This study collected data about the effect of patient characteristics (life expectancy, frailty a... more This study collected data about the effect of patient characteristics (life expectancy, frailty and comorbidity) on treat ment decisions in elderly people with keratinocyte carcinoma, by searching PubMed database. Literature about how patient characteristics affect treatment decision is sparse and is mostly based on small retrospective studies. Therefore, it is difficult to give firm recommendations. A "one-size-fits-all" approach to this population is not sufficient: life expectancy, frailty and comorbidities must be taken into account in the decision-making about treatment, and registered using a validated scoring system, especially before major treatment modalities. There are straightforward guidelines for treatment of keratinocyte carcinoma (formerly known as non-melanoma skin cancer); however, there are no clear recommendations specifically for elderly patients. The aim of this review was to provide an overview of the current literature about the effect of patient characteristics, specifically life expectancy, frailty and comorbidity, on treatment decisions in elderly patients with keratinocyte carcinoma, by searching PubMed database. It was found that the literature is limited and based mostly on small retrospective studies. Therefore, it is difficult to give firm recommendations about how to treat elderly people who have keratinocyte carcinoma. A "one-sizefits-all" approach to this population is not sufficient: life expectancy and frailty need to be considered in the decision-making process regarding treatment for elderly people with keratinocyte carcinoma. Among the comorbidity scores, Adult-Comorbidity-Evaluation-27-index seems to have the best prognostic value. Prospective studies are needed to generate more individualized recommendations for this increasing and often vulnerable group.
در سالهای اخیر، پژوهش‌های متعددی در زمینه خودترمیمی با استفاده از شبکه آوندی در کامپوزیت‌ها انجا... more در سالهای اخیر، پژوهش‌های متعددی در زمینه خودترمیمی با استفاده از شبکه آوندی در کامپوزیت‌ها انجام شده است. با توجه به اینکه وجود شبکه آوندی در کامپوزیت‌ها منجر به افت خواص مکانیکی اولیه می‌شود، تعیین طرح بهینه شبکه آوندی برای دستیابی به حداقل افت خواص، اهمیت بسزایی دارد. در این پژوهش، به مطالعه تجربی و عددی اثر وجود و جهتگیری آوندهای شیشهای توخالی بر رفتار کششی در کامپوزیت اپوکسی- الیاف شیشه پرداخته شده است. جهتگیری آوندهای شیشه در سه سطح 0، 45 و 90 درجه نسبت به راستای الیاف شیشه تقویت‌کننده، و فاصله آوندها از یکدیگر 200 میکرومتر در نظر گرفته شد. نتایج آزمون‌های تجربی نشان داد که وجود آوندهای شیشهای در کامپوزیت باعث افت خواص کششی می‌شود و کمترین کاهش خواص کششی در نمونه کامپوزیتی حاوی آوندهای شیشهای در راستای 45 درجه است. وجود و شکست آوندهای شیشهای در نمونه‌های کامپوزیتی با استفاده از میکروسکوپ الکترونی روبشی مطالعه شد. در مرحله بعد، شبیه‌سازی المان محدود سه‌بعدی با استفاده از المان حجمی نماینده، برای نمونه‌های حاوی سیستم آوندی توخالی با جهت‌گیری‌های مختلف با استفاده از نرم...
