Experimental Mechanics

, Volume 14, Issue 4, pp 145–151 | Cite as

Moiré techniques for measuring strains during welding

Dynamic strain patterns in the parent plate around a welding arc can be determined by a modified grid-analyzer moiré-fringe technique and a computerized strain-computation scheme
  • Lytle Johnson


The present work measures dynamic strains near welds using a projected-grating moiré technique. Experimental procedures are described for producing the orthogonal submaster gratings and etched heat-resistant specimen gratings necessary for this work. A modification of the gridanalyzer method allows all strain information to be obtained from a single photograph. A mathematical procedure combines fringe patterns from small adjacent sections of a surface into a larger continuous pattern. Computerized regression techniques enable more rapid and accurate analysis of the data. Results from welds in an Al−Mg alloy show the feasibility of dynamic welding-strain analysis using this approach. Welding deformation is found to be almost entirely shear straining, which explains the nature and orientation of high-temperature cracks sometimes found near welds.


Welding Mechanical Engineer Fluid Dynamics Shear Strain Regression Technique 

List of Symbols

X, Y

cartesian coordinates perpendicular and parallel to the direction of welding, respectively, with the welding electrode as the origin

\(\varepsilon _{xx} , \varepsilon _{yy}\)

normal strain in cartesian coordinatesX, Y

\(\varepsilon _{xy}\)

shear strain in cartesian coordinates,X, Y

\(\varepsilon _{max}\)

maximum shear strain


rigid-body rotation of the specimen


nominal pitch of the moiré gratings being used


fringe orders for the original moiré patterns

A, B

fringe orders after subtracting the initial moiré pattern

u, U

relative displacements represented by moiré-fringe orders


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Copyright information

© Society for Experimental Mechanics, Inc. 1974

Authors and Affiliations

  • Lytle Johnson
    • 1
  1. 1.Nuclear DivisionUnion Carbide CorporationOak Ridge

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