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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
Article

Abstract

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.

Keywords

Welding Mechanical Engineer Fluid Dynamics Shear Strain Regression Technique 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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

α

rigid-body rotation of the specimen

g

nominal pitch of the moiré gratings being used

Ao,Bo

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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