Measuring mode I cohesive law of wood bonded joints based on digital image correlation and fibre Bragg grating sensors

Abstract

This work addresses the experimental identification of mode I cohesive law of wood bonded joints. The approach combines the double cantilever beam (DCB) test with both digital image correlation (DIC) and embedded fibre Bragg grating (FBG) sensors. The spectrum geometric mean of the FBG reflected spectral response was determined, and the wavelength evolution was used to define the fracture process zone (FPZ) development phase. This evaluation allowed a consistent selection of experimental range of over which the identification procedure of mode I cohesive law is build up. Mode I crack length, Resistancecurve and cohesive law parameters are characterised and discussed. The strain energy release rate (G I) is determined from the P-d curve by the compliance-based beam method (CBBM). The crack tip opening displacement (w I) is determined by post-processing displacements measured by DIC. The cohesive law in mode I (r I-w I) is then obtained by numerical differentiation of the G I-w I relationship.

Biosensor for label-free DNA quantification based on functionalized LPGs

“…An alternative method was used based in a technique developed for the analysis of highly deformed reflection spectra of Fiber Bragg Gratting (FBG) sensors used by (Xavier et al, 2015). This method was modified to fit the LPG transmission spectral features.…”

Fracture characterization of human cortical bone under mode II loading using the end-notched flexure test

“…DIC is an imaged-based technique which provides the measurement of displacements on subregions defined across images of a target object under deformation [11,20,22]. The object surface of interest must be locally characterized by a textured pattern with suitable contrast, isotropy and average size.…”

“…Since measurement noise is prone to be amplified by numerical differentiation, experimental data are fitted using a suitable function approximation to smoothen noise data before differentiation. Attending to a theoretical knowledge of the shape of the G II = f(u) function [2,14,21,22], a suitable trial function can be used in least-squares regression, such as the logistic function [20,22]. However, in order to hold the LT and…”

Photogrammetric, Geometrical, and Numerical Strategies to Evaluate Initial and Current Conditions in Historical Constructions: A Test Case in the Church of San Lorenzo (Zamora, Spain)

“…A total of three virtual extensometers were placed on the ROI: (i) A-A' and B-B' in the longitudinal direction; and (ii) C-C' in the transversal direction. Concerning accuracy, there are different studies [15,21,22] that endorse the DIC's precision for the assessment of the material's mechanical properties. For a standard test configuration, the accuracy may range from values of 0.01-0.04 pixels.…”

“…Once the stress-strain curve has been obtained (by a relationship between the stress applied by the compression press and the strains obtained by DIC) (Figure 3b), it is possible to extract the mechanical properties of the materials as follows (Table 2): (i) the Young Modulus was considered as the ratio between one third of the maximum force achieved and the mean strain provided by the longitudinal extensometers (A-A' and B-B'); (ii) for the Poisson ratio, the relationship between the strains provided by the longitudinal extensometers and those obtained by the transversal extensometer (C-C') was taken into account; and (iii) the compression strength was considered as the maximum pressure supported by the specimen. Concerning accuracy, there are different studies [15,21,22] that endorse the DIC's precision for the assessment of the material's mechanical properties. For a standard test configuration, the accuracy may range from values of 0.01-0.04 pixels.…”