Cyclic elastic modulus and low cycle fatigue life of woven-type GFRP coated aluminum plates

Abstract

In this study, the mechanical properties and low-cycle fatigue behavior of woven-type glass-fiber reinforced plastic (GFRP) coated on one side of an Al 6061 aluminum alloy plate are investigated based on the GFRP layer thickness. Tensile and fatigue tests are performed with one, three, and five plies of GFRP coating. The strain-life method and total strain energy density (TSED) method are used to evaluate the fatigue behavior and life expectancy of these materials. From the results of the tensile test, the maximum load of the GFRP-Al specimens increased with a thick coating layer; however, the yield stress and tensile elastic modulus decreased. The behavior of the cyclic elastic modulus in repeated strains was different from that of the tensile elastic modulus. The hysteresis behavior of GFRP-Al according to the strain magnitudes was virtually the same as that of the uncoated monolithic Al, and both materials seemed like a Masing behavior. The fatigue life was greater than that of the uncoated Al. Coating GFRP with three plies on the Al substrate demonstrated the highest fatigue performances despite the specimen thickness increase of approximately 14%. In the tensile test, an initial crack occurred in the GFRP coating layer leading to the fracture. However, the fatigue tests with low and high strains indicated an initial crack and fracture in the Al substrate as opposed to the tensile test result. The fatigue life test data of the GFRP-Al specimens and the predicted values obtained through the total strain energy density (TSED) method agreed well, indicating a value of R-2 > 0.92 in the linear regression analysis of strain versus life and TSED versus life data.