Non-destructive evaluation of ropes by using transverse impulse vibrational wave method

A non-destructive method for evaluating a rope under tension comprising the steps of:

• striking said rope at a single point with a force transverse to its length, said force sufficient to produce an incident vibrational wave in said rope, said incident vibrational wave travelling said length of said rope and producing flaw-reflected waves upon encountering a flaw in said rope and producing end-reflected waves upon encountering an end of said rope;
• sensing said flaw-reflected waves and said end-reflected waves in said rope at a single point with sensor means adjacent to said rope, said sensor means producing electrical signals having amplitudes directly proportional to amplitudes of said flaw-reflected waves and said end-reflected waves, said electrical signals having a time distribution directly related to a time distribution of said flaw-reflected waves and said end-reflected waves;
• receiving and processing said electrical signals from said sensor means whereby said electrical signals may be depicted graphically by display means in amplitude versus time arrangement;
• displaying said amplitude and said time distribution of said electrical signals with said display means, said amplitude and said time distribution of said electrical signals representative of said amplitude and said time distribution of said flaw-reflected waves and said end-reflected waves;
• monitoring said display means during and after striking said rope to determine said amplitude and said time distribution of said electrical signals produced by said sensor means;
• detecting a sequential pattern of low amplitude electrical signals caused by said flaw-reflected waves intervening higher amplitude electrical signals caused by said end-reflected waves;
• measuring an end-to-end time (t.sub.r) between a first said end-reflected wave and a next said end-reflected wave;
• calculating propagation velocity of said end-reflected waves and said flaw-reflected waves in said rope by a propagation velocity formula
• v=2L/t.sub.r
• where v represents said propagation velocity, L represents said length of said rope and t.sub.r represents said end-to-end time;
• calculating tension on said rope by a rope tension formula
• T=Cv.sup.2
• where T represents said tension on said rope, C represents mass per unit length of said rope and v represents said propagation velocity;
• measuring a flaw-to-end time (t.sub.f) between a first said flaw-reflected wave and a next said end-reflected wave;
• calculating a position of a flaw indicated by said flaw-reflected waves by a flaw position formula
• D=L(t.sub.f /t.sub.r)
• where D represents distance of said flaw from an end of said rope closest to said sensor means, L represents said length of said rope, t.sub.r represents said end-to-end time and t.sub.f represents said flaw-to-end time;
• measuring amplitude (P.sub.i) of a first said end-reflected wave;
• measuring amplitude (P.sub.j) of a next said end-reflected wave;
• measuring distance traveled (L.sub.ij) by said end-reflected waves during a time interval between said first end-reflected wave and said next end-reflected wave;
• and
• calculating an attenuation coefficient for said rope whereby overall flaw population in said rope may be determined by an attenuation coefficient formula
• alpha=-20 log (P.sub.j /P.sub.i)/L.sub.ij
• where alpha represents said attenuation coefficient, P.sub.i represents said amplitude of said first end-reflected wave, P.sub.j represents said amplitude of said next end-reflected wave, L.sub.ij represents said distance travelled by said end-reflected waves during said time interval between said first end-reflected wave and said next end-reflected wave and log indicates a logarithmic function operation.

An apparatus for testing a rope under tension comprising:

• means for striking said rope transversely at a single point to produce an incident vibrational wave along said rope, said incident vibrational wave producing flaw-reflected waves upon encountering a flaw in said rope and producing end-reflected waves upon encountering an end of said rope;
• sensor means fixed in a position adjacent said rope for detecting said flaw-reflected waves and said end-reflected waves in said rope at a single point, said sensor means producing an electrical signal having amplitudes and a time distribution proportional to said flaw-reflected waves and said end-reflected waves;
• means for amplifying said amplitudes of said electrical signal to detectable and measurable levels;
• and
• means for analyzing said electrical signal, said analyzing means detecting and measuring said amplitudes and said time distribution of said electrical signal and discriminating a first portion of said electrical signal indicative of said flaw-reflected waves from a second portion of said electrical signal indicative of said end-reflected waves, so as to locate said flaw.