Increased Service Life Research Articles

Influence of the aging factor on the reliability of agricultural machinery

In the course of time a number of machine significant changes related to machine aging occur. The reasons for these changes are quite diverse. They are inevitable and irreversible in the time process of a gradual transition of the machine to a lower qualitative state. The article contains the data about the change in the indicators of no-failure and repairability of tractors (average restoration time) in the before-repair and between-repairs periods, which should be considered as a result of their aging. Data on the ratio of the lifetime of units and parts indicate the decisive role of the aging factor, but the lifetime can be strongly influenced by the assembly technology and the main thing - the run-in of parts. The degree of the aging of a machine can be estimated by reducing the lifetime of components, MTBF, machine productivity, etc., in the form of an aging factor, Kc. It shows how many times the lifetime of the part replaced in the machine is less than the nominal lifetime of the original part. The MTBF of the ageing machine is less than that of the new machine, or the labor input for the restoration of the old machine is greater than that of the new machine. By determining the aging rate of the parts to be replaced over the time interval under consideration, we constructed an aging function. The aging process of agricultural machinery was evaluated by the time and moment of resistance to unscrewing the uncoated threaded joints with a service life of 0.2 to 4 years. According to the obtained distribution functions, the average time increases with increasing service life, and the moment of resistance to unscrewing approaches the maximum values. With a service life of more than 4 years, the number of non-disassembled bolt connections, which break at the moment of unscrewing, increases, and the maintenance time also increases. The dynamics of the aging factors of threaded connections can be represented in the form of quadratic functions.

Research and development of the structures of highly loaded bunton dampers to decrease dynamic effects in the "vehicle–reinforcement" system

The authors study the horizontal loads arising from the movement of vehicles under the action of dissipative forces (torsion of ropes, aerodynamic forces, loading the vehicle with eccentricity in the frontal and lateral planes) which act on rope-profile guides (hereinafter referred to as RPGs or guides). The structures of damper buntons are developed that reduce vibrations by the interaction of guides with damper elements of buntons of various structures, which are located at the meeting point of vehicles and further along the shaft. The step of limiting buntons at the meeting point of vehicles in the middle part of the shaft has minimum value, and then the step increases stepwise and further remains constant. A kinematic connection of the RPG and the bunton in the form of a bunton leg and connecting inserts is developed, which allow the guide to move up and down and bend to a safe amount in the frontal and lateral directions; then the horizontal load is damped with the help of bunton dampers and the bunton structure. Console buntons, located along the shaft depth with a constant step, are equipped with dampers, which consist of rubber inserts with soft metal plates, assembled using bolted connections on a console bunton. At the meeting point of vehicles in the middle part of the shaft, the console bunton dampers have a more complex structure and consist of shock absorbe rs built into the box-shaped bunton which rod is built into the bunton leg, which moves in the guides and damps the load. Bunton dampers consist of a shock absorber and a built-in pneumatic cylinder and have a greater absorbing effect. The development of various structural solutions for buntons with dampers for different shaft sections and a kinematic connection for a bunton operation with rope-profile guides makes it possible to achieve: – high reliability during RPG operation; – increased service life due to a significant decrease in the level of dynamic effects; – reduced labor intensity of maintenance and operation, compared to rigid reinforcement; – reduced metal consumption compared to rigid reinforcement. Keywords: mine vertical shafts, rope-profile guides, console-damper buntons, pneumatic cylinder, shock absorbers, draft gears, frame buntons, horizontal forces in the frontal and lateral directions.

МНОГООПЕРАЦИОННЫЙ ПОЧВООБРАБАТЫВАЮЩИЙ АГРЕГАТ

The use of single-operation and double-operation soil-cultivating tools for main and pre-sowing tillage leads to an increase in agrotechnical terms and the production cost. To combine several operations and increase the economic efficiency of tillage, a multi-operation tillage unit has been developed. The proposed unit is designed in such a way that the working tools are fixed on the racks of the main frame and are located with an overlap on the rear frames. The working tool is a cultivator center hoe, under the wings of which there are slitters mounted on three plates with grooves, corresponding to the parameters of the center hoe wings. One slitter is fixed in the center of the center hoe, and two – on the sides under the wings. Removing the central slitter doubles the distance between the slitters. The authors decided to make a slitter in the form of an arbitrary trapezoid with sides having a different inclination angle to the horizontal surface. It has been experimentally established that the optimal ratio of the frontal area of the slitter to its height is 1:10. The soil-cultivating working tool with the changing angle of its location by 180° and the changing curvature of the cutting edge of the working surface of the slitter can be used in different soil conditions and features the increased service life. It is recommended that pre-sowing cultivation be carried out to a depth of 10 cm. Performing four operations in one cycle by a tillage device: slitting, surface tillage with weed control, the final phase of tillage and surface compaction – ensure the increased economic efficiency of the entire process.

