A new mixed mode fracture test specimen covering positive and negative values of T-stress
, Pages: 67-72
M. M. Mirsayar PDF (256K)
Abstract: A new fracture test specimen is suggested and analyzed using finite element method. The mode I and mode II stress intensity factors as well as the T-stress were calculated for three geometries and loading conditions. It is shown that the specimen, called single edge cracked ring (SECR), covers different mixed mode loading conditions from pure mode I to pure mode II. The SECR specimen also covers negative and positive values of T-stresses. From the practical view point, the suggested specimen can be used easily for mixed mode II fracture tests.
Keywords: Brittle fracture mechanics; SECR specimen; Mixed mode loading conditions; T-stress; Numerical analyses
Analysis of necking in tube hydroforming by means of extended forming limit stress diagram
, Pages: 73-82
R. Hashemi PDF (256K)
Abstract: In this paper, an extended forming limit stress diagram (EFLSD) was applied to predict neck initiation failure in tube hydroforming of metal bellows. The proposed EFLSD was used in conjunction with ABAQUS/ EXPLICIT finite element simulations to predict the onset of necking in tube hydroforming of metal bellows. The amount of calibration pressure and axial feeding required to produce an acceptable part in finite element method (FEM) were compared with the published experimental data and a satisfactory agreement between the FEM and published test results was achieved. Therefore, the present approach can be used as a reliable criterion for designing metal bellows hydroforming processes and reducing the number of costly trials.
Keywords: Hydroforming; Simulation; Bursting
The flow stress assessment of austenitic-martensitic functionally graded steel under hot compression
, Pages: 83-90
H. Salavati, F. Berto and Y. Alizadeh PDF (256K)
Abstract: 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 (γ) 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.
Keywords: Hot deformation; Functionally graded steel; Rule of mixture; Zener-Hollomon constitutive equations
Numerical method to measure velocity integration, stroke volume and cardiac output while rest: using 2D fluid-solid interaction model
, Pages: 91-100
Arezoo Khosravi, Hamidreza Ghasemi Bahraseman, Kamran Hassani, and Davood Kazemi-Saleh PDF (256K)
Abstract: 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.
Keywords: Echo-Doppler flow; Fluid-structure interaction; Hemodynamics; Natural aortic valve
Investigation of delamination and damage due to free edge effects in composite laminates using cohesive interface elements
, Pages: 101-118
Bijan Mohammadi and Davood Salimi-Majd PDF (256K)
Abstract: 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.
Keywords: Delamination; Cohesive zone model; Damage variable; Matrix cracking; Free edge effects
Vibrational response of functionally graded circular plate integrated with piezoelectric layers: An exact solution
, Pages: 119-130
A. A. Jandaghian, A. A. Jafari and O. Rahmani PDF (256K)
Abstract: 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 ﬁnite 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.
Keywords: Functionally graded material; Piezoelectric; Circular plate; Classical plate theory; Forced vibration
Residual strains around cold worked holes from statistical view
, Pages: 131-138
E. Pooladi and Kh. Farhangdoost PDF (256K)
Abstract: 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.
Keywords: Cold work; Experimental study; Residual strain; Residual stress; Statistical distribution
Effect of double thermal modulation on heat transfer in a square cavity heated from bellow
Aziz Akhiate, Al alami Semma, El Ganaoui and Abdelah Anouar PDF (256K)
Abstract: 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.
Keywords: Thermo-vibrational convection; Square cavity; Finite volumes method
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