# Multi-directional composite laminates: fatigue delamination propagation in mode I—a comparison

- Authors
- Type
- Published Article
- Journal
- International Journal of Fracture
- Publisher
- Springer Netherlands
- Publication Date
- Aug 29, 2019
- Volume
- 219
- Issue
- 2
- Pages
- 175–185
- Identifiers
- DOI: 10.1007/s10704-019-00388-4
- Source
- Springer Nature
- Keywords
- License
- Yellow

## Abstract

Double cantilever beam (DCB) specimens composed of carbon fiber reinforced polymer laminate composites were tested. Two material systems were investigated. One consisted of plies from a woven prepreg alternating with tows in the 0∘/90∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$0^{\circ }/90^{\circ }$$\end{document}-directions and the +45∘/-45∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$+45^{\circ }/-45^{\circ }$$\end{document}-directions. The second was fabricated by means of a wet-layup process with the same multi-directions as the prepreg. In addition, for the second material system, a unidirectional (UD) fabric ply was added. The delamination for this laminate was between the UD fabric and the woven ply with tows in the +45∘/-45∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$+45^{\circ }/-45^{\circ }$$\end{document}-directions. Both fracture resistance R-curve and fatigue delamination propagation tests were carried out. It is found that the initiation value of the interface energy release rate is substantially lower for the wet-layup; whereas, their steady state values are quite similar. The fatigue delamination propagation tests were performed at various cyclic R-ratios. The delamination propagation rate da/dN was calculated from the experimental data and plotted using a modified Paris equation with different functions of the mode I energy release rate. As expected, the da/dN curves depend upon the R-ratio. By using another parameter based on the Hartman–Schijve equation for metals, it is possible to obtain a master-curve for all R-ratios. It is seen that the propagation rate for the prepreg is faster than that of the wet-layup.