A comparative study on glass and carbon fibre reinforced laminated composites in scaled quasi-static indentation tests

Mohamad Fotouhi,Mahdi Damghani,Mun Choong Leong,Sakineh Fotouhi,Meisam Jalalvand,Michael R Wisnom

doi:10.1016/j.compstruct.2020.112327

Abstract

This paper investigates the effect of fibre properties of composite structures on the mechanical performance and formation of low-velocity impact damage. Quasi-static indentation tests were conducted on a comprehensive set of scaled Quasi Isotropic (QI) S-glass/8552 epoxy and QI IM7-carbon/8552 epoxy laminates, comparing changes in both in-plane dimensions and fully three-dimensionally scaled cases. Due to the higher thickness of the S-glass laminates, the mechanical results were normalized by a thickness scaling rule to have a fair comparison between the mechanical behaviour. The results demonstrated that the shape of the load-displacement of the S-glass/epoxy laminates is similar to that of the IM7-carbon laminates, with evident changes in rigidity appearing due to the onset and propagation of delamination and final failure caused by fibre breakage. The S-glass/8552 epoxy laminates had smaller load drops, higher deflection and higher mechanical energy absorption before failure compared to the IM7-carbon/8552 epoxy laminates. X-ray computed tomography scanning revealed that delamination is the dominant failure mode for the investigated laminates, and the shape of delamination was influenced by the ply angles at the interfaces. Comparing the glass and carbon laminates, ultrasonic C-scan results indicated similar delamination damage size for the initiation stage, however the damage size was found to be dependent on the fibre properties and layup sequence in the propagation stage.

Highlights

The past three decades have seen a notable increase in the use of composite materials in various engineering fields such as aerospace, military and automotive industries
This is the case in this paper, where, as listed in Table 3, the investigated S-glass/epoxy laminates are only 24% thicker than the carbon laminates, so the load values for the Sglass/epoxy will be multiplied by the scaling factor of 0.72 (=(2/ 2.48)1.5) to make a fair comparison between the glass/epoxy and carbon/epoxy laminates
In another study [27] on quasi-static indentation of IM7/8552 epoxy laminates with quasi-isotropic layup of [60/0/-60]4S, and the same dimensions as sub-laminate scaling (SS) samples in [14], the samples indicated compression side failure from the early stage of the loading just after the first load drop, whereas the tensile side fibre failure appeared at a later stage when the load was close to the maximum load

Summary

Introduction

The past three decades have seen a notable increase in the use of composite materials in various engineering fields such as aerospace, military and automotive industries. Applications of composites in these areas are typically to make light and strong structures. Various damage mechanisms such as delamination, matrix cracking and fibre breakage have limited the operational life and load-bearing capacities of these materials. One of the most critical loading conditions for composite structures is impact. Low velocity impact (LVI) leads to Barely Visible Impact Damage (BVID) which significantly affects compressive strength. It is of great importance to understand and characterize damage evolution in these materials

Objectives

Results

Conclusion