Angle Of 45o Research Articles

Effects of Th doping on mechanical properties of U<sub>1–</sub><i><sub>x</sub></i>Th<i><sub>x</sub></i>O<sub>2</sub>: An atomistic simulation

Since thorium (Th) owns high conversion ratio in thermal neutron spectrum, high melting temperature, high thermal conductivity and good corrosion resistance in high-temperature water, it can be doped into UO<sub>2</sub> based fuel to initiate the fission reaction, and improve the physical properties of UO<sub>2</sub>. Owing to the challenging experimental conditions and technologies, molecular dynamics (MD) simulations are conducted to investigate the influences of Th doping on the mechanical properties of U<sub>1–</sub><i><sub>x</sub></i>Th<i><sub>x</sub></i>O<sub>2</sub>. The phase transition from initial fluorite structure to the metastable scrutinyite phase when loading along the [001] direction is observed, which accords well with the previous density functional theory calculations. However, if U<sub>1–</sub><i><sub>x</sub></i>Th<i><sub>x</sub></i>O<sub>2</sub> is loaded along the [111] direction, only brittle fracture is observed. It is found that both the elastic modulus and fracture stress decrease linearly with elevating temperature but the fracture strain increases. As the Th concentration increases from 0 to 0.55, the elastic modulus first decreases and then increases; if the Th concentration is larger than 0.1, the fracture stress increases and the fracture strain decreases monotonically. The cracks are nucleated with an angle of 45º to the loading direction, propagate rapidly, and are characteristic of brittle fracture, which accords well with the classical failure criteria and experimental results for brittle materials. By comparison, the uniaxial tensile loading is also performed for polycrystalline U<sub>1–</sub><i><sub>x</sub></i>Th<i><sub>x</sub></i>O<sub>2</sub>. It is found that the elastic modulus and fracture stress decrease as the temperature increases. However, the elastic modulus is not sensitive to the Th concentration and the fracture increases as the Th concentration increases. The brittle intergranular fracture is observed in each of all polycrystalline samples. The obtained physical parameters are useful for designing the fuels in nuclear reactors.

Numerical evaluation of effects of shear span, stirrup spacing and angle of stirrup on reinforced concrete beam behaviour

Shear and bending strength of reinforced concrete beams depend on many parameters. It is extremely important to take the necessary precautions in terms of shear in order for the beams to reach their bending capacity. For this reason, it is necessary to determine the effective parameters especially on shear capacity in beams. However, the actual capacity calculation is quite difficult according to regulations that are very conservative in terms of design. Therefore, many experimental studies have been conducted on the shear capacity of the beams. However, this situation is not meaningful in terms of both time and cost, since many experiments will be required to interpret the beam shear behavior, which depends on many parameters. For this reason, the use of advanced software whose verification is performed according to experimental data has become widespread. In this study, a numerical study was carried out on 36 different beam models using the ABAQUS finite element program to examine the effect of the shear span/effective depth (av/d) ratio, stirrup spacing (sw) and the angle of stirrup (a). The results showed that as the av/d increase, the behavior of a shear deficient beam tends to typical bending behavior. Although the effect of stirrup angle on shear capacity is quite high, stirrup angles of 30o and 60o give very similar results. The effect of stirrup spacing is quite limited at relatively high av/d. Stirrups with 90o do not contribute to ductility in beams with high av/d.

Хвилеводно-щілинний фідерний тракт антен з коловою поляризацією

Modern information systems use circularly polarized signals. Among them are tracking systems, remote sensing systems, satellite television systems. The use of circularly polarized signals in satellite communication systems allows to combat multipath propagation of signals in the environment, which reduces interference. By reflecting signals from different objects, they transform their polarization. This makes it possible to reduce signal distortions in the receiving device, which increases the information capacity of wireless data transmission channels. In satellite communications, multi-band horn antennas are widely used. The use of such devices allows transmission of signals with high power and reception of signals with low noise level. Such systems are used as powering a reflector antenna with a wide bandwidth. For such applications, a horn antenna device has been proposed in which signals can be excited that produce left-hand circularly polarized signals and right-hand circularly polarized signals. The proposed horn antenna was powered through a slot that was cut in a rectangular waveguide. Due to the 45º angle of the slot, the antenna can generate signals with double circular polarization. The proposed design can be used without polarizing devices, which must be developed separately. The developed design of the horn antenna at the operating frequency of 16 GHz provides a peak antenna gain of 24 dB for signals with right circular polarization and a peak value of a gain of 18 dB for signals with left circular polarization. The polarization isolation is greater than 12 dB. Moreover, at the operating frequency, the maximum value of the reflection coefficient takes on a value of –17 dB. Thus, the developed waveguide slot feed section for antennas with circular polarization provide rather good characteristics in a narrow frequency band.

