Off-campus UMass Amherst users: To download dissertations, please use the following link to log into our proxy server with your UMass Amherst user name and password.

Non-UMass Amherst users, please click the view more button below to purchase a copy of this dissertation from Proquest.

(Some titles may also be available free of charge in our Open Access Dissertation Collection, so please check there first.)

The roles of matrices and glass fibers on the deformation and fracture of short glass fiber-reinforced thermoplastics

Ming-Liang Shiao, University of Massachusetts Amherst

Abstract

In this study, the deformation and fracture behavior of short glass fiber reinforced thermoplastics are examined. Emphases are given to the roles of fiber reinforcements on thermoplastic matrices with varying ductility. The results indicate that in the amorphous matrices of SAN and ABS composites, the addition of glass fibers does not influence the morphology of the matrix materials. In the semi-crystalline matrix of nylon 6,6, however, the glass fiber reinforcements are found to reduce the spherulite size and lower composite's matrix crystallinity. The tensile properties of a short glass fiber reinforced thermoplastics are found to be more influenced by glass fibers than by the matrix ductility. The fracture toughness of the thermoplastic composites, on the other hand, are found to depend both on the glass fiber reinforcement and on the matrix ductility. In this study, the toughness dependence is further separated into two stages of crack initiation and crack propagation. In the crack initiation stage, the initiation toughness of a thermoplastic composite strongly depends on its matrix ductility. In the crack propagation stage, the propagation toughness of a thermoplastic composite is found to be dominated by matrix ductility and by fiber/matrix interfaces. The fracture and toughening mechanisms of a glass fiber reinforced thermoplastic composites are found to relate to the deformation mechanisms of the matrix, to the fiber-matrix interactions, and to the fiber-fiber interactions. In the brittle SAN composite the fracture occurs by debonding and void formation at fiber ends. In the rubber toughened ABS composites, the fracture at crack tip is associated with the matrix crazing deformation at larger rubber particles and is facilitated by the void formation at fiber ends. In the nylon 6,6 composites, on the other hand, the fracture mechanism is strongly associated with fiber-fiber interactions and the observed toughening mechanism is resulted from enhanced matrix crystallographic shear plasticity due to stress field interactions of nearby glass fiber ends. A strong relationship between the fracture toughness, fracture mechanisms, and microstructures are also observed in thermoplastic composites. The fracture toughness parameters, J-integral toughness or $K\sb{IC}$ values, are therefore microstructure sensitive and can be used to provide general guidance of toughness improvement in thermoplastic composites. (Abstract shortened by UMI.)

Subject Area

Materials science|Plastics|Mechanical engineering|Mechanics

Recommended Citation

Shiao, Ming-Liang, "The roles of matrices and glass fibers on the deformation and fracture of short glass fiber-reinforced thermoplastics" (1993). Doctoral Dissertations Available from Proquest. AAI9408349.
https://scholarworks.umass.edu/dissertations/AAI9408349

Share

COinS