Development of Localized Deformation in AA 2024-O

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
S. Kweon ◽  
A. J. Beaudoin ◽  
P. Kurath ◽  
M. Li
Keyword(s):  
Temperature Gradient ◽  
Work Hardening ◽  
Mechanical Response ◽  
High Strain ◽  
Strain Rates ◽  
Compression Tests ◽  
Localized Deformation ◽  
Aa 2024 ◽  
Higher Temperature ◽  
Lower Temperature

An experimental study is presented to (1) quantify the rate-sensitive mechanical response and (2) examine the localized deformation behavior under an applied temperature gradient in the alloy AA 2024. Isothermal flow stresses are obtained at temperatures from −100°C to 495°C and strain rates from 10−2/s to 10−5/s using routine compression tests and a novel cyclic test, which expedites the characterization. The material displays two distinct kinetic responses with both being amenable to localization phenomena. The lower temperature/high strain rate regime displays a rate-insensitive yield with Stage III/IV work hardening. At higher temperature/low strain rates, a rate-sensitive response with little work hardening is observed. In order to relate the material constitutive behavior to the development of localized deformation, a temperature gradient test is performed wherein temperature differences of approximately 30°C are enforced between the top and bottom surfaces of a cylindrical compression test specimen. Deformation heterogeneity developed in the two distinct regimes of material response is illustrative of warm and hot working conditions typical of industrial processes, such as rolling.

scholarly journals Research on the Static Recrystallization and Precipitation Behaviors of a V-N Microalloyed Steel

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Baochun Zhao ◽  
Tan Zhao ◽  
Guiyan Li ◽  
Qiang Lu
Keyword(s):  
Static Recrystallization ◽  
Microalloyed Steel ◽  
Time Interval ◽  
Main Role ◽  
Recrystallization Process ◽  
Compression Tests ◽  
Double Compression ◽  
Higher Temperature ◽  
Lower Temperature ◽  
Temperature Strain

Double compression tests were performed on a Gleeble-3800 thermomechanical simulator to study the softening behaviors of deformed austenite in a V-N microalloyed steel. The static recrystallization volume fractions were calculated by stress offset method, and the kinetic model of static recrystallization was constructed. The effects of temperature, strain, and time interval on the softening behaviors were analyzed, and the interactions between precipitation and recrystallization were discussed. The results show that the softening behaviors of the deformed austenite at lower temperature or higher temperature are markedly different. At the temperature of 850°C or 800°C, pinning effects of the precipitates play the main role, and the recrystallization process is inhibited, which leads to the formation of plateaus in the softening curves. An increase in strain promotes the precipitation and recrystallization processes while reduces the inhibition effect of precipitation on recrystallization as well.

Measurement of the Material State Including the Effects of Recovery and Recrystallization

2000 ◽  
Author(s):  
M. E. Bange ◽  
A. J. Beaudoin ◽  
M. G. Stout ◽  
S. R. MacEwen
Keyword(s):  
Elevated Temperatures ◽  
High Strain ◽  
Quantitative Measure ◽  
Experimental Program ◽  
Strain Rates ◽  
Compression Tests ◽  
State Variable ◽  
Mechanical Threshold ◽  
Material State

Abstract Deformation at elevated temperatures in combination with high strain rates leads to recovery and recrystallization in aluminum alloys. Previous work in recrystallization has emphasized the detailing of microstructural trend in progression from the deformed to the annealed state. In the following, we examine the effect of rate dependence on deformation on AA 5182 and AA 6061. It is demonstrated that identification of underlying microstructural mechanisms is critical. An experimental program is then outlined for characterization of recovery and recrystallization of AA 5182. Instantaneous hardening rate and flow stress are developed from interrupted compression tests. These data are used to establish a quantitative measure of recovery through evaluation of a state variable for work hardening, the mechanical threshold. It is intended that the results serve as a foundation for development of relations for evolution of a mechanical state variable in the presence of recrystallization. Such a framework is necessary for the practical prediction of interstand recrystallization in hot rolling operations.

