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Because they retain strength and stiffness at temperatures as high as 180°C (356°F), injection molded, glass-filled phenolic composites have been used in structural applications. However, the strength of this material as measured with ASTM three-point flexure tests may be as much as 80% higher than the strength measured in tension tests. The objects of this investigation were to study the relative effects of fiber alignment, residual stress, and flaw distribution upon these measured values of strength and to assess the application of these data to the design process. There was no differential alignment of fibers observed between skin and core areas of the specimens which might lead to elevated flexural strengths. Residual compressive stresses between 7 MPa (1.0 ksi) and 14 MPa (2.0 ksi) were measured at the surface of the bend specimens. Finally, although the tensile strength data are well represented by a two-parameter Weibull model, there remains a 30% unexplained discrepancy between predicted and measured flexural strength.
ultimate strength, glass-filled phenolic, injection molded, short glass fibers, critical flaw sensitivity, Weibull statistical analysis, size effect, residual stresses, tension tests, flexure tests, fiber orientation
Mechanical engineer, General Electric Co., Corporate Research and Development, Schenectady, NY
Manager, CAD Technology, General Electric Co., Plastics Technology Center, Pittsfield, MA