The influence of the lath morphology on the yield stress and transition temperature of martensitic- bainitic steels

1979 ◽  
Vol 10 (7) ◽  
pp. 861-873 ◽  
Author(s):  
J. P. Naylor
Keyword(s):  
Transition Temperature ◽  
Yield Stress ◽  
Bainitic Steels ◽  
Lath Morphology

scholarly journals Modelling the Mechanical and Strain Recovery Behaviour of Partially Crystalline PLA

Polymers ◽  
2019 ◽  
Vol 11 (8) ◽  
pp. 1342 ◽  
Author(s):  
John Sweeney ◽  
Paul Spencer ◽  
Karthik Nair ◽  
Phil Coates
Keyword(s):  
Finite Element ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Stress Relaxation ◽  
Shape Memory ◽  
Yield Stress ◽  
Amorphous Phase ◽  
Strain Recovery ◽  
Stress Strain

This is a study of the modelling and prediction of strain recovery in a polylactide. Strain recovery near the glass transition temperature is the underlying mechanism for the shape memory in an amorphous polymer. The investigation is aimed at modelling such shape memory behaviour. A PLA-based copolymer is subjected to stress–strain, stress relaxation and strain recovery experiments at large strain at 60 °C just below its glass transition temperature. The material is 13% crystalline. Using published data on the mechanical properties of the crystals, finite element modelling was used to determine the effect of the crystal phase on the overall mechanical behaviour of the material, which was found to be significant. The finite element models were also used to relate the stress–strain results to the yield stress of the amorphous phase. This yield stress was found to possess strain rate dependence consistent with an Eyring process. Stress relaxation experiments were also interpreted in terms of the Eyring process, and a two-process Eyring-based model was defined that was capable of modelling strain recovery behaviour. This was essentially a model of the amorphous phase. It was shown to be capable of useful predictions of strain recovery.

Radiation hardening in magnox pressure-vessel steels

1985 ◽  
Vol 315 (1532) ◽  
pp. 301-332 ◽  
Keyword(s):  
Transition Temperature ◽  
Brittle Fracture ◽  
Yield Stress ◽  
Pressure Vessel ◽  
Pressure Vessels ◽  
Nuclear Industry ◽  
Spherical Particles ◽  
Irradiation Hardening ◽  
Copper Precipitation ◽  
Pressure Vessel Steels

The ferritic steels used for reactor pressure vessels undergo a marked transition from ductile to brittle fracture behaviour over a relatively narrow temperature range. For most unirradiated mild steels the ductile to brittle transition temperature (d.b.t.t.) is between — 50° and 20 °C. The process of irradiation hardening, through the formation of clusters of interstitial or vacancy defects, increases the friction stress of these steels and thereby raises the transition temperature. Given the inherent tendency of these steels to fail in a brittle manner, the raising of the transition temperature under neutron irradiation poses a problem of considerable technological importance in the nuclear industry. At the time (1962) when the first of the Central Electricity Generating Board (C.E.G.B.) Magnox nuclear stations began operation the phenomenon of brittle fracture was already comparatively well understood. A theory of the process had already been developed and applied to the problem of radiation embrittlement. However, as the results from the Magnox pressure-vessel surveillance scheme accumulated, it gradually became evident that the measured changes in yield stress in the monitoring specimens could not be accounted for simply on the basis of irradiation hardening through the formation of damage clusters. By the late 1970s, sufficient data had been gathered from the surveillance programme to enable a detailed investigation of the processes occurring in the Magnox steels to be instituted. The form of the investigation was to subsequently evolve into two phases; an initial com prehensive microstructural study of the steels, followed by the formation of an interpretative model based on the observations. In this paper we present the Magnox yield-stress monitoring measurements and then briefly describe the principal findings from our microstructural studies. The Magnox pressure-vessel steels contain between 0.05 and 0 .4 % by mass of copper and we show that under certain conditions this element may precipitate as small spherical particles within the matrix of the steels. A review of previous work on copper precipitation in ferrite is then followed by a description of our model. This assumes that the changes in yield stress generally arise from the combined effects of irradiation damage loops and copper precipitates. The formation of the latter may be enhanced by irradiation and in some steels their contribution is dominant. It is shown that the model successfully accounts for the measurements made on both plate and weld steels in all the Magnox stations. Experimental support for the model comes from our own microstructural observations and from other studies, in the U.K. and elsewhere, using techniques which allow the detection of sub-microscopic particles in steels. The model may be applied to pressure-vessel steels in other reactor systems. Indeed, it predicts that the yield-stress changes in steels with a high copper content irradiated under p.w.r. (pressurized water reactor) conditions will be dominated by the contribution from copper precipitation.

In situ Tensile Experiments at Low Temperatures on Niobium Single Crystals by H.V.E.M.

1975 ◽  
Vol 33 ◽  
pp. 58-59
Author(s):  
F. H. Louchet ◽  
L. P. Kubin
Keyword(s):  
Electron Microscope ◽  
Transition Temperature ◽  
Low Temperature ◽  
Slip System ◽  
Low Temperatures ◽  
Tensile Axis ◽  
Image Intensifier ◽  
Screw Dislocations ◽  
Source Operation

Experiments have been carried out on the 3 MeV electron microscope in Toulouse. The low temperature straining holder has been previously described Images given by an image intensifier are recorded on magnetic tape.The microtensile niobium samples are cut in a plane with the two operative slip directions [111] and lying in the foil plane. The tensile axis is near [011].Our results concern:- The transition temperature of niobium near 220 K: at this temperature and below an increasing difference appears between the mobilities of the screw and edge portions of dislocations loops. Source operation and interactions between screw dislocations of different slip system have been recorded.

The structure of membranes and membrane proteins embedded in amorphous ice

1992 ◽  
Vol 50 (1) ◽  
pp. 432-433
Author(s):  
Uwe Lücken ◽  
Joachim Jäger
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Membrane Proteins ◽  
Phase Transition Temperature ◽  
Lipid Vesicles ◽  
Freezing Stress ◽  
Amorphous Ice ◽  
Different Temperatures ◽  
Band Pass ◽  
Lipid Polymorphism

TEM imaging of frozen-hydrated lipid vesicles has been done by several groups Thermotrophic and lyotrophic polymorphism has been reported. By using image processing, computer simulation and tilt experiments, we tried to learn about the influence of freezing-stress and defocus artifacts on the lipid polymorphism and fine structure of the bilayer profile. We show integrated membrane proteins do modulate the bilayer structure and the morphology of the vesicles.Phase transitions of DMPC vesicles were visualized after freezing under equilibrium conditions at different temperatures in a controlled-environment vitrification system. Below the main phase transition temperature of 24°C (Fig. 1), vesicles show a facetted appearance due to the quasicrystalline areas. A gradual increase in temperature leads to melting processes with different morphology in the bilayer profile. Far above the phase transition temperature the bilayer profile is still present. In the band-pass-filtered images (Fig. 2) no significant change in the width of the bilayer profile is visible.

Sign in / Sign up

Export Citation Format

Share Document