The Effect of Uniaxial Cyclic Deformation on the Evolution of Phase Transformation Fronts in Pseudoelastic NiTi Wire

2001 ◽  
Author(s):  
Mark A. Iadicola ◽  
John A. Shaw
Keyword(s):  
Mechanical Response ◽  
Infrared Imaging ◽  
Partial Transformation ◽  
Niti Wire ◽  
Full Field ◽  
Temperature Experiment ◽  
Background Temperature ◽  
Higher Temperature ◽  
Lower Temperature ◽  
Niti Wires

Abstract Experiments are presented of the response of pseudoelastic NiTi wires subjected to displacement controlled cycles. A custom built thermo-mechanical testing apparatus is used to control the background temperature field of the wire specimen while allowing the evolution of transformation fronts to be tracked by full field infrared imaging. Two experiments under similar end-displacement histories, but at temperatures ≈8°C apart, are shown to give remarkably different cyclic responses. The mechanical response for the lower temperature experiment continued to soften but retained its shape through 43 partial transformation cycles, and the pattern of transformation fronts seemed to reach a steady state. The response for the higher temperature experiment showed a change in shape of the mechanical response and distinct changes in transformation front patterns over 31 partial transformation cycles.

Deformation and Fracture of a Silicate Melt Around Tg: Implications to Dynamics of Volcanic Eruptions

2008 ◽  
Author(s):  
Mie Ichihara ◽  
Daniel Rittel ◽  
M. B. Rubin
Keyword(s):  
Strain Rate ◽  
Work Hardening ◽  
High Strain ◽  
Elastic Solid ◽  
Volcanic Eruptions ◽  
Strain Rates ◽  
Stress Strain Relation ◽  
Deformation And Fracture ◽  
Fracture Transition ◽  
Low Strain Rate

The mechanical properties of magma around the glass transition temperature have not been characterized yet, though this subject is considered to be important in dynamics of volcanic eruptions. In this paper, we present an experimental investigation of stress-strain relation of synthetic magma at various temperatures and strain rates. The material behaves as an elastic solid at low temperature and/or high strain rate, and as a viscous fluid at high temperature and/or low strain rate. In the transition, it reveals work-hardening response. Although the work-hardening nature has not been reported for noncrystalline magma, it is important in constructing a mathematical model to represent the flow-to-fracture transition of magma, namely the transition of eruptions from effusive to explosive styles.

Using Split Hopkinson Pressure Bars to Perform Large Strain Compression Tests on Neoprene at Intermediate and High Strain Rates

2013 ◽  
Vol 631-632 ◽  
pp. 458-462 ◽  
Author(s):  
Peng Duo Zhao ◽  
Yu Wang ◽  
Jian Ye Du ◽  
Lei Zhang ◽  
Zhi Peng Du ◽  
...  
Keyword(s):  
High Strain ◽  
Split Hopkinson Pressure Bar ◽  
Large Strain ◽  
Rate Sensitivity ◽  
Strain Rates ◽  
Compression Tests ◽  
Hopkinson Pressure Bar ◽  
High Strain Rates ◽  
Split Hopkinson ◽  
Pressure Bar

The strain rate sensitivity of neoprene is characterized using a modified split Hopkinson pressure bar (SHPB) system at intermediate (50 s-1, 100 s-1) and high (500 s-1, 1000 s-1) strain rates. We used two quartz piezoelectric force transducers that were sandwiched between the specimen and experimental bars respectively to directly measure the weak wave signals. A laser gap gage was employed to monitor the deformation of the sample directly. Three kinds of neoprene rubbers (Shore hardness: SHA60, SHA65, and SHA70) were tested using the modified split Hopkinson pressure bar. Experimental results show that the modified apparatus is effective and reliable for determining the compressive stress-strain responses of neoprene at intermediate and high strain rates.

