Paper number 976

INFLUENCE OF SPECIMEN PREPARATION AND SPECIMEN SIZE ON THE TRANSVERSE TENSILE STRENGTH AND SCATTER OF GLASS EPOXY LAMINATES

T. Kevin O'Brien¹, Arun D. Chawan², and Kevin DeMarco³

1U.S. Army Research Laboratory, Vehicle Technology Center
NASA Langley Research Center, Hampton, Virginia, U.S.A.
2Syracuse University. Syracuse, New York, U.S.A.
3Virginia Polytechnic Institute, Blacksburg, Virginia, U.S.A.

Summary

The influence of specimen polishing, specimen configuration, and specimen size on the transverse tension strength of two glass epoxy materials loaded in three and four point bending was evaluated. Polishing machined edges, and/or tension side failure surfaces, was detrimental to specimen strength characterization instead of yielding a higher, more accurate, strength as a result of removing inherent manufacture and handling flaws. Transverse tension strength was sensitive to span length due to the classical weakest link effect. However, strength was less sensitive to volume changes achieved by increasing specimen width. The Weibull scaling law over-predicted changes in transverse tension strengths in three point bend tests and under-predicted changes in transverse tension strengths in four point bend tests. Furthermore, the Weibull slope varied with specimen configuration, volume, and sample size. Hence, the utility of this scaling law for predicting transverse tension strength is unclear.

Keywords

transverse tensile strength, matrix cracking, Weibull distribution, scale effects, glass epoxy, bending tests.