Rubber abrasion is one of the most important properties for rubber products, such as tyres. However, due to its complexity rubber abrasion is still a very challenging topic in rubber research. Rubber abrasion is not governed by a single mechanism. Different mechanisms can dominate the abrasion behaviour depending on the rubber compound, base polymer type, loading severity, contact conditions, testing temperature and chemical environment. This study investigates the different mechanisms for rubber abrasion and the transition between these mechanisms using two types of abrasion apparatus, a blade abrader and a surface abrader, respectively. Blade abrasion was used to generate the abrasion pattern. Once the abrasion pattern was formed on the rubber surface under unidirectional sliding, the underlying mechanism was primarily one of fatigue crack growth, which is referred as "fatigue wear" in the literature. An independent pure shear fatigue test with various loading profiles was conducted to predict the crack growth rate using a fracture mechanics approach during these abrasion tests. The tearing energy during blade abrasion was calculated using a fracture mechanics approach. A Finite Element Analysis (FEA) technique using the Virtual Crack Closure Technique (VCCT) was adopted. The VCCT approach was a simpler, faster and more reliable approach to derive the tearing energy under these complicated large strain contact conditions. The prediction of the abrasion rate using this independent measurement of the crack growth resistance of materials worked best for unfilled SBR material. A bespoke surface contact abrasion machine was used to investigate rubber abrasion on silicon carbide sandpaper under both dry and wet conditions. Depending on the materials, contact conditions and sliding velocity, two different mechanisms were observed. The first being a mechanochemical degradation, during which a sticky layer was generated on the rubber surface. This behaviour is also called "smearing wear". The second failure mode resulted from a purely mechanical fracture named "abrasive wear". It seemed that the carbon black filled rubber was more susceptible to smearing wear than the silica filled one. Higher sliding velocities promoted smearing wear, possibly due to higher temperatures being generated at the interface. Alternatively, water lubrication was seen to promote abrasive wear. Therefore, the abrasion mechanism changed to more rapid abrasive wear under wet conditions, which resulted in a significant increase in the rate of weight loss. Finally, the sticky debris generated during the smearing wear was characterised using various different techniques. This revealed that the sticky debris had more oxygen and lower carbon and sulphur content. It contained a greater amount volatiles and generated more char formation during its degradation in the air. The molecular weight of the sticky debris was much lower when compared to the original uncured rubber. It seemed that in the sticky debris the filler network can slowly recover and the degraded polymer chains can re-absorb back onto filler surface forming "bound rubber", which leads to faster rates of weight loss.

No description available.

This study aimed to compare the effectiveness of an 8% arginine and calcium carbonate in-office desensitizing prophylaxis paste with that of a home-use toothpaste having the same active ingredients in reducing dentine hypersensitivity. The study was a randomized controlled clinical trial involving 55 subjects who had at least one tooth with sound exposed dentine on the cervical region of the buccal surface displaying hypersensitivity. The subjects were recruited from students and staff, other than those from the Faculty of Dentistry, of The University of Hong Kong. After receiving scaling performed by a dental hygienist at baseline, subjects were randomly assigned to either the in-office desensitizing prophylaxis paste treatment group or the home-use desensitizing toothpaste group. Clinical assessments of dentine hypersensitivity to tactile and to thermal stimuli were performed prior to the treatment at baseline, week 4 and week 12 by a blinded examiner and subjective global assessments of dentine hypersensitivity were recorded. The responses of the subjects to both stimuli were recorded by using a pain score scale from 0 to 10 (from no pain to unbearable pain). Reponses to both tactile and thermal hypersensitivity assessments in the home-use desensitizing toothpaste group showed statistically significant differences between baseline and week 12 (tactile: 2.4 vs. 0.9; cold: 5.8 vs. 3.5, both p<0.05). There was a statistically significant difference in the tactile assessment scores (1.8 vs. 1.0, p<0.05) but not in the thermal hypersensitivity assessment scores (5.5 vs. 5.3, p>0.05) for the in-office desensitizing prophylaxis paste group. There was also a statistically significant difference in the change in thermal assessment scores between the two groups (in-office: -0.2 vs. home-use: -2.3, p<0.05) but not in the tactile hypersensitivity assessment scores (in-office: -0.9 vs. home-use: -1.2, p>0.05). There were no statistically significant differences in global subjective responses to external stimuli in the telephone interviews. Daily use of an 8% arginine and calcium carbonate toothpaste was able to reduce dentine hypersensitivity over 12 weeks but a single in-office application of prophylaxis paste of similar content was not able to provide instant and long-lasting benefits for subjects with a mild-to-moderate degree of dentine hypersensitivity. / published_or_final_version / Dentistry / Master / Master of Philosophy

Thesis (M.S.)--University of Michigan, Ann Arbor, 1971. / Typescript (photocopy). Includes bibliographical references (leaves 42-43). Also issued in print.