در این پژوهش به مطالعه تجربی اثر جهتگیری عامل خودترمیم آوندی بر استحکام کششی و بازدهی ترمیم در ک... more در این پژوهش به مطالعه تجربی اثر جهتگیری عامل خودترمیم آوندی بر استحکام کششی و بازدهی ترمیم در کامپوزیت اپوکسی-الیاف شیشه پرداخته شده است. ابتدا الیاف شیشه توخالی (با قطر خارجی 450±10 میکرومتر و کسر تهینگی 50%-55%) با استفاده از یک دستگاه اکسترودر تولید شد. سپس، الیاف شیشه توخالی با اجزای خود ترمیم پر شد و به عنوان خودترمیم آوندی در چند لایه کامپوزیتی استفاده شد. جهتگیری آوندهای خودترمیم در سه سطح 0، 45 و 90 درجه نسبت به راستای الیاف شیشه تقویت‌کننده، و فاصله آوندها از یکدیگر 200 میکرومتر در نظر گرفته شد. نمونه‌های شاهد، آسیب دیده و ترمیم شده تحت آزمون کشش قرار گرفتند و بازدهی ترمیم مطالعه شد. نتایج آزمون کشش نشان داد که وجود آوندهای خالی در زوایای 0، 45 و 90 درجه در ساختار کامپوزیت سبب به ترتیب 17%، 14% و 21% کاهش در استحکام کششی می شود. آسیب در نمونه‌های کشش با کرنش 1.2% ایجاد شد و سپس فرایند خودترمیم در دمای ℃ 70 و مدت زمان 48 ساعت انجام شد. در مرحله بعد، بازدهی ترمیم با استفاده از آزمون کشش اندازه‌گیری شد. نتایج آزمون های کشش و بازدهی ترمیم نشان داد که بهترین جهتگیری برای چ...
The present work deals with the micro-macro analysis of shape memory alloy (SMA) fiberreinforced ... more The present work deals with the micro-macro analysis of shape memory alloy (SMA) fiberreinforced Epoxy/Aluminum matrix composite cylinders under combined thermo-mechanical loadings. A robust phenomenological constitutive model is implemented to simulate martensite transformation, reorientation of martensite variants, pseudo-elasticity and shape memory effects of SMAs. Epoxy is assumed to behave as a linearly elastic material while Aluminum is considered to behave as an elasticplastic material with linear kinematic hardening. A representative volume element (RVE) consisting of SMA fibers surrounded with Epoxy/Aluminum matrix is simulated to determine the overall constitutive response of the composite in the generalized plane-strain state. Deformations of the RVE and macro composite cylinder are described based on the small strain and large displacement regimes. Finite element solutions coupled with an iterative elastic-predictor inelastic-corrector procedure are developed to analyze the RVE and macro composite cylinder. In particular, the micro-mechanical solution is implemented to evaluate the constitutive behavior of structural elements made of SMA composite at each iteration of each load step. Parametric studies are performed to examine the effects of pre-strain, SMA fiber volume fraction, fiber orientation, stacking sequence and loading order on the macro-thermo-mechanical responses of long composite cylinders subjected to internal pressure, axial, torsional and thermal loadings.
In this paper, an attempt is made to obtain a closed form solution for both natural frequency and... more In this paper, an attempt is made to obtain a closed form solution for both natural frequency and buckling load of nonlocal FG beams resting on nonlinear elastic foundation. Implementing Eringen's nonlocal elasticity theory, the effect of nonlocality is introduced into the Euler-Bernoulli beam theory to obtain the nonlinear governing partial differential equation. Application of the Galerkin technique to the governing equation leads to a nonlinear ODE in the time-domain. Finally, natural frequency of the FG nano beam is obtained using He's variational method. It is shown that considering the nonlocal effects decreases the buckling load as well as natural frequency. Results also reveal that effects of nonlocal parameters on fully clamped beams are more than other types of boundary conditions. Moreover, it is shown that the effect of nonlocality decreases by increasing length of the beam.
On the basis of an efficient numerical solution methodology, the free vibration response of third... more On the basis of an efficient numerical solution methodology, the free vibration response of third-order shear deformable nanobeams made of functionally graded materials (FGMs) around the postbuckling domain is investigated incorporating the effects of surface free energy. Gurtin-Murdoch elasticity theory in conjunction with von Karman geometric nonlinearity is implemented into the classical third-order shear deformation beam theory. In order to consider balance conditions on the surfaces of nanobeam, it is assumed that the bulk normal stress is distributed cubically through the thickness. The material properties are assumed to be graded in the thickness direction based on power-law distribution. Using Hamilton's principle, the non-classical nonlinear governing differential equations of motion and associated boundary conditions are derived. Then generalized differential quadrature method is employed to dictretize the governing equations and solution domain according to the Chebyshev-Gauss-Lobatto grid points. Subsequently, the pseudo-arc length continuation technique is utilized to solve the nonlinear problem. It is demonstrated that in contrast to the prebuckling domain, in the postbuckling domain, the natural frequency of FGM nanobeam decreases by increasing the value of material property gradient index. Also, it is revealed that the surface effect plays more important role on the vibration characteristics of the buckled FGM nanobeams with lower thicknesses.
