Publications
89 results found
Khafidh M, Schipper DJ, Masen MA, et al., 2019, Friction and wear mechanism of short-cut aramid fiber and silica reinforced elastomers, Wear, Vol: 428-429, Pages: 481-487, ISSN: 0043-1648
© 2019 Elsevier B.V. Important phenomena during sliding contact of elastomeric materials are friction and wear. Wear reduction of elastomers can be achieved by minimizing the propagation of cracks in the elastomer during sliding contact. Adding fillers like silica and fibers is a way to reduce the propagation of cracks and as a result reduction of wear. In the present study, the wear processes of short-cut aramid fiber reinforced elastomers as a function of sliding distance and their relation to friction are investigated. Two different types of systems are considered, i.e. (1) elastomers reinforced by solely short-cut aramid fibers and (2) elastomers reinforced by short-cut aramid fibers and silica. A pin-on-disc tribometer and a microscope are used to analyze the friction and wear mechanisms of the elastomeric composites in sliding contact with a granite counter surface. The results show that the coefficient of friction of the composites consists of different stages, these stages are influenced by the wear processes during sliding. For elastomers which are reinforced by short-cut aramid fibers and silica, a higher energy input is needed to achieve all stages since the presence of silica in the elastomer matrix increases the resistance of matrix particle detachment. A general friction behavior of short-cut aramid fiber and silica reinforced elastomers is proposed.
Klaassen M, de Vries EG, Masen MA, 2019, Friction in the contact between skin and a soft counter material: Effects of hardness and surface finish, Journal of the Mechanical Behavior of Biomedical Materials, Vol: 92, Pages: 137-143, ISSN: 1751-6161
The interaction behaviour of skin with a counter surface depends strongly on the surface roughness of the counter surface. For relatively hard surfaces this effect is described in various literature, but for soft, or compliant, materials this is much less studied. Inside the contact, the protuberances on the surface will deform substantially. In order to gain insights into the effect of surface roughness and hardness on the frictional behaviour between skin and a soft counter surface a range of experiments were performed using artificial skin and various silicone compounds which are commonly used in medical devices that interact with the human skin. Using these results, a 'friction map' was created that shows the friction behaviour as a function of the elastic modulus and the surface roughness. When the surface roughness is increased the friction coefficient decreases due to the reduction in the real area of contact, which weakens the adhesion between the two surfaces. A minimum coefficient of friction was observed at a surface roughness of approximately 4 µm. For the softest compounds tested there was minimal effect of surface roughness on friction because the roughness protuberances inside the contact will be flattened. Silicone compounds with increased hardness showed a larger sensitivity of the friction to the surface roughness, because these harder surface roughness protuberances are more resistant against deformation. The friction map provides a tool when designing products that require certain frictional properties: for products that are required to adhere to skin a smooth and soft material is recommended, whereas for products that require a low coefficient of friction a harder compound with a surface roughness of approximately 4 µm is recommended.
