Quasi‐static fracture characterization of fiber metal laminate with crack resistance curve based on δ₅

Abstract

Fiber metal laminate (FML) is a hybrid composite typical in aircraft industry. It is necessary to effectively characterize the quasi‐static fracture performance of FML, considering the importance of damage tolerance design of aircraft structures and the complicated fracture mechanism of FML. In present investigation, glass fiber reinforced aluminum laminates (Glare) with middle cracks were tested under quasi‐static tensile load. The experimental crack resistance curve (R curve) based on the special crack opening displacement at original crack tip (δ5) was used for revealing the superior crack resistance of Glare laminate to aluminum sheet, which expressed in crack extension aspect was the extended critical crack length. This was thought to be benefit from the contributions of glass fiber layers and fiber/metal delamination, by performing the progressive damage analysis. Since δ5 can embody the elastic–plastic response of the crack but without need to interactively correct for crack tip plasticity. The δ5‐R curve‐based macro and meso fracture models were proposed to accurately predict the residual strength and stable crack extension of Glare laminate, which gave further evidence for the effectiveness of δ5‐R curve in characterizing the quasi‐static fracture performance of FML.

Identifying the contributions of constituents to the fracture performance and failure mechanism of fiber metal laminate

“…In the P-Δa curve of Glare, a significant plateau is obtained in the vicinity of the ultimate load point, and it is extended by thickening the aluminum, while this is not such obvious for the monolithic aluminum. Similarly as stated in our previous investigation, [36] it may suggest the significant contribution of GFRP layers, which will be discussed in detail in the following. Beyond the ultimate load, the Glare presents shorter unstable crack extension than the monolithic aluminum, which implies that GFRP will lose its load-sharing capacity when unstable crack extension appears in aluminum.…”

“…Effect of metal layer thickness on the macro and micro damage patterns of GFRP in Glare (the damage pattern of Glare3‐3/2‐0.4 is the same as that present in our previous investigation). [ 36 ] …”

“…The subitems in them that exclude t and n are used for calculating the stress–strain relationships of the constituents. Details about the calculation methods can be referred to our previous investigation, [ 36 ] which will not repeat here.…”

“…The test method was the same as that described in our previous investigation. [ 36 ] As seen in Figure 3, the optical microscopy method by using two high‐resolution microscopes was adopted for measuring the crack extension and crack opening displacement δ 5 . One microscope was positioned at the original crack tip for measuring δ 5 , while the other one at the opposite side was intermittently moved with the propagating crack tip for measuring the crack extension length.…”

“…[37,38] This makes it a promising fracture parameter under plane stress condition, and it has proven to be effective for Glare in our previous investigation. [36] The crack extension of Glare is described by the P-Δa curve, which includes stable and unstable parts, similar to that of the metallic material. From this curve, the residual strength and the critical crack length can be obtained at the ultimate load point.…”