Long-Term Properties of Interlaminar Shear Strength of Composite Laminates

Components made of fiber reinforced polymers (FRP) are frequently used in environments with fluctuating temperatures and moisture levels. These environmental factors lead to a degradation of the FRP in the long term. The mechanisms behind the degradation of FRPs and its effect on mechanical performance are not fully understood. For this reason, the main objective of this master thesis is to study how environmental factors, i.e. water and heat, affect the interlaminar shear strength (ILSS) of FRPs. This was achieved by conducting static and fatigue four-point flexural bending tests on I-beam shaped glass fiber/epoxy specimens. Both dry and conditioned specimens were tested. Conditioned specimens were immersed in a distilled water bath at 60°C for three months prior to testing. The tests were performed at temperatures of 40°C and 60°C. The obtained data were compared to data obtained at room temperature. An increase in test temperature led to a decrease in shear strength, shear modulus and yield strength and an increase in deflection at failure. This was also seen as a result of conditioning. An increase in test temperature led to a shorter fatigue life for the specimens. Conditioning showed similar effects. The degradation in mechanical performance should be considered when designing FRP components intended for use in harsh environments. The results obtained in this study can potentially be used in the development of models aiming to predict long-term properties of FRPs