16 research outputs found
Laterally unrestrained bearing strength of hot-wet conditioned pultruded FRP material
No full textPresented in this paper are test results of a study pertaining to the reduction in bearing strength due to the effect of hot-wet conditioning on specimens cut from a polyester matrix based pultruded FRP structural shape. A total of 100 coupons (for 20 batches of five) were immersed in distilled water for three and six months at a constant temperature of 40°C. Subsequently, they were load tested using stainless steel ‘pins’ of M10 and M20 sizes with material orientations of 0o, 45o and 90o
to the direction of pultrusion. Furthermore, this test series considered the effect of loading with and without bolt thread in the bearing zone. Testing employed a non-standard set-up that accommodates smaller test coupons, allowing material to be sourced from the web
and flange of a 254×254×9.53 mm wide flange shape. An evaluation of the salient results provides characteristic bearing strength values (in accordance with Annex D of EN1990) and comparisons are drawn between equivalent strengths for non-aged (zero months) material from a previous test series. The degree of strength reduction is found to be influenced by both the ‘pin’ size and type, and observations are drawn towards the safe and reliable design of bolted connections
Aspects of bolted connections in pultruded fibre reinforced polymer structures.
No full textThis thesis presents an extensive test programme for bolted connections using SuperStructural Pultruded Fibre Reinforced Polymer (PFRP) materials with an emphasis on characterising strengths for the pin-bearing failure mode and linking coupon results to bearing failure in lapshear bolted connections. The motivation for the research is to address key gaps in knowledge that are known to be hindering the preparation of recognised design guidelines for PFRP (frame) structures, which upon becoming available shall broaden exploitation in civil engineering works.
Prominent among these knowledge gaps has been the need to have statistically verified pinbearing and bolted connections strengths that are with connection configurations complying with current design practice. Thread in bearing, as found in practice, is investigated together, for the first time, with the plain shaft situation. Both as-received and environmental (hot-wet aging) conditioned PFRP materials are characterized to study long-term behaviour. A nonstandard pin-bearing strength test methodology, developed at The University of Warwick, is used to provide targeted test results for a comprehensive test matrix of 150 batches having 5 or 10 nominally identical specimens per batch.
A key contribution from the pin-bearing strength characterisation is that the in-house test method (WUTS) is shown to be suitable for the determination of pin-bearing strengths for flange and web materials, for bolting with or without thread and sizes from M10 to M20, and with a PFRP material orientated at 0o, 45o or 90o to the direction of pultrusion. Thread in bearing does not always have an adverse effect, and it is found that both thread pitch and material orientation have a significant contribution on the measured pin-bearing strength. It is recommended, for the situation when thread is in bearing, a reduction factor of 0.7 is applied to the characteristic plain pin-bearing strength value in the bearing strength equations. Accelerated aging regimes and long-term strength prediction modelling has shown a mean pinbearing strength reduction of up to 25% over 7.8 years, at UK service temperature of 10.5 °C. This value is found to lie within the bounds set by an American Load and Resistance Factor Design (LRFD) Pre-standard and gives confidence to the mandatory design requirements.
The thesis also reports on a series of strength tests following the methodology for pin-bearing characterization with single and double lap-shear bolted connections having configurations for single and two-rows, and for single and multi-bolts. Reported are a series of open-hole tension tests carried out to characterise the by-pass load situation in multi-rowed connections. A reduction factor of 0.6 between single and double lap configuration is found, with the possibility of multiple mixed failure modes, including block shear. The SuperStructural material has a tri-axial stitched fabric mat reinforcement (usually in pultrudates the mat is a continuous filament mat) which is influencing the strength of bolted connections. Using the procedure in Eurocode 1990, a partial factor of 1.3 for pin-bearing resistance has been calibrated by combining the WUTS and lap-shear bolted connection tests results. Results from an open-hole tension study have shown that the correlation coefficient proposed in the 1970s by Hart-Smith does not satisfactorily relate the isotropic stress concentration factor to the orthotropic stress concentration factor.
