scholarly journals Effects of Temperature on the Evolution of Yield Surface and Stress Asymmetry in A356–T7 Cast Aluminium Alloy

Materials ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 7898
Author(s):  
Elanghovan Natesan ◽  
Johan Ahlström ◽  
Stefan Eriksson ◽  
Christer Persson
Keyword(s):  
Flow Stress ◽  
Aluminium Alloy ◽  
Internal Combustion Engines ◽  
Elevated Temperatures ◽  
Internal Combustion ◽  
Effect Of Temperature ◽  
Mean Stress ◽  
Cast Aluminium ◽  
Stress Asymmetry ◽  
Mean Strain

As the electrification of vehicle powertrains takes prominence to meet stringent emission norms, parts of internal combustion engines like cylinder heads are subjected to an increased number of thermal load cycles. The cost-effective design of such structures subjected to cyclic thermo-mechanical loads relies on the development of accurate material models capable of describing the continuum deformation behaviour of the material. This study investigates the effect of temperature on the evolution of flow stress under cyclic loading in A356-T7 + 0.5% Cu cast aluminium alloy commonly used in modern internal combustion engine cylinder heads. The material exhibits peak stress and flow stress asymmetry with the stress response and flow stress of the material under compressive loading higher than under tension. This peak and flow stress asymmetry decrease with an increase in temperature. To compare this stress asymmetry against conventional steel, cyclic strain-controlled fatigue tests are run on fully pearlitic R260 railway steel material. To study the effect of mean strain on the cyclic mean stress evolution and fatigue behaviour of the alloy, tests with tensile and compressive mean strains of +0.2% and −0.2% are compared against fully reversed (Rε = −1) strain-controlled tests. The material exhibits greater stress asymmetry between the peak tensile and peak compressive stresses for the strain-controlled tests with a compressive mean strain than the tests with an identical magnitude tensile mean strain. The material exhibits mean stress relaxation at all temperatures. Reduced durability of the material is observed for the tests with tensile mean strains at lower test temperatures of up to 150 °C. The tensile mean strains at elevated temperatures do not exhibit such a detrimental effect on the endurance limit of the material.

scholarly journals The influence of pressure on the spontaneous ignition of inflammable gas-air mixtures. I.—Butane-air mixtures

1933 ◽  
Vol 141 (844) ◽  
pp. 484-493 ◽  
Keyword(s):  
Internal Combustion Engines ◽  
Elevated Temperatures ◽  
Internal Combustion ◽  
Adiabatic Compression ◽  
Spontaneous Ignition ◽  
Time Lags ◽  
Combustion Engines ◽  
Compression Method ◽  
Present Communication ◽  
Slow Combustion

As part of an investigation into explosions of various hydrocarbon-air media at elevated temperatures and pressures, we have recently been deter­mining the influence of varying initial pressures up to 15 atmospheres on their reactivities during slow combustion up to their ultimate ignition points. And as the results obtained in the experiments on the spontoneous ignition of butane-air mixtures have presented some very striking new features, which seem of undoubted importance in regard to the problem of “knock” in internal combustion engines, we are submitting them in the present communication. Hitherto, few investigators have determined spontaneous ignition tempera­tures under pressure and, in particular, little is known concerning the behaviours of mixtures with air of the higher members of the paraffin hydrocarbons. The principal research on this problem has been that of Tizard and Pye, who, employing the adiabatic compression method, found with pentane-, hexane-, heptane-, and octane-air mixtures that with compression ratios of 6·09 to 1 ignition occurred at temperatures of circa 300° C. which ( a ) were dependent upon the observed time-lags between compression and ignition, ( b ) varied but little with mixture composition, and ( c ) were lowered slightly as the paraffin series was ascended.

scholarly journals A Constitutive Relation Based on the Johnson–Cook Model for Ti-22Al-23Nb-2(Mo, Zr) Alloy at Elevated Temperature

Crystals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 754
Author(s):  
Yanju Wang ◽  
Duo Zhou ◽  
Yi Zhou ◽  
Aixue Sha ◽  
Huaxing Cheng ◽  
...  
Keyword(s):  
Elevated Temperature ◽  
Flow Stress ◽  
Constitutive Relation ◽  
Deformation Behavior ◽  
Elevated Temperatures ◽  
Peak Stress ◽  
Testing Temperature ◽  
Effect Of Temperature ◽  
Different Temperatures ◽  
Zr Alloy

Although several schemes have been proposed to modify the classical Johnson–Cook (J-C) model, the effect of temperature on the flow stress of materials at different temperatures has not been clarified. In the current study, to investigate the deformation behavior of Ti-22Al-23Nb-2(Mo, Zr) alloy at different temperatures, uniaxial tension experiments were performed at both room (RT, 28 °C) and elevated temperatures, and a modified J-C model was developed to describe the temperature-dependent plastic flow. In tensile experiments, Ti2AlNb-based alloy showed a continuous work hardening until reaching the ultimate strength at RT, while an apparent drop appeared in the flow stress after the peak stress at elevated temperature. Moreover, the experimental peak stress significantly depends on the testing temperature. To correctly describe the different variations of flow stresses at different temperatures, a parameter, S, which represents the softening behavior of flow stress, is integrated into the classical J-C model. In addition, the applicability and validity of the proposed J-C model were verified by calibration with experimental curves of different temperatures. On the other hand, the fractography of post-test specimens was examined to interrupt the increased fracture brittleness of Ti2AlNb-based alloy at elevated temperatures. The proposed constitutive relation based on the J-C model is applicable to predict the deformation behavior of other Ti2AlNb-based alloys at different temperatures.

Effect of Temperature, Velocity Gradient and I.V. Heparin on in Vitro Blood Coagulation and Platelet Aggregation

1967 ◽  
Vol 17 (01/02) ◽  
pp. 112-119 ◽  
Author(s):  
L Dintenfass ◽  
M. C Rozenberg
Keyword(s):  
Blood Coagulation ◽  
Velocity Gradient ◽  
Elevated Temperatures ◽  
Morphological Changes ◽  
Effect Of Temperature ◽  
Clotting Time ◽  
Progressive Change ◽  
Aggregation Of Platelets ◽  
Microscopic Techniques

SummaryA study of blood coagulation was carried out by observing changes in the blood viscosity of blood coagulating in the cone-in-cone viscometer. The clots were investigated by microscopic techniques.Immediately after blood is obtained by venepuncture, viscosity of blood remains constant for a certain “latent” period. The duration of this period depends not only on the intrinsic properties of the blood sample, but also on temperature and rate of shear used during blood storage. An increase of temperature decreases the clotting time ; also, an increase in the rate of shear decreases the clotting time.It is confirmed that morphological changes take place in blood coagula as a function of the velocity gradient at which such coagulation takes place. There is a progressive change from the red clot to white thrombus as the rates of shear increase. Aggregation of platelets increases as the rate of shear increases.This pattern is maintained with changes of temperature, although aggregation of platelets appears to be increased at elevated temperatures.Intravenously added heparin affects the clotting time and the aggregation of platelets in in vitro coagulation.

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