Delamination Resistance in Stitched and Unstitched Composite Plates Subjected to Impact Loading

Abstract

The delamination resistance of a composite plate subjected to low-velocity impact is dependent on the interlaminar strengths and the level of interlaminar stress. The former is strongly influenced by the material properties such as matrix toughness and fiber-matrix bonding strength while the latter can be affected by the specimen geometry and loading parameters. In this study, some thin composite plates were fabricated and sub jected to low-velocity impact. The delamination in every specimen was examined. Experi mental results revealed that the delamination area was proportional to the lamina thickness and the difference of fiber angle between adjacent laminae. A Mismatch Theory based on the difference of bending stiffness between adjacent laminae was used to interpret the cause of high interlaminar stress level. The effect of interlaminar strengths on the delami nation resistance was also discussed. It was found that through-the-thickness stitching could reduce the delamination area in a composite plate subjected to low-velocity impact as high as 40%.

Improvement of Mode I Interlaminar Fracture Toughness of Stitched Glass/Epoxy Composites

“…Liu's findings [22] show that stitching enhances the interlaminar strength and diminishes the damage area. The delamination resistance was inspected with respect to the effectiveness of various stitch patterns and across a variety of stitch densities.…”

“…The delamination resistance was inspected with respect to the effectiveness of various stitch patterns and across a variety of stitch densities. Liu pointed out [22] that stitching impedes the propagation of delamination and reduces the delamination area in accordance with the increase of stitch density.…”

Analysis of stitched laminated ENF specimens for interlaminar mode II fracture toughness

“…The use of thermoplastic and toughened thermoset matrices is one possibility [9][10][11]. However, it has been observed that through-thickness reinforcement is the most effective way to suppress delamination [12][13][14][15][16][17][18][19]. The simplest way to achieve through-thickness reinforcement is by means of transverse stitching.…”

Survivability of Affordable Aircraft Composite Structures. Volume 3: Characterization of Affordable Woven Carbon/Epoxy Composites Under Low-Velocity Impact Loading

“…Methods of reducing interply delamination include the use of tougher matrix systems, woven fabrics, and through-thickness reinforcement. The main methods of through-thickness reinforcement include 3-D weaving, pinning, and stitching, of which stitching has been demonstrated to be most effective in improving the delamination resistance [14][15][16][17][18][19][20][21][22][23][24][25]. The early attempts of improving delamination resistance were made by Huang et al [14] in the late 1970s where steel wires of 0.33 mm diameter were placed at ±45° angles to the thickness of the laminate separated by 1.6 mm.…”