Examinando por Autor "Diaz-Garrido, Francisco Alberto"
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Ítem A meshfree approach for analyzing strain fields near crack tips from Digital Image Correlation displacement data(Wiley, 2024-03-24) Gómez-Gonzales, Giancarlo Luis; Camacho-Reyes, Alonso; Ortiz-González, Julián Andrés; Diaz-Garrido, Francisco AlbertoThe element-free Galerkin (EFG) meshfree method is employed in this research to compute strain fields based on discrete displacement data obtained from digital image correlation (DIC). To validate the method's accuracy, both simulated images with highly heterogeneous deformations and real tests conducted on notched specimens with known solutions are initially employed. The study then investigates the strain field near the crack tip in an AISI 1020 steel specimen through a multiscale experiment. From the macroscale experiment, the strain data are used to determine the crack-tip plastic zone size, and the solution is compared with predictions from linear-elastic fracture mechanics. The stress intensity factor is also determined. Furthermore, the high strain gradient ahead of the crack tip is determined from the microscale experiment and compared against commercial DIC software. Experimental results confirm the effectiveness of the proposed formulation in crack tip analysis.Ítem Characterisation of fatigue crack growth using digital image correlation measurements of plastic CTOD.(Elsevier, 2019-03-27) Vasco, José Manuel; Diaz-Garrido, Francisco Alberto; Antunes, Fernando Ventura; James, NeilCrack tip opening displacement (CTOD) was measured using digital image correlation (DIC) and resolved into elastic and plastic CTOD components via an offset compliance technique. The plastic CTOD range gave a single linear correlation for fatigue crack growth rate at stress ratios of 0.1 and 0.6 in compact- tension (CT) specimens of Grade 2 titanium. A sensitivity analysis was performed to find the optimum position in the crack wake to make the CTOD measurements. The results are the first time (to the authors knowledge) that plastic CTOD has been found directly from experimentation and demonstrate that plastic CTOD is a useful alternate characterising parameter for fatigue crack growth to the stress intensity factor defined by Irwin.Ítem Experimental analysis of the plastic CTOD to characterize the variable amplitude fatigue crack growth in Grade 2 titanium samples(Elsevier, 2023-05-23) Gómez-Gonzales, Giancarlo Luis; Vasco, José Manuel; Antunes, Fernando Ventura; Neto, Diogo Mariano; Diaz-Garrido, Francisco AlbertoIn this paper, the plastic component of the crack-tip opening displacement (CTODp) is experimentally evaluated to characterize the fatigue crack growth behavior in a Grade 2 titanium sample under single overload with constant amplitude loading conditions. The CTOD measurements were performed with the 2D-Digital Image Correlation (DIC) technique. The experimental results show a linear correlation between CTODp and fatigue crack growth rates, suggesting the independence of this relationship to load-interaction effects. Therefore, this study demonstrates that the CTODp can be a suitable crack-driving parameter to study crack propagation behavior under variable amplitude loading. Furthermore, it suggests that the fatigue crack growth process is primarily caused by cyclic plastic deformation.Ítem Experimental evaluation of plastic wake on growing fatigue cracks from the analysis of residual displacement fields(Wiley, 2022-02-19) Vasco, José Manuel; Diaz-Garrido, Francisco Alberto; Camacho-Reyes, Alonso; James, Neil; Antunes, Fernando VenturaA growing fatigue crack gives rise to a plastically deformed wake of material that envelops the crack. In this work, the plastic wake extent during fatigue crack growth is experimentally quantified by analyzing the crack tip displacement fields measured with digital image correlation. A novel technique based on use of a yield criterion is proposed that uses the undamaged state of the specimen as the reference state in the image processing. The plastic wake was identified by differentiation of the residual displacement fields obtained with a near-zero load level to avoid any rigid body motion. The plastic wake extent was then found by assuming that the boundary between the elastic and plastic regions would occur when the equivalent stress was higher than the yield stress of the material. The results presented can contribute to a better understanding of the mechanisms driving fatigue crack propagation.Ítem Investigation of Plasticity Effects on Growing Fatigue Cracks Using the CJP Model of Crack Tip Fields(MDPI, 2023-08-22) Vasco, José Manuel; Camacho-Reyes, Alonso; Gómez-Gonzales, Giancarlo Luis; Diaz-Garrido, Francisco AlbertoA growing fatigue crack gives rise to a plastic enclave that envelops the crack and can exert a shielding effect on the crack from the global elastic stress field driving fatigue propagation. This work presents the potential of the CJP model of crack tip fields to investigate the plasticity-induced shielding effects on growing fatigue cracks as well as its ability to characterise the size and shape of the plastic zone generated at the tip of a growing fatigue crack. The model was specifically developed to consider the influence of the plastic enclave generated around a fatigue crack on the surrounding elastic material. Different aspects related to fracture mechanics and its implications for fatigue crack growth have been investigated, namely plasticity-induced crack shielding, the retardation effect induced on fatigue crack growth due to the application of an overload and the estimate of the size and shape of the crack tip plastic zone. The model has been successfully applied by analysing displacement fields experimentally measured by DIC in different CT specimens made of 2024-T3 aluminium alloy and commercially pure titanium. Results presented in this work intend to contribute to a better understanding of the shielding effects during fatigue crack growth.