Early Stage Cavitation Erosion within Ceramics: An Experimental Investigation

Six ceramic material types were considered within an experimental investigation to identify the erosion damages mechanisms resulting from cavitation exposure. These materials were a Y-TZP type of zirconia, different commercially available silicon nitrides, a high purity alumina and an hardened high nitrogen stainless steel. An ultrasonic transducer was utilised to produce cavitation conditions and the configuration was “static specimen method” using a 5mm diameter probe, 20kHz and 50μm of amplitude. The exposure times were periods from 15 seconds to 2 hours. Experimental methods employed to characterise wear mechanisms were light microscopy, scanning light interferometry, scanning electronic microscopy. It was found that the zirconia and silicon nitrides demonstrated evidence of local pseudoplastic deformation or depression prior to more pronounced erosion damages by fracture. Zirconia showed evidence of delayed surface changes when the sample is at rest stored in air possibly by spontaneous phase transformation after the completion of the erosion tests. Alumina showed evidence of brittle surface fracture and negligible or no pseudo-plastic deformation. All wear mechanisms are discussed and the materials are ranked in terms of cavitation resistance performance

New dimensionless number to predict cavitation in accelerated fluid

Cavitation is the formation of vapour cavities in a liquid due to a local low pressure. The traditional cavitation number is used to predict the occurrence of cavitation in liquid flows through devices such as pumps, propellers or dam spillways. However this number can only be applied when cavitation is produced by changes of dynamic and static pressure in a liquid flow. There are other means to produce cavitation where the traditional cavitation number cannot be applied. The purpose of this research is to formulate a new dimensionless number valid to predict cavitation in some scenarios where the traditional cavitation number fails. The “tube-arrest” method produces cavitation by subjecting a column of liquid to a high acceleration without the need of any velocity between the liquid and the tube. In this scenario the traditional number is not useful due to the low values of relative velocity between liquid and walls. However the dimensionless number reported here predicts accurately the occurrence of cavitation in the “tube-arrest” method, as it is shown by Finite Element Method analysis. There is another scenario where the dimensionless number is tested successfully that is the bulk of a liquid downstream of a closing valve. A systematic comparison between the values of the dimensionless number and the occurrence of cavitation predicted by the FEM analysis is given. On the other hand the values of the traditional cavitation number are calculated and it is shown that these values are meaningless in these scenarios. In contrast, the agreement between the prediction of the dimensionless number and the simulations is excellent. It is concluded that the new dimensionless number predicts cavitation in scenarios where the traditional number is meaningless. It can also be used for a better design of experiments with the “tube-arrest” method as a practical application

Assessing lubricating film thickness between compression rings and engine cylinders: A comprehensive comparison of theoretical predictions and experimental measurements

The purpose of piston rings in combustion engines is to provide an effective seal between the combustion chamber and the crankcase while allowing rapid linear movement of the piston. In this paper a review of around 50 experimental studies and 30 theoretical studies is presented. Papers describing experimental studies report lubricating film thicknesses between 0 µm to 20 µm, while papers describing theoretical results for fully flooded analyses tend to report smaller values (0 µm to 9 µm). Theoretical studies including starvation phenomena normally give even thinner films, typically between 0 µm and 5 µm. The paper presents a discussion of these discrepancies

