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The purpose of this paper was to explore the mechanisms of scuffing propagation of heavily loaded lubricated friction pair elements coated with low-friction WC/C coating for various material combinations.

The investigations were performed for low-friction coatings WC/C (a-C:H:W) deposited by the reactive sputtering physical vapour deposition (PVD) process. Experiments were carried out using a four-ball tester with continuously increasing loads. Tests were conducted for the following four material combinations: steel/steel tribosystem (all balls uncoated); steel/coating tribosystem (one upper ball uncoated/three lower balls WC/C-coated); coating/steel tribosystem (one upper ball WC/C-coated/three lower balls uncoated); and coating/coating tribosystem (all balls WC/C-coated).

The better scuffing resistance is achieved by coating only one element (coating/steel tribosystem) than all elements (coating/coating tribosystem). The description of scuffing propagation for all investigated tribosystems was done. The high scuffing resistance of the coating/steel tribosystem resulted from reducing the adhesion between rubbing surfaces due to low chemical affinity (similarities) between the steel and the coating material and the presence of solid lubricant in the friction zone.

In all cases, when a coating is applied, an increase in scuffing resistance is observed. However, it is better to coat only one element than all. Furthermore, the scuffing resistance for the coating/steel tribosystem is significantly higher than for the steel/coating tribosystem.

The main value of this paper is description of scuffing propagation and revealing the new aspects in application of low-friction WC/C coating for heavily loaded lubricated friction pair elements. The overlapping ratio has been defined as an important factor influencing the scuffing resistance of the coated tribosystems.

The purpose of this study was to investigate the frictional characteristics of the mechanical seals by using an efficient pairing by providing a suitable lubricant. Among all techniques and lubrication, deposition of solid lubricants on the sliding surface of the mechanical seal was found to be the most effective method to reduce frictional coefficient, frictional force and seal face temperature, thereby increasing the life time of mechanical seal.

In this study, two coatings, diamond-like carbon (DLC) and tungsten carbide/carbon (WC/C), was deposited over the stationary high-carbon high-chromium steel ring paired with resin-impregnated carbon. Their frictional characteristics were studied under various classes of liquid lubricants such as organic liquids, synthetic oil, mineral oil and vegetable oils using an experimental approach. Further, among all classes of liquid lubricants, the one which showed better frictional characteristics was mixed with 0.5, 1 and 2 wt% of potential environmental friendly solid lubricant – boric acid powder.

The high hardness and low surface roughness of DLC- and WC/C-coated seal with the lubricant of palm olein oil containing 1 wt% of boric acid powder contributed a hybrid tribofilm and resulted in low and stable friction coefficient in the range of 0.04-0.05 without any measurable wear.

A pair involving stationary DLC- and WC/C-coated seal ring and resin-impregnated carbon seal rotating ring for the application of mechanical seal was suggested and its frictional characteristics were studied under various classes of lubricants.

This paper describes the effect of factors on the strength characteristics of cement treated clay from laboratory tests performed on cement mixed clay specimens. It is considered that several factors such as soil type, sample preparing method, quantity of binder, curing time, etc. can have an effect on strength characteristics of cement stabilized clay. A series of unconfined compression tests have been performed on samples prepared with different conditions. The results indicated that soil type, mixing method, curing time, dry weight ratio of cement to clay (Aw), and water‐clay to cement (wc/c) ratio were main factors which can have an influence on unconfined compressive strength, modulus of elasticity, and failure strain of cement stabilized clay. Unconfined compressive strength of soil‐cement samples prepared from dry mixing method was higher than those prepared from wet mixing method.

7075-T6 is the most widespread structural aluminium alloy due to its high mechanical strength. However, use of this alloy in critical aeronautic, maritime, and automotive sectors is limited by the susceptibility of T6 treatment to cracking and pitting corrosion. To improve fatigue behaviour in aggressive environments, several authors have proposed the use of different coatings to protect the substrate. Studies have investigated the application of thin hard coatings on light alloys by physical vapour deposition (PVD). Different contributions of residual stresses, thermal modification of the substrate, and mechanical interaction between the coating and aluminium substrate were investigated. The purpose of this paper is to investigate the rotating bending fatigue behaviour (R=−1) of 7075-T6 PVD diamond-like carbon (DLC)-coated specimens in air and in a corrosive environment. Tests were conducted at different applied stresses. Scanning electron micrographs of the fracture surface are provided to investigate the influences of mechanical and environmental driving forces on the failure mechanism.

