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Fiber metal laminates (FMLs) are usually more complicated in the failure aspect as compared to their constituents, especially when complex load is applied. In this paper, notched FMLs and the constituents, i.e., the aluminum and glass fiber reinforced plastic (GFRP) were subjected to off-axis tensile loading to evaluate the failure mechanism. Initial attention was paid on the off-axis dependence of mechanical responses, especially on its relation to the notch size. As expected, off-axis dependence of notched strength and notch sensitivity were closely related to the notch size, but different for GFRP laminates and FMLs due to their different damage behavior. Finite element model was employed to predict accurately the mechanical responses of FMLs, particularly for elucidating the damage mechanism. Failure of notched FMLs under off-axis loading was a combined transverse fracture and shear-off, while it was shear-dominated in notched GFRP laminates. Transverse fracture in aluminum appeared first, followed by the fiber breakage, which was postponed by the extensive subcritical damage. Thereafter, shear-failure in fiber and aluminum layers were encountered instantaneously at the descending part. Thus, the critical failure of off-axis notched FMLs was still tension-dominated as that in the on-axis case, but aluminum played the critical role.

Experimental investigations were carried out to determine the low velocity impact behavior of woven carbon fabric/polyphenylene sulfide (CF/PPS) laminates at room temperature (RT) and high-temperature (95 °C and 125 °C). The relationships of impact response and damage with temperature were established with the aid of macro- and micro-scopic observations and C-scan inspections. The analysis on impact behavior of CF/PPS composite at RT indicated that increasing incident impact energy led to increased low velocity impact-induced damage initiation and propagation. The results revealed that temperature increasing could lead to evident decrease of stiffness, energy based damage degree and delamination area, as well as evident increase of the permanent indentation. Take the specimens at 15 J and 125 °C as example, the permanent indentation and delamination were increased and decreased by 40.2% and 57.45%, respectively. The temperature influence on impact responses was closely associated with the plastic deformation of matrix and its coupling effect with the resin-rich regions and fiber-bridging mechanism that induced by the specific weave architecture. It has specified that the failure mechanism was transformed from brittle manner to ductile manner with increasing the temperature, which was characterized by the variation of intra- and inter-laminar cracks as well.

Characterization of the complicated failure behavior in fiber metal laminate (FML) depends on well understanding of the contributions from metal and composite layers. It seems to be very cumbersome to deal with this by conventionally collecting the stress, strain and damage patterns through experiments or numerical simulations, especially when complicated load (e.g., off-axis load) or a more hybrid degree is adopted. Since all mechanical responses in nature are governed by energy principles, in the present study an energy dissipation approach was introduced in FML. Analyses were carried out with employing the available history outputs in Abaqus, where four kinds of energy variables in terms of internal or total strain energy ( E int ), elastic or recoverable strain energy ( E elast ), energy dissipated by plastic deformation ( E plast ) and damage ( E dam ) were requested for both the constituents and the laminates. Two issues were clarified by this energy approach: off-axis dependence of mechanical response and damage behavior in notched glass fiber reinforced aluminum laminate (Glare), and the reinforced effect of titanium on notched Glare (a more hybrid case). Results have shown the potentiality of energy approach in straightforwardly and effectively characterizing the failure behavior of FMLs.