High Thread Research Articles

Tapping of Al–Si alloys with diamond-like carbon coated tools and minimum quantity lubrication

The deep hole drilling and tapping of automotive powertrain components made of hypoeutectic Al–Si alloys are of considerable importance. This work investigates the dry and minimum quantity lubricated (MQL) tapping of Al–6.5%Si (319 Al) alloys as alternatives to conventional flooded tapping. Two types of tests were done in comparison with flooded tapping. In the first set dry tapping experiments were performed using diamond-like carbon (DLC) coated and uncoated HSS taps. HSS-dry tapping caused immediate tool failure within less than 20 holes due to aluminum adhesion, resulting in high forward and backward torques. DLC-dry tapping improved tool life considerably and exhibited small torques. The second set of tapping experiments used MQL and only uncoated HSS taps. The use of MQL at the rate of 80 ml/h produced similar average torques to flooded tapping, and a high thread quality was observed. DLC coatings’ low COFs against 319 Al limited the temperature increase during DLC-dry tapping to 75 °C. The low COF of DLC against aluminum was responsible for preventing built-up edge (BUE) formation and thus, instrumental in improving thread quality. The use of MQL reduced the tapping temperature to 55 °C. The mechanical properties of the material adjacent to tapped holes, evaluated using hardness measurements, revealed a notable softening in the case of HSS-dry tapping, but not for MQL tapping. The presence of sulphur and phosphorus-based additives in MQL fluids proved beneficial in preventing aluminum adhesion.

Pyriform Spidroin 1, a Novel Member of the Silk Gene Family That Anchors Dragline Silk Fibers in Attachment Discs of the Black Widow Spider, Latrodectus hesperus

Spiders spin high performance threads that have diverse mechanical properties for specific biological applications. To better understand the molecular mechanism by which spiders anchor their threads to a solid support, we solubilized the attachment discs from black widow spiders and performed in-solution tryptic digests followed by MS/MS analysis to identify novel peptides derived from glue silks. Combining matrix-assisted laser desorption ionization tandem time-of-flight mass spectrometry and cDNA library screening, we isolated a novel member of the silk gene family called pysp1 and demonstrate that its protein product is assembled into the attachment disc silks. Alignment of the PySp1 amino acid sequence to other fibroins revealed conservation in the non-repetitive C-terminal region of the silk family. MS/MS analysis also confirmed the presence of MaSp1 and MaSp2, two important components of dragline silks, anchored within the attachment disc materials. Characterization of the ultrastructure of attachment discs using scanning electron microscopy studies support the localization of PySp1 to small diameter fibers embedded in a glue-like cement, which network with large diameter dragline silk threads, producing a strong, adhesive material. Consistent with elevated PySp1 mRNA levels detected in the pyriform gland, MS analysis of the luminal contents extracted from the pyriform gland after tryptic digestion support the assertion that PySp1 represents one of the major constituents manufactured in the pyriform gland. Taken together, our data demonstrate that PySp1 is spun into attachment disc silks to help affix dragline fibers to substrates, a critical function during spider web construction for prey capture and locomotion.

High performance thread forming breakthrough

High performance thread forming breakthrough

New threadlock is oil tolerant

Loctite 278 is a new high strength thread locking adhesive that is both oil tolerant and resistant to elevated temperature.

High performance thread forming

High performance thread forming

The development of the high strength silk suture thread

The development of the high strength silk suture thread

Impact of Stitching Processes on the Compaction Behavior of Glass Fiber Reinforcements

The objective of this project is to investigate the application influences of stitching techniques on the compaction and relaxation behavior of preforms made of three different semi-finished glass fabric types. Particular attention is directed to the impact of stitching parameters (i.e., thread tension and seam spacing) and the compaction procedure (single-stage vs multi-stage) on the experimental results. The experiments prove that there is no difference between single-stage and multi-stage compaction. Furthermore, it is shown that the stitching of the preforms leads to an increase in compaction force due to the additional volume of thread to be compacted. Comparing high and low thread tension reveals that an increasing thread tension causes pre-compaction of the preform, thus reducing the required compaction force, though the degree of pre-compaction seems to be confined to a limit above which no reduction in compaction force can be observed any more. Regarding the spacing of the seams, it turns out that only the narrow spacing (5 mm) has a significant influence on compaction, whereas the wide spacing (20 mm) does not lead to a notable change in compaction behavior compared to the unstitched preforms. Finally, visual inspection of the preforms during compaction and relaxation shows that the morphologic change of the preform surfaces is a very complex phenomenon which cannot easily be modeled. No visual change of the preform surfaces are observed during relaxation. Therefore, it is assumed that relaxation is caused by invisible microstructural reorientation of glass filaments within single rovings.

