Here is a list of terms particular to stress and strain measurement with their definitions.
Glossary
Transformation relationships for stress, strain
A set of transcendental functions for calculating stress and strain at a point on one set of orthogonal axes from those on another set of axes having a different orientation.
Transverse sensitivity
<ol><li>The behavior of a gage in responding to surface strains which are perpendicular to the primary sensing axis of the gage.</li><li>The ratio, expressed as a percentage, of the unit change of resistance of a strain gage mounted perpendicular to a uniaxial strain field (transverse gage) to the unit resistance change of a similar gage mounted parallel to the same strain field (longitudinal gage).</li></ol>
Tresca failure criterion
Failure model based on the maximum shearing stress required to initiate yielding.
Type, strain gage
Description for a group of strain gages which are nominally identical with respect to physical and manufacturing characteristics.
Unbalanced bridge
A Wheatstone bridge for which the arm resistances are such that they produce an output voltage between the signal corners when an input voltage is applied between the power corners.
Uncertainty
A statistically defined discrepancy between a measured quantity and the true value of that quantity that cannot be corrected by calculation or calibration.
Uniaxial strain field
Strain field in which only one of the principal strains is nonzero. Atypical because Poisson strains are usually present.
Uniaxial strain gage
Strain gage having a single linear grid designed to measure strain primarily along the longitudinal axis of the grid.
Uniaxial stress field
Stress field in which one of the principal stresses is zero. Typical, for example, of simple tension or compression for which a load is applied in a single direction and the transverse stress is zero.
Unit strain
A strain defined by the change in length per unit length of a line, either Eulerian or Lagrangian.
Voltage injection
Method of zero-balancing an instrument by injecting a voltage of opposite sign but like magnitude into the output from an unbalanced Wheatstone bridge.
Von Mises failure criterion
Failure model based on the distortional energy necessary to initiate yielding.
Weldable strain gage
Strain gage on a metal shim that can be spot-welded to a test structure or component.
Wheatstone bridge
A four-arm, four-terminal resistance-measuring network, with two terminals (P+, P-) for voltage input (E); the remaining two (S+, S-) for signal output (Eo).
X-axis
The horizontal axis in a system of rectangular Cartesian coordinates; the axis of abscissas. Usually representing the independent variable.
Y-axis
The vertical axis in a system of rectangular Cartesian coordinates; the axis of ordinates. Usually representing the dependent variable.
Yield point
The coordinate on the stress-strain curve of a material in uniaxial tension or compression representing the onset of significant plastic deformation. Typically the fracture point for brittle materials and the coordinate at an offset strain of 0.2% for ductile materials. Synonym:: elastic limit
Yield strength
<ol><li>The stress necessary to produce significant plastic deformation in a material under uniaxial tensile or compressive load.</li><li>The stress on a stress-strain curve at the yield point.</li></ol>
Young's modulus, Elastic modulus, modulus of elasticity,
A materials property defined as the ratio of (a) the uniaxial stress along an axis of the material to (b) the accompanying normal strain along that axis.
Zero balance
State of a strain gage instrument which has been adjusted to yield no output. The instrument may be zero-balanced even if the Wheatstone bridge is resistively unbalanced. Related: null balance, resistive balance
Zero Drift
Gradual, normally permanent change in the resistance of an installed strain gage, bridge completion resistor, or leadwire that is unrelated to strain.
Zero Return
The ability of a strain-gage measurement system to return to its initial condition after an applied load is removed.
Zero shift
A normally temporary, reversible change in the resistance of an installed strain gage, bridge completion resistor, or leadwire that is unrelated to strain.