Study on the effects of fiber orientation on the mechanical properties of natural fiber reinforced epoxy composite by finite element method

Natural Fibers being environment friendly and sustainable materials are gaining the interest of scientists, researchers and industrialists all over the world. Natural Fibers composite being lighter and cheaper than the synthetic fiber composites are seen as a scope for advancement in the ever evolving field of material science. Moreover, natural fibers unlike synthetic fibers are biodegradable in nature which draws the eyes of environmentalists towards them in these high times. In the present study, the optimization of most commonly discussed natural fiber reinforced composites such as Banana fiber, Jute fiber, Kenaf fiber, Hemp fiber and Pineapple Leaf fiber (PALF) on the basis of fiber orientation has been discussed. Finite element models of each fiber reinforced epoxy composite was prepared at constant fiber volume percent of 30% with fiber orientation angles of 0°, +22.5°/−22.5°, 45°/−45°, +67.5°/−67.5° and 90° measured from horizontal axis. The models were loaded for different standard loading conditions, i.e., tensile, flexural, and hardness test. From the results it was observed that for tensile and flexural test all the fibers showed minimum stress at the orientation of 0° and 90°. In Brinell harness test, composites with 45o angle of orientation shows the best results.

Composite material selection for aircraft structures based on experimental and numerical evaluation of mechanical properties

In this paper determination of mechanical properties of composite material using experimental and numerical approach is presented. The mechanical properties of a laminate obtained in the experiment are used for verification of numerically obtained values, as well as estimation of the load-carrying capacities of composite engine cover of light aircraft. Composite specimens, consisting of epoxy matrix and glass fibers with orientation angles 0º, 450, and 900, have been made according to standards, and the mechanical properties were investigated in tensile and three-point bending tests. The tensile strength, bending strength, elasticity modulus, strain, and force at laminate failure have been evaluated and then compared to values obtained in numerical simulations with the aim of verifying the FE model used for failure prediction of structural laminates. Good agreement of experimental and numerical values provides a solid foundation for further improvements of the numerical model.

PENGUJIAN DAN PERAWATAN MESIN GRANULAR

This paper discusses the granulator machine testing process. This test aims to determine the process of occurrence of granular. Granular pellets are one form of feed pellets, granular (rounded) and light in weight. Granular pellets are not easy to sink but are easily broken down in water. This type of pellet is made without going through the process of pressing, so that it can produce feed grains that are light weighted, not easily submerged but easily decomposed in water. The goal is to determine the optimal state of the granulator machine with three angular tilt positions, it can perform maintenance on the granulator machine. The granulator machine testing process is carried out by means of the plate angle measurement process, the water mixture measurement process, the plate speed measurement process. Material used for the testing process uses flour and water. While the tools used in the granulator machine testing process are spray, 14 key, sieve, and container. After testing at 3 angles at an angle of 25o, angle of 30o and angle of 35o the authors conclude that this machine can produce small granules at a slope of 250 with an engine speed of 17 rpm and average weight of granular which is produced 236 grams. While the results of hourly 3 kg / hour.

