Papers by Keyword: Deformation Behavior

Abstract: In order to comprehensively evaluate the performance of dilution type cold patch asphalt mixture (CPAM), basic performances and deformation behaviors of dilution type CPAM under different stress modes were tested. The compaction performance and stability increasing property of CPAM were tested by rotation compaction test and Marshall stability test. The deformation behaviors of CPAM were tested by rolling test, small beam bending test and penetration shear test. Results show that when the using temperature is below 25°C, the compaction ability of CPAM is affected by temperature. The evaporation rate of organic solvents is slow, and affects the strength growing and rolling deformation behavior. It needs about 10d for the stability of CPAM rising to 3kN. The residue of organic solvents may lead the deformation of CPAM to constantly instability under rolling load. The stretching deformation and penetration shear deformation are affected by temperature. The low temperature and high temperature performance of CPAM is below standard requirements of hot asphalt mixture (HMA).

Abstract: The DP1000 cold-rolled dual phase steel, the thickness of which is 1.2 mm, was required to do the tensile test under nine different strain rates from 10^-4 s^-1 to 1000 s^-1. The mechanical properties and morphologies of the steel were obtained and analyzed. According to the C-J model, the plastic deformation characteristics of dual phase steel under different strain rates were studied. By means of transmission electron microscope (TEM), the morphologies of ferrite and martensite in the dynamic were observed. Finally, the constitutive models of quasi-static and high strain rate were established by using the modified Johnson-Cook model. The results reveal that DP1000 dual phase steel has obvious strain rate sensitivity, and it is a relatively pure ferrite and martensite dual phase structure. There are two stage strain hardenging characteristics in DP1000. In the first stage, the strain hardening ability of ferrite is higher, and the second stage is martensite deformation stage, the strain hardening ability is lower. The modified J-C constitutive model has high fitting effect, and the experimental results are matched with the fitting values.

Abstract: The hot working flow stress of as-cast and two different extruded magnesium alloys AZ31was examined by uniaxial compression tests. It was found that the hot deformation behavior was affected by the deformation conditions and initial microstructure. The peak flow stress was sensitive to deformation temperature and strain rate, and the value was decreased with decreasing the deformation rate or increasing the deformation temperature. The extruded samples, instead of as-cast samples, have better ductility at high strain rate and high temperature. The temperature increment for Mg alloy with different extrusion ratios was also investigated. These key features of the deformation behavior were explained in terms of twinning, dynamic recrystallization and grain rotation.

Abstract: Tooling feature size to minimum thickness becomes small in micro scale products and its ratio affects the deformation behavior in micro sheet forming significantly. In this study, the effect of this relative tooling feature size on drawing characteristics and effects to improve the drawability, such as friction holding effect, hydrodynamic lubrication effect and compression effect by blank edge radial pressure, in micro hydromechanical deep drawing (MHDD) are investigated using plasticity theory and numerical simulation. The results show that the micro drawing characteristics in MHDD can be improved by applying counter pressure. However, the required fluid pressures for friction holding and hydrodynamic lubrication effects increase as the relative punch diameter and/or die shoulder radius to thickness decrease, although the compression effect by radial pressure on the blank edge is independent of the relative tooling feature size.

Abstract: Microforming process is a promising approach to manufacture microparts for its high productivity, high material usage and good part properties. However, when the part size is scaled down from macro to micro level, the deformation behaviors of materials change and the size effects occur. This makes it difficult to use microforming process in industry. In the last decade, many studies have been conducted with different test methods and materials. In this paper, the main test apparatus and the methods used to study the size effect and the significant results are reported.

