The Effect of Transverse Scratches on the Strength of Sheet Glass

JSGT 1937 V21 T383-T394

The effect of transverse scratches made by a .cutting diamond on the strength of strips of flat drawn sheet glass of mean thickness 0·275 cm and 0·8 cm wide, has been investigated with particular reference to (1) the load on the diamond when making the scratch, (2) the time interval between scratching and breaking, and (3) the rate of scratching. For loads less than 300 g the strength was proportional to the scratch width, but above 500 g increasing the load had little effect on the strength. The minimum width which brings about a reduction in strength is different for the ordinary cutting diamond on the one hand, and a conically ground and polished diamond or a gramophone needle on the other. The effect is probably dependent on the form of the scratch and on its depth. With low rates of scratching the diamond scratch was not so efficient in reducing the strength of the strip, the greatest reduction in strength resulting from scratching at 8 cm/s. The effectiveness of the scratch is reduced by increasing the time interval between scratching and breaking. It was noted that the deviation of the breaking strength values from the mean was substantially less in the case of scratched than the unscratched specimens.

A. J. Holland & W. E. S. Turner