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

• US 4,979,125 A
• Filed: 04/13/1990
• Issued: 12/18/1990
• Est. Priority Date: 11/20/1987
• Status: Expired due to Fees

• Current Assignee: Southwest Research Institute
• Original Assignee: Southwest Research Institute
• Inventors: Burkhardt, Gary L., Kwun, Hegeon
• Primary Examiner(s): Lall, Parshotam S.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US07/512,037
• Time in Patent Office: 249 Days
• Field of Search: 364/507, 364/508, 364/552, 364/469, 73/596, 73/598, 73/599, 73/600, 73/602, 73/651, 73/158, 340/677, 340/683
• US Class Current: 702/35
• CPC Class Codes: B65H 63/06 responsive to presence of irregularities in running material, e.g. for severing the material at irregularities ; Control of the correct working of the yarn cleaner
• CPC Class Codes: G01H 1/04 of vibrations which are transverse to direction of propagation
• CPC Class Codes: G01N 2291/2626 Wires, bars, rods
• CPC Class Codes: G01N 29/045 by imparting shocks to the workpiece and detecting the vibrations or the acoustic waves caused by the shocks measuring resonant frequency G01H13/00; measuring strength properties by application of mechanical stress G01N3/00
• CPC Class Codes: G01N 29/227 related to high pressure, tension or stress conditions

Abstract

A non-destructive method for evaluating ropes, cables, and strands for flaws and tension is shown. The method permits detecting flaws by recognizing certain vibrational wave amplitude and distribution patterns resulting from striking a test subject with a transverse force. Tension on a test subject is calculated by measuring propagation velocity of the vibrational waves through the test subject. An apparatus is provided which produces vibrational waves in a test subject, measures the amplitude and time distribution of the waves, and displays the measurements for analysis.

Claims

1. 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; and

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.

2. The method of claim 1 further comprising the steps of:

measuring an end-to-end time (t_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

space="preserve" listing-type="equation">v=2L/t.sub.r

where v represents said propagation velocity, L represents said length of said rope and t_r represents said end-to-end time;

calculating tension on said rope by a rope tension formula

space="preserve" listing-type="equation">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.

3. The method of claim 2 further comprising the steps of:

measuring a flaw-to-end time (t_f), between a first said flaw-reflected wave and a next said end-reflected wave; and

calculating a position of a flaw indicated by said flaw-reflected waves by a flaw position formula

space="preserve" listing-type="equation">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_r represents said end-to-end time and t_f represents said flaw-to-end time.

4. The method of claim 3 further comprising the steps of:

measuring amplitude (P_i) of a first said end-reflected wave;

measuring amplitude (P_j) of a next said end-reflected wave;

measuring distance traveled (L_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

space="preserve" listing-type="equation">alpha=-20 log (P.sub.j /P.sub.i)/L.sub.ij

where alpha represents said attenuation coefficient, P_i represents said amplitude of said first end-reflected wave, P_j represents said amplitude of said next end-reflected wave, L_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.

5. The method of claim 4 further comprising the step of connecting computing means to said display means, said computing means receiving data representing said amplitude of said flaw-reflected waves and said end-reflected waves and said time distribution of said flaw-reflected waves and said end-reflected waves;

said computing means receiving input of said length of said rope and said mass per unit length of said rope;

said computing means deriving said t_r, said t_f, said P_j, said P_i, and said L_ij from said data;

said computing means calculating said flaw position by said flaw position formula, said tension on said rope by said tension formula, and said attenuation coefficient by said attenuation coefficient formula.

6. 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_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

space="preserve" listing-type="equation">v=2L/t.sub.r

where v represents said propagation velocity, L represents said length of said rope and t_r represents said end-to-end time;

calculating tension on said rope by a rope tension formula

space="preserve" listing-type="equation">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_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

space="preserve" listing-type="equation">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_r represents said end-to-end time and t_f represents said flaw-to-end time;

measuring amplitude (P_i) of a first said end-reflected wave;

measuring amplitude (P_j) of a next said end-reflected wave;

measuring distance traveled (L_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

space="preserve" listing-type="equation">alpha=-20 log (P.sub.j /P.sub.i)/L.sub.ij

where alpha represents said attenuation coefficient, P_i represents said amplitude of said first end-reflected wave, P_j represents said amplitude of said next end-reflected wave, L_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.

7. The method of claim 6 further comprising the step of connecting computing means to said display means, said computing means receiving data representing said amplitude of said flaw-reflected waves and said end-reflected waves and said time distribution of said flaw-reflected waves and said end-reflected waves;

said computing means receiving input of said length of said rope and said mass per unit length of said rope;

said computing means deriving said t_r, said t_f, said P_j, said P_i, and said L_ij from said data;

said computing means calculating said flaw position by said flaw position formula, said tension on said rope by said tension formula, and said attenuation coefficient by said attenuation coefficient formula.

8. 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.

9. The apparatus for testing a rope as given in claim 8 wherein said analyzing means includes a digitizing oscilloscope for generating a visually perceptible indication of said electrical signal.

10. The apparatus for testing rope as given in claim 9 wherein said analyzing means further includes electronic data processing means, said electronic data processing means receiving output data from said digitizing oscilloscope, said electronic data processing means calculating from said output data a distance from said end of said rope to said flaw.

11. The apparatus for testing a rope as given in claim 8 including between said amplifying means and said analyzing means a signal conditioner to eliminate unwanted noise from said electrical signal.