Measurement of interface pressure in interference fits

When components such as bearings or gears are pressed onto a shaft, the resulting interference induces a pressure at the interface. The size of this pressure is important as many components fail because fatigue initiates from press-fit stress concentrations. The aim of the present work was to develop ultrasound as a tool for non-destructive determination of press-fit contact pressures. An interference fit interface behaves like a spring. If the pressure is high, there are few air gaps, so it is very stiff and allows transmission of an ultrasonic wave. If the pressure is low, then interface stiffness is lower and most ultrasound is reflected. A spring model was used to determine maps of contact stiffness from interference-fit ultrasonic reflection data. A calibration procedure was then used to determine the pressure. The interface contact pressure has been determined for a number of different press- and shrink-fit cases. The results show a central region of approximately uniform pressure with edge stress at the contact sides. The magnitude of the pressure in the central region agrees well with the elastic Lamé analysis. In the more severe press-fit cases, the surfaces scuffed which led to anomalies in the reflected ultrasound. These anomalies were associated with regions of surface damage at the interface. The average contact pressure in a shrink-fit and press-fit joint were similar. However, in the shrink-fit joint more uneven contact pressure was observed with regions of poor conformity. This could be because the action of pressing on a sleeve plastically smooths out long wavelength roughness, leading to a more conforming surface

An ultrasonic approach for contact stress mapping in machine joints and concentrated contacts

The measurement of pressure at a contact in a machine part is important because contact stresses frequently lead to failure by seizure, wear or fatigue. While the interface might appear smooth on a macroscale, it consists of regions of asperity contact and air gaps on a microscale. The reflection of an ultrasonic pulse at such a rough contact can be used to give information about the contact conditions. The more conformal the contact, the smaller is the proportion of an incident wave amplitude that will be reflected. In this paper, this phenomenon has been used to produce maps of contact pressure at machine element interfaces. An ultrasonic pulse is generated and reflected at the interface, to be received by the same piezoelectric transducer. The transducer is scanned across the interface and a map of reflected ultrasound (a c-scan) is recorded. The proportion of the wave reflected can be used to determine the stiffness of the interface. Stiffness correlates qualitatively with contact pressure, but unfortunately there is no unique relationship. In this work, two approaches have been used to obtain contact pressure: firstly by using an independent calibration experiment, and secondly by using experimental observations that stiffness and pressure are linearly related. The approach has been used in three example cases: a series of press fitted joints, a wheel/rail contact and a bolted joint

The Importance of Being Useless: Revolution and Judgment in \u27The Picture of Dorian Gray\u27

The preface to The Picture of Dorian Gray is often dismissed as merely an addendum to the novel intended to detract hostile readers and absolve the text itself of any accusations of immorality. When coupled with the narrative itself, however, the novel shows both the impossibility of producing the new through traditional notions of revolution, as well as the way in which the Deleuzian conception of judgment inhibits Dorian from ever viewing the portrait as insignificantly amoral, as not symbolic of his sins. Yet the preface, coupled with the various aesthetic objects in the text, is productive of a new form of judgment, one that does not reproduce the same moral order. This takes the form of a useless judgment. When Lord Henry claims he wishes to change nothing in England but the weather, this is the same as the portrait, returned to its original form, hanging over Dorian\u27s body at the novel\u27s end: neither is a judgment with a use, but rather a judgment of a work of art that produces nothing in the work of art. Lord Henry cannot change the weather, and the portrait\u27s changes do not help or affect Dorian in any way. Thus we see the answer to Deleuze\u27s question of what the refusal of work would look like. Art is quite useless in that it is both extremely removed from any and all spheres concerned with moral order, and also fairly indifferent to this fact and Dorian\u27s concern with maintaining a world organized by useful symbols

