Metin Sayer

Thermal stress analysis of functionally graded rotating discs

The present study deals with stress analysis on functionally graded rotating annular discs subjected to temperature distributions parabolically decreasing with radius. Authors used infinitesimal deformation theory of elasticity and for graded parameters power law functions in the solution procedure. With the increasing temperature, the tangential stress component decreased at the inner surface whereas increased at the outer surface, and the radial stress component reduced gradually for all the temperature distributions. The magnitude of the tangential stress component was higher than ones of the radial stress component under the room temperatures for both discs. But, the tangential stress component decreased more at the inner surface whereas it increased at the outer surface when the temperature increased further. Finally, the radial displacement at the outer surface had higher value than that of the inner surface with the increasing temperature.

Thermo-Elastic Stress Analysis in a Thermoplastic Composite Disc

This study deals with thermo-elastic stress analysis on a thermoplastic composite disc reinforced curvilinearly with Ε-glass fibers. Its mechanical properties are obtained by using an Instron testing machine. The modulus of elasticity in the tangential direction is measured by using strain gauges due to the fitting of a solid disc into the composite disc. An analytical method is performed to determine thermal stresses for both uniform and linearly changing temperatures. The magnitude of the tangential stress component in polar coordinates is the highest at the inner surface of the disc. INTRODUCTION The stress analysis of discs has long been an important issue in engineering design. Due to high specific stiffness and strength, improved fracture toughness and increased impact resistance, thermoplastic composites have gained popularity. Ito et al. I\l have presented an attempt at tailoring thermoplastic laminates with near-zero coefficients of thermal expansion in one particular in-plane direction by using conventional low-cost glass fibers. Sayman and Qallioglu 121 have investigated elastic-plastic stress analysis in steel fiber reinforced thermoplastic composite cantilever beam analytically. Timoshenko and Goodier /3/ have presented a thermal stress analysis in an isotropic thin disc. Genta and Gola /4/ have investigated an analytical linear stress analysis in orthotropic rotating discs reinforced by fibers rectilinearly. Giiven and Altay 151 have studied thermal stresses in a linear hardening solid disc under a uniform heat source. Tütüncü 161 has determined stresses and deformations resulting from centrifugal forces in rotating specially orthotropic circular plates are determined. Trende et al. Ill have investigated residual stresses and dimensional changes in the compression moulded glass-mat reinforced thermoplastic (GMT) parts. A heat transfer and crystallization model with temperature dependent matrix properties has been used to obtain input to the subsequent thermal stress analysis. Shabana and Nöda /8/ have examined the thermoelastoplastic stresses in functionally graded composite materials by the finite element technique. Mackin et al. 191 have studied thermal cracking in disc brakes during hard braking. In this study, a low-density thermoplastic composite disc reinforced with Ε-glass fibers is manufactured, and its mechanical properties are determined. An analytical method is carried out on the composite disc to obtain thermo-elastic stresses under uniform and linear temperature distribution. PRODUCTION OF THE COMPOSITE DISC The composite material consists of a thermoplastic matrix with a low-density polyethylene and E-glass fibers. For preparing a polyethylene layer, 20 grams polyethylene granules were placed into the mould and heated up to 160°C by an electrical resistance. The material was kept for a five minute period at 160°C under 2.5 MPa pressure by means of a hydraulic press. Subsequently, the temperature was decreased to 30°C in five minutes under 15 MPa pressure. At the result of this process, a polyethylene layer with a thickness of 1 mm was produced. After the wound Ε-glass fibers were placed between two polyethylene layers, these materials were heated up 251 Vol. 12, No. 4, 2005 Thermo-Elastic Stress Analysis in a Composite Disc to 160°C under 2.5 MP a pressure for ten minutes. As a result of this process, an Ε-glass fiber-reinforced composite disc was produced as shown in Figure 1. The thickness of the composite disc and the outer radius are 2.5 mm and 75 mm, respectively. DETERMINATION OF MATERIAL PROPERTIES For the composite material, the volume fraction of fibers is Vf =10%. Test specimens were used to determine the material properties of the composite disc. The modulus of elasticity in the transverse direction of Ε-glass fibers was defined as Er and it was given in the direction of Ε-glass fibers as Eg . Poissons ratio (vre) and Er were measured by strain gauges bonded onto the test specimen as shown in Fig. 2a. The strains were measured as εΓ = \25μ and εβ = \.5μ . Therefore, Er and Poissons ratio (v r g ) were found as 190 MP a and 0.012, respectively. Determination of Εθ In order to find E

Investigation of notch effect on vibration behavior of filled and unfilled composite beam

a circular aluminum solid disc was fitted into the thermoplastic composite disc as shown in Figure 3. Because of this fitting, a pressure ρ appeared, which caused the aluminum solid disc to shrink. Strains measured in the radial and tangential directions in the aluminum solid disc were -8 μ. The external pressure in the solid disc was found as p=-0.8 MPa. Furthermore, the strains on the composite ring were obtained in the radial and tangential directions, respectively as εΓ=-\52μ and £ # = 1 4 5 / / . Hooks laws for the stresses in the radial and tangential directions are given as

Vibration analysis of sandwich beams with variable cross section on variable Winkler elastic foundation

In this study, the effect of the notches on natural frequencies of ceramic particles filled and unfilled unidirectional composite beams are investigated numerically. Shape, number, size and location of the notch are examined for unfilled unidirectional composite beam. Moreover, the effect of the particle additives on the natural frequency of the composite beam with V notch is also examined. Three types of notch shape are considered: U, V and square (S). SiC, Al2O3 and B4C are used as the additive particles. According to the results, minimum natural frequency is found in the S notch. Furthermore, it can be seen from the results that natural frequency of S notch is the most affected by increase in the number, size and location of notch. As for the effect of the particle additives, maximum natural frequency is found in the beam with filled B4C and V notch as compared with the others.

An experimental investigation on the impact behavior of hybrid composite plates

Abstract In this study, free vibration behavior of a multilayered symmetric sandwich beam made of functionally graded materials (FGMs) with variable cross section resting on variable Winkler elastic foundation are investigated. The elasticity and density of the functionally graded (FG) sandwich beam vary through the thickness according to the power law. This law is related to mixture rules and laminate theory. In order to provide this, a 50-layered beam is considered. Each layer is isotropic and homogeneous, although the volume fractions of the constituents of each layer are different. Furthermore, the width of the beam varies exponentially along the length of the beam, and also the beam is resting on an elastic foundation whose coefficient is variable along the length of the beam. The natural frequencies are computed for conventional boundary conditions of the FG sandwich beam using a theoretical procedure. The effects of material, geometric, elastic foundation indexes and slenderness ratio on natural frequencies and mode shapes of the beam are also computed and discussed. Finally, the results obtained are compared with a finite-element-based commercial program, ANSYS®, and found to be consistent with each other.