Search results

The purpose of this paper is to investigate the frictional behavior of polytetrafluoroethylene (PTFE) composites under oil‐free sliding conditions.

The friction force and power consumption of pressure packing seals, which were, respectively, made of common filled PTFE, 30 wt% CF (carbon fiber) + PTFE and C/C (carbon/carbon) + PTFE, are studied in a reciprocating oil‐free compressor arrangement. Their coefficient of friction is tested on a block‐on‐ring type tribometer.

The results indicate that influence of mean sliding velocity on filled PTFE composites is apparently more predominant than the others. The friction force curvilinear path of 30 wt% CF+PTFE is hardly influenced by changing crankshaft turn angle. For C/C+PTFE, the effect of mean piston velocity on friction force is not evident. The results also indicate that the friction coefficient of C/C+PTFE is lower than that of 30 wt% CF+PTFE if their applied normal force exceeds 9.8 N. Furthermore, their variation curve of friction force is little different and the power consumption of C/C+PTFE is slightly higher than that of 30 wt% CF+PTFE.

Neither the effect of real contact area on friction coefficient measured in a tribometer nor the influence of the temperature on friction force and power tested in a compressor is not taken into consideration here.

Owing to its good mechanical performances and frictional behaviors, C/C+PTFE is an optimum and promising material under conditions with sealing pressure up to 10 MPa and sliding velocity exceeding 4.0 m/s.

A novel material called C/C+PTFE is considered to make packing rings for oil‐free reciprocating compressors and its friction behaviour is tested on a refitted compressor.

Based on the mechanical model of typical shear tests, this study aims to propose the test principle and method of freshwater/seawater ice adhesion shear strength of carbon ceramic brake pads for amphibious aircraft, designs and builds the test equipment, prepares the freshwater/seawater ice samples and completes the tests.

This study examines the influence of the icing process, mechanism, temperature and freshwater/seawater on ice adhesion shear strength of carbon ceramic brake pads and puts forward a test method for the freshwater/seawater ice adhesion shear strength of amphibious aircraft brake pads.

The obtained results examine the influence of the icing process, mechanism, temperature and freshwater/seawater on ice adhesion shear strength of carbon ceramic brake pads. The adhesion shear strength of frozen freshwater and of the seawater of Dalian, Qingdao, Fuzhou and Zhuhai on the surface of aircraft brake pads is measured at –10 to –50°C. It is found that the shear strength of freshwater increases first and then decreases with the decrease of temperature. The adhesion shear strength of seawater; however, increases mainly linear with the decrease of temperature.

The value of this paper is that the test method proposed and test results for the freshwater/seawater ice adhesion shear strength of amphibious aircraft brake pads provide technical support for the anti-icing design of amphibious aircraft brake devices.

The education services sector faces ever-changing global market dynamics with creative disruptions. Building knowledge brands can push the higher education sector beyond its geographical boundaries into the global arena. This study aims to identify key constructs, their theoretical background and dimensions that aid in building a global knowledge brand. The authors' research focuses on adapting and validating scales for global knowledge and education services brands from well-established academic literature.

The authors have adopted a mixed methodology approach and a systematic literature review. Authors interviewed 18 subject matter experts as part of content and face validity to arrive at select constructs, dimensions and items. Quantitative methods with random sampling were adopted as the primary methodology. Initially, the survey was administered to 390 students to test preliminary results. The survey was also administered to 5,112 students at a later part of this study. Valid responses stood at 3,244 with a 63% response rate. Further, the authors conducted confirmatory factor analysis, exploratory factor analysis and structural equation modeling to test the reliability and validity of scales. This study analyzed composite reliability, convergent validity and discriminant validity to finalize items for scales. The authors also validated the hypotheses based on the discriminant validity assessment scores.

Authors' key research findings are that academic stimulus, campus infrastructure and student intent play a significant role in campus culture and events design and experience at campus. Authors were able to bring out 16 key constructs and 55 critical dimensions vital to global education services brand building. This study also adapted and validated 99 items that meet construct validity and composite reliability criteria. This study also highlights that constructs such as student intent, academic stimulus, campus infrastructure scalability, selection mechanism, pedagogical content knowledge, brand identity, events experience and campus culture play a vital role in global brand recognition.