Investigation of Failure Criteria and Experimental Process of the Composite Specimen with Mechanical Joints under Tensile Loading

Generally, composite materials are used to obtain better engineering properties, including higher hardness, greater strength, lower weight, heat resistance, moisture and corrosion, which are not present in homogeneous materials such as metals, which are more commonly used in composite design. In this article, experimental study of the composite specimen with mechanical joints under tensile loading, joints of composite material structures, failure criteria in composite materials, tensile impact test is investigated. The results of research work it shows that maximum strength, the hand lay-up can be designed with [0º, 45º, 90º, -45º] s and layers with 45º fibers is very important, because these fibers in these layers have a significant role in increasing the resistance of the piecework under shear stresses due to the passage of stress lines along the hole; In other words, the maximum cut occurs at a 45º angle, and these layers resist this shear stress.

A 3-D Finite Element Analysis of a Single Implant Retained Overdenture Reinforced with Short Versus Long Frameworks.

Due to its simplicity and patient satisfaction, an implant-retained overdenture has become the most preferred treatment for edentulous patients. Due to the presence of an attachment system at mandibular anterior region, however, base fracture is the most common complication of overdenture. This study aimed to evaluate the stress distribution and deformation on a symphyseal single implant retained mandibular overdenture using a three-dimensional finite element. Zirconia versus acrylic overdenture was investigated. Acrylic overdentures reinforced with short (over inter-canine distance) or long (extending between first molars) zirconia, cobalt-chromium alloy or polyetherketoneketone framework were also investigated. A load of 100 N was applied to the incisal edge of mandibular central incisors at a 30º angle. Results showed that zirconia overdenture had lower von Mises stress and deformation in its components than acrylic. Reinforcement of an acrylic overdenture with cobalt chromium or zirconia short frameworks reduced von Mises stress and deformation on its components. Reinforcement of an acrylic overdenture with polyetherketoneketone framework did not show any significant reduction in von Mises stress and deformation. Therefore, it can be concluded that using zirconia overdenture or reinforcing an acrylic overdenture with cobalt chromium or zirconia framework could increase the longevity of the prosthesis.

Experimental and computational analysis of mechanical properties of RGD840 material manufactured through PolyJet process

PurposeNowadays, the PolyJet technique is used to fabricate low volume functional parts in engineering and biomedical applications. However, the mechanical properties of the components fabricated through this process are inferior in comparison to components fabricated through the traditional manufacturing process. This paper aims to attempt to investigate the influence of process parameters, i.e. raster angle, orientation and type of surface finish on mechanical properties of RGD840 material manufactured by the PolyJet process.Design/methodology/approachInitially, this study focuses on experimental evaluation of elastic modulus, ultimate tensile strength and percentage elongation of the material. Further detailed experimental study of true stress, true strain, and plastic strain are conducted. Computational analysis of plastic strain is performed by using finite element analysis (FEA) software ABAQUS. The value of strength coefficient (K) and strain hardening coefficient (n) is calculated by using the graphical method from the true stress-plastic strain curve.FindingsIt is observed that 90º raster angle, flat orientation and glossy surface are the best level of process parameters for the tensile strength, true stress and modules of elasticity of the RGD840 material and the obtained value are 27.88, 30.134 and 2891.5 MPa, respectively. The percentage elongation is maximum at 60º raster angle, flat orientation, and matte finish type and the obtained value is 23.38%. The optimum level of process parameters are 90° raster angle, Flat orientation, with Glossy surface finish. SEM analysis of the fracture surface of the tensile test specimen proves that the fracture surface is brittle in nature.Originality/valueThe novelty of this work lies in the fact that no attempts were made to investigate the computational investigation of mechanical properties of RGD840 material.

PENGARUH SUDUT BUKAAN GUIDE VANE DAN TEKANAN AIR TERHADAP KECEPATAN PUTAR DAN DAYA OUTPUT PADA PROTOTYPE PEMBANGKIT LISTRIK TENAGA MIKROHIDRO DENGAN TURBIN CROSSFLOW

