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TECHNICAL ARTICLE—PEER-REVIEWED

Fracture Surface Morphology of Delamination Failure of Polymer Fiber Composites Under Different Failure Modes Pasa Yayla

Submitted: 22 October 2015 / in revised form: 31 December 2015 Ó ASM International 2016

Abstract The delamination of fiber reinforced polymer composites is one of the most common failures encountered in industrial applications. The most unique macroscopic and microscopic fracture surface features of the delaminations under different failure modes are of interests not only for practical failure analysis investigations but also it helps to reveal the physics behind the delamination phenomenon. In this work, fracture surface morphology of the delaminated carbon fiber polymer composites under mode I, mode II, and mixed-mode I/II loading conditions is investigated mainly with scanning electron microscopy. The unique fractographic features are identified and discussed. The results on ductile and brittle matrix composites have shown their own features, and most important of all the alignment angle of fibrils in the resin-rich ductile matrix could be correlated with the delamination mode. Keywords Delamination
Fiber composites
Fractograph
Failure modes

Introduction Post-mortem investigation of damaged or fractured components at macroscopic as well as microscopic levels could be one of the most effective ways of studying the type and magnitude of applied stress state to the structure and the response of the structure to it. Moreover, the microscopic failure investigation of the broken specimen could be used P. Yayla (&) Mechanical Engineering Department, Engineering Faculty, Marmara University, Goztepe Campus, 34722 Istanbul, Turkey e-mail: [email protected]; [email protected]

to verify the failure mechanism and compare different composite systems. The fracture surface morphology of delaminated fiber reinforced composite materials has been investigated by many researchers. Friedrich [1] investigated the failure mechanisms of delamination in epoxy and poly-etherether-ketone (PEEK) composites. He concluded that the principal mechanisms of energy absorption in the composites could be categorized as: (i) fiber bridging, (ii) fiber fracture, (iii) formation of the main fracture surface, (iv) formation of side cracks, and (v) plastic deformation and microcracking of the matrix around the fibers. Johannesson and his co-workers [2] studied fractograph of delaminated graphite/epoxy laminates. Purslow [3, 4] studied the general fractographic features of delamination under peel (mode I) and shear (mode II) failures, respectively. Greenhalgh [5], and Bascom and Gweon [6] detailed delamination micro-mechanisms and matrix fracture morphologies of polymer composites. The aim of the present study is to investigate the fracture surface of carbon fiber reinforced polymer composites which fractured in different failure modes and analyze the microscopic features in order to understand the mechanism of delamination. Moreover, special attention is given as to whether the failur