Sandwiched‐Beam Procedure for Precracking Brittle Materials

Abstract

A technique for precracking brittle materials is presented. This procedure, which is called the sandwiched-beam (SB) technique, allows the production of sharp throughthickness cracks with predetermined length in specimens with a rectangular section. A bar, in which an initial notch is produced by using a conventional saw, is inserted between two supporting beams and the sandwich assembly is loaded in three-point bending. Conditions can be defined that allow the stable propagation of a sharp flaw from the notch as the applied load is increased. Then, the cracked bar can be used to determine the fracture toughness. The SB technique is applied to different brittle materials, including soda-lime-silica glass, alumina, Si 3 N 4 , a SiC w -Si 3 N 4 composite, graphite, a Ti-Al intermetallic, and Carrara marble.

A method to determine the macroscopic toughness scatter of brittle materials

“…Test methods that measure fracture toughness of materials are necessary for reliable design and accurate failure analysis. For brittle materials, different techniques can be used [1,2]. One key aspect is related to the creation of a sharp (pre)crack in the material.…”

“…One key aspect is related to the creation of a sharp (pre)crack in the material. Various procedures use notches made by a diamond saw, cracks propagating from prenotches or indentation cracks for ceramics [3][4][5]2]. For example, the SENB (i.e., single-edge notched beam) technique uses prenotched beams and the toughness associated with a notch may differ from that of a sharp crack [6].…”

Subcritical crack growth of edge and center cracks in façade rock panels subject to periodic surface temperature variations

“…There are various sources on the mechanical and thermal parameters of marbles, especially Carrara marble (Bortz and Wonneberger, 1997;Mahmutoglu, 1998;Sglavo et al, 1999;Alber and Hauptfleisch, 1999;Cardani and Meda, 1999). Carrara marble had been the choice of structural stones since the time of Renaissances.…”

An ESPI experimental study on the phenomenon of fracture in glass. Is it brittle or plastic?

“…2; when a fracture in glass forms at midspan, the metallic parts refrain the glass element and crack growth is stabilized. A major difference with Sglavo et al (2004) consisted in the use of 1.5 mm-thick ionoplast-polymeric spacers between glass and metal (in this case aluminum), fitted in place after mollification through heating. These efficiently limited the stress concentrations in glass and reduced the shear stress at the interface.…”

“…The natural pre-crack was obtained following the ''sandwich-beam'' method proposed in Sglavo et al (2004). This consists in encompassing the glass beam with two external metallic beams and loading the composite structure under 3P-bending according the scheme described in Fig.…”