Research for thermal load and procedure to predict fatigue life up to form a fatigue crack on CFRP/Aluminum alloy hybrid joints

icaf2023 Tracking Number 118

icaf2023 presentation

At ICAF 2015, JAXA and NRC presented the life distribution up to first linkup of adjacent fatigue cracks formed in the riveted Aluminum lap joint under constant amplitude fatigue load. The fatigue life up to 0.5mm crack formation was predicted by SWT equation and the life up to first linkup was predicted using in house code. Currently, JAXA have been conducted the research to evaluate the fatigue life up to form a fatigue crack in a metal/composite hybrid joint. Thermal stress at high and low temperature is occurred in metal/composite hybrid joints due to the difference of coefficient of thermal expansion between metal and composite materials. For application of SWT equation to predict the fatigue life of the metal/composite hybrid joints, accurate calculation of stress and strain in the joint including thermal effect is very important. In this study, thermal load in a mechanically fastened hybrid joint under temperature cycle was investigated experimentally and numerically. In addition, material constants of aluminum sheets were obtained with the strain-controlled fatigue tests for precise prediction by SWT equation. For the investigation of the thermal load in the hybrid joint, the mechanically fastened hybrid joint specimens composed of two aluminum plates and a composite plate were prepared. Experimental results indicated that relationships between temperature and elastic strain on specimen surface in temperature cycle exhibit hysteresis loop. Finite element analysis for the hybrid joint was also conducted and captured the hysteresis loop obtained by the experiment. In the material data measurements, the fatigue life for the aluminum alloy in relation to the product of the strain amplitude and the maximum stress has been obtained by the strain controlled fatigue tests. The strain-controlled fatigue tests are terminated when applied load is reduced by the fatigue crack. The obtained cycles are planned to evaluate the life for formation of certain crack size by fracture surface observation and the relationship between the crack formation cycles and the product of the maximum stress and the strain amplitude are obtained. The obtained relationship would be used to preliminary predict a fatigue crack formation life of the hybrid joint using FEM result.