Glass fracture in edge flaking

Abstract

Fracture resistance of technical quartz and normal window glasses was investigated in testing polished rectangular parallelepipeds by edge flaking their long edges with Rockwell and Vickers indenters (EF method) and by scratching the specimen surface with a Rockwell indenter followed by flaking its edge (S+EF method). It was established that the fracture of those glass specimens in their edge flaking with a Rockwell indenter was started with the formation of a Hertzian ring crack and their corresponding chip scars had the form of Hertzian "quasi-cones." Fractographic data were used in analysis of test results.Introduction. One can hardly find any field of human activities where silicate glasses are not in use. Despite brittleness and inconsiderable deformability inherent in such materials, they turn out indispensable for many technical and other fields of application. This gives impetus to studies on the mechanical behavior of those materials and, in particular on their ability to resist fracture. Their fracture toughness was evaluated by different methods, including fracture of the specimen surface with sharp and blunt indenters [1]. As a result, a great body of experimental data was accumulated, which contributed to the enhancement of glass capabilities and to the gain in reliability of glass items in operation.As was mentioned earlier [2], glass is a material very complicated for comprehension. Its fracture behavior is still not clearly understood, and the choice of an optimum method for determining its fracture resistance is unresolved as yet. Therefore, the investigation of glass fracture in flaking the edges of rectangular parallelepipeds with standard indenters was carried out, which turned out to be an effective approach to studying different ceramics and allowed new information on their behavior under loading to be obtained [3].Materials and Methods. This investigation was targeted for getting the general notion of glass behavior in its edge flaking. For this purpose the two types of glass varying in their compositions were taken: "normal" (silica contents are less than 70-75%) and "anomalous", i.e., containing up to 99.9% silica [4]. The mechanical behavior of the former is believed to be similar to the behavior of other brittle materials, while glass of the second type exhibits certain differences associated with its structure. Therefore, both technical quartz glass, containing about 90-95% silica doped with Na 2 O and Al 2 O 3 , and normal window glass with about 72% silica were studied. Experiments were also performed on industrial hardened sheet glass. Those glasses were manufactured commercially, thus, their correct compositions, being "know-how" of enterprises, are unknown.The tests made use of specimens in the form of polished rectangular beams of standard sizes (3 4 × -mm

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

“…The comparison of the present test results with those obtained earlier [4,11], has shown that, while not contradicting each other, these results only increase the amount of useful information on the behavior of glasses under the loading conditions considered. In the analysis, the results were plotted on the base diagram [12] where both the relation between the fracture resistance F R and the critical stress intensity factor K c I values (the EF base line) [5] and the relation constructed using the values of the fracture resistance F RV of specimens in edge flaking caused by indentations with a Vickers indenter [11] are presented (Fig.…”

Glasses: New approach to fracture behavior analysis

“…Then the chip separates from its body when the contact point of the indenter approaches closer the specimen edge. And the chip scar on the side surface acquires the form of a Hertzian quasi-cone [21]. Secondary cracks continue growing till no less than a half of the ring crack is formed, then only fragments of ring cracks develop without additional cracking (Fig.…”

Numerical analysis of glass edge chipping by impact loading

“…In the early works, Almond and McCormick (1986) examined chipping of various brittle materials using a conical diamond indenter and observed that the size of chip scars depended on the indentation distance d (distance between an indentation point and an edge). Also, several researches investigated the critical indent force F required for edge chipping and found that there were linear correlation between F and d (Chai and Lawn 2007a;Gogotsi and Mudrik 2009;Gogotsi et al 2007;Morrell and Gant 2001). The ratio of F to d is referred to as "edge toughness" and the edge toughness depends only on the investigated material and the indenter geometry (Danzer and Hangl 2001).…”

“…The ratio of F to d is referred to as "edge toughness" and the edge toughness depends only on the investigated material and the indenter geometry (Danzer and Hangl 2001). Therefore, several attempts have been made to predict the fracture toughness K c from the edge toughness whose value is given by the edge chipping test (Chai and Lawn 2007b;Danzer and Hangl 2001;Gogotsi 2013;Gogotsi and Mudrik 2009;Gogotsi et al 2007;Morrell and Gant 2001). For example, Chai and Lawn (2007b) performed the edge chipping tests of soda-lime glass by Vickers indentation and reported that they could provide the value of K c directly from the critical indent force F to within an accuracy of about 25%.…”