Mechanical Analysis of Dead Load Crown and Structure Parameter of Hydraulic Elastic Bulging Roll

The dead load crown of hydraulic elastic bulging roll was discussed using the theory of elastically supported beam,and the dead load experiment was carried out. The theoretical calculation is consistent with the experimental result. The structure parameters for the thickness of roll sleeve,the length of the oil groove and the crown of roll were discussed. The fundamental principle of determining the parameters was put forward. The theoretical basis of the application of the hydraulic elastic bulging roll was established.

Numerical Simulation of Magnetic Pressure in Tube-electromagnetic Bulging with Die

Calculation of magnetic pressure is the basis of application of electromagnetic forming (EMF). This paper carries out a numerical simulation of magnetic pressure under the influence of die by means of finite element method. The analysis model of electromagnetic bulging with die is created by using ANSYS, and the distribution of magnetic pressure acting on the tube and the die is obtained. The differences between EMF and other technologies and the effect of die on tube formability are analyzed. The die has important influence upon the calculation accuracy. The simulating conclusions with different discharge energy and current frequency are verified through the technologic tests. The distribution of magnetic pressure acting on the tube agrees well with the measurements of the deformed tube.

SIMUUTION OF ELECTROMAGNETIC TUBE BULGING BASED ON LOOSE COUPLING METHOD

A loose coupling method is used to solve the electromagnetic tube bulging. ANSYS/ EMAG is used to model the time varying electromagnetic field with the discharge current used as excitation, in order to obtain the radial and axial magnetic pressure acting on the tube, the magnetic pressure is then used as boundary conditions to model the high velocity deformation of tube with DYNAFORM, The radial magnetic pressure on the tube decreases from the center to the tube end, axial magnetic pressure is greater near the location equal to the coil height and slight in the other region. The radial displacement of deformed workpicces is distributed uniformly near the tube center and decreases from the center to the end; Deformation from the location equal to coil height to the tube end is little. This distribution is consistent with the distribution of radial pressure; Effect of the axial magnetic pressure on deformation can be ignored, The calculated results show well agreements with the experimental results.

Analytical Solution for Three-dimensional Forging Taking into Account Bulging of Sides by Mean Yield Criterion

Currently, for some complex plastic deformations, the analytical solution can not be obtained by using Mises yield criterion, because Mises yield criterion is nine dimensions, the velocity field is complex, and the solving methods are not innovative. Corresponding solutions of these problems are that yield criterion is linearized to reduce the variable numbers, and the velocity field and the solving methods are reasonably simplified, respectively. In this paper, a new linear yield criterion--mean yield（MY） criterion and inner-product of strain rate vector are used to analytically solve 3D forging taking into account bugling of sides. The velocity field is expressed as a vector in three dimensions, and rotation and divergence are applied to confirm that the velocity field is kinematically admissible. Then, the corresponding strain rate tensor of the velocity field is transformed into principal one by making the determinant of coefficients of the tensor cubic equation be zero. By using MY criterion, the plastic power is term by term integrated and summed according to inner-product of strain rate vector. An upper bound analytical solution is obtained for the forging, and verified by a pure lead press test. The test result turns out that the total pressure calculated by MY criterion is higher by 2.5%-15% than measuring value. In addition, a measuring formula of bulging parameter （a） is proposed, but the values of a measured by the formula are lower than those optimized by the golden section search. The total pressure calculated by MY criterion is compared with the ones by twin shear, Trasca yield, and Mises yield criterion. The comparing result shows that the total pressure calculated by MY criterion is slightly higher than the mean value of that by twin shear and Trasca yield criterion, and lower than that by Mises yield criterion, but more close to that by Mises yield criterion compared with that by other two. The proposed analytical solving methods can be effectively used to other complex plastic deformation, simplifying the solving process and obtaining the reasonable results.

Structure parameters and function of hydraulic elastic bulging roller

The fundamental principle and method of the determining of structure parameters for the hydraulic elastic bulging roller were discussed. The relationship among crown of roller, hydraulic pressure and thickness of roller sleeve was studied. Aluminum was chosen as experimental material to accomplish the dynamic load experiment. The hydraulic elastic bulging roller exerts good effect on shape control and therefore has a broad application prospect in engineering. [

Finite Element Analysis and Experiment on Viscous Warm Pressure Bulging of AZ31B Magnesium Alloy

Aiming at overcoming the low plasticity of magnesium alloy at room temperature, we researched viscous warm pressure bulging（VWPB） of AZ31B magnesium alloy based on the excellent thermal stability of viscous medium under the warm forming condition. The potential improvements of plastic deformation ability and forming quality of AZ31B magnesium alloy are expected with the aid of thermal characteristics of viscous medium. During bulging process the velocity field variation and pressure stress field distribution of viscous medium are observed at different temperatures through which the effect of temperature on the mechanical property of viscous medium and AZ31B magnesium alloy are analyzed. The results show that the formability of AZ31B magnesium alloy increases first and then decreases as the temperature increases and it is the best at 200 ℃. On the other hand, the viscous medium which can build non-uniform pressure stress field also exhibits a good flow property at elevated temperature, and it is helpful to improving the formability of AZ31B magnesium alloy.

