Abstract
The photo-elastic method has been employed to determine stress concentration factor (SCF) for square plates containing holes and inclined slots when the plate edges are subjected to in-plane tension combined with compression. Analyses given of the isochromatic 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 isochromatic fringe by the Kuske method [1]. FE provides a comparable full-field view in which contours of maximum shear stress may be identified with the isochromatic 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 isochro-matic fringe pattern, within which lie the points of maximum tension and maximum compression.
Highlights
It is well known that small holes and slots raise the stress in loaded plates locally by factors of 3 or 4
The two, principal stresses lying along axes of symmetry in the region surrounding the notch are separated within each isochromatic fringe by the Kuske method [1]
Because the principal stress lying normal to a notch boundary is zero, the isochromatic fringe pattern is sufficient to find the greatest concentration in the tangential principal stress around the hole directly
Summary
It is well known that small holes and slots raise the stress in loaded plates locally by factors of 3 or 4 This becomes important to an assessment of fatigue life when, in localised regions of high stress, cyclic loading accelerates the crack initiation process. The technique adopted is verified by two alternative methods: 1) from the analytical solution to the stress concentration around a hole in a bi-axially stressed plate and 2) from a numerical FE simulation. Both methods 1) and 2) can provide the contours of maximum shear stress in the surrounding material which photoelasticity reveals within its isochromatic fringe pattern.
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