670 research outputs found
Plain fatigue resistance of shot peened high strength aluminium alloys: Effects of loading ratio
No full textThe effect of different shot-peening treatments on the reverse and pulsating bending fatigue behaviour of Al 7075 T651 was studied. The fatigue improvements with respect to the unpeened condition and the influence of the peening intensity on fatigue were discussed accounting for the effects of surface modifications and residual stresses. In particular, the extent of the residual stress redistribution during loading was investigated by means of X-ray diffraction (XRD) measurements. No significant residual stress relaxation was observed in samples tested to a load level corresponding to the fatigue endurance at 5x10^6 cycles. Residual stress relaxation was observed only when the material plastic flow stress was achieved during the compressive part of the fatigue load cycle. Accordingly, shot peened samples with deep sub-superficial compressive residual stress peak showed a reversed fatigue endurance level corresponding to the condition of incipient plastic flow. This phenomenon was also accompanied by sub-superficial fatigue crack initiation. On the contrary, samples tested at shorter fatigue lives or under pulsating loading conditions showed crack initiation close to the surface. The initial and the stabilised residual stress profiles were considered for discussing the improvement in the fatigue behaviour due to peening. For this purpose, a multiaxial fatigue criterion was adopted to account for the biaxial residual stress field. The fatigue life was quite accurately predicted as long as fatigue initiation occurs on the surface
Cumulative Trauma Disorders: Their Recognition and Ergonomic Measures to avoid them
No full textCumulative Trauma Disorders (CTD) refers to a large category of disorders of the muscles, tendons, or nerves and are the summary results of microtrauma caused, precipitated, or aggravated by repeated exertion or movements of the body. They go by many names in the literature. They have become a matter of urgent ergonomic concerns for manufacturers, insurance companies, health care provides, and government agencies. Since CTD are usually caused by repeated and/or forceful exertions, often in the hand-arm-shoulder region. They predominantly occur to soft tissues, such as tendons and ligaments, and to nerves and blood vessels. They are commonly associated with certain occupational and leisure activities. Many CTD can be avoided by a set of fairly simple and straightforward ergonomic procedures. In this presentation, the author will share his views on the epidemiology, pathogenesis and treatment including the ergonomic measures to avoid CTD
Development of a simplified model for the vibration analysis of lawn movers
No full textThe vibrational behavior of vehicles is a crucial issue for the comfort, especially for the professional vehicles. This paper presents a simplified modelling approach for studying the vibrational behavior of a lawn tractor. The vibrational response of a real vehicle is analyzed by an extensive experimental modal analysis and Finite Element model (FE) simulating the modal behavior of the whole tractor. The FEM was then validated by the comparison with the experimental results and then used for identifying the components and connections effectively driving the modal response. Based on these results, a simplified Multi-Body (MB) model, able to reproduce the vibrational response of the studied lawn mower, was then setup, showing good correspondences with experimental results. General guidelines for defining effective vehicles Multi-Body modal models were also derived
How Hong Kong students learn using the study process questionnaire: Cross-cultural comparisons
No full textAnecdotal evidence abounds in Hong Kong to the effect that students entering tertiary education are predisposed to a “rote” learning approach. Until the research studies at City Polytechnic of Hong Kong and Hong Kong Polytechnic, there have been no systematic studies performed locally and as such in the absence of cross-cultural research, there is a tendency to rely on anecdotal statements about Hong Kong students’ approaches to learning. This study was designed to see if Hong Kong Chinese students predisposed to a surface or deep approach to learning react differently when moving progressively from one stage to the next stage in their undergraduate occupational therapy curriculum. This study adopted a longitudinal design method which followed a cohort of 80 undergraduate occupational therapy students over two years and measured their changes in their approaches to learning using the Biggs’ Study Process Questionnaire The internal consistency reliability estimates alpha for SPQ scales for samples of Hong Kong, Australian and British students was compared. The alpha estimates of this study varied from 0.56 to 0.75 which compares favourably with other studies reported in Hong Kong, Australia and U.K. The results of this study indicated that the Hong Kong Chinese students demonstrated a higher mean for the deep approach to learning (47.3 in Year 1 and 46.3 in Year 3) and a lower mean for the surface approach (42.7 in Year 1 and 42.4 in Year 3), similar to other Hong Kong studies from other tertiary institutions in Hong Kong and Australia. From the findings, it is reasonable to conclude that students change their approach according to the different demands imposed by their varied learning needs. Based on this belief, the author while ruling out the potential for misunderstandings about Asian students, draws attention to the cross-cultural differences in approaches to learning which highlights on the changing nature of tertiary classroom and the implications for teaching and learning, with the major shift in the characteristic of student population
