2,733 research outputs found
The Water Uptake of Experimental Soft Lining Materials
No full textPhDIn order to develop a successful soft lining material various factors have to be
considered; physical strength, adhesion to the denture base ( or prosthetic) and the
durability of the material's properties when in the mouth. It has been recognised that in
order to fulfil these criteria the material must be stable and have a low water uptake from
the aqueous environments of the mouth.
In the dental field comparatively little work has focused on how soft lining materials
behave in water where as water in polymers has received a considerable amount of
interest, with many different types of behaviour being observed and explained. It has
been realised by previous authors that the water uptake of elastomers is primarily driven
by soluble impurities, these form solution droplets within the material. The nature of the
growth is somewhat more debatable, with both Fickian and dual sorption kinetics being
reported.
Two basic types of materials were used in the study; silicone polymers and elastomer /
methacrylate materials. Silicone polymers are characterised by a low water uptake and
form the basis of perhaps the most successful soft lining material ('Molloplast B'). The
elastomer / methacrylate materials were based on those developed by Parker (1982),
Parker and Braden (1990) which showed considerable promise but suffered from an
extensive protracted uptake. Water uptake at 370C in conjunction with the tensile
strength were used to evaluate the materials produced as these simple tests enabled the
behaviour of the material in service to estimated.
Three different types of silicone polymers were used during the study classified by the
curing mechanism (condensation, peroxide and hydrosilanised), various fillers and
additives (such as calcium stearate) were incorporated into the materials and different
uptakes observed. The condensation silicones demonstrated large weight losses (up to
20 wt%) in water which is attributed to hydrolytic instability of the siloxane bridge in the
presence of an organo tin compound leading to a leaching of siloxane. The pure
peroxide and hydrosilanised materials both demonstrated a low water uptake but when
doped they form solution droplets in a similar way to that described in the literature.
Other additives showed different behaviour with the formation of cracks within the
silicone due to failure of the material around the droplets, the action of hydrophilic but
insoluble fillers also promotes the uptake. The hydrosilanised silicone polymers showed
considerable promise as soft lining materials with low water uptake and good tensile
strength.
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The elastomer / methacrylate materials were based initially on butadiene styrene
copolymer and a higher methacrylate monomer which formed a gel this was then free
radically cured. The water uptake of these materials was attributed to soluble separating
agent added to the butadiene styrene (to prevent particle agglomeration) during the
production of the powdered elastomer. The extent of the uptake could be controlled by
improving the strength of the material but the overall uptake remained too high. When
the material was placed in an osmotic solution (Na CI or glucose) the water uptake was
significantly reduced and the behaviour could be described by a modified (for small
strains) version of the Thomas and Muniandy (1987) theory for the growth of water
droplets in a elastomer.
In order to reduce the water uptake of the elastomer / methacrylate materials butadiene
styrene copolymers without separating agent was used. The emulsion polymerised
material contained soluble impurities from the polymerisation (i.e. soap)which acted to
drive the water uptake. Solution polymerised butadiene styrene also demonstrated a high
uptake but this is attributed to a clustering behaviour of carboxylic and hydroxyl groups
which formed post production. Similar behaviour is also seen for a solution polymerised
isoprene styrene elastomer. The role of crosslinking the material in restraining the
growth of the droplets is also investigated with dramatic reductions in the uptake being
observed as the crosslink density increased. The employment of a reinforcing silica filler
proved more effective than simply using a dimethacrylate. Oxidation is another problem
(characterised by an upturn in the absorption), although not observed in every case it was
a problem for all of the unsaturated elastomers and was found to be promoted by ions
present within saliva. Saturated butyl based (including chloro and bromo butyl)
elastomers were used instead and did not show any tendency for oxidation but they still
showed an uptake of approximately 3 to 4 wt%. Their stability however and reasonable
strength makes them suitable for further development as soft lining materials.
