In this research, the flow stress of dual layer austenitic-martensitic functionally graded steels (FGSs) under hot deformation loading has been modelled considering the Zener-Hollomon constitutive equations as a function of temperature and strain rate. Functionally graded austenitic-martensitic steels consist of austenite (?) and martensite (M) phases placed on each other in different configurations and produced via Electro Slag Remelting (ESR). The boundary layers properties are obtained by experimental investigation on single phase materials. Finally, the theoretical model is compared with the experimental results measured in the temperature range 1000-1200 °C and strain rate 0.01-1 s-1 and a good agreement is found.

Development of knowledge of cardiovascular diseases and treatments strongly depends on understanding of hemodynamic measurements. Hemodynamic parameters, therefore, have been investigated using simulation-based methods. A two-dimensional model was applied for seven healthy subjects with echo-Doppler at rest. Echocardiography imaging was also utilized to gain the geometry of the aortic valve. Fluid-Structure Interaction (FSI) model was carried out, coupling an Arbitrary Lagrangian-Eulerian mesh. Pressure loads were used as boundary conditions on the valve’s ventricular and aortic sides. Pressure loads used were the calculated brachial pressures plus differences between brachial, central and left ventricular pressures. The FSI model predicted the velocity integration, stroke volume and cardiac output over a range of heart rates while rest. Numerical results generally had a difference of 5.4 to 15.87% with Doppler results. Linear correlations between numerical and clinical approaches have been applied. This makes possible predictions achieved from the FSI model to be gained which are highly accurate (e.g. correlation factor r = 0.995, 0.990 and 0.990 for velocity integration, stroke volume and cardiac output, respectively). The obtained numerical results showed that numerical methods can be combined with clinical measurements to provide good estimates of patient specific hemodynamics for different subjects.

Composite materials due to high strength and stiffness to their weight ratio are widely used in different structures. Hence, it is necessary to predict their failure behavior under loading. The delamination due to interlaminar stresses at free edges is one of the most important damage modes in laminated composites. In this study, this mode in cross-ply and angle-ply laminates has been investigated using a cohesive zone model. The advantage of this method is the possibility of modeling the delamination initiation and propagation without requirement to the presence of initial crack and remeshing. Hence, at first an interface element based on bilinear cohesive law was implemented in Ansys. Next, laminated plates with different lay-ups under uniaxial tension loading were modeled. Also Hashin’s failure criteria were used to predict ply damage initiation. Numerical results show that in angle-ply laminates with small fiber angle orientation, delamination in the shear mode is the dominant mode in the loss of structural strength. The numerical and experimental results for global load-displacement response show a good agreement. Also numerical results show that in cross-ply laminates even under in-plane loading, the damage behavior extremely depends on the stacking sequence. Studies show that in cross-ply laminates under uniaxial tension, if 90o plies are inserted in top and bottom surface of the laminate, the mode I delamination and matrix cracking will start later.

In this paper, harmonic forced vibration of circular functionally graded plate integrated with two uniformly distributed actuator faces made of piezoelectric material is studied. The material properties of the functionally graded substrate layers are assumed to be graded in the thickness direction according to the power-law distribution, also the distribution of electric potential field along the thickness direction of piezoelectric layers is modeled by a quadratic function. The governing equations are solved for simply supported boundary condition of the sandwich circular plate and the solutions are presented by elementary Bessel functions. The performance of the present model is compared with that of ?nite element analyses as well as other available literature by the presentation of comparative results obtained for several examples encompassing different power indexes and vibration modes. The results show that thickness of piezoelectric layer and changing the power index in FG material has a significant influence on the deflection and natural frequencies of system.

Cold working a hole decreases tendency of fatigue crack initiation and growth near the hole. It is due to creation of some compressive tangential residual stresses around the hole. But there are many uncertainties which affect the residual strain and residual stress field. In fact these uncertainties lead to have scatter in the test results and considering the residual strains and residual stresses as random variables. In this paper strains recorded by strain gages mounted around the hole during cold working process in seven pieces specimens, were analyzed by statistical tests and stochastic properties of mentioned random variables were obtained using SPSS software. The residual strains have been also distributed by normal probability distribution function.

