Abrasive processes, primarily the local slip, are the dominant contributor to friction and wear of vehicle tires in service. The time history of forces accompanying acceleration, braking, and ...cornering in particular, lead constantly to changing contact conditions under the tire. Consequently, a laboratory test taking into account not only surface texture but also tire contact times (in the range of milliseconds) as well as realistic contact forces in a freely controllable temporal sequence is desirable. This paper presents the study of the dynamic contact between a rubber block and the abrasive surface at conditions close to those in a tire footprint. In our case, the test samples are a miniaturized tread block allowing to reproduce the intermittent tire contact including correct contact timings, pressure and friction coefficients in dependence on the driving maneuver to be tested. An analysis and comparison of friction and wear mechanisms for continuous contact and defined contact times is presented surpassing the characterization capabilities of DIN abrasion testers.
Two different compounds with a variation of stiffness are examined. The grip and wear rates are analyzed and compared. It is shown that understanding the dominant mechanisms and quantifying tire tread friction and wear in detail require the consideration of realistic transient dynamics of a tire tread block impacting the road at each revolution of the tire.
•Intermittent tire contacts (contact timings, pressure, friction coefficients) are reproduced with a miniaturized tread block.•Effect of rubber dynamic modulus on the contact conditions, direct high-speed cam observations of sample deformations.•Grip and abrasion depend very much on the snap-out conditions in the trailing edge.•Contrasting the DIN-Abrader, significant differences in friction energy between compounds are revealed in dynamic test mode.•Rubber wear in such kind of dynamic system can be correlated well to frictional energy.
Electronic health record (EHRs) have largely replaced obsolete paper medical charts. This replacement has produced an increased demand on physicians' time and has compromised efficiency. In an ...attempt to overcome this perceived obstacle to productivity, physicians turned to medical scribes to perform the work required by EHRs. In doing so, they have introduced an uninvited participant in the physician-patient relationship and compromised patients' confidentiality. Scribes may be a successful work around for physicians frustrated by EHRs, but patients' confidentiality should not be sacrificed in the process.
The focus of this study is on the effect of form deviations of a partial journal bearing's sliding surface on the friction force in mixed lubrication conditions. The measured friction varied ...considerably when the bearing was rotated in the opposite direction at the same speed and normal load. This unexpected observation motivated the presented simulation study. The overall form deviations of the surface of the test bearing were measured with white light interferometry and used as simulation input. The two-scale simulation approach considers the effect of the surface roughness on a microscopic and the global bearing geometry with the surface form deviations on a macroscopic scale. Simulation results show that the surface form deviations can have a noticeable effect on the pressure distribution of the lubricant and hence on the size of the asperity contact area which leads to the differences in friction. The influence of the lubricant viscosity, the clearance gap and the surface roughness were analysed in a parametric simulation study. Results show that the clearance and the surface roughness control the impact of the surface form deviations on the friction force. All in all, the results show the necessity to include all scales of surface form deviations in the simulation of journal bearings in a mixed lubrication regime.
•The impact of roundness deviations of a journal bearing on mixed friction is analyzed with simulation and experiment.•The measured roundness deviations considered in simulation influence the computed hydrodynamic pressure build-up.•Comparison shows a good coincidence of simulation and experiment.
The focus of this study is on the effect of form deviations of a partial journal bearing's sliding surface on the friction force in mixed lubrication conditions. The measured friction varied ...considerably when the bearing was rotated in the opposite direction at the same speed and normal load. This unexpected observation motivated the presented simulation study. The overall form deviations of the surface of the test bearing were measured with white light interferometry and used as simulation input. The two-scale simulation approach considers the effect of the surface roughness on a microscopic and the global bearing geometry with the surface form deviations on a macroscopic scale. Simulation results show that the surface form deviations can have a noticeable effect on the pressure distribution of the lubricant and hence on the size of the asperity contact area which leads to the differences in friction. The influence of the lubricant viscosity, the clearance gap and the surface roughness were analysed in a parametric simulation study. Results show that the clearance and the surface roughness control the impact of the surface form deviations on the friction force. All in all, the results show the necessity to include all scales of surface form deviations in the simulation of journal bearings in a mixed lubrication regime.
The maximum endurance time (MET) in static force exertions was used as a parameter for the assessment of five working postures. By applying the methodology of Rohmert to the construction of a general ...model for static muscular work and evaluating the measured MET results, the need for a new static posture model has been shown.
The aim of the present pilot study was to test MET in load situations that would indicate when the general model can be used or when a new static postural force model is needed.
Subjects exerted static postural forces at different load levels until exhaustion. In the first two postures, the strain was concentrated on the upper limbs, where active forces (muscular) play a key-role and justify the use of the model. In the remaining postures, the strain affected mainly the back/trunk, where the mechanical equilibrium of the body is brought about by active (muscles) and passive (skeleton and ligaments) structures.
During the tests electromyographic (EMG) measurements of selected muscles (objective measurements) as well as rated perceived exertion (RPE; subjective measurements on Borg's CR-10 scale) were recorded.
