Experimental evaluation of plasticity-induced crack shielding from crack tip displacements fields

In this work it is proposed a methodology for the evaluation of plasticity-induced crack shielding from the analysis of the crack tip displacements fields measured by digital image correlation. This methodology is based on the evaluation of the stress intensity factors determined from the displacements fields measured at the vicinity of the tip of a growing fatigue crack. For the characterisation of the crack tip displacements field, CJP model has been implemented. This model considers the shielding effects due to plasticity generated during fatigue crack growth. For the purpose of the current work, several fatigue experiments at different R-ratios have been conducted on Al2024-T3 compact tension specimens. In addition, compliance based methods have been adopted to perform a comparison of the results with those obtained by DIC. Results show a good level of agreement, illustrating the enormous potential of DIC technique for the study of fracture mechanics problems

Fatigue crack characterisation in 2024-T351 aluminium alloy through SEM observation combined with the CJP model

This work characterises crack growth in AA2024-T315 by combining different methods to further increase the reliability of the results. The Christopher-James-Patterson (CJP) model was fitted to experimental data obtained by digital image correlation (DIC). The effective value of the CJP stress intensity factors were successfully correlated with the ΔK-da/dN curve as obtained with Scanning Electron Microscopy measurements of the depth of striations on the fracture surface. This approach based on fitting the CJP model with DIC data and SEM observations allowed estimation of opening and closure loads and allowed the propagation rate and fracture mode to be effectively characterised.The authors would like to acknowledge the financial support of Programa Operativo FEDER from the Junta de Andalucia (Spain) through grant reference UMA18-FEDERJA-250. Industrial support from Bettergy SL and from Dr N Ordonez and M Carrera is also greatly acknowledged, as well as access to different components and materials in the energy industry. The authors would also like to acknowledge the financial support from Junta de Andalucia through the research project “1380786” funded by the program “Proyectos de I + D + I en el Marco del Programa Operativo FEDER Andalucia 2014-2020. Convocatoria 2020.” We would also like to acknowledge funding for open access charge: Universidad de Malaga / CBU

Investigation of effective stress intensity factors during overload fatigue cycles using photoelastic and DIC techniques

© 2018 Elsevier Ltd This work uses DIC and photoelastic techniques to investigate the effect of single overload cycles applied during constant amplitude fatigue. Effective values of the range of stress intensity factor were calculated using the CJP model of crack tip stress and displacement fields, as this model considers both wake contact and compatibility-induced influences on the applied elastic field arising from the plastic enclave generated around a fatigue crack. Values of the effective stress intensity factor are related to the observed crack growth acceleration and retardation. In addition, the paper compares the CJP results with those obtained using a compliance-based method. The present work demonstrates the utility of the CJP model in characterising fatigue crack growth rates during variable amplitude loading. It is also possible with the CJP model, through changes in the coefficient values and hence, for the first time, to shed explicit light on the contributions made by different mechanisms to the shielding effects of an overload

Experimental evaluation of plasticity-induced crack shielding from crack tip displacements fields

In this work it is proposed a methodology for the evaluation of plasticity-induced crack shielding from the analysis of the crack tip displacements fields measured by digital image correlation. This methodology is based on the evaluation of the stress intensity factors determined from the displacements fields measured at the vicinity of the tip of a growing fatigue crack. For the characterisation of the crack tip displacements field, CJP model has been implemented. This model considers the shielding effects due to plasticity generated during fatigue crack growth. For the purpose of the current work, several fatigue experiments at different R-ratios have been conducted on Al2024-T3 compact tension specimens. In addition, compliance based methods have been adopted to perform a comparison of the results with those obtained by DIC. Results show a good level of agreement, illustrating the enormous potential of DIC technique for the study of fracture mechanics problems