The effects of surface energy are generally ignored in traditional continuum elasticity. However,... more The effects of surface energy are generally ignored in traditional continuum elasticity. However, due to the high surface to volume ratio in nanostructures, this is not the case for them. In this work, the nonlinear postbuckling characteristics of circular nanoplates are predicted in the presence of surface energy effects including surface elasticity and residual surface tension. For this objective, Gurtin-Murdoch elasticity theory is implemented into the classical higher-order shear deformation plate theory. In order to satisfy the balance conditions on the surfaces of nanoplate, it is assumed the normal stress of the bulk is distributed cubically through the thickness of nanoplate. Hamilton's principle in conjunction with von Karman geometric nonlinearity is utilized to derive non-classical nonlinear governing differential equations of motion and related boundary conditions. Afterwards, an efficient numerical methodology based generalized differential quadrature (GDQ) method is carried out using the shifted Chebyshev-Gauss-Lobatto grid points to discretize the governing partial differential equations. Then, the Galerkin's method is employed to reduce the set of nonlinear equations into a time-varying set of ordinary differential equations of Duffing type. At the end, the pseudo arc-length continuation technique is utilized in order to obtain the solution of the parameterized equation.
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2012
Free transverse vibration of thin rectangular plates locally suspended on deformable beam is pres... more Free transverse vibration of thin rectangular plates locally suspended on deformable beam is presented using generalized differential quadrature method. The plate is completely free at all edges except a local region which is attached to a thin beam with rectangular cross section. The other side of the beam is fixed and the whole system is subjected to free transverse vibrations. According to classical plate theory and Euler–Bernoulli beam assumption, two coupled partial differential equations of the system are obtained. The governing equations and solution domain are discretized based on the generalized differential quadrature method and natural frequencies of the plate attached to the beam are obtained. Accuracy of the predictions is investigated using four simplified cases which show reasonably good agreement. For the general case, however, due to lack of data in the literature, predictions are compared with finite element results, which also demonstrate close agreement.
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2010
This study aims to investigate the effects of spinning parameters on the balloon tension and conf... more This study aims to investigate the effects of spinning parameters on the balloon tension and configuration. A novel experimental set-up was designed to measure the yarn tension at the pigtail. Experimental results were then used to implement boundary conditions in a multivariate analysis. Also, a finite-element (FE) code was used to predict the yarn balloon profile and stresses induced in the yarn. In particular, Coriolis acceleration and twist effects are considered on the model. It was observed that the equations governing the yarn path and the movement equation of twist in the yarn were completely dependent on each other. FE analysis revealed that while the Coriolis acceleration increases the tension in the yarn, it has little influence on the balloon configuration. Results of this study can be used to obtain optimized production parameters to increase the yarn quality and productivity.
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2013
Vibration analysis of axially moving functionally graded plates with internal line supports and t... more Vibration analysis of axially moving functionally graded plates with internal line supports and temperature-dependent properties is investigated using harmonic differential quadrature method. The plate is subjected to static in-plane forces while out-of-plane loading is dynamic. Stability of an axially moving plate, traveling at a constant velocity between different supports and experiencing small transverse vibrations are considered. The series of internal rigid line supports parallel to the plate edges are considered together with various arbitrary combinations of boundary conditions. Material properties of the plate are assumed temperature-dependent which is a non-linear function of temperature and differ continuously through thickness according to a power-law distribution of the volume fractions of the plate constituents. Two types of micromechanical models, namely, the Voigt and Mori–Tanaka models are considered. Based on the classical plate theory, the governing equations are ...
