Research on grading expanding process and crack for rings

Aiming at existing insufficient of mechanical expanding for rings,the grading expending process has been developed and applied.The process characteristics have been introduced in the text.Taking double grading process as an object,the calculation formula of expanding force and stroke have been theoretically derived.The expanding process has been simulated by use of software ABAQUS,and the influence law of parameter of material on pressure cone stem in expanding process has been gained,which verifies the accuracy of theoretical derivation.In order to prevent cracking in the process of expanding,the theory of critical void growth ratio in damage mechanics has been applied to establish the condition of expanding forming without cracking with help of plastic mechanics equation.The condition is the criterion for the fracture forecast,which has been verified by experiments.