Anomalies in flow stress and work-hardening coefficient of polycrystalline metals at low temperatures

1987 ◽  
Vol 6 (1) ◽  
pp. 54-56 ◽  
Author(s):  
Muhammad Zakria Butt ◽  
Syed Mohsin Raza
Keyword(s):  
Flow Stress ◽  
Work Hardening ◽  
Low Temperatures ◽  
Polycrystalline Metals ◽  
Work Hardening Coefficient ◽  
Hardening Coefficient

scholarly journals Autowave nature of plasticity. Scale invariance

2019 ◽  
Vol 221 ◽  
pp. 01019
Author(s):  
Lev Zuev
Keyword(s):  
Work Hardening ◽  
Flow Localization ◽  
Localized Deformation ◽  
Quasi Particle ◽  
Localization Of Plastic Deformation ◽  
Work Hardening Coefficient ◽  
Reciprocal Value ◽  
The Given ◽  
The Waves ◽  
Hardening Coefficient

The generality of localization of plastic deformation, which is observed at the stage of linear work hardening for HCP, BCC and FCC monoand polycrystals of pure metals and alloys, is considered. It was found previously that the motion rate of localized flow autowave is related to the reciprocal value of the work hardening coefficient by a linear law, which is universal in character. This is further substantiated by the results of the given study. The waves of plastic flow localization are found to have dispersion law. It has been established that in order to address the autowave of localized deformation, a quasi-particle may be introduced. The quasi-particle’s characteristics have been defined.

Identification of the constitutive equation by the indentation technique using plural indenters with different apex angles

2001 ◽  
Vol 16 (8) ◽  
pp. 2283-2292 ◽  
Author(s):  
Masatoshi Futakawa ◽  
Takashi Wakui ◽  
Yuji Tanabe ◽  
Ikuo Ioka
Keyword(s):  
Constitutive Equation ◽  
Yield Stress ◽  
Work Hardening ◽  
Indentation Technique ◽  
Work Hardening Coefficient ◽  
The Relationship ◽  
Stress Work ◽  
Hardening Coefficient ◽  
Depth Curve ◽  
Work Hardening Exponent

This paper describes a novel technique for determining the constitutive equation of elastic–plastic materials by the indentation technique using plural indenters with different apex angles. Finite element method (FEM) analyses were carried out to evaluate the effects of yield stress, work hardening coefficient, work hardening exponent, and the apex angle of indenter on the load–depth curve obtained from the indentation test. As a result, the characterized curves describing the relationship among the yield stress, work hardening coefficient, and the work hardening exponent were established. Identification of the constants of a constitutive equation was made on the basis of the relationship between the characterized curves and the hardness given by the load–depth curve. This technique was validated through experiments on Inconel 600 and aluminum alloy. The determined constitutive equation was applied to the FEM analyses to simulate the deformation including necking behavior under uniaxial tension. The analytical results are in good agreement with experimental results.

Development of Universal Methodology of Specimen Free Nondestructive Inspection (Control) of Mechanical Properties of NPP Equipment Metal in All Stages of Lifetime

2009 ◽  
Author(s):  
Murat Bakirov ◽  
Sergei Chubarov ◽  
Igor Frolov ◽  
Joerg Gastrock
Keyword(s):  
Mechanical Properties ◽  
Life Cycle ◽  
Work Hardening ◽  
Pressure Vessel Steel ◽  
Universal Method ◽  
Hardness Testing ◽  
Vessel Steel ◽  
Work Hardening Coefficient ◽  
Hardening Coefficient ◽  
Inspection Control

Ever-increasing requirements for reliability and safety of equipment in nuclear power plants (NPP) dictate a necessity to obtain reliable and validated information about the condition of materials in the most safety-relevant and economically vital systems structures and components (SSC). Thus it is a state of science and technology approach to use one method, one methodic and one methodology to facilitate these goals with the purpose of keeping NPPs operating safely by virtue of knowing the state of ageing they are in (with respect to design limits and margins). Method of the control/measurement/testing - how to conduct measurements; methodic - how to interpret the results of measurement; methodology - the program of the control/inspection and testing programmes: localities to conduct the tests, how often, and to follow evolution of test results with the aim of acting before a failure occurs. Such methodology should be based on the use of specimen-free nondestructive method of the inspection (control), which could be used successfully at all stages of life cycle of the equipment: manufacturing, construction, installation of NPP, operation and during the NPP operation through integration into the Plant Life Management (PLiM) programme [1]. It will facilitate a real picture of change (degradation) of a SSC material’s condition in the zones subjected to the harschest stressors (neutron irradiation, erosion-corrosion/flow, thermal fatigue, vibration etc). Currently, there are various approaches used in the world to follow NPP ageing degradation, but until now, no specific methodology is used that could supply all the necessary information [2]. Therefore, there is no way to use various results. Thanks to considerable advances over the last 20 years or so, the science of hardness testing offers an elegant, non-destructive way to obtain vital materials properties — even in-situ on operating SSC [3–6]. In particular, the material’s elastic-plastic condition may be measured, giving indications on tensile yield stress elevation due to hardening and also loss in ductility. The work-hardening index may be easily obtained, giving information on the ability of the material (e.g. pressure vessel steel and weld) to deform plastically without brittle fracture. Taking into account the experience of the Center of Material Science and Lifetime Management Ltd. (CMSLM Ltd.) in the use of methods of hardness testing for the inspection of the equipment of NPP of Russian manufacture in Russia, Germany, Czech, Slovakia, Bulgaria [7], and also similar successful works in this direction in USA (Oakridge) [8], to Czech (NRI Rez) and other countries, it can be seen that the most promising direction in the field of specimen-free inspection of mechanical properties by use of hardness and hardness-related characteristics is use of the kinetic indentation method (KIM, ABIT). This method is based on recording the process of elastoplastic deformation caused by the indentation of a ball indenter. This method allows one to obtain, besides hardness values, tensile properties, elongation, work hardening coefficient, true-stress/true strain diagrammes which normally required the destructive testing of small specimens. However, till now there is no universal method of interpreting the information obtained, although it is generally known that irradiation causes a loss in ductility and increase in hardness and lowering of the work-hardening coefficient. Thus, it is necessary to develop a uniform methodology of using KIM, ABIT with reference to the inspection of materials which will allow to unify the inspection of materials of various classes of the equipment of NPP over all stages of life cycle. With the purpose of introduction of such a methodology it is necessary to develop and realize the program in the frames of IAEA with the above name.

