Application of a finite element method to stress distribution in buried patch repaired polyethylene gas pipes

Advantages of polyethylene pipes over traditional steel or metal pipes have increased industry interest in the use of polyethylene (PE) pipelines for underground applications and especially in gas distribution networks. In this study, finite element analysis is used to calculate the stress distribution in a patch repaired defective gas pipe under internal pressure. The pipe is assumed to be buried at a depth of 125 cm. The material is assumed to be medium density PE80B, where the patch material was selected from high density polyethylene (HDPE). During the loading process, the seasonal pipe temperature changes, surcharge loads, soil column weight, and soil–pipe interaction were included in the analysis. Four types of patch arrangements were selected to repair the damaged pipe. The shape of the defect hole was deemed as circular or elliptic. With respect to elliptic defects, various minor to major diameter ratios, a/b, were selected to simulate a circular to a crack shaped defect. Based on the results, the semi-circular and saddle fusion patches decrease the peak von Mises stress in the pipe by almost the same amount. However, the minimum peak von Mises stress in the patch corresponds to the saddle fusion repair arrangement. Based on the results, with respect to a saddle fusion repair, when the shape of the defect approaches a crack, the peak von Mises stress in the pipe almost doubles and exceeds the pipe allowable stress for a working life of 50 years. With respect to higher values of a/b, the stress level in the patch repaired pipe is significantly below its limiting value for the same life expectancy. Keywords: Patch repair, Buried gas pipe, MDPE, HDPE, Temperature variatio

Finite Element Study of Three Different Treatment Designs of a Mandibular Three Implant-Retained Overdenture

Abstract This study compares ball, bar-clip and bar-ball attachment systems for implant-retained mandibular overdentures with three implants. The first implant is placed in the middle of the mandible and the other two are imbedded in the first premolar regions. Linear elastic finite element analysis is used for design analysis. Three dimensional geometry of the mandible is generated from computed tomography. Other parts are modeled using SolidWorks software. The foodstuff is positioned at the right first molar, representing the most frequent masticating situation. To obtain accurate mesh-independent results, finite element models are solved using several mesh grids. They are then validated by means of a detailed convergence analysis. The results demonstrate that the highest von-Mises stress in the bone is always located around the neck of the implant, at its upper threads. Ball and bar-ball attachments transfer the highest and lowest stresses to the bone surrounding the implants, respectively. The lowest stresses in the cortical and cancellous bones are due to bar-ball attachment. Yet, the overdenture gets its maximum movement for this arrangement. Consequently, the use of bar-ball attachment is only recommended for the cases in which stress transferred to peri-implant bone is more important than overdenture stability. Among the three treatment designs, ball attachment seems to exhibit the lowest lateral and overall displacements and hence, better overdenture stability

Magneto-Elastic Analysis of an Annular FGM Plate Based on Classical Plate Theory Using GDQ Method

Abstract Using GDQ method, the radial and circumferential stresses in an annular FGM plate with a uniform thickness under a transverse axisymmetric load is investigated. It is assumed that a uniform radial magnetic field acts on the top surface of the plate. The modulus of elasticity E and the magnetic permeability coefficient μ of the plate along its thickness are assumed to vary according to the volume distribution function. The Poisson's ratio ν is considered to be constant. Based on the classical plate theory (CPT), equilibrium equations are deduced and the displacement fields are determined. The radial and circumferential stresses as well as transverse and radial displacements are obtained accordingly. The effect of volume fraction function power m on the maximum deflection in the absence and presence of the magnetic field is also investigated. Moreover, the effect of t/a and b/a ratios on displacements, stresses, induction magnetic field intensity and the resulting Lorentz force are also investigated. According to the results, for different points along the radial direction, the application of radial magnetic field to the top surface of the plate completely changes the state of stress in both tangential and radial directions, resulting in tensile and compressive stresses in these two directions. The results also indicate that in presence of magnetic field, the plate displacement and stress components are lowered considerably

SYNTHESIS AND CORROSION PROTECTION BEHAVIOR OF EPOXYTiO2-MICACEOUS IRON OXIDE NANO - COMPOSITE COATING ON St-37

The micro layers micaceous iron oxide and nano-TiO 2 were incorporated into the epoxy resin by mechanical mixing and sonication process. Optical micrographs showed that the number and diameter size of nanoparticle agglomerates were decreased by sonication. The structure and composition of the nanocomposite was determined using transmission electron microscopy which showed the presence of dispersed nano-TiO 2 in the polymer matrix. The anticorrosive properties of the synthesized nano-composites coating were investigated using salt spray, electrochemical impedance spectroscopy and polarization measurement. The EIS results showed that coating resistance increased by addition of micaceous iron oxide micro layers and nano-TiO 2 particles to the epoxy coatings. It was observed that higher corrosion protection of nanocomposite coatings obtained by the addition of 3 %wt micaceous iron oxide and 4%wt nano-TiO 2 into epoxy resin