Boyle CJ, Carpanen D, Pandelani T, et al., 2019, Lateral pressure equalisation as a principle for designing support surfaces to prevent deep tissue pressure ulcers
<jats:title>Abstract</jats:title><jats:p>When immobile or neuropathic patients are supported by beds or chairs, their soft tissues undergo deformations that can cause pressure ulcers. Current support surfaces that redistribute under-body pressures at vulnerable body sites have not succeeded in reducing pressure ulcer prevalence. Here we show that adding a supporting lateral pressure can counter-act the deformations induced by under-body pressure, and that this ‘pressure equalisation’ approach is a more effective way to reduce ulcer-inducing deformations than current approaches based on redistributing under-body pressure.</jats:p><jats:p>A finite element model of the seated pelvis predicts that applying a lateral pressure to the soft tissue reduces peak von Mises stress in the deep tissue by a factor of 2.4 relative to a standard cushion — a greater effect than that achieved by using a more conformable cushion. The ratio of peak lateral pressure to peak under-body pressure was shown to regulate deep tissue stress better than under-body pressure alone. By optimising the magnitude and position of lateral pressure, tissue deformations can be reduced to that induced when suspended in a fluid.</jats:p><jats:p>Our results explain the lack of efficacy in current support surfaces, and suggest a new approach to designing and evaluating support surfaces: ensuring sufficient lateral pressure is applied to counter-act under-body pressure.</jats:p>
Limbert G, Masen MA, Pond D, et al., 2019, Biotribology of the ageing skin—Why we should care, Biotribology, Vol: 17, Pages: 75-90, ISSN: 2352-5738
Ageing of populations has emerged as one of the most pressing societal, economic and healthcare challenges currently facing most nations across the globe. The ageing process itself results in degradation of physiological functions and biophysical properties of organs and tissues, and more particularly those of the skin. Moreover, in both developed and emerging economies, population ageing parallels concerning increases in lifestyle-associated conditions such as Type 2 diabetes, obesity and skin cancers. When considered together, these demographic trends call for even greater urgency to find clinical and engineering solutions for the numerous age-related deficits in skin function.From a tribological perspective, detrimental alterations of skin biophysical properties with age have fundamental consequences on how one interacts with the body's inner and outer environments. This stems from the fact that, besides being the largest organ of the human body, and also nearly covering its entirety, the skin is a multifunctional interface which mediates these interactions.The aim of this paper is to present a focused review to discuss some of the consequences of skin ageing from the viewpoint of biotribology, and their implications on health, well-being and human activities. Current and future research questions/challenges associated with biotribology of the ageing skin are outlined. They provide the background and motivation for identifying future lines of research that could be taken up by the biotribology and biophysics communities.
Khafidh M, Schipper DJ, Masen MA, 2019, The formation of a modified surface layer on elastomeric materials, Tribology Letters, Vol: 67, Pages: 27-27, ISSN: 1023-8883
Surface modification of an elastomer may be formed during sliding contact with a rigid counter surface. This alteration leads to a change of mechanical properties at the surface and as a result a change in frictional behavior. Therefore, investigations related to the formation of a modified surface layer on elastomers and its effect on friction are of importance. In the present study, the formation of a modified surface layer on elastomer reinforced by silica is studied. Sliding friction is performed using a pin-on-disc tribometer. Several parameters are varied, namely contact pressure, velocity, and roughness of the counter surface. The existence of a modified surface layer is investigated by using a scanning electron microscope. The results show that the existence of a modified surface layer depends on the competition between the formation rate of the layer and the wear rate. The formation of the layer depends on the contact pressure, velocity, and sliding distance. A general formulation to calculate the volume of formation is proposed. Furthermore, a map of the formation of a modified surface layer is developed.
Porte E, Cann P, Masen M, 2019, Fluid load support does not explain tribological performance of PVA hydrogels, Journal of The Mechanical Behavior of Biomedical Materials, Vol: 90, Pages: 284-294, ISSN: 1751-6161
The application of hydrogels as articular cartilage (AC) repair or replacement materials is limited by poor tribological behaviour, as it does not match that of native AC. In cartilage, the pressurisation of the interstitial fluid is thought to be crucial for the low friction as the load is shared between the solid and liquid phase of the material. This fluid load support theory is also often applied to hydrogels. However, this theory has not been validated as no experimental evidence directly relates the pressurisation of the interstitial fluid to the frictional response of hydrogels. This lack of understanding about the governing tribological mechanisms in hydrogels limits their optimised design. Therefore, this paper aims to provide a direct measure for fluid load support in hydrogels under physiologically relevant sliding conditions. A photoelastic method was developed to simultaneously measure the load on the solid phase of the hydrogel and its friction coefficient and thus directly relate friction and fluid load support. The results showed a clear distinction in frictional behaviour between the different test conditions, but results from photoelastic images and stress-relaxation experiments indicated that fluid load support is an unlikely explanation for the frictional response of the hydrogels. A more appropriate explanation, we hypothesized, is a non-replenished lubricant mechanism. This work has important implications for the tribology of cartilage and hydrogels as it shows that the existing theories do not adequately describe the tribological behaviour of hydrogels. The developed insights can be used to optimise the tribological performance of hydrogels as articular cartilage implants.
