Comparison of the sandwiched beam (SB) and opposite roller loading (ORL) techniques for the pre-cracking of brittle materials

The “sandwiched beam” (SB) and “opposite roller loading” (ORL) methodologies suitable to introduce sharp through-thickness cracks in brittle materials are critically reviewed and compared in this work. In both cases a sharp crack is obtained in a notched specimen by means of a suitable loading. In the SB technique the specimen is placed between two support bars and bent in a 3- or 4-point configuration. The ORL procedure is based on the symmetrical loading by four rollers which induces a local tensile stress. Results show that both techniques are successfully usable on brittle materials: in both cases suitable specimens are obtained for fracture toughness measurements. The crack length can be reasonably controlled and varies in a wide range. The SB procedure typically provides cracks with α≌0.5, while shorter cracks are obtained by the ORL technique. Fracture toughness is measured on specimens prepared using the two techniques. The obtained values result in good agreement with literature data.