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THE STRENGTH OF GLASS AS AFFECTED BY CASING 1
Author(s) -
Bailey James
Publication year - 1931
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1931.tb16574.x
Subject(s) - composite material , materials science , modulus , tension (geology) , annealing (glass) , young's modulus , compression (physics) , surface tension , elastic modulus , thermodynamics , physics
Considerable regarding the strengthening of glass by surface chilling has been written. Theoretically it has been shown that the modulus of rupture of slabs toughened glass may have a maximum of 3.4 times that of annealed glass. Complicated shapes and large surfaces cannot be satisfactorily treated by this method. Very similar results may be obtained by the method commonly called “casing,” wherein the article consists of three layers, the two outer ones being of glass having a lower coefficient of expansion than the inner layer. After annealing in the usual way the outer layers are left in compression and the central layer is in tension. By combining these initial stresses with those set up during a test to determine the modulus of rupture, a set of equations was derived. These equations were expressed in graph form, one of which gave the relation of case thickness expressed in tenths of the total thickness to the relative strength compared to flawless annealed glass. A number of curves were shown based upon the ratio of maximum internal tension to the maximum tension at the surface. These curves enabled the proper case thickness to be found in order to develop optimum strength for any assumed ratio of maximum internal tension to external tension. Another graph showed the corresponding initial tension and compression due to casing for the conditions outlined above. These curves showed that the case thickness could vary considerably without greatly affecting the strength and also that the initial stresses are smaller than those usually thought necessary. The maximum relative strength as developed by “casing” had a somewhat smaller value than that developed by “toughening.”