# Examination of Stress Intensity Factors for Composite Materials by FEM (II)

## Abstract

** Background/Objectives: **In this paper, an automated stress intensity factor (SIF) analysis for three-dimensional surface cracks in composite materials is described. Three-dimensional (3D) finite element method (FEM) is used to calculate the stress intensity factor for surface cracks in composite materials.

** Methods/Statistical analysis: **To check the accuracy of the system, the stress intensity factor for the semi-elliptical surface cracks in the plate under uniform loading was calculated and compared with Raju-Newman's solution. The developed system was then used to analyze the cladding effects of cracks in the composite. The analysis results of the cracks in the composite material were compared with those of the cracks in the homogeneous material and applied to analyze the cladding effect of the surface cracks in the composite material.

** Findings:**As a result, the SIFvalue at the maximum depth point tends to decrease as the depth ofthe crack increases, and the SIF value increases at the two surface points.As the distance d between cracks increases, that is, the distance between the two cracks decreases, the SIF value tends to decrease little by little.In particular, it can be seen that as the distance d between the cracks increases, the mutual interference effect between the cracks is smaller.These analyzes clearly demonstrate that the SIF of subsurface cracks is less than the SIF of surface cracks. In addition, the SIF values for the internal defects of the cladding material were significantly lower than those of the surface cracks without cladding. The smaller the crack depth ratio, i.e. the thinner the crack, the greater the effect by the cladding. Also, as the thickness of the cladding increases, the SIF value decreases as a whole.

** Improvements/Applications: **In the case of homogeneous materials with two surface cracks, the closer the distance between the two cracks, the greater the stress intensity factor. However, the mutual interference effect on the twin subsurface cracks had little effect.