The deformation of metals under small stresses during phase transformations

1965 ◽  
Vol 283 (1394) ◽  
pp. 403-422 ◽  
Keyword(s):  
Phase Transformation ◽  
Flow Stress ◽  
Phase Transformations ◽  
Plastic Flow ◽  
Reasonable Agreement ◽  
Creep Behaviour ◽  
External Stress ◽  
Random Orientation ◽  
Transformation Front ◽  
Theory And Experiment

Stresses are developed internally in metals when a change in density and strength arises from a phase transformation. It is shown that plastic flow, generally confined to the weaker phase, results from the accommodation of strain due to the transformation front. The form of the plastic flow is considered in terms of the extreme cases of yield and creep behaviour. It is deduced that, for a complete cycle both ways through the transformation temperature, the resultant deformation varies linearly with the applied stress (provided this is small), the fractional volume change on transformation and inversely as the flow stress of the weaker phase. The deformation is not zero in the absence of external stress except where the phase transformation front has random orientation and movement. The theoretically deduced relations are examined experimentally by observing the deformation of specimens with attached weights, giving small tensile stresses, while their temperature was cycled through a transformation point. Phase transformations were examined in a number of metals involving a variety of crystal structures: reasonable agreement between theory and experiment was obtained in all cases.

Heat capacities and enthalpies of fusion and transformation for solvates of some salts with dimethyl sulfoxide and dimethylformamide

1988 ◽  
Vol 53 (12) ◽  
pp. 3072-3079
Author(s):  
Mojmír Skokánek ◽  
Ivo Sláma
Keyword(s):  
Heat Capacity ◽  
Phase Transformation ◽  
Phase Transformations ◽  
Dimethyl Sulfoxide ◽  
Liquidus Temperature ◽  
Molar Heat Capacity ◽  
Solid Phase ◽  
Zinc Nitrate ◽  
Heat Capacities ◽  
Liquid Phases

Molar heat capacities and molar enthalpies of fusion of the solvates Zn(NO3)2 . 2·24 DMSO, Zn(NO3)2 . 8·11 DMSO, Zn(NO3)2 . 6 DMSO, NaNO3 . 2·85 DMSO, and AgNO3 . DMF, where DMSO is dimethyl sulfoxide and DMF is dimethylformamide, have been determined over the temperature range 240 to 400 K. Endothermic peaks found for the zinc nitrate solvates below the liquidus temperature have been ascribed to solid phase transformations. The molar enthalpies of the solid phase transformations are close to 5 kJ mol-1 for all zinc nitrate solvates investigated. The dependence of the molar heat capacity on the temperature outside the phase transformation region can be described by a linear equation for both the solid and liquid phases.

Unbalance Response of a Dual Rotor System: Theory and Experiment

1993 ◽  
Vol 115 (4) ◽  
pp. 427-435 ◽  
Author(s):  
K. Gupta ◽  
K. D. Gupta ◽  
K. Athre
Keyword(s):  
System Theory ◽  
Transfer Matrix ◽  
Mode Shape ◽  
Reasonable Agreement ◽  
Complex Variables ◽  
Rotor System ◽  
Experimental Results ◽  
Unbalance Response ◽  
Theoretical Results ◽  
Theory And Experiment

A dual rotor rig is developed and is briefly discussed. The rig is capable of simulating dynamically the two spool aeroengine, though it does not physically resemble the actual aeroengine configuration. Critical speeds, mode shape, and unbalance response are determined experimentally. An extended transfer matrix procedure in complex variables is developed for obtaining unbalance response of dual rotor system. Experimental results obtained are compared with theoretical results and are found to be in reasonable agreement.

scholarly journals Internal stress created by plastic flow in mild steel, and stress-strain curves for the atomic lattice of higher carbon steels

1944 ◽  
Vol 182 (991) ◽  
pp. 404-414 ◽  
Keyword(s):  
Mild Steel ◽  
Internal Stress ◽  
Plastic Flow ◽  
Carbon Steels ◽  
External Stress ◽  
Stress Strain ◽  
Atomic Lattice ◽  
X Ray ◽  
Elastic Range ◽  
Residual Strains

