Development of image based crack measurements, to investigate delamination in different weave Fibre Reinforced Polymers

Harnekar, Abraar

Development of image based crack measurements, to investigate delamination in different weave Fibre Reinforced Polymers

Master Thesis

2019

Abstract

This project investigates the delamination dependence of fibre reinforced polymers, of different weave patterns, using an image-based crack measurement method. Glass fibre reinforce polymer (FRP) with three different weave pattern namely Unidirectional, Plain weave and Twill weave patterns were manufactured using the infusion process. Waterjet cutting was used to cut the panels to produce the test specimens. The Double Cantilever Beam (DCB) test was used to measure the Mode I fracture toughness, following the standardised test method ASTM D5528. DCB tests requires two hinge blocks to be bonded to the specimens and is conducted using the Zwick machine which actively measures force and opening displacement. In order to calculate the fracture toughness from a DCB test, the crack length must be measured. An image-based crack measurement method was developed, using still images that were extracted from a digital video of the DCB experiment. The image-base method involved scripting a MATLAB file to detect the specimen surface as edges. The specimen was painted white and the test had a black background. This caused a sharp change in intensity which made the specimen edge easier to detect. The detection algorithm only catered for accuracy and not speed. A series of tests were conducted to verify the detection algorithm, of which included designing an Ultrasound Wedge device. The Wedge device was used to emulate a DCB tests in a static position whereby an Ultrasound Thickness Tester was used to obtain and verify the position of the crack tip obtained by the algorithm. DCB tests showed that the Twill weave specimens had the greatest resistance to delamination, while the Unidirectional weave offered the least resistance to delamination. The Plain weave pattern was inconclusive due to the large variation between the Plain weave specimens.

Keywords

Engineering

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