The paper conducted an experimental study of the fatigue resistance of DLC coatings on a 7075-T6 substrate for corrosion protection at long and short fatigue lives, which includes rotating bending fatigue tests, step-loading fatigue test procedure, tests in aggressive environment (methanol), tests at high and low fatigue lives, analysis of the fracture surface, and analysis of the driving forces.

Tests performed in air showed that the coating anticipates crack nucleation for high applied loads, whereas for lower loads, the difference among fatigue curves decreases. This result is very interesting from an industrial standpoint because the obtained material shows improved corrosion and wear resistance, without the fatigue resistance loss generally associated with hard coatings. The methanol environment accelerates crack nucleation and propagation, resulting in a sensible deterioration of the fatigue behaviour. A minimum soaking time seems to be necessary before the damaging effect of the environment begins. The coating has a certain protective effect against the environment, but this protection is insufficient for the specimen to achieve fatigue limits beyond those of the uncoated specimens. This deficiency can be related to small pores or defects in the coating, which allow contact between the substrate and the environment. Further tests are necessary to verify whether there exists a load under which the fatigue behaviour of the coated specimens is better than that of the uncoated specimens. Crack nucleation due to fatigue occurs close to the outer surface for all observed samples. For coated samples tested at the lowest stress level, crack nucleation seems to be located below the surface. This observation means that premature coating cracking, which characterises the nucleation mechanism at higher loads, did not occur at lower stress levels. The fracture surface of uncoated samples was clearly damaged by the aggressive solution, justifying the poor fatigue resistance.

The obtained data do not represent actual S-N curves, which would necessitate a larger number of tests with proper statistics. Nevertheless, some indications of the DLC effects on 7075-T6 specimens in air and methanol environments can be deduced. The step-loading technique seems to be critical for tests in corrosive environments, probably because the total soaking time in the corrosive environment is generally higher than it is for the single-run test.

The originality of the paper lies in the application of the step-loading test procedure to quickly detect the mechanical and chemical driving forces that control the damage and structural integrity of light alloys components in very aggressive environments.

Provide tribological information about the applicability of multi‐layer carbon‐chromium composite coatings to gears. Discuss the protection provided against scuffing failures, wear and the influence on gear power losses.

Several screening tests, such as Rockwell indentations, ball cratering, pin‐on‐disc and reciprocating wear tests, were performed in order to evaluate the adhesion to the substrate and the tribological performance of the carbon/chromium composite coating. Afterwards, twin‐disc tests were performed at high contact pressure and high slide‐to‐roll ratios to confirm the good adhesive and tribological properties of the coating under operating conditions similar to those found in gears. Gear tests were performed in the FZG machine in order to evaluate the anti‐scuffing performance of the carbon/chromium coating using additive free gear oils. Finally, the carbon/chromium composite coating was also applied to the gearing in a gearbox and its influence on the gearbox efficiency was analysed.

The C/Cr has got very good adhesion to the steel substrate, provides low friction coefficients between contacting solids in relative movement, gives excellent protection against scuffing and wear reduction in gears, and promotes a slight improvement of the gears efficiency.

The protection of this carbon/chromium coating against gear micro‐pitting should be investigated.

This study confirms the applicability of this coating to industrial gear applications, especially in two particular applications: severe applications involving high contact pressures and high sliding, frequent start‐ups and inefficient lubrication; and acting as tribo‐reactive material and substituting non‐biodegradable and toxic additives in environmental lubricants.

This work validates and quantifies the influence of this C/Cr multi‐layer composite coating in gear applications in terms of adhesion to the substrate, anti‐scuffing performance and efficiency.

There is currently a lack of research describing the best way to design learning environments for increasing numbers of children with autism. The purpose of this study was to determine the impact of classroom design on the learning and behaviour of pupils with severe autism. The research variables of interest were classroom layout; furniture, fittings and equipment (FFE); materials; colour scheme; wayfinding; lighting; acoustics; and security.