Theoretical considerations were investigated by HI NMR imaging with the formation of
droplets being observed, the profiles seen indicating the absorption to be two stage
rather than Fickian. The role of creep or stress relaxation is also identified as a
mechanism for extending the uptake by reducing the restraining force. Further reasoning
on all the data presented here concluded the role of chemical potential change associated
with the water into the matrix or the droplets will determine the nature of the uptake
observed
Acuaria irhami Dewi & Zhang 2010
No full textAcuaria irhami Dewi & Zhang, 2010. Journal of Helminthology, 84, 245–252; Figs. 3–4 (Dewi & Zhang, 2010). MZBNa 419 (Holo. 1♂, Para. 1♂). Type locality: Kangean Island, Indonesia (06 o 52’41.6”S and 115 o 25’ 12.7”E); type host: Dicrurus hottentottus jentincki (under lining of gizzard).Published as part of Animalesto, Gloria, Dewi, Kartika & Apriyanti, Yuni, 2022, The helminth endoparasite type specimens of the Museum Zoologicum Bogoriense Indonesia, pp. 281-293 in Zootaxa 5159 (2) on page 284, DOI: 10.11646/zootaxa.5159.2.6, http://zenodo.org/record/677725
Lining of the induction furnaces
No full textThis work deals with lining of electric induction furnaces. The first part describes the preparation of lining, its function during the running of furnace and also its tearing down at the end of work process. In the thesis is also discussed the use of rammed crucibles. The materials used for lining and rammed crucibles are described also in the sense of their chemical properties in connection with the possibilities of their use under different conditions. The practical part of the thesis describes the process of lining the electric induction furnace, which was realized by the author under the supervision of the supervisor
Reliability analysis of a steel fibre reinforced concrete tunnel lining
No full textAt the moment, there are no Dutch regulations giving criteria for the design of bored tunnels. These regulations are necessary to prove that the required safety and serviceability are guaranteed by the proposed design. The scope of the study presented in this report consists of a reliability analysis of a SFRC tunnel lining. This consists of the definition of the load and resistance factors that are considered necessary to make a design of a SFRC lining and the calculation of the failure probability of the tunnel in the ultimate limit state. The study carried out in this report is based on the ITM tunnel design case with a lining thickness of 0,40 m and a radius of 4,70 m. The tunnel lining can fail by several mechanisms. The mechanism that is examined in this study, consists of the failure of the tunnel lining under strain of the soil stresses in the ultimate limit state. The analysis is executed with a level II probabilistic design method. The basis of this method is that the parameters used in the structural design are not specified constants, but stochastic variables. The most advanced method of this level is the so-called Approximate Full Distribution Approach (AFDA). This method is used for the reliability analysis executed in this report. First of all, the reliability of the tunnel design is approached with a linear calculation model, i.e. with the analytical Duddeck model. The most remarkable conclusion drawn from the linear reliability analysis, is that the safety requirements are on the whole better met in case of more flexible and thinner inings. As this conclusion does not meet the expectations and as the use of a (simple) linear model has a real benefit, the impact of non-linear effects on the cross-section forces is examined in order to determine whether the assumption of linearity is likely to be acceptable within the limitations of the non-linear tunnel analysis. An important conclusion drawn from the non-linear reliability analysis is that the safety decreases with decreasing lining thickness. The latter refutes the conclusion drawn at the linear reliability analysis that the safety increases with decreasing lining thickness. Moreover, from the non-linear reliability analysis follows that it is not safe to use the (linear) analytical Duddeck method for the design of slender constructions. In general, it can be concluded that the examination of the safety of a tunnel lining is very extensive and that still a lot of work is left to be done.Hydraulic EngineeringCivil Engineering and Geoscience
Bored Tunnel Lining Behaviour in Discontinuous Rock: Railway Tunnel in Middle-East
No full textIn a bored railway tunnel project in the Middle-East, difficulties in terms of ovalization, water leakages and settlement of several lining rings located in a fault zone were observed at the end of the construction stage. The present research attempted to find the cause for this lining behaviour. The determination of critical loading conditions, the application of the longitudinal beam model and the analytical and numerical modelling (in Plaxis) of a monolith tunnel lining in abrupt ground property transition were analyzed. Thereby, the global lining stiffness reduction due to joints was also considered. The literature review led to the following expected factors that caused difficulties in the Middle-East case: the squeezing and submerged ground conditions, the rock mass disturbance and the improper backfilling of the rings. Additionally, the ring stiffness reduction due to joints was an essential factor for lining behaviour. The geotechnical conditions, the lining design and the observed difficulties in the case were defined in the next section. Critical missing information, such as geotechnical properties of the fault zone material and limited monitoring data, led to essential assumptions. The settlements were expected to be caused by rock mass disturbance and improper backfilling. These altered the water flow during and after the boring operations and led to lowering of the groundwater level and increase of effective stresses. The water leakages were caused by ring ovalization in the soft fault zone, leading to opening of joints. The analysis for this research was divided in 2D transversal, 2D longitudinal and 3D modelling of the lining in and around the fault zone. The 3D model was seen as the integral model, which took into account the transversal and longitudinal behaviour of the lining. However, most of the behaviour of the lining was analyzed by carrying out parametric analysis for both directions in 2D. Moreover, the 2D models were used to validate the results of the 3D model to identify the influence of the third dimension. The assessment of the results from these analyses led to the following conclusions. The behaviour of the tunnel lining in small width fault zones was governed by the transversal action. The ovalization was mainly influenced by the ground stiffness, the vertical to horizontal stress ratio, the backfilling stiffness and the ring stiffness. Using Erdmann's analytical solution, the approximate lining forces can be determined. However, this overestimated the ground pressures acting on the lining, especially in cases where vertical to horizontal stress ratios were not equal to 0.5. This was because the 2D transversal behaviour did not take into account the longitudinal arching effect, which depended mostly on the stiffness ratio between ground types. The final conclusion was that the global reduction of lining stiffness due to the joints led to a discrepancy with regard to the distribution of the longitudinal displacements. A complementary analysis using a numerical model taking into account the joint structure and discontinuous behaviour between rings would probably allow a better prediction of longitudinal displacements.Geotechnical Engineerin
