The bending of marble

Abstract

Cut slabs of marble are often noticeably bent. An old marble mantelpiece, say 1·5 metres long, will always show a depression in the middle when tested with a stretched thread. This depression is often 1 to 2 mm., and I have heard of cases where it is much more. My interest in this phenomenon was aroused by a conversation with the late Dr. D. W. Dye, F. R. S., and a few preliminary experiments were made. My first notion was that the marble bent by viscous flow as a stick of sealing wax will do when loaded in the middle, and I even speculated as to whether it would be possible by the continued application of force to bend a piece double. the well-known experiments of Adams and Nicholson on the flow of marble under high pressures seemed at first glance to give this notion some plausibility. Bent pieces of marble were obtained from a local marble merchant, Mr. J. B. Slythe, of Witham. He was not able to say anything definite about strip was supported at the ends with the concave side up, and loaded at the middle with as much weight as it was judged safe to put on. A suitable index was fixed at the middle and observed by a microscope with eyepiece scale. There was noticeable motion the first day, but it rapidly diminished in amount from day to day, until it practically ceased after a few weeks. I then reversed it, thinking that if there were a limit to the bending it would at least be possible to restore its original straightness. Again, there was noticeable motion at first, but it soon almost stopped, and calculation showed that decades would be required at the least to straighten the piece in this way, even under the favourable conditions of the experiment. This made it improbable that the piece could have been bent cold. It then seemed that it might have been bent by the application of force while hot. A similar experiment was accordingly tried at a higher temperature. A strip of new marble was placed on the hot-water pipes, similarly supported at the ends and heavily loaded in the middle. It was covered with cotton-wool lagging, and thus maintained at from 45° to 50° C. throughout the winter. But tests with a spherometer showed that only very slight bending had occurred; and this was nearly all in the first week or two.