This study conducted a post-occupancy evaluation of classrooms for pupils with severe autism aged 3–19 in a school ten years after its completion. Data collection included a visual assessment of the building and an online survey to educators and administrators asking how satisfied they were that the research variables benefited pupils with severe autism.

Key findings were that zoned areas for different activities met students’ needs. Withdrawal rooms off the classroom, access to shared hygiene facilities and a secure outdoor area received high ratings. The main criticisms were the lack of robustness of FFE and the inability to control temperature. Results were collated into a table of recommendations for classroom design for severely autistic pupils.

The findings demonstrate classroom features that support the needs of pupils with severe autism, an area with limited prior research. Some findings support previous research and some adds new knowledge to our understanding of design for this population. The results provide empirical evidence for professionals involved in designing classrooms for pupils with severe autism.

The serious friction and wear problem occurs on the mechanical seal’s faces during the start-up stage of the high-speed turbopump for a liquid rocket engine. This paper aims to propose a kind of thick metal alloy coatings on the surface of the seal’s rotor so as reduce the friction and wear.

With the pin-disk (the graphite pin and the disk with the metal coating) tribology-tester, the tribological behaviors of four metal coatings are investigated. The special friction coefficients under the dry friction, boundary friction and different temperatures of water-lubricated conditions were obtained.

The test results show that the thick metal coating has a good performance of the wear resistance and friction reduction; and the friction coefficients of a Sn-Sb-Cu coating under the dry friction and water-lubricated conditions are 0.377 and 0.043, respectively, and the corresponding mass wear volumes are only 2.74 and 0.81 mg, respectively.

The thick metal coating scheme for the mechanical seal’s faces might lend itself to the harsh working conditions of the low-viscosity liquid rocket engine.

Achieving project objectives in constructionprojects such as time, cost and quality is a challenging task. Minimizing project cost often results in additional project duration and might jeopardize quality, and minimizing project duration often results in additional cost and might jeopardize quality. Also, increasing construction quality often results in additional cost and time. The purpose of this paper is to identify and analyze trade-offs among the project objectives of time, cost and quality.

The optimization model adopted a quantitative research method and is developed in two main steps formulation step that focuses on identifying model decision variables and formulating objective functions, and implementation step that executes the model computations using multi-objective optimization of Non-Dominated Sorting Genetic Algorithms to identify the aforementioned trade-offs, and codes the model using python. The model performance is verified and tested using a case study of construction project consisting of 20 activities.

The model was able to show practical and needed value for construction managers by identifying various trade-off solutions between the project objectives of time, cost and quality. For example, the model was able to identify the shortest project duration at 84 days while keeping cost under $440,000 and quality higher than 85 percent. However, with an additional budget of $20,000 (4.5 percent increase), the quality can be increased to 0.935 (8.5 percent improvement).

The present research work is limited to project objectives of time, cost and quality. Future expansion of the model will focus on additional project objectives such as safety and sustainability. Furthermore, new optimization models can be developed for construction projects with repetitive nature such as roads, tunnels and high rise buildings.

The present model advances existing research in planning construction projects efficiently and achieving important project objectives. On the practical side, the optimization model will support the construction industry by allowing construction managers to identify the highest quality to deliver a construction project within specified budget and duration, lowest cost for specified duration and quality or shortest duration for specified budget and quality.

The present model introduces new and innovative method of increasing working hours per day and number of working days per shift while analyzing labor working efficiency and overtime rate to identify optimal trade-offs among important project objectives of time, cost and quality.

This article deals with the problem of cost estimation for increased warranty time of a multi‐module product. The warranty policy of interest is two‐dimensional involving warranty limits on both age and usage of the product. Failure of the product is caused due to malfunctioning of its module(s). Warranty service is rendered through repair or replacement of the respective module(s). From the past data, it is observed that age and usage are highly correlated. Based on life (age) data, the joint life distribution of the modules is well described by multivariate exponential distribution of Marshall and Olkin. The same is utilized to estimate cost for desired warranty times by the method of simulation.