Study on Crack Development of Concrete Lining with Insufficient Lining Thickness Based on CZM Method
No full textThe most common structural defect of a tunnel in the operation period is the cracking of concrete lining. The insufficient thickness of tunnel lining is one of the main reasons for its cracking. This study studied the cracking behavior of standard concrete specimens and the failure behavior of tunnel structures caused by insufficient lining thickness using Cohesive Zone Model (CZM). Firstly, zero-thickness cohesive elements were globally inserted between solid elements of the standard concrete specimen model, and the crack development process of different concrete grades was compared. On this basis, a three-dimensional numerical model of the tunnel in the operation period was established. The mechanism and characteristics of crack propagation under different lining thicknesses were discussed. In addition, the statistics of cracks were made to discuss the development rules of lining cracks quantitatively. The results show that the CZM can reasonably simulate the fracture behavior of concrete. With the increase in concrete strength grade, the number of cohesive damaged elements and crack area increases. The insufficient lining thickness changes the lining stress distribution characteristics, reduces the lining structure’s overall safety, and leads to the cracking of the diseased area more easily. When surrounding rock does not contact the insufficient lining thickness, its influence on the structure is more evident than when surrounding rock fills the entire lining thickness. The number of cohesive damaged elements and the size of the crack area increases significantly
sj-docx-1-jis-10.1177_01655515221074323 – Supplemental material for Collaboration of issuing agencies and topic evolution of health informatisation policies in China
No full textSupplemental material, sj-docx-1-jis-10.1177_01655515221074323 for Collaboration of issuing agencies and topic evolution of health informatisation policies in China by Wenli Zhang, Rui Yao, Richard Evans, Wenjing Huang, Guang Cao and Lining Shen in Journal of Information Science</p
Study of contact pressure between primary lining and secondary lining for tunnels of passenger dedicated lines
No full textTo systematically study the mechanical properties of the secondary lining for tunnels of the passenger dedicated lines(PDL), in-site monitoring is used to measure the contact pressures between the primary lining and the secondary lining for some typical tunnels of different Lines, such as Guiguang Line, Lanyu Line and Jinghu Line. According to the research, the contact pressure reaches its maximum value at the moment when the tunnel lining trolley is removed. The load acting on secondary lining is the actual deformation pressure, which is totally different from the loose pressure prescribed in Chinese tunnel criteria. The safety factor for secondary lining under the measured load is higher than that under the criteria load and satisfies the safety requirements. It is therefore possible for the primary lining to sustain the entire surrounding rock pressure with the help of necessary auxiliary method and suitable installation time. The result given in this research enhances our understanding towards the mechanical characteristics of secondary lining for the PDL tunnel and it will be helpful for secondary lining design.link_to_subscribed_fulltex
Influence of Existing Defects on Mechanical Properties of NC Lining
No full textThe mechanical properties of the lining are directly affected by defects such as voids behind the lining and insufficient thickness of the lining. In order to quantitatively evaluate this effect, the mechanical behavior of the lining under the influence of the void behind the lining, the insufficient thickness of the lining, and the combination of the two kinds of defects are adopted by the 1/5 scale model test. Based on the experimental research, numerical calculation models based on the CDP model for defect lining are established, with the effects of load direction, stratum stiffness, defect location, defect type, and degree on the mechanical behavior of the lining analyzed by the numerical simulation. The experimental and numerical results show that the void weakens the stiffness of the lining. As the void range increases, the lining becomes more deformable and its bearing capacity decreases with the “S” curve. Thinning significantly reduces the deformation properties of the lining and the bearing capacity and stiffness of the thinned section. The lining bearing capacity decreases linearly with the increase of the thinning ratio, when the load is applied at the thinning. With the influence of combined defects on the load-displacement curve of the lining fluctuating drastically, the mechanical properties of the lining are significantly reduced. The bearing capacity of lining decreases with the increase of composite defects in a “S” shape. The effect of void and lining thinning on the lining bearing capacity increases with the increase of the stiffness of the formation. The loss rate equation of the concrete lining bearing capacity under the influence of existing defects is established by using the L-M nonlinear regression analysis, a provision of scientific guidance for the safety evaluation of the defect lining
sj-docx-2-jis-10.1177_01655515221074323 – Supplemental material for Collaboration of issuing agencies and topic evolution of health informatisation policies in China
No full textSupplemental material, sj-docx-2-jis-10.1177_01655515221074323 for Collaboration of issuing agencies and topic evolution of health informatisation policies in China by Wenli Zhang, Rui Yao, Richard Evans, Wenjing Huang, Guang Cao and Lining Shen in Journal of Information Science</p
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