Journal of the Mechanics and Physics of Solids, 2000
The initial yield and collapse behaviour of ®bre reinforced metal matrix composites (MMCs) have b... more The initial yield and collapse behaviour of ®bre reinforced metal matrix composites (MMCs) have been investigated using ®nite element micro-mechanical models. Initial yield occurs as the loading on the MMC is increased until the most heavily loaded point within the matrix reaches the yield stress. Collapse occurs when the MMC is unable to support a higher load. The results of this work show that loads to cause collapse of MMCs are higher than those to cause ®rst yield, particularly when the eect of residual stress arising from manufacture is included in the analysis. Initial yield and collapse envelopes have been generated for a Silicon Carbide-Titanium MMC for biaxial and shear loading. These envelopes include the eect of residual stress and also various interface conditions between the ®bre and matrix: either perfectly bonded or de-bonded, with and without friction. An analytical micro-mechanical model has been developed using the method of cells to predict the collapse behaviour. The results of the analytical model compare reasonably well with those of the ®nite element method. Using the analytical model the eect of varying the ®bre volume fraction on the collapse behaviour has been studied.
Journal of Mechanics of Materials and Structures, 2010
A generalized plane strain micromechanical model is developed to predict the behavior of a unidir... more A generalized plane strain micromechanical model is developed to predict the behavior of a unidirectional fiber-reinforced composite subjected to combined thermal and mechanical loads. An appropriate meshless local Petrov-Galerkin formulation is presented for the solution of the governing partial differential equations of the problem. To reduce computation time, a unit step function is employed as test function. A direct method is presented for enforcement of the continuity of displacement and traction at the fiber-matrix interface to model the fully bonded interface. Results of this study revealed that the model provides highly accurate predictions with relatively small number of nodes. Numerical results for glass/epoxy and SiC/Ti composites subjected to thermomechanical loading show that predictions for both local and global responses of the composites are in good agreement with results of theoretical, experimental and finite element methods.
Journal of Mechanics of Materials and Structures, 2009
This paper deals with the application of the differential cubature method (DCM) to the bending an... more This paper deals with the application of the differential cubature method (DCM) to the bending analysis of laminated cylindrical panels. Symmetric and unsymmetric laminate, with various combinations of clamped, simply supported and free boundary conditions, are considered, with either uniform or sinusoidal transversely distributed loads. Using first-order shear deformation theory, fifteen first-order partial differential equations are obtained, containing as many unknowns in terms of displacements, rotations, moments, and forces. Comparison of the results obtained by DCM shows very good agreement with those of other numerical and analytical methods, with decreased computational effort. Further, in this method, a free boundary condition and unsymmetric laminates do not violate the accuracy of the results.
A truly meshless method based on the integral form of equilibrium equations is developed and form... more A truly meshless method based on the integral form of equilibrium equations is developed and formulated to study the micro-stresses in the unidirectional fiber reinforced composite material which is subjected to the normal and shear load. The presented meshless method is ...
In this study, a micromechanical model is presented to study the combined normal, shear and therm... more In this study, a micromechanical model is presented to study the combined normal, shear and thermal loading of unidirectional (UD) fiber reinforced composites. An appropriate truly meshless method based on the integral form of equilibrium equations is also developed. This meshless method formulated for the generalized plane strain assumption and employed for solution of the governing partial differential equations of the problem. The solution domain includes a representative volume element (RVE) consists of a fiber surrounded by corresponding matrix in a square array arrangement. A direct interpolation method is employed to enforce the appropriate periodic boundary conditions for the combined thermal, transverse shear and normal loading. The fully bonded fiber-matrix interface condition is considered and the displacement continuity and traction reciprocity are imposed to the fiber-matrix interface. Predictions show excellent agreement with the available experimental, analytical and finite element studies. Comparison of the CPU time between presented method and the conventional meshless local Petrov-Galerkin (MLPG) shows significant reduction of the computational time. The results of this study also revealed that the presented model could provide highly accurate predictions with relatively small number of nodes and less computational time without the complexity of mesh generation.
