Tension-Compression Fatigue Induced Stress Concentrations in Woven Composite Laminate

Eldho Mathew,Sunil Chandrakant Joshi,Rajaram Attukur Nandagopal,Pasi Matteo,Pinter Armando

doi:10.3390/jcs5110297

Eldho Mathew, Sunil Chandrakant Joshi + Show 3 more

Open Access

https://doi.org/10.3390/jcs5110297

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Abstract

Tension-compression (T-C) fatigue response is one of the important design criteria for carbon-fibre-reinforced polymer (CFRP) material, as well as stress concentration. Hence, the objective of the current study is to investigate and quantify the stress concentration in CFRP dog-bone specimens due to T-C quasi-static and fatigue loadings (with anti-buckling fixtures). Dog-bone specimens with a [(0/90),(45/−45)4]s layup were fabricated using woven CFRP prepregs and their low-cycle fatigue behaviour was studied at two stress ratios (−0.1 & −0.5) and two frequencies (3 Hz & 5 Hz). During testing, strain gauges were mounted at the centre and edge regions of the dog-bone specimens to obtain accurate, real-time strain measurements. The corresponding stresses were calculated using Young’s moduli. The stress concentration at the specimen edges, due to quasi-static tension, was significant compared to quasi-static compression loads. Furthermore, the stress concentration increased with the quasi-static loading within the elastic limit. Similarly, the stress concentration at the specimen edges, due to tensile fatigue loads, was more significant and consistent than due to compressive fatigue loads. Finally, the effects of the stress ratio and loading frequency on the stress concentration were noted to be negligible.

Highlights

Over the years, lightweight and high-strength composite materials have gradually replaced conventional isotropic materials in the aerospace, marine and automotive industries [1]
The fatigue response of a composite laminate is one of the essential design criteria, which is considered during any structural certification exercise
ASTM and ISO standard fatigue tests are performed to characterize the fatigue behaviour of the laminate at various environmental conditions [4]. These tests are conducted on small specimen sizes resulting in the overestimation of the laminate fatigue strength due to size effects [5,6]

Summary

Introduction

Lightweight and high-strength composite materials have gradually replaced conventional isotropic materials in the aerospace, marine and automotive industries [1]. The superior design tailorability of composite materials, due to their inhomogeneity and potential variety in its constituent materials and orientation, is one of their several benefits [2]. Such design versatility demands extensive coupon and component level testing to ensure certification compliance [3]. These tests are conducted on small specimen sizes resulting in the overestimation of the laminate fatigue strength due to size effects [5,6]. The primary objective of this study is to quantify the stress concentrations in large dog-bone specimens subjected to quasi-static and axial fatigue loadings

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