Ítem Limitations of small-scale yielding for fatigue crack growth(Elsevier, 2021-05-28) da-Silva-Veloso-Marques, Bruno Miguel; Borges, Micael Frias; Antunes, Fernando Ventura; Vasco, José Manuel; Diaz-Garrido, Francisco Alberto; James, NeilThe work described here has led to a simple criterion that defines the boundary of the small-scale yielding, SSY, regime to avoid invalid use of the LEFM parameter, ΔK, as the characterising parameter for fatigue crack growth rate. The approach proposed is based on the analysis of crack tip opening displacement, CTOD, and its separation into elastic and plastic components. SSY conditions are shown to dominate when the elastic component of CTOD is >75% of the total CTOD measured at a distance of 8 μm (the finite element mesh size) behind the crack tip, i.e., Δδe/Δδt > 75%. Large-scale yielding, LSY, conditions become dominant for relatively large values of plastic CTOD, Δδe/Δδt < 60%. An increase in crack length (and therefore of ΔK), a decrease in yield stress of the material and the existence of plane stress conditions all promote LSY. The results obtained from various loading and geometric conditions simulated in this work demonstrate that caution should be used in assuming that the use of ΔK is valid even for high strength alloys like Ti6Al4V. In this material, the boundary of the elastic regime was crossed and SSY conditions lost, for the longest crack lengths studied and in the case of overloads.Ítem On the experimental characterisation of crack tip displacement fields on nonplanar elements: Numerical and experimental analysis(Elsevier, 2023-02-04) Camacho-Reyes, Alonso; Antunes, Fernando Ventura; Vasco, José Manuel; Diaz-Garrido, Francisco Alberto; Felipe-Sesé, LuisIn this work, a numerical and experimental study about crack tip fields characterisation on curve-cracked elements has been performed. This study combines a novel differential geometry approach combined with 3D-DIC and FEA results to determine crack-tip parameters from the displacement field on a curved cracked element. The work aims to validate and compare some aspects that cannot be addressed using 3D-DIC. SIFs for different crack lengths are determined using DIC and FEA data and compared In addition, a comprehensive comparison between experimental and numerical fields is done using an Image Decomposition technique based on Tchebichef polynomials.Ítem Plastic CTOD as fatigue crack growth characterising parameter in 2024-T3 and 7050-T6 aluminium alloys using DIC(Wiley., 2020-03-03) Vasco, José Manuel; Diaz-Garrido, Francisco Alberto; Antunes, Fernando Ventura; James, NeilThe plastic range of crack tip opening displacement (CTOD) has been used for the experimental characterisation of fatigue crack growth for 2024-T3 and 7050-T6 aluminium alloys using digital image correlation (DIC). Analysis of a complete loading cycle allowed resolving the CTOD into elastic and plastic components. Fatigue tests were conducted on compact tension specimens with a thickness of 1 mm and a width of 20 mm at stress ratios of 0.1, 0.3 and 0.5. The range of plastic CTOD could be related linearly to da/dN independent of stress ratio for both alloys. To facilitate accurate measurements of CTOD, a method was developed for correctly locating the crack tip and a sensitivity analysis was performed to explore the effect of measurement position behind the crack tip on the CTOD. The plastic range of CTOD was demonstrated to be a suitable alternate parameter to the stress intensity factor range for characterising fatigue crack propagation. A particularly innovative aspect of the work is that the paper describes a DIC-based technique that the authors believe gives a reliable way to determine the appropriate position to measure CTOD.Ítem Study of Effective Stress Intensity Factor through the CJP Model Using Full-Field Experimental Data(MDPI, 2023-08-20) Camacho-Reyes, Alonso; Vasco, José Manuel; Gómez-Gonzales, Giancarlo Luis; Diaz-Garrido, Francisco AlbertoIn this work, the Christopher–James–Patterson crack tip field model is used to infer and assess the effective stress intensity factor ranges measured from thermoelastic and digital image correlation data. The effective stress intensity factor range obtained via the Christopher– James–Patterson model, which provides an effective rationalization of fatigue crack growth rates, is separated into two components representing the elastic and retardation components to assess shielding phenomena on growing fatigue cracks. For this analysis, fatigue crack growth tests were performed on Compact-Tension specimens manufactured in pure grade 2 titanium for different stress ratio levels, and digital image correlation and thermoelastic measurements were made for different crack lengths. A good agreement (~2% average deviation) was found between the resultsobtained via thermoelastic stress analysis and digital image correlation indicating the validity of theChristopher–James–Patterson model to investigate phenomena in fracture mechanics where plasticityplays an important role. The results show the importance of considering crack-shielding effects usingthe Christopher–James–Patterson model beyond considering an exclusive crack closure influence.