A three-dimensional finite element micromechanical model was developed to study effects of therma... more A three-dimensional finite element micromechanical model was developed to study effects of thermal residual stress, fiber coating and interface bonding on the transverse behavior of a unidirectional SiC/Ti–6Al–4V metal matrix composite (MMC). The presented model includes three phases, i.e. the fiber, coating and matrix, and two distinct interfaces, one between the fiber and coating and the other between coating and
This study collected data about the effect of patient characteristics (life expectancy, frailty a... more This study collected data about the effect of patient characteristics (life expectancy, frailty and comorbidity) on treat ment decisions in elderly people with keratinocyte carcinoma, by searching PubMed database. Literature about how patient characteristics affect treatment decision is sparse and is mostly based on small retrospective studies. Therefore, it is difficult to give firm recommendations. A "one-size-fits-all" approach to this population is not sufficient: life expectancy, frailty and comorbidities must be taken into account in the decision-making about treatment, and registered using a validated scoring system, especially before major treatment modalities. There are straightforward guidelines for treatment of keratinocyte carcinoma (formerly known as non-melanoma skin cancer); however, there are no clear recommendations specifically for elderly patients. The aim of this review was to provide an overview of the current literature about the effect of patient characteristics, specifically life expectancy, frailty and comorbidity, on treatment decisions in elderly patients with keratinocyte carcinoma, by searching PubMed database. It was found that the literature is limited and based mostly on small retrospective studies. Therefore, it is difficult to give firm recommendations about how to treat elderly people who have keratinocyte carcinoma. A "one-sizefits-all" approach to this population is not sufficient: life expectancy and frailty need to be considered in the decision-making process regarding treatment for elderly people with keratinocyte carcinoma. Among the comorbidity scores, Adult-Comorbidity-Evaluation-27-index seems to have the best prognostic value. Prospective studies are needed to generate more individualized recommendations for this increasing and often vulnerable group.
در سالهای اخیر، پژوهش‌های متعددی در زمینه خودترمیمی با استفاده از شبکه آوندی در کامپوزیت‌ها انجا... more در سالهای اخیر، پژوهش‌های متعددی در زمینه خودترمیمی با استفاده از شبکه آوندی در کامپوزیت‌ها انجام شده است. با توجه به اینکه وجود شبکه آوندی در کامپوزیت‌ها منجر به افت خواص مکانیکی اولیه می‌شود، تعیین طرح بهینه شبکه آوندی برای دستیابی به حداقل افت خواص، اهمیت بسزایی دارد. در این پژوهش، به مطالعه تجربی و عددی اثر وجود و جهتگیری آوندهای شیشهای توخالی بر رفتار کششی در کامپوزیت اپوکسی- الیاف شیشه پرداخته شده است. جهتگیری آوندهای شیشه در سه سطح 0، 45 و 90 درجه نسبت به راستای الیاف شیشه تقویت‌کننده، و فاصله آوندها از یکدیگر 200 میکرومتر در نظر گرفته شد. نتایج آزمون‌های تجربی نشان داد که وجود آوندهای شیشهای در کامپوزیت باعث افت خواص کششی می‌شود و کمترین کاهش خواص کششی در نمونه کامپوزیتی حاوی آوندهای شیشهای در راستای 45 درجه است. وجود و شکست آوندهای شیشهای در نمونه‌های کامپوزیتی با استفاده از میکروسکوپ الکترونی روبشی مطالعه شد. در مرحله بعد، شبیه‌سازی المان محدود سه‌بعدی با استفاده از المان حجمی نماینده، برای نمونه‌های حاوی سیستم آوندی توخالی با جهت‌گیری‌های مختلف با استفاده از نرم...
