ONE DIAGRAMMATIC SOLUTION ON TRUE STRESS-STRAIN CURVE——ANALYSIS FOR NECKING PROCESS

For finding the true stress on necking period,the necking process of sample is analysed,and the result is that,the moving track on minimum necking section is a dummy cone with concave surface,different from necking body,the true stress should be by the former sectional area (or radius) ,not the latter. The reasoning proves that the track of necking radius point (the cross point of necking minimum section and necking top generatrix) is a curve with upper concave,monotony strictly decreasing and derivative lowering gradually. A diagrammatic solution on truce formula is put forword, and the beginning length pointed out is concerning necking length when calculating necking period true stress,not sample’s scale distance.