Advancing cement-based materials design through data science approaches

The massive scale of concrete construction constrains the raw materials’ feedstocks that can be considered – requiring both universal abundance but also economical and energy-efficient processing. While significant improvements– from more efficient cement and concrete production to increased service life – have been realized over the past decades through traditional research paradigms, non-incremental innovations are necessary now to meet increasingly urgent needs, at a time when innovations in materials create even greater complexity. Data science is revolutionizing the rate of discovery and accelerating the rate of innovation for material systems. This review addresses machine learning and other data analytical techniques which utilize various forms of variable representation for cementitious systems. These techniques include those guided by physicochemical and cheminformatics approaches to chemical admixture design, use of materials informatics to develop process-structure-property linkages for quantifying increased service life, and change-point detection for assessing pozzolanicity in candidate supplementary cementitious materials (SCMs). These latent variables, coupled with approaches to dimensionality reduction driven both algorithmically as well as through domain knowledge, provide robust feature representation for cement-based materials and allow for more accurate models and greater generalization capability, resulting in a powerful design tool for infrastructure materials.

Failure Analysis of Wire Ropes Used in Multi-Wire Machines for Cutting Blocks of Stone

ABSTRACT: This paper reports the analyses carried out with the company Pedrini SpA ad unico socio, located in Carobbio degli Angeli, Bergamo (IT). Wire ropes with diamond beads, used as cutting tools in multi-wire machines for cutting blocks of stone, were considered and a failure analysis of the wire ropes was carried out. The aim of the paper is to highlight the damage mechanisms of the wire ropes to increase service life of these cutting tools. Microscope observations and the penetrating liquids method were used to analyze the damaged wire ropes. Fatigue, corrosion and contact fatigue problems were observed and the effect of the centering of the beads on the wire rope was studied.

Dimensional effect when measuring Martens hardness

One of the most common methods of non-destructive testing, hardness testing, is used to evaluate the properties of materials. This is due to the ease of measurement and testing of the finished part, which will be used in the future, high productivity of the method, the ability to assess other mechanical properties of the material: elasticity, creep, tensile strength. An important aspect in the study of the hardness using in the range the Berkovich and Vickers indenters, which are more consistent with non-destructive testing, while the methods of Brinell and Rockwell leave quite large deformations, in our opinion, which further promote the development of structural defects and reduce the service life, which are not acceptable in critical products. Due to the improvement of product manufacturability, more and more manufacturers are trying to minimize the size of the part, while increasing their performance by applying a reinforced layer, which, in turn, should seek to reduce the thickness with increased service life. It is also impossible to study the hardness of very small products in the micro range due to the large mismatch between the dimensions of the product under test and the test method. In our opinion, the study of hardness by the Berkovich method in comparison with the Vickers method is more expedient for use with the same physicochemical properties of the material because of a larger scatter of hardness values between the compared methods, although they should be almost the same, with a small difference. An important omission to a certain year was the dimensional effect. Goal. The aim of the study is to assess the nature of the change in hardness with increasing load on the indenter, using the functional dependence of the hardness on the depth of the indenter. For this purpose, it is necessary to establish such connection for an indenter of various geometry. In this regard, we consider it appropriate to check the validity of the Meyer equation, which relates the load to the size of the imprint, for different indenters and materials. Results. When the hardness is calculated according to the Martens scales, the Vickers and Berkovich indenters are applied to the function of the surface area of the working part of the tip. An important factor of the consistency of the results in the increase in hardness is the small effect. The reasons for this can be very negligible. The sizeable effect is significantly infused into the results of increasing hardness, changing from 2,5 to 3,0 folds.

Effect of high-voltage spark discharges on reduction of the concentration of total bacterial count in wastewater

The limited supply of fresh water on the planet stimulates the reuse of wastewater in various areas. It is proposed to use disinfected wastewater for irrigation in agriculture. The possibility of reducing the total bacterial count in wastewater by high-voltage spark discharges using a developed experimental setup has been investigated. The total bacterial count was measured by the rapid method using a luminometric mini-laboratory EnSURE Touch and a standard method for counting bacteria, capable of forming colony-forming units on nutrient agar. Wastewater from the Zhulebinsky storm collector with an initial concentration of 1012 CFU ml−1 with a volume of 103 ml is disinfected up to the norm 6 log in 120 s with capacitance 0.1 μF and in 180 s with capacitance 0.05 μF. Wastewater from the Kuryanovsky storm channel with an initial concentration of 109 CFU ml−1 with a volume of 103 ml is disinfected up to the norm 6 log in 100 s with capacitance 0.1 μF and in 160 s with capacitance 0.05 μF. To reduce the concentration of total bacterial count by 1 log, the minimum duration of disinfection of 103 ml of wastewater it took about 30 s at a discharge energy of 5 J ml−1. The advantages of bacterial inactivation in wastewater by high-voltage spark discharges were revealed, such as low operating voltage of 10 kV, high energy efficiency of 600 J l−1 and capacity 30 l h−1, increased service life and operational reliability, portability and environmental friendliness.