Influence of Cold Rolling Threads Before or After Heat Treatment on the Fatigue Resistance of High Strength Fine Thread Bolts for Multiple Preload Conditions

Abstract SI class 12.9 high strength steel bolts were used to investigate the fatigue behavior of bolt threads rolled before/after heat treatment at five different preload values. Bolts used were 3/8 UNRF-24 (fine) and preloads were taken as 1, 50, 75, 90, and 100 % of roll before heat treatment proof stress. Since proof stress was lowered 10 % for roll after heat treatment, these preloads for roll after heat treatment bolts were then actually 1.1, 55, 83, 100, and 110 % of proof stress (to keep load the same). The tests produced a range of R ratios (R=Smin/Smax) between 0.03 and 0.92. Maximum near surface residual compressive stresses, obtained via x-ray diffraction, ranged from −500 to −1000 MPa. Axial loads were applied through the nut and all fatigue failures occurred at the first thread of the nut/bolt interface with crescent shaped cracks dominating in most tests. Multiple ratchet marks (separate crack nucleation sites) occurred for roll before heat treatment bolts, while fewer or no ratchet marks, were evident for the roll after heat treatment. Scanning electron microscopy evaluation indicated all fatigue crack growth regions contained multiple fatigue facets, while final fracture regions contained ductile dimpling. Cyclic creep/ratcheting was monitored and little, or none, was observed for preload tests equal to or less than 75 %. Replication data indicated a log-normal distribution on life was very reasonable. The fatigue resistance for fine threads rolled after heat treatment with preload stresses of 1 % (R ratio less than 0.05) caused very large increases (158 %) in 107 cycles fatigue strength compared to roll before heat treatment. This is in agreement with other roll before/after low R-ratio results. The roll after heat treatment bolts when tested at the higher proof loads had 107 fatigue strengths of 69 to 30 % increase. These increases are much less than the 158 % at 1 % preload, but still significant. Constant life Haigh diagrams at 105 and 107 cycles were in qualitative agreement with VDI 2230 bolt preload guidelines.

Influence of Cold Rolling Threads Before or After Heat Treatment on the Fatigue Resistance of High Strength Coarse Thread Bolts for Multiple Preload Conditions

Abstract SI class 12.9 high strength steel bolts were used to investigate the fatigue behavior of bolt threads rolled before/after heat treatment using five different preload values. Bolts were 3/8 UNRC-16 (coarse) and preloads were taken as 1, 50, 75, 90, and 100 % of roll before heat treatment proof stress. Since proof stress was lowered 10 % for roll after heat treatment, these preloads for roll after heat treatment bolts were then actually 1.1, 55, 83, 100, and 110 %. The tests produced a range of R-ratios between 0.03 and 0.92. Maximum near surface residual compressive stresses, obtained via X-ray diffraction, ranged from −600 to −1000 MPa. Axial loads were applied through the nut and all fatigue failures occurred at the first thread of the nut/bolt interface with crescent-shaped cracks dominating in most tests. SEM evaluation indicated all fatigue crack growth regions contained multiple fatigue facets, while final fracture regions contained ductile dimples. Cyclic creep/ratcheting was monitored and little, or none, was observed for preload tests equal to or less than 75 %. The fatigue resistance of the threads rolled after heat treatment with preload stresses of 1 % caused a 147 % increase in 107 cycles fatigue strength compared to roll before heat treatment. This is in agreement with other roll before/after low R-ratio results. However, with higher preload stresses, the roll after heat treatment fatigue strength did not increase. Constant life Haigh diagrams at 105 and 107 cycles were not always in agreement with VDI 2230 bolt preload guidelines.

