Effect of Unit-Cell Size on the Barely Visible Impact Damage in Woven Composites

Hassan M El-Dessouky,Ying Wang,Mohamed Nasr Saleh,Mohamed S Alotaibi

doi:10.3390/app11052364

Abstract

The effect of the weaving architecture and the z-binding yarns, for 2D and 3D woven composites on the low-velocity impact resistance of carbon fibre reinforced composites, is investigated and benchmarked against noncrimp fabric (NCF). Four architectures, namely: NCF, 2D plain weave (2D-PW), 3D orthogonal: plain (ORT-PW) and twill (ORT-TW), were subjected to 15 J impact using a 16 mm-diameter, 6.7 kg hemispherical impactor. Nondestructive techniques, including ultrasonic C-scanning, Digital Image Correlation (DIC) and X-ray computed tomography (CT) were used to map and quantify the size of the induced barely visible impact damage (BVID). The energy absorption of each architecture was correlated to the damage size: both in-plane and in-depth directions. The 3D architectures, regardless of their unit-cell size, demonstrated the highest impact resistance as opposed to 2D-PW and the NCF. X-ray CT segmentation showed the effect of the higher frequency of the z-binding yarns, in the ORT-PW case, in delamination and crack arresting even when compared to the other 3D architecture (ORT-TW). Among all the architectures, ORT-PW exhibited the highest damage resistance with the least damage size. This suggests that accurate design of the z-binding yarns’ path and more importantly its frequency in 3D woven architectures is essential for impact-resistant composite structures.

Highlights

Due to their unique mechanical properties, composite materials have been largely used in high-tech manufacturing techniques
Images of the optical cross-sections were obtained for all architectures, namely: noncrimp fabric (NCF), 2D plain weave (2D-PW), ORT-PW and ORT-TW
For the ORT-PW and ORT-TW, in order to fully inspect the microstructure of these complex architectures, micrographs are taken along both the warp and weft directions

Summary

Introduction

Due to their unique mechanical properties, composite materials have been largely used in high-tech manufacturing techniques. Their unique performance is clear in their high strength, stiffness, and low density. Damage eventually occurs to composites even without being noticed; this is known as barely visible impact damage (BVID) The recurrence of these dents is dangerous for the structural health of composites as they promote instability within the structure leading to catastrophic failures. These low-velocity impacts are sometimes undetectable on closer inspection, since they manifest as cracks propagating through the matrix and interlaminar delamination within the composites [1]. Tan et al [9] and Yoshimura et al [10] conclude that the importance of the thicker stitch thread becomes obvious as the impact energy becomes higher

Methods

Results

Conclusion