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.
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Abbreviations
- 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
- N m :
-
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
- R d :
-
sensitivity ratio of the MDS to the SGS, when the magnetic detector is placedd cm away from the LTZ bar
- R l :
-
reaction at the support S1 due to loading on the aluminum bar
- R m :
-
slope of the magnetic-detector-output characteristic
- R r :
-
reaction at the support S2 due to loading on the aluminum bar
- R s :
-
slope of the strain-gage-system output characteristic
- s :
-
stress
- S :
-
absolute signal level
- S m :
-
measured signal
- V l :
-
load-cell-output voltage
- α d :
-
attenuation factor of the MDS at a distanced cm
- α:
-
strain
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Reddy, G.N., Saha, S. A highly sensitive noncontacting electromagnetic device for detecting dynamic stress in structures. Experimental Mechanics 23, 418–424 (1983). https://doi.org/10.1007/BF02330058
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DOI: https://doi.org/10.1007/BF02330058