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Glossary of Common Terms
Here is a list of terms particular to stress and strain measurement with their definitions.


  • 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.