193 research outputs found
Modified Design of Pin-on-Ring Tribometer for Hip Joint Prostheses Measurement; Case Study on Salat Activity_Peer Review
Get PDF, Jamari Jamari, Sulardjaka Sulardjaka, Mohamad Tauviqirrahman, Emile van der Heid
Boundary lubrication of bearing steel in water-based lubricants with functional additives
No full textThis thesis focuses on the effect of additives on boundary lubrication of bearing steel for water-based lubrication systems. The oil-in-water (O/W) emulsion and the water-glycol based liquid were selected as the base fluids for research. Sulfur compounds, nitrogen heterocycles and graphene derivatives were synthesized and used as additives. The tribological properties and corrosion resistance of the bearing steel friction couple in water-based lubricants are investigated. Based on the results of tribological tests and the analysis of friction surfaces, various tribochemical mechanisms are suggested to explain the friction processes, as well as the formation of a boundary lubricating film. In addition, the design of water-based additives and the effects of additives and working conditions on the tribological properties of water-based lubricants are described. Firstly, the effect of the interfacial film on the lubrication performance of O/W emulsion was researched. For that, graphene oxide (GO) underwent asymmetric chemical modification with myristyltrimethylammonium bromide (TTAB) to get modified graphene oxide (MGO). This MGO was used as an emulsifier and additive in oil-in-water emulsion. The emulsifying tests showed that MGO greatly improved the stability of base emulsion and decreased its droplet size. Tribological test results showed that under the boundary lubrication condition with MGO emulsion, the friction coefficient (COF) and the wear rate of the steel ball decreased by about 18% and 48% respectively in comparison with base emulsion lubrication. The tribological mechanism of MGO emulsion could be explained by the strong film-forming ability on the metal surface, the high lubricity of its small droplets, and the formed adsorption film, transfer film and tribofilm between the contact surfaces. Secondly, the effect of the oil phase on lubrication performance of O/W emulsion was researched. For that, graphene oxide (GO) was single and double-sided modified with octadecylamine (ODA) to get MGO1 and MGO2 respectively. MGO1 and MGO2 were incorporated into the O/W base emulsion to change the composition of the interface and the oil phase. It was found that the tribological properties of MGO1-containing emulsion were better than those of MGO2-containing emulsion. Chemical composition analysis of the worn surfaces suggests that MGO1 nanosheets might adsorb more easily onto the metal surface and react better with metal surfaces to produce C-N-O-Fe-containing compounds than do MGO2 nanosheets, which means MGO1 nanosheets are more actively involved in the shear process that occurs in the contact area. Nanoindentation indicated that there was a non-uniform softer MGO1 tribofilm present on the metal substrate. Thirdly, the effect of the water phase on lubrication performance of O/W emulsion was researched. For that, two nitrogen-containing water-soluble additives are synthesized and used as an additive in O/W emulsion. The friction tests results showed that the two water-soluble additives might be more rapidly adsorbed to the metal surface than the emulsion droplets could be “plated out” on the metal surface, thereby changing the friction-reducing and anti-wear performance of base emulsion. In addition, it was found that the tribological properties of these two additives were related not only to nitrogen content but also to the functional groups formed by the nitrogen atoms. Fourthly, the effects of sulfur element and applied load on the tribological performance of water-glycol fluid were studied. For that, two triazine derivatives, STB and STC were synthesized and used as additives in water-glycol base fluid (mass ratio 1:1). Water solubility tests indicated that STB and STC met the solubility prerequisite for a water-soluble additive. The tribological tests using a four-ball tribometer showed that STB and STC both improved greatly the PB value, anti-wear and friction-reducing capacities of the base fluid. Based on friction test results and wear scar analysis, it was concluded that the differences in tribological performances of STB and STC samples were due mainly to the differences of the sulfur content and the sulfur activity in additives. XPS found that STB-tribofilm mainly contained sulfate, but STC tribofilm contained sulfide as well. Finally, the effect of molecular chain length, additive concentration and sliding velocity on the tribological performance of water-glycol fluid was investigated. For that, three novel xanthate-containing water-soluble triazine derivatives, EXT, BXT and HXT, were synthesized and used as additives in water-glycol base fluid. It was found that the additive-containing samples had no corrosive effect on the cast iron and copper surface within 2.5 wt.% additive. The tribological test results using a four-ball tribometer showed that the three additives greatly improved the PB value, friction-reducing and anti-wear performances of water-glycol. XPS results indicated that the additives had reacted with the contact metal surfaces and formed complex tribofilms composed of iron oxide, iron sulfide and iron sulfate, which may contribute to the reduction of friction coefficient and wear rate of the friction system. In summary, for O/W emulsion lubrication, if the droplets can be quickly adsorbed onto metal surface, forming an oily layer between the rubbing surfaces, the COF will be reduced. If coupled with the formation of an effective adsorption film and tribofilm by additives, the COF will be further reduced. For water-glycol lubrication, the differences in the tribological performances are due mainly to the differences of the formed adsorption film and the tribofilm on the rubbing surface, including the forming velocity, strength and thickness and the composition. These change not only with the additives but also with the working conditions
