The Development of Thermal Stresses in Polyimide Matrix Composite Materials as a consequence of Three-dimensional Thermal Gradients – Analysis and Experiment

Abstract

Composite material parts may experience service exposure to three-dimensional (3D) temperature gradients where temperature differences may exceed 150 C. The effect of these conditions on a glass fabric-reinforced BMI resin laminate has been analyzed as a function of location using a 3D model. According to analysis predictions, in a situation of thermal load and temperature gradients, compression stresses develop in the center of the heated zone, which is surrounded by a tensile-stressed annular region. The stresses and strains developed are small compared to the ultimate mechanical properties of the material. The analysis has been verified by subjecting an instrumented sample to nonuniform heating. This confirmed that in the absence of absorbed moisture, the damageinducing potential of local heating was small. This observation suggests that less conservative design approaches can be used for thick laminates compared to the current, with a consequent weight saving potential.

Prediction of Process-Induced Residual Stress for Laminated Composites with Metallic Plate

“…From above-stated, it was known that the residual stress in the along fiber direction of composite part is compressive stress while the metal has tensile residual stress during the curing process, which is different from that in the vertical fiber direction. Based on previous study [5], residual stress arises after the gelation point of the matrix. It means that the interface begin to bear load between the fiber and the matrix.…”

“…Due to the presence of compressive residual stress in the transverse loading direction at preferential damage locations, the transverse tensile mechanical properties of the resin is improved [4]. In order to utilize laminated composites safely, the mechanisms that cause process-induced residual stress during the curing process should be understood and analyzed by numerical and experimental methods further [5]. Many efforts have been made to study the process-induced residual stress during curing process [6][7][8][9][10][11].…”

Propagation of 'popcorn' failure in composite plates by Mode I delamination

“…A temperature-controlled hot air gun was used for spot heating of test plates that were instrumented with thermocouples and gauges for measuring in plane radial and circumferential strain and out-of-plane deflection [2].…”