د. حسام جواد عبد الصمد الحمد الاسدي

This study represents investigation of the critical buckling load in columns, which consist of two different materials for case of (fixed–free) loading in order to choose the suitable compound ratio. The investigation is done with two methods: analytical method through suggested equation for calculation of equivalent modulus of elasticity and numerical finite-element method with ANSYS APDL 17.2. The analytical and numerical results showed excellent agreement with each other because of the qualification of the suggested equation of the equivalent modulus of elasticity for the compound column. The critical buckling load is sensitive to the difference between the modulus of elasticity for the two different materials of the compound column, which also affects the ratio of the critical buckling load to the mass of the compound column.

Beam is a structural element and can be used in different shapes according to its applications and the tapered beam is one of these struc-tural elements. The frequency of tapered beam was investigated in this work using three calculation methods. These methods were Clas-sical Rayleigh Method (CRM), Modified Rayleigh Method (MRM) and Finite Element Method (FEM) using ANSYS Workbench (17.2). The basic idea of Classical Rayleigh Method (CRM) and Modified Rayleigh Method (MRM) was changing the tapered beam into stepped beam with N-steps. The results showed that there was a good agreement between the natural frequency which was calculated by ANSYS and Modified Rayleigh Method (MRM) when the number of steps was (6) and the natural frequency increases when the larger width (or height) increases for different values of smaller width (or height).The frequency ratio is constant when the smaller width (or height) increases. Also, the frequency ratio increases when the width ratio (WL/WS) increases and when the number of divisions (N) increases, the slope of frequency ratio increases too.

This study includes an experimental investigation for rotating bending fatigue in five types of composite material shaft with comparison to a standard type made of pure polyester material. In addition, an artificial neural network ANN prediction is compared with experimental part. The five types vary according to the type of glass fiber fabric (thin and thick fiber fabric) and fiber volume fraction (10.2 and 14.6% for thin fibers, and 14.6, 29.3 and 43.9% for thick fibers). Tensile tests are performed to identify the range of applied fatigue stress for every type. Specimens weight is measured in order to calculate the ratio of strength to weight. The rotating bending fatigue tests are performed to record the fatigue behavior for each type. Results show that the type with (29.3%) volume fraction of thick fiber has the maximum tensile strength to weight ratio with (290%) improvement compared with the standard type. The best fatigue behavior is for type with (14.6%) volume fraction of thin glass fibers. This type has the maximum value of fatigue stress at life limit of (106 cycles) with (362%) improvement compared with the standard type. Then, the types with (29.3%) and (43.9%) volume fractions of thick glass fibers make (356%) and (331%) improvement of fatigue stress, respectively. The ANN gives satisfactory results and it is a good prediction tool for fatigue life of composite materials.

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