Rational parameters of profiled workpieces for an upsetting process

An upsetting process of specially profiled workpieces was proposed. Modeling of a workpiece upsetting, profiled as a cylinder with conical and cylindrical ledges was done using a finite element method. During the upsetting of these workpieces, buckling occurs. Schemes of upsetting a workpiece with conical ledges result in a decrease in the irregularity of the equivalent strain distribution in the longitudinal section. This scheme produces a zone of minimal equivalent strain decrease in the workpiece. It was found that during the upsetting process of the workpiece with a conical ledge on the lateral surface and in the center, compressive stresses appear. These stresses contribute to the closure of voids in an ingot during the upsetting process. Rational workpiece parameters were found which allow the production of forgings with minimal irregularity of equivalent strain distribution, minimal formation of a barrel, and a favorable stress state in the workpiece. Experimental research, which confirms the advantages of upsetting specially profiled workpieces, was done.     

On Correlation of the Temperature Stability of Oil in Friction and the Surface Energy of Adhesion of Oil to Metal

In this work it has been shown experimentally that the temperature stability in friction of a highly purified oil with a fatty-acid additive is comparable to the surface energy of adhesion of the given oil, in the case of tests conducted with a group of iron-base ternary alloys, having a constant carbon content, and different alloying element contents (of chromium, tungsten, or nickel).     

Solving Linear Systems with Error Control: Minisymposium within the 4th International Conference NMA'98

Reliable Computing -     

High-frequency welding of plastics in a working condenser with a non-uniform distribution of the electrical field

A method for calculating the conditions of high-frequency (HF) welding of plastics in a working condenser with the non-uniform distribution of the electric field is described. The method determines the instantaneous specific power of the internal heat sources on the basis of capacitance and voltage in the working condenser which is not completely filled with the welded material. An example of calculating the temperature distribution in the thermoplastic material in the process of HF welding of components in equipment with a working condenser of the ‘thin edge against isolated plane’ type is outlined.     

Electric conductivity of metal-dielectric-metal structures with dielectric layer formed by spherical metal oxide nanoparticles

The electrical properties of metal-dielectric-metal (MDM) structures with the dielectric layer representing a monolayer of spherical Al₂O₃ or ZrO₂ oxide nanoparticles have been studied. It is established that these heterogeneous structures exhibit electric conductivity according to the mechanism for which the differential resistance dU/dI is negative and reversibly approaches zero with increasing current I. The electric conductivity strongly depends on the polarity of the applied voltage U, provided that electrodes are made of basically different metals or the same metal with different surface conditions. The mechanism of the electric conductivity in the given MDM structure depends on the diameter of nanoparticles in the dielectric layer.     

Creep-to-rupture tests of T91 steel in flowing Pb-Bi eutectic melt at 550 °C

Uniaxial creep-to-rupture tests were performed on T91 in air and in flowing lead-bismuth eutectic melts. Compared to specimens tested in air, the specimens tested in liquid-metal show: (i) strain and strain rate increase up to a factor of about 50 (strain rate); (ii) time-to-rupture decrease; (iii) rapid transition into the third creep stage at high stress (above 180 MPa). The analysis of the test results revealed several important surface phenomena, which lead to different behavior of the specimens tested in lead-bismuth eutectic melts compared to those tested in air. Under high stress, and therefore high strain, the crack propagation process is mostly controlled by the reduction of the surface energy due to Pb and Bi adsorption on the steel surface. Under low stress (140 and 160 MPa) and low strain, this process is delayed due to the competing mechanism of healing the oxide scale cracks.     

End of life and termination of life: opinions of elderly persons with health problems

OBJECTIVE: To determine the views of elderly persons with physical limitations about a number of aspects of the end stage of life and termination of life. DESIGN: Enquiry. SETTING: University of Groningen, the Netherlands. METHOD: An enquiry was conducted in 1995 among 575 elderly (429 females, 146 males; age 57-99 years; 281 living alone) with physical restrictions (mostly heart disease, hypertension, rheumatism or other articular diseases). The group had been selected from the 'Groningen longitudinal aging study'. The respondents were asked (a) what they thought about euthanasia, (b) whether they worried about the end stage of life, (c) whether they were afraid of death and how much they were 'preoccupied with death'. For the last-mentioned two questions a visual analogue scale was used. RESULTS: Almost one-third of the elderly were not preoccupied with death and over half were not afraid of death. Very few scored high on these scales. Respondents' views about the acceptability of active termination of life varied greatly: almost half were of the opinion that their life had to be terminated once they themselves had developed complete dementia. Regarding the end stage of life, respondents mostly worried about being a burden to others, being completely dependent on others, having to say goodbye to their loved ones and having to suffer greatly. Elderly persons with poorer health were more preoccupied with death and worried more about the problems of the end stage of life. CONCLUSION: Most of those interviewed were not greatly preoccupied with or afraid of death. They did worry, however, about the problems that might be associated with the end stage of life.     

Pulmonary and systemic fat embolization after medullary canal pressurization: a hemodynamic and histologic investigation in the dog

BACKGROUND: The potential to produce fat embolism may be important in determining the ideal method and timing of fracture treatment in patients with preexisting lung injury. METHODS: Four dogs underwent femoral and tibial canal reaming and pressurization. Blood gas samples were analyzed, and pulmonary arterial pressure was monitored at 1 and 72 hours. Animals were killed 72 hours postoperatively, and the lungs, kidneys, and brain were examined histologically and compared with equivalent specimens from four control dogs that had not undergone femoral and tibial canal reaming and pressurization. RESULTS: Postmortem, intravascular fat persisted for 72 hours after induction of pulmonary fat embolism. Mean PaO2 was unchanged from baseline at 72 hours after canal pressurization. Canal pressurization caused a sustained increase in pulmonary arterial pressure (p=0.02) for 1 hour after canal pressurization. The mean pulmonary edema score at 72 hours was 29+/-3. Only a scant polymorph infiltrate (zero to two polymorphs per high-power field) was present at any time. No hyaline membranes were seen at any time. The percentage area occupied by intravascular fat in the lungs was 0.0214+/-0.0058 at 72 hours. No signs of ischemia or inflammation were seen in either the cerebral or the renal specimens. CONCLUSION: This study is the first to show that intravascular fat persists in the lungs, kidneys, and brain for 72 hours after canal pressurization and, by itself, does not cause pathologic evidence of acute inflammation.