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The extent of plastic deformation that occurs in the C_v specimen’s cross section during testing also is a quantifiable value, and this feature undergoes a marked transition in the bcc metals with the lowering of test temperature. When a C_v specimen is broken, a small amount of lateral contraction ordinarily occurs across the width, close to and parallel with the root of the notch, conversely expansion should occur across the width opposite the notch. Both changes in dimension from original 10 mm (0.394 inch) width of the specimen are easily measured, and both dimensional changes are indicators of ductility in the presence of a notch. The extent of lateral expansion opposite the notch is the value presently favored for appraising the capacity of metal flow plastically during fracture under impact load.