# Study on the Properties and Fatigue Characteristics of Glass Fiber Composites Due to Porosity
## 5 Conclusions  
In this paper, the nonlinear properties of lamina composites were modeled and analyzed to determine their physical properties and fatigue life reduction due to porosity. At this point, the MLT fracture condition based on continuum damage mechanics and the Tsai-Hill 3D Transversely Isotropic Failure Indicator were applied. Through this study, the following conclusions were reached.  
According to the approach of this study, as the porosity increased by 1%, the rigidity decreased by 2% in the case of 0 degree lamination, by 3% at 45 degrees, and by 5% at 90 degrees.  
At 0-degree lamination the strength reduced by 2%, at 45-degree stacking the reduction was 3%, at 90-degree stacking it was 5%, at 0-degree stacking it was 2%, at 45-degree stacking it was 3%, and at 90-degree stacking it was 5%, excluding initial error.  
Figure 5: Graph of \(\mathrm{S_{max}}\) (largest expected value of stress) versus \(\mathrm{N_{C}}\) (critical cycle count) as a void fraction.  
Figure 6: Graph of Shanke \(S_{a}\) (stress amplitude) versus \(N_{C}\) (critical cycle count) as a void fraction.  
In the case of predicting fatigue life caused by pores, the drop in Smax was 0.5% as the porosity based on \(Nc\)\(10^{5}\) increased, but a very high drop of 5% was confirmed when the porosity increased from 2% to 2.5%.  
Compared to other studies [7; 8; 9; 10; 11; 16; 17; 18; 19], this study showed that the mechanical properties tend to deteriorate excessively as the number and size of voids increase, which also affects the prediction of fatigue life.  
Further study is needed to model and predict the nonlinear properties of material damage more precisely. This will enable more accurate fatigue life predictions. Additionally, research is required to quantitatively evaluate the impact of porosity size, distribution, and shape on fatigue life. This will lead to a more systematic understanding and prediction of porosity.  
H.L.: Writing--original draft: Preparation, creation and/or presentation of the published work, specifically writing the initial draft (including substantive translation). Y.C.: Investigation: Conducting a research and investigation process, specifically performing the experiments, or data/evidence collection. H.P.: writing--review and editing and work guidance. All authors have read and agreed to the published version of the manuscript.  
This work was supported by a Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea Government (MOTIE) (20213030020120, Development of product quality and O&M technology to improve all-steps reliability of offshore wind turbine blades). This work was supported by Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government (MOTIE) (20213030020380, Development of adhesive-type modular over 70 m for overcoming onshore transportation limitation).  
Not applicable.  
The data presented in this study are available on reasonable request from the corresponding author. The data are not publicly available due to privacy.  
The authors would like to thank [PERSON].  
The authors declare no conflicts of interest.