The physical and computing significance of an electrical analogue of creep and recovery

Abstract

The instrument described is basically a simple non-inductive transmission line, made up of identical sections, with the capacitance divided into recoverable and irrecoverable elements, in series, by the use of rectifiers. A voltage programme can be set up and applied automatically to simulate the stressing, and the charge taken by the network, with time, is integrated and recorded as the creep strain analogue. The simple power-type creep curve exhibited by solids (in particular the cubic type) is accurately reproduced. The time-functions which relate the character of the creep in metals with the times of stress and off-stress are very similar to those obtained with the analogue. Creep recovery, permanent flow and creep under changed stress (including reversed stress) can all be satisfactorily handled. The character of transient creep and recovery does not, therefore, demand special models involving arbitrary distributions of relaxation times. Problems must be set up on the machine using data obtained from short-term tests: calculations of prolonged intermittent creep can then be quickly completed. No account can at present be taken of temperature changes. On this basis, a comprehensive analogue creep computer, of a much higher operating speed, appears possible. This would be complex and expensive, but no more so than many analogue machines now in use for other purposes, and the cost and delay of extensive long-term testing would be much reduced.