Wang L, Hu Y, Zheng Y, et al., 2019, Development of an interactive friction model to predict aluminum transfer in a pin-on-disc sliding system, Tribology International, Vol: 130, Pages: 216-228, ISSN: 0301-679X
In aluminum forming processes, it is observed that the coefficient of friction increases and a transfer layer is formed on the tool surfaces. In the current paper, this phenomenon is studied via pin-on-disc dry sliding tests with aluminum alloy 6082 sliding against cast iron G3500. The results showed that the aluminum transfer layers generated at the sliding interface were identified as the origin of this behaviour that affects both friction and wear. To model this phenomenon, an interactive friction model was developed enabling the prediction of friction and the evolution of the transfer layer from the running in to the steady state. This mechanism based model can be used for representing friction variations and material transfer in sliding systems.
Jean-Fulcrand A, Masen M, Bremner T, et al., 2019, Effect of temperature on tribological performance of polyetheretherketone-polybenzimidazole blend, Tribology International, Vol: 129, Pages: 5-15, ISSN: 0301-679X
Polyetheretherketone (PEEK) is one of the most commonly used High Performance Polymers (HPP) although its high temperature performance is poor. In this study, polybenzimidazole (PBI), a HPP with one of the highest glass transition temperatures currently available, is blended to PEEK to form a 50:50 blend (TU60). Tribological performance of the blend (TU60) was investigated by rubbing it against steel at temperatures up to 280 °C. Results obtained are compared to those from neat PEEK and neat PBI. All three polymers were thermally stable during the duration of tests. However chemical analyses on polymeric transfer layers on steel surfaces and polymer debris suggest polymer degradation. The degradation observed is shear-assisted, possibly promoted by shear heating. Indeed the estimated interfacial temperature based on Jaeger model was above the melting point of PEEK in some cases. TU60 outperforms PEEK in all test conditions and PBI at 280 °C. TU60 formed transfer layers on steel similar to that of PEEK. When contact temperature is closed to the melting point of PEEK, PEEK in the TU60 creates a low strength transfer layer which acts as an interfacial lubricant. This reduces friction which in turn reduces PBI degradation in TU60 at high temperature. This work provides a strategy for creating interfacial layers to improve polymer tribological performance while maintaining the integrity of the polymer.
Masen MA, Veijgen N, Klaassen M, 2019, Experimental Tribology of Human Skin, SKIN BIOPHYSICS: FROM EXPERIMENTAL CHARACTERISATION TO ADVANCED MODELLING, Editors: Limbert, Publisher: SPRINGER INTERNATIONAL PUBLISHING AG, Pages: 281-295, ISBN: 978-3-030-13278-1
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Khafidh M, Setiyana B, Jamari J, et al., 2018, Understanding the occurrence of a wavy wear track on elastomeric materials, Wear, Vol: 412-413, Pages: 23-29, ISSN: 0043-1648
Elastomeric materials are used in daily applications, such as tires and conveyor belts. Sliding friction of elastomeric materials often produces a unique periodic wear pattern. In general, the periodic wear pattern has to be prevented because it generates surface instabilities and, as a result, vibration. Sliding contact between an elastomer and a rigid ball may cause the development of a periodic wear pattern like a wave on the elastomer surface, called a wavy wear track. The present study has investigated the occurrence of the wavy wear track on the elastomers under several operating conditions. The elastomers used were a Styrene-Butadiene Rubber (SBR) and Butadiene Rubber (BR) reinforced with two types of fillers, i.e., highly dispersible silica and short-cut aramid fiber. A pin-on-disc tribometer was used to study the wavy wear track of the materials under several operating conditions. An analytical model was used to predict the wave length of the wear pattern and to study the occurrence of the wavy wear track. The results show that the occurrence of the wavy wear track depends on the mechanical properties of the elastomer, the operating conditions (such as sliding velocity and force), the inertia mass of the counter surface frame and the circumferential length of the wear track. The analytical model is in good agreement with the experimental results.
