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From measured strain t o

Analysis of the biaxial stress state with unknown principal directions

The principle of experimental stress analysis using strain gages consists in using strain gages to measure strains on the component surface. From these measured strains and the known material properties such as modulus of elasticity and Poissons ratio, the absolute value and the direction of these mechanical stresses are determined. These calculations are based on Hookes Law which applies to the elastic deformation range of linear-elastic materials.In experimental stress analysis, so-called 3-grid rosettes are used for strain measure-ment. These are available in 0/45/90and 0/60/90versions which have a historical background. It is up to the user to choose which version to use.The 3 measuring grids of the rosettes are designated with the letters a, b and c.Therefore, a 3-grid rosette measures the three strains ε
a , ε
b and ε
c .The principal normal stresses σ
1 and σ
2 for the 0/45/90rosette are calculated asfollows: and for the0/60/120rosette: 0/45/90rosette,e.g. RY3x 0/60/120rosette,e.g. RY7x 18Strain Gages and Accessories