The findings and recommendations from the 1500 individual and 230 batch strength test results presented in this thesis have been successful in addressing or partially addressing a number of the key gaps in knowledge
Plain and threaded bearing strength for the design of bolted connections with pultruded FRP material
No full textPresented are results from testing 28 batches of 5 or 10 nominally identical specimens to characterise the laterally unrestrained pin-bearing strength when bolting is with and without thread. For the test series flange material is taken from a 254x254x9.53 mm Pultex® SuperStructural 1525 series shape. Strengths are measured with the Fibre Reinforced Polymer (FRP) material oriented at either 0° or 90° to the direction of pultrusion. Four steel bolt sizes of M10, M12, M16 and M20 are used, and when threaded there are different standard teeth (pitch) geometries. To remove this variable in a comparison with plain pin strengths a unique test series of 12 batches was carried out with three non-standard thread profiles. The effect on pin-bearing strength of having a threaded bolt is evaluated using mean and characteristic strengths, the latter determined in accordance with EN 1990. A key finding is that the proposed reduction factor of 0.6 in a forthcoming American LRFD standard to calculate a thread characteristic strength from the plain value is acceptable. Other findings are important to the determination of pin-bearing strength, and to us having knowledge and understanding to prepare a universal design procedure for resistances in bolted connections when the mode of failure is bearing
Virtual characterization of delamination failures in pultruded GFRP angles
No full textThis paper deals with the application of cohesive zone models to study delamination failures in leg-angles of pultruded glass fibre reinforced polymer material using the general-purpose finite element software Abaqus. The objective of the study is present a finite element modelling methodology that can, for example, help to fill-in knowledge gaps in the available experimental data pertaining to the tying force resistance of angle-cleated jointing in frame construction. It may be used to optimize cleat shape and laminate lay-up (dependent on composite processing method) for the strongest cleat against a minimum cost requirement. A benchmark example taken from literature is used to show that the numerical predictions from the authors’ simulations are reliable. The approach is next used to analyse an equal leg-angle component where one leg is fixed and the other orthogonal leg is being deformed by a tensile force applied over the free end surface. Numerical results from Abaqus are used to show that a lamination produced by the pultrusion processing method fails unstably by delamination cracks radiating around the curved region and extending into the leg panels. As a preliminary study to show the potential of the new modelling methodology it is used to show the influence of the radius of curvature at the junction between the legs on the tying force resistance; based on the load at delamination onset a smaller radius reduces the cleat’s strength
Boron nitride nanoscrolls: structure, synthesis, and applications
No full textThis is the author accepted manuscriptBoron nitride nanoscrolls (BNS) are open-ended, one-dimensional (1D) nanostructures made by the process of rolling boron nitride nanosheets (BNNS) into a scroll-like morphology. BNS offer a high surface area to volume ratio and possess many unique properties (similar to carbon nanotubes (CNT), carbon nanoscrolls (CNS) and boron nitride nanotubes (BNT)) such as high resistance to oxidation, chemical stability, increased lubrication, high-temperature resistance, electrical insulation, the ability to cap molecules inside and at the ends,and a wide band gap regardless of chirality. Despite these attractive featuresand properties well suited for applications in biotechnology, energy storage, and electronics, the true potential of boron nitride, and BNS as the next ‘miracle material’ is yet to be fully explored. In this critical review, we assess, for the first time, various studies published on the formation, structural and dynamic characteristics of BNS, potential routes for BNS synthesis, and the toxicology of BNS. Finally, the future perspectives of BNS are discussed in view of its unique and exceptional candidacy for many (real-world) applications
Development of gas turbine combustor preliminary design methodologies and preliminary assessments of advanced low emission combustor concepts
No full textIt is widely accepted that climate change is a very serious environmental
concern. Levels of carbon dioxide (CO2) and other emissions in the global
atmosphere have increased substantially since the industrial revolution and now
increasing faster than ever before. There is a thought that this has already led
to dangerous warming in the Earth’s atmosphere and relevant changes around.
Emissions legislations are going to be stringent as the years will pass. Hydro
carbon fuel cost is also increasing substantially; more over this is non-
renewable source of energy.
There is an urgent need for novel combustor technologies for reducing emission
as well as exploring alternative renewable fuels without effecting combustor
performance. Development of novel combustors needs comprehensive
understanding of conventional combustors. The design and development of gas
turbine combustors is a crucial but uncertain part of an engine development
process. At present, the design process relies upon a wealth of experimental
data and correlations. Some major engine manufacturers have addressed the
above problem by developing computer programs based on tests and empirical
data to assist combustor designers, but such programs are proprietary. There is
a need of developing design methodologies for combustors which would lead to
substantial contribution to knowledge in field of combustors. Developed design
methodologies would be useful for researchers for preliminary design
assessments of a gas turbine combustor.
