numero25

F.A. Díaz et alii, Frattura ed Integrità Strutturale, 25 (2013) 109-116 ; DOI: 10.3221/IGF-ESIS.25.16 109 Special Issue: Characterization of Crack Tip Stress Field Application of thermoelastic stress analysis for the experimental evaluation of the effective stress intensity factor Francisco A. Díaz Universidad de Jaén, Departamento de Ingeniería Mecánica y Minera, Campus las Lagunillas, Edificio A3, 23071, Jaén, Spain Eann A. Patterson University of Liverpool, School of Engineering, Harrison Hughes Building, The Quadrangle, Liverpool L69 3GH, UK John R. Yates University of Manchester, School of Mechanical, Aerospace and Civil Engineering, George Begg Building, Manchester, M60 1QD, UK A BSTRACT . In recent years, the advent of staring array detectors has made Thermoelastic Stress Analysis (TSA) a technique with considerable potential for fatigue and fracture mechanics applications. The technique is non- contacting and provides full field stress maps from the surface of cyclically loaded components. In addition, the technique appears to have a great potential in the evaluation of the effective stress intensity factor range during fatigue since fracture mechanics parameters are derived directly from the temperature changes in the vicinity of the crack tip rather than from remote data. In the current work TSA is presented as a novel methodology for measuring the effective stress intensity factor from the analysis of thermoelastic images. Δ K values inferred using TSA have been employed to estimate an equivalent opening/closing load at different R -ratios in a cracked aluminium 2024 CT specimen. Results have been compared with those obtained using the strain-offset technique showing a good level of agreement. K EYWORDS . Thermoelastic Stress Analysis (TSA); Fatigue; Effective Stress Intensity Factor. I NTRODUCTION atigue cracks have been one of the main sources of structural failures in machines for two centuries. The application of fracture mechanics to engineering design has led to more efficient use of structures and components, which leads to great economic benefits by avoiding premature retirement of serviceable machines. However, there are still some aspects of fatigue that remain partially understood, such as the crack closure effect. This lack of understanding arises principally from the difficulties associated in quantifying the phenomenon and measuring its effect on the crack driving force [1]. In recent years, advances in infrared thermography together with the development of infrared staring array radiometer detectors have made it possible to apply this technology to fatigue damage assessments. Such an example is Thermoelastic Stress Analysis (TSA). This experimental technique makes it possible to infer the in-plane stresses on a solid structure by measuring the small temperature changes induced as a result of a cyclic load. From the fatigue point of view, TSA constitutes a breakthrough over other experimental stress analysis techniques. With TSA the stress intensity factor is directly obtained by computing the cyclic stress field ahead of the crack tip, which makes it possible to evaluate the actual crack driving force for the fatigue advance [2 and 3]. The outcome is that the TSA F