Showing 5 results for Stress Concentration
Mehdi Ghannad, Mohammad Jafari, Amin Ameri,
Volume 15, Issue 6 (8-2015)
Abstract
Because of the continuous changes of mechanical properties of functionally graded materials and therefore reducing the effects of stress concentration, many researchers are interested in studying the behavior and use of these materials in various industries. For the correct design of perforated inhomogeneous plate is needed to know the accurate information about the deformation and stress distribution in different points of the plate especially around the hole. In this paper, is tried to present the analytical solution to calculate the 2D stress distribution around the circular hole in long FG plate, by using the complex potential functions method. The plate subjected to constant uniaxial or biaxial stress. One of the most important goal of this research is to study the effect of compression load applied to the hole boundary on stress distribution around the hole. The variation of material properties, especially Young's modulus is in a radial direction and concentric to the hole. The special exponential function is used to describe the variation of mechanical properties. The finite element method has been used to check the accuracy of analytical results for homogeneous and heterogeneous plates, also for all loading cases. In the presence of applied load at the boundary of circular hole, amount of radial stress in addition to hoop stress is considerable. Therefore the Von Mises stress is used to study the stress around the hole. The results showed that inhomogeneous plate with increased modulus of elasticity has greater load bearing capacity with respect to homogeneous plate.
Mohammad Jafari, Iman Ghandi Varnosefaderani,
Volume 15, Issue 8 (10-2015)
Abstract
In this paper, by expanding Muskhelishvili’s stress functions and with use of Schwarz’s alternating method, the stress distribution in a plate with two quasi-rectangular cut outs has been studied. Muskhelishvili represented the mentioned stress functions for studying the stress distribution in an isotropic plate with a circular or an elliptical cut out. In order to expand the Muskhelishvili’s analytical solution for deriving the stress functions related to quasi-rectangular cut outs, a conformal mapping function has been used. This conformal mapping transformed the area external of the quasi-rectangular cut out into the area outside the unit circle. Considering Schwarz’s alternating method, for calculating the stress distribution around two cut outs, complex series with unknown coefficients have been used. In this study, the effect of different parameters such as the location of the cut outs relative to each other, bluntness and aspect ratio of cut out sides on stress concentration factor can be investigated. The finite element method has been used to verify the accuracy of semi-analytical results. Comparison of two methods demonstrates the precision of obtained semi-analytical solution and indicates that it can be used for computing stress distribution in plates with two rectangular cut outs. Analysis of the proposed solution shows that the mentioned parameters have a significant effect on stress distribution and stress concentration factor decreases noticeably with selection of appropriate values of these parameters.
Saeed Rahnama, Mehdi Maleki,
Volume 15, Issue 12 (2-2016)
Abstract
In this paper by using of modified shear-lag model and superposition technique, the stress concentration factor in a unidirectional composite lamina with angled and staggered cracks is investigated. Unlike classical shear-lag model, in modified model, both the fiber and matrix are able to sustain axial loads. For a unit cell of fiber and matrix , the differential-difference equations of equilibrium were derived and solved for displacements and stress fields within the lamina. For a total fiber N and row of r, number of break fiber ,by superposition technique, The maximum stress concentration factor of lamina with angled and staggered breaks was calculated. Results show that the classical shear-lag model can not predict the stress concentration factor accurately when value of Matrix-to-Fiber moduli ratio is increased. In glass-epoxy lamina with staggered and angled cracks, the maximum stress concentration factor decreases by 39% and 43%, respectively, versus the aligned fiber breaks. By increasing the Matrix-to-Fiber moduli and Matrix-to-Fiber volume fraction ratios the maximum stress concentration factor decreases. As Em/Ef approaches to zero, results have a good agreement with primary shear-lag model.
Ali Abbasnia, Mohammad Jaffari, Abbas Rohani,
Volume 18, Issue 5 (9-2018)
Abstract
One of the concerns of designers of engineering structures is structural failure due to stress concentration caused by geometric discontinuities in the structures. Therefore, by considering that perforated composite plates are used in most engineering structures, their study is very important. The purpose of this paper is to present a new model based on the regression method for estimating stress concentration factor of a circular hole in orthotropic plates. One of the important applications of providing stress distribution around holes in terms of mechanical properties is the use of these relationships in the stress analysis of perforated viscoelastic plate using the effective modulus method or Boltzmann's superposition principle. First, using different values of the mechanical properties of the composites plates, and employing an analytical solution based on the complex variable method, the stress concentration factor of circular hole is calculated for a number of these materials. Then, using multiple linear regression, an explicit expression for the stress concentration factor is given in terms of mechanical properties. The results show that the multiple regression model is able to predict the circumferential stress with a maximum error of less than 1%.
A.r Ghasemi, H. Khabaz Kashani,
Volume 19, Issue 1 (1-2019)
Abstract
In this research, the analysis of the effects of circular hole and thermal cycle fatigue on the mechanical properties in multi-layer polymer composite reinforced with nanoparticles are investigated. First, multi-walled carbon nanotubes with 0.1% weight fraction of nanoparticles are added to the epoxy resin ML506. The. In order to homogenize particle in the resin, it is mixed with a magnetic stirrer for 30 minutes. The material is placed in an ultrasonic device for 40 minutes to homogenize the resin and nanoparticle completely. The resin reinforced with glass fibers constitute symmetric cross ply laminates stacking sequence [02/902]s, and nanocomposite samples are made with hand layup method. In this study, open-hole specimens with diameter of 2 and 4mm are investigated. To study the thermal cycles, nanocomposite samples of 3 levels of thermal cycles including 0, 180, and 360 cycles were investigated. The samples are exposed to a temperature range of 0 to 100oC. After that, the specimens undergo tensile testing. Using the tensile test, the modulus of elasticity and tensile strength are compared for the different thermal cycles and the diameter of the holes. By increasing the number of thermal cycles, the tensile strengths of nanocomposite samples are not significantly changed. Also, with increasing the diameter of the hole, the tensile strength is decreased. The elasticity modulus with increasing thermal cycles for all specimens have been minimal changes. Also, a linear regression model was developed, using MINITAB software for strength and elastic modulus in terms of number of thermal cycles and diameter to width ratio.