در این پژوهش به مطالعه تجربی اثر جهتگیری عامل خودترمیم آوندی بر استحکام کششی و بازدهی ترمیم در ک... more در این پژوهش به مطالعه تجربی اثر جهتگیری عامل خودترمیم آوندی بر استحکام کششی و بازدهی ترمیم در کامپوزیت اپوکسی-الیاف شیشه پرداخته شده است. ابتدا الیاف شیشه توخالی (با قطر خارجی 450±10 میکرومتر و کسر تهینگی 50%-55%) با استفاده از یک دستگاه اکسترودر تولید شد. سپس، الیاف شیشه توخالی با اجزای خود ترمیم پر شد و به عنوان خودترمیم آوندی در چند لایه کامپوزیتی استفاده شد. جهتگیری آوندهای خودترمیم در سه سطح 0، 45 و 90 درجه نسبت به راستای الیاف شیشه تقویت‌کننده، و فاصله آوندها از یکدیگر 200 میکرومتر در نظر گرفته شد. نمونه‌های شاهد، آسیب دیده و ترمیم شده تحت آزمون کشش قرار گرفتند و بازدهی ترمیم مطالعه شد. نتایج آزمون کشش نشان داد که وجود آوندهای خالی در زوایای 0، 45 و 90 درجه در ساختار کامپوزیت سبب به ترتیب 17%، 14% و 21% کاهش در استحکام کششی می شود. آسیب در نمونه‌های کشش با کرنش 1.2% ایجاد شد و سپس فرایند خودترمیم در دمای ℃ 70 و مدت زمان 48 ساعت انجام شد. در مرحله بعد، بازدهی ترمیم با استفاده از آزمون کشش اندازه‌گیری شد. نتایج آزمون های کشش و بازدهی ترمیم نشان داد که بهترین جهتگیری برای چ...
The present work deals with the micro-macro analysis of shape memory alloy (SMA) fiberreinforced ... more The present work deals with the micro-macro analysis of shape memory alloy (SMA) fiberreinforced Epoxy/Aluminum matrix composite cylinders under combined thermo-mechanical loadings. A robust phenomenological constitutive model is implemented to simulate martensite transformation, reorientation of martensite variants, pseudo-elasticity and shape memory effects of SMAs. Epoxy is assumed to behave as a linearly elastic material while Aluminum is considered to behave as an elasticplastic material with linear kinematic hardening. A representative volume element (RVE) consisting of SMA fibers surrounded with Epoxy/Aluminum matrix is simulated to determine the overall constitutive response of the composite in the generalized plane-strain state. Deformations of the RVE and macro composite cylinder are described based on the small strain and large displacement regimes. Finite element solutions coupled with an iterative elastic-predictor inelastic-corrector procedure are developed to analyze the RVE and macro composite cylinder. In particular, the micro-mechanical solution is implemented to evaluate the constitutive behavior of structural elements made of SMA composite at each iteration of each load step. Parametric studies are performed to examine the effects of pre-strain, SMA fiber volume fraction, fiber orientation, stacking sequence and loading order on the macro-thermo-mechanical responses of long composite cylinders subjected to internal pressure, axial, torsional and thermal loadings.
In this paper, an attempt is made to obtain a closed form solution for both natural frequency and... more In this paper, an attempt is made to obtain a closed form solution for both natural frequency and buckling load of nonlocal FG beams resting on nonlinear elastic foundation. Implementing Eringen's nonlocal elasticity theory, the effect of nonlocality is introduced into the Euler-Bernoulli beam theory to obtain the nonlinear governing partial differential equation. Application of the Galerkin technique to the governing equation leads to a nonlinear ODE in the time-domain. Finally, natural frequency of the FG nano beam is obtained using He's variational method. It is shown that considering the nonlocal effects decreases the buckling load as well as natural frequency. Results also reveal that effects of nonlocal parameters on fully clamped beams are more than other types of boundary conditions. Moreover, it is shown that the effect of nonlocality decreases by increasing length of the beam.
On the basis of an efficient numerical solution methodology, the free vibration response of third... more On the basis of an efficient numerical solution methodology, the free vibration response of third-order shear deformable nanobeams made of functionally graded materials (FGMs) around the postbuckling domain is investigated incorporating the effects of surface free energy. Gurtin-Murdoch elasticity theory in conjunction with von Karman geometric nonlinearity is implemented into the classical third-order shear deformation beam theory. In order to consider balance conditions on the surfaces of nanobeam, it is assumed that the bulk normal stress is distributed cubically through the thickness. The material properties are assumed to be graded in the thickness direction based on power-law distribution. Using Hamilton's principle, the non-classical nonlinear governing differential equations of motion and associated boundary conditions are derived. Then generalized differential quadrature method is employed to dictretize the governing equations and solution domain according to the Chebyshev-Gauss-Lobatto grid points. Subsequently, the pseudo-arc length continuation technique is utilized to solve the nonlinear problem. It is demonstrated that in contrast to the prebuckling domain, in the postbuckling domain, the natural frequency of FGM nanobeam decreases by increasing the value of material property gradient index. Also, it is revealed that the surface effect plays more important role on the vibration characteristics of the buckled FGM nanobeams with lower thicknesses.
