جستجوی مقالات مرتبط با کلیدواژه "laminated composite" در نشریات گروه "مکانیک"

Today, the use of composite materials has become widespread. Composite parts are subjected to different loading rates under mechanical loads and therefore must have sufficient strength against such various loads. In this paper, the behavior of hybrid composite with layers of glass and kenaf fibers under impact loading is investigated and analyzed. The effect of a number of layers on energy absorption, initial peak force as well as damage area was discussed. In the following, the results of experimental tests are compared with the numerical method by ABAQUS/EXPLCIT software, and the results show that the two methods are in good agreement and close to each other. The results showed that increasing the number of layers from 5 to 13 layers increases the initial strength and peak force by 85%. Also, by studying the specific energy absorption (SEA), it was found that increasing the number of layers at the optimal point increases the SEA so that increasing the number of layers from 5 to 9 layers causes a decrease of 3% and then increasing the number of layers up to 13 layers Increases SEA by 26%. It was observed that the energy absorption improved by 51% with the proper arrangement of layers of glass fibers and kenaf. At the end of the study, the failure mode of composites showed that the main mechanism of energy absorption in the back surface of composite plates is the debonding of layers with matrix fracture and fiber breakage.

Fiber Metal Laminates (FML’s) are being used in many applications ranging from aircraft, submarines and ships to pressure vessels and automotive parts. In this study, the theoretical and numerical analysis of fiber metal laminates (FML’s) subjected to time-dependent uniform pressure load have been investigated. For this purpose, the plate is modeled based on the Reddy’s higher order shear deformation plate theory and the effects of the von Kármán geometric nonlinearity are included in the derivation of the motion equations. The FML is assumed to rest on the Pasternak foundation and simply supported boundary conditions are considered for all edges of the plate. Then, Nonlinear Partial differential Equations (PDEs) of motion are separated by using of the Galerkin method and finally solved using the Runge Kutta method. The results of conducted theoretical analyses compared with the presented results in the literature and good agreement is found. Also, in order to investigate the effective parameters, the effect of aspect ratio, Pasternak foundation and type of pressure pulses on the dynamic response of the plate have been examined. According to the obtained results, by reducing the positive phase time of loading and increasing the waveform parameter, the effect of the negative phase of loading is amplified and leads to an increase in dimensionless displacement in the center of the plate. Also, it was realized that the linear stiffness parameter in comparison with the shear layer parameter has less effect on the dynamic response.

In the present study, the effect of natural microfibers (cork particles) on the mode I fracture toughness of plain-woven laminated composites has been investigated. For this purpose, double cantilever beam (DCB) specimens manufactured using hand lay-up method with stacking sequence of [0]28. To investigate the effect of cork particles on fracture toughness, samples with two different weight percentages (1% by weight and 3% by weight) were manufactured and the experimental results were compared with one obtained from sample with pure epoxy resin. Experimental results show that as the amount of cork particles increases, the onset of crack growth requires more energy. The amount of improvement in initiation fracture toughness for the DCB sample with 1% and 3% cork weigh has been increased by 67.15% and 71.96%, respectively which is due to the role of the cork in the resin rich area near the crack tip that arrested the delamination growth. Unlike the initiation fracture toughness, the propagation value is reduced by adding cork particles to the resin.   During delamination growth, due to the agglomeration of micro fiber at delamination interface and role of stress concentration of these particles, hence, micro-cork fibers have not been able to increase the propagation fracture toughness and in some cases have slightly reduced the propagation fracture toughness of the delamination. Also, in order to investigate the mechanisms of damage, the fracture surfaces of the samples were scanned using scanning electron microscopy.

Plates made of laminated composite materials with variable stiffness can have wide applications in various branches of engineering due to such advantages as high strength /stiffness to weight ratio. In these composites, curved fibers are used to reinforce each lamina instead of the straight fibers. In this paper, the application of finite strip method for the buckling analysis of moderately thick composite plates with variable stiffness is investigated. For buckling analysis, a semi-analytical finite strip method based on the first-order shear deformation theory is employed. In this method, all displacements are presumed by the appropriate harmonic shape functions in the longitudinal direction and polynomial interpolation functions in the transverse direction. The minimum potential energy method has been used to develop the stability formulations. This analysis examines the effect of using curved fibers instead of straight fibers on the laminate composites. The critical loads obtained from this analysis are compared with those of other researchers and the efficiency and accuracy of the developed finite strip method are confirmed. Comparison of the analysis results of these plates shows that changing the slope of the fibers can lead to a significant change in the buckling response. Also, increasing the number of the terms of shape functions in the longitudinal direction has a significant effect on the convergence to the desired results.

In this paper, a new inverse hyperbolic shear deformation theory is proposed, formulated and validated for a variety of numerical examples of laminated composite beam for the static responses. The proposed theory based upon shear strain shape function yields nonlinear distribution of transverse shear stresses and also satisfies traction free boundary conditions. Principle of virtual work is employed to develop the governing differential equations. A Levy type closed form solution methodology is also proposed for crossply simply supported beams which limits applicability. However, it provides accurate solution which is free from any numerical /computational error. It is observed that the present theory can be more accurately applied for the modeling of laminated composite beams at the same computational cost as that of other shear deformation theories.

