Abstract
BackgroundThe Stress Intensity Factor (SIF) is used to describe the stress state and the mechanical behaviour of a material in the presence of cracks. SIF can be experimentally assessed using contactless techniques such as Thermoelastic Stress Analysis (TSA). The classic TSA theory concerns the relationship between temperature and stress variations and was successfully applied to fracture mechanics for SIF evaluation and crack tip location. This theory is no longer valid for some materials, such as titanium and aluminium, where the temperature variations also depend on the mean stress.ObjectiveThe objective of this work was to present a new thermoelastic equation that includes the mean stress dependence to investigate the thermoelastic effect in the proximity of crack tips on titanium.MethodsWestergaard’s equations and Williams’s series expansion were employed in order to express the thermoelastic signal, including the second-order effect. Tests have been carried out to investigate the differences in SIF evaluation between the proposed approach and the classical one.ResultsA first qualitative evaluation of the importance of considering second-order effects in the thermoelastic signal in proximity of the crack tip in two loading conditions at two different loading ratios, R = 0.1 and R = 0.5, consisted of comparing the experimental signal and synthetic TSA maps. Moreover, the SIF, evaluated with the proposed and classical approaches, was compared with values from the ASTM standard formulas.ConclusionsThe new formulation demonstrates its improved capability for describing the stress distribution in the proximity of the crack tip. The effect of the correction cannot be neglected in either Williams’s or Westergaard’s model.
Highlights
The evaluation of the stress state in the proximity of the crack tip represents an important topic in structural engineering
The aim of the present work is to show a new Thermoelastic Stress Analysis (TSA) formulation that considers the variations of the material properties (i.e., Young’s modulus) with temperature in the proximity of a crack tip loaded in mode I on titanium
The overdeterministic system was solved for each point and the solution was obtained by minimizing deviations using a direct research method based on the Nelder– Mead method [45]
Summary
The evaluation of the stress state in the proximity of the crack tip represents an important topic in structural engineering. SIF can be assessed by adopting different experimental techniques, such as DIC (Digital Image Correlation) [1, 2], photoelasticity [3], and TSA (Thermoelastic Stress Analysis) [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19] This latter presents some advantages that make it suitable for in-service applications on real components when cycling loading conditions are applied. The effect of the correction cannot be neglected in either Williams’s or Westergaard’s model
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