A New Instrument for Tensile Testings of Thin Free Standing Films at High Strain Rates

2008 ◽  
Author(s):  
Eran Ben-David ◽  
Doron Shilo ◽  
Daniel Rittel ◽  
David Elata
Keyword(s):  
Mechanical Response ◽  
High Strain ◽  
Measurement Techniques ◽  
Experimental System ◽  
Uniaxial Tensile ◽  
Strain Rates ◽  
High Strain Rates ◽  
Optical Encoder ◽  
Free Standing ◽  
New Instrument

The design of more reliable and sophisticated Micro Electro Mechanical Systems (MEMS) relies on the knowledge, understanding, and ability to control their mechanical response. In recent years, enormous progress has been made in developing new measurement techniques for studying the mechanical response of sub-micro scale specimens. However, there is still a lack of knowledge and testing techniques regarding the response of MEMS structures to mechanical shocks, which can appear during fabrication, deployment, or operation. We present an instrument for testing the mechanical response of thin free standing films under uniaxial tensile stress at high strain rates of up to 2×103 sec-1. The experimental system consists of a micro-device, which contains the freestanding specimen, and an external system, which includes instrumentation for measuring its mechanical response. The components of the external system are controlled by a single interface, and allow for a variety of displacement profiles to be applied to the specimens. All the instrumentation operates at high sampling rates (above 1 MHz) to allow for high strain rate application. The freestanding specimen is produced by MEMS fabrication techniques on a micro-device that also includes S-springs to protect the specimen and aluminum grating lines for measuring the displacement. One side of the chip is pulled by a piezoelectric translation stage, which allows controlling the displacement with a nanometric resolution and applying high velocities and accelerations. The specimen displacement is monitored by an optical encoder device that measure the displacement of the aluminum grating located on the micro-device close to the specimen with an accuracy of about 10 nm. The load is determined by measuring the charge on a piezoelectric PMN-30%PT shear plate, which is connected to the pin that holds the micro-device. The new instrument is applied for studying the response of thin aluminum films with thickness of 0.5–1 μm, width that varies between 5 to 50 μm, and length of 120 μm. The mechanical response of these specimens is measured at different strain rates and is compared to measurement done by nanoindentation.

AN IMAGE BASED INERTIAL IMPACT TEST TO EXTRACT VISCOELASTIC CONSTITUTIVE PARAMETERS

2021 ◽  
Author(s):  
ANDREW MATEJUNAS ◽  
LLOYD FLETCHER ◽  
LESLIE LAMBERSON
Keyword(s):  
Strain Rate ◽  
Polymer Matrix ◽  
Mechanical Response ◽  
High Strain ◽  
High Rate ◽  
Strain Rates ◽  
High Strain Rates ◽  
Full Field ◽  
Viscoelastic Parameters ◽  
Constitutive Parameters

Polymer matrix composites often exhibit a strong strain rate dependance in their mechanical response. In many of these materials, the viscoelastic behavior of the polymer matrix drives the rate dependence in the composite, however identifying these parameters at high strain rate presents a significant challenge. Common high-rate material characterization techniques such as the Kolsky (split-Hopkinson pressure) bar require a large test matrix across a range of strain rates. Kolsky bars also struggle to identify constitutive parameters prior to the yield due to inertial effects and the finite period of time required to reach force equilibrium. The Image Based Inertial Impact (IBII) test has been successfully used to identify linear elastic constitutive behavior of composites at high strain rates, but, to date, has only been used to extract constitutive properties at a single nominal strain rate in each test. Here, we propose an adaptation of the IBII test to identify viscoelastic parameters at high strain rates using full-field displacement data and the nonlinear virtual fields method (VFM). We validate the technique with finite element simulations of an IBII test on a model viscoelastic material that is characterized with a Prony series formulation of the generalized Maxwell model. The nonlinear VFM is then used to extract the Prony pairs for dynamic moduli and time constants from the full-field deformation data. The nonlinear viscoelastic identification allows for characterization of the evolution of mechanical response across a range of strain rates in a single experiment. The experimentally identified viscoelastic parameters of the matrix can then be used to predict the behavior of the composite at high strain rates. This approach will also be validated experimentally using a single-stage gas-gun to characterize the high-rate viscoelastic response of PMMA.

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