Prediction of equivalent static loads act on a micro satellite via modal analysis
, Pages: 75-84
M. Safarabadi and S. Bazargan PDF (650K)
Abstract: In this research, the influences of modal properties of a micro cubic satellite on equivalent static loads (due to combination of quasi-static and dynamic loads during launch time) have been studied. The study shows that the magnitude of equivalent static loads can be affected by satellite effective modes and effective mass distribution along natural frequencies. Besides, when to distinct launchers with different dynamic environments candidate for launch, analytical results illustrate that sometimes the equivalent static combined load value can be higher for the launcher with smaller quasi-static loads. This phenomenon is due to effective modal mass distribution of the satellite. Consequently, a higher combined load may be occurred during launch for smaller quasi-static conditions. Furthermore, in separation phase of satellite from the launcher, the satellite modal parameters influence the magnitude of applied shock load in both axial (launch) and lateral directions, importantly. Thus the present study yields reliable input values for separation shock test which considers dynamic properties of the satellite in comparison with some standards and launcher manuals, suggest a rough estimation of shock load, neglecting the satellite structure dynamic behavior.
Keywords: Quasi-static load, Random vibration, Low frequency load, Equivalent static load, Shock Phenomenon, Modal effective mass
Finite element analysis and optimization of a mono parabolic leaf spring using CAE software
, Pages: 85-92
Krishan Kumar and M. L. Aggarwal PDF (650K)
Abstract: Parabolic leaf spring is one of the vital components in vehicle suspension system, and it is commonly used in heavy vehicles. It needs to have an excellent static load bearing capacity and fatigue life too. The purpose of this work is to make computer aided engineering (CAE) analysis of mono parabolic leaf spring and to see the effect of change of material in the optimized leaf. A mono steel leaf spring and a mono leaf spring made of composite material have been selected for this comparative analysis. The material of the mono steel leaf spring is EN45A and Glass Reinforced Plastic (GRP) as composite material which is having high strength to weight ratio. The mono leaf spring model is having one full length leave with eyes at both ends, two pins in each eye end and a rubber pad on the upper face of leave center. The CAD modelling of parabolic leaf spring has been done in CATIA and for analysis the model is imported in ANSYS workbench. It was shown that the use of composite material instead of steel resulted into large deflection, small variation in stresses and also a large amount of weight reduction.
Keywords: Finite Element Analysis, CAE, Leaf Spring, EN45A, GRP
Study of loading waveform, loading duration, rest period and stress level on fatigue life of asphalt mixtures
, Pages: 93-102
Ali MansourKhaki, Alireza Samdzadeh and Majid Jebalbarezi PDF (650K)
Abstract: The main objective of this paper is to study the effects of haversinse and triangular loading waveforms on the fatigue life of Hot Mix Asphalt (HMA) specimens. Effects of load duration, rest period and stress level are also studied for the asphalt mixtures at 25oC. An indirect tensile test with strain control was performed to determine the fatigue life of asphalt. The fatigue tests were performed at two stress levels (170 and 250 kPa), two waveforms (haversine and triangle), three load duration (100, 200, 400 ms), and two rest period to load duration ratios (4 and 9). The obtained results showed that fatigue life of haversine waveform is less than fatigue life of triangle waveform. As the area under the loading curve is increased (stress level is increased or deformed), effect of rest period on the fatigue life decreases. On the other hand, as the tire contact area is increased, the induced tire pressure reduction decreases its destructive effects on the asphalt layer. As the load duration is decreased, fatigue life will increase. This effect is more pronounced for lower stress levels than the higher stress levels.