Thesis (M.S.)--University of Michigan, Ann Arbor, 1971. / Typescript (photocopy). eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 42-43).

Thesis (doctoral)--Karolinska Institutet, Stockholm, 1987. / Added t.p. with thesis statement inserted. Includes bibliographical references.

The adoption of Electrical Discharge Machining (EDM) technologies to mainstream manufacturing saw dramatic advances in the process starting in the 1980's. Wire Electrical Discharge Machining (WEDM) in particular achieved enhancements in cutting speed of over 800% between 1980 and 1992 due to improvements in generator and wire technology. Since then, increases in cutting speed have been gradual. To achieve dramatic improvements to the process once again, a paradigm shift, from improving upon existing technologies to introducing and developing new one is required. In this light, an investigation into the proof-to-concept and development of a novel hybrid machining process based upon Wire Electrical Discharge Machining (WEDM) and abrasive technologies is presented. In the process termed Abrasive Wire Electrical Discharge Machining (AWEDM), material removal is shown to occur by the simultaneous action of electrical erosion and abrasion. Through experimental evaluation, this combination is shown to bring about a manyfold improvement in the material removal rate and to generate machined surfaces with minimal recast layer, in comparison to conventional WEDM processes. To understand the operation of the process and to control the proportion of abrasion and EDM taking place, the effect of varying the process conditions is studied. The servo-reference voltage and peak discharge current, in particular, provide effective means to control the process. Practical implementation of the process presents several challenges, such as accurately guiding an abrasive wire; a discussion of some of these issues and possible solutions is included. The need for a wire that is specially suited to AWEDM is demonstrated with a discussion of the requirements and possible designs for such a wire. Whether or not a manufacturing process sees practical industrial use is chiefly dictated by economics. By considering the increase in both productivity and wire cost, AWEDM is shown to be economically feasible and offer potentially substantial benefits. This work ultimately serves as the basis for future work with respect to AWEDM. The work herein covers a broad range of topics in hopes of guiding future areas of research. / Thesis / Master of Applied Science (MASc)

A interação entre rocha e metal, na forma de operações como perfuração, escavação e cominuição, dá origem a dois efeitos: um desejado, desagregação da rocha e outro indesejado, desgaste do metal. Como o desgaste, dramaticamente, influencia o desempenho dos equipamentos, é fundamental para estabelecer uma base para equações de predição de taxas de desgaste potencial. Neste contexto, Golovanevskiy e Bearman (2008), propuseram mais um método para avaliação da abrasividade. Este método, ensaio de abrasão por impacto deslizante (Gouging Abrasion Test), é realizado em condições de alta tensão/alto impacto de desgaste e é caracterizado pela maior taxa de remoção de material de todos os modos de desgaste e, portanto, representa o modo mais severo de desgaste abrasivo.O método consiste, basicamente, de uma ponteira cilíndrica com uma ponta cônica de 90º. Esta ponteira, em trajetória pendular, atinge uma amostra de rocha com energia de impacto de aproximadamente 300 joules e velocidade da ordem de 5,2 m/s. Semelhante à metodologia de cálculo de abrasividade Cerchar (CAI), o Gouging Abrasion Index (Gi) é calculado como sendo a média do diâmetro da ponta cônica, após desgaste, em milímetros e multiplicado por 10. Este trabalho verificou a adequabilidade do Gouging Abrasion Test, para um pequeno número de amostras de rocha que representam, qualitativamente, os principais tipos de rocha encontrados no Brasil e a sua correlação com outros ensaios consagrados como resistência à compressão, desgaste Amsler e dureza Knoop. Está análise mostrou alta correlação entre Gi e dureza knoop (R² = 0,94), baixa correlação com desgaste Amsler (R² = 0,41) e nenhuma correlação com resistência à compressão uniaxial. / The rock-metal interaction, like occurs in operations as drilling, excavation and crushing, generates two effects: the desired rock degradation and the undesirable metal wear. As the wear dramatically influences the process performance of the equipment, it is critical to establish a basis for predictive equations to estimate potential wear rates. Following this context, in 2008 Golovanevskiy and Bearman proposed a method for abrasiveness evaluation. The method, Gouging Abrasion Test, employs high-stress load gouging/sliding impact wear and is characterized by the highest material removing rate than all wear modes, therefore representing the most severe type of abrasive wear. The method consists, in a few words, of a steel wear tool with a 90o sharp conical tip. This tip attacks a rock sample in a swinging trajectory with a impact energy of more than 300 joules and a speed around 5,2 m/s. Like the Cerchar Abrasivity Index (CAI) calculation, the Gouging Abrasion Index (Gi) is determined as 10 times de average diameter in millimeters of de conical tip (now flat) after one event of wear. This work intends to improve the knowledge about Gouging Abrasion Test, and evaluates its suitability in a small group of rocks that represents some of the main types to be found in Brazil\'s rock cutting, drilling and crushing works. Its relation to other frequent tests like uniaxial compressive strength, Amsler abrasive wear and Knoop hardness were also verified. The results show high correlation between Gi and Knoop hardness (R2 = 0,94), low correlation with Amsler wear (R2 = 0,41) and no relation to uniaxial compressive strength.

