Thread Shape Research Articles

The evolution of a viscous thread pulled with a prescribed speed

We examine the extension of an axisymmetric viscous thread that is pulled at both ends with a prescribed speed such that the effects of inertia are initially small. After neglecting surface tension, we derive a particularly convenient form of the long-wavelength equations that describe long and thin threads. Two generic classes of initial thread shape are considered as well as the special case of a circular cylinder. In these cases, we determine explicit asymptotic solutions while the effects of inertia remain small. We further show that inertia will ultimately become important only if the long-time asymptotic form of the pulling speed is faster than a power law with a critical exponent. The critical exponent can take two possible values depending on whether or not the initial minimum of the thread radius is located at the pulled end. In addition, we obtain asymptotic expressions for the solution at large times in the case in which the critical exponent is exceeded and hence inertia becomes important. Despite the apparent simplicity of the problem, the solutions exhibit a surprisingly rich structure. In particular, in the case in which the initial minimum is not at the pulled end, we show that there are two very different types of solution that exhibit very different extension mechanics. Both the small-inertia solutions and the large-time asymptotic expressions compare well with numerical solutions.

Interactions of carbon nanotubes in a nematic liquid crystal. II. Experiment.

Multiwall carbon nanotube (CNT) colloids with different anchoring conditions are dispersed in pentyl-cyanobiphenyl (5CB), a thermotropic liquid crystal (LC) that exhibits a room-temperature nematic phase. The experiments make use of CNTs treated for strong planar, homeotropic, or Janus anchorings. Observations with a polarizing microscope show that the CNTs placed in a uniform nematic field stabilize parallel or perpendicular to n depending on their anchoring conditions. In the presence of a splay-bend disclination line, they are first attracted toward it and ultimately, they get trapped on it. Their orientation relative to the line is then found to be parallel or perpendicular to it, again depending on the anchoring conditions. When a sufficient number of particles are deposited on a disclination line, they form a micro- or nanonecklace in the shape of a thin thread or of a bottle brush, with the CNTs being oriented parallel or perpendicular to the disclination line according to the anchoring treatment. The system exhibits a rich versatility, even if until now the weak anchorings appear to be difficult to control. In a next step, the necklaces may be glued by means of pyrrole electropolymerization. In this manner, we realize a true materialization of the disclination lines, and we obtain nanowires capable of conducting the electricity in the place of the initial disclinations that just worked as templates. The advantage of the method is that it finally provides nanowires that are automatically connected to predesignated three-dimensional (3D) electrodes. Such a 3D nanowiring could have important applications, as it could allow one to develop electronic circuits in the third dimension. They could thus help with increasing the transistor density per surface unit, although downsizing of integrated circuits will soon be limited to atomic sizes or so. In other words, the predicted limitation to Moore's law could be avoided. For the moment, the nanowires that we obtain are not completely satisfactory, particularly because they are thickened by aggregates in some places. However, the method is far from being optimized. A few electric charges deposited on the CNTs could remedy those aggregates.

Interactions of carbon nanotubes in a nematic liquid crystal. I. Theory.

Elongated and rodlike objects such as carbon nanotubes (CNTs) are studied when immersed in a nematic liquid crystal. Their interaction energy in a uniform nematic field depends on their orientation relative to the director n, and its minimum determines if they stabilize parallel or perpendicular to n. Using free energy calculations, we deduce the orientation at equilibrium that they choose in a uniform director field n or when they are in contact with a splay-bend disclination line. Naturally, the CNT orientations also depend on the anchoring conditions at their surface. Essentially, three types of anchorings are considered, planar, homeotropic, and Janus anchorings in the cases of weak and strong anchoring strengths. In the presence of a splay-bend disclination line, they are attracted toward it and ultimately, they get out of the colloidal dispersion to stick on it. Their orientation relative to the line is found to be parallel or perpendicular to it, again depending on the anchoring conditions. When a sufficient number of particles are deposited on a disclination line, we finally obtain a micro- or nanonecklace in the shape of a thin thread or of a bottle brush, according to the CNTs being oriented parallel or perpendicular to the disclination line, respectively. The system exhibits a rich versatility even if up to now the weak anchorings appear to be difficult to control. As discussed in the associated experimental paper, these necklaces could be a step toward interesting applications for realizing nanowires self-connected in three dimensions to predesignated electrodes. This method could provide a way to increase the number of transistors that may be connected together on a small volume.

