GB1135836A - Method and apparatus for the determination of principal stresses and their directions - Google Patents

Abstract

1,135,836. Stress computer. MACHINNOELEKTROTECHNITCHESKI INSTITUT. 9 March, 1966, No. 10439/66. Heading G4G. An apparatus for measuring the magnitudes and directions of the principal stresses at a point of the surface of a body stressed by static or dynamic loading comprises plural modulators M 1 , M 2 , M 3 which convert strain signals, received from electric strain gauges operating at the point in the body, into corresponding sinusoidal amplitude-modulated signals, the latter being applied to a combination of selectively interconnected analogue containing units A, B, C, D, E, F and G. These units are such that input signals x, y applied to them produce functions a i x + b i y from units A and E; c i x - d i y from units B, C and D; (x<SP>2</SP> + y<SP>2</SP>)<SP>¢</SP> from unit F, and arc tg (x/y} from unit G, where a i , b i , c i , d i are constants which may be varied as appropriate. The strain gauges may be arranged in standard rectangular or delta rosettes producing strain signals E 1 , E 2 , E 3 , applied to the circuits of Figs. 3(a), 3(b) or alternatively in a T-delta rosette which produces a further strain signal E 4 and requires a further modulator (M 4 ) (Fig. 3 (c), not shown). The principal stresses # min, # max and the angle α between one of the principal stresses and a particular direction of strain are then calculated by the interconnected units A to G according to the formulµ and the particular values of functions f 1 . . . f 4 for predetermined straingauge arrangements being determined according to the corresponding combination of units used, and by varying the constants a i , b i , c i , d i . The values of a min, # max, and α are then represented by the outputs of units D, E and G respectively. It is shown that the requisite functions for different straingauge. arrangements are as follows