Evaluation of Mechanical Properties of Hybrid Aluminium/Fiber-Reinforced Composites
Mutasher, Saad A. (2006) Evaluation of Mechanical Properties of Hybrid Aluminium/Fiber-Reinforced Composites. PhD thesis, Universiti Putra Malaysia.
The purpose of drive shaft is to transmit static and dynamic torques with vibration stability. Extensive researches have been carried out on the fiber-reinforced composite drive shaft for the last two decades. Hybrid shafts made of unidirectional glass fiber or carbon fiber epoxy and steel or aluminum have high fundamental bending natural frequency as well as high torque transmission capability. The fiber increases the fundamental bending natural frequency due to its high specific stiffness and aluminum or steel transmits the required torque. In the present work experimental tests were carried out to study the bending fatigue life, static torsion capacity and power transmission capacity of a hybrid aluminum/ composite drive shaft. The composite used are glass and carbon fiber/epoxy. A tensile test was carried out to find the mechanical properties of composite materials used throughout this work. A hybrid shaft was fabricated using a wet filament winding method by winding glass and carbon fibers onto aluminum tube with different winding angles, numbers of iv layers and stacking sequence. A filament winding machine was developed to fabricate the hybrid aluminum/ composite drive shaft. A special mechanism was designed and fabricated for carrying out the static torsion test of the hybrid shaft. In addition, an apparatus was designed and fabricated to investigate the power transmission capacity of the hybrid shaft. Minor modifications were made for the rotating bending fatigue machine to perform the bending fatigue test. Flexural moment fatigue life relationships were obtained and the failure modes of the hybrid shaft were studied under fully reversed bending load, R = -1. The results show that the fatigue life for a winding angle of 45o is larger than that for 90o, for both glass and carbon fibers. The [±45]3 carbon fiber/epoxy laminates enhanced the fatigue life of aluminum tube up to 54% and the hybrid specimen did not fail till 107 cycles at 14.7 N.m applied bending moment. In the hybridized specimens two carbon percentage contained 34% and 51% were examined. The results show that the percentage contained of carbon and glass fibers were significantly affected the fatigue life of the hybrid shaft at high and low levels of bending load. The use of matrix inside the aluminum tube increased the fatigue life by 6.5% and increases the weight of the hybrid specimen by 16%. The results of fatigue test on a macroscopic level indicate that the cracks initiated in the fiber free zones or in the outer skin of resin and increased with increasing number of cycles until failure of specimen. On other hand the micro damage shows that the delamination completely took place between the composite layer and surface of aluminum tube before the catastrophic failure of a hybrid specimen. In addition, the aluminum tube failure was perpendicular to the applied bending load and this phenomenon is the same as that for the aluminum shaft under bending fatigue test. There is no fiber breakage being observed from the rotating bending fatigue test. v The torque-angle-of-twist response under static torsion load was obtained and the failure modes of the hybrid shaft were studied. The results show that the static torque capacity for a winding angle of 45o is larger than that for 90o, for both glass and carbon fibers. The maximum static torsion for aluminum tube wound by [+45/-45]3 laminates are 273.2 N.m and 173.5 N.m for carbon and glass fiber respectively. The percentage difference is approximately 36%. The aluminum tube yielded first at the central region of the shaft, followed by crack propagation in the composite part along the fiber direction, which eventually caused delamination of the composite layers from the aluminum tube. This due to the matrix crack and finally the fibers broke and the catastrophic failure took place. For a hybrid shaft wound with fiber configurations of [90/+45/-45/90] and [+45/- 45/90/90], the torque-angle-of-twist response results were similar and this satisfied the Classical Lamination Theory. In addition, the torque capacity increased by approximately 12 times for the case of an aluminum tube wound with six layers of the carbon fiber at winding angle of 45o compared to the aluminum tube alone. From the power transmission test, it was found out that the difference between the static torque and dynamic torque is approximately 7%-15%. The finite element analysis has been used to analyzed the hybrid shaft under static torsion. ANSYS finite element software was used to perform the numerical analysis for the hybrid shaft. Full scale hybrid specimen was analyzed. Elasto-plastic properties were used for aluminum tube and linear elastic for composite materials. The predicted results gave good agreement with the experimental results, the percentage differences between the experimental and theoretical results is approximately 3.5%-25%.
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