Fracture resistance of technical and optical glasses: edge flaking of specimens

Abstract

We present the results of fracture resistance tests for technical and optical glasses performed by indentation flaking of the rectangular specimen edge. The features of crack propagation in these glasses are analyzed during chipping fracture caused by indentation with blunt and sharp diamond indenters. By comparative analysis of the values for resistance to edge flaking and those for fracture resistance, new data on the mechanical behavior of the above glasses in fracture are obtained. In particular, it is shown that these glasses, along with ceramic materials used to produce armor, have an enhanced resistance to the onset of fracture.Introduction. The importance of glasses in engineering and daily usage cannot be overestimated. Although glass is a very brittle and catastrophically failing material which, in many applications, is forced to withstand high mechanical loads, its ability to resist fracture has, however, received little attention in recent years. The fracture resistance of glasses is evaluated by the methods developed to test ceramics [1], since there is no standard regulating their specific behavior in fracture. Here, the IF method (Vickers indentation on a polished surface of the specimen and measurement of crack sizes near its indentation corners) is used quite often [2], however, with this method, it is in effect impossible to obtain reliable data on the actual resistance of brittle materials at critical loads [3]. To eliminate random dangerous damage to edges of glass items, facets are applied to them or they are rounded off without any estimates being made for this effect.In view of the above-said, an attempt has been undertaken to study the fracture resistance of glasses [4] using a non-traditional experimental method, such as the EF method (involving the flaking of the rectangular specimen edge [5]), which was found to be efficient in evaluating various ceramics [6, 7, et al.]. This paper presents the results of new investigations in this field, special emphasis being placed on the fracture of glasses with the variation in the stress concentration due to different indenters employed.Materials and Procedures. Silicate glasses (both technical and lead-containing ones (such as flint glass) were the main objects of this investigation, whereas heavy crown glass was the auxiliary object [8]. Specimens of these materials were manufactured in the form of rectangular beams measuring 3 4 20´mm. The specimen surfaces were initially ground, and then their faces of 4 mm in width were buffed. Five such specimens were glued together at the treated faces with the Loctite ® Super Glue (Henkel Corp., USA) to form a package whose planes were additionally ground and subsequently polished. In this way, the sufficient sharpness of rectangular specimen edges and the absence of any chip scars thereon, which are hard to remove by usual mechanical treatment of glasses, were provided.In this paper, the fracture resistance of glasses was evaluated by the SEVNB method [9], according to which the fracture of a rectangular ...

Evaluations on Ceramic Fracture Toughness Measurement by Edge Chipping

“…free edge, until a chip formed. Danzer [47] and Gogotsi [48][49][50][51][52] demonstrated the material independence of chip geometrical similarity by conducting a series of edge-chipping experiments on various kinds of brittle solids, such as ceramics, glass, flint, and quasi-brittle metals. However, they also stated that the chipping force possesses a strong material dependency, indicating a constant quotient between peak chipping force (𝐹 ) and indenting distance (ℎ)-which is defined as the edge toughness (ET) of the material-to evaluate the resistance of an edge to damage.…”