Destruction of polymer insulation and threshold amplitudes of current pulses of different temporal shapes for electric wires and cables in the low- and high-current circuits of pulse power engineering, electrical engineering and electronic devices

Goal. Development of engineering method for settlement of threshold amplitudes Impk of single-pulse current ip(t) of different temporal shapes for electric wires and cables with polyethylene (PET), polyvinylchloride (PVC) and rubber (R) half-length insulation, used in modern pulsed power engineering, electrical engineering and electronics in their low- and high-current circuits. Methodology. Basis of the theoretical and applied electrical engineering, electrical power engineering, electrophysics bases of technique of high-voltage and large pulsed currents, bases of low- and high-current electronics, measuring technique, electromagnetic compatibility and standardization. Results. Development of engineering method is executed on close calculation determination of threshold amplitudes Impk of single-pulse axial-flow current ip(t) of different temporal shapes for electric wires and cables with copper (aluminum) current-carrying parts and PET, PVC and R half-length insulation, used in the ow- and high-current circuits of pulsed electrical power engineering, electrical engineering and electronics. Electrothermal resistibility of half-length insulation of the examined cable and wire products (CWP), proper maximum to the possible temperatures of heating of current-carrying and insulating parts of the probed wires and cables and shutting out the offensive of the phenomenon destruction in the indicated insulation of CWP, was fixed based on this method. Calculation analytical correlations are obtained for finding in probed CWP of threshold numeral values of Impk amplitudes of pulses of current ip(t), time-varying both on aperiodic dependence of type τf/τp with duration of their front τf and duration of their pulses τp and by law of exponential attenuation sinewave. It is shown that at Imp>Impk destruction of their half-length insulation, resulting in the decline of service life of CWP, will come from the thermal overheat of current-carrying parts of the examined electric wires and cables. The examples of practical application of the offered method are resulted upon settlement for a radiofrequency coaxial cable RC 50-4-11 with middle sizes is easily soiled with continuous PET insulation of threshold amplitudes of Impk of standard aperiodic pulses of current ip(t) from nano-, micro- and millisecond temporal ranges of shape of τf/τp=5 ns/200 ns, τf/τp=10 μs/350 μs and τf/τp=7 ms/160 ms. It is shown that with the proper growth of parameter τp>>τf for flow on a continuous copper tendon and split copper shell of radiofrequency coaxial cable RC 50-4-11 with middle sizes is easily soiled indicated homopolar pulses of current ip(t) substantial diminishing of their threshold amplitudes of Impk (with 531,2 кА for the nanosecond pulse of current of type 5 ns/200 ns to 1.84 кА for the millisecond impulse of current of type of 7 ms/160 ms takes place). Originality. An engineering method is first developed for close settlement of threshold numeral values of Impk amplitudes of single-pulse axial-flow current ip(t) of arbitrary peak-temporal parameters for electric wires and cables with copper (aluminum) current-carrying parts and PET, PVC and R half-length insulation. Practical value. Application in electrical engineering practice of the offered engineering method for determination of threshold amplitudes Impk of the indicated pulses of axial-flow current ip(t) for the probed electric wires and cables will allow considerably to increase service life of examined CWP.

Novel technique for the retrofitting and refurbishment of a damaged offshore quay: a case study application

ABSTRACT A number of unpredictable accidents have taken place in some ports, as a result of unexpected manoeuvring circumstances inside the port basin at the front of the quays. This study presents novel technique for rehabilitating damaged quays constructed with sheet piles’ drum-type cells. The novel approach demonstrates how to separate the vertical and horizontal loads acting on the cell using numerical solution software, which gives the structure more reliability and durability and increases service life of the structure. The case study accident occurred in container terminal No. 4 of the Damietta port in 1993, and the cell was extremely damaged. Through this study, the authors introduce various design procedures, monitoring systems and evaluation methodologies using the numerical solution model. The case study results and feasibility assessment prove the effectiveness of the proposed solution and the validity of applying this novel technique to other similar cases instead of constructing a new structure at higher costs.

Semi-active control of jacket platforms under wave loads considering fluid-structure interaction

Jacket platforms are among the most used offshore platforms for energy extraction from seabed and are prone to failure caused by the inherent dynamic nature of wave loads. Therefore, vibration control of these structures with the goal of enhancing efficiency and preventing structural damage is of outmost importance. In current work, semi-active control of the Ressalat jacket platform using a large-scale magnetorheological (MR) damper with fuzzy logic controller is investigated with the aid of the computationally efficient modified endurance wave analysis (MEWA), considering waves with return periods of 2