Analysis of macroscopic crack branching patterns in chemically strengthened glass
- PDF / 939,791 Bytes
- 12 Pages / 585 x 783 pts Page_size
- 9 Downloads / 234 Views
R. Tandona) and S.J. Glass, Sandia National Laboratories, Albuquerque, New Mexico 87185
J.J. Mecholsky, Jr. University of Florida, Gainesville, Florida 32611 (Received 7 August 2007; accepted 25 September 2007)
Residual stress profiles were introduced in sodium aluminosilicate glass disks using an ion-exchange process. They were fractured in two loading conditions: indentation and biaxial flexure. The fractal dimension of the macroscopic crack branching pattern called the crack branching coefficient (CBC), as well as the number of fragments (NOF) were used to quantify the crack patterns. The fracture surfaces were analyzed to determine the stresses responsible for the crack branching patterns. The total strain energy in the body was calculated. The CBC was a good measure of the NOF. They are directly related to the tensile strain energy due to the residual stress profile for fractures due to indentation loading. However, in general for materials with residual stresses, CBC (or NOF) is not related to the strength or the stress at fracture, or even to the total stored tensile strain energy. Instead, the CBC appears to be related, in a complex manner, to the distribution of stresses in the body. Therefore, in general, the characterization of the CBC of fractured materials cannot be used to ascertain the prior stress distribution.
I. INTRODUCTION
Glass is a brittle material and fails catastrophically at stresses well below its theoretical strength. It also has very low reliability (i.e., it fails over a wide range of stresses) and produces fragments that are large and have sharp edges. Characterizing and understanding the fragmentation behavior of glass is critical in several aspects of national security. For instance, during the Oklahoma City bombing in 1995, glass was broken in some 300 nearby buildings and as far away as one mile; the resulting glass shards injured more than 400 people.1 Fragmentation phenomena are also encountered in the fracture of glass (or glass-like) armor materials under ballistic impact. In service, glass failures may occur with vastly different degrees of severity and violence depending on the loading conditions. For instance, a crack in the windshield of an automobile that is initiated by a pebble impact may propagate over a period of months to traverse the entire glass pane. However, under shock loading
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0020 214 J. Mater. Res., Vol. 23, No. 1, Jan 2008 http://journals.cambridge.org Downloaded: 14 Mar 2015
(such as in an accident), the same windshield may shatter into numerous fragments. In the laboratory, simulating complex loading conditions is not easily accomplished; however, as will be shown, valuable insight into fragmentation behavior may be gained by subjecting glass to tempering treatments that dramatically change its strength. An additional benefit of this approach is that tempered glasses are used in a variety of applications, and the knowledge gained may be directly applicable.
Data Loading...
