Determining mode II cohesive law of Pinus pinaster by combining the end-notched flexure test with digital image correlation

This work aims to determine the orthotropic linear elastic constitutive parameters of Pinus pinaster Ait. wood from a single uniaxial compressive experimental test, under quasi-static loading conditions, based on two different specimen configurations: (a) on-axis rectangular specimens oriented on the radial-tangential plane, (b) off-axis specimens with a grain angle of about 60(radial-tangential plane). Using digital image correlation (DIC), full-field displacement and strain maps are obtained and used to identify the four orthotropic elastic parameters using the finite element model updating (FEMU) technique. Based on the FE data, a synthetic image reconstruction approach is proposed by coupling the inverse identification method with synthetically deformed images, which are then processed by DIC and compared with the experimental results. The proposed methodology is first validated by employing a DIC-levelled FEA reference in the identification procedure. The impact of the DIC setting parameters on the identification results is systematically investigated. This influence appears to be stronger when the parameter is less sensitive to the experimental setup used. When using on-axis specimen configuration, three orthotropic parameters of Pinus pinaster (ER, ET and νRT) are correctly identified, while the shear modulus (GRT) is robustly identified when using off-axis specimen configuration.

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SIF determination with digital image correlation

International Journal of Structural Integrity ◽

10.1108/ijsi-03-2015-0010 ◽

2015 ◽

Vol 6 (6) ◽

pp. 668-676 ◽

Cited By ~ 10

Author(s):

Paulo J Tavares ◽

Tiago Ramos ◽

Daniel Braga ◽

Mario A P Vaz ◽

Pedro Miguel Guimarães Pires Moreira

Keyword(s):

Experimental Data ◽

Digital Image Correlation ◽

Digital Image ◽

Fatigue Testing ◽

Image Correlation ◽

Image Method ◽

Mode Ii ◽

Pure Mode ◽

Great Success ◽

Content Type

Purpose – Hybrid methods, wherefore numerical and experimental data are used to calculate a critical parameter, have been used for several years with great success in Experimental Mechanics and, in particular, in fracture mechanics. The purpose of this paper is to report on the comparison of the strain field from numerical modelling forecasts against the experimental data obtained with the digital image correlation method under Mode II loading in fatigue testing. The numerical dual boundary element method has been established in the past as a very reliable method near singular regions where stresses tend to grow abruptly. The results obtained from the strain data near the crack tip were used in Williams expansion and agree fairly well with both the numerical results and the analytical solution proposed for pure Mode II testing. Design/methodology/approach – The work presented in this note is experimental. The proposed methodology is of an hybrid experimental/numerical nature in that a numerical stress intensity factor calculation hinges upon a stress field obtained with an image method. Findings – The obtained results are an important step towards the development of a practical tool for crack behaviour prediction in fatigue dominated events. Research limitations/implications – The results also stress the necessity of improving the experimental techniques to a point where the methods can be applied in real-life solicitations outside of laboratory premises. Originality/value – Although several research teams around the globe are presently working in this field, the present research topic is original and the proposed methodology has been presented initially by the research team years ago.

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