جستجوی مقالات مرتبط با کلیدواژه "ماده مرکب" در نشریات گروه "مکانیک"

In this study, the response surface method is used to investigate the effect of drilling process parameters including cutting speed, feed rate, , drill bit point angle and drill bit relief angle on the thrust force of cotton phenol composite. This polymer-based composite material is used in various industries including electronics and aerospace industries. Investigating the effect of the drill bit relief angle as one of the effective parameters in the drilling process is one of the strength points of this research. Design of experiments was conducted using Box–Behnken method and the response surface method was used to express the trust force as a quadratic function of investigated process parameters. Variance analysis was used to check the influence of each parameter on the trust force. According to the obtained results, it was determined that cutting speed (i.e. tool revolution speed) and drill bit relief angle have the greatest and least effect on the trust force, respectively. Also, according to the quadratic equation fitted to express the trust force as a function of the investigated process parameters, the minimum trust force was obtained in the conditions of the drill bit point angle of 106.4 degrees and the drill bit relief angle of 8.4 degrees.

With the introduction of additive manufacturing processes and 3D printers, a lot of research has been done and is being done in this field. Methods based on polymer extrusion, known as fused deposition modeling, are one of the most widely used additive manufacturing methods. Most of the research done in the fused deposition modeling method is related to increasing the mechanical properties of the printed samples. Optimization of process parameters, addition of metal and non-metal filler particles, use of post-processing operations (types of heat treatment, use of ultrasonic waves, etc.), and use of continuous fibers are the main methods used. The most effective method for increasing mechanical properties, especially tensile mechanical properties, is the use of continuous fibers with high strength such as carbon, glass, and aramid. Of course, the use of continuous natural fibers such as linen, hemp, etc. has also been considered. This research aims to investigate the compressive properties of 3D-printed samples using the fused deposition modeling method. In this regard, the compressive strength of polymer samples made of neat polylactic acid and composite samples of polylactic acid/continuous glass fiber is investigated. It is clear that if the continuous fibers are placed in the direction of applying the compressive load, they are not able to withstand the compressive load. Therefore, in this research, by placing the fibers in the direction perpendicular to the direction of the load and considering the phenomenon of transverse strain, the fibers are subjected to tension, and the compressive strength of the composite sample increases by 10% compared to the pure polymer sample.

In this paper, nonlinear vibration analysis of a composite cylindrical shell with internal pressure, subjected to a low velocity impact is investigated using analytical and FE methods. The governing coupled partial differential equations of motion are derived using Donnel’s nonlinear shell theory. The impact force is modeled by employing the modified Hertzian contact theory. To model the low velocity impact, the model proposed by Shivakumar is exploited. The governing nonlinear coupled partial differential equations of motion for the shell are solved using the Galerkin method. Then, the dynamic response and generated stresses of the cylindrical shell subjected to a low velocity impact are analyzed using the ABAQUS FE software and a mathematical code developed in the environment of Mathematica software. Finally, the effect of some parameters on the impact response is studied. These parameters include the number of layers, ply orientation, shell thickness and shell radius and characteristics of the striker. It is seen that ply orientation of the composite layer has a significant effect on the dynamic response of the shell under impact and when the ply angle increases the amplitude of dynamic response of the shell decreases. Moreover, for a shell with smaller radius the response frequency is higher and when the radius of the shell increases, its effect on the frequency variation, decreases.

In this paper, the nonlinear vibration analysis of a symmetric laminated composite cylindrical shell on a viscoelastic foundation under a subsonic external air flow has been investigated. The boundary conditions for both ends of the cylindrical shell are clamped conditions. The governing equations of motion in the longitudinal, circumferential and radial directions are derived in conducture with the Donnel’s nonlinear shell theory. Using Galerkin method, three nonlinear partial differential equations of motion are transformed to a nonlinear ordinary equation of motion governing lateral (radial) vibration of the shell. Then, the relations for linear and nonlinear natual frequencies and amplitude-dimensionless natural frequency of the shell are calculated. The effects of variations in different values of parameters including orientation angles of lamina in layerwise laminate, stiffness and damping of viscoelastic foundation and the external applied load on the free and forced vibration behavior of the shell are all studied in this paper analyses. Moreover, the time history of radial displacement of midpoint of the shell using linear and nonlinear analyses. Are also presented.

In this paper time-dependent creep evolution analysis of thick-walled rotating FGM cylinders made of Al-SiC composite has been carried out, using method of successive elastic solution. The material creep constitutive model has been described by Norton’s law, considering the experimental results of Pandey on Al-SiC composite. All mechanical and thermal properties except Poisson’s ratio are radial dependent, based on the volume content of SiC reinforcement. Loading is composed of an inertia body force due to rotation and a distributed temperature field because of steady state heat conduction from the inner to the outer surface of the cylinder. It has been found that the volume-content distribution of SiC reinforcement has a significant effect on initial elastic stress distribution. It has been concluded that radial stresses are increasing with time during creep evolution, while circumferential and effective stresses become more uniform, due to stress redistribution and finally the solution converges to stationary stresses, displacement and strains almost after fifty years.

Composite materials are used frequently in industrial structures such as airplane and space vehicles. Strength and probability of failure is an important challenge for designer engineers. In this paper a practical method to determine ultimate strength of a composite laminate is explained, this method based on reliability prediction. Strength of each layers and total strength is calculated using First Order Reliability Method and failures sequence is determined by Branch & bound method. In this study two modes for failure are assumed: fiber fracture and matrix fracture. At first step, stress distribution is calculated by FE software (ANSYS Package) then according to failure mode and first order reliability method, reliability index is determined. At the second step, probability of failures mode in all layers are determined. At the end, the important sequences for the failures are determined using branch and bound method. Comparison of this method result with Monte Carlo simulation shows accuracy of this method to predict failure mode and probability of composite laminate failure.