Crack-Tip Shielding by Swelling in Silica Proved from Measurement
of Crack-Terminating Angles in DCDC-Tests
P. Hetticha, K. G. Schella, *, E. C. Bucharskya, G. Rizzia, S. Wagnera, and T. Fetta
a Karlsruhe Institute of Technology, Institute for Applied Materials, Karlsruhe, 76131 Germany
Correspondence to: *e-mail: g.schell@kit.edu
Received 22 April, 2021
Abstract—Cracks terminating at free surfaces are affected by local stresses in the surface region. Under residual compression, the crack front must retard, whereas residual tensile stresses lead to an advance, both compared with the crack contour in the absence of stresses. This effect can be used for an estimation of residual surface stresses in silica generated during the silica/water reaction and caused by volume swelling. A strong shielding stress intensity factor of about –2.5 MPa√m was found for Double Cleavage Drilled Compression specimens heat-treated for 192 h at 250°C in water vapour under saturation pressure and in liquid water. This result is a clear indication for compressive stresses developing in the water diffusion zone at the surface.
Keywords: residual surface stresses, shielding stress intensity, crack-terminating angles
DOI: 10.1134/S1087659622010060