Bulging intervertebral disc:an asymptotic elasticity solution

A bulging intervertebral disc (IVD) occurs when pressure on a spinal disc damages the once healthy disc,causing it to compress or change its normal shape.In medicine,most attention has been paid clinically to diagnosis of and treatment for such problems,which little effect has been made to understand such issues from a mechanics perspective,i.e.,the bulging deformation of the soft IVD induced by excessive compressive load.We report herein a simple elasticity solution to understand the bulging disc issue.For simplicity,the soft IVD is modeled as an incompressible circular composite layer consisting of an inner nucleus and outer annulus,sandwiched between two vertebral segments which are much stiffer than the IVD and can be treated as rigid bodies.Without adopting any assumptions regarding prescribed displacements or stresses,we obtained the stress and displacement fields within the composite layer when a certain compressive stain is applied via an asymptotic approach.This asymptotic approach is very simple and accurate enough for prediction of the bugling profile of the IVD.We also performed finite-element modeling (FEM) to validate our solutions;the predicted stress and displacement fields inside the composite are in good agreement with the FEM results.

Analysis and Simulation of Superplastic Sheet-Metal Bulging by Finite Element Method

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NUMERICAL SIMULATION AND EXPERIMENT OF CAVITY GROWTH DURING SUPERPLASTIC BULGING OF MAGNESIUM ALLOY ZK60

Numerical simulation and experimental studies on cavity growth were carreed out dur-ing the bulging process of saperplastic magnesium Alloy. A three--dimensional rigid-viscoplastic finite element program has been developed and applied to predict the cav-ity radiusand volume fraction of cavity growth. The final prediction on the cavityradius and volume fraction distribution was exhibited as colorful shade pictures. Theexperimental studies wereperformed under similar conditions to the numerical oneand provided for quantitativecomparison. According to the metallography observation,the radius and volume fraction of cavity growth was quantitative achieved by usingProfound--Iron & steel software. The numerical results were in reasonable quantita-tive agreement with the experiment.

Superplasticity and Superplastic Bulging Behavior of ZrO_2/Ni Nanocomposite

ZrO2/Ni nanocomposite was produced by pulse electrodeposition and its superplastic properties were investigated by the tensile and bulging tests. The as-deposited nickel matrix has a narrow grain size distribution with a mean grain size of 45 nm. A maximum elongation of 605% was observed at 723 K and a strain rate of 1.67×10-3s-1 by tensile test. Superplastic bulging tests were subsequently performed using dies with diameters of 1 mm and 5 mm respectively based on the optimal superplastic forming temperature. The effects of forming temperature and gas pressure on bulging process were experimentally investigated. The results indicated that ZrO2/Ni nanocomposite samples can be readily bulged at 723 K with H/d value （defined as dome apex height over the die diameter） larger than 0.5, indicating that the nanocomposite has good bulging ability. SEM and TEM were used to examine the microstructure of the as-deposited and bulged samples. The observations showed that significant grain coarsening occurs during superplastic bulging, and the microstructure is found to depend on the forming temperature.

SUPERPLASTICALLY FREE BULGING OFDURA LUMINLY12CZ UNDER AN EXTERNAL STRONG ELECTRIC FIELD

Superplastically free bulging of duralumin LY 12CZ (approximately corre-sponding to ASTM 2024) without any pretreatment has been investigated under an ex-ternal strong electnc field. The experimental results show that the electric field makesthe relative maximum height of the superplastically formed parts increase by 15%.Moreover, the determination of grain size and aspect ratio of grains and themetallographic observation of cavities have also been done. These results have verifiedthat the electric field improves the superplasticity during superplastically free bulging ofduralumin LY12CZ and that it is possible to utilize superplastic defonnation with elec-tric field in industrial practice.

Analysis of bulging for high speed continuous casting

In order to research the temperature distribution and mechanical deformation of slab bulging during high speed continuous casting, mathematical models have been developed to analyze the thermal and mechanical behavior of the slab. The thermal history of the slab has been predicted by a two-dimensional transient finite element heat transfer model, whose results serve as the input to the stress model. The stress model has been formulated for a two-dimensional longitudinal plane. In this case,the maximum tensile strain during the bulging process is located at the solidification fi＇ont just past the top of the upstream roll,which may contribute to crack formation. The maximum tensile stresses are located at the cold surface in the middle of the two back-up rolls ,just at the point of the maximum bulging. Stresses near the solidification fi＇ont are small because of the high temperatures which produce lower elastic modulus values. Finally,the effect of the casting speed on the bulging deformation is discussed.

