Abstract

Variation of cyclic loading effect on fatigue crack growth is investigated under plane strain and small scale yielding (SSY) conditions. The material is characterized by a finite strain elastic viscoplastic constitutive model with hardening and hardening-softening-hardening hardness functions. Displacements corresponding to the isotropic linear elastic mode I crack field are prescribed on a remote boundary. The influence of cyclic stress intensity factor range ($\Delta \mathrm{K}$), load ratio (R), number of cycles (N), plastic compressibility ($\mathrm{\alpha }),$ overload and material softening on near tip deformation was studied in detail. For comparison purpose, a few results pertaining to plastically incompressible solids are also considered. The crack tip opening displacement (CTOD), plastic crack growth, deformed crack tip shape, plastic zone shape and size near the crack tip appear to depend significantly on $\Delta \mathrm{K},$ R, N, $\mathrm{\alpha },$ overload and material softening. The overload produces strong plastic deformation ahead of the crack tip and decreases the fatigue crack growth substantially.

• Highlights

• Variation of cyclic loading effect on fatigue crack growth is investigated for materials characterized by a finite strain elastic viscoplastic constitutive model with hardening and hardening-softening-hardening hardness functions. Both plastically compressible and incompressible solids are considered.

• The influence of cyclic stress intensity factor range ($\Delta \mathrm{K}$), load ratio (R), number of cycles (N), plastic compressibility ($\mathrm{\alpha }),$ overload and material softening on near tip deformation was studied in detail.

• The crack tip opening displacement, plastic crack growth, plastic zone shape and size near the crack tip appear to depend significantly on $\Delta \mathrm{K},$ R, N, $\mathrm{\alpha },$ overload and material softening.

• The combination of softening or softening-hardening material response and plastic compressibility leads to major deviations in crack tip blunting and fatigue crack growth from those that prevail for a hardening material.

摘要

在平面应变和小规模屈服（SSY）条件下，研究了循环载荷对疲劳裂纹扩展的影响。该材料的特征是具有硬化和硬化-软化-硬化硬度函数的有限应变弹性粘塑性本构模型。对应于各向同性线弹性模式 I 裂纹场的位移在远程边界上进行了规定。循环应力强度因子范围的影响 ($\Delta \mathrm{ķ}$)、载荷比 (R)、循环次数 (N)、塑性压缩率 ($\mathrm{\alpha }),$详细研究了近尖端变形的过载和材料软化。为了比较的目的，还考虑了一些与塑性不可压缩固体有关的结果。裂纹尖端张开位移 (CTOD)、塑性裂纹扩展、变形裂纹尖端形状、塑性区形状和裂纹尖端附近的尺寸似乎显着取决于$\Delta \mathrm{ķ},$R, N,$\mathrm{\alpha },$过载和材料软化。过载会在裂纹尖端之前产生强烈的塑性变形，并大大减少疲劳裂纹的扩展。

• 强调

• 针对具有硬化和硬化-软化-硬化硬度函数的有限应变弹性粘塑性本构模型的材料，研究了循环载荷对疲劳裂纹扩展影响的变化。考虑了塑性可压缩和不可压缩固体。

• 循环应力强度因子范围的影响 ($\Delta \mathrm{ķ}$)、载荷比 (R)、循环次数 (N)、塑性压缩率 ($\mathrm{\alpha }),$详细研究了近尖端变形的过载和材料软化。

• 裂纹尖端张开位移、塑性裂纹扩展、裂纹尖端附近的塑性区形状和尺寸似乎显着取决于$\Delta \mathrm{ķ},$R, N,$\mathrm{\alpha },$过载和材料软化。

• 软化或软化-硬化材料响应和塑性可压缩性的结合导致裂纹尖端钝化和疲劳裂纹扩展与硬化材料的主要偏差。