Investigation of Stress Concentration Factor of Composite for Bending Specimen using Polariscope

This paper presents the experimental estimation of stresses in the epoxy based material for varying weight percentage of copper particles using Photoelasticity method. The study deals with the stress distribution within the diametrical disc under compression loading which uses the property birefringence. Photoelasticity method used to calculate the stresses for the intricate shapes models where the analytical solutions are too complex. The significance of the method is to do the variety of stress analyses and even for routine use in design, particularly before the advent of numerical methods, such as for instance finite elements or boundary elements. It is very important for the engineer to be aware of the effects of stress raisers such as notches, Holes or sharp corners in his/her design work. Stress concentration effects in machine parts and Structures can arise from internal holes or voids created in the casting or forging process, from excessively sharp corners or fillets at the shoulders of stepped shafts, or even from punch marks left during layout work or during inspection of parts. The photo-elastic method has been employed to determine stress concentration factor (SCF) for square plates containing circular hole, elliptical hole, and crack model when the plate edges are subjected to in-plane tension combined with compression. Analyses given of the isochromatics fringe pattern surrounding the hole provides the SCF conveniently. The model material is calibrated from the known solution to the stress raiser arising from a small circular hole in a plate placed under biaxial tension-compression. These results also compare well with a plane stress FE analysis. Consequently, photo-elasticity has enabled SCF’s to be determined experimentally for a biaxial stress ratio, nominally equal to –4, in plates containing a long, thin slot arranged to be in alignment with each stress axis. The two, principal stresses lying along axes of symmetry in the region surrounding the notch are separated within each isochromatics fringe. FE provides a comparable full-field view in which contours of maximum shear stress may be identified with the isochromatics fringe pattern directly. The principal stress distributions referred to the plate axes show their maximum concentrations at the notch boundary. Here up to a fourfold magnification occurs in the greater of the two nominal stresses under loads applied to the plate edges. Thus, it is of importance to establish the manner in which the tangential stress is distributed around the slot boundary. Conveniently, it is shown how this distribution is also revealed from an isochromatics fringe pattern, within which lie the points of maximum tension and maximum compression.