EFFECT OF INTERFACIAL PROPERTIES ON STATIC AND FATIGUE OF SHORT GLASS FIBER REINFORCED THERMOPLASTICS

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Firstly, the effect of interfacial properties between fibers and thermoplastic matrix (mainly Polypropylene) on static and fatigue failure of short glass fiber reinforced thermoplastics fabricated by injection molding and stamping was studied. From the test results it was revealed that the static strength of the FRTP sample fabricated using long fiber pellets was higher than that of the sample fabricated by conventional injection molding using short fiber pellets. The yielding stres was also increased by using long fiber pellets. However, the longitudinal modulus does not increase due to long fiber pellets. As fibers in the pellets are broken during injeciton molding process, 8 to 10 mm in length in pellets is enough to improve the static strength for long fiber pellets. On the other hand, no significant effect of usage of long fiber pellets on high cycle fatigue is found although long fiber pellets are effective to increase the fatigue life at low cycle fatigue. The fatigue life is in … More creased 30-80% longer by using long fiber pellets at low cycle fatigue. The creep behavior is also improved much due to long fibers.Although PP matrix itself does not absorb water, PP matrix short glass fiber composites (FRTP) absorbs appreciable water. Water penetrates inside through the interface between blass fibers and the matrix. Due to water absorption, not only static strength but also fatigue strength decrease. However, the strength reduction under static loading is only about 20%.A possibility for fabricating PP-based FRTP which have high performance but being not expensive was shown by using low temperature plasma. In this method, PP sheets whose surfaces have been previously treated are stacked with glass fabrics and pressed to form FRTP.Due to this surface treatment, peeling strength increases as high as 50%. The static strength increases about 20%.Lastly, the effect of rubber modification of epoxy matrix using cross-linked NBR submicron spheres on both static and fatigue strengths of CFRP were shown. Due to rubber modification, the interfacial strength between carbon fibers and epoxy matrix is improved. Less