An Analysis Of Health Interest Of Selected Secondary School Students

The National Conference on Undergraduate Professional Preparation in Physical Education, Health Education, and Recreation states the basic philosophy on which any educational program of health must be based. Health is of primary importance in the development of the individual in our society and is recognized as one of the basic objectives of all education. The achievement of this objective, therefore, becomes the concern of all leaders who work for the welfare of the people. Health education, as an area of general education, is based on a recognition of the value of human life and the realization that to preserve and improve life, attention must be focused on the healthful function of the entire organism, interacting with the physical and social environment. Specifically, the objectives of the program of health education are to guide young people in the conservation of their health? to assist them in developing habits and principles of living which will serve as a basis for their happiness as members of the family and community? and to influence parents and adults through the child\u27s health education so that the school may promote health education in the community and in the family. The Joint Committee on Health Problems in Education of the National Education Association and the American Medical Association stated in 1930 the following objectives: To improve the individual and community life of the future? to insure a better generation, and still better third generation? a healthier and fitter nation and race In the past, as Kilander points out. Health education has of necessity been centered upon those areas of health needs which could be approached collectively through community motivation

Experimental characterization of wheel-rail contact patch evolution

The contact area and pressure distribution in a wheel/rail contact is essential information required in any fatigue or wear calculations to determine design life, re-grinding, and maintenance schedules. As wheel or rail wear or surface damage takes place the contact patch size and shape will change. This leads to a redistribution of the contact stresses. The aim of this work was to use ultrasound to nondestructively quantify the stress distribution in new, worn, and damaged wheel-rail contacts. The response of a wheel/rail interface to an ultrasonic wave can be modeled as a spring. If the contact pressure is high the interface is very stiff, with few air gaps, and allows the transmission of an ultrasonic sound wave. If the pressure is low, interfacial stiffness is lower and almost all the ultrasound is reflected. A quasistatic spring model was used to determine maps of contact stiffness from wheel/rail ultrasonic reflection data. Pressure was then determined using a parallel calibration experiment. Three different contacts were investigated; those resulting from unused, worn, and sand damaged wheel and rail specimens. Measured contact pressure distributions are compared to those determined using elastic analytical and numerical elastic-plastic solutions. Unused as-machined contact surfaces had similar contact areas to predicted elastic Hertzian solutions. However, within the contact patch, the numerical models better reproduced the stress distribution, as they incorporated real surface roughness effects. The worn surfaces were smoother and more conformal, resulting in a larger contact patch and lower contact stress. Sand damaged surfaces were extremely rough and resulted in highly fragmented contact regions and high local contact stress. Copyright © 2006 by ASME

Motor Performance After Four Kinds of Verbal Pretraining

Four groups of 20 Ss each were given 36 paired-associates trials on each of six random shapes. The four groups learned verbal responses which were, respectively, high in association value and formally distinct (HD), high in association value and formally similar (HS), low in association value and formally distinct (LD), and low in association value and formally similar (LS). An additional group (A) attended to motor task stimuli during 216 nonverbal pretraining trials, while a control group (I) learned medium association value distinct syllables to stimuli different from those which subsequently appeared in the motor task. Errors and correct responses were recorded. Subsequent to verbal or attention pretraining, all Ss were given 36 trials on a discriminative motor task provided by the Star Discrimeter. Errors and correct responses were recorded for each Star trial. A significant interaction on motor performance was found between the distinctiveness and association value variables, indicating that in some manner the association value of pretraining responses is an effective variable. Significant differences among experimental groups HD and HS, LD and LS, and between groups HD and I were taken as compatible with the postulation of a verbally mediated cue for the prediction of differential criterion performance after different kinds of verbal pretraining

Hyperbolicity preservers and majorization

The majorization order on \RR^n induces a natural partial ordering on the space of univariate hyperbolic polynomials of degree $n$. We characterize all linear operators on polynomials that preserve majorization, and show that it is sufficient (modulo obvious degree constraints) to preserve hyperbolicity.Comment: 4 pages, Published as C. R. Math. Acad. Sci. Paris 348 (2010), 843-84