Fiber Metal Laminates (FMLs), as high-performance composite materials, demonstrate exceptional potential in a wide range of applications, such as aeronautical and astronautical industries. However, the traditional cured FMLs possess complex interlayer stresses and low forming limits, restricting further promotion and application of FMLs. Low-constraint FMLs exhibit a lower forming resistance and better formability due to no curing during the forming process; however, the formation mechanism and response are not clear. This paper presents the Forming Limit Diagram (FLD) of low-constraint GLARE (glass fiber reinforced aluminum laminates) based on the forming limit test, and compares it with the conventionally cured laminates to evaluate the differences in the forming limit. In addition, combined with the analysis of failure mechanism and micro-deformation mechanism of specimens, the influence of different temperatures (20–80 ℃) and forming states (width) on the deformation performance of laminates is further explored. The results reveal that the forming limit curve of low-constraint laminates shifts up with the increase of temperature, the forming limit initially increases with the increase of width, then followed by a gradual decrease, and the maximum principal strain of low-constraint laminates is increased by 29% at 80 ℃ compared to 20 ℃. The cured laminate has a principal strain range of 0–0.02, while the low-constraint laminates have a principal strain range of 0.03–0.14. Compared with cured laminates, low-constraint laminates possess a higher forming limit due to the improvement in deformable degree between layers by resin flow and fiber slippage, which enhances their formability. This study is expected to serve as a reference for establishing forming limit criteria and optimizing forming schemes for low-constraint laminates.

The considerable uncertainty in mechanical properties of composite bolted joints not only prevents advanced composite materials from efficient applications, but also threatens the safety and reliability of the aircraft structures. In this paper, the uncertainty in bearing fatigue properties of a CFRP double-lap, single-bolt joint was evaluated by combing a Progressive Fatigue Damage Model (PFDM) with the interval analysis method. In the PFDM, a residual-strain-based gradual material degradation model and a strain-based fatigue failure criterion were combined with a micromechanics-based sudden material degradation model to predict fatigue properties of the joint. Based on the interval analysis, the key uncertain parameters, which were firstly picked out from eighteen structural parameters of the joint, were described by estimated intervals, and the envelope cases were determined to estimate the lower and upper bounds of fatigue properties of the joint. The predicted results have the same tendency with the experimental results in literatures, which indicates that the PFDM combined with the interval analysis shows potential in efficiently evaluating the fatigue reliability of the complex bolted joints with an adequate accuracy.