A interação entre rocha e metal, na forma de operações como perfuração, escavação e cominuição, dá origem a dois efeitos: um desejado, desagregação da rocha e outro indesejado, desgaste do metal. Como o desgaste, dramaticamente, influencia o desempenho dos equipamentos, é fundamental para estabelecer uma base para equações de predição de taxas de desgaste potencial. Neste contexto, Golovanevskiy e Bearman (2008), propuseram mais um método para avaliação da abrasividade. Este método, ensaio de abrasão por impacto deslizante (Gouging Abrasion Test), é realizado em condições de alta tensão/alto impacto de desgaste e é caracterizado pela maior taxa de remoção de material de todos os modos de desgaste e, portanto, representa o modo mais severo de desgaste abrasivo.O método consiste, basicamente, de uma ponteira cilíndrica com uma ponta cônica de 90º. Esta ponteira, em trajetória pendular, atinge uma amostra de rocha com energia de impacto de aproximadamente 300 joules e velocidade da ordem de 5,2 m/s. Semelhante à metodologia de cálculo de abrasividade Cerchar (CAI), o Gouging Abrasion Index (Gi) é calculado como sendo a média do diâmetro da ponta cônica, após desgaste, em milímetros e multiplicado por 10. Este trabalho verificou a adequabilidade do Gouging Abrasion Test, para um pequeno número de amostras de rocha que representam, qualitativamente, os principais tipos de rocha encontrados no Brasil e a sua correlação com outros ensaios consagrados como resistência à compressão, desgaste Amsler e dureza Knoop. Está análise mostrou alta correlação entre Gi e dureza knoop (R² = 0,94), baixa correlação com desgaste Amsler (R² = 0,41) e nenhuma correlação com resistência à compressão uniaxial. / The rock-metal interaction, like occurs in operations as drilling, excavation and crushing, generates two effects: the desired rock degradation and the undesirable metal wear. As the wear dramatically influences the process performance of the equipment, it is critical to establish a basis for predictive equations to estimate potential wear rates. Following this context, in 2008 Golovanevskiy and Bearman proposed a method for abrasiveness evaluation. The method, Gouging Abrasion Test, employs high-stress load gouging/sliding impact wear and is characterized by the highest material removing rate than all wear modes, therefore representing the most severe type of abrasive wear. The method consists, in a few words, of a steel wear tool with a 90o sharp conical tip. This tip attacks a rock sample in a swinging trajectory with a impact energy of more than 300 joules and a speed around 5,2 m/s. Like the Cerchar Abrasivity Index (CAI) calculation, the Gouging Abrasion Index (Gi) is determined as 10 times de average diameter in millimeters of de conical tip (now flat) after one event of wear. This work intends to improve the knowledge about Gouging Abrasion Test, and evaluates its suitability in a small group of rocks that represents some of the main types to be found in Brazil\'s rock cutting, drilling and crushing works. Its relation to other frequent tests like uniaxial compressive strength, Amsler abrasive wear and Knoop hardness were also verified. The results show high correlation between Gi and Knoop hardness (R2 = 0,94), low correlation with Amsler wear (R2 = 0,41) and no relation to uniaxial compressive strength.

No description available.