This paper presents a novel strain-based continuum damage mechanics (CDM) model for predicting forming limit curve (FLC) of AA5754 under warm forming conditions. The model is formulated and calibrated based on two different sets of experimental data; isothermal uniaxial tensile data at temperature range of 20-300°C and strain rate range of 0.001-10 s -1 and isothermal FLC data at temperatures range of 20-300°C and forming speeds of 20-300 mm s -1. A good agreement has been achieved between the experimental and numerical results.
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Abstract: The hot deformation behaviors and microstructure in Al-Cu-Li alloy containing small amount of Ag and Mg were investigated by transmission electron microscopy and isothermal compression tests.When the strain rate is 0.1, 0.01 and 0.001s-1(the deformation temperature within the range of 360-520 ) and 1 s-1(deformation temperature 520 )respectively, the flow stress decreases after a peak value, showing dynamic recrystallization,while the steady-state flow characteristics exist on the other deformation conditions. The flow stress of Al-Cu-Li-Mg-Ag alloy during hot deformation can be expressed by a Zener-Hollomon parameter in the hyperbolic-sine function with the hot deformation activation energyDH of 250.45kJ/mol. The dislocations may climb with support from many vacancies generated during hot deformation, thus forming lots of helical dislocations. The dynamic precipitation and successive dynamic particles coarsening during hot compression have been assumed to be responsible for further flow softening when deformed at low strain rates. Abstract: Uni-axial tensile plastic deformation behavior of rolled magnesium alloy AZ31B under the temperature range from room temperature(RT) to 250°C with strain rates between 10 -3 and 10 -1s -1 has been systematically investigated. Microstructure evolution and texture were determined using optical microscopy (OM) and electron back-scattered diffraction (EBSD) techniques, respectively.
Our results indicated that the strength and elongation-to-fracture were more sensitive to strain rates at elevated temperature rather than that at room temperature; dynamic recrystallization (DRX) and relaxation of stress at elevated temperature resulted in dramatic change of mechanical properties. Compared with strain rate, the temperature played a more important role in ductility of AZ31B Mg alloy sheet. Abstract: One of the ways for determination of flow curves is the application of a ring test.
Using this method, friction in the interface between the die and the specimen leads to a bulging of the sample and thereby to an inhomogeneous stress and strain state. The calculation of the flow stress from experimentally determined force–displacement curves implies a uniaxial stress state, but this will produce an error because of the above-mentioned bulging, when friction occurs.
One method of avoiding these sources of error is to use the sigmoid curves, but the sigmoid curves are varied by the change of temperature and strain rate. Calculations of numerical sigmoid curves were done by the use of an iterative procedure, applying a corrective function. The paper presents a complete investigation of the AZ41 magnesium alloy sigmoid curves at temperature ranging between 473 K and 513 K and strain rates ranging between 0.025 s-1 and 0.00025 s-1. Ring tests are used to determine the numerical sigmoid curves sensitivity to temperature and strain rate. Abstract: This paper presents an investigation about the occurrence of the dynamic recrystallization (DRX) during hot forming. Two 7075 aluminum alloy samples in different initial states were examined by compression tests at temperatures between 573 K and 723 K and constant strain rates ranging from 0.002 to 2 (s-1) with the maximum strain of 0.5 mm/mm.