Seasonal influence of wave action on thread production in Mytilus edulis

The blue mussel Mytilus edulis maintains a strong attachment to the substrate in high energy environments by producing byssal threads. On the shores of Rhode Island, USA, mussel attachment strength increases twofold in spring compared to that in the fall. While many factors could influence attachment strength (temperature, food supply, predator cues, etc.), it has been proposed that the variation observed is primarily due to increased thread production during winter and spring in response to increased wave action. This study evaluates the influence of three aspects of wave action on the thread production of M. edulis. Mussels were exposed to flow, acceleration and byssal loading stimuli and the subsequent number of byssal threads produced in the laboratory was monitored. Increased flow elicited the strongest response, significantly decreasing thread production in mussels. This result was confirmed in flume experiments exposing mussels to a range of flows, with reduced thread production above 15 cm s-1. The influence of both acceleration and byssal loading was sporadic and inconsistent across seasons. Surprisingly, overall thread production in the laboratory was lowest in winter, a time when mussels typically peak in attachment. A similar seasonal pattern was observed in field assays, with high thread production during periods of elevated temperature, reduced wave action, and high reproductive condition. These results suggest that seasonal variation in attachment strength does not reflect increased thread production in response to wave action, and that other possible factors, such as seasonal variability in both the material properties of byssal threads and thread decay rates, warrant further investigation.

Heterogeneous chip multiprocessors

Heterogeneous (or asymmetric) chip multiprocessors present unique opportunities for improving system throughput, reducing processor power, and mitigating Amdahl's law. On-chip heterogeneity allow the processor to better match execution resources to each application's needs and to address a much wider spectrum of system loads - from low to high thread parallelism - with high efficiency.

Simulation of complex liquids in micropump

Complex liquids can be encountered in many applications of microdevices. In the present study, the performance of microscrew pump using complex liquid is investigated numerically. The microscrew pump operation depends on the surface sweep forces. It consists of a screw placed inside a microchannel. When the screw rotates, a net force is transferred to the fluid due to differential pressure on the depth of the thread and pressure gradient along the screw axis, thus causing the fluid to displace. Three-dimensional complex liquid simulations of micropump were performed.The effect of screw pitch, thread, Reynolds number and pump load on the micropump performance has been studied. The simulations of complex liquids indicate that the highest bulk velocity is achieved with high thread depth at low Reynolds number. However, effective pumping is accomplished at low Reynolds number, high pressure load and high thread depths.

Single-ISA Heterogeneous Multi-Core Architectures for Multithreaded Workload Performance

A single-ISA heterogeneous multi-core architecture is achip multiprocessor composed of cores of varying size, performance,and complexity. This paper demonstrates that thisarchitecture can provide significantly higher performance inthe same area than a conventional chip multiprocessor. It doesso by matching the various jobs of a diverse workload to thevarious cores. This type of architecture covers a spectrum ofworkloads particularly well, providing high single-thread performancewhen thread parallelism is low, and high throughputwhen thread parallelism is high.This paper examines two such architectures in detail,demonstrating dynamic core assignment policies that providesignificant performance gains over naive assignment, andeven outperform the best static assignment. It examines policiesfor heterogeneous architectures both with and withoutmultithreading cores. One heterogeneous architecture we examineoutperforms the comparable-area homogeneous architectureby up to 63%, and our best core assignment strategyachieves up to 31% speedup over a naive policy.

고정도 Spindle Screw 전조공정에서의 최적 소재경 선정

This paper describes the numerical determination of optimum blank diameter for sound material flow and high precise thread profile of a spindle screw through external thread rolling using two-three roll dies. Initial blank diameter affects the dimensional accuracy and surface finish qualities of a spindle screw in thread rolling process, therefore it is very important to determine the optimum blank diameter in thread rolling process. In order to determine the optimum blank diameter, this paper suggests the calculation method of initial bland diameter considering the real shape of tooth. The finite element code DEFORM is applied to analyze the metal flow of tooth, and these analytical results are verified by thread rolling experiment for spindle screw.

Symbiotic jobscheduling with priorities for a simultaneous multithreading processor

Simultaneous Multithreading machines benefit from jobscheduling software that monitors how well coscheduled jobs share CPU resources, and coschedules jobs that interact well to make more efficient use of those resources. As a result, informed coscheduling can yield significant performance gains over naive schedulers. However, prior work on coscheduling focused on equal-priority job mixes, which is an unrealistic assumption for modern operating systems.This paper demonstrates that a scheduler for an SMT machine can both satisfy process priorities and symbiotically schedule low and high priority threads to increase system throughput. Naive priority schedulers dedicate the machine to high priority jobs to meet priority goals, and as a result decrease opportunities for increased performance from multithreading and coscheduling. More informed schedulers, however, can dynamically monitor the progress and resource utilization of jobs on the machine, and dynamically adjust the degree of multithreading to improve performance while still meeting priority goals.Using detailed simulation of an SMT architecture, we introduce and evaluate a series of five software and hardware-assisted priority schedulers. Overall, our results indicate that coscheduling priority jobs can significantly increase system throughput by as much as 40%, and that (1) the benefit depends upon the relative priority of the coscheduled jobs, and (2) more sophisticated schedulers are more effective when the differences in priorities are greatest. We show that our priority schedulers can decrease average turnaround times for a random jobmix by as much as 33%.