In this study, step by step design methodologies of dual annular radial and axial
combustor, triple annular combustor and reverse flow combustor have been
developed. Design methodologies developed could be used to carry out
preliminary design along with performance analysis for conventional combustion
chambers. In this study the author has also proposed and undertaken
preliminary studies of some novel combustor concepts.
A novel concept of a dilution zone less combustor has been proposed in this
study. According to this concept dilution air would be introduced through nozzle
guide vanes to provide an optimum temperature traverse for turbine blades.
Preliminary study on novel dilution zone less combustor predicts that the length
of this combustor would be shorter compared to conventional case, resulting in
reduced weight, fuel burn and vibrations. Reduced fuel burn eventually leads to
lower emissions.
Another novel concept of combustor with hydrogen synthesis from kerosene
reformation has been proposed and a preliminary studies has been undertaken
in this work. Addition of hydrogen as an additive in gas turbine combustor
shows large benefits to the performance of gas turbine engines in addition to
reduction in NOx levels. The novel combustor would have two stages,
combustion of ~5% of the hydrocarbon fuel would occur in the first stage at
higher equivalence ratios in the presence of a catalyst, which would eventually
lead to the formation of hydrogen rich flue gases. In the subsequent stage the
hydrogen rich flue gases from the first stage would act as an additive to
combustion of the hydrocarbon fuel. It has been preliminary estimated that the
mixture of the hydrocarbon fuel and air could subsequently be burned at much
lower equivalence ratios than conventional cases, giving better temperature
profiles, flame stability limits and lower NOx emissions.
The effect of different geometrical parameters on the performance of vortex
controlled hybrid diffuser has also been studied. It has been predicted that
vortex chamber in vortex controlled hybrid diffuser does not play any role in
altering the performance of diffuser.
The overall contribution to knowledge of this study is development of combustor
preliminary design methodologies with different variants. The other contribution
to knowledge is related to novel combustors with a capability to produce low
emissions. Study on novel combustor and diffuser has yielded application of two
patent applications with several other publications which has resulted in a
contribution to knowledge. A list of research articles, two patents, awards and
achievements are presented in Appendix C
Measurement Error of Cardiac Output Determined by Nitrous Oxide Rebreathing and Impedance Cardiography in Healthy Adults
No full textCardiac output (Q̇) is a fundamental physiological variable but remains challenging to measure. Exercise Q̇ is commonly measured by inert gas rebreathing using acetylene or nitrous oxide (Q̇N2O-IGR) and impedance cardiography (Q̇IC), but device measurement error has not been assessed at different workloads, or in females. This study determined the precision of Q̇N2O-IGR (Innocor, COSMED Inc., USA) and Q̇IC (Physioflow Enduro, Manatec Biomedical, France) in duplicate in sixty adults (30 females; 22±5 years; V̇O2max: 41.2±8.6 mL.kg-1.min-1) during upright rest and cycling at 50W and 90% peak power output (PPO) (277±71W). Measurement variance was higher for Q̇N2O-IGR vs. Q̇IC (pThe presentation of the authors' names and (or) special characters in the title of the pdf file of the accepted manuscript may differ slightly from what is displayed on the item page. The information in the pdf file of the accepted manuscript reflects the original submission by the author
Correction to: European headache federation guideline on the use of monoclonal antibodies acting on the calcitonin gene related peptide or its receptor for migraine prevention (Journal of Headache and Pain (2019) 20:6 DOI: 10.1186/s10194-018-0955-y)
No full textFollowing publication of the original article [1], the authors notified us of some misreported data due to the publication of the EVOLVE-2 trial (Cephalalgia. 2018;38:1442-1454), which substantially changed the level of evidence of galcanezumab for the prevention of episodic migraine. All changes are marked in bold and with red in Figure 1 and Figure 2. Please note that the final recommendations remain unchanged. Reference #51 was added: Skljarevski V, Matharu M, Millen BA, Ossipov MH, Kim B-K, Yang JY. Efficacy and safety of galcanezumab for the prevention of episodic migraine: Results of the EVOLVE-2 Phase 3 randomized controlled clinical trial. Cephalalgia. 