Keywords: Hot mix asphalt, Fatigue life, Loading waveform, Duration and rest period xperimental study
Prediction of J-Integral dependence to residual stress and crack depth on NACA 0012-34 using FE and ANN
, Pages: 103-110
A.R. Hosseinzadeh and Mh. Karimi PDF (650K)
Abstract: This paper presents an approach of linking finite element method with artificial neural network to predict J-Integral parameter in desirable airfoil condition. Finite Element (FE) and Artificial Neural Network (ANN) have been employed for the purpose. In other words, a prediction of finite element results has been done using ANN. Ultimately results of two methods have been compared for different cases. Wing fracture is a well-known problem of the planes which depends on various parameters. The J-integral is a vital parameter in evaluations of structure fracture phenomena. On the other hand residual stresses play an influential role in fracture formation. In the current work, effect of residual stresses and crack depth on J-Integral has been investigated in a standard NACA0012-34 airfoil. As will be seen, residual stresses and crack depth influence J-Integral values. It also will be shown that predictions of ANN method are in a good agreement with those obtained by finite element method.
Keywords: Residual stress, J-Integral, Crack, Finite element, ANN
Extension of linear elastic strain energy density approach to high temperature fatigue and a synthesis of Cu-Be alloy experimental tests
, Pages: 111-116
F. Berto and P. Gallo PDF (650K)
Abstract: The present paper summarizes the results from uniaxial-tension stress-controlled fatigue tests performed at different temperatures up to 650°C on Cu-Be specimens. Two geometries are considered: hourglass shaped and plates weakened by a central hole (Cu-Be alloy). The motivation of the present work is that, at the best of authors’ knowledge, only a limited number of papers on these alloys under high-temperature fatigue are available in the literature and no results deal with notched components. The Cu-Be specimens fatigue data are re-analyzed in terms of the mean value of the Strain Energy Density (SED) averaged over a control volume. Thanks to the SED approach it is possible to summarize in a single scatter-band all the fatigue data, independently of the specimen geometry.
Keywords: High-temperature fatigue, Copper-cobalt-beryllium alloy Fatigue strength, Notched specimens, Strain energy density
An elastic analysis for thick cylindrical pressure vessels with variable thickness
, Pages: 117-130
Mehdi Ghannad, Mehdi Jabbari and Mohammad Zamani Nejad PDF (650K)
Abstract: This paper derives a semi-analytical solution to determine displacements and stresses in a thick cylindrical shell with variable thickness under uniform pressure based on disk form multilayers. The proposed study partitions the thick cylinder into disk-layer parts based on their thickness of the cylinder. According to the existence of shear stress in the thick cylindrical shell with variable thickness, the equations governing disk layers are acquired based on first shear deformation theory (FSDT), which are in the form of a set of general differential equations. In this study, the cylinder is partitioned into n different disks and n sets of differential equations are derived. The solution of these equations provides displacements and stresses based on the boundary conditions and continuity conditions between the layers. The results are compared with those obtained through the analytical solution and the numerical solution. For the purpose of the analytical solution, matched asymptotic method (MAM) and for the analytical solution, the finite element method (FEM are implemented.
Keywords: Thick cylindrical shell with variable thickness, Disk form multilayers, Matched asymptotic method, Finite element method
Small-scale effects on transverse vibrational behavior of single-walled carbon nanotubes with arbitrary boundary conditions
, Pages: 131-144
Farzad Ebrahimi and Parisa Nasirzadeh PDF (650K)
Abstract: In the present paper, the differential transformation method is employed to develop a semi-analytical solution for free transverse vibration of single-walled carbon nanotube (SWCNT) with arbitrary boundary conditions. The small scale effect is taken into consideration via Eringen’s nonlocal elasticity theory while the transverse shear deformation effects and rotary inertia are taken into account in presented Timoshenko beam theory. Through variational formulation and the Hamilton's principle the governing differential equations and the boundary conditions are derived and then solved by a semi-analytical method called differential transformation method (DTM) for various frequency modes of beams and different edge conditions. Comparisons made between the present results and results reported by well-known references for special cases treated before, have confirmed accuracy and efficiency of the presented approach. The effects of several parameters such as transverse shear deformation effects, slenderness ratios, boundary conditions and small scale on vibration characteristics of SWCNT are examined. The present study illustrates that the vibration characteristics of an SWCNT are strongly dependent on the small scale parameters.
Keywords: Free vibration, Nanobeam, Eringen nonlocal elasticity theory
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