The effects of surface energy are generally ignored in traditional continuum elasticity. However,... more The effects of surface energy are generally ignored in traditional continuum elasticity. However, due to the high surface to volume ratio in nanostructures, this is not the case for them. In this work, the nonlinear postbuckling characteristics of circular nanoplates are predicted in the presence of surface energy effects including surface elasticity and residual surface tension. For this objective, Gurtin-Murdoch elasticity theory is implemented into the classical higher-order shear deformation plate theory. In order to satisfy the balance conditions on the surfaces of nanoplate, it is assumed the normal stress of the bulk is distributed cubically through the thickness of nanoplate. Hamilton's principle in conjunction with von Karman geometric nonlinearity is utilized to derive non-classical nonlinear governing differential equations of motion and related boundary conditions. Afterwards, an efficient numerical methodology based generalized differential quadrature (GDQ) method is carried out using the shifted Chebyshev-Gauss-Lobatto grid points to discretize the governing partial differential equations. Then, the Galerkin's method is employed to reduce the set of nonlinear equations into a time-varying set of ordinary differential equations of Duffing type. At the end, the pseudo arc-length continuation technique is utilized in order to obtain the solution of the parameterized equation.
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2012
Free transverse vibration of thin rectangular plates locally suspended on deformable beam is pres... more Free transverse vibration of thin rectangular plates locally suspended on deformable beam is presented using generalized differential quadrature method. The plate is completely free at all edges except a local region which is attached to a thin beam with rectangular cross section. The other side of the beam is fixed and the whole system is subjected to free transverse vibrations. According to classical plate theory and Euler–Bernoulli beam assumption, two coupled partial differential equations of the system are obtained. The governing equations and solution domain are discretized based on the generalized differential quadrature method and natural frequencies of the plate attached to the beam are obtained. Accuracy of the predictions is investigated using four simplified cases which show reasonably good agreement. For the general case, however, due to lack of data in the literature, predictions are compared with finite element results, which also demonstrate close agreement.
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2010
This study aims to investigate the effects of spinning parameters on the balloon tension and conf... more This study aims to investigate the effects of spinning parameters on the balloon tension and configuration. A novel experimental set-up was designed to measure the yarn tension at the pigtail. Experimental results were then used to implement boundary conditions in a multivariate analysis. Also, a finite-element (FE) code was used to predict the yarn balloon profile and stresses induced in the yarn. In particular, Coriolis acceleration and twist effects are considered on the model. It was observed that the equations governing the yarn path and the movement equation of twist in the yarn were completely dependent on each other. FE analysis revealed that while the Coriolis acceleration increases the tension in the yarn, it has little influence on the balloon configuration. Results of this study can be used to obtain optimized production parameters to increase the yarn quality and productivity.
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2013
Vibration analysis of axially moving functionally graded plates with internal line supports and t... more Vibration analysis of axially moving functionally graded plates with internal line supports and temperature-dependent properties is investigated using harmonic differential quadrature method. The plate is subjected to static in-plane forces while out-of-plane loading is dynamic. Stability of an axially moving plate, traveling at a constant velocity between different supports and experiencing small transverse vibrations are considered. The series of internal rigid line supports parallel to the plate edges are considered together with various arbitrary combinations of boundary conditions. Material properties of the plate are assumed temperature-dependent which is a non-linear function of temperature and differ continuously through thickness according to a power-law distribution of the volume fractions of the plate constituents. Two types of micromechanical models, namely, the Voigt and Mori–Tanaka models are considered. Based on the classical plate theory, the governing equations are ...