2018;38:1442-1454. Please find below the updated text, tables, and figures. Results We identified 29 studies eligible to be considered in the present guidelines (Fig. 1) [23-51]. Fifteen of the selected studies (Tables 1 and 2) were phase II or III randomized clinical trials (RCTs) reporting data on safety or efficacy of the CGRP mAbs [26,27,31-36,41-45,50,51]; 14 additional studies were post-hoc or pooled analyses from the RCTs, open label-extension of the RCTs, or open label studies [23-25,28-30,37-40,46-49]. Risk of bias summary for the selected studies is reported in Fig. 2. Certainty assessment of outcomes for studies in EM and CM is reported in Tables 3 and 4. Recommendations related to the use of CGRP mAbs for prevention of EM and CM are reported in Table 5. PICO question 1: In patients with EM, is preventive treatment with CGRP mAbs as compared to placebo, effective and safe? Population: patients with EM Intervention: any preventive CGRP mAb Comparison: placebo Outcome: reduction in days of migraine or headache, reduction in the use of acute attack medication, improvement in function, responder ratio (patients with > 50% reduction in migraine or headache days), serious adverse events (SAEs), mortality (grade of importance: critical) Analysis of evidence We found 15 eligible studies which evaluated whether treatment with CGRP mAbs as compared to placebo is effective and safe [26,27,31-36,41-45,50,51]. Among the eligible studies one was on eptinezumab [32], five studies on erenumab [35,36,44,45,50], four studies on fremanezumab [26,27,34,41], and five studies on galcanezumab [31,33,42,43]. One phase IIIb study on erenumab was not included in the PICO question 1 because it included only patients with previous drug failure [50]. Eptinezumab Summary of findings for treatment with eptinezumab quarterly injection compared with placebo for prevention of EM is provided in Table 6. (Figure presented). © 2019 The Author(s)
What predicts citation counts and translational impact in headache research? A machine learning analysis
No full textBACKGROUND: We aimed to develop the first machine learning models to predict citation counts and the translational impact, defined as inclusion in guidelines or policy documents, of headache research, and assess which factors are most predictive. METHODS: Bibliometric data and the titles, abstracts, and keywords from 8600 publications in three headache-oriented journals from their inception to 31 December 2017 were used. A series of machine learning models were implemented to predict three classes of 5-year citation count intervals (0-5, 6-14 and, >14 citations); and the translational impact of a publication. Models were evaluated out-of-sample with area under the receiver operating characteristics curve (AUC). RESULTS: The top performing gradient boosting model predicted correct citation count class with an out-of-sample AUC of 0.81. Bibliometric data such as page count, number of references, first and last author citation counts and h-index were among the most important predictors. Prediction of translational impact worked optimally when including both bibliometric data and information from the title, abstract and keywords, reaching an out-of-sample AUC of 0.71 for the top performing random forest model. CONCLUSION: Citation counts are best predicted by bibliometric data, while models incorporating both bibliometric data and publication content identifies the translational impact of headache research
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CLEAR: Emission-line Ratios at Cosmic High Noon
No full textWe use Hubble Space Telescope Wide Field Camera 3 G102 and G141 grism spectroscopy to measure rest-frame optical emission-line ratios of 533 galaxies at z ∼1.5 in the CANDELS Lyα Emission at Reionization survey. We compare [O iii]/Hβ versus [S ii]/(Hα + [N ii]) as an "unVO87"diagram for 461 galaxies and [O iii]/Hβ versus [Ne iii]/[O ii] as an "OHNO"diagram for 91 galaxies. The unVO87 diagram does not effectively separate active galactic nuclei (AGN) and [Ne v] sources from star-forming galaxies, indicating that the unVO87 properties of star-forming galaxies evolve with redshift and overlap with AGN emission-line signatures at z > 1. The OHNO diagram does effectively separate X-ray AGN and [Ne v]-emitting galaxies from the rest of the population. We find that the [O iii]/Hβ line ratios are significantly anticorrelated with stellar mass and significantly correlated with log(LHβ), while [S ii]/(Hα + [N ii]) is significantly anticorrelated with log(LHβ). Comparison with MAPPINGS V photoionization models indicates that these trends are consistent with lower metallicity and higher ionization in low-mass and high-star formation rate (SFR) galaxies. We do not find evidence for redshift evolution of the emission-line ratios outside of the correlations with mass and SFR. Our results suggest that the OHNO diagram of [O iii]/Hβ versus [Ne iii]/[O ii] will be a useful indicator of AGN content and gas conditions in very high-redshift galaxies to be observed by the James Webb Space Telescope. © 2022. The Author(s). Published by the American Astronomical Society.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
