2,255 research outputs found
Influence of stress concentration and multiaxial stress state on low cycle fatigue
No full textTorsion tests were performed on thin tubular specimens made of 34CrMo4 steel. The low-cycle curves obtained from torsional tests were compared with the ones obtained from axial tests. Experimental tests were executed on notched specimens made of the same material and the fatigue behaviour was studied. Microscopic observations and profile measurements of the fracture surfaces permitted to put in evidence the different kind of fractures and the fracture surface changes induced by the shape of the specimen and the load amplitude. The experimental tests together with a numerical analysis (conducted by using a finite element model) enabled the determination of all the useful parameters to perform a low-cycle fatigue life prediction. The calculation of the multiaxial stress and strain state near the notch was performed by the Neuber's rule and the ESED method
Plasma electrolytic oxidation (PEO) for production of anodised coatings on lightweight metal (Al, Mg, Ti) alloys
No full textThe introduction of plasma electrolytic oxidation (PEO) as a surface finishing technique has enabled a range of hard, dense oxide coatings to be produced on aluminium, magnesium, titanium and other lightweight alloy substrates. As with all surface coating technologies, successful development of PEO coatings requires adequate attention to substrate pretreatment together with careful control of electrolyte conditions and process variables. The principles and applications of the PEO coating process are considered, including the fundamentals of oxide deposition, the technology involved and the typical characteristics of the coatings. Industrial applications are considered together with their coating requirements. Plasma electrolytic oxidation coating is a specialised but well developed process. Suitable control of electrolyte and process conditions can realise a novel range of coatings having technologically attractive physical and chemical properties. The development of PEO technology over the last decade has provided coatings having controlled appearance, hardness, corrosion resistance and other tribological properties across an extending range of industrial sectors. Continuing developments are concisely reviewed and the PEO process is illustrated by the characterisation of anodised coatings on an AZ91 magnesium alloy surface
Influence of stress concentration and multiaxial stress state on low cycle fatigue
No full textTorsion tests were performed on thin tubular specimens made of 34CrMo4 steel. The low-cycle curves obtained from torsional tests were compared with the ones obtained from axial tests. Experimental tests were executed on notched specimens made of the same material and the fatigue behaviour was studied. Microscopic observations and profile measurements of the fracture surfaces permitted to put in evidence the different kind of fractures and the fracture surface changes induced by the shape of the specimen and the load amplitude. The experimental tests together with a numerical analysis (conducted by using a finite element model) enabled the determination of all the useful parameters to perform a low-cycle fatigue life prediction. The calculation of the multiaxial stress and strain state near the notch was performed by the Neuber's rule and the ESED method
Musculoskeletal disorders in farmers and farm workers
No full textFarming is a physically arduous occupation and this places farm workers at potential risk of musculoskeletal disorders such as osteoarthritis (OA) of the hip and knee, low back pain (LBP), neck and upper limb complaints, and hand–arm vibration syndrome (HAVS). This review considers the epidemiological evidence concerning such risks. The strongest evidence relates to OA of the hip, for which the public health impact is likely to be considerable. There is also weaker, but suggestive evidence that farmers more often have knee OA and LBP than workers in occupations with fewer physical demands. Tractor drivers, in particular, seem to have more LBP. Relatively little information exists on the risks of soft tissue rheumatism in the limbs and neck. For some outcomes, the link with occupational risk factors (such as heavy loading of joints and whole-body vibration) is sufficient to suggest the course that future prevention should take, but for several outcomes more research is first needed
Prevalence and determinants of low back pain in a cross-cultural sample: findings from the CUPID study
No full text
Effect of Stabilizer on the Mechanical Properties of Rigid PVC
No full textTitle: Effect of Stabilizer on the Mechanical Properties of Rigid PVC, Author: Karl K.T. Woo, Location: ThodeIn this study commercial suspension polymerized polyvinyl chloride resin with different stabilizer contents was first compounded and injuctioned molded into small dumbbell shape specimens. Most of the specimens after annealing were then tested on the Instron Tensile Tester while the rest on iniature Tensile Tester for difference in mechanical properties. Four parameters from the stress-strain curves were of interest in this study: tensile yield stress, tensile modulus, elongation at fracture and ultimate fracture strength. The differences in mechanical properties were explained by the change in molecular structure of polyvinyl
chloride brought about by the reaction between the stabilizer and PVC molecules. In the second part of the experiment, the effects of heat treatment and molecular weight on the mechanical properties of rigid PVC were also investigated.ThesisMaster of Engineering (ME
Work relatedness of chronic neck pain with physical findings - a systematic review.