The static friction behavior of skin with relevance to pressure ulcer prevalence
Get PDFPressure ulcers develop as a result of sustained mechanical loading and are commonly observed in patients with reduced mobility and reduced tissue viability as well as in patients that have undergone an amputation. Shear loading is known to be a risk factor that accelerates the onset of tissue damage. In this thesis it is hypothesized that pressure ulcer prevalence can be reduced by decreasing the shear load acting on the skin. The susceptibility of developing pressure ulcers whilst applying a range of shear loads for a prolonged period is demonstrated by means of cytokine measurements performed on volunteers. The expression of the IL-1α cytokine, which triggers the inflammatory response, was found to have a shear stress threshold value; at low levels of applied shear loading no increase was observed, whereas an increased expression was observed when the shear load was raised. The exact level of the threshold varies from one person to another. Considering the critical threshold for cytokine release, people who exhibit a high coefficient of friction might be more prone to developing pressure ulcers as it is more likely that a high shear load might be acting on the skin. Although previous researchers have established that skin hydration might be responsible for causing interpersonal differences in friction behaviour, correlation was only obtained within individuals, whereas this was not obtained for groups. In this thesis, Fourier transfer infrared spectroscopy (FTIR) has been identified as a useful tool for identifying skin characteristics that may be linked to interpersonal differences in friction behaviour. A strong correlation was obtained between the coefficient of friction and FTIR peaks relating to the hydration of the skin and the a measure for the viscosity of the sebum layer, meaning that a direct relationship between FTIR spectrum and an individual's friction behaviour has been obtained. To reduce the friction coefficient between skin and various counter surfaces, a selection of parameters can be altered to change the frictional behaviour. Results from friction experiments using smooth counter surfaces showed that the interfacial shear strength depends primarily on the environmental conditions while the material of the counter surface is of secondary importance. It was shown that the microenvironment has a major influence on the coefficient of friction. Both temperature and relative humidity had strong effects on the frictional behaviour. This work suggested that, from a tribological point of view, reducing the humidity should be the primary focus. The effect of surface roughness and hardness was studied using silicone counter surfaces which are commonly used for prosthetic liners. Employing surface roughness and varying the compliance of the silicone compound allowed the coefficient of friction to be altered. The results obtained are combined into two design maps: one for optimising the micro-environment in the skin-object interface, and one relating to surfaces in contact with skin exhibiting controlled levels of friction, with the objective of optimizing conditions for preventing pressure injury
The frictional behaviour of surgical suture interacting with skin substistute
No full textSurgical sutures are essential for the re-approaching of divided tissues, for the ligation of the cut ends of vessels, and play a significant role in wound repair by providing support to healing tissues. Frictional behaviour is one important part of the physical and handling characteristics and knot security of surgical suture. High friction between surgical sutures and tissues may cause inflammation and pain to the person, leading to a longer recovery time. Therefore, it is essential to investigate the frictional behaviour of surgical suture sliding through tissue. Based on the literature review of the frictional behaviour of surgical suture, little is actually understood about the frictional behaviours of surgical suture in sliding contact with tissue and about the simulation of friction of surgical suture during stitching. The aim of this thesis is to investigate the frictional behaviour of surgical suture penetrating through skin substitute by means of experimental and modelling work, in order to generate guidelines for the development of surgical suture with desirable tribological performance. In line with this, firstly, the frictional behaviour of three commercialized surgical sutures interacting with skin substitute is investigated in this thesis, with respect to surgical suture material and structure, by means of a capstan experiment approach and a contact area model. The results indicated that structure and surface topography of the surgical suture had a pronounced effect on the tribological interactions. In the stitching process, it is well known that the needle penetrates the tissue and creates a freshly formed counter surface with a damaged tissue. The needle is slightly larger in diameter than the surgical suture, which results in the spring back and subsequent normal force over the circumference of the surgical suture. Hence, from the tribological point of view, the sliding contact between the surgical suture with tissue is not restricted to surface phenomena, but