Papers by Keyword: Strain Rate Sensitivity (SRS)

Abstract: The strength enhancement of cellular materials under dynamic compression was experimentally studied in the present paper. A phenomenological model was employed to investigate the entrapped air contribution by introducing a parameter, namely the leaking rate of air. The strength enhancement caused by the entrapped air was then studied for both aluminum honeycombs and foams. It has been found that the pressure change in the entrapped air during dynamic compression is a direct source of strain hardening for aluminum honeycombs whereas it has smaller influence on the strain hardening of aluminum foams. Other sources that might contribute to the strain hardening of cellular materials are also discussed.

Abstract: The dynamic response of the turbine blade materials is indispensable for analysis of erosions of turbine blades as a result of impulsive loading associated with gas flow. This paper is concerned with the dynamic hardening equation of the Nickel-based superalloy Inconel 718 which is widely used in the high speed turbine blade. Reported representative dynamic hardening equations have been constructed and evaluated using the dynamic hardening characteristics of the Inconel 718. Dynamic hardening characteristics of the Inconel 718 have been obtained by uniaxial tensile tests and SHPB tests. Uniaxial tensile tests have been performed with the variation of the strain rate from 0.001/sec to 100/sec and SHPB tests have been conducted at the strain rate ranging up to 4000/sec. Several existing models have been constructed and evaluated for Johnson-Cook model, Zerilli-Armstrong model, Preston-Tonks-Wallace model, modified Johnson-Cook model, and modified Khan-Huang model using test results at various strain rate conditions. The most applicable equation for the Inconel 718 has been suggested by comparison of constructed results.

Abstract: An experimental investigation on the dynamic compressive behaviour of the aluminium alloy, AA6063-T6 in the strain rate range from 0.001s^-1 to 850s^-1 is reported here. Cylindrical specimens of AA6063-T6 are tested under universal testing machine at quasi-static (0.001s-1) condition, whereas, experiments at high strain rates (110s-1,400s^-1,550s^-1,700s^-1 and 850s^-1) are conducted on the traditional split Hopkinson pressure bar setup. The strain hardening in the material is found to increase with increasing strain rate. It is observed that the existing Johnson-Cook material model with appropriate material parameters predicts the dynamic compressive flow stress of AA6063-T3 aluminium alloy precisely.

Abstract: Superplastic forming in Al6063/SiCp composites having a wide range of applications in aerospace and automobile industries due to the high strength and wear resistance[7]. High percentage of elongation was obtained only at high temperatures. At high temperatures liquid phase will form in the grain boundaries. Due to the liquid phase, grain boundary sliding was easy to get the Newtonian viscous flow[1]. In composites high ductility was obtained only the temperature more than 560°C. The maximum dome height of 19 mm was obtained at 580°C. Temperature is more than 600°C the material was failed, fracture was occurred.

Abstract: A fully dense nanocrystalline Ni-Co alloy with 18 nm grain size exhibited high strength of about 2200 MPa and ductility of 8.19.2% at strain rates of 1.04×10-5 to 1.04 s-1 and room temperature. The alloying of Co element induces the grain refinement, solid solution hardening and decrease of stacking fault energy should contribute to the favorable combination of mechanical performance. The obvious distinctions of fracture-surface morphologies with strain rate alteration were attributed to underlying deformation mechanism transition. The high strain rate sensitivity exponent and small activation volume indicate that grain boundary activity may be expected in this alloy.

Abstract: The purpose of the present paper is to investigate the mechanical properties of multi phase 800 high yield strength (MP800HY) steel under compressive loading at different strain rates (-4700s^-1 to-0.001s^-1). Specimens of MP800HY steel are tested on universal testing machine to study their stress-strain behavior under quasi-static (-0.001s^-1) condition. Then, the specimens are tested under split Hopkinson pressure bar (SHPB) to study the strain rate sensitivity of the material under different rates of compressive loading (-4700s^-1, -4300 1/s, -3800 1/s, -2900s^-1 and-1600s^-1). The effect of pulse shaper in SHPB experiments has been studied. Thereafter, the applicability of the existing Johnson-Cook material model to represent the flow stress of MP800HY is examined.

Abstract: Two novel methods of obtaining microduplex structures, ferrite plus spherical carbides, in ultrahigh strength steels (~2000MPa) are introduced. One is through an adequate deformation just below the austenite-ferrite equilibrium transformation temperature (i.e. Ae₃ temperature, ~983K) followed by water quenching. The adequate deformation directly leads to the formation of a (ferrite plus spherical carbides) microduplex structure. The microstructure evolution during the deformation includes pearlite transformation, cementite spheroidization and ferrite recrystallization. The other is through an adequate deformation above Ae₃ temperature (~1003K) followed by water quenching to produce martensite firstly and then obtain a (ferrite plus spherical carbides) microduplex structure during warm deformation of martensite. Microstructural analysis on the microduplex structure shows that submicron carbides are located at ferrite grain boundaries while nanometer ones are dispersed inside ferrite grains. This kind of carbide distribution may suppress the coarsening of ferrite grains and form a dynamic equilibrium of ferrite grain size on a specific deformation condition. The strain rate sensitivity of the (ferrite plus spherical carbides) microduplex structures is about 0.4 at 973K and strain rate of 10^-4s^-1.

Abstract: Backward extrusion process of aluminum-alloy wheel forging is analyzed by the finite element method. The influence of punch speed and forming temperature on the backward extrusion height of 6061 aluminum alloy wheel is discussed. Studies show that the backward extrusion height increases with increasing forming temperature, and with decreasing punch speed at the same deformation load. It is indicated that when the ranges of forming temperature is from 450 to 500°C and the punch speed is 0.5-1 mm/s, the aluminum alloy wheel has the optimal forming quality. The analysis and conclusions in this paper are helpful in developing the hot extrusion technology specification of 6061 aluminum alloy.

Abstract: Supersaturated Mg-Gd-Y alloy followed by aging at 225 °C with different times were subjected to quais-static and dynamic strain rates to determine the influence of precipitate phase β′ on the strain rate sensitivity of magnesium alloy. Strain rate sensitivity (SRS) decreases with the increase of the size of β′. SRS decreases from initial condition to peak-aged condition due to the β′ increases the athermal component of flow stress. On the other hand, the influence of precipitate interfaces on dislocation generation and storage mechanisms may be responsible for the decrease of SRS from peak-aged to over-aged condition.

Abstract: Concrete is a material used all over the world for civil engineering but the mechanisms governing its dynamic behaviour are still not well understood. In this work, spalling tests and edge-on impact experiments have been used to determine the influence of the free-water contained in pores and micro-cracks on the dynamic strength and on the fragmentation process. Moreover, spalling tests have been also used to identify the main mechanisms leading to the difference of behaviour observed between wet and dry concrete.