Home About us Contact
|
Home About us Contact | ||
|
|
||
Constant Load (constant + load)
Selected AbstractsLocalization Events and Microstructural Evolution in Ultra-Fine Grained NiTi Shape Memory Alloys during Thermo-Mechanical Loading,ADVANCED ENGINEERING MATERIALS, Issue 6 2010Andreas Schaefer Subjecting a thin NiTi specimen to uniaxial tension often leads to a localized martensitic transformation: macroscopic transformation bands form and propagate through the specimen, separating it into regions of fully transformed martensite and original austenite. In the present study, the alternating current potential drop (ACPD) technique is used to analyze the change in electrical resistance of ultra-fine grained NiTi wires subjected to a broad range of thermo-mechanical load cases: (i) uniaxial tensile straining at constant temperatures (pseudoelastic deformation); (ii) cooling and heating through the transformation range at constant load (actuator load case); (iii) a combination of mechanical and thermal loading. We monitor the ACPD signals in several zones along the gauge length of specimens, and we demonstrate that a localized type of transformation is a generic feature of pseudoelastic as well as of shape memory deformation. Moreover, the ACPD signals allow to differentiate between temperature-induced martensite (formed during cooling at no or relatively small loads), stress-induced martensite, and reoriented martensite (formed under load at low temperatures). [source] Stress-Dependent Elastic Properties of Porous Microcracked Ceramics,ADVANCED ENGINEERING MATERIALS, Issue 12 2009Irina Pozdnyakova Abstract Although ceramics are considered linear elastic materials, we have observed a non-linear pseudo-elastic behavior in porous cellular microcracked ceramics such as , -eucryptite. This is attributed to the evolution of microstructure in these materials. This behavior is particularly different from that of non-microcracked ceramics such as silicon carbide. It is shown that in microcracked materials two processes, namely stiffening and softening, always compete when a compressive external load is applied. The first regime is attributed to microcrack closure, and the second to microcracks opening, i.e. to a damage introduced by the applied stress. On the other hand rather a continuous damage is observed in the non-microcracked case. A comparison has been done between the microscopic (as measured by neutron diffraction) and the macroscopic stress-strain response. Also, it has been found that at constant load a significant strain relaxation occurs, which has two timescales, possibly driven by the two phenomena quoted above. Indeed, no such relaxation is observed for non-microcracked SiC. Implications of these findings are discussed. [source] Is high strength concrete more susceptible to explosive spalling than normal strength concrete in fire?FIRE AND MATERIALS, Issue 3 2002Faris Ali There is a belief, within the fire research community, that high strength concrete is more susceptible to explosive spalling than normal strength concrete. This impression is based on studying concrete properties and collecting experimental data from different research sources. But there are still doubts about the credibility of this conjecture due to the lack of integrated experimental research, particularly designed to address this issue. This paper represents the outcomes of experimental study involving normal and high strength concrete columns tested under fire. The columns were subjected to a constant load and to different values of axial restraint. The paper attempts to address the question of the susceptibility of normal and high strength concrete to explosive spalling under fire. Copyright © 2002 John Wiley & Sons, Ltd. [source] Influence of advanced injection timing on the performance and emissions of CI engine fueled with ethanol-blended diesel fuelINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2008Cenk Sayin Abstract Ethanol has been considered as an alternative fuel for diesel engines. On the other hand, injection timing is a major parameter that sensitively affects the engine performance and emissions. Therefore, in this study, the influence of advanced injection timing on the engine performance and exhaust emissions of a single cylinder, naturally aspirated, four stroke, direct injection diesel engine has been experimentally investigated when using ethanol-blended diesel fuel from 0 to 15% with an increment of 5%. The original injection timing of the engine is 27° crank angle (CA) before top dead center (BTDC). The tests were conducted at three different injection timings (27, 30 and 33° CA BTDC) for 30 Nm constant load at 1800 rpm. The experimental results showed that brake-specific energy consumption (BSEC), brake-specific fuel consumption (BSFC), NOx and CO2 emissions increased as brake-thermal efficiency (BTE), smoke, CO and HC emissions decreased with increasing amount of ethanol in the fuel mixture. Comparing the results with those of original injection timing, NOx emissions increased and smoke, HC and CO emissions decreased