The results show that the maximum endurance times in upper extremity postures are predicted by the general model whilst in the back/trunk postures the measured MET was longer than predicted by the model. New models are presented for static postural force on the back.
The EMG measurements supported the conclusion that the muscles studied play a key role in the chosen upper-extremity postures but gave no clear indication in the back-oriented postures. Ratings of perceived exertion coincided with the EMG measurements in upper extremity postures and proved to be a good substitute for measurement and calculation of the load levels studied. The initial RPE can therefore be used in models for predicting maximal endurance times in complex cases.
For the range of relative postural loads tested, an exponential function for predicting MET in static posture exertions produced the best fit curve.
A device for three-dimensional registration of human movement was tested. For this, a special garment with 43 attached light-emitting diodes was developed. The garment was specially designed for ...biomechanical purposes and made of a highly elastic material in the form of an overall. A recording system working with infra-red light was also tested considering both technical aspects and software. Test recordings of predetermined body movements within a defined work area of over 10m
2
showed that the device satisfies general practical requirements. The garment worked very well for different movements and for bodies of different shapes and sizes. Technically the system was tested with respect to noise and linearity, operating function, range and manageability. It worked well with some limitations such as reflections. The tested software functions, such as recording speed, processing time, interpolation and user compatibility, proved to fulfil their main needs.
Narrative is the most important underlying ingredient in a successful doctor-patient encounter. The patient's story provides an attentive listener with the necessary clues for a proper diagnosis. ...Moreover, narrative competence allows the physician to simultaneously hear the human sentiments contained in the storyteller's tale. The Medical Humanities movement promotes the close reading of literature in order to develop narrative abilities and sensibilities but prose and poetry are not the only sources of narrative. Telling stories through art is an innate human process that is as old as cave painting and as contemporary as a public mural. Many of the concepts that aid in dissecting a novel are operative in the close reading of figurative art. Knowledge of these areas can promote narrative competence in physicians who are trained to be both attentive readers and viewers. The practice of medicine demands both narrative and visual skills. This intertwining is the inspiration for employing figurative paintings with medical narrative content in the Medical Humanities curriculum. Narrative art teaches narrative competence. This dissertation will demonstrate that the use of narrative paintings is a valuable epistemological tool for developing narrative abilities in medical students and residents.
In two experimental series a panel of observers rated the perceived exertion of a worker performing different tasks. The first experiment involved the lifting of boxes of different weights. The ...second experiment comprised combined static and dynamic work of the assembly-line type during a full working day.
The results show that the observers were able to discriminate between the different loads in all stress situations. Since the loads ranged from low to maximal stress, all were able to make assessments over the full range. Furthermore, the relationship between observer ratings and self-ratings approximated a logarithmic function with the observers tending to overestimate the low stresses while there was closer agreement in the rating of high stresses.
A technique for registering vibration and deformation patterns has been adapted for the measurement of whole-body vibration in humans. Double-exposure holographic interferometry produces three ...dimensional pictures of the body, allowing exact measurement of the subject's movement between the two pulses. In this study an interval of 600 microseconds between the two pulses was used, producing measurements with a resolution of less than 0.3 X 10(-6)m. The subject standing in a fixed posture, was exposed to the laser beams first without vibration and then with vibration. The picture without vibration is needed as certain movements due to life functions of the body such as heartbeat, blood circulation etc are involved therein. This basic pattern should be considered when analysing the pictures with vibration. Different types of vibration in various postures were studied. Tests were also conducted when a reflective coating was applied to the skin. The results show that the method is applicable for measuring whole-body vibration and suggests further tests with more modern laser equipment which is now available. Such equipment can produce pulses with a high repetition rate and of much better quality than those obtained in this study. Once coordinated to the heartbeat and to the working frequency of the vibrating object, a reliable analysis of whole-body vibration can be maintained.
Perception of Efforts in Working Postures Wangenheim, M.; Carlsöö, S.; Nordgren, B. ...
Upsala journal of medical sciences,
1986, Letnik:
91, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The aim of this study is to obtain an understanding of the subjective discomfort of working postures and the degree of physical effort these postures give rise to. 31 students have rated their ...perceived exertion on Borg's scale (1982) based on a collection of photographs of different work postures of varying complexity, including a kinaesthetic description (2). Each one of the 78 postures was held for 45 seconds, with rated perceived exertion (RPE) given after 15, 30 and 45 seconds. The whole test series was repeated twice. The results show that it is possible to evaluate different body postures by RPE achieving a total reliability α-value over 0.96. Despite the fact that the rating pattern between the different postures was the same for all subjects, it is shown that each person assessed according to a certain individually-influenced pattern. A certain person can for example, deviate consistently towards higher values on Borg's scale, a so-called "high rater". Finally, the different postures were grouped according to how the ratings changed in time (regression slope between the RPE's after 15, 30 and 45 seconds). The third-cluster, which showed a high basic rating-level and the greatest regression slope, included only extreme outer limits of movement. This indicates that the outer limit postures have a tendency to static load and need to be studied by more additional methods when remaining unchanged even for short periods.
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