DIOPTRA-L: Digital Opinions on Translated Literature
No full textA collection of reviews from Goodreads of various well-known fiction and non-fiction books, and their translations. The metadata has been enriched with computed and annotated values:
- the identifier of the review
- the title of the reviewed book
- the original language in which the book was published
- the edition to which the review refers
- the text of the review
- the language of the review (computed)
- the author of the review (username which cannot be related to a person)
- a computed estimate of the author gender (based on the username)
- the age category of a book's target audience (children / young adult / adult), annotated by experts
- the genre of the book, annotated by experts
- the star rating of the book (1 to 5)
- the tokenised text of the review
- whether or not the review mentions translation (0 for false,1 for true)
- how many tokens are in the review
- how many translation lemmas were found in the revie
High temperature fatigue testing of gas turbine blades
No full textWith the increasing use of renewable energy sources, Gas Turbines (GTs) are currently required to accomplish more flexible operations for supplying the back-up energy. As a result, thermo-mechanical fatigue issues in the GTs components are emphasized. In this paper, the design of a novel rig for assessing the fatigue behavior in the trailing edge of full scale GTs blades is presented. Based on a detailed Finite Element (FE) analysis of the blade response under thermo-mechanical loads, it is demonstrated that the stress and strain cycles arising in this area during a start-up/shut-down transient can be accurately reproduced by clamping the blade in the shank zone and applying a transversal load to
the trailing edge. It is also shown that the stress/strain states can be obtained using a Test Article (TA) extracted from the actual blade. In this configuration, the load magnitude and direction, and the distance of the application point from the blade platform are the test control parameters. A FE model simulating the TA test is developed to determine the test parameters. A tooling for clamping and loading the TA is finally proposed along with a rig apparatus consisting of standard equipment used in material testing
Experimental study of hydrogen embrittlement in Maraging steels
No full textThis research activity aims at investigating the hydrogen embrittlement of Maraging steels in connection to real sudden failures of some of the suspension blades of the Virgo Project experimental apparatus. Some of them failed after 15 years of service in working conditions. Typically, in the Virgo detector, blades are loaded up to 50-60% of the material yield strength. For a deeper understanding of the failure, the relationship between hydrogen concentration and mechanical properties of the material, have been investigated with specimens prepared in order to simulate blade working conditions. A mechanical characterization of the material has been carried out by standard tensile testing in order to establish the effect of hydrogen content on the material strength. Further experimental activity was executed in order to characterize the fracture surface and to measure the hydrogen content. Finally, some of the failed blades have been analyzed in DICI-UNIPI laboratory. The experimental results show that the blades failure can be related with the hydrogen embrittlement phenomenon
Analysis of the Elastic-plastic Properties of Metallic Materials by Instrumented Spherical Indentation Testing
No full textAbstractSpherical indentation testing is regarded as an effective technique for deducing the constitutive properties of metallic materials, e.g. the determination of the stress-strain curve (<r-e curve) from the characteristic loadL vs. penetration depth h curve (L-h curve). However, the uniqueness between the L-h curve and the <r-e curve has not systematically addressed yet. The existence of materials having different constitutive laws but visually indistinguishable L-h curves has been probed, thus requiring the development of refined methodologies for distinguishing such materials in the reverse analysis. These topics are deeply discussed in the present paper. The indentation responses of an aluminum alloy (Al 6082-T6) and of a distinct material having apparently indistinguishable L-h curves are examined via a proper experimental characterization and Finite Element Analysis (FEA). For both materials the strain processes occurring in the subsurface region are especially examined and compared. The analysis probes that the actual constitutive properties of the indented material can be distinguished once proper functions accounting for the strain processes promoted by the indenter are formulated. Based on these findings, a suitable L-h curve expression and a new reverse analysis algorithm ensuring the one-to-one correspondence between the L-h curve and the <r-e curve of the indented materials are proposed
Ecological Systems Thinking
No full textWhile the science of ecology has expanded markedly in the past century, that knowledge has not significantly changed the pace of economic growth or deflected the momentum of human expansion. Warnings, including that from the Millennium Ecosystem Assessment team, multiply but without a corresponding societal response. The author traces the problem to the realm of politics and the ineffectiveness of statutes such as the National Environmental Policy Act. The article ends with suggestions about how to extend science more effectively into the political realm. © 2019 Elsevier B.V. All rights reserved
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