A Combined Experimental and Numerical Modeling Study of the Deformation and Rupture of Axisymmetric Liquid Bridges under Coaxial Stretching.

The deformation and rupture of axisymmetric liquid bridges being stretched between two fully wetted coaxial disks are studied experimentally and theoretically. We numerically solve the time-dependent Navier-Stokes equations while tracking the deformation of the liquid-air interface using the arbitrary Lagrangian-Eulerian (ALE) moving mesh method to fully account for the effects of inertia and viscous forces on bridge dynamics. The effects of the stretching velocity, liquid properties, and liquid volume on the dynamics of liquid bridges are systematically investigated to provide direct experimental validation of our numerical model for stretching velocities as high as 3 m/s. The Ohnesorge number (Oh) of liquid bridges is a primary factor governing the dynamics of liquid bridge rupture, especially the dependence of the rupture distance on the stretching velocity. The rupture distance generally increases with the stretching velocity, far in excess of the static stability limit. For bridges with low Ohnesorge numbers, however, the rupture distance stay nearly constant or decreases with the stretching velocity within certain velocity windows due to the relative rupture position switching and the thread shape change. Our work provides an experimentally validated modeling approach and experimental data to help establish foundation for systematic further studies and applications of liquid bridges.

Development of the light weight carbon composite tie bar

Stacks of energy conversion systems, such as proton exchange membrane fuel cells (PEMFCs), are composed of several hundreds of components, and they are compacted with tie bars to decrease electrical contact resistance and prevent the leakage of fuels. Since the sealing performance deteriorates over long operation times due to creep deformation of the stack, it is important to maintain a consistent clamping force under the creep deformation of the stack for long-term reliability.In this work, a light weight carbon composite tie bar was developed to replace the conventional steel tie bar. This new composite tie bar can achieve high elastic strain and provides a consistent compaction pressure to the stack over long operation time. To form the complex thread shape of the tie bar without compromising its tensile strength, different types of material were adopted for the thread and rod parts. A carbon fiber mat was used for the thread part because it has a higher drapability compared to other types of carbon fiber, such as unidirectional (UD) or the fabric type. The UD and fabric were adopted for the rod part for their high strength and elongation. Based on the tension test of the fabricated tie bar specimens, an optimum configuration of the carbon composite tie bar has been suggested.

Cribellate thread production in spiders: Complex processing of nano-fibres into a functional capture thread

Spider silk production has been studied intensively in the last years. However, capture threads of cribellate spiders employ an until now often unnoticed alternative of thread production. This thread in general is highly interesting, as it not only involves a controlled arrangement of three types of threads with one being nano-scale fibres (cribellate fibres), but also a special comb-like structure on the metatarsus of the fourth leg (calamistrum) for its production. We found the cribellate fibres organized as a mat, enclosing two parallel larger fibres (axial fibres) and forming the typical puffy structure of cribellate threads. Mat and axial fibres are punctiform connected to each other between two puffs, presumably by the action of the median spinnerets. However, this connection alone does not lead to the typical puffy shape of a cribellate thread. Removing the calamistrum, we found a functional capture thread still being produced, but the puffy shape of the thread was lost. Therefore, the calamistrum is not necessary for the extraction or combination of fibres, but for further processing of the nano-scale cribellate fibres. Using data from Uloborus plumipes we were able to develop a model of the cribellate thread production, probably universally valid for cribellate spiders.