In this paper, transient impact on a composite plate is studied using the spherical nose . The governing equations of the plate based on the first shear deformation, are discretized using the Galerkin finite element method. The mass, stiffness and force matrices are obtained such that the terms of bending and shear in the matrices are considered separately, and the Gaussian integration method is used to overcome the shear locking phenomena. The model is developed so that it is capable to taking frequent loading and unloading during the impact. The governing equations of the plate and the projectile are solved in the time domain using the Nikolson and Newmark integration methods. The results are compared with the results of other researchers and the accuracy of the model is verified. According to the numerical analysis, it is observed that the present model has accurate results for thick and thin plates. The low velocity impact on a composite plate with clamped and mixed boundary conditions is studied and the time history of response of the plate such as deflection, penetration, contact force and kinetic energy are presented.

The vibration analysis of curved composite structures under the moving vehicles, is rarely investigated in litreture. Therefore, this paper is studied the dynamic response of a simply supported laminated deep curved beam under a moving load based on Timoshenko beam theory.It is assumed that the curvature of the beam and the amplitude and the speed of the moving load areconstant.The governing equations of motion for the system is extracted by Hamilton principles. A numerical and analytical methods are applied to obtain the dynamic response of the system.Also, the critical speed of the moving load and the fundamental frequency of the beam are obtained. The effects of the moving load characteristics, geometrical and material parameters such as the moving load speed, the radius of curvature and the modulus of elasticity in principal direction on the dynamic responses, fundamental frequency and critical speed of the system are investigated. The results show that the minimum and maximum deflection of the beam are occurred for lay-up [90/0/90/0] and [45/-45/-45/45]respectively. Furethermore, the increasing of the speed movingload leads to the decreasing thedynamic deflection. It is also shown that the increasing of the radius of the curved beams leads to the decreasingof the frequency and critical speed moving load.

In this paper¡ the propagation of the waves in the laminated composite plates which is subjected to low velocity impact is investigated using the finite element method. Considering a finite element model the governing equations of the problem are discretized and the mass¡ stiffness and force matrix are obtained. The governing equations of the plate and the projectile are solved in the time domain using the Newmark and Nicolson numerical integration method. The contact force is modeled using the modified Hertz contact law. The propagation of the waves in the plate with different sets of edge boundary conditions are studied in the numerical results. The node dependency of the results is investigated and the effects of boundary conditions of the plate on the maximum impact load are studied. Various results for the propagation of the wave in the time domain are presented and the time history of the contact force¡ impact time duration and second impacts are studies in the numerical results. The analysis of results indicates that the wave propagation depends on the boundary conditions of the plate and the layer stacking of the composite plate.

The purpose of this study is to estimate the fatigue life of laminated composites using a novel model based on continuum damage mechanics. For this purpose, a closed form criterion based on the energy method has been presented in the context of damage mechanics such that considers the difference of damage in three directions and moreover is not limited to a special layup. The proposed model has been implemented in the ANSYS finite element software using the material coded by the user (Usermat). The method of characterization of the model constants has been presented in this paper and the constants have been determined for AS4/3501-6 Carbon-Epoxy composite and finally, validation of the model for unidirectional and multidirectional layered composites has been evaluated. For multidirectional laminates, results of fatigue life for cross-ply laminates with hole with the layups [04/904]s and [904/04]s compared with experimental results. The results show that the developed model can predict the fatigue life of laminated composites only by using the material constants which is obtained from experiments of unidirectional laminates in two stress levels.

Polymeric Due to high strength to weight ratio of polymeric composites and their directional properties, they are extensively used in engineering, particularly in aerospace industry. However, the difference in material properties of composites makes their failure prediction complicated especially under cyclic loading. Present study is carried out to develop a new method for estimation of the intralaminar fatigue damage of fibrous composites based on continuum damage mechanics. In order to include the influence of microscopic defects in three material orientations, three internal material state variables namely damage variables are defined in thermodynamics framework. By considering a 3-directional damage propagation, suggested model is able to make a good prediction of laminated composites fatigue life. To achieve this, a closed form solution by energy method in framework of thermodynamics is presented. The solution is in a way to include the differences in damages of various directions yet maintaining the independency on the layup. The model is implemented in ANSYS software by using a user material code (Usermat). This method gives us an advantage to estimate the fatigue life of any laminate with arbitrary layup under different loading conditions only by having static and fatigue properties of a unidirectional ply. Characterization of constants of model is presented and they are also determined for a certain composite material. Comparison between the predicted results of proposed model and the available experimental data verifies the great precision of the model.

In this thesis for improving in samand behavior in besides collision، internal part of B-pillar of SAMAND modeling by use of laminated composite made up of carbon – epoxy and simulation beside collision test based on FMVSS-214 standard. This survey is performance on finite element analys and show the condition and quality of stacking sequence of difrent layers. Since change in orientation layers cause of change in structure resistance affected by collision، using of Genetic Algurithm and neural lattice get better result for minimum transfiguration of B-pillar. Also to achive the steady stacking sequence use the result of 49 Taguchi’s studys and simulation for 8 layers in -90 to 90 degree and 120 Hamersly’s tests for 8 layers in 0 to 90 degree، and 120 Hamersly test for 4 layers in 0 ti 90 degree. Based on this result and gained data from optimization algoritm and complet survey of test result، the best collision behavior of structure occure in 40 to 50 degree stacking sequence. Stracture we offer in this study own minimum transfiguration and displacement. And System in this manner، exist maximum safty and security for passengers that is the most important chalengein besides couission.