This paper deals with the investigation of thermo-vibrational convection induced by harmonic vibrations of the temperature boundary conditions in a square cavity heated from bellow and containing a low Prandtl number fluid. The governing equations are solved by using a finite volumes method. Effects of thermal modulation on the all regimes occurring in the cavity when convection intensity increases are analyzed. A characteristic modulation frequency allowing the reduction of the average intensity of the flow and heat transfer at the cold wall has been identified. The effect of phase difference between hot and cold temperature is also studied.

The present study deals with optimization of hydraulic efficiency and shaft fatigue life of a micro cross-flow hydraulic turbine. A micro cross-flow turbine (KTP-B60) with shaft fatigue failure was considered as a case study. Numerical flow simulations were performed using a 3D- two phase flow solver, and the results have shown a good agreement with experimental data. Using an analytical method, the shaft fatigue factor of safety (FOS) was extracted from numerical simulation. CFD results were utilized in the optimization process in order to improve hydraulic efficiency and shaft fatigue life simultaneously using a meta- model (Artificial Neural Network) and genetic algorithm (GA). The priority of hydraulic efficiency and shaft fatigue life was altered by defining different objective functions in the optimization process. In one of the cases comparison of initial and optimal turbine showed a hydraulic efficiency improvement of 10.14 % and relative shaft FOS improvement of 4.86 %. The proposed optimization method could be exploited as an efficient and low cost procedure for energy generation improvement in micro hydro turbines.

Buckling is one of the most complicated concepts in mechanical engineering. Buckling often happens by compressive loads on thin structures. Thermal gradient between two ends of a column may cause a deflection in it. This will add an extra deformation to the one provided by compressive loads on the column. This phenomenon occurs when two ends of the column are at different temperatures, which can be seen at various structures. Because of the considered temperature gradients, the critical load of the column will decrease. In the current paper, various columns are modeled and the effect of thermal gradient and compressive load and other parameters on the Bi-material columns are studied. In other words, influences of compressive load and temperature gradient on critical load of Bi-material columns with interface crack are investigated. Effect of change in each parameter on critical load of column and crack opening was investigated. First, the thermal gradient was only applied to the model and in the next step; only the effect of mechanical loading was studied. Furthermore, artificial neural network (ANN) was used to extend the results to a bigger range of temperature conditions through the columns. Based on the results, ANN and finite element results are in a good agreement and the thermal effects may have a significant role in buckling of the column.

Functionally Graded Steels (FGSs) are possible solutions to improve the properties of steels made by Martensite and Bainite brittle phases. These phases are usually present in the interface between the carbon ferritic steel and the stainless austenitic steel. FGSs materials are widely investigated in the recent literature but only few works have been devoted to investigate the impact energy in the case of crack arresters. To partially fill this gap, the effect of the distance between the notch tip and the position of the median phase on the Charpy impact energy is investigated in the present paper. The results show that when the notch apex is close to the median layer the impact energy reaches its maximum value due to the increment of the absorbed energy by plastic deformation ahead of the notch tip. On the other hand, when the notch apex is far from the median layer, the impact energy strongly decreases. Keeping into account the relationship between the Charpy impact energy and the plastic volume size, a new theoretical model has been developed to link the composite impact energy with the distance from the notch apex to the median phase. The results of the new model show a sound agreement with previous results taken from the literature.

This paper deals with exact solution for free vibration analysis of simply supported rectangular plates on elastic foundation. The solution is on the basis of three dimensional elasticity theory. The foundation is described by the Pasternak (two-parameter) model. First, the Navier equations of motion are replaced by three decoupled equations in terms of displacement components. Then, these equations are solved in a semi-inverse method. The obtained displacement field satisfies all the boundary conditions of the problem in a point wise manner. The solution is in the form of a double Fourier sine series. Then free-vibration characteristics of rectangular plates resting on elastic foundations for different thickness/span ratios and foundation parameters are studied. The numerical results are compared with the available results in the literature. Important parameters on the accuracy of plate theories and free-vibration characteristics of rectangular plates resting on elastic foundations are discussed.