Damage detection device and method

• US 6,748,791 B1
• Filed: 10/06/1997
• Issued: 06/15/2004
• Est. Priority Date: 10/18/1996
• Status: Expired due to Term

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Georgeson, Gary E., Kollgaard, Jeffrey R., Lea, Scott W., Hansen, Jeffrey M., Bopp, J. Robert
• Primary Examiner(s): Noori, Max
• Application Number:
  US08/944,885
• Time in Patent Office: 2,444 Days
• Field of Search: 73/120.1, 73/120.4, 73/120.5, 73/120.6, 73/120.7, 73/121.3
• US Class Current: 73/12.13
• CPC Class Codes: G01M 7/08 Shock-testing
• CPC Class Codes: G01N 2203/0039 Hammer or pendulum
• CPC Class Codes: G01N 2203/0658 using acoustic or ultrasonic detectors
• CPC Class Codes: G01N 2291/0231 Composite or layered materials
• CPC Class Codes: G01N 2291/0258 Structural degradation, e.g. fatigue of composites, ageing of oils
• CPC Class Codes: G01N 2291/02827 Elastic parameters, strength or force
• 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 29/4427 with stored values, e.g. threshold values
• CPC Class Codes: G01N 3/30 by applying a single impulsive force, e.g. by falling weight

Abstract

A damage detection device is used to detect damage in bonded and laminated composite structures. A tap hammer or tap coin containing an acceleration sensor is connected to a circuit that can measure the width of an impact signal and then display the result. The result correlates to local stiffness of a structure. A method of determining the desired signal width and the method of using the damage detection device, includes tapping a known good region and then tapping a suspect region. Readings from the two areas are used to determine whether the suspect region is within an acceptable range. The circuit determines the desired signal width by measuring from the time the impact signal exceeds a threshold to the time it falls below the threshold.

Claims

1. An apparatus for detecting defects in composite structures, comprising:

(a) a head for striking a suspect area on the composite structure,

(b) an accelerometer sensor mounted inside the head for detecting impact of the head against the composite structure and producing an impact signal,

(c) a circuit connected to the sensor for converting the impact signal into a representative alphanumeric readout value by determining whether the impact was adequate to reliably measure characteristics of the impact signal representing the integrity of the composite, the circuit including a threshold comparator to make such determination, and, if the impact was adequate by rising above a predetermined threshold value, measuring with a clock the length of time that the impact was above the threshold value, the clock producing the readout value in the form of the measured, elapsed time or an equivalent value; and

(d) an alphanumeric readout for displaying the readout value.

2. A method of determining an impact width from a test tap, comprising:

(a) receiving an impact signal from an acceleration sensor;

(b) passing the signal to a timing circuit in the event that the impact signal reaches in amplitude a timing threshold;

(c) starting a clock upon passing the signal to the timing circuit and timing the duration of the amplitude of the impact signal above the timing threshold;

(d) stopping the clock once the impact signal falls in amplitude below the timing threshold;

(e) detecting with circuitry associated with the accelerometer whether the impact signal reached a predetermined, high amplitude threshold above the timing threshold to determine that the impact signal was created by an impact adequate for making reliable measurements of the integrity of the composite;

(f) displaying an “

insufficient impact”

signal on an alphanumeric display associated with the accelerometer, if the high amplitude threshold has not been reached; and

(g) displaying as a number on the display representative of the time measured by the timing circuit, if the high amplitude threshold has been reached.

3. A method of detecting defects in composite structures, comprising the steps of:

(a) manually striking a hand-held tool including an accelerometer against a composite structure to produce an impact;

(b) determining whether the impact was adequate to allow a reliable measurement of integrity of the composite structure by determining with a comparator connected to the accelerometer whether the impact produces a signal in the accelerometer that has an amplitude above a predetermined threshold;

(c) if the impact was above the threshold, then measuring the length of time in seconds that the signal remains above a measurement amplitude threshold by triggering a clock upon the rise and fall of the test signal;

(d) displaying the time as a value on an alphanumeric readout; and

(e) reading the time value displayed on an alphanumeric output display.

4. A method of detecting defects in composite structure, comprising the steps of:

(a) manually striking an accelerometer by hand against a composite structure to produce an output signal;

(b) amplifying the output signal;

(c) determining whether the output signal exceeds a timing threshold value;

(d) if the output signal exceeds the timing threshold value, then measuring and recording a time during which the output signal exceeds the timing threshold value with a clock; and

(e) then, displaying the numerical value of the time measured by the clock on an alphanumeric display of the tool.

5. A method for detecting defects in a composite structure, comprising the steps of:

(a) manually striking a hammer by hand against a composite structure to define an impact signal in seconds from a tap at a first location which is known to be good, the hammer having an accelerometer attached to a display and a memory;

(b) recording a good numerical value for the tap in the memory, the good value being the length of time that the amplitude of the impact signal exceeds a predetermined timing threshold as measured by a clock associated with the accelerometer;

(c) manually striking the hammer a second time by hand against the composite structure defining a test signal for a test tap at a suspect location on the composite structure;

(d) recording a second numerical value in seconds in the memory being the length of time that the amplitude of the test signal of the test tap is over the timing threshold;

(e) comparing in a comparator associated with the memory the second numerical value with the good numerical value to determine whether the second value is within an acceptable range; and

(f) generating a signal based upon the comparison indicative of whether the value is in the acceptable range.