Optimized Interlaminar Shear Strength Of Thick Laminates

Abstract

Static and fatigue properties are important factors when developing design rules to optimize the reduction of damage in the middle of a composite component loaded under a three point bending test. The progressive damage which occurs in a composite laminate during fatigue will affect the mechanical properties of the component to an extent which depends on the material type and lay-up of the composite and on the mode of testing. By choosing an appropriate combination of ply materials and ply stacking sequence for the composite laminate, a better static condition, as well as better fatigue behavior of the component is expected under in-service conditions. In order to minimize the through-thickness damage in the middle of a composite laminate under a short beam shear test, the present work focuses on determining the best stacking sequence, combining two different materials through-thickness of a composite component. The use of an algorithm that has been created to run all possible combinations of angles and materials was the key to finding the best stacking sequence for a composite component. Through the optimization method, two different hybrid laminate lay-ups were obtained for a maximum of 40% of glass plies within a composite laminate. The laminates developed through the algorithm, which are, the Hybrid Design 1([(0c)2/(±45c)2/(±45g)2/(±45c)]s ) and Hybrid Design 2 ([(0c)2/(±45g)/(90c)4/(±45g)/(90c)2]s ), have shown that the best ply orientations to minimize the damage in the middle of a composite component occur when the value of the variable angle θ in ±θ plies has a maximum value of 90 degrees. The algorithm used showed that best laminates were obtained when glass plies were not used as the central plies in a glass/carbon composite laminate, with a maximum 40% of glass plies. Static and fatigue tests were performed on both hybrid designs and on a quasi-isotropic composite laminate ([(0/45/90/-45)3 ]s) made of carbon plies. The results of the static and fatigue tests have demonstrated that the best design, giving the best static and fatigue behavior is the Hybrid Design 1. Also, it has been demonstrated through experimental tests that 90 degree plies within a composite laminate subject to a three point bending condition will cause the component to be weaker in terms of fatigue and static properties due to the tendency to develop inclined cracks in the through-thickness direction on the 90 degree plies of the composite laminate, causing delamination and loss of stiffness of the component.

Date of Award	28 Jul 2014
Original language	English
Awarding Institution	University of Bath
Sponsors	AgustaWestland Limited
Supervisor	Richard Butler (Supervisor)