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The transition temperature provides somewhat similar criteria for analyzing C_v test results. This method requires C_v test over a range of temperatures from a relatively high temperature where the metal exhibits its best toughness down to a low temperature at which cleavage can initiate. The obtained energy levels are then plotted against temperature. Metal with bcc crystalline structures undergo a precipitous drop in energy over a relatively narrow mid-range span of temperature. The drop in energy coincides with the occurrence of cleavage during the fracture.