Session: Research Posters

Paper Number: 119818

119818 - A Novel Experimental Setup for Characterizing the Bearing Failure Strain of Advanced Composite Materials Using 3d-Digital Image Correlation 

Advanced fibre composite materials are characterized by their high specific strength and stiffness and are used in applications involving weight saving and cost efficiency. Composite structures are assembled by various means (e.g through mechanical fastening or bonding) with the design of joints being one of the key challenges. Poor understanding of crack formation mechanisms around joints often leads to overdesign due to the lack of reliable strength prediction models. This study focuses on mechanically-fastened joints (e.g. bolted) for a range of applications not limited to aerospace or automotive. There have been numerous studies focused on the mechanical failure of composite structures assembled through bolted joints. However, the failure mechanisms are complex and not well-understood. This study focuses on generating new insight into the mechanical conditions leading to the formation of cracks around holes manufactured in carbon fibre composite specimens and loaded through a standard plain-pin bearing strength test. Based on BS ISO 12815:2013 for fibre-reinforced plastic composites, a new experimental procedure has been developed to enable full-field strain measurements around the loading pin area throughout the test. The experimental setup includes two cameras to carry out 3D digital image correlation (DIC) measurements of strain distributions around the hole in the loaded composite specimens. The new design which follows the guidance from the standard has been validated through a comparison with load-displacement curves obtained with the version of the test not including DIC cameras. The load displacement curves from both methods have shown a good agreement for this research study. Woven composite specimens with drilled holes were then covered with a fine speckle pattern for full-field strain measurements using DIC. The specimens were then progressively loaded and recorded optical images were subsequently processed using the Correlated Solutions VIC3D software. Results show a successful image capture of crack development, including initiation at the very edge of the hole followed by the propagation of various cracks generated as the load progressively increases. Strain distributions around the hole have also been successfully measured using DIC with strain component values analysed in relation to crack development. This new experimental procedure therefore provides new insight into the conditions leading to the appearance of cracks during the test in terms of mechanical strain fields. It is anticipated that results from these tests will also help the development and validation of finite element models aimed at predicting the strength of mechanically fastened joints in advanced composite structures for the next generation aircraft. 

Presenting Author: Abdulaziz Alzurahi The University of Sheffield, Department of Mechanical Engineering

Presenting Author Biography: Abdulaziz Alzurahi is a postgraduate (MSc) student at The University of Sheffield. He is conducting his MSc degree in Advanced Mechanical Engineering. He has a research background in the area of mechanical tests of lightweight materials, composite structure tests and characterization, design innovations, and innovative material experimental studies.

Authors:

Abdulaziz Alzurahi The University of Sheffield, Department of Mechanical Engineering
Zilei Chen The University of Sheffield, Department of Mechanical Engineering
Fatma Omrani Composites Centre, AMRC with Boeing, The University of Sheffield
Christophe Pinna The University of Sheffield, Department of Mechanical Engineering