Ultrasonic method of measuring residual stress in a pretensioned rod

摘要

To be measured in situ, the residual tension f1 of a bar of the prestress is stretched between two anchors, the trace time - return t1 of an ultrasonic wave between the two ends of the bar, and the f1 by the formula f1 = f0 + kb . (T1 - t0 ). During a calibration carried out without dismantling, the bar is subjected to a traction force variable f, is measured for each value of the trace time - return t of an ultrasonic wave between the two ends of the bar, it records a curve (c) of the force f at the time t, one determines the constant t0 as being the trace time - return t measured for f = o, it approaches the curve, in the vicinity of the value f = 0, by a first straight line (d1) of the slope ka, it approaches a top portion of the curve with a second straight line (d2) of the slope k 1, it determines the constant f0 as being the tensile force f, corresponding to the point of intersection of the first and second straight lines, and it determines the constant kb according to the relationship 1 / kb = (1 / k 1) - (1 / ka).