The pattern of power plants development in Indonesia is still relying on the availability of fossilfuels based energy sources. Meanwhile, Human are faced with a situation of depleting reserves offossil energy sources and increasing environmental damage due to the use of fossil fuels basedenergy sources. Renewable Energy development can be a solution to these problems. One of them isthe development of a Micro Hydro Power Plant. In the realization of Micro Hydro Power Plant inIndonesia, the crossflow water turbine type can be used. It is a type of impulse turbine with a goodcharacteristic at a low head for micro-scale generator capacity. This study analyzes the effect of guidevane opening angle and water pressure on rotation and output power of crossflow turbine. Theopening angle of the guide vane studied was 15º, 30º, 45º, 60º, 75º, and 90º in each water pressurecondition of 4 psi, 8.5 psi and 13 psi. The test is carried out by simulating direct measurements on theprototype of the Micro-hydro Power Plant that has been built. Every combination of parameterstested, the maximum value of rotational speed and output power is obtained at the guide vaneopening angle of 30º and water pressure of 13 psi. Turbine rotation values generated before and aftercoupled with a generator are 591.9 rpm and 522.7 rpm. The values of the generator rotation beforeand after the load coupled are at 3490 rpm and 2368 rpm. And the power value generated by thegenerator is 11.8 Watts.

PENGARUH TEKANAN AIR DAN SUDUT NOZZLE TERHADAP KARAKTERISTIK OUTPUT PADA PROTOTYPE PLTMH DENGAN TURBIN PELTON

Pelton turbine is an impulse turbine that is different from other turbines where the peltonturbine utilizes a large high water fall (head), even with a small water discharge. The problemwith Pelton turbine is that the head is still difficult to control because this type of turbine uses ahigh head to rotate the turbine runner and there is no formula / equation to determine the angleof the nozzle which produces maximum output. Based on the problems described, it isnecessary to make a micro hidro power plant prototype using a pelton turbine with a laboratoryscale so that it can do the testing of the influence of water and the nozzle angle to obtainmaximum output results on a micro hidro power plant using a pelton turbine. The prototypetesting in this study used various water pressures, namely 5 psi, 9 psi, 13 psi, 17 psi, 21 psi,and 25 psi with nozzle angles, namely 60º, 75º, and 90º. Based on the results of the study, anincrease in the value of water pressure provided with an optimal nozzle angle will cause themicro hidro power plant performance to increase. The maximum output obtained is when thewater pressure is 25 psi with a nozzle angle of 90º which produces a turbine rotation of 917 rpmbefore the generator is coupled and 326 rpm after the generator is coupled, the generatorrotation is 1321 rpm, the generator voltage is 12.9 Volts, generator power is 30.96 Watt, torque is 0.98 Nm, and the highest efficiency occurs when the water pressure is 21 psi with a nozzleangle of 90º which is 3.91%.

Robust parameter design of shielded metal arc welding (smaw) for optimum tensile strength

Shielded Metal Arc Welding (SMAW), an arc welding process that uses a consumable electrode consisting of a filler metal rod coated with chemicals that provide flux and shielding, is widely used in engineering applications. SMAW parameters that usually applied in practice is still possible to be optimized to improve the process to become robust. This work is focus on an optimization of SMAW process on ASTM A500 Hollow Square Pipe, as it is widely found in applications. The welding parameters such as welding current, electrode angle, root gap, and electrode type are adopted as process parameters. Taguchi robust optimization is applied as optimization strategy, and L9 fractional orthogonal array is selected as design of experiment. The optimization objective is to maximize tensile strength of SMAW welded joint. The optimization results found that welding current 100A, electrode angle 90o, root gap 2 mm, and electrode type E7018 of SMAW parameters give the optimum tensile strength. The tensile strength gain of robust design based on the initial design was carried out by 98,39 MPa (from 259,45 MPa of initial design to 357,84 MPa of optimum design).

