مقالات رزومه دکتر علی طالع زاده لاری

Here the healing process of glass/epoxy composites is studied experimentally. The healing agent is composed of ML506 epoxy resin and HA-11 hardner which is charged into microtubes. The microtubes are interleaved between the first and the second and the fifth and the sixth layers. The initial damage is introduced to the samples by drop weight impact tests and the recovery percentage of the tensile strength due to healing process is measured by tensile test. The effects of healing time (without thermal cycles), number of healing units and thermal cycles are investigated on the recovery of the tensile strength. Composite samples containing 8, 16 and 32 healing units are studied in the periods of 1, 6 and 12 days after the initial damage. Also, some damaged samples are set to 1, 3, 5 and 7 thermal cycles and after one day, tensile tests are carried out. The results show that without thermal cycles the healing process is almost completed after 6 days with an 83% recovery. In addition, the maximum amount of tensile strength recovery is equal to 86% which is related to the samples with 32 healing units after 12 days. This amount of healing efficiency can also be achieved by means of 5 thermal cycles. This is also true for thermal cycles where the effect of thermal cycles is tangible up to 5 cycles.

In this study, the vibration of a composite cylindrical shell in the presence of a longitudinal and circumferential crack was investigated. The governing equations were derived based on the first-order shear deformation theory and could be converted to Donnell’s, Love’s, and Sanders’ theories by selecting proper parameters. A multi-domain generalized differential quadrature method was used to solve the problem. In this technique, a physical domain was decomposed into several elements. Then, a generalized differential quadrature method was employed to discretize the governing equations, boundary conditions at shell edges, and the compatibility conditions at the interface boundaries of adjacent elements in both longitudinal and circumferential directions. Assembling these discretized equations led to a system of algebraic equations, which could be solved through an eigenvalue solution to calculate the natural frequency of the shell. This procedure was coded in Matlab environment. Numerical results obtained by the presented method were compared with Abaqus results and those available in the literature. After verifying the accuracy and precision of the proposed method, it was employed to study the effect of different parameters on the vibrational behavior of cracked composite shells. The obtained results can be used as a benchmark for further studies.

In this paper, the free vibration of a composite shell with and without a rectangular cutout was studied based on the first-order shear deformation theory. The equations were derived in a general form and can be converted to Donnell`s, Love`s, and Sanders` theories. To investigate the perforated shell a physical domain was decomposed into several elements with uniform boundary and loading conditions in each element edges. In each element, the governing equations were discretized in both longitudinal and circumferential directions by the use of generalized differential quadrature method (GDQM) as well as the boundary conditions at the cutout edges, and the compatibility conditions at the interface boundaries of adjacent elements. Assembling these discretized relations, a system of algebraic equations was generated. Finally, the natural frequencies were calculated by an eigenvalue solution. To validate the presented method, the results of GDQM were compared with the available ones in the literature and also with the ABAQUS finite element model. Then a parametric analysis was performed to investigate the effects of different parameters on the vibrational behavior of the shells with and without cutouts. This study illustrated that small cutouts (c/L<0.3) had no significant effect on the natural frequency of the shell. This was independent of both shell material and layup. In addition, decreasing the length to radius ratio or increasing the shell thickness decreased the effect of cutout on natural frequency. Moreover, circumferential cutouts had less effect than longitudinal ones.

Due to the widespread use of unstiffened and stiffened composite shells in different industries, investigating their vibrational behavior has great importance. In this paper, the effects of different parameters on the vibration of these shells are studied using experimental and numerical analysis. Specimens used for modal analysis are fabricated by filament winding machine. The mechanical properties of fibers and resin matrix are determined based on the standard tests as the fiber volume fraction in the shell and the stiffeners. Finally, the mechanical properties are calculated using micromechanical relations. These properties are used for finite element modeling by ABAQUS package. FE results are validated in comparison with empirical tests. Finally, the effects of different parameters on the vibrational behavior of composite shells are studied using this FE model. The results show that using the stiffeners does not necessarily increase the natural frequencies of the shell. From the vibrational point of view, the results of the stiffened shell with circumferential rings, kagome grid, and triangle grid are similar. So, considering the manufacturing procedure, stiffening the shell with circumferential rings is preferred.