Biaxial failure response of composite laminates
Phua, Chia Siang
Date of Issue2016-05-11
School of Mechanical and Aerospace Engineering
Natural composite materials such as wood and bone have been used since ancient times. However, the development and application of man-made composite materials only took off in the middle of the 20th century, especially in aerospace and wind turbine applications, when people started to notice their superb properties. Composites have many great properties, such as high resistance to corrosion and high fatigue strength. Their most distinct property is their high strength to density ratio, which is highly valuable in many applications, especially within the aerospace industry. Humans have also found out that these properties can be tweaked to suit various engineering needs. However, unlike most engineering materials, composites exhibit anisotropic properties because of the way fibres are stacked to increase material strength. The anisotropic property causes the material to behaviour much differently under biaxial loading conditions. Hence, the usual failure criteria such as Von-Mises effective stress used to characterise metals, are generally not applicable to composites. Because of the anisotropic nature of composite laminates, the damage initiation and propagation under multiaxial loading conditions need to be understood for better practical design with composite laminates. In this predominantly experimental research, author has fabricated long glass fibre reinforced epoxy composite laminates, cut them into cruciform configuration using water jet cutting and machined a 30° crack to probe the failure envelope in biaxial tensile loading conditions. The strain field data is obtained through digital image correlation (DIC) technique. The failure envelopes in stress and fracture toughness space are obtained and compared with 0° and 45° measurements of previous students.
Final Year Project (FYP)
Nanyang Technological University