Optimization of TIG Welding Parameters for the 202 Stainless Steel Using NSGA-II

Tungsten Inert Gas welding is a fusion welding process having very wide industrial applicability. In the present study, an attempt has been made to optimize the input process variables (electrode diameter, shielding gas, gas flow rate, welding current, and groove angle) that affect the output responses, i.e., hardness and tensile strength at weld center of the weld metal SS202. The hardness is measured using Vicker hardness method; however, tensile strength is evaluated by performing tensile test on welded specimens. Taguchi based design of experiments was used for experimental planning, and the results were studied using analysis of variance. The results show that, for tensile strength of the welded specimens, welding current and electrode diameter are the two most significant factors with P values of 0.002 and 0.030 for mean analysis, whereas higher tensile strength was observed when the electrode diameter used was 1.5 mm, shielding gas used was helium, gas flow rate was 15 L/min, welding current was 240A, and a groove angle of 60o was used. Welding current was found to be the most significant factor with a P value of 0.009 leading to a change in hardness at weld region. The hardness at weld region tends to decrease significantly with the increase in welding current from 160-240A. The different shielding gases and groove angle do not show any significant effect on tensile strength and hardness at weld center. These response variables were evaluated at 95% confidence interval, and the confirmation test was performed on suggested optimal process variable. The obtained results were compared with estimated mean value, which were lying within ±5%.

Determination of Optimal Solar Power and Corresponding Tilted Angle in Different Geoclimatic Zones in Nigeria

Aims: To estimate the optimum tilt angle and maximum solar power for different geoclimatic zones in Nigeria.
 Methodology: In this study, the surface data of direct and diffuse solar radiations spanning 2013 to 2017 were obtained from the archives of the Modern-Era Retrospective Analysis for Research and Application for 20 stations spread across Nigeria. To study the direct relationship between the solar power on a photovoltaic panel and the solar radiation, the values of the direct, diffuse, and ground-reflected components of solar radiation were calculated for six tilt angles ranging from 15° to 90° using anisotropic models. Afterwards, the maximum values of the solar power and the corresponding tilt angles, as well as the average number of solar panels that can be used to cater for the electricity needs of households in all the geoclimatic zones, were estimated.
 Results: Analyses showed that the maximum solar power was received at tilt angles of 30° and 45° from October till February, and tilt angles of 15° and 30° from March till September in all the study locations. For instance, the Sahel and Guinea Savanna zones had the highest solar power, whereas Derived Savanna and Coastal zones had relatively low power. Based on the results, it was determined that the number of solar panels required in the sahel zone would be lower than those of the other zones.
 Conclusion: It can be inferred from the results that the reception of maximum solar power is at the tilt angle of 45o in Sahel, Guinea, and Derived Savanah regions, and at 30o in the Coastal region. The results of this research will provide solar engineers with accurate information on the orientation and tilt of PV modules for efficient power generation.

Combustion and Emission Characteristics of a Diesel Engine Operating with Varying Equivalence Ratio and Compression Ratio - A CFD Simulation

The performance of diesel engine highly depends on atomization, vaporization and mixing of fuel with air. These factors are strongly influenced by various parameters e.g. injection pressure, injection timing, compression ratio, equivalence ratio, cylinder geometry, in cylinder air motion etc. In this study, a diesel engine has been investigated by employing a commercial CFD software (ANSYS Forte, version 18.1) especially developed for internal combustion engines (ICE) modeling; focusing primarily on the effects of equivalence ratio and compression ratio on combustion and emission characteristics. RNG k-ε model was employed as the turbulence model for analyzing the physical phenomena involved in the change of kinetic energy. In order to reduce the computational cost and time, a sector mesh of 45o angle with periodic boundary conditions applied at the periodic faces of the sector, is considered instead of using the whole engine geometry. Simulations are performed for a range of equivalence ratio varying from 0.6 to 1.2 and for three compression ratios namely, 15:1, 18:1 and 21:1. Results show that, improvement in combustion characteristics with higher compression ratio could be achieved for both lean and rich mixtures. Peak in-cylinder pressure and peak heat release nearer to TDC are achieved for compression ratio of 18:1 that could results in more engine torque. For compression ratio beyond 16:1, effects of fuel concentration on ignition delay is more pronounced. At lower compression ratio, in-cylinder temperature is not sufficiently high for atomization, vaporization, mixing of fuel with air, and preflame reactions to occur immediately after the fuel injection. NOx emission in diesel engine increases due to higher pressure and temperature inside the cylinder associated with relatively higher compression ratio. Rich mixture leads to more CO and unburnt hydrocarbon emission compared to lean mixture as result of incomplete combustion. Engine operation with too high compression ratio is detrimental as emission is a major concern.

