Abstract：The size effect has been the major subject in the research of micro forming. For the phenomena of the stress change in the metal hydraulic bulge experiment could not be explained properly by the classical plasticity theory, a new constitutive mode based on the strain gradient theory is built to study the size effect. Based on the model，the influences of the thickness of metal sheet and the die diameter on the stress in hydraulic bulge experiment is studied. Compared with the experiment, the stress under the second order size effect can be described well by theoretical analysis basing on the model. And its rationality is testified.
2013, Vol. 34 
