Digital Photoelastic Evaluation of Crack-Tip Response Under Combined Axial Tension, Bending and Contact Loading

Abstract

Background

Structural members such as welded rails are subjected to bending and localized contact stresses during service and may additionally experience axial stresses arising from restricted strains leading to combined loading scenarios that influence crack behaviour.

Objective

This study examines variations in fracture parameters under the combined action of contact loading, bending, shear and axial tension in a beam to understand the crack-tip response.

Methods

Photoelastic experiments are conducted on a cracked beam model subjected to axial tension combined with contact loads at different positions using a specially fabricated loading jig. The isolated influence of contact loading and axial restraint is examined. Whole-field isochromatics representing constant principal stress difference (σ₁-σ₂) are processed using a multiparameter formulation. The stress intensity factors (K_I, K_II) and T-stress are extracted from the leading coefficients of the converged solution.

Results

For practical cracks, the response under combined loading is governed by interacting stress fields and requires consideration of crack face displacements. For a given axial tension, K_I increases more than K_II with increasing contact load. With increasing axial tension and constant contact load, K_I increases while K_II remains largely unaffected. The sign and magnitude of T-stress show strong dependence on load position, attaining high positive values when the contact load is directly above the crack.

Conclusion

Contact loading in the presence of high axial tension leads to an increase in crack-tip constraint. These findings are useful in assessing crack behaviour in components such as welded rails subjected to combined axial and contact loading during service.