The authors' work is fairly generalizable to education services and the higher education sector. However, this study must be extrapolated and empirically validated in other industry sectors. The research implications of this study are that it aided the authors in building theoretical background for student brand loyalty theory, student expectation theory and study loyalty theory. This study adds to the body of knowledge by contributing to theoretical concepts on students, knowledge culture, events, infrastructure and branding. Researchers can adopt the scales proposed in this study to build research models in higher education branding. This study acts as a catalyst for building theories in education services areas. Researchers can delve deep into proposed research aspects of campus infrastructure, knowledge infrastructure, campus knowledge culture, events design and events experience.

This study aids educators and brand managers to develop global education services and optimize their effort and budget. Administrators in the education services sector must focus on practical aspects of student perception, campus infrastructure, culture and events experience. Practically administrators can reorient their efforts based on this study to achieve global brand recognition.

This study highlights that students are not customers but are co-creators of value in the education sector. This study provides scales and dimensions needed to build co-creation frameworks and models.

Most research in higher education branding has not covered wider aspects of global brand building. Existing theories proposed in higher education and education services articles cover only narrower aspects of campus infrastructure, culture, events design and branding. This study presents a comprehensive list of critical factors that play a vital role in global knowledge brand building. This study highlights the constructs and scales integral to building a global education services brand.

The purpose of this study was to investigate wear behaviours of brake pads produced from carbon–carbon (C/C) composites in both wet and dry friction sliding conditions. Carbon is probably the most remarkable element in science and also C/C composites are a family of advanced composite materials. They are the most advanced form of carbon and consist of fibre based on carbon precursors embedded in a carbon matrix. In the present work, wear test specimens were prepared according to the related standards and they were exposed to pin-on-disc wear testing in wet and dry sliding conditions with different loads as 10, 20, 30 and 40 N with 1 m/s constant sliding speed. Wet friction process was conducted on all specimens by means of rain water collected from the nature.

Pin-on-disc wear test tribology lubrication was used.

Mechanical and physical property measurements of C/C composite brake pad materials: hardness, modulus of elasticity, density and water absorption capacity. Wear performance of materials were measured as coefficient of friction, volumetric loss and specific wear rate.

C/C composite brake pads are used in railway vehicles. Wear performances of them are very important for safety. In this study, wear behaviours of these materials were investigated not only in dry sliding friction condition but also in wet sliding one. Because safety braking is important in all weather conditions for trains, and we used natural rain water to observe the wet sliding friction behaviour of brake pads. “Water lubrication” is an important aspect mentioned in tribology handbooks.

This paper aims to review the research status of fatigue behavior and fracture mechanism for C/C composites.

The fatigue behavior is related to many factors. The mechanical and physical properties were compared to evaluate the effect of fatigue under various experimental conditions, including different load type, loading frequency and stress ratio. Special attention is put on the high‐temperature fatigue research.

The strength has improved by fatigue loading. And most researchers considered that the weaken interface was the main reason for fatigue enhancement. However, the research on high‐temperature fatigue behavior is especially scarce.

This review provides a guideline on the current and future research on fatigue behavior of C/C composites.

The carbon/carbon (C/C) composite finger seal experiment was performed on a high-speed seal tester. The purpose of this paper is to investigate the leakage and wear characteristics of C/C composite finger seal under various operating conditions.

Static, dynamic, endurance and post endurance tests were carried out. For static and performance tests, the pressure differential changed from 0.1 to 0.6 MPa and the rotor speed varied from 1,000 to 9,000 r/min. Two endurance tests were conducted for 4 h, with each mounting two finger seals. The seal leakage was monitored by mass flowmeters, and the wear depth was measured and calculated by using three-dimensional profilometer.

Results showed that the seal leakage increases with pressure differential but decreases with rotor speed. Leakage rate is lower when speed is decelerated than that with the speed stepped up. During a time history, material removal caused by wear has significant influence on leakage data causing higher leakage than the results before endurance test. Particular interest is that the uneven wear characteristic on finger foot bottom was firstly revealed, showing severe wear in foot heel area than that in foot toe.

This study could provide experimental guidance for finger seal designers. Additionally, the uneven wear characteristic of finger foot was firstly revealed, which showed the necessity of further theoretical research on finger seal wear.

