Abstract

Stress Intensity Factor (SIF) of opposite surface cracks presented in an un-notched round bar has been determined under tension and combined load conditions. The influence of loading modes on SIF of opposite surface cracks has been attempted using numerical method. Crack depth ratio [(a/d); ‘a’ crack depth and ‘d’ diameter of the bar] ranging 0.1 to 0.4 and crack aspect ratio [(a/c); ‘a’ crack depth and ‘c’ semi major axis of the ellipse] ranging 0.2 to 1.0 were considered. Mixed mode SIF was calculated with consideration of mode-II and mode-III fractures. When the bar was subjected to pure tensile loading, as the crack depth ratio (a/d) increases, a crossover (higher SIF value changes from middle region to surface region) in SIF distribution was observed for an aspect ratio of 0.6. This implies that the growing crack has changed its propagation behavior as the depth ratio increases. In addition to tension, when torque was applied, nonuniform and asymmetric SIF spread was observed for semi elliptic crack [(a/c) = 0.2] compared to semi-circular [(a/c) = 1.0] crack. It was also noted that mode-I fracture is higher at the middle region [P/P₀ = 0] of the rack border, whereas mode-II and mode-III fracture is higher at the crack surface region [P/P₀ = ±1]. Due to combined loading, more influence of mode-II and mode-III fracture failure was observed and their effect is marginal at the middle region [P/P₀ = 0] of the crack border. Using surface plots, SIF of opposite cracks located in un-notched round bar has been determined.

摘要

已确定在拉力和组合载荷条件下，无缺口圆棒中出现的相对表面裂纹的应力强度因子（SIF）。尝试使用数值方法来研究加载方式对相对表面裂纹的SIF的影响。裂纹深度比[（a / d）; 棒的“ a”裂纹深度和“ d”直径）范围为0.1至0.4，裂纹纵横比[（a / c）；考虑了“ a”裂纹深度和“ c”椭圆半长轴]，范围为0.2到1.0。考虑到II型和III型骨折计算混合模式SIF。当钢筋受到纯拉伸载荷时，随着裂纹深度比（a / d）的增加，对于深宽比为0.6的情况，观察到SIF分布发生交叉变化（较高的SIF值从中间区域到表面区域变化）。这意味着，随着深度比的增加，不断扩展的裂纹已改变了其扩展行为。除了张力外，当施加扭矩时，与半圆形[（a / c）= 1.0]裂纹相比，半椭圆形裂纹[（a / c）= 0.2]观察到不均匀且不对称的SIF扩展。还应指出，I型骨折在中部区域较高[P / P齿条边界的“ ₀ = 0”，而II型和III型断裂在裂纹表面区域[P / P ₀ =±1]较高。由于组合载荷，观察到了II型和III型断裂破坏的更多影响，并且其影响在裂纹边界的中间区域[P / P ₀ = 0]处很小。使用表面图，确定了无缺口圆棒中相对裂纹的SIF。