In previous work, stress-strain curves for the atomic lattice of certain metals have been obtained from X-ray diffraction measurements of the lattice dimensions of test specimens under tension or compression, and it has been shown that when the external yield stress is exceeded, there is a systematic departure from Hooke’s Law. It is pointed out in the present paper that this departure indicates that the external applied stress above the yield is no longer balanced primarily by simple displacement of the atoms but also by a new type of secondary internal stress brought about by the process of plastic flow; and that this secondary stress, being of a permanent nature, can be measured by the residual lattice strains exhibited by the lattice after removal of the external stress. These residual strains are measured in various directions to the stress direction for mild steel subjected to tension, and it is shown that the lattice after tension exhibits a longitudinal compression and a transverse expansion in the ratio of 2:1, which means that the density of the material is thereby kept constant. Comparisons of X-ray and mechanical measurements further show that the hysteresis loop exhibited by the external stress-strain curve of mild steel after overstrain can disappear and the linear elastic relation be recovered without any corresponding change in the internal stress, which is therefore a more fundamental physical property. It is also shown that when the elastic range is extended by overstrain in tension, there is no symmetrical increase in the elastic range in subsequent compression, thus confirming the existence and direction of the secondary internal stress. Finally, the lattice stress-strain curves are also obtained for a 0.4 % C steel (partially pearlitic) and a 0.8 % C steel (pearlitic), and by comparison with the results on pure iron and 0.1 % C steel (annealed) it is shown that the maximum residual internal strain developed by the lattice increases markedly with the fineness to which the crystallites can be broken down by the plastic deformation.

Calculations of Phase Transformations in Welding Simulations

2014 ◽  
Vol 611 ◽  
pp. 46-53 ◽  
Author(s):  
Ladislav Novotný ◽  
Vladimír Ivančo
Keyword(s):  
Heat Flux ◽  
Phase Transformation ◽  
Boundary Conditions ◽  
Phase Transformations ◽  
Diffusion Processes ◽  
Transient Solution ◽  
Welding Simulation

In the paper the principle of welding simulation is presented and the methods of solution of phase transformation are described. The first part characterizes elementary equations of heat transient solution, boundary conditions during welding simulation (prescribing moving heat flux, convection, radiation). The methods of phase transformations’ solution are described for diffusion processes as well as diffusionless processes.

Influence of Phase Transformations on Residual Stresses in Welded Structures

2013 ◽  
Author(s):  
R. J. Dennis ◽  
R. Kulka ◽  
O. Muransky ◽  
M. C. Smith
Keyword(s):  
Phase Transformation ◽  
Residual Stresses ◽  
Phase Transformations ◽  
Numerical Models ◽  
Material Model ◽  
Transformation Model ◽  
Austenitic Steels ◽  
Beam Specimen ◽  
Welded Structures ◽  
The Impact

A key aspect of any numerical simulation to predict welding induced residual stresses is the development and application of an appropriate material model. Often significant effort is expended characterising the thermal, physical and hardening properties including complex phenomena such as high temperature annealing. Consideration of these aspects is sufficient to produce a realistic prediction for austenitic steels, however ferritic steels are susceptible to solid state phase transformations when heated to high temperatures. On cooling a reverse transformation occurs, with an associated volume change at the isothermal transformation temperature. Although numerical models exist (e.g. Leblond) to predict the evolution of the metallurgical phases, accounting for volumetric changes, it remains a matter of debate as to the magnitude of the impact of phase transformations on residual stresses. Often phase transformations are neglected entirely. In this work a simple phase transformation model is applied to a range of welded structures with the specific aim of assessing the impact, or otherwise, of phase transformations on the magnitude and distribution of predicted residual stresses. The welded structures considered account for a range of geometries from a simple ferritic beam specimen to a thick section multi-pass weld. The outcome of this work is an improved understanding of the role of phase transformation on residual stresses and an appreciation of the circumstances in which it should be considered.

Analysis of Hot Deformation Dynamics of TC18 Titanium Alloy

2013 ◽  
Vol 747-748 ◽  
pp. 878-884 ◽  
Author(s):  
Qing Rui Wang ◽  
Ai Xue Sha ◽  
Xing Wu Li ◽  
Li Jun Huang
Keyword(s):  
Titanium Alloy ◽  
Phase Transformation ◽  
Flow Stress ◽  
Strain Rate ◽  
Hot Deformation ◽  
Deformation Temperature ◽  
Relationship Model ◽  
Deformation Dynamics ◽  
Deformation Mechanics ◽  
Versus Strain

The effect of strain rate and deformation temperature on flow stress of TC18 titanium alloy was studied through heat simulating tests in 760~960 with temperature interval and the strain rate interval in 0.01~10s-1. Relationship model of flow stress versus strain was established and hot deformation mechanics of TC18 titanium alloy was analyzed. The results show that the flow stress reduces obviously as the deformation temperature increases or the strain rate decreases. Dynamic recovery occurs at high strain rate above phase transformation point, while dynamic recrystallization occurs at low strain rate as well as at the temperature below phase transformation point.

Sign in / Sign up

Export Citation Format

Share Document