No full textObjectives - This paper systematically reviews the work-relatedness of neck–shoulder disorders with associated physical findings.Methods - Studies incorporating a physical examination were focused upon. Four detailed reviews were searched, and a systematic search of the MEDLINE, Embase BIDS, and Psychinfo databases was conducted until May 2006, the key words for the outcome and various occupational exposures being combined. The quality of each paper was rated by criteria related to study design, power, sampling methods, response rate, potential for bias, or confounding, and approaches to the assessment of exposure outcome. Weight was given to studies with objective exposure–response information.Results - Twenty-one relevant reports (four prospective) were found. Most considered the outcome neck pain with palpation tenderness (tension neck syndrome) or mixed neck–shoulder disorder (predominantly tension neck syndrome). Most investigations shared common limitations—small sample size, potential for confounding, incomplete blinding, and crude exposure assessment. The overall quality of the information was rated as excellent for only two reports. Exposures included repetitive work (14 studies), static loading (12 studies), neck flexion (7 studies), force (5 studies), and occupational psychosocial factors (7 studies). Moderate evidence was found for a causal relation for repetition at the shoulder and for neck flexion allied with repetition. Limited evidence was found for hand–wrist repetition, neck flexion with respect to static loading and force in the absence of repetition, and high job demands, low control, low job support and job strain.Conclusion - There is some evidence that neck pain with palpation tenderness is causally related to workplace exposures. However, evidence is lacking on the validity, clinical course, and functional importance of this diagnostic entity<br/
Disabling musculoskeletal pain in working populations: is it the job the person or the culture?
No full textOBJECTIVES: To compare the prevalence of disabling low back pain (DLBP) and disabling wrist/hand pain (DWHP) among groups of workers carrying out similar physical activities in different cultural environments, and to explore explanations for observed differences.METHODS: Standardised questionnaires were used to ascertain pain that interfered with everyday activities and exposure to possible risk factors in 12,426 participants from 47 occupational groups (mostly nurses and office workers) in 18 countries. Associations with risk factors were assessed by Poisson regression.RESULTS: The one-month prevalence of DLBP in nurses varied between countries from 9.6% to 42.6%, and that of DWHP in office workers from 2.2% to 31.6%. Rates of disabling pain at the two anatomical sites co-varied (r = 0.76), but DLBP tended to be relatively more common in nurses and DWHP in office workers. Established risk factors such as occupational physical activities, psychosocial aspects of work and tendency to somatise were confirmed, and associations were found also with adverse health beliefs and group awareness of people outside work with musculoskeletal pain. However, after allowance for these risk factors, up to eightfold differences in prevalence remained. Systems of compensation for work-related illness, and financial support for health-related incapacity for work appeared to have little influence on the occurrence of symptoms.CONCLUSIONS: There is large international variation in the prevalence of disabling forearm and back pain among occupational groups carrying out similar tasks. This is only partially explained by the personal and socio-economic risk factors that were analysed.<br/
Instability of fixed, low-thrust drag compensation
No full textFORCED drag compensation using continuous low-thrustpropulsion has been considered for satellites in low Earth orbit. This simple, but nonoptimal, scheme merely requires that the thrust vector is directed opposite to the drag vector and that the magnitude of the two are equal. In principle, the drag force acting on the spacecraft could be determined onboard using accurate accelerometers. However, for small, low-cost spacecraft such sensors may beunavailable. An alternative strategy would be to Ž x the thrust magnitude equal to the expected air drag that would be experienced by the spacecraft. The thrust levelwould be periodically updated based on ground-based orbit determination. In this Engineering Note, it is shown that such a forced circular orbit with a Ž fixed thrust levelis exponentially unstable for all physically reasonable atmosphere models
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