1,659 research outputs found
Influence of temperature and crystal orientation on tool wear during single point diamond turning of silicon
No full textOwing to the capricious wear of cutting tools, ultra precision manufacturing of silicon through single point diamond turning (SPDT) operation becomes a challenging task. It thus becomes non-trivial to understand the contribution of temperature and crystal orientation during the SPDT process in order to suppress tool wear. Molecular dynamics (MD) simulation is an appropriate tool to study nanoscale processes occurring at the femtosecond/picosecond timescale which cannot otherwise be studied experimentally or by the finite element method (FEM). Accordingly, MD simulation has been deployed with a realistic analytical bond order potential (ABOP) formalism based potential energy function to simulate the single point diamond turning operation of single crystal silicon in order to understand the influence of temperature and crystal orientation on the tool wear mechanism. Results showed the strong influence of crystal orientation on the wear resistance of a diamond tool; cubic orientation performed better than dodecahedral orientation. It was also observed that high pressure phase transformation (HPPT) in the cutting zone was accompanied by the formation of dangling bonds of silicon. Under the influence of cutting temperature, the newly formed dangling bonds of silicon chemically combine with the pre-existing dangling bonds on the surface of the diamond tool resulting in the formation of silicon carbide (SiC), the main appearance of which was evident at the tool flank face. Continuous abrasion of the diamond cutting tool with SiC causes sp3–sp2 disorder of the diamond tool. Hence, both these processes proceed in tandem with each other. The mechanism proposed here is in good agreement with a recent experimental study, where silicon carbide and carbon like particles were observed using X-ray photoelectron spectroscope (XPS) technology after machining a silicon wafer with a diamond tool
A study of the wear process related to twin-screw extruders
No full textExtruders are used in a wide range of process industries and high reliability is essential if cost
effective manufacturing is to be maintained. A critical part of twin-screw extruders is the barrel
that must withstand many different wear and corrosion environments depending on the end user.
For many applications the extruder barrel is a critical component and it is essential that it performs
in a predictable manner, providing the necessary design life-time.
This project has addressed these aims by considering the wear/corrosion behaviour of current and
potential extruder barrel materials from which a life prediction model has been developed.
A wide range of engineering materials has been evaluated in the laboratory for abrasive wear
resistance using a dry sand abrasive wear test according to ASTM G 65-93. An appraisal of the
tests and the applicability of the results to the in-service conditions of an extruder has lead to
further testing for abrasion and abrasion-corrosion resistance of four materials, namely Mild Steel,
440C, N18 and N18+5%TiC+5%TiN.
Plastic deformation was the main feature of the damaged surfaces in the form of ploughing which
has been modelled in terms of a low-cycle fatigue process. The relative hardness between material
and abrasive was found to be an important parameter in controlling the rate of material removal.
It has also been shown that the synergistic effect of abrasion-corrosion results in an accelerated
material removal rate.
The information from these tests has been used to develop a model of the wear of extruder barrels
by abrasive particles. It is shown that there is a correlation between the particle size, wear debris
size and wear groove size distributions. From a knowledge of the particle flux, the particle size
distribution and the loading conditions, metal recession is predicted based on a low-cycle fatigue
process. The wear rates for a wide range of Fe- and Ni-based materials are predicted to better
than a factor of two.
When corrosion is also present, the mechanism of metal recession depends on whether passive
surface films are formed. For the Fe-based materials which exhibit direct dissolution of material,
the wear/corrosion rate can be estimated by combining the metal loss rate under pure wear and
pure corrosion conditions only. For the Ni-base alloys, thin passive films form in all the aqueous
environments studied and corrosion rates are extremely low. However, during abrasive wear the
passive films are removed and the overall metal recession rate is a combination of metal loss due
to abrasive wear of the substrate and the continual formation and removal of surface passive films
LeTourneau modified tank-tree crusher with R.G. LeTourneau and unidentified man.
