Multiaxial experimental determination of failure of composite materials through digital image correlation to calibrate composite failure theories

Abstract

The purpose of this study is to experimentally test uniaxial, biaxial, and triaxial fiberglass laminates to failure via multiaxial testing. These tests provided force and strain data that can be used to calibrate existing composite failure theories to better predict failure of composite materials. Multiaxial testing consisted of loading fiberglass coupon samples of two different notch geometries, with each notch geometry repeating four specific testing directions. The force and strain data from each test were recorded, with force data being extracted through load cells, and strain data being recorded through Digital Image Correlation (DIC). Both strain and force data consisted of three directional components each. The three directional strain components from each test were used as three-dimensional coordinates in a scatter plot for each laminate. These plots showed the relationship of how different combinations of strain directions result in failure of a given composite. Recorded directional force data at the point of failure for each test will provide a critical basis for reconstructing testing conditions in Finite Element Analysis (FEA) to calculate the actual experienced stresses in the coupon. Calculated stresses and measured strains will be used as a foundation for any future calibration of failure theories for composite materials. The resulting scatter plots displayed patterns that represented understandings of the limits of strain combinations that result in failure of uniaxial, biaxial, and triaxial layups, and how those patterns may grant insight into how the combinations of strains that result in failure can be predicted through the knowledge of failure of the laminae that make up the laminate.