Issue 13

Ahanchian Mohammad et alii, Frattura ed Integrità Strutturale, 13 (2010) 31-35 ; DOI: 10.3221/IGF-ESIS.13.04 32 element method is coded in MathCAD program to inspect fracture behavior and the results are compared with the ANSYS analysis. The effects of crack configurations, closure stresses and temperature on the failure load have also been investigated. C ONSTITUTIVE MODEL OF OPTICAL FIBER he model of optical fiber is a composition of aluminum and silica glass as core which is developed within the framework of Small Static Displacement. The material properties are presented in Tab. 1. Two isotropic and homogeneous materials, joining to constitute a model of fiber optic in two-dimensional plane stress geometry with an initial circular crack on their meeting line are considered. According to the mentioned significance of optical fiber, ability of FEM and since computer modeling is useful to conduct virtual experiments with lower cost [7]; the authors decided to simulate a proper model on this design. Material Density, Kg/m 3 Modulus of Elasticity, MPa Modulus of rigidity, MPa Poisson's Ratio Thermal Conductivity, W/m.K Thermal expansion, 1/C Glass 25400 46200 18600 0.245 6.21 8.00E-05 Aluminum 26600 71000 26200 0.334 237 2.36E-05 Table 1 : Typical property of materials [8, 9]. The diameter of optical fiber as standard is assumed to be 125 µm having a circular crack in the intersection line of two materials. Three different cases considering crack lengths of 3.5, 7 and 10.5 µm are investigated. In the first situation, the crack has the smallest length that is in two dimensional polar coordinate r (radius of crack tip) is equal to the radius of core and θ (angle between crack tip and X direction) had been assumed to be 15 degree. For other cases, radius had been kept constant and θ had been incremented by 15 degree in order to increase crack length. The problem is investigated in Linear Elastic Fracture Mechanics (LEFM) with Plane stress approach. Due to symmetry of the problem, a quarter segment of the model is analyzed. Boundary conditions are imposed such as horizontal line is constrained in Y direction and vertical line is constrained in X direction; both lines are considered as symmetric along their direction. Applied forces are imposed in X any Y directions with constant values and the breaking forces are calculated for each case. Thermal condition is assumed to have constant value in each half of the quarter model, the lower part of quarter model has 50 °C and the upper part has 60 °C in order to have thermal gradient as presented in Fig 1. Figure 1 : Applied forces and Thermal conditions on the model. T