SEDL / STP / STP1174-EB / STP18053S

Determination of a Load, Heat, Time-to-Failure Surface of Polymeric Composites

Milke, JA
Assistant professor, Composites Research Laboratory, University of Maryland, College Park, MD

Vizzini, AJ
Assistant professor, Composites Research Laboratory, University of Maryland, College Park, MD

Pages: 12    Published: Jan 1993

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Abstract

A small-scale experiment is developed to examine the failure of loaded composite structures exposed to a thermal insult for short durations. The test consists of imposing a tensile load of a prescribed magnitude to the specimen, then applying a moderate heat flux to a portion of one surface using a thermofoil micro heater clamped to the specimen. The heat flux is maintained for a period of 3 600 s or until failure of the specimen. A threedimensional failure envelope, with percent load, heat flux, and time-to-failure as the three axes, is determined for a given layup. In this study, 13-mm-thick test specimens were manufactured from a glass-fiber reinforced thermoplastic with the following layups: [90²/0]^11S, [0/(±60/0)¹¹]^S, and [0/(± 30/0)¹¹]^S. Over the range of loads and heat fluxes tested, initial failure locations occurred in the melted and unmelted regions of the specimens. The time-to-failure increases with decreasing flux for all laminates since the temperature gradients and damage level decreases. Differences in the time-to-failure for the three layups increase with decreasing heat flux or decreasing load. Thus, at low flux or load levels, the phenomenon is multidimensional; whereas at high flux or load levels, failure is one-dimensional, primarily dependent on the thickness of the specimen. As the ply angles comprising the laminate decrease, (that is, the laminate becomes more unidirectional), the time-to-failure increases for a given load and heat flux.