Application of high strength plate bolts in friction grip joints

High Tension Bolts (HTB) are known to exert a significant influence on the strength characteristics of connections and have a significant influence on the ductility and behaviour of the joint. Normally HTB failure occurs in the shape resultant high stress concentration neck and thread areas resulting in relatively low ductility characteristics. Creep and relaxation occur after HTB tightening causing shaft tension loss and further stress redistribution in the connected components. Past research has shown that waisting the HTB shaft diameter reduces stress concentrations, shaft tension loss and increases ductility. With the further modification of making the HTB head plate shape counter sunk, a plate HTB with an aesthetically pleasing flat surface less susceptible to rain corrosion results. In this research, tensile, relaxation and friction grip joint slip experiments were done on waisted shank, counter sunk plate head HTB to ascertain the ductility improvement, the resulting decrease in shaft tension loss and its magnitude, as well as their applicability in friction grip steel connections. Apart from significant shaft tension loss reduction, no detrimental effects are induced in the slip coefficient results when these HTBs are applied in friction grip joints. Within these experimental parameters, the closest to ideal HTB shape is proposed. (Journal of Civil Engineering, JKUAT: 2002 7: 67-80)

The role of ‘splashing’ in the collapse of a laser-generated cavity near a rigid boundary

Vapour cavities in liquid flows have long been associated with cavitation damage to nearby solid surfaces and it is thought that the final stage of collapse, when a high- speed liquid jet threads the cavity, plays a vital role in this process. The present study investigates this aspect of the motion of laser-generated cavities in a quiescent liquid when the distance (or stand-off) of the point of inception from a rigid boundary is between 0.8 and 1.2 times the maximum radius of the cavity. Numerical simulations using a boundary integral method with an incompressible liquid impact model provide a framework for the interpretation of the experimental results. It is observed that, within the given interval of the stand-off parameter, the peak pressures measured on the boundary at the first collapse of a cavity attain a local minimum, while at the same time there is an increase in the duration of the pressure pulse. This contrasts with a monotonic increase in the peak pressures as the stand-off is reduced, when the cavity inception point is outside the stated interval. This phenomenon is shown to be due to a splash effect which follows the impact of the liquid jet. Three cases are chosen to typify the splash interaction with the free surface of the collapsing cavity: (i) surface reconnection around the liquid jet; (ii) splash impact at the base of the liquid jet; (iii) thin film splash. Hydrodynamic pressures generated following splash impact are found to be much greater than those produced by the jet impact. The combination of splash impact and the emission of shock waves, together with the subsequent re-expansion, drives the flow around the toroidal cavity producing a distinctive double pressure peak.

High Performance Thread Migration on Clusters of SMPs

Thread migration is established as a mechanism for achieving dynamic load sharing and data locality. However, migration has not been used with fine-grained parallelism on workstation clusters due to the relatively high overheads associated with thread and messaging packages. This paper describes a portable, high performance thread migration system, implemented with user level threads and active messages. The thread system supports an extensible event mechanism which permits an efficient interface between the thread and active message system. Migration is supported by user level primitives; applications may implement different migration policies on top of the migration interface provided. The system runs on a cluster of SMPs and the performance obtained is orders of magnitude better than other reported measurements.

Breaking the 100 MG Barrier: The First High Field Magnetic CV

AbstractWe present results from IUE and optical spectra, optical photometry and circular polarimetry during high and low states of the highly luminous soft X-ray cataclysmic variable AR UMa that identifies the primary in this system as a white dwarf with a magnetic field of 230 MG. The high magnetic field likely threads accretion blobs all the way from the secondary to below the surface of the white dwarf, resulting in a lack of polarised cyclotron emission and an extreme soft-X-ray luminosity during the high state.

A Fatigue Design Procedure for Screw Threads Using Predicted S-N Curves.

This study was carried out in order to develop a new design procedure for screw threads based on the fatigue strength, in which the influence of mean stress was also considered. The Haigh diagram, which is a simple and useful tool for the design of screw threads, was newly constructed using the prediction procedure of S-N curves developed by us for different initial fastening loads. It was found that the design values recommended in the JIS application series may cause fatigue failure in the bolt and nut fastener especially for during use of high strength level screw threads.