Wave phase analysis for computing density of states, group velocity, and lateral shift in a 1D quasiperiodic structure containing layers of uniaxial medium and SiO2.

In this paper, by considering wave phase analysis, the density of modes, group velocity, and lateral shift in one-dimensional multilayer are theoretically computed by using the transfer matrix method in the terahertz domain. The proposed structure is based on the Fibonacci sequence constituted of uniaxial indefinite medium and SiO2 layers. It is found that for both TE and TM beams, around an angle of 90º, the lateral shift is highly negative, while it is positive at the rest of the angles. Also, for non-vertical angles, a positive peak is observed about an angle of 60º (near the Brewster angle). Our numerical analysis shows that at angles less than about 10º, the lateral shift is negative for the TM mode. It is shown that for both polarizations the density of states (the group velocity) has maximum (minimum) value near the band gap edges, while inside the band gap it becomes minimum (maximum). Superluminal and subluminal cases can be defined here.

THE EFFECTS OF SWIRL AND TUMBLE RATIOS ON THE ENGINE PERFORMANCE OF MOTORBIKES

Nowadays, motorbikes are still the main and most popular transport in Asian countries, especially, in Vietnam. However, the manifold intake systems in motorbikes are usually designed in a simple structure, which can reduce engine performance and increases fuel consumption in motorbikes. This paper presents the study of the improvement of the intake system in a 125cc motorbike engine to enhance air-fuel mixing quality that can increase the engine performance. The study employs the ANSYS software to obtain an optimal intake systemthrough the tumble and swirl ratios in different simulation cases. Another model wasalso built by Matlab/Simulink to examine the effects of swirl and tumble ratios on engine performance and fuel consumption at various engine speeds. The simulation results show that the modified intake system withan incline angle of 30o has optimal tumble and swirl ratios. Accordingly in conclusion, power output and torque of the engine with the modified intake system are higher, while the fuel consumption is lower than previouslyfound.

Влияние окружающей среды влажных субтропиков на цветовые характеристики защитных полимерных покрытий

To increase the reliability and durability of structures and equipment, various protection methods are used, the most common of which is the application of protective and decorative polymer coatings. The surface layers of the coatings are most sensitive to external factors. The processes occurring in these layers are one of the main reasons for the change in decorative properties, including color indicators. At the same time, high weather resistance of the outer layer provides enhanced protective properties of the entire paint system. The paper studies the persistence of color indicators of various polymer coatings in a subtropical climate, characterized by high aggressiveness of the factors. Using instrumental methods for field exposure of samples in an open atmospheric area for 2.5 years, the colorimetric indicators in the CIELAB system and their color difference between the initial state and after aging were determined. The test samples were exhibited on the coastal test site on the Black Sea coast in the Imereti Lowland at Cape Imeretinsky (43o23′ N, 39o59′ E) 40 meters from the water edge. The tests were carried out on open atmospheric stands at an angle of 45o to the horizon with the control of the environmental parameters during the exposure of the samples. High color stability was shown by the coatings of the fluoroplastic group – enamel Viniftor and VE-46, while the worst performance was shown by perchlorovinyl enamel XV-518. The results of such studies under natural conditions are most valuable for a comparative assessment of the effectiveness of the protective and decorative properties of coatings.

Finite element analysis of torque induced orthodontic bracket slot deformation in various bracket-archwire contact assembly