Wong J, Jean-Fulcrand A, Masen M, 2018, Effect of temperature on tribology of PBI/PEEK blend, 256th National Meeting and Exposition of the American-Chemical-Society (ACS) - Nanoscience, Nanotechnology and Beyond, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Khafidh M, Schipper DJ, Masen MA, et al., 2018, Tribological behavior of short-cut aramid fiber reinforced SBR elastomers: the effect of fiber orientation, JOURNAL OF MECHANICAL ENGINEERING AND SCIENCES, Vol: 12, Pages: 3700-3711, ISSN: 2289-4659
Masen M, Cann PME, 2018, Friction Measurements with Molten Chocolate (vol 66, 24, 2018), Tribology Letters, Vol: 66, Pages: 1-1, ISSN: 1023-8883
Correction to: Tribology Letters (2018) 66:24 https://doi.org/10.1007/s11249-017-0958-x
Masen M, Cann PME, 2018, Friction measurements with molten chocolate, Tribology Letters, Vol: 66, Pages: 1-13, ISSN: 1023-8883
A novel test is reported which allows the measurement of the friction of molten chocolate in a model tongue–palate rubbing contact. Friction was measured over a rubbing period of 150 s for a range of commercial samples with different cocoa content (85–5% w/w). Most of the friction curves had a characteristic pattern: initially a rapid increase occurs as the high-viscosity chocolate melt is sheared in the contact region followed by friction drop as the film breaks down. The exceptions were the very high (85%) and very low (~ 5%) cocoa content samples which gave fairly constant friction traces over the test time. Differences were observed in the initial maximum and final friction coefficients depending on chocolate composition. Generally, the initial maximum friction increased with increasing cocoa content. At the end of the test, the rubbed films on the lower slide were examined by optical microscopy and infrared micro-reflection spectroscopy. In the rubbed track, the chocolate structure was severely degraded and predominately composed of lipid droplets, which was confirmed by the IR spectra. The new test provides a method to distinguish between the friction behaviour of different chocolate formulations in a rubbing low-pressure contact. It also allows us to identify changes in the degraded chocolate film that can be linked to the friction profile. Further development of the test method is required to improve simulation of the tongue–palate contact including the effect of saliva and this will be the next stage of the research.
Eijnde WVD, Masen M, Lamers E, et al., 2018, The load tolerance of skin during impact on artificial turf using ex-vivo skin as the readout system, Science and Medicine in Football, Vol: 2, Pages: 39-46, ISSN: 2473-3938
Jean-Fulcrand A, Masen M, Bremner T, et al., 2017, High Temperature Tribological Properties of Polybenzimidazole (PBI), Polymer, Vol: 128, Pages: 159-168, ISSN: 0032-3861
Polybenzimidazole (PBI) is a high performance polymer that can potentially replace metal components in some high temperature conditions where lubrication is challenging or impossible. Yet most characterisations so far have been conducted at relatively low temperatures. In this work, the tribological properties of PBI were examined with a steel ball-PBI disc contact at 280 °C under high load and high sliding speed conditions. The dry friction coefficient is relatively low and decreases modestly with increasing applied load. Surface analysis shows that PBI transfer layers are responsible for the low friction observed. In-situ contact temperature measurements were performed to provide for the first time direct links between the morphology and distribution of the transfer layer, and the temperature distribution in the contact. The results show that high pressure and high temperature in heavily loaded contacts promote the removal and the subsequent regeneration of a transfer layer, resulting in a very thin transfer layer on the steel counterface. FeOOH is formed in the contact at high loads, instead of Fe2O3. This may affect the adhesion between PBI and the counterface and thus influence the transfer layer formation process. To control PBI wear, contact temperature management will be crucial.