Journal of the Mechanics and Physics of Solids, 2000
The initial yield and collapse behaviour of ®bre reinforced metal matrix composites (MMCs) have b... more The initial yield and collapse behaviour of ®bre reinforced metal matrix composites (MMCs) have been investigated using ®nite element micro-mechanical models. Initial yield occurs as the loading on the MMC is increased until the most heavily loaded point within the matrix reaches the yield stress. Collapse occurs when the MMC is unable to support a higher load. The results of this work show that loads to cause collapse of MMCs are higher than those to cause ®rst yield, particularly when the eect of residual stress arising from manufacture is included in the analysis. Initial yield and collapse envelopes have been generated for a Silicon Carbide-Titanium MMC for biaxial and shear loading. These envelopes include the eect of residual stress and also various interface conditions between the ®bre and matrix: either perfectly bonded or de-bonded, with and without friction. An analytical micro-mechanical model has been developed using the method of cells to predict the collapse behaviour. The results of the analytical model compare reasonably well with those of the ®nite element method. Using the analytical model the eect of varying the ®bre volume fraction on the collapse behaviour has been studied.
Journal of Mechanics of Materials and Structures, 2010
A generalized plane strain micromechanical model is developed to predict the behavior of a unidir... more A generalized plane strain micromechanical model is developed to predict the behavior of a unidirectional fiber-reinforced composite subjected to combined thermal and mechanical loads. An appropriate meshless local Petrov-Galerkin formulation is presented for the solution of the governing partial differential equations of the problem. To reduce computation time, a unit step function is employed as test function. A direct method is presented for enforcement of the continuity of displacement and traction at the fiber-matrix interface to model the fully bonded interface. Results of this study revealed that the model provides highly accurate predictions with relatively small number of nodes. Numerical results for glass/epoxy and SiC/Ti composites subjected to thermomechanical loading show that predictions for both local and global responses of the composites are in good agreement with results of theoretical, experimental and finite element methods.
Journal of Mechanics of Materials and Structures, 2009
This paper deals with the application of the differential cubature method (DCM) to the bending an... more This paper deals with the application of the differential cubature method (DCM) to the bending analysis of laminated cylindrical panels. Symmetric and unsymmetric laminate, with various combinations of clamped, simply supported and free boundary conditions, are considered, with either uniform or sinusoidal transversely distributed loads. Using first-order shear deformation theory, fifteen first-order partial differential equations are obtained, containing as many unknowns in terms of displacements, rotations, moments, and forces. Comparison of the results obtained by DCM shows very good agreement with those of other numerical and analytical methods, with decreased computational effort. Further, in this method, a free boundary condition and unsymmetric laminates do not violate the accuracy of the results.
A truly meshless method based on the integral form of equilibrium equations is developed and form... more A truly meshless method based on the integral form of equilibrium equations is developed and formulated to study the micro-stresses in the unidirectional fiber reinforced composite material which is subjected to the normal and shear load. The presented meshless method is ...
In this study, a micromechanical model is presented to study the combined normal, shear and therm... more In this study, a micromechanical model is presented to study the combined normal, shear and thermal loading of unidirectional (UD) fiber reinforced composites. An appropriate truly meshless method based on the integral form of equilibrium equations is also developed. This meshless method formulated for the generalized plane strain assumption and employed for solution of the governing partial differential equations of the problem. The solution domain includes a representative volume element (RVE) consists of a fiber surrounded by corresponding matrix in a square array arrangement. A direct interpolation method is employed to enforce the appropriate periodic boundary conditions for the combined thermal, transverse shear and normal loading. The fully bonded fiber-matrix interface condition is considered and the displacement continuity and traction reciprocity are imposed to the fiber-matrix interface. Predictions show excellent agreement with the available experimental, analytical and finite element studies. Comparison of the CPU time between presented method and the conventional meshless local Petrov-Galerkin (MLPG) shows significant reduction of the computational time. The results of this study also revealed that the presented model could provide highly accurate predictions with relatively small number of nodes and less computational time without the complexity of mesh generation.
A three-dimensional finite element micromechanical model was developed to study effects of therma... more A three-dimensional finite element micromechanical model was developed to study effects of thermal residual stress, fiber coating and interface bonding on the transverse behavior of a unidirectional SiC/Ti–6Al–4V metal matrix composite (MMC). The presented model includes three phases, i.e. the fiber, coating and matrix, and two distinct interfaces, one between the fiber and coating and the other between coating and
Uploads
Papers by محمد اقدم