Thread Pitch Variant in Orthodontic Mini-screws: A 3-D Finite Element Analysis

Orthodontic miniscrews are widely used as temporary anchorage devices to facilitate orthodontic movements. Miniscrew loosening is a common problem, which usually occurs during the first two weeks of treatment. Macrodesign can affect the stability of a miniscrew by changing its diameter, length, thread pitch, thread shape, tapering angle and so on. In this study, a 3-D finite element analysis was done to show the effect of thread pitch variant on the stress distribution pattern of the screw-cortical bone interface. While orthodontic forces were applied, stresses were usually concentrated at the first thread of the screw in contact with the cortical bone. The cortical bone provided a significant percentage of stability compared to the trabecular bone against orthodontic forces. Therefore, spongy bone was removed from the finite element analysis. The changes of maximum von Mises stresses were shown on the charts. The results showed that stresses decreased with decrease in thread pitch, but they increase when thread pitch becomes less than a certain value. The pattern of stress distribution differed when the stresses were increased. The results are beneficial for the design of an ergonomic dual miniscrew, with better properties than the commercially available miniscrews and based on the results, a new dual miniscrew is recommended.

Experimental Study on the Influence of Drillhole Roughness on the Pullout Resistance of Model Soil Nails

Pullout resistance of cement-grouted soil nails is a key factor affecting the safety conditions of retaining walls, slopes, and excavations. The mobilized frictional resistance at the interface between soil nails and surrounding soils depends on various parameters such as saturation ratio, water content, grouting under gravity or pressure, etc. The interface roughness condition between soil nail and soil is a critical factor but difficult to control in both laboratory and field owing to technical difficulties in creating a rough drillhole surface. The present study focuses on the pullout behavior of model soil nails with different interface roughness conditions in the laboratory to establish quantified correlations between frictional resistance and roughness angles of internal drillhole surface. Cross-sectional shapes of internal drillhole surfaces were created using four plastic rods with various shapes of external threads (four different values of roughness angles). Measured peak values of pullout resistance of soil nails with rough drillhole surface were compared with the soil nails with smooth drillhole surface. The present test results were verified with a previous analytical model, which considered the soil dilation to be an important factor influencing the pullout resistance of soil nails. Test results also indicate that the peak pullout resistance increases almost linearly with an increase in roughness angles. In addition, the pullout resistance values decrease approximately linearly with an increase in pullout displacement after peak pullout resistance is approached. The soil-nail diameter values of the soil nails with rough drillhole surfaces expanded substantially after being pulled out of the ground. This leads to a substantial increase in pullout resistance of soil nails.

소재와 나사산 변화에 따른 정밀나사의 체결력 향상에 관한 연구

In this study, we compare the performance of the screw through the Clamping force of the test materials to change shape and structure, one of the ways to maintain and improve the engaging force to cope with the miniaturization of the fastener threads are further thinner and lighter precision way that can improve the fastening force of the screw results were as follows. The clamping force according to the materials was 7.57Nㆍcm in SUS XM7 and SWCH18A was 5.97 Nㆍcm. This result was to be found to average 13.5% high in the Clamping force of SUS XM7 materials. In the case of the clamping force of the screw thread shape change, the clamping force of symmetrical and asymmetrical thread was 6.78 Nㆍcm and 7.57 Nㆍcm. The clamping force of the asymmetrical thread showed an average high of 11.6%.

Should we use cortical bone screws for cortical bone trajectory?

In 2009, Santoni et al. reported cortical bone trajectory (CBT) as a method of inserting pedicle screws to obtain more solid fixation, and proposed the use of cortical trajectory screws with a more closely placed thread (cortical screws) for CBT. Since the entry trajectory in CBT differs from that in the traditional trajectory, it is unclear whether the increased strength derives from the specific trajectory or the shape of the screw thread in contact with the cortical bone. Whether the use of cortical screws is always required with CBT thus remains unclear. The authors therefore investigated the relationship between screw entry trajectory and screw thread characteristics and pullout strength in animal experiments. Lumbar vertebrae (L1-L4) from 4-month-old female pigs were randomly assigned to one of 4 groups, with cancellous screws or cortical screws inserted via the traditional trajectory or CBT. For pullout strength testing, the screw was pulled out vertically against the direction of insertion. Rod pullout testing (toggle testing) was also performed, and the peak breaking strength was measured. The maximum pullout strength was significantly greater for CBT using cortical screws than for the traditional trajectory using cancellous screws. Pullout strength tended to be higher when cortical screws were used in both CBT and the traditional trajectory, although the difference was not significant. Toggle testing showed no significant differences among the 4 groups. The specific unconventional trajectory seemed to have a major impact on the increased strength obtained with CBT.