ANALYSIS SOLUTION OF BULGING CONVEXITY OF THE HYDRAULIC ELASTIC BULGING ROLL

The hydraulic elastic bulging roll system is a new roll system being developed in recent years.It is the first time in home that dead load test and study on this system has been made.Based on the experiment,the analysis solution of the bulging convexity of the hydraulic elastic bulging roll was obtained by selecting appropriate displacement function and adopting inverse solution of the elasticity theory.In evaluating,a variable displacement function and its solving method was advanced.The analysis results are in accord with the experiment's.Some conclusions have laid the foundation of establishing close-loop controlled mathematical model of the hydraulic elastic bulging roll system.

MATHEMATIC MODEL FOR FORMABILITY CRITERIA OF SUPERPLASTIC AIR BULGING COMPONENTS

A proposal for two types of press close to die,including blank coming in die and Blank cov- ering die,and four criteria for formability is put forward in the study of the superplastic air bulge forming of the metallic thin wall components.A dimensionless weigh mathematic model for the criteria of superplastic air bulge forming is developed to be: Q_w=1.56(WS)/(HF)+2.37(0-(?)π/(180)-r/(r_0)+0.19 The superior formability of components is approaching,if Q_W≥1,and the worse,if Q_W<1.It was confirmed by practice that the above mentioned model is accurate sufficiently.

Bulging Distortion of Austenitic Stainless Steel Sheet on the Partially Penetrated Side of Non-Penetration Lap Laser Welding Joint

Non-penetration laser welding of lap joints in austenitic stainless steel sheets is commonly preferred in fields where the surface quality is of utmost importance.However,the application of non-penetration welded austenitic stainless steel parts is limited owing to the micro bulging distortion that occurs on the back surface of the partial penetration side.In this paper,non-penetration lap laser welding experiments,were conducted on galvanized and SUS304 austenitic stainless steel plates using a fiber laser,to investigate the mechanism of bulging distortion.A comparative experiment of DC01 galvanized steel-Q235 carbon steel lap laser welding was carried out,and the deflection and distortion profile of partially penetrated side of the sheets were measured using a noncontact laser interferometer.In addition,the cold-rolled SUS304 was subjected to heat holding at different temperatures and water quenching after bending to characterize its microstructure under tensile and compressive stress.The results show that,during the heating stage of the thermal cycle of laser lap welding,the partial penetration side of the SUS304 steel sheet generates compressive stress,which extrudes the material in the heat-affected zone to the outside of the back of the SUS304 steel sheet,thereby forming a bulge.The findings of these experiments can be of great value for controlling the distortion of the partial penetrated side of austenitic stainless steel sheet during laser non-penetration lap welding.

Best Technological Specification of High Speed Superplastic Bulging Under Back Pressure

Superplastic alloys have very low flow stress, extraordinarily high elongation insuperplastic state, and elastic recover and static storage effect of strain hardening canhardly be found. So space parts in complex shape and high dimension accuracy maybe formed under pressure. Unfortunately, the optimum strain rate of elongation is verylow(generally below 10-2 s-1) even at optimum superplastic temperature, and this be-

MATHEMATIC MODELS OF THINNING PATTERN FOR NON-SPHERE SUPERPLASTIC FREE BULGING(Ⅰ)

As clamping periphery is fixed during superplastic bulging, the thinning of thickness iscertainly inhomogeneous. There are large deviations between the mathematic model of athinning pattern established formerly for free bulging and the real deformation. In this paper,the mathematic model of a thinning pattern about non-spheric free bulging is establishedfor the first time by means of a function simulation method, and a simple and convenientmethod to determine the concrete form of this model in application is suggested. The agree-ment between the theoretical curve and the measured values proved to be perfect. Since themodel is established according to the experimental data of typical superplastic alloys, it canbe considered as a proper representation. This method is of general significance to bothnon-typical superplastic alloys and tough materials.

THE FORMULA OF MEASURING m VALUE IN SUPERPLASTIC BULGING BY MEANS OF JUMP PRESSURE

Ⅰ. INTRODUCTIONThe index m value of strain rate sensitivity is an important mechanical factor for evaluating superplasticity. The authors have established the analytically mechanical theories of m value on the basis of many formulae for measuring rn value by means of tension and have given out a unified measuring methodt. m value is affected by stress status because

THE m-VALUE FORMULAE AND MEASURING METHODS OF SUPERPLASTIC BULGING UNDER DIFFERENT PRESSURING METHODS

Ⅰ. INTRODUCTIONBecause of the strong structural sensitivity of superplastic deformation, the m-value, which is an important index for the evaluation of superplasticity of materials, is related not only to stress state, but also to pressuring method. In the superplastic bulging re.value formula measured by means of fixed height jump-pressure established by the author,