mohammad mohammadi fesharaki

In this research, the determination of curvature and the effect of carbon nanotubes (CNTs) on it in cured three-phase un-symmetric cross-ply composite laminate have been studied. The un-symmetric cross-ply composite laminates is including three different phases: carbon fiber, polymer epoxy and carbon nanotube particles that different volume fraction of CNTs including %0, %1, %2 and %3 have been considered. Different micromechanical models such as Halpin-Tsai, bridging and Schapery models have been used to determine the mechanical and thermal properties. Adding of %1 volume fraction of CNTs has been caused decreasing the longitudinal and transverse coefficient thermal expansions and increasing the longitudinal, transverse and shear modulus ones. Developed Hyer model's has been employed to investigate different parameters such as curvature, critical length and deformed shape in different lengths of square un-symmetric cross-ply laminates. Addition of 1% volume fraction of CNTs decreases the critical length and curvature about 9% and 14%, respectively. In addition, the results of finite element analysis have been compared with the developed Hyer model and showed less than 10% error.

In this study, the distribution of residual stress in fiber-reinforced nanocomposites is investigated. Fiber-reinforced nanocomposite is composed of three substances: carbon fiber, carbon nanotube (CNT), and polymer matrix. Unit cells in hexagonal packing array with different arrays as unit cell, 3*3 and 5*5 arrays have been selected as suitable for finite element analysis of residual stresses. Radial and tangential residual stress have been determined in different directions by finite element analysis using ABAQUS commercial software for each phase individually. The effect of the CNTs’ various volume fractions (0%, 1%, 2%, and 3%) on residual stress distribution has been studied in different directions and compared to one another for each phase. Results show that the 3*3 unit cells arrays are suitable for modeling micro-residual stresses, and the results of this array are reliable. In addition, adding a 3% volume fraction of CNTs to the matrix is the best option for reduction of overall residual stresses with minimal fluctuation in local micro-residual stresses.

In this research، hydrodynamic distribution pressure in continuous times is done and stress and displacement of a high speed vessel are studied. Hydrodynamic distribution pressure is studied for different dead rise angle according to vertical and horizontal vessel velocity at dry chine and wet time steps and is applied to vessel at continues times of vessel variable position. Vessel body is divided to some parts according to different dead rise angles and loading is applied as incremental loading. Shell of composite vessel is modeled using ABAQUES commercial finite element software as layer to study the effect of ever layer in stacking sequences، then change of the core thickness and optimization of vessel structure is studied that causing safety factor is increased and weight is decreased. At the end، results of critical stress and maximum displacement of different parts of vessel is compared and evaluated in initial and optimized vessel.