might also lead to deformations beneath the surface layer. The capstan method could not simulate the frictional conditions of the surgical suture in the stitching process. Hence, a new penetration friction apparatus (PFA) was developed that allowed for the evaluation of the frictional behaviours of various surgical needles and surgical sutures during the suturing process, under similar contact conditions. It considered the deformation of tissue and could realize the puncture force measurements of surgical needles as well as the friction force of surgical sutures. The developed PFA could accurately evaluate the penetration friction behaviour of surgical suture - tissue under the simulating clinical conditions. The developed test method provides a new way to investigate the frictional behaviour of surgical suture. Additionally, based on the new test method, the relationship between the friction force and the normal force was established when the surgical suture penetrated through skin substitute. The friction force was measured by the PFA. The normal force that acted on the surgical suture was estimated based on a uniaxial deformation model, a Hertzian contact model and a finite element model (FEM), respectively. Furthermore, it is expected that the structure of the suture significantly affects the friction during sliding and possibly influences the amount of tissue abrasion. As a result, the influence of monofilament and multifilament structures on the frictional behaviour of the surgical suture was evaluated. Meanwhile, the difference of abrasion at the pull-in boundary and pull-out boundary of skin substitute was discussed. Lastly, based on the above research, two kinds of biopolymeric composite films were developed on the surgical suture, and their influence on the tribological performance of the surgical suture was explored
A mechanistic approach to tactile friction
Get PDFTo a large extent, the functionality and comfort experienced during the use of everyday products, such as apparel, household appliances and sports equipment, are determined by the frictional behaviour of contact that occurs with the skin. For product engineers who aim to control and optimize the sensorial properties of a product surface interacting with the skin, it is essential to understand this frictional behaviour. This involves the study of local friction behaviour at the scale of the surface roughness. In this work a mechanistic approach was adopted in which analytical models from contact mechanics theory were used to develop a model which describes the tactile friction behaviour against the human fingerpad as a function of asperity geometry and operational conditions
Design of a tongue equivalent for astringency assessment of plant based proteins
Get PDFConsumption of food products containing polyphenols has resulted in a feeling of dryness, roughness and puckering of the oral epithelium which is known as astringency. At high concentrations, astringent food compounds are perceived by consumers as unpleasant and has led food scientist to initiate multiple studies with the aim of reducing the unwanted effects of astringency. This project proposes a tongue equivalent design that closely mimics the properties of oral surfaces which are relevant for assessing changes to oral lubrication resulting from astringency. The nature of interactions occurring at oral interfaces containing astringents point towards a system dependence of astringency and shows the importance of adopting a tribosystems approach. By adopting a systems engineering approach, this project has been able to identify the main stakeholders and the influence they possess on the system under design. This was followed by the identification of needs from the main stakeholders which were translated into system requirements. Design concepts with the aim of satisfying the system’s requirements were proposed alongside some planned evaluation methods, performance indicators and expectations from the project main stakeholders. A final design concept was chosen based on the conceptual designs proposed to the stakeholders. The final design considers the topography, mechanical properties and operating conditions of the human tongue during oral assessment. Experiments have been used to verify the properties of several aspects of the design including Direct Mechanical Analysis, Dynamic Light Scattering and Tribological work. This thesis concludes by making recommendations on possible applications and future developments to the proposed design. Based on the investigation into the mechanism of astringency, it is recommended that current test protocols must undergo further development, making them capable of investigating the tribochemical basis of astringency
Lubricant failure in sheet metal forming processes
Get PDFThe application of tribology to sheet metal forming processes (SMF) contributes to a general industrial aim i.e., to make products of high quality at an increasingly competitive way, by enhancing the tool life and maintaining a constant level of friction during forming. Both aspects are served by the development of models, able to predict friction and wear. This thesis provides such a model, restricted to lubricated SMF-operations and focused on prediction and control of galling (initiation). The main hypothesis of the work - galling initiation in lubricated sheet metal forming processes occurs at the asperity level as a result of the fact that the lubricant’s critical temperature is exceeded, due to frictional heating -, is validated by a combination of modelling, experimental work and industrial trials
Slijtvaste coatings voor het omvormen van tailored blanks met gietijzeren gereedschappen
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