Examinando por Autor "Vasco-Olmo, José M."
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Ítem A higher order thermoelastic analysis of fatigue crack growth can assess crack tip shielding(Wiley, 2023-06-30) Camacho-Reyes, Alonso; Vasco-Olmo, José M.; James, M. Neil; Díaz, Francisco A.The present work uses a more accurate thermoelastic formulation than the classical equation, based on the inclusion of a higher order term, to analyze crack tip thermoelastic data. It is shown that this thermoelastic analysis (TSA) model can be fitted to the Christopher–James–Patterson crack tip field model and hence provides information on crack tip shielding. To validate the results of this analysis, stress intensity factors (SIFs) were compared with results obtained from digital image correlation (also fitted to the CJP model). A comparison was also made between these CJP-derived SIF values and those obtained using a purely elastic Irwin–Westergaard approach. A high level of agreement was observed between DIC and TSA results in assessing ΔKCJP that is the net result of the driving and the shielding forces on the crack tip. The ability to assess shielding using TSA is a significant step forward in its potential use in a more accurate characterization of crack tip fields.Ítem Characterization of non-planar crack tip displacement fields using a differential geometry approach in combination with 3D digital image correlation(Wiley, 2022-03-03) Camacho-Reyes, Alonso; Vasco-Olmo, José M.; James, M. Neil; Díaz, Francisco A.This paper describes a novel differential geometry method that is used in combination with 3D digital image correlation (3D-DIC) for crack tip field characterization on non-planar (curved) surfaces. The proposed approach allows any of the two-dimensional crack tip field models currently available in the literature to be extended to the analysis of a 3D developable surface with zero Gaussian curvature. The method was validated by analyzing the crack tip displacement fields on hollow thin-walled cylindrical specimens, manufactured from either 304L or 2024-T3 alloy that contained a central circumferential crack. The proposed approach was checked via a comparison between experimentally measured displacement fields (3D-DIC) and those reconstructed from a modified 2D crack tip model (utilizing either 2, 3, or 4 terms of the William's expansion series) and implementing a 3D geometrical correction. Further validation was provided by comparing model-derived stress intensity factors with values provided by empirical correlations.Ítem Experimental evaluation of effective stress intensity factor using thermoelastic stress analysis and digital image correlation(Elsevier, 2020-02-25) Díaz, Francisco A.; Vasco-Olmo, José M.; López Alba, Elías; Felipe-Sesé, Luis A.; Molina-Viedma, Ángel J.; Nowell, DavidDuring the last decades, the debate over the mechanisms governing fatigue crack shielding has been mainly focused on demonstrating the existence of fatigue crack closure and the difficulties on quantifying the induced stress during crack propagation. Hence, most adopted experimental methods have been based on the direct or indirect measurement of contact loads between crack surfaces as the crack starts closing. Nevertheless, these methods depend on many factors sometime difficult to control, which has contributed to question their reliability by many authors. For this reason, two modern well established, full-field, non-contact experimental techniques, namely Thermoelastic Stress Analysis (TSA) and 2D Digital Image Correlation (2D-DIC), have been analysed to evaluate the influence of crack shielding during fatigue experiments conducted on two aluminium alloys (Al2024-T3 and Al7050) tested at different stress ratios. In the particular case of TSA, the technique appears to have a great potential in the evaluation of fatigue crack shielding since crack tip events are inferred directly from the temperature changes occurring at the crack tip rather than from remote data. Experimental data from both techniques have been employed in combination with two different mathematical models based on Muskhelishvili’s complex potentials to infer the effective range of stress intensity factor. Results from both techniques agree quite well, showing a variation in the stress intensity factor range as the R-ratio changes from 0.1 to 0.5 and illustrating the potential ability of both techniques to account for the shielding effect due to crack closure.Ítem Towards a new methodology for the characterisation of crack tip fields based on a hybrid computational approach.(Elsevier, 2022-04-22) Camacho-Reyes, Alonso; Vasco-Olmo, José M.; James, M. Neil; Díaz, Francisco A.This work presents a hybrid optimisation technique for the simultaneous calculation of crack tip characterising parameters and its spatial location, which can significantly affect the characterising parameters if the position used is inaccurate. The hybrid technique combines initial use of a genetic algorithm to obtain a well-conditioned set of initial parameter values that is then passed to an interior point optimisation algorithm for subsequent fast optimisation. Use of the hybrid technique is also amenable to easy automation. The capability of the technique is demonstrated using the CJP crack tip field model, with digital image correlation (DIC) being used to measure the 2D crack tip displacement field. This model was chosen, not only for its demonstrated sensitivity to accuracy in crack tip location, but also for its proven utility in providing effective crack growth correlation in the presence of plasticity-induced shielding across a wide range of growth rates. The results obtained from the hybrid technique are shown to be reliable through comparison with results obtained using other established techniques.