Cann P, Masen M, 2017, The 3 rd International Conference on Biotribology (ICoBT) Imperial College London, 11-14 th September 2016, Biotribology, Vol: 11, Pages: 1-2, ISSN: 2352-5738
wang A, liu JUN, gao H, et al., 2017, Hot stamping of AA6082 tailor welded blanks: experiments and knowledge based cloud FE (KBC-FE) simulation, Journal of Materials Processing Technology, Vol: 250, Pages: 228-238, ISSN: 0924-0136
A novel hot stamping technique known as ‘Solution Heat treatment, Forming and in-die Quenching (HFQ®)’ was employed to manufacture lightweight structural components from AA6082 tailor-welded blanks (TWBs) of different thickness combinations: 1.5–1.5 and 2.0–1.0 mm. A finite element (FE) model was built to study the deformation characteristics during the hot stamping process. The FE model was successfully validated by comparing simulation results with experimental ones. Subsequently, the verified simulation results were analysed through a novel multi-objective FE platform known as ‘Knowledge-Based Cloud – Finite Element (KBC-FE)’. KBC-FE operates in a cloud environment and offers various advanced unique functions via functional modules. The ‘formability’ module was implemented in the current study to predict the limiting dome height and failure mode during the hot stamping process. Good agreements were achieved between the predicted and experimental results, from which studies were extended to predict the forming features of 2.0–1.5 mm TWBs. The ‘formability’ module has successfully captured the complex nature of a hot stamping process, featuring a non-isothermal and non-linear loading path. The formability of TWBs was found to be dependent on forming speed and blank thickness, out of which the latter has a dominant effect.
Klaassen M, de Vries EG, Masen MA, 2017, The static friction response of non-glabrous skin as a function of surface energy and environmental conditions, Biotribology, Vol: 11, Pages: 124-131, ISSN: 2352-5738
The (local) environmental conditions have a significant effect on the interaction between skin and products. Plasticisation of the stratum corneum occurs at high humidity, causing this layer to soften and change its surface free energy. In this work we study the effects of the micro-climate on the frictional behaviour of skin in contact with materials with varying wettability. Friction measurements are performed under a range of micro-climate conditions using four different materials with a smooth surface finish. All measurements are performed twice on a single subject in order to minimise variation in skin properties. Results show that materials with a higher wettability show a larger increase in friction coefficient when exposed to warm, moist conditions. The friction force is modelled using the skin micro-relief, the elastic properties of the different skin layers, the surface chemistry of both skin and counter surface, and the environment, as input parameters.
Tsui S, Tandy J, Myant C, et al., 2016, Friction measurements with yoghurt in a simulated tongue-palate contact, Biotribology, Vol: 8, Pages: 1-11
The perception of many food attributes is related to mechanical stimulation and friction experienced in the tongue-palate contact during mastication. Friction in the tongue-palate is determined by the changing film properties (composition, component distribution, thickness) in the conjunction. We suggest this evolution is essentially determined by tongue-palate film loss rather than shear flow entrainment which predominates in conventional bearing lubrication. The paper reports friction measurements in a simulated tongue-palate contact for a range of high and low fat dairy foods. A reciprocating, sliding contact with restricted stroke length (< contact width) was used; under these conditions there is negligible shear-entrainment of fluid from outside the contact area. The tongue-palate contact was simulated by a PDMS ball and glass surface. The effect of hydrophobic and hydrophilic surfaces on friction was investigated for different fat contents (0, 4.2, 9.5% wt fat). Friction was measured over 60 s of rubbing. Significant differences were observed in the friction change with time for different fat contents (μ 9.5 < μ 4.2 < μ 0 wt%) and for different surface energy conditions (μ hydrophilic < μ hydrophobic). Post-test visualisation of the rubbed films showed that low friction coefficient was associated with the formation of a thin oil film on deposited particulate solids.
