A New Approach Of Mechanical Autofrettage Theory And Photoplasticity Digital Speckle Correlation

In the present thesis, the solution of axisymmetrical space full plastic problems of ideal elastoplastic material is proposed from the fundamental equations, the possibility of using Tresca's yielding condition and the influence of longitudinal stress are discussed therefore the analytic formulae of plastic strain are also derived. Depending on the characteristics of mechanical autofrettage, the cyclical loading feature of the gun tube material and the solution of axisymmetrical space full plastic problem, the simple analytic formulae of mechanical autofrettage about loading, unloading and residual parameteres that satisfy all the elastoplastic equations and the realistic situations are derived by a new way that different from the previous papers completely. On the other hand the pressure distribution between mandrel and tube, the shape and the size of the plastic zone, the critical value of the loading displacement A in cavity when reyielding or full plasticity is taking place, and the reyielding zone etc. are given. The reasonable reyielding loading function is proposed. All the parameteres of the mechanical autofrettage can be obtained directly by the excess δ, the geometric size and the material constants using this method. The influences of Bauschinger's effection and reyielding with it's hardening coefficient to residual stresses are analyzed. The experimental result of the previous papers agree well with the presented theoretical analysis, it prove the reliability of the theory in the present paper.The Digital Speckle Correlation Method (DSCM)for measuring the displacement and deformation is improved in this paper and a new searchingmethod-----cross searching method is proposed. The technique conditionsfor enhancing the measuring accuracy that made DSCM more practical are discussed. The transparent photoplastic material polycarbonate is chosen to simulate gun tube and DSCM is adopted for guaging the deformation inloading area of the tube. The loading procedure of the tube is successfully simulated by the experimental testing and it makes the mechanism of the deformation in mechanical autofrettage more intuitive. The regularity of deformation calculated by the present theory agree well with the result of simulated experiment.