Influence of pin geometry on mechanical and structural properties of butt friction stir welded 2024-T351 aluminum alloy

The aim of this work was to investigate the combined effect of small difference in pin geometry, together with rotation and welding speed on the weldability, mechanical and structural properties of FSW 2024-T351 Al plates. The only difference in tool pin design was the shape of thread: regular and rounded. Specimens were welded using rotation rate of 750 rev/min and welding speeds of 73 and 93 mm/min. In all four cases, specimens were defect free, with good or acceptable weld surface. Modification in pin design showed strong influence on macro structure and hardness distribution. Weak places are identified as low hardness zone, close to the nugget zone and are in good agreement with fracture location in tensile testing. Weld efficiency, as a measure of weld quality, are better in case of 310 tool, while UTS values can differ up to 13% for the equal welding parameters. Therefore, it can be assumed that small modification in tool design, particularly in pin geometry, can have great influence on weld formation and mechanical properties.

The Simulation Study of Fluid Physical Properties on Drop Formation of Drop-on-demand Inkjet Printing

Inkjet printing is a method for directly patterning and fabricating patterns without the need for masks. However, the physical phenomenon in inkjet printing process is very complicated with the coupling of piezoelectricity, elasticity, and free surface fluid dynamics. The authors use the volume of fluid (VOF) method as implemented in the commercial code FLUENT to model the details of the drop formation process. The influence of viscosity and surface tension of the liquid on the droplet formation process is investigated. Consequently, we find that the speed of liquid plays an important role for the jet stability. The viscosity of liquid greatly influences the final speed of droplet. However, the surface tension of liquid does not much affect the speed of droplet. It changes the shape of the liquid thread and final droplet.

The effect of the thread depth on the mechanical properties of the dental implant

PURPOSEThis study aimed to evaluate the effect of implant thread depth on primary stability in low density bone.MATERIALS AND METHODSThe insertion torque was measured by inserting Ti implants with different thread depths into solid rigid polyurethane blocks (Sawbones) with three different bone densities (0.16 g/cm3, 0.24 g/cm3, and 0.32 g/cm3). The insertion torque value was evaluated with a surgical engine. The static compressive strength was measured with a universal testing machine (UTM) and the Ti implants were aligned at 30° against the loading direction of the UTM. After the static compressive strength test, the Ti implants were analyzed with a Measurescope.RESULTSThe Ti implants with deeper thread depth showed statistically higher mean insertion torque values (P<.001). Groups A and group B had similar maximum static compressive strengths, as did groups C and D (P>.05). After the static compressive strength, the thread shape of the Ti implants with deeper thread depth did not show any breakage but did show deformation of the implant body and abutment.CONCLUSIONThe implants with deeper thread depth had higher mean insertion torque values but not lower compressive strength. The deep threads had a mechanical stability. Implants with deeper thread depth may increase the primary stability in areas of poor quality bone without decreasing mechanical strength.

Processing of Threads on a Magnesium Alloy Using a Special Process

Tapping is a complex process largely applied on metal cutting industry. The tapping process can be carried out using cutting or forming tools. This work presents a study of the form tapping process using a tool without cutting edge and helix angle and with external diameter much smaller than the final thread. The experimental tests were carried out with three forming speeds and three helical feed rates to produce M12 threads into the AM60 Magnesium alloy. The results showed that these specfic forming taps provided internal threads with good thread shapes and finishing forms that were as good as the traditional forming tap, which uses tools with the same final thread hole diameter. In addition, the increase of helical feed rate decreases the torque and thrust force, but the differences were greater in torque than in thrust force. The greatest decrease of torque occurred for the lowest forming speed, and the lowest decrease of torque occurred for the highest forming speed. Moreover, the thrust force and torque recorded in the experimental tests were lesser than in traditional form tapping for the same thread area, at least for the magnesiun alloy used.

Erratum to “Comparative Evaluation of Osseointegrated Dental Implants Based on Platform-Switching Concept: Influence of Diameter, Length, Thread Shape, and In-Bone Positioning Depth on Stress-Based Performance”

Erratum to “Comparative Evaluation of Osseointegrated Dental Implants Based on Platform-Switching Concept: Influence of Diameter, Length, Thread Shape, and In-Bone Positioning Depth on Stress-Based Performance”

The influence of thread geometry on implant osseointegration under immediate loading: a literature review.

