Fracture toughness of urethane‐modified methacrylate resins

SYNOPSISThe tensile properties of three urethane-methacrylate resins that varied in the soft segment content of the urethane were characterized. The strain birefringence at a circular hole was observed during loading-unloading cycles to progressively higher displacements. The shear strain distribution at the hole was calculated from the isochromatic fringe contours and compared with results from linear elastic analysis. When the onset of nonlinearity, and the subsequent appearance of residual strain at the root of the hole, were correlated with features of the macroscopic stress-displacement curves, three regions of prefracture deformation were defined. A region of linear elastic behavior was observed at the lowest strains. The maximum shear strain at the linear limit was the same in all the resins, and appeared to correlate with the yield condition at the hole. When the shear strain at the hole exceeded about 2.8%, the fringe patterns started to deviate from the elastic prediction. However, strain was fully recoverable in this region as indicated by the absence of residual birefringence at the hole after unloading. This region of nonlinear, recoverable deformation extended to progressively higher strains as the amount of urethane soft segment increased. This feature was attributed to the network structure of the urethane-methacrylate resins. A region characterized by nonrecoverable deformation at the hole followed at higher strains; the urethane soft segment content had a major effect on the amount of permanent deformation sustained before fracture. The fracture surfaces exhibited features typical of brittle fracture without crazing. 0 1995 John Wiley & Sons, Inc

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Deformation and fracture of urethane–methacrylate resins

Elleithy

Hiltner

Baer

et al. 1995

J of Applied Polymer Sci

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Delamination Failure of a Single Yarn Glass Fiber Composite

Ebeling

Hiltner

Baer

et al. 1997

Journal of Composite Materials

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When the constraint of the fill yarns was removed from a woven fiber composite, delamination followed an intrayarn pathway. Despite extensive fiber-matrix debonding during crack growth, resin toughness translated directly to composite toughness. This suggests that damage from intrayarn cracking contributes significantly to toughness of woven fiber composites even though the crack is expected to follow an interply pathway. Effects of fiber undulation were isolated from the effects of yarn interlacing by studying specimens a single yarn in width. In the double cantilever beam (DCB) test, intrayarn crack growth caused the crack to follow the undulating pathway of the fibers. The orientation of the crack changed as the crack moved along the undulating fibers; thus, the extent of mode II loading relative to mode I loading increased as the fibers deviated from the plane normal to the loading direction. Because composite toughness increases with the degree of mode II loading, the variation in toughness induced a characteristic stop-start crack growth mechanism. The toughness of the matrix was varied by changing the soft segment content of the urethane-methacrylate resin. Soft segment content affected the crack initiation toughness more than crack arrest toughness. Consequently, longer crack jumps were observed with the tougher resins.

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Fracture toughness of urethane‐modified methacrylate resins

Cited by 2 publications

References 13 publications

Deformation and fracture of urethane–methacrylate resins

Deformation and fracture of urethane–methacrylate resins

Delamination Failure of a Single Yarn Glass Fiber Composite

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