Effect of elliptical notches on mechanical response and progressive damage of FMLs under tensile loading

This paper aims to explore the residual strength and elucidate the failure mechanisms of elliptical notched FMLs with different design variables through experimental investigations and numerical simulations. Quasi-static tensile experiments are carried out to investigate the effects of off-axis angle, inclination angle and aspect ratio on the tension behaviors with the aid of digital image correlation technique (DIC). Subsequently, a progressive damage model integrated with a VUMAT subroutine is employed to study the progressive damage evolution and failure mechanism, considering thermal residual stress. Meanwhile, damage initiation and evolution as well as the finial damage patterns are explored systemically combining the strain distributions from DIC technique, equivalent plastic strain distributions of aluminum layers and final damage morphologies of specimens. Results show that the notch strength is more sensitive to off-axis angle and inclination angle as compared with the aspect ratio. The failure morphology exhibits a neat and straight crack for on-axis cases, whereas it presents a fracture along the fiber direction of adjacent layer with apparent pull out of fiber for off-axis cases. With the increase of off-axis angle, the ultimate failure mode gradually transfers from fiber-driven to aluminum-driven accompanied by the corresponding critical failure mechanism varying from tension to tension-shear.