Marginal Wear Research Articles

A simulation investigation on the influence of pantograph crack defect on graphite contact strip wear

The pantograph commonly suffers from two types of defects in metro-rail transit: abnormal wear and crack defect. It very often suffers both, thereby increasing the risks posed to train-operation safety. Previous research has not considered the influence of pantograph cracks on contact strip wear. This study establishes a pantograph–catenary dynamics model with crack defect to investigate the influencing pattern of crack defect, as well as the catenary arrangement form under cracked condition on graphite contact strip wear. Results show that the presence of pantograph cracks accelerates the wear rate and induces the eccentric wear and marginal wear problem. An 8 m span and a splayed arrangement form of the pull-out value are preferred.

Dynamics in rail infrastructure provision: Maintenance and renewal costs in Sweden

In this paper, we extend to the literature on marginal wear and tear cost estimation in railways, by applying a panel vector autoregressive model to rail infrastructure renewals and maintenance costs, using an extensive dataset from Sweden. This study is significant given the inherent difficulties in modelling the substantial renewals element of infrastructure costs, as well as the need to account for the dynamics in renewals and maintenance. The dynamic model allows us to estimate equilibrium cost elasticities with respect to train usage, which are significantly larger than their static counterparts. Overall, this work highlights that dynamics in rail infrastructure costs are important to consider when setting track access charges with respect to the wear and tear caused by traffic. This is particularly important given several countries, for example France, Sweden and Switzerland, are now setting access charges at marginal costs based on econometric studies.

Of mice and mutations: Phenotypic effects of the diabetic db/db and ob/ob mutations on the skull and teeth of mice

To compare the phenotypic appearance of the skull bones and teeth of wild type C57BL/6J mice with that of diabetic leptin-deficient (ob/ob) and diabetic leptin receptordeficient (db/db) mice used as models for diabetes. Skulls were extracted from the carcasses of mice belonging to wild-type C57B/6J mice, db/db mice on a C57BLKS/J background, and ob/ob mice on a C57B/6J background. After removal of overlying tissue, the skulls and mandibles were then left to dehydrate and examined for phenotypic variations in structure and wear. Bone surfaces of the skulls of wild type mice had a whiter and smoother surface compared with a yellowish colour with a grainy texture in the two mutant strains. The frontal, parietal and occipital bones were translucent in the two mutant strains. Breakages of the zygomatic arches and mandibles were more common in the ob/ob and db/db mice than in the wild type mice. Half of the teeth of the db/db mice and 90% teeth of the ob/ob mice showed considerable wear compared with marginal wear in the wild type mice. These observations suggested that the teeth of the two diabetic mutant strains are exhibiting considerable signs of hypomineralization with increased fragility and decreased bone thickness.

A model for estimating road wear on in-service roads

This article presents a new approach to estimating road wear, where the observation units are in-service roads of the Norwegian national road network, operating under normal traffic conditions. Since the early 1990s, Norway has deployed automatic traffic control units along its national roads. These units can, by a simple modification, be used as weigh-in-motion devices. This makes collecting axle load data from a relatively large number of observation sites cost effective. The new data from weighing vehicles in motion, and from the regular monitoring of the road surface, enable a new approach to modelling road wear developments. A first rutting model is developed based on these data, and the results obtained from it, suggest that Norwegian national roads may be so solid that there is no significant marginal impact from heavy axle loads. Total annual marginal road wear costs based on these estimates appear to be significantly lower than anticipated.

EU Task Force on Rail Infrastructure Charging. Summary Findings on Best Practice in Marginal Cost Pricing

This paper sets out alternative best practice approaches to marginal cost pricing of rail infrastructure adopted in a number of EU Member States. It draws on the findings of a report submitted to the European Commission in June 2002 and provides a summary of two different approaches to the adoption of marginal cost pricing. The Swedish/Finnish approach uses econometric modelling to estimate marginal wear and tear costs whereas the UK model first provides a top-down estimate of the aggregate level of variable costs across the network and then uses relationships between vehicle characteristics and wear and tear costs to allocate the aggregate level of variable costs across vehicle types. Significant differences between countries are found in the variability of infrastructure wear and tear costs to levels of traffic. The resulting derived marginal cost also differ widely. The paper provides possible reasons for these differences but recognises that the understanding of the interface between wheel and rail and hence knowledge of cost causation remains fairly limited. The findings of the paper therefore need to be read in the context of further research being required into railway infrastructure cost causation.

The clinical performance of ceramic inlays: a review.

The availability of improved ceramic materials, bonding techniques, new technology and issues of amalgam safety have led to a revival of interest in ceramic inlays in dentistry over the past ten years. Clinical studies have been carried out during this time using various evaluation techniques to assess the clinical performance of these restorations. In this paper, recent clinical studies are examined and a review of the current state of knowledge regarding the clinical performance and survival statistics of ceramic inlays is presented. The major problems associated with ceramic inlay therapy appear to be fracture, hypersensitivity, degree of fit, maintenance of marginal integrity, microleakage, bond failures and cement wear. Other areas which also affect the clinical performance of ceramic inlays are ceramic wear, opposing tooth wear, plaque accumulation, gingivitis, secondary caries, colour stability, anatomic form and radiopacity. Recommendations based on the findings of clinical studies are also presented and whilst no specific material or technique has been shown to be clearly superior, certain principles which predispose to success can be identified. When compared with other forms of aesthetic intracoronal restorations, ceramic inlays perform well. However, their high cost and extreme technique sensitivity would appear to restrict their use to certain limited clinical situations.