A relatively inexpensive and easy to operate custom built infrared thermography (IRT) system was developed and utilized for the detection and characterization of defects in Carbon-Carbon (C/C) composite aircraft brake disks. This method uses an active infrared thermography (IRT) approach, i.e. Flash Heating method, for a non-destructive evaluation (NDE) of C/C brake disk materials. The experimental results obtained from the developed system were then compared with commercial IRT turn-key system. In addition, Finite Element Analysis (FEA) was also carried out to determine the detectible defect depth and diameter of the defects in C/C composites to validate the experimental results. The experimental results were compared to the FEA results and it was found that they were in good agreement with one another.

The aim of this paper is to study the effect of strategic and project related potential risks on project delivery in Qatar. Two objectives have been defined. The first is to identify potential risk indicators (manifest variables) and categorize them (constructs/latent variables) based on a literature review, while the second is to examine and rank the relationships between the indicators and constructs by developing a structural equation model.

Twenty-five indicators were identified from the literature review and categorized into five groups. To collect the data, an online questionnaire was distributed in Qatar, and 116 responses were obtained. Structural equation modeling (SEM) was used to examine the model. The model that was developed based on the research hypothesis met goodness-of-fit, reliability and validity requirements.

The results showed that all constructs contributed well to the model and that the project parties (PPs) have the highest contribution with an effect weight of 0.209 followed by economic and legal (EL) conditions with an effect weight of 0.205. Site and safety (SS) conditions were third with an effect weight of 0.200 while environmental, natural and technological (ENT) conditions were fourth with an effect weight of 0.1989. The last ranked construct is political and social (PS) conditions with an effect weight of 0.186. Based on the outcome of the SEM, recommendations were provided to industry professionals in Qatar about mitigating the impact of potential risks on construction project.

To the authors' best knowledge, this is the first study to quantify the effects of strategic and project related risks on a construction project using SEM, considering the risk management indicators of SS, EL, ENT, PS in Qatar. The study's practical implications are to enlarge the project's risk management plan by considering the strategic and project related risks to enhance the project performance for the cost overrun and delay. The study is intended for construction projects in Qatar, but it can easily be adapted to other parts of the world given the local circumstances.

The purpose of this paper is to study the ablative behavior of the silicone resin-coated carbon fabric (coated fabric) that will swell significantly during ablation.

The ablation experiments of three coated fabrics were conducted by quartz lamp radiant. Based on the experimental analysis, a numerical model was proposed for the coated fabrics to study the ablative process in term of the energy balance, mass conservation and thermal decomposition equations.

Results showed that the average relative errors between the simulated temperatures and experimental values of back surfaces of coated fabric 1, 2 and 3 were 10.01, 7.53 and 7.32%, respectively. The average density of silicone resin of coated fabric 1 was reduced by 47.96%, and the closer the distance from the heated surface was, the more the density decreased. The thermal conductivity and specific heat capacity of silicone resin of coated fabric 1 increased with time. Before 50 s, each decomposition rate curve showed an inflection point, at which the silicone resin decomposed most intensely.

Based on experimental observations, the ablative behavior of the material with fixed expansion layer was simulated. In the further research, the moving expansion layer could be considered.

This paper provides the theoretical basis to evaluate the effectiveness of thermal protection materials that will swell during ablation.

This paper presents the synthesizing of carbon-carbon (CC) composites by preformed yarn (PY) method, by varying the percentage of carbon fiber volume. The PY used is carbon fiber bundle surrounded by coke and pitch which is enclosed in nylon-6. Three types of samples with fiber weight fractions of 30%, 40% and 50% respectively, are fabricated and tested. In each case, the PY is chopped and filled into a die of required shape and hot pressed at 600°C to get the carbonized composite. To obtain the graphitic structure, the specimen is heat treated at 1800°C followed by soaking for two hours. Further, one cycle pitch impregnation is done by hot isostatic pressing, to eliminate the voids. The characteristics such as hardness, compressive strength, creep, density and oxidation resistance are studied. It is observed that, as the carbon fiber percentage increases the properties also improved, provided sintering is done at fairly higher temperatures. The superiority of the new class of CC composites made by the proposed PY technique over those obtained by the conventional methods is also demonstrated.