for all test fuels at the advanced injection timings. For BSEC, BSFC and BTE, advanced injection timings gave negative results for all test conditions. Copyright © 2008 John Wiley & Sons, Ltd. [source] Structures and properties of ternary blends of recycled poly(ethylene terephthalate)/bisphenol-A polycarbonate/(E/nBA/GMA)JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Yong Peng Abstract Recycled poly(ethylene terephthalate)/bisphenol-A polycarbonate/PTW (ethylene, butylacrylate (BA), and glycidylmethacrylate (E/nBA/GMA) terpolymer) were blended in different sequence through low temperature solid state extrusion (LTSSE) was studied. R-PET/PC blends were toughened by PTW, resulting in the improvement of impact strengths. In tensile test, the (PC/PTW)/r-PET blends made by mixing r-PET with the preblend of PC/PTW had noticeable strengthening effect on its tensile properties, which was not impaired by the rubber content due to its strain-hardening occurred following its necking at the constant load. Morphological study by scanning electron microscopy (SEM) was in conformity with the mechanical result. For the (PC/PTW)/r-PET blends, the PC particles were well embedded in the PET matrix and the smooth morphology exhibited. The DSC thermographs for heating and cooling run indicated that the crystallinity of PET rich phase was affected by different blending sequence. In the FTIR test, the different absorption intensity of PC aromatic carbonate carbonyl band was clearly illustrated. The results indicated different blending sequence led to different blending effect. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Robustness improvement of a nonlinear H, controller for robot manipulators via saturation functionsJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 8 2005Manuel G. Ortega In this paper, previous works on nonlinear H, control for robot manipulators are extended. In particular, integral terms are considered to cope with persistent disturbances, such as constant load at the end-effector. The extended controller may be understood as a computed-torque control with an external PID, whose gain matrices vary with the position and velocity of the robot joints. In addition, in order to increase the controller robustness, an extension of the algorithms with saturation functions has been carried out. This extension deals with the resulting nonlinear equation of the closed-loop error. A modified expression for the required increment in the control signal is provided, and the local closed-loop stability of this approach is discussed. Finally, simulation results for a two-link robot and experimental results for an industrial robot are presented. The results obtained with this technique have been compared with those attained with the original controllers to show the improvements achieved by means of the proposed method. © 2005 Wiley Periodicals, Inc. [source] Delayed Failure of Hi-Nicalon and Hi-Nicalon S Multifilament Tows and Single Filaments at Intermediate Temperatures (500°,800°C)JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2009W. Gauthier Previous results have shown that tows of SiC Nicalon fibers are sensitive to the phenomenon of delayed failure, at temperatures below 700°C. The present paper examines the static fatigue of Hi-Nicalon and Hi-Nicalon S when subjected to constant load, at temperatures between 500° and 800°C in air. Multifilament tows and single filaments were tested. Experimental data show that the rupture times of tows depend on the applied stress according to the conventional power law t,n=A. In contrast, the stress-rupture time data obtained on single filaments exhibit significant scatter. A model based on slow crack growth in single filaments shows that the stress-rupture of fiber tows follows the conventional time power law. The dependence on temperature was introduced. The model allowed sound calculations of tow lifetimes and characteristics of the slow crack growth phenomenon to be extracted from the tow stress-rupture time data. [source] Separation of a sphere from a flat in the presence of couple stress fluidsLUBRICATION SCIENCE, Issue 1 2008Abdallah A. Elsharkawy Abstract A mathematical model for couple stress fluid is presented to analyse the separation flow of a fully flooded sphere from a flat under the condition of constant load. Assuming the lubricant between the sphere and the flat to contain additives, the couple stress effect, presented by the characteristic length of the additives, has been considered to account for the non-Newtonian behaviour. In addition, the effect of the sphere inertia on accelerating the separation process has been considered. Compared with the Newtonian fluid case, the results of the numerical solution indicated that the separation time increases with increasing the characteristic length of the additives. It was also found that the additive characteristic length has negligible effect on the thickness of the lubricant film at the separation point. Copyright © 2007 John Wiley & Sons, Ltd. [source] Hydrogen degradation of structural steels in technical