Determination of Time- Temperature Dependent Tensile Strength of Unidirectional CFRP by Strand Test

摘要

This paper concerns the determination of time andtemperature dependent tensile strength in the longitudinal directionof unidirectional carbon fiber reinforced plastics (CFRP).Applying the strand-testing method with the newly-devisedtemperature chamber and grip ends to carbon fibers/epoxycomposite strands (CF/Ep strand; T400/828), the tensile strengthsunder constant strain-rate (CSR) and fatigue loadings weremeasured at various loading-rates and temperatures. Samestrengths were measured also by the conventional split-diskmethod, in which carbon fibers/epoxy composite rings (CF/Ep ring)were used as the specimens. Similarities and differences betweenthe two results, one by the proposed method and another by thesplit-disk method, are discussed. Our proposed strand-testingmethod is excellent for the determination of tensile strength in thelongitudinal direction of unidirectional CFRP because of its smallsize of the apparatus and unidirectional state of stress for the entirespecimen except the grip region. Furthermore, the tensile CSRstrengths under various loading rates and temperatures of fourtypes of CF/Ep strand (T400/828, T800/828, M40J/828, andXN40/25SX) are determined by this strand testing method. It isconfirmed that the time and temperature dependence on tensilestrength for all of four types of CF/Ep strand is controlled by theviscoelastic behavior of corresponding matrix resin. However, thetime and temperature dependence on these tensile strengths differwith the type of carbon fiber.