The Effect of Width on the Breaking Strength of Sheet Glass
JSGT 1936 V20 T072-T083
A more detailed study than in our previous paper has been made of the effect of width on the modulus of rupture of strips of 26 oz sheet glass varying from approximately 0·4 to 1·2 cm in width, the sides of the strips being in different cases (a) ground and mechanically polished, (b) ground and mechanically polished followed by fire polishing, (c) cut with the diamond and tested with the residual flaws in tension. Progressive increase in the modulus of rupture was found with diminution in width. For fire finished strips of 0·395 cm width, values as high as nearly 1700 kg/cm2 were obtained, the mean being 1299. It was demonstrated that the Karmarsch equation relating the strength (F) of metallic wires to their diameter d, namely, F=a+b/d, where a and b are constants, applies equally well to our results in which d is regarded as the width of the specimen. From Griffith's modified equation, values for the “ultimate strength” of glass were calculated. Straight fractures were consistently obtained for widths of 0·7 cm (and, in general, below 0·8 cm) when the sides were not fire polished. In the latter condition more complex fractures were either usual or at least frequent even for specimens of 0·4 cm width.
A. J. Holland & w. E. s. Turner
