Experimental Mechanics

, Volume 17, Issue 9, pp 347–353 | Cite as

The measurement and significance of energy in acoustic-emission testing

Purpose of investigation is to present an approach to measuring the energy sensed by an acoustic-emission transducer and to present experimental results that compare energy measurements with couting and RMS measurements in several different types of tests
  • D. O. Harris
  • R. L. Bell
Article

Abstract

A technique for measuring the energy sensed at an acoustic-emission transducer is presented that utilizes a squaring circuit and digital integrator. Theoretical relationships between energy and other more conventional acoustic-emission parameters, such as counts and RMS voltage, are derived for certain idealized cases. Experimental results from the following types of tests are presented: (1) unflawed tensile (‘continuous’ emission); (2) precracked stress-corrosion cracking; (3) precracked fracture toughness; and (4) fatigue-crack growth. Energy, counts, RMS-voltage, energy/event and counts/event measurements are included. In the case of unflawed tensile specimens, energy techniques appeared somewhat superior to counts. In all other cases, a direct relationship between counts and energy was obtained. Energy measurements tended to give a larger weight to higher amplitude events. Other than this, energy measurements appeared to have no advantage over counts. The theoretical relationship predicted between energy/event and count/event agreed quite well with experimental observations. Overall, the test results presented indicate that energy techniques provide no significant advantage over counting threshold crossings in cases in which crack extension in metals is the primary source of acoustic emission.

Keywords

Fracture Toughness Fluid Dynamics Acoustic Emission Tensile Specimen Idealize Case 

Notation

C

a constant [see eq (3)]

f

frequency of oscillations in an acoustic-emission signal

Gn

gain of amplifier chain to counter

Gu

gain of amplifier chain to energy processor

n

counts for a single event

N

total acoustic-emission counts

N

acoustic-emission count rate

N

acoustic-emission counts/load cycle

P

tensile load

S

value of RMS-voltage signal above background noise

t

time

tn*

time for acoustic-emission signal to counter to ring down below trigger level of counter

tu*

time for acoustic-emission signal to digital integrator in energy processor to ring down to trigger level of processor

u

energy for a single event

U

total acoustic-emission energy

У

energy rate/s, V2-s/s

U

acoustic-emission energy/load cycle

V(t)

volts

Vo

amplitude of continuous-emission signal

Von

initial amplified and filtered voltage from single event to counter

Von

initial amplified and filtered voltage from single event to energy processor

Vn

amplified and filtered acoustic-emission signal to counter

Vu

amplified and filtered acoustic-emission signal to energy processor

Vtn

threshold voltage in counter

Vtu

threshold voltage in energy processor

ε

tensile strain, percent

τ

decay time of acoustic-emission signal [see eq (3)]

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Copyright information

© Society for Experimental Mechanics, Inc. 1977

Authors and Affiliations

  • D. O. Harris
    • 1
  • R. L. Bell
    • 2
  1. 1.Science Applications, Inc.Palo Alto
  2. 2.Celesco IndustriesCanoga Park

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