No full textPhotograph of a Tree Crusher Tender built in Vicksburg, Mississippi and intended for use at the Tournata complex in Liberia, according to author Eric Orlemann. Shown with the tank are R.G. LeTourneau, left, and an unidentified man. The tank was never actually shipped to Tournata
A model of friction for a pin-on-disc configuration with imposed pin rotation
No full textA friction model is developed by considering the Coulomb friction model, a probabilistic
approach of wear prediction, the kinematics of the pin-on-disc configuration and the elastic
theory of bending. The model estimates the magnitude and direction of the frictional force, the
pin torque, the probability of asperity contact and the real area of contact distinguishing
between the part due to elastic and plastic asperity contacts respectively. Therefore, the
proposed model is suitable for the prediction of adhesive wear. It can be applied to metal
contacts for conductance characterisation through the plastically deformed asperities which is
of great interest for electrical contact resistance studies
Occlusal wear pattern analysis of functional morphology in Neanderthals and early Homo sapiens dentition
No full textVery little is known about the occlusal wear pattern in the Neanderthal posterior dentition. Usually dental wear is closely related to the physical properties of the ingested food, and consequently can be used to obtain information about diet. Neanderthal dietary reconstructions have been mostly based on the analysis of accompanying faunal remains and isotopic signatures of bones and tooth enamel, suggesting that they exploited larger portions of animal proteins from large and medium-sized herbivores. Probably these studies may do not reflect the bulk diet, tending to underestimate plant consumption and to overestimate meat consumption. In the present work the occlusal wear pattern of maxillary molars of Homo neanderthalensis (N=19) and early Homo sapiens (N=12)have been analyzed, applying non-destructive methods based on virtual three-dimensional polygonal models generated from surface scanning of dental casts. The sample groups occupied different geographical areas at different chronological times. The 3D digital tooth models were analyzed using the “Occlusal Fingerprint Analysis” (OFA) method (Kullmer et al. 2009), describing and quantifying the occlusal wear pattern derived from two wear facet angles (dip and dip direction), wear facet area and occlusal relief index (ORI). The OFA method provides information about the dynamics of the occlusal relationships and their function, permitting the reconstruction of the mandibular movements responsible for the contacts created during the chewing cycle. Since jaw movements and diet are closely related, the results obtained, can be used to interpret the diet of the two Pleistocene hominin species. In order to evaluate how dietary differences influence the occlusal wear pattern, upper molars of modern hunter-gatherers (N=42) with known diet and different dietary habits, have been included in the sample and compared with those of Neanderthals and early Homo sapiens. Results show that within the modern hunter-gatherers sample, the occlusal wear pattern of carnivorous populations differs from those who relied on a mixed-diet. In particular, the study of relative facet areas clearly distinguish meat-eaters from mixed-diet hunter-gatherers, while ORI results and wear facet inclinations (dip angle) seem to reflect directly the abrasiveness of the diet, including the influence of exogenous materials during food preparation. The Neanderthal occlusal wear pattern is characterized by an ecogeographic variation, suggesting the exploitation of different food resources. In particular Neanderthals who inhabited relatively warm environments of southern Europe and the Near East exhibit an occlusal wear pattern different from those of meat-eaters hunter-gatherers from tempered and cooler regions, displaying some features similar to those of Bushmen. These results suggest the exploitation of a broad variety of food sources. The analysis of the occlusal wear pattern in Neanderthals and early Homo sapiens who inhabited Europe during the cooler Oxygen Isotope Stage 3 (OIS3) shows many similarities between the two hominid species. These