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In this study, creep behavior of a CFRP laminate subjected to a constant stress is analyzed based on the time-dependent homogenization theory developed by the present authors. The laminate is a unidirectional carbon fiber/epoxy laminate T800H/#3631 manufactured by Toray Industries, Inc. Two kinds of creep analyses are performed. First, 45° off-axis creep deformation of the laminate at high temperature (100°C) is analyzed with three kinds of creep stress levels, respectively. It is shown that the present theory accurately predicts macroscopic creep behavior of the unidirectional CFRP laminate observed in experiments. Then, high temperature creep deformations at a constant creep stress are simulated with seven kinds of off-axis angles, i.e., θ = 0°, 10°, 30°, 45°, 60°, 75°, 90°. It is shown that the laminate has marked in-plane anisotropy with respect to the creep behavior.

Strengthening steel structures using carbon fiber reinforced polymer (CFRP) materials has attracted much attention in recent years owing to their potential for fatigue crack repair and their convenience in construction. However, little is known about the efficiency of this strengthening method when applied to steel plates at different crack propagation stages. An experimental study was carried out on notched steel plates strengthened using CFRP laminates. 20 specimens were tested to evaluate the fatigue performance of the strengthened steel plates with emphasis on various degrees of initial damage, simulated by different lengths of slots, including 2%, 10%, 20%, 30% and 40% of the plate width. The effects of the retrofitted configuration and CFRP stiffness were also investigated. The "beach marking" technique and crack propagation gauges were adopted to monitor the fatigue crack propagation. The experimental results were very encouraging, demonstrating that the CFRP patches could effectively slow crack growth and extend fatigue life, regardless of the initial damage levels. More effective strengthening was found by using ultra-high modulus CFRP laminates, covering the initial cracks with CFRP and repairing at an earlier stage (i.e. smaller damage level).

In this study, creep behavior of a CFRP laminate subjected to a constant stress is analyzed based on the time-dependent homogenization theory developed by the present authors. The laminate is a unidirectional carbon fiber/epoxy laminate T800H/#3631 manufactured by Toray Industries, Inc. Two kinds of creep analyses are performed. First, 45° off-axis creep deformation of the laminate at high temperature (100°C) is analyzed with three kinds of creep stress levels, respectively. It is shown that the present theory accurately predicts macroscopic creep behavior of the unidirectional CFRP laminate observed in experiments. Then, high temperature creep deformations at a constant creep stress are simulated with seven kinds of off-axis angles, i.e., θ = 0°, 10°, 30°, 45°, 60°, 75°, 90°. It is shown that the laminate has marked in-plane anisotropy with respect to the creep behavior.

In this study, the distributions of microscopic stresses at a free edge of a unidirectional carbon fibre-reinforced plastic laminate (CFRP laminate) are analysed three-dimensionally, based on a homogenisation theory. For this, the mathematical homogenisation theory for elastic materials is reconstructed for unidirectional CFRP laminates with free edges using a traction-free boundary condition. The present theory is then applied to the analysis of microscopic stress distributions at a free edge of a unidirectional carbon fibre/epoxy laminate subjected to in-plane uniaxial tension. It is shown that microscopic shear stress noticeably occurs at the free edge, especially at the interface region between a carbon fibre and its surrounding epoxy matrix.

In order to identify the distribution character of void defects in carbon fiber reinforced polymer (CFRP), the ultrasonic resonance in CFRP containing voids was studied. The ideal model within no voids, model within uniformly distributed voids and model within centralized voids were built respectively based on finite element analysis software ANSYS. Then the ultrasonic spreading in the above models were numerically calculated. The ultrasonic echoes and their spectrums were analyzed. At last, the time-frequency images of the ultrasonic echo signals were generated for further analysis. The results are as follows. When the ultrasonic whose center frequency is close to the resonance frequency of the CFRP is used to test the CFRP, the ultrasonic in the ideal model within no voids can generate resonance and the frequency is consistent with the CFRP theoretical resonance frequency. The frequency of ultrasonic in model within uniformly distributed voids will slightly deviate from the theoretical resonance frequency. The frequency of ultrasonic in model within centralized voids will greatly deviate from the theoretical resonance frequency of CFRP. These conclusions can be used as the criterion for detecting void defects and the distribution of voids in CFRP.