Background and ObjectivesOrthodontic fixed appliance therapy involves alignment of teeth through the bracket and archwires. The archwire twist (torque) imparts significant forces inside the bracket slot in refining the teeth position at the end of treatment. The objective of this in- silico study was to evaluate the torque induced bracket slot deformation in the commonly used 0.018 inch (") and 0.022" conventional Stainless Steel (SS) brackets with clinically relevant archwires during various angles of twist. MethodsSS maxillary central incisor brackets of 0.018" width × 0.022" depth (0.457 mm × 0.558 mm) and 0.022" width × 0.028" depth (0.558 mm × 0.711 mm) were used. The SS archwires of 0.016" width × 0.022" depth (0.406 mm × 0.558 mm), 0.017" width × 0.025" depth (0.431 mm × 0.635 mm), 0.019" width × 0.025" depth (0.482 mm × 0.635 mm) and 0.021" width × 0.025" depth (0.533 mm × 0.635 mm) were engaged in the respective bracket slots. The assembled bracket-archwire Finite Element (FE) models were constructed. The archwire torque, the top, middle and bottom slot deformations (TSD, MSD, BSD) were obtained for the bracket-archwire combinations for various angles of archwire twist using FE Analysis (FEA). ResultsThe torque, TSD, MSD and BSD for 30o twist of 0.016" × 0.022" archwire in 0.018" slot were 28.13 Nmm, 35.71 µm, 21.51 µm and 15.67 µm respectively, and for 0.017" × 0.025" archwire were 50.18 Nmm, 54.52 µm, 32.47 µm and 19.11 µm respectively. Similarly for 0.019" × 0.025" archwire in 0.022" slot and 0.021" × 0.025" archwire in 0.022" slot they were 38.82 Nmm, 50.78 µm, 31.47 µm and 16.82 µm, and 60.22 Nmm, 65.22 µm, 36.44 µm and 22.68 µm respectively. ConclusionsThe slot deformation was present in both 0.018" and 0.022" brackets which increased as the angle of twist increased. The TSD were higher than the MSD and BSD in all the bracket-archwire combinations. We conclude that there is only elastic deformation of bracket slots upto 30o angle of twist and clinicians could maintain within this torque limits to avoid plastic deformation leading to improper teeth position.

Erosion dynamics of compacted raw or homoionic MX80 bentonite in a low ionic strength synthetic water under quasi-stagnant flow conditions

Bentonite is planned to be used as a backfill material in deep geological repositories (DGR) notably for those to be established in crystalline rock. Potential erosion processes have to be clearly understood in order to properly assess its long-term barrier function. A likely scenario over the lifetime of a DGR in certain geographical locations is the intrusion of low mineralized glacial melt water through low transmissivity bedrock fractures that could interact with bentonite and favor release of clay colloids. The objective of this work was to determine the dynamic of erosion under a glaciation scenario for Na-exchanged, Na-Ca-exchanged, Ca-exchanged and raw bentonite. The different bentonite types cover different potential materials used for backfill and different stages of cation loading via cation exchange processes upon contact with groundwater of different composition. To this end, erosion experiments were carried out with highly compacted bentonite confined by a porous filter (20 μm) under dynamic conditions simulating the presence of a hydraulically active fracture filled with fault gauge and fracture filling minerals.The <500 μm size fractions of untreated MX80 bentonite and after Na- or Ca-homoionization, were used. Two compacted clay pellets (1.6 ± 0.1 g/cm3) of identical composition were placed in separate compartments of double-side reactors. Post-mortem visual inspection and the observed washout of water soluble MX80 components indicated full equilibration of the bentonite with simulated groundwater taking place during the experiment. The erosion was investigated by circulating a low ionic strength (1.6 10−3 M) water at pH 8.4. Bentonite swelling was confined by stainless steel filter plates.The erosion (clay colloid detachment) via a low mineralized groundwater flow was quantified by determining an average eluted mass loss rate (AMLR). AMLR values integrated over 1466 days (4 years) erosion time for the raw MX80 bentonite, the Na-MX80 and the Na-Ca-MX80 are at 0.019 ± 0.003 kg/y/m2, 0.245 ± 0.007 kg/y/m2 and 0.10 ± 0.02 kg/y/m2, respectively. Only by the sensitive ICP-MS analysis of clay-bound Th and U a tiny detachment of particles from Ca-MX80 could be identified, which shows the highest resistivity against erosion (0.004 ± 0.002 kg/y/m2). The experiments pointed to the swelling pressure as main driving force for colloid generation. A possible inhibiting effect of accessory minerals on erosion can also be deduced from this study. Assuming erosion via a groundwater flow from a single fracture intersecting a deposition hole filled with raw MX80 bentonite at an angle of 90o and with a fracture aperture of up to 200 μm, the present estimations indicated that under the given scenario the mass loss limit of 1200 kg bentonite will not be reached during the first 106 years.