Abstract
Bistable composite laminates have exhibited enormous potential in morphing and energy harvesting followed by a wide range of application in aerospace, power generation and automobile industries. This study presents the fatigue analysis of bistable laminates in terms of stiffness degradation and loss of bistability. Moisture saturation of the specimens are ensured by keeping them in a controlled laboratory environment for an extended period of time. Mass of the specimens have been measured to quantify the moisture saturation. Fatigue tests are performed at 1 Hz frequency, and R = −1 stress ratio which is the ratio of minimum stress to maximum stress. Specimens are tested for 3 million cycles in displacement control. Load-displacement plot from the test is divided into 5 stiffness regions. A piecewise study of each region has demonstrated good agreement with existing analytical model. Stiffness degradation in 4 regions corresponding to 2 stable configurations follows general trend for composites up to the second stage of damage in three stage damage progression model while the remaining region corresponding to unstable configuration is not considered in this analysis. Test results have been reproduced with minor discrepancy at the specified environmental and loading condition, ply configuration, and size of the laminate. Test protocols, results, and damage analysis presented in this study can be utilized to evaluate the fatigue performance of multistable CFRP structures subjected to higher amplitudes and frequencies.
