Algebraic Approximations of Stress-Strain Curves for Kevlar-Reinforced Composites

Abstract

Abstract Stress-strain curves for Kevlar-cloth reinforced epoxy composites have been approximated by two-part analytic functions. Autographic test records are digitized using a computer-assisted procedure, and the digitized data are automatically processed using regression analyses routines. Tensile data are best approximated by a bilinear function; compressive data are best fit to either a parabolic-linear or a parabolic-exponential function. The errors of fit of the analytic functions to the test data are smaller than the experimental errors of the test. One application of the technique is for economic computer storage of stress-strain curves. A maximum of four constants and a one-digit code number are all that are required to store an entire stress-strain curve. Also, average stress-strain curves can readily be obtained and various moduli are easily calculated.