Implantation of N 2+, O + and CO + ions into titanium and Ti-6A1-4V

The marginal wear resistance of titanium-based alloys is known to increase significantly when hard compounds are formed at the surface. In particular the ion implantation technique has proved to be successful when polished surfaces have to be treated without modifications to the surface roughness. Therefore polished titanium and titanium alloys were implanted with high doses of N 2 +, O + and CO + ions up to an energy of 200 keV. The ion beam was generated by running the ion source with either nitrogen or carbon dioxide. The fragmentation of the molecular gases was investigated by mass separation of the beam with a mass-analyzing magnet. High beam currents of molecular CO + and atomic O + could be extracted when the source was operated with carbon dioxide, whereas molecular N 2 + was extracted by running the source with nitrogen. A chemical analysis of the modified surface layers, which have depths below 400 nm, was carried out using X-ray photoelectron spectroscopy (XPS). Implantation of high doses between 3 × 10 17 and 1 × 10 18 ions cm −2 resulted in the formation of hard wear-resistant phases, which were identified by the chemical shift in the XPS signal. The spectra revealed the formation of TiN in the case of N 2 + implantation and the formation of TiO in the case of O + implantation. At low concentrations of implanted CO +, the formation of Ti(C, O) was observed whereas, at high concentrations, carbon-carbon bonds were identified.

Wear patterns in two amalgams and three posterior composites after 5 years' clinical service

Objectives: The purpose of this research was to evaluate the wear patterns of three posterior composites (Clearfil Posterior. Occlusin and P-30) and two amalgams (New True Dentalloy, Solila Nova) after 5 years' clinical service. Methods: Marginal wear was measured using the stepwedge technique which determines the maximal marginal wear by any one cusp together with the mean marginal value. The overall maximum depth of wear, occurring at any site on the occlusal surface, was determined using an impression technique with epoxy models. Results: The mean values (± standard deviations) for the overall maximum wear were; New True Dentalloy. 203 ± 98 μm; Solila Nova. 200 ± 96 μm; Clearfil Posterior. 252 ± 141 μm; Occlusin, 324 ± 189 μm; P-30, 380 ± 273 μm. These values were significantly different (ANOVA F = 2.86 P = 0.05). There was no correlation between the marginal scores and the overall maximum depth of wear ( P > 0.05). With some restorations the maximum wear occurred at the margins, marginal ridges or cavity extensions rather than sites of occlusal contact. Conclusions: After 5 years' service the overall wear of three posterior composites exceeded that of two amalgams; however, for a number of restorations the difference was not significant. Marginal wear values cannot be used to predict the overall maximal depth of wear.

Four-year in vivo evaluation of the composite/bonding resin-tooth interface

The objective of this study was to evaluate the color match, marginal discoloration, recurrent caries, anatomic form, and marginal adaptation of 41 paired Class III and Class V preparations restored with a conventional chemically cured resin composite with and without a low-viscosity bonding resin (LVBR). In addition, the wear of the restorations was evaluated from scanning electron micrographs of epoxy replicas of the restorations. The subjects were re-called 48 months after placement of the restorations. The marginal discoloration and wear of the composite restorations placed without a LVBR were significantly greater than in restorations placed with a LVBR. The results of this clinical study suggest that a LVBR should be applied prior to the placement of a conventional chemical-activated resin composite.

4885530 Device for early detection of breaks and marginal wear in the cutting edges of tools : Kurt Mayer, Volker Richey, Hans-Pete Schneider, Essen, Federal Republic Of Germany assigned to Fried Krupp GmbH

The consolidation of plasma sprayed monotapes is emerging as a promising route for producing metal and intermetallic matrix composites reinforced with continuous ceramic fibers. Significant fiber fracture has been reported to accompany the consolidation of some fiber/matrix systems, particularly those with creep resistant matrices. Groves et al. [Acta metall. mater.42, 2089 (1994)] determined the predominant mechanism to be bending at monotape surface asperities and showed a strong dependence of damage upon process conditions. Here, a previous model for the densification of monotapes [Elzey and Wadley, Acta metall. mater.41, 2297 (1993)] has been used with a stochastic model of the fiber failure process to predict the evolution of fiber fracture during either hot isostatic or vacuum hot pressing. Using surface profilometer measured roughness data for the monotapes and handbook values for the mechanical properties of different matrices and fibers, this new model is used to elucidate the damage dependence on process conditions, monotape surface roughness, and the mechanical properties both of the fiber and matrix. The model is used to investigate the “processibility” of several currently important matrix and fiber systems and to identify the factors governing this. An example is also given of its use for the simulation of a representative consolidation process cycle. This approach to the analysis of a complex, nonlinear, time-varying process has resulted in a clear understanding of the causal relationships between damage and the many process, material and geometric variables of the problem and identified new strategies for its elimination.

Scanning electron microscope investigation of in vivo performance of eight composite resins

Retention. At 6 months, five restorations were lost due to retention failure. The remaining restorations were retained to 24 months and/or 30 months. The study of one material was discontinued because of numerous retention failures. Marginal wear. Facial wear along the margin in the center portion of the restoration was appreciably greater than lingual, proximal, and incisal wear. In general, most composite resins began to display evidence of wear during the first 6 months of service. Over the study period, three restorations were lost because of excessive marginal wear. Surface texture. Most materials were clinically acceptable with regard to surface texture over the course of the study. Extended studies of greater durations are indicated.