Prediction method for inherent frequency decrease of composite unidirectional laminates under narrow-band random vibration load

When composite laminates are subjected to random vibration loads, internal fatigue damage alters the material properties, which in turn affects the stress-strain response of the laminates. This forms an evolving process where response, damage, and material properties interact with each other. In this paper, a method is proposed to simulate the fatigue process of composite laminates under random vibration loads. The method quantifies the fatigue damage induced by random vibrations through stiffness degradation. Starting from the initial stage, damage accumulation (i.e., stiffness degradation) is performed periodically, and the response is recalculated after each update. This iterative process continues until the entire stiffness and inherent frequency degradation throughout the fatigue life under random vibration is predicted. The method is implemented through a Python-based secondary development of ABAQUS. Constant-amplitude fatigue tests and random vibration fatigue tests were conducted on 2D woven glass fiber reinforced polymer composite laminates. The experimental results confirm the effectiveness of the proposed method.