Measurement of R-curve in clay brick blocks using optical measuring technique

• Digital Image Correlation was used to measure R-curve of clay brick blocks.
• DIC allows to collect data from crack propagation up to the total rupture of samples.
• An average KIC of clay brick blocks equal to 0.36 MPa m1/2 was estimated.
• A quite accurate R-curve of clay brick blocks was traced.

Clay brick has proven to be a very brittle material and is very difficult to calculate the fracture toughness because of the right identification of crack-tip position with standard techniques. The aim of this investigation is to determine the stress intensity factor and to draw the R-curve of clay brick blocks by using Digital Image Correlation (DIC) method. After-the-notch pre-cracks are introduced in 30 × 260 × 60 mm notched samples by using sandwiched beam technique. The DIC method is used to measure the full displacement fields on the sample’s surface, and the crack tip position is then reconstructed by post-processing the experimental data. Due to the high precision of the DIC, we have collected many points during crack propagation, thus we have obtained a quite accurate R-curve. An average critical stress intensity factor of clay brick blocks equal to about 0.36 MPa m1/2 was estimated.