Dislocation Exhaustion During Plastic Deformation

2000 ◽  
Vol 653 ◽  
Author(s):  
Olivier Couteau ◽  
Corinne Charbonnier ◽  
Tomas Kruml ◽  
Jean-Luc Martin
Keyword(s):  
Plastic Deformation ◽  
Stress Relaxation ◽  
Single Crystals ◽  
Work Hardening ◽  
Mobile Dislocation ◽  
Deformation Parameters ◽  
Work Hardening Coefficient ◽  
Relaxation Experiments ◽  
Two Parameters ◽  
Hardening Coefficient

AbstractRepeated stress-relaxation experiments are used to characterize the deformation parameters in 3 types of single crystals (Cu, Ni3Al and Ge) in which different dislocation mechanisms are known to operate. Mobile dislocation exhaustion rates and the amplitude of the yield point at reloading after stress-relaxation are measured. These two parameters are discussed in terms of the work-hardening coefficient in monotonic tests.

Experimental and Numerical Simulation Study of Plasticity-Induced and Roughness-Induced Fatigue Crack Closure

2014 ◽  
Vol 891-892 ◽  
pp. 307-312
Author(s):  
Kenichi Masuda ◽  
Sotomi Ishihara ◽  
Yuya Sugai ◽  
A.J. McEvily
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Crack ◽  
Carbon Steel ◽  
Crack Closure ◽  
Work Hardening ◽  
Crack Opening ◽  
Fatigue Crack Closure ◽  
Work Hardening Coefficient ◽  
Hardening Coefficient ◽  
Alloy 6061

In this study, fatigue crack closure behavior was investigated in the aluminum alloy 6061-T6 and the carbon steel JIS. S25C. It was found that crack closure in the aluminum alloy 6061-T6 showed the characteristics of plasticity-induced fatigue crack closure (PIFCC), whereas the carbon steel JIS. S25C showed the characteristics of roughness-induced fatigue crack closure (RIFCC). The experiments included the determination of the crack-opening levelsKopas a function of stress intensity factor range ΔKand the effect of surface removal on the crack-opening level. In order to simulate the behaviors of the plasticity-and the roughness-induced fatigue crack closure, the finite element method was adopted. The results of FEM were in good agreement with the experimental results. It was cconcluded that at a given yield strength level , a low Youngs modulus and a low work-hardening coefficient will favor PIFCC, whereas a high Youngs modulus and a high work-hardening coefficient will favor RIFCC.

Least squares computation of the prestrain and work hardening parameters of sheet metal

1980 ◽  
Vol 15 (3) ◽  
pp. 113-116 ◽  
Author(s):  
E H Twizell ◽  
I Adak
Keyword(s):  
Least Squares ◽  
Work Hardening ◽  
Optimization Methods ◽  
True Stress ◽  
Large Strains ◽  
Linear Least Squares ◽  
Elementary Methods ◽  
Work Hardening Coefficient ◽  
Least Squares Optimization ◽  
Hardening Coefficient

For most metals the load-extension and stress-strain graphs are too complicated for easy mathematical analysis, and empirical equations must be formed. One such equation, which is especially useful when large strains are experienced, is Swift's equation σ = A( B + ∊) n where ∊ and σ represent logarithmic strain and true stress, respectively. The prestrain and work hardening coefficient are represented by B and n respectively, and A is a constant for the metal being used. Non-linear least squares optimization methods are more accurate than elementary methods for computing A. B. and n from discrete data pairs (∊i,σi)i= 1,2,…, N (N≥3) determined experimentally, and a model is developed which adapts the Gauss-Newton and Levenberg-Marquardt algorithms for this purpose. Numerical results for a number of specimen sheets are reported, and comparisons of the reliability and efficiency of the two algorithms are made.

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