Three-Dimensional Stress Intensity Factor Correction Method Based on Thickness Size Effect

Xiaochen Zhang,Weiying Meng,Xiao Lv,Tian Zhang,Zhenpeng Liu,Hanwen Li,Georgios I Giannopoulos

doi:10.1155/2021/9987079

Abstract

This paper presents the fatigue crack growth test of 7N01 aluminum alloy specimens with different thicknesses under three-point bending. Moreover, the effect of specimen thickness on the fatigue crack growth life was analyzed. The influence mechanism of the thickness size effect on the stress intensity factor was explored. A three-dimensional stress intensity factor calculation model based on the thickness size effect was proposed by combining the finite element method and the interaction integral method. The results show that the fatigue crack growth life of 7N01 aluminum alloy decreases with the increase of specimen thickness. The numerical solutions of the stress intensity factor (the proposed model) are higher than the analytical solutions (the traditional formula) in the steady-state crack growth stage. The difference between numerical solutions and analytical solutions increases with the increase of crack growth length and specimen thickness. Compared with the analytical solutions, the relationship curve between crack length “a” and cycle number “N” from the numerical solutions is closer to the experimental data. This result proves that the proposed calculation model can correct the stress intensity factor with the thickness size effect.

Highlights

From the perspective of fracture mechanics, the solution of stress intensity factor is an important subject for evaluating fracture mechanical properties of materials [1, 2]
E main methods to calculate the stress intensity factor are the analytical method and numerical method. e analytical method, as a traditional method, is generally used in practical engineering, and its accuracy is limited by the geometric structure and static load conditions. e numerical method is widely concerned at home and abroad because it is not affected by the geometric structure or load conditions, which mainly includes the finite element method [9], meshless method [10], and boundary element method [11]
Because the stress intensity factor at the crack tip has a strong three-dimensional effect, if we want to accurately evaluate the fracture mechanical properties of materials and reasonably predict their fatigue crack growth life, we need to start from the three-dimensional point of view, reasonably describe the total energy change of the system, and correct the calculation results of the stress intensity factor with the thickness size effect

Summary

Introduction

From the perspective of fracture mechanics, the solution of stress intensity factor is an important subject for evaluating fracture mechanical properties of materials [1, 2]. Because the stress intensity factor at the crack tip has a strong three-dimensional effect, if we want to accurately evaluate the fracture mechanical properties of materials and reasonably predict their fatigue crack growth life, we need to start from the three-dimensional point of view, reasonably describe the total energy change of the system, and correct the calculation results of the stress intensity factor with the thickness size effect. In order to study the fatigue crack growth behavior of materials and the influence of the thickness size effect on the stress intensity factor at the crack tip, according to the relevant provisions in GB/T 6398-2017 [17] on the thickness design size range for the three-point bending SE (B) specimen, the specimen is designed in two thickness sizes. Intensity factor is neglected, which will lead to inaccurate calculation results

Finite Element Analysis of the ThreeDimensional Stress Intensity Factor

Thickness Size Effect of the ThreeDimensional Stress Intensity Factor

Findings

Conclusion