accurate results. Numerical simulations are performed to connect crack propagation rate with various combinations of fatigue stress amplitude, initial crack length and number of loading cycles. Distance between characteristic points of stresses distribution in the crack tip area are compared to experimental fatigue crack growth rates in order to assess the validity of the present approach. Findings: It is found that saturation of plastic strains, i.e. maximization of von Mises equivalent stress, is a prerequisite for hydrostatic stress to take a critical-maximum value, outside the plastically saturated zone. At the point of maximum hydrostatic stress brittle fracture is initiated, driving to separation of the ligament up to crack tip, without formation of new plastic strains. The length of this ligament is defined as crack propagation step, showing good agreement with experimental data. Originality/value: The present approach seems to constitute a reasonable and adequate method for the description of fatigue crack propagation in terms of continuum mechanics, not necessitating microscopic considerations or empirical criteria lacking theoretical or physical basis. In addition, it liberates from the notion of stress intensity factors, strongly disputed beyond linear elasticity. Improved constitutive equations and numerical models are expected to drive in a complete fatigue failure criterion similar to those of static loading. © Emerald Publishing Limited.

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