Compressive strength of production parts without compression testing

The purpose of this paper is to present a methodology to estimate the compressive strength of fiber-reinforced composite prototype and production parts. The procedure is based on test data that incorporate the effects of sample size and sample preparation hut are simpler to obtain than compression test data. A simple formula is derived to relate the compressive strength to the shear stiffness, shear strength, and standard deviation of fiber misalignment. The formula is completely defined in terms of these three parameters, all of which can be measured by standard experimental procedures. It is proposed to use the shear stiffness and shear strength from coupon tests, usually available from the material supplier or from the characterization phase of the design/build project. Since these two parameters are relatively insensitive to part size and sample preparation, the coupon data are reliable and representative of the actual production part. Since fiber misalignment depends on the processing conditions, the third parameter used is the standard deviation of fiber misalignment, measured on samples from actual production parts. These three values characterize the compressive strength of the carbon/epoxy layups for which experimental data are found in the literature and those evaluated in this investigation. The predictions are then validated against data from a variety of specimens tested at high and low temperatures, as well as data from production prototype parts.