Wang L, Politis DJ, Masen MA, 2016, Development of an interactive friction model for the prediction of lubricant breakdown behaviour during sliding wear, Tribology International, Vol: 110, Pages: 370-377, ISSN: 1879-2464
In this paper, a novel interactive friction-lubricant thickness model was developed to predict the evolution of coefficient of friction and the useful life of lubricant film. The developed model was calibrated by experimental results determined from pin-on-disc tests. For these experiments, a grease lubricant was applied on a Tungsten Carbide ball which slides against a disc made from AA6082 Aluminium alloy. In the pin-on-disc tests, the lubricant film thickness decreased with time during single path sliding leading to a rapid increase in the coefficient of friction. The breakdown of lubricant was divided into three stages, namely, the Stage I low and stable coefficient of friction region, Stage II region in which the coefficient of friction sees a rapid rise, and Stage III in which the coefficient of friction reaches a plateau with a value similar to that of dry sliding. In order to characterise the evolution of coefficient of friction throughout these stages, a novel interactive friction model was developed combining the effects of sliding distance, sliding speed, contact pressure and initial lubricant amount on the evolution of the coefficient of friction. This interactive friction model can be applied to situations involving lubricant breakdown in a dynamic environment such as the metal forming industry, where the use of traditional constant coefficient of friction values present limits in predictive accuracy.
Woldman M, Van Der Heide E, Tinga T, et al., 2016, A finite element approach to modeling abrasive wear modes, Tribology Transactions, Vol: 60, Pages: 711-718, ISSN: 1040-2004
Machine components operating in sandy environments will wear because of the abrasive interaction with sand particles. In this work, a method is derived to predict the amount of wear caused by such abrasive action, in order to improve the maintenance concept of the components. A finite element model is used to simulate various tips scratching a smooth surface. The model is verified by comparing the obtained results with a set of experiments performed earlier (M. Woldman, et al., 2013, Wear, 301(1–2), pp 76–81).
Wang A, Zheng Y, Liu J, et al., 2016, Knowledge Based Cloud FE simulation – data-driven material characterization guidelines for the hot stamping of aluminium alloys, 10th International Conference and Workshop on Numerical Simulation of 3D Sheet Metal Forming Processes, Numisheet 2016, Publisher: IOP Publishing, Pages: 032042-032042, ISSN: 1742-6588
The Knowledge Based Cloud FEA (KBC-FEA) simulation technique allows multi-objective FE simulations to be conducted on a cloud-computing environment, which effectively reduces computation time and expands the capability of FE simulation software. In this paper, a novel functional module was developed for the data mining of experimentally verified FE simulation results for metal forming processes obtained from KBC-FE. Through this functional module, the thermo-mechanical characteristics of a metal forming process were deduced, enabling a systematic and data-driven guideline for mechanical property characterization to be developed, which will directly guide the material tests for a metal forming process towards the most efficient and effective scheme. Successful application of this data-driven guideline would reduce the efforts for material characterization, leading to the development of more accurate material models, which in turn enhance the accuracy of FE simulations.
Jean-Fulcrand A, Wong J, Masen M, et al., 2016, Tribological properties of PBI and PEEK polymers on steel, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Wang A, Zheng Y, Liu J, et al., 2016, Knowledge based cloud FE simulation a multi-objective FEA system for advanced FE simulation of hot stamping process, The 10th International Conference and Workshop on Numerical Simulation of 3D Sheet Metal Forming Processes, Numisheet 2016, Publisher: IOP Publishing, ISSN: 1742-6588
. A knowledge Based Cloud (KBC) FE simulation technique has been developed to enable advanced, efficient and multi-objective finite element analyses (FEA), which operates on a cloud computing environment. The core FE simulation is conducted using a commercial FE code, e.g. PAM-STAMP, and its capability is enhanced through the implementation of advanced functional modules instead of user defined sub-routines. KBC-FE simulation offers great flexibility and variability to engineers as modules could be used collectively or individually. In this paper, case studies were conducted for the hot stamping of tailor welded blanks. Multi-objective FE simulations were performed for ‘Forming Limit’ prediction under non-isothermal and non-linear loading conditions. In addition, ‘Tool-life’ prediction was conducted under multi-cycle loading conditions.
