Experimental Mechanics

, Volume 23, Issue 4, pp 418–424 | Cite as

A highly sensitive noncontacting electromagnetic device for detecting dynamic stress in structures

  • G. N. Reddy
  • S. Saha
Article
  • 39 Downloads

Abstract

A highly sensitive, noncontacting electromagnetic device has been developed to detect stress waves in structures. It is shown that for detecting an induced strain this device is over 500 times more sensitive than conventional bonded strain gages. The principle of detecting the strain by this device is based on the fact that dynamic stresses in a structure induce similar stresses in a bonded piezoelectric material. This, in turn, creates a magnetic field which extends beyond the material itself. An electromagnetic device has been built to detect this magnetic field and thus monitor the dynamic stresses. This method provides a noncontacting means of measuring strain in structures with improved sensitivity.

Keywords

Magnetic Field Mechanical Engineer Fluid Dynamics Strain Gage Piezoelectric Material 

List of Symbols

a

distance between the support S1 and the loadP

b

distance between the support S2 and the loadP

d

distance between the LTZ bar and the magnetic detector

D

diameter of the aluminum bar

E

modulus of elasticity

F

force

G

gain of amplifiers

I

moment of inertia

L

length of the aluminum rod

M

bending moment

Nm

measured value of ambient-base noise

N

absolute noise level

P

static load

r

radius of the aluminum bar

R

sensitivity ratio of the MDS to the SGS

Rd

sensitivity ratio of the MDS to the SGS, when the magnetic detector is placedd cm away from the LTZ bar

Rl

reaction at the support S1 due to loading on the aluminum bar

Rm

slope of the magnetic-detector-output characteristic

Rr

reaction at the support S2 due to loading on the aluminum bar

Rs

slope of the strain-gage-system output characteristic

s

stress

S

absolute signal level

Sm

measured signal

Vl

load-cell-output voltage

αd

attenuation factor of the MDS at a distanced cm

α

strain

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Copyright information

© Society for Experimental Mechanics, Inc. 1983

Authors and Affiliations

  • G. N. Reddy
    • 1
  • S. Saha
    • 2
  1. 1.Electrical Engineering DepartmentMichigan Technological UniversityHoughton
  2. 2.Department of Orthopaedic SurgeryLouisiana State University Medical CenterShreveport

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