3 Experimental Observations on the Fracture of Metals 21 Fig. 3.1 U and V patterns of a tensile specimen with vertical and horizontal gratings of pitch p Fig. 3.2 Vector displacements in a tensile specimen of constant cross section Figure 3.2 represents the vectors of relative displacements if the reference axis is taken at the center of the specimen. The specimen elongates in the y-direction and contracts in the x-direction due to the Poisson’s effect. In the elastic range, the corresponding values of the displacement components are v ≈ σy E δv (3.6) u ≈−ν σy E δu (3.7) In Eq. (3.7), ν is the Poisson’s ratio. The modulus of the displacement vector is
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