Abstract
An analysis of gross pressure effect for strain gages is presented. This is defined as the difference between the predicted hydrostatic strain and the experimental strain. Values of the theoretical strain per unit pressure are based on the Voigt-Reuss-Hill approximation using published values of elastic moduli and compliances. These theoretical values are adjusted by the pressure effect calculated from an equation based on the assumption that the pressure effect is independent of the elastic properties of the substrate. The modified values of theoretical strain per unit pressure are then compared with the experimentally observed values. The differences are small except for the substrate materials of zinc, cadmium and lead.
Experimental pressure-strain data are presented for constantan foil gages mounted on tungsten, copper, tin, molybdenum, titanium, cadmium, brass, zinc and lead as well as constantan wire gages mounted on steel, aluminum and magnesium for hydrostatic pressures up to 140 ksi. Data for foil and wire gages mounted with various adhesives are presented and show that the adhesive or backing materials appear to have a relatively minor effect on the over-all gage performance.
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Abbreviations
- E :
-
modulus of elasticity(F/L 2)
- ν:
-
Poisson's ratio
- ε:
-
uniaxial engineering strain
- R :
-
resistance (ohms)
- ρ:
-
resistivity
- β:
-
linear compressibility of the gage grid materia
- GF m :
-
(‡R/R)/(‡L/L)=gage factor for bonded gage subjected to uniaxial strain
- SF β :
-
strain-sensitivity factor for unbacked gage subjected to hydrostatic pressure
- m 11,m 12 :
-
elastoresistivity coefficients
- K :
-
bulk modulus (F/L 2)
- K v ,K R :
-
Voigt and Reuss compressibilities (F/L 2)
- K VRH :
-
Voigt-Reuss-Hill compressibility (F/L 2)
- C ij :
-
elastic moduli (F/L 2)
- S ij :
-
elastic compliances (L 2/F)
- k T :
-
theoretical strain (per unit pressure);k T=f(C ij ) (F/L 2) org(S ij ) (L 2/F)
- k D :
-
pressure effect (indicated strain per unit pressureL 2/F)
- k T * :
-
theoretical strain (per unit pressure) adjusted for pressure effect
- k E :
-
experimental strain (per unit pressure) (L 2/F)
- k ‡ρ :
-
strain (per unit pressure) due to change in resistivity of the strain-gage grid with pressure (L 2/F)
- k ‡β :
-
strain (per unit pressure) due to change in dimensions of the strain-gage grid with pressure (L 2/F)
References
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Fisher, E. S., andRenken, C. J., “Single-Crystal Elastic Moduli and the hep → bcc Transformation in Ti, Zr and Hf,”Phys. Rev.,135 (2A),A482-A494 (July 1964).
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Milligan, R.V. The gross hydrostatic-pressure effect as related to foil and wire strain gages. Experimental Mechanics 7, 67–74 (1967). https://doi.org/10.1007/BF02326709
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DOI: https://doi.org/10.1007/BF02326709