Abstract: The isothermal compression tests of semi-solid ZCuSn10P1 alloy by strain induced melt activation (SIMA) process are carried out by Gleeble-1500 thermo-mechanical simulator, and the same tests are finished to samples of as-cast ZCuSn10P1 alloy. The deformation temperature respectively is 910°C, 920°C and 930°C, and the strain respectively is 0.4 and 0.6, the strain rate is 0.5s^-1, 1s^-1 and 10s^-1. The experimental results indicate that the deformation resistance of semi-solid ZCuSn10P1 copper alloy with smaller, more uniform and rounder solid grain is about half of the as-cast ZCuSn10P1 copper alloy. The deformation resistance of ZCuSn10P1 alloy by SIMA process decreases with the deformation temperature increasing, and the deformation resistance increases with the strain rate increasing.

Abstract: Deformation and fracture behaviors of Ti-6Al-4V-0.1B alloy with Widmanstätten, equiaxed and bimodal microstructures were investigated by Split Hopkinson Pressure Bar (SHPB) under high strain rates of 2100-3200 s^-1. The results showed that the equiaxed and bimodal structures had a higher bearing capacity at high strain rates than that of the Widmanstätten structure. With the same microstructure, the increase of strain rate gave rise to an improved uniform plastic deformation. According to an observation on the deformed microstructure, it was found that adiabatic shear behavior was the main reason for failure and fracture of the alloy. The formation and propagation of adiabatic shear bands (ASBs) was the precursor for the failure and fracture of the material. Cavities at the interface between TiB phase and the matrix readily formed due to the uncoordinated deformation, which are not the dominate reason for the failure and fracture.

Abstract: Ni-Ti foams of varying relative densities have been made by varying the size and volume fraction of NH₄(HCO₃), which was used as space holder. The green compacted pellets, after evaporation of NH₄(HCO₃), were sintered at 1100°C for 2 hrs. The XRD and EDX analysis confirms that there is no residual space holder. The extent of openness of cell walls increases with increase in porosity. The compressive stress-strain behavior of these foams varies with the relative density. The peak stress and energy absorption of these foam increases with relative density following power law and linear relationships respectively, and the densification strain decreases with relative density following a linear relationship. The pseudo elastic recovery strain and shape recovery strain decrease with increase in porosity. The overall recovery increases with decrease in degree of deformation. This phenomenological behavior indicates that these foams can be used for their shape memory effect.

Abstract: The equal channel angular extrusion (ECAE) is one of the most important methods used for bulk metal forming. In which die angles are the most importent parameter. This paper attempts to determine the effect of different die angles during ECAE process for 6062 aluminum alloy deformation. Numerical simulations are performed for ECAE process on cylindrical billet of 6062 aluminum alloy at a constant frictional coefficient (μ) of 0.08 and punch speed of 15 mm/sec. Die has made with inner corner angles of (φ) =105^°, 115^°, 125^°and 135^° by fixing the outer corner angle (ψ) of 6^°, punch is designed with a radii (R) of 4.75mm and height of 50mm. From the simulation results, tha data has been obtained in the form of load stroke behavior, and energy consumend during the punch stoke. It is observed that the maximum load and more energy consumption during the process is noted for lower angle.

Abstract: In the manufacturing industry, metal cross-sections and profiles are manufactured by using extrusion as the primary process. Subsequently, the products are generally subjected to bending in a secondary process. However, long products with the same cross-sections are typically mass-produced by one extrusion. In industries that manufacture such products, there have been increasing demands for flexible manufacturing systems that can be used for low-volume diverse products. However, it is difficult to adapt traditional manufacturing systems to this requirement. In this study, we aimed to develop a new bending method that can be used to deform the cross-sections of existing versatile extruded sections, such as channel materials and rectangular tubes, to several types of cross-sectional shapes and to simultaneously impose a desired curvature on them. The rotary draw bending process for an aluminum alloy channel material without tensile flanges was investigated by using the finite element method and experiments. The effects of the bend angle and thickness ratio on the cross-sectional deformation were examined. Furthermore, the influence of additional axial tension on the channel materials was studied. Additional axial tension can be used to control the outward and inward deformations of the webs. In addition, it was confirmed that the axial tension is very effective in preventing wrinkling and folding.