Klaassen M, Schipper DJ, Masen MA, 2016, Influence of the relative humidity and the temperature on the in-vivo friction behaviour of human skin, Biotribology, Vol: 6, Pages: 21-28
© 2016 Elsevier B.V. Both temperature and relative humidity are known to influence the frictional behaviour of human skin. However, literature does not completely cover to what extent both parameters play a role. Measurements were conducted using an in-house built reciprocating tribometer inside an enclosure in which both the humidity and the temperature can be controlled independently. Friction measurements were performed in varying climates ranging from 25 °C and 40% RH to 37 °C and 80% RH at respectively 3 °C and 10% RH intervals. Using the obtained results a ‘friction map’ was created which shows that the coefficient of friction increases by a factor of two when the environment is changed from ‘cold and dry’ to ‘warm and moist’. A statistical analysis shows that the product of the temperature and relative humidity appears to be the driving factor describing the observed frictional behaviour. Results indeed show a more pronounced effect of either parameter at the warmer, moister conditions, in contrast to the colder, drier conditions where a smaller effect on the coefficient of friction is observed. The findings will be of importance, e.g. for bedridden patients who are prone to pressure ulcer development as it indicates the importance of maintaining a healthy microclimate.
Khafidh M, Rodriguez NV, Masen MA, et al., 2016, The dynamic contact area of elastomers at different velocities, Tribology - Materials, Surfaces and Interfaces, Vol: 10, Pages: 70-73, ISSN: 1751-5831
Yuan X, Zhou D, politis DENIS, et al., 2015, Tool-life prediction under multi-cycle loading during metal forming: a feasibility study, Manufacturing Review, Vol: 2, ISSN: 2265-4224
In the present research, the friction and wear behaviour of a hard coating were studied by using ball-on-disc tests to simulate the wear process of the coated tools for sheet metal forming process. The evolution of the friction coefficient followed a typical dual-plateau pattern, i.e. at the initial stage of sliding, the friction coefficient was relatively low, followed by a sharp increase due to the breakdown of the coatings after a certain number of cyclic dynamic loadings. This phenomenon was caused by the interactive response between the friction and wear from a coating tribo-system, which is often neglected by metal forming researchers, and constant friction coefficient values are normally used in the finite element (FE) simulations to represent the complex tribological nature at the contact interfaces. Meanwhile, most of the current FE simulations consider single-cycle loading processes, whereas many metal-forming operations are conducted in a form of multi-cycle loading. Therefore, a novel friction/wear interactive friction model was developed to, simultaneously, characterise the evolutions of friction coefficient and the remaining thickness of the coating layer, to enable the wear life of coated tooling to be predicted. The friction model was then implemented into the FE simulation of a sheet metal forming process for feasibility study.
Woldman M, Tinga T, Van Der Heide E, et al., 2015, Abrasive wear based predictive maintenance for systems operating in sandy conditions, Wear, Vol: 338-339, Pages: 316-324, ISSN: 0043-1648
Machines operating in sandy environments are damaged by the abrasive action of sand particles that enter the machine and become entrapped between components and contacting surfaces. In the case of the military services the combination of a sandy environment and the wide range of tasks to be fulfilled results in extreme and uncertain operating conditions. All of this hinders the ability to establish efficient maintenance strategies prior to deployment and increases the risk of mechanical failure. To prevent such problems, it would be desirable to perform maintenance based on the prevailing condition of both the components and the environment. By monitoring the loading situation as well as the characteristics of the sand particles, the wear of components is quantified, allowing maintenance to be performed when necessary. The development and implementation of such a predictive maintenance concept requires knowledge of the operational and environmental conditions and how they relate to the principal wear mechanisms. Based on previously established relationships between the abrasive particles and the resulting abrasive wear, the current work focuses on the implementation of these results into a predictive maintenance concept for vehicles that operate in a sandy environment. For this, the local parameters that govern the wear mechanism, such as the normal forces and sliding distances need to be linked to machine usage parameters including the type of terrain and the driving distance. The proposed concept is demonstrated using a case study on the sprockets of a military vehicle, where the sprockets wear progressively during use of the vehicle due to the abrasive action of sand. The predictive maintenance concept is shown to support the determination of maintenance intervals under a range of usage profiles and sand varieties.
Masen M, Myant C, 2015, Second International Conference on Biotribology (ICoBT), Tribology International, Vol: 89, Pages: 1-1, ISSN: 1879-2464
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