Piston-ring film thickness: theory and experiment compared

A review of the published literature has demonstrated a large variability and discrepancies in the measured and predicted values of piston-ring lubricating film thickness in internal combustion engines. Only 2 papers have been found that compare experiments in firing engines directly with outputs from sophisticated ring-pack lubrication models. The agreement between theory and experiment in these comparisons was limited, possibly because of inadequacies in the models and/ or inaccuracies of measurement. This paper seeks to contribute to the literature by comparing accurately calibrated experimental measurements of piston-ring film thickness in a firing engine with predictions from an advanced, commercial software package alongside details of the systematic analysis of the measurement errors in this process. Suggestions on how measurement accuracy could be further improved are also given. Measurements of oil film thickness with an error (standard deviation) of +/-15% have been achieved. It is shown that this error can be reduced further, by changes in the design and installation of the sensors. Detailed experimental measurements of film thickness under the top compression ring in a firing petrol engine have been made and compared with the predictions from a commercial, state-of-the art modelling package. The agreement between theory and experiment is excellent throughout the stroke in most cases, but some significant differences are observed at the lower load conditions. These differences are as yet unexplained, but may be due to the sensor topography influencing the hydrodynamic lubrication, lubricant availability, out-of-roundness in the cylinder, or squeeze effects. This a topic that requires further stud

Prediction of ultrasonic cavitation with a dimensionless number, towards higher reproducibility

Ultrasonic cavitation is the formation of vapour cavities within a liquid due to the action of an ultrasound source. It is widely used for homogenization, dispersion, deagglomeration, erosion, cleaning, milling, emulsification, extraction, disintegration and sonochemistry. On the other hand, the so-called cavitation number is used to assess the likelihood of cavitation in fluid flows within a conduit or around a hydrofoil but it is not valid in ultrasonic cavitation since there is no fluid flow. A recently formulated number predicts the cavitation in case of sudden accelerations. The tip surface of an ultrasonic probe is subjected to a continuous repetition of alternating accelerations at high frequency. Therefore, the use of the recently formulated number in ultrasonic cavitation is explored here. Simulations of the ultrasonic probe in water just at the condition of cavitation onset have been performed for a combination of probe diameters from 0.2 to 100 mm and frequencies 20, 30, 40, 100 and 1000 KHz. The recently formulated number is applied to these combinations and it is found that can be used to predict ultrasonic cavitation. Consequently, the dimensionless number can be used to decide the conditions to avoid or generate cavitation when a fluid is sonicated and to increase reproducibility in such conditions.Comment: 11 pages, 3538 words, 8 figure

A survey of owners' perceptions of fear of fireworks in a sample of dogs and cats in New Zealand

AIMS: To establish reliable information regarding the behavioural responses of dogs and cats to fireworks in New Zealand; record interventions used by owners, and their perceived efficacies; and establish the prevalence of firework-related injury, and quantify owners' attitudes towards fireworks. METHODS: A questionnaire targeting dog and cat owners was distributed via the Auckland Society for the Prevention of Cruelty to Animals (SPCA) Animals Voice magazine and 25 veterinary clinics. The questionnaire covered demographics of animals, fear of fireworks, severity of the fear, and behaviours exhibited. Also included were treatments tried, source and perceived efficacy, prevalence of injury, and owners' attitudes towards the sale of fireworks for private use. RESULTS: From a total of 8,966 questionnaires distributed, 1,007 valid questionnaires were returned, representing 3,527 animals. Of these 1,635 (46%) animals displayed a level of fear of fireworks recognisable to their owners. Owners of dogs identified a significantly higher fear response than owners of cats but the duration of these fear responses did not differ between species. Fear of fireworks frequently resulted in dogs exhibiting active fear behaviours, whereas cats were more likely to exhibit hiding and cowering behaviours. A significantly increased severity and duration of fear response over time in dogs and cats was associated with owners who comforted them when they displayed a fearful response. Only 141/890 (15.8%) of owners sought professional treatment from a veterinarian, animal behaviourist or animal trainer for their animals, with variable efficacy. Six percent (51/923) of animals had received physical injuries from fireworks. The majority (837/1,007; 83%) of respondents, regardless of whether they owned a fearful animal or not, supported a ban on the sale of fireworks for private use. CONCLUSIONS: The results provide valuable information that is, as yet, unsubstantiated in New Zealand, although potential biases exist due to the non-random selection of respondents. Differences between dogs and cats were likely due to differing responses to fear-provoking stimuli between the species. Owner-reported increase in fearful response over time for comforted animals may indicate a negative impact on the longer-term psychological welfare of their animal. CLINICAL RELEVANCE: The greater the awareness of effective treatment plans for animals that suffer from a fear of fireworks, the greater the possibility that this fear can be reduced. Wider dissemination of effective owner behaviour and treatment programmes for firework fears is needed to improve levels of professional treatment for dogs and cats

