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When two bodies slide on each other the asperities are engaged and deformed which causes the dynamic friction. By superposing ‎ultrasonic oscillation to one of the bodies, the friction force is reduced . The experiments show that the friction force may be reduced by ‎about 60 percent depending on material properties and the kinetics of the two bodies. This phenomenon is widely used in metal forming ‎and metal cutting. This phenomenon may be used as a replacement of lubricants in such processes due to its higher efficiency and less ‎pollution effects . ‎ In this research an elastic-plastic model for the surface contact is given which is capable of predicting the friction force when ultrasonic ‎vibrations are superimposed to macroscopic motion . The result of this model is compared with that of the experimental values. The ‎differences between these values are shown to be less than 10 percent . The result of the model is also compared with that of the Dong ‎model. The comparison show that the present model ‎‏ ‏‎ has better accuracy of the Dong model .‎

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When two bodies slide on each other, friction is created. By superposing ultrasonic oscillation to one of the bodies, the friction force is reduced .This phenomenon is widely used in metal forming and metal cutting. For the production and transmission of ultrasonic vibrations to a target it is required to use an ultrasonic system the components of which are a generators, a transducers and a horn. Horn constitutes an important part of the Ultrasonic systems. The main task of the horn is to transmit the ultrasonic vibrations and amplify the ultrasonic vibration amplitude at the output. In this study, an Aluminum horn was designed in cylindrical-conical-cylindrical shape geometry and was analyzed by the finite-element method(FEM) using the Abaqus software was manufactured. The resonance frequency obtained in Abaqus was equal to 19976 Hz. The resonance frequency obtained from the generator was equal to 19920 Hz. Hence there is a very good agreement between the experimental result and the FEM simulation. The difference between the finite element simulation results and the experimental ones is less than one percent. Moreover, a horn –workpiece assembly for applying the ultrasonic sliding friction was designed and manufactured. Then the fixture and the tool holder clamp were designed for the vibrating tool so that it can be installed on a milling machine and the friction force measurement is possible while the ultrasonic vibrations are applied.

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When two bodies slide on each other the asperities are engaged and friction is created. By superposing ultrasonic vibrations to one of the bodies, the friction force is reduced .This phenomenon is widely used in metal forming and metal cutting. In this research, experimental study of the effect of ultrasonic vibrations has been on sliding friction force in longitudinal direction. For this purpose, set-up was designed and fabricated. The main components of the set-up, including generators, transducers, first engaged body and second engaged body. The Set-up was installed on the machine lathe for investigation of the effect of ultrasonic vibrations on sliding friction force in longitudinal direction. The experiments were performed for eight different performance conditions. Next, the effect of each parameter ultrasonic wave velocity, roughness and material of contact surfaces were studied on the reduction of the friction force due to addition of ultrasonic vibrations. The result show that range of reduction friction force due to addition of ultrasonic vibrations in longitudinal direction is between 40 to 100% for the different performance conditions also friction force significantly reduced by increasing ultrasonic wave velocity so that friction force can be brought to zero by significant increase in ultrasonic wave velocity. The results also show that friction force has a more reduction for the surface has a less roughness. Aluminum-aluminum surfaces can be more reduction friction force from aluminum – steel surfaces.

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With the arrival of composite materials, because of their unique properties, the ideas were presented in order to strengthen and improve their performance. The ideas were causing building of Grid composite structures. These structures have most widely used in the aerospace, missile and Marine industry because have made ideal mechanical properties: special stiffness and high strength against impact and fatigue. Grid composite plates are made from thin composite shell connected by series composite ribs. Ribs network results in a significant increase in stiffness and strength of structure. In this research, experimental and numerical investigations of effect of Shape of ribs have been on flexural behavior of grid composite plates. For this purpose, three types of Grid plates were considered with triangle, square and rhombic ribs. For the building these plates, silicone mold was designed and built and also was used for making plates from hand lay-up and hand-wound layer technique. Samples were subjected to three-point bending test that for this purpose, the fixture was designed and built. From numerical solution of the problem and compared with experimental results was observed that there is very little difference between experimental and numerical results. Experimental results show that special flexural stiffness of plate with square rib is 1.92 and 1.88 plate with triangular and rhombic ribs, respectively. Also, the flexural strength of plate with square rib is 1.58 plate with triangular rib. Thus plate with square rib is the highest stiffness and bending strength Keywords

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Due to unique properties, lattice composite structure are used extensively in aviation, marine and automotive industry. In this research, experimental and numerical investigation of the free vibration of composite sandwich plates with triangular grid has been studied. For the fabrication of this plates, silicone mold, filament winding, and hand lay-up method were used. Stiffened plates and simple plates are fabricated, separately. Then, composite sandwich plates with triangular grid were created by attaching the two parts together. The modal test is done on the plates and natural frequencies have been extracted.The comparison of numerical and experimental results showed that there is a good agreement between them. By using Taguchi method, a parametric study was performed on the vibrational behavior of sandwich plates with triangular cores via three parameters that such as stiffeners’ number, stiffener thickness and skin thickness. The results show that the natural frequency of sandwich plates with triangular grid has a most sensitive to the stiffener thickness, and least sensitive to stiffeners’ number. The sensitivity of natural frequency is almost identical to stiffener thickness and skin thickness.To evaluate the efficiency of sandwich plates with triangular grid, the natural frequency of sandwich plates are compared with simple plates in the different boundary condition. The results show that the natural frequency of sandwich plates with the triangular grid is 133% and 138% higher than an equivalent simple shell at free and clamp boundary condition, respectively.

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Due to unique properties, grid stiffened composite cylinder shells are used extensively in aviation, marine and automotive industry. In recent decades, several studies are done to predict the critical buckling load of grid stiffened composite cylinder shells without breakdown or failure. Vibration Correlation Technique (VCT) is one of the most important non-destructive methods that based on nonlinear vibration analysis. The aim of this research is the prediction of the critical buckling load of stiffened composite cylinder shells with lozenge grid by using VCT. For this purpose, linear and nonlinear vibration analysis of composite cylindrical shells were performed in different compressive loads by using finite element software ABAQUS, firstly. In the next step, linear buckling critical load was determined by using numerical methods. Then, non-linear critical buckling load of grid stiffened composite cylinder shells was predicted by using VCT. To validate the results of VCT, five composite cylindrical shells were fabricated by using filament winding method with same conditions and was placed under axial compression test. Finally, the critical buckling load was measured experimentally. The results show that the difference between the critical buckling load of VCT with experimental buckling load is less than 3%. This subject implies that VCT is suitable for prediction of critical buckling load of stiffened composite cylinder shells with lozenge grid with very high accuracy.

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