hydrocarbon liquidsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 4 2008B. Swieczko-Zurek Abstract Hydrogen absorption, mechanical testing under different loading mode and electrochemical measurement were done for 0.3C low alloy steels used in the ship engine parts at immersion in the boiler fuel and in the used engine mineral oil at elevated temperatures corresponding to the operating conditions. The hydrogen charging of steels has been found to reach a level causing their plasticity loss. No effect, a plasticity loss and a significant decrease in the number of cycles have been stated in constant load, slow strain rate and fatigue tests, respectively. The results showed the local active plastic deformation proceeded close to the surface of hydrogen ingress to provide the highest possibility for hydrogen induced metal degradation in hydrocarbon environments. Although the source of hydrogen evolved in the case of technical hydrocarbons has been discussed, the promoting effect of formed H2S should be recognized as the important factor influencing the hydrogen charging from those environments. Some variation in the steel microstructure, chemical composition and hardness of steels, even allowed by the standard may affect their susceptibility to hydrogen degradation in hydrocarbons. [source] Mechanical Response Analysis and Power Generation by Single-Cell StretchingCHEMPHYSCHEM, Issue 4 2005Alexandre Micoulet Dr. Abstract To harvest useful information about cell response due to mechanical perturbations under physiological conditions, a cantilever-based technique was designed, which allowed precise application of arbitrary forces or deformation histories on a single cell in vitro. Essential requirements for these investigations are a mechanism for applying an automated cell force and an induced-deformation detection system based on fiber-optical force sensing and closed loop control. The required mechanical stability of the setup can persist for several hours since mechanical drifts due to thermal gradients can be eliminated sufficiently (these gradients are caused by local heating of the cell observation chamber to 37,°C). During mechanical characterization, the cell is visualized with an optical microscope, which enables the simultaneous observation of cell shape and intracellular morphological changes. Either the cell elongation is observed as a reaction against a constant load or the cell force is measured as a response to constant deformation. Passive viscoelastic deformation and active cell response can be discriminated. The active power generated during contraction is in the range of Pmax=10,16Watts, which corresponds to 2500 ATP molecules,s,1at 10 kBT/molecule. The ratio of contractive to dissipative power is estimated to be in the range of 10,2. The highest forces supported by the cell suggest that about 104molecular motors must be involved in contraction. This indicates an energy-conversion efficiency of approximately 0.5. Our findings propose that, in addition to the recruitment of cell-contractile elements upon mechanical stimulation, the cell cytoskeleton becomes increasingly crosslinked in response to a mechanical pull. Quantitative stress,strain data, such as those presented here, may be employed to test physical models that describe cellular responses to mechanical stimuli. [source] Determination of both the time constant of v,O2 and ,v,O2/,W from a single incremental exercise test: validation and repeatabilityCLINICAL PHYSIOLOGY AND FUNCTIONAL IMAGING, Issue 5 2004Anita G. M. Wisén Summary A single incremental cycle exercise test including a steady-state load, combined with respiratory gas exchange, was performed with the objective of determining the time constant (o2) and the amount of oxygen required at each load (o2/,W) by using a novel equation. The protocol was validated using four exercise tests at different constant loads and conventionally fitted mono-exponential functions to determine o2, and interpolation of o2 versus load to determine o2/,W. No significant differences were seen between the means of either o2 or o2/,W determined with the two protocols. The correlation coefficient was 0·62 for o2 and 0·48 for o2/,W. The absolute differences (2 SD) were 11·6 s for o2 and 1·1 ml min,1 W,1 for o2/,W. The equations were compared in the same steady-state test and good agreement of o2 was obtained (R = 0·99). The 5,6-week repeatability (incremental test) was evaluated. No statistical differences were seen between the mean of the repeated tests. The difference between the tests (2 SD) were 20 s for o2 and 1·2 ml min,1 W,1 for o2/,W. In conclusion, o2 and o2/,W can be determined from a single incremental test. The validation showed an acceptable agreement, although the variations in absolute values were not negligible. This could partly be explained by the natural day-to-day variation and fluctuations in incoming raw data. The test,retest variation in absolute values was considerable, which must be taken into account when using o2 and o2/,W for evaluation of aerobic function. [source] | |||||||||||||