Use of two Public Distributed Ledgers to track the money of an economy

A tool to improve the effectiveness and the efficiency of public spending is proposed here. In the 19th century banknotes had a serial number. However, in modern days the use of digital transactions that do not use physical currency has opened the possibility to digitally track almost each cent of the economy. In this article a serial number or tracking number for each cent, pence or any other monetary unit of the economy is proposed. Then, almost all cents can be tracked by recording the transactions in a public distributed ledger, rather than recording the amount of the transaction, the information recorded in the block of the transaction is the actual serial number or tracking number for each cent that changes ownership. In order to keep the privacy of the transaction, only generic identification of private companies and individuals are recorded along with generic information about the concept of transaction, the region and the date/time. A secondary public distributed ledger whose blocks are identified by a hash reference that is recorded in the bank statement available to the payer and the payee allows for checking the accuracy of the first public distributed ledger by comparing the transactions made in one day, one region and one type of concept. However, the transactions made or received by the government are recorded with a much higher level of detail in the first ledger and a higher level of disclosure in the second ledger. The result is a tool that is able to accurately track public spending, to keep privacy of individuals and companies and to make statistical analysis and experiments or real tests in the economy of a country. This tool has the potential to assist public policymakers in demonstrating the societal benefits resulting from their policies, thereby enabling more informed decision-making for future policy endeavours.Comment: 10 pages, 1 figure

Surface response of ceramics subject to erosive wear.

Research concerning the surface of technical ceramics is carried out from the viewpoint of their mechanical performance subjected to relevant operating conditions. The selected materials are silicon nitride, zirconia and alumina. They are subjected to cavitation erosion and other wear processes. When polished ceramics are subjected to cavitation, a pseudoplastic deformation pit is discovered, as well as a delayed phase transformation or ageing of the zirconia stored at room temperature. Measured ageing times recorded are of the order of one month. These two discoveries are novel and a full explanation is explored. The creation of cracks that release the slip planes of ceramic grains allowing plastic deformation is proposed to be the main mechanism. In order to understand the relationship of the zirconia surface degradation with its oxides (yttria or magnesia), several material compositions are tested. It is concluded that the delay of phase transformation relies on the existence of partially stabilized tetragonal zirconia regardless of the oxide used to stabilize it. Part of this research consists of understanding the effects of the experimental procedure that is utilised on the behaviour of the material. An unexpected non homogeneous cavitation erosion shape is obtained when an ultrasonic horn of small diameter is used to produce the bubbles. This non homogeneous region, referred to as ring region for this research, affects the erosion pattern of the material and it differs from the typical ones obtained when following the standard test. The acoustic theory does not explain this phenomenon. Therefore, a new approach is followed. This approach consists of using fluid mechanics equations combined with analytical mechanics principles. It is concluded that the location of cavitation clusters fulfils a condition of minimum energy. On the other hand, there are important differences between this experimental set up and the set up suggested by the published standards. These differences are discussed and a criterion for cavitation erosion resistance is developed. The comparison of cavitation resistance of materials is achieved by means of surface loss as criterion instead of volume loss

Demography and disorders of German Shepherd Dogs under primary veterinarycare in the UK

The German Shepherd Dog (GSD) has been widely used for a variety of working roles. However, concerns for the health and welfare of the GSD have been widely aired and there is evidence that breed numbers are now in decline in the UK. Accurate demographic and disorder data could assist with breeding and clinical prioritisation. The VetCompassTM Programme collects clinical data on dogs under primary veterinary care in the UK. This study included all VetCompassTM dogs under veterinary care during 2013. Demographic, mortality and clinical diagnosis data on GSDs were extracted and reported