一种薄壁矩形管弯曲胎具的设计

介绍了一种薄壁矩形管弯曲胎具.利用金属材料弯曲变形时的塑变硬化特性来弯曲矩形管,较好地解决了雨阳棚骨架现场弯曲加工的问题.

Analysis of plane strain bending of a strain hardening curved beam based on unified yield criterion

The analysis of plane strain elastic-plastic bending of a linear strain hardening curved beam with a narrow rectangular cross section subjected to couples at its end is conducted based on a unified yield criterion. The solutions for the mechanical properties of plane strain bending are derived, which are adapted for various kinds of non-strength differential materials and can be degenerated to those based on the Tresca, von Mises, and twin-shear yield criteria. The dependences of the two critical bending moments, the radii of the interfaces between the elastic and plastic regions and the radial displacements of the points at the symmetrical plane on different yield criteria and Poisson’s ratios are discussed. The results show that the influences of different yield criteria and Poisson’s ratio on the two critical bending moments, the radii of the interfaces between the elastic and plastic regions and the radial displacements of the points at the symmetrical plane of the curved beam are significant. Once the value of bis obtained by experiments, the yield criterion and the corresponding solution for the materials of interest are then determined.

Construction and solution of strain model along thickness of aluminum alloy plate under plastic deformation

A thickness strain model of aluminium alloy plate under plastic deformation,based on thin plate assumption was proposed.It is found that when ratio of stress fractions is constant during in-plane loading,ratios of strain components under various loading conditions are linearly related and these points of ratios form a η-η line.Under these simple loadings,strains in thickness direction can be easily calculated by the η-η line equation without integral and differential work.When the plate is under more complicated loading conditions,the thickness can be computed by the proposed optimization and piecewise calculation model.Validation computations indicate that the relative error of the results of the presented model is less than 0.75% compared with the proven theories and FE simulation.Therefore,the developed model can be applied to engineering calculation,e.g.pre-stretching analysis of aerospace aluminium thick plate,with acceptable accuracy.

Plastic characterization of metals by combining nanoindentation test and finite element simulation

Materials with the same elastic modulus E and representative stress and strain （σr,εr） present similar indentation-loading curves, whatever the value of strain hardening exponent n. Based on this definition, a good approach was proposed to extract the plastic properties or constitutive equations of metals from nanoindentation test combining finite element simulation. Firstly, without consideration of strain hardening, the representative stress was determined by varying assumed representative stress over a wide range until a good agreement was reached between the computed and experimental loading curves. Similarly, the corresponding representative strain was determined with different hypothetical values of strain hardening exponent in the range of 0-0.6. Through modulating assumed strain hardening exponent values to make the computed unloading curve coincide with that of the experiment, the real strain hardening exponent was acquired. Once the strain hardening exponent was determined, the initial yield stress ay of metals could be obtained by the power law constitution. The validity of the proposed methodology was verified by three real metals： AISI 304 steel, Fe andA1 alloy.

Determination of work-hardening exponent for sheet metal using three-point method

Three characteristic points in the deformation history of a fractured tensile specimen are selected tocalculate two values of n( n1 and n2 ) to represent the hardening ability of material during the homogeneous plas-tic deformation and the following large plastic deformation. Experimental results obtained with mild streel andred copper show that n determined using the three-point method proposed is better to describe the hardening a-bility of material. It is therefore concluded that three-point method can be used to describe the hardening prop-erty of material during both homogeneous deformation and large plastic deformation.

Formability of the AMS 5596 Sheet in Comparison with EDDQ Steel Sheet

Some materials form better than others, moreover, a material that has the best formability for one stamping may behave very poorly in a stamping of another Configuration. The forming limit of a metal sheet is generally given in terms of the limiting principal strains under different loading conditions and represented by the so-called FLD （forming limit diagram）. In view of the difficulty to experimentally determine the forming limits, many researchers have sought to predict FLD. The formability of sheet metal has frequently been expressed by the value of strain hardening exponent and plastic anisotropy ratio. The stress-strain and hardening behaviour of a material is very important in determining its resistance to plastic instability. For these reasons, extensive test programs are often carried out in an attempt to correlate material formability with value of some mechanical properties. In this study, mechanical properties and the FLD of the AMS 5596 sheet metal was determined by using uniaxial tensile test and Marciniak＇s flat bottomed punch test respectively.

A particle-breakage critical state model for rockfill material

Particle breakage has a significant influence on the stress-strain and strength behavior of rockfill material.A breakage critical state theory(BCST)was proposed to describe the evolution of particle breakage.The breakage critical state line in the breakage critical state theory was correlated with the breakage factor,which was fundamentally different from that of the original critical state theory.A simple elastoplastic constitutive model was developed for rockfill in the frame of BCST.An associated flow rule was adopted in this model.Isotropic,contractive and distortional hardening rules were suggested in view of the particle breakage.It was observed that the proposed model could well represent the complex deformation behaviors of rockfill material,such as the strain hardening,post-peak strain softening,volumetric contraction,volumetric expansion,and particle breakage under different initial confining pressures.

Generalized Aifantis strain gradient plasticity model with internal length scale dependence on grain size,sample size and strain

The internal length scale(ILS)is a dominant parameter in strain gradient plasticity(SGP)theories,which helps to successfully explain the size effect of metals at the microscale.However,the ILS is usually introduced into strain gradient frameworks for dimensional consistency and is model-dependent.Even now,its physical meaning,connection with the microstructure of the material,and dependence on the strain level have not been thoroughly elucidated.In the current work,Aifantis'SGP model is reformulated by incorporating a recently proposed power-law relation for strain-dependent ILS.A further extension of Aifantis'SGP model by including the grain size effect is conducted according to the Hall-Petch formulation,and then the predictions are compared with torsion experiments of thin wires.It is revealed that the ILS depends on the sample size and grain size simultaneously;these dependencies are dominated by the dislocation spacing and can be well described through the strain hardenmg exponent.Furthermore,both the original and generalized Aifantis models provide larger estimated values for the ILS than Fleck-Hutchinson's theory.