Implant success is achieved by the synergistic combination of numerous biomechanical factors. This report examines the mechanical aspect of implants. In particular, it is focused on macrodesign such as thread shape, pitch, width and depth, and crestal module of implants. This study reviews the literature regarding the effect of implant thread geometry on primary stability and osseointegration under immediate loading. The search strategy included both in vitro and in vivo studies published in the MEDLINE database from January 2000 to June 2014. Various geometrical parameters are analyzed to evaluate their significance for optimal stress distribution, implant surface area, and bone remodeling responses during the process of osseointegration.

Cache-Conscious Thread Scheduling for Massively Multithreaded Processors

Highly multithreaded architectures introduce another dimension to fine-grained hardware cache management. The order in which the system's threads issue instructions can significantly impact the access stream seen by the caching system. This article studies a set of economically important server applications and presents the cache-conscious wavefront scheduling (CCWS) hardware mechanism, which uses feedback from the memory system to guide the issue-level thread scheduler and shape the access pattern seen by the first-level cache.

Nonlinear viscoelasticity of polymer nanocomposites under large amplitude oscillatory shear flow

In this study, the nonlinear response of polymer nanocomposites under large amplitude oscillatory shear (LAOS) flow was investigated. We first investigated polycaprolactone (PCL)/multiwall nanotube (MWNT) composites under LAOS flow using different analyzing methods including Lissajous plot analysis, stress decomposition, and Fourier transform rheology (FT-rheology). The nonlinear parameter Q (≡I3/1/γ02) was obtained from the FT-rheology as a function of strain amplitude, and the zero-strain nonlinearity Q0 (≡limγ0→0Q) was also calculated. We compared the linear and nonlinear viscoelastic properties as we increase MWNT concentration (ϕ). It was found that the zero-strain nonlinearity (Q0) was more sensitive to detect the effect of MWNT concentration than the linear viscoelastic properties. We also investigated the effect of particle shape on nonlinear viscoelastic properties of the polymer composites containing particles of different shape, e.g., PCL/MWNT (one-dimensional thread shape), PCL/organomodified ...

Comparative Evaluation of Osseointegrated Dental Implants Based on Platform-Switching Concept: Influence of Diameter, Length, Thread Shape, and In-Bone Positioning Depth on Stress-Based Performance

This study aimed to investigate the influence of implant design (in terms of diameter, length, and thread shape), in-bone positioning depth, and bone posthealing crestal morphology on load transfer mechanisms of osseointegrated dental implants based on platform-switching concept. In order to perform an effective multiparametric comparative analysis, 11 implants different in dimensions and in thread features were analyzed by a linearly elastic 3-dimensional finite element approach, under a static load. Implant models were integrated with the detailed model of a maxillary premolar bone segment. Different implant in-bone positioning levels were modeled, considering also different posthealing crestal bone morphologies. Bone overloading risk was quantified by introducing proper local stress measures, highlighting that implant diameter is a more effective design parameter than the implant length, as well as that thread shape and thread details can significantly affect stresses at peri-implant bone, especially for short implants. Numerical simulations revealed that the optimal in-bone positioning depth results from the balance of 2 counteracting effects: cratering phenomena and bone apposition induced by platform-switching configuration. Proposed results contribute to identify the mutual influence of a number of factors affecting the bone-implant loading transfer mechanisms, furnishing useful insights and indications for choosing and/or designing threaded osseointegrated implants.

Cautious use of thread shape factor

Sir, Recently, Migliorati et al . (2012) evaluated the correlation between thread depth, thread pitch and thread shape factor (TSF), and maximum insertion torque (MIT) and found the strongest correlation between TSF and MIT ( r = 0.902, P = 0.001) with a 2.2-mm cortical thickness of experimental bone. The article is interesting and among few studies in Orthodontics evaluating the prediction power of TSF for clinical decisions. I have some comments on the way they applied the Chapman equation. Originally, …