results indicate the exploitation of similar and low-diversified food sources, based mostly on the consumption of animal proteins, as suggested through the clear similarities with the wear patterns found in modern meat-eaters hunter-gatherers. In both studied groups, Neanderthals and early Homo sapiens the occlusal wear pattern is characterized by high ORI and dip angle values, suggesting the intake of a low-abrasive diet, probably due to the absence of sophisticated food preparation techniques introducing external silica grains, e.g. from soil (grinding of seeds) or plant cells, as those, seen in modern hunter-gatherer populations. The analysis of the occlusal fingerprints in Neanderthal and early European Homo sapiens upper molars suggests that both species followed very similar adaptive dietary strategies, based on a distinctive versatility and flexibility in the daily diet, depending on availability of resources according to environmental circumstances.Die Neandertaler (Homo neanderthalensis) lebten in Westeurasien zwischen 200.000 bis 30.000 Jahren vor unserer Zeit. Im späten Pleistozän. Sie bewohnten unterschiedliche Lebensräume die von klimatischen Veränderungen geprägt waren. Viele Untersuchungen haben sich mit der Nahrungsgrundlage der Neandertaler befasst und es wurde oft diskutiert, ob die Neandertaler eher Aasfresser oder aktive Jäger waren. Die Analyse der Begleitfaunen an den Fundstellen der gefundenen Steinwerkzeuge und die Isotopenzusammensetzung von Knochen und Zähnen, haben zu der Hypothese geführt, dass die Neanderthaler tatsächlich aktive Jäger waren. Sie haben sich wahrscheinlich vorwiegend von tierischen Proteinen von großen bis mittelgroßen Pflanzenfressern ernährt. Das Erscheinen von Homo sapiens in Europa während des Sauerstoffisotopenstadiums 3 (OIS3) hat wahrscheinlich infolge der Lebensraumveränderungen einen starken Konkurrenzkampf um die knappen Fleischressourcen zwischen den Neandertalern und Homo sapiens ausgelöst. Eine höherentwickelte Werkzeugtechnologie in Verbindung mit komplexeren Sozialstrukturen und einer guten Ausnutzung abwechslungsreicherer Nahrungsquellen (inklusive pflanzlicher Nahrung, Kleinsäuger und anderer Tiere) hat vermutlich den Bevölkerungszuwachs der frühen Homo sapiens Populationen in Europa gefördert. Diese wiederum haben im Laufe der Zeit die Neandertaler Populationen in Europa (zusehend) ersetzt. Die Möglichkeiten der detaillierten Nahrungsrekonstruktion sind sehr begrenzt. Typischerweise sind Knochen besser fossil erhaltben als pflanzliche Überreste. Dies lässt den Eindruck entstehen, dass Fleisch die Hauptnahrung gewesen ist, denn an den Neandertaler Fundorten wurden z.T. größere Mengen von Knochenresten gefunden, die z.B. Bearbeitungsspuren zeigen. Deshalb ist es durchaus möglich, dass Untersuchungen eher dazu neigen, den Konsum tierischer Nahrung über zu bewerten und den Konsum pflanzlicher Nahrung zu unterschätzen. Isotopenanalysen von Knochenkollagen (das weitgehend aus Proteinen besteht) zeigen, dass tierische Proteine konsumiert wurden, aber die Ergebnisse lassen nicht direkt den Schluss zu, dass dies der Hauptbestandteil der Nahrung war. Da tierische Nahrungsquellen sehr proteinreich sind, ist tierische Nahrung durch das Knochenkollagen überrepräsentiert, während der Anteil von Proteinen aus pflanzlicher Nahrung geringer ist, und deshalb ist die Menge pflanzlicher Kost nur schwer abzuschätzen.. Neue Untersuchungen aus Neandertaler Fundregionen in Südeuropa und dem Nahen Osten zur sogenannten „Microwear―, den Mikrospuren der Zahnabnutzung zeigen, dass die Neandertaler unterschiedliche Nahrung verwertet haben; inklusive Pflanzenmaterial und Meerestiere. Dies steht nun im Widerspruch zu den Ergebnissen, die man von den tierischen Überresten und aus den Isotopenanalysen gewonnen hat. In der vorliegenden Untersuchung wurden nun erstmals die okklusalen Abnutzungsmuster von Oberkieferbackenzähnen von Neandertalern und frühen Homo sapiens analysiert, die aus unterschiedlichen geografischen Gebieten und aus unterschiedlichen Zeiträumen stammen. Hierfür wurde eine zerstörungsfreie Methode angewendet, die auf der digitalen Analyse von dreidimensionalen virtuellen Zahnmodellen basiert. Die Computermodelle wurden mit daten aus Oberflächenscans von Zahnabgüssen rekonstruiert. ....
The Influence of Stem Design and Fixation Methods on the Lifetime of Total Hip Replacement
No full textTotal hip replacement is one of the most common surgical procedures performed both in the UK
and worldwide, with aseptic loosening cited as the primary reason for revision. Aseptic loosening
is attributed to the wear debris generated by wear of the components. Recently, as great progress has been achieved in reducing wear at the head–cup interface, there has been a shift of research interest to other load bearing surfaces.
The main purpose of this thesis is to study fretting wear mechanisms at the polished femoral stem–bone cement interface.
The initial studies have investigated the bond strength at the stem–cement interface using seven
brands of bone cement and femoral stems with different surface finishes. It can be confirmed that debonding at this interface is inevitable, which subsequently facilitates generation of fretting wear on the stem surface.
A new test methodology has been developed to reproduce fretting wear clinically seen on polished stems through in vitro wear simulations, and it shows great success in comparison with previous attempts. In addition, migration of the stem within the cement mantle has been investigated, and it has been indicated that the simulation setup more realistically mimics clinical situations.
The influence of two factors on generation of fretting wear, i.e. the duration of in vivo service of the hip implant and bone cement brand, has been studied. A potential fretting wear initiator that is concerned with polymerisation of bone cement has been identified, with both experimental (the results of wear simulations) and theoretical (finite element analysis) evidence being provided.
In summary, the overall contribution of this research is that it has gained a deep insight into the fretting wear mechanism between polished femoral stem and bone cement
Longview manufacturing plant under construction, LT21 Misc Photos Archive 062.
No full textPhotograph of the Longview manufacturing plant of R.G. LeTourneau, Inc. The plant's construction began in 1945 and completed in 1946. At the time, according to Otis Hays, author of R.G. LeTourneau: Move of Men and Mountains, at the time it was the world's largest welding and manufacturing plant under one roof, covering more than 100 acres
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The design of an effective sensor fusion model for condition monitoring systems of turning processes
No full textHigh energy price and the increasing requirements of quality and low cost of products have created an urgent need to implement new technologies in current automated manufacturing environments. Condition monitoring systems of manufacturing processes have been recognised in recent years as one of the essential technologies that provide the competitive advantage in many manufacturing environments. This research aims to develop an effective sensor fusion model for turning processes for the detection of tool wear. Multi-sensors combined with a novelty detection algorithm and Learning Vector Quantisation (LVQ) neural networks are used in this research to detect tool wear and provide diagnostic and prognostic information. A novel approach, termed ASPST, (Automated Sensor and Signal Processing Selection System for Turning) is used to select the most appropriate sensors and signal processing methods. The aim is to reduce the number of sensors needed in the overall system and reduce the cost. The ASPST approach is based on simplifying complex sensory signals into a group of Sensory Characteristic Features (SCFs) and evaluating the sensitivity of these SCFs in detecting tool wear. A wide range of sensory signals (cutting forces, strain, acceleration, acoustic emission and sound) and signal processing methods are also implemented to verify the capability of the approach. A cost reduction method is also implemented based on eliminating the least utilised sensor in an attempt to reduce the overall cost of the system without sacrificing the capability of the condition monitoring system. The experimental results prove that the suggested approach provides a responsive and effective solution in monitoring tool wear in turning with reduced time and cost
The Big Plow with 6-Foot Disc, J5G, Photo 35, L-8312
No full textPhotograph of R.G. LeTourneau's Series H (Model 6-16) Disc Plow, designed for land-clearing operations. It was powered by a front longitudinally mounted diesel, according to author Eric Orlemann
Wear Improvement in Ti-6Al-4V by Ion Implantation
No full textABSTRACTThe friction and wear of Ti-6Al-4V are found to be sharply reduced by carbon implantation followed by heat treatment. Optimum wear resistance is developed at 400° C, at which the microstructure of the implanted layer shows a dense array of TiC precipitates up to 60 nm in size. The implanted layer in this case is worn through in a few thousand cycles of the ball on disc test, but by implanting at two energies to achieve a deeper carbide layer, negligible wear was found even after 20,000 cycles. No wear improvement was found for nitrogen implantation.</jats:p
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