Fractographic analysis of tensile failures of aerospace grade composites

Masa Suresh Kumar,Honnudike Venkateshwararao Ramachandra,Magalapalaya Anjanappa Venkataswamy,Kesarabandi Raghavendra

doi:10.1590/s1516-14392012005000141

Masa Suresh Kumar, Honnudike Venkateshwararao Ramachandra + Show 2 more

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https://doi.org/10.1590/s1516-14392012005000141

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Abstract

This paper describes fractographic features observed in aerospace composites failed under tensile loads. Unidirectional Carbon Fibre Reinforced Plastic (UD CFRP) and Unidirectional Glass Fibre Reinforced Plastic (UD GFRP) composite specimens were fabricated and tested in tension. The morphology of fractured surfaces was studied at various locations to identify failure mechanism and characteristic fractographic features. CFRP composites displayed transverse crack propagation and the fracture surface showed three distinct regions, viz., crack origin, propagation and final failure. Significant variations in the fractographic features were noticed in crack propagation and final failure regions. Crack propagation region exhibited brittle fracture with chevron lines emanating from the crack origin. The entire crack propagation region exhibited radial marks on the individual fibre broken ends. On the other hand, the final fracture region revealed longitudinal matrix splitting and radial marks in majority of locations, and chop marks at some locations. The change in fracture mode in the final fracture was attributed to superimposition of bending loads. GFRP composites exhibited broom like fracture with extensive longitudinal splitting with radial marks present on individual fibre broken ends. Transverse fracture was observed at a few locations. These fracture features were analyzed and correlated with the loading conditions.

Highlights

Composite materials have become an alternative to metallic materials because of their unique properties like high specific stiffness, specific strength and tailorable properties
The objective of the present study is to identify the tensile failure mechanism and characteristic fracture features in present generation aerospace grade Unidirectional Carbon Fibre Reinforced Plastic (UD CFRP) and GFRP composites through fractographic analysis
Fracture morphology in UD CFRP varies as the crack progresses under tensile load;

Summary

Introduction

Composite materials have become an alternative to metallic materials because of their unique properties like high specific stiffness, specific strength and tailorable properties. During the past couple of decades, there has been growing interest in use of carbon and glass fibre reinforced composite materials for the fabrication of aerospace structures. It is estimated that the use of composites in commercial transport aircraft would be about 50%, whereas the same in the military aircraft could be as high as 80% by weight[1]. Failures in composite structures can occur during various stages in the manufacturing process development, during simulation tests or during service. There is a need to conduct failure analysis to identify the cause of failure in an effort to provide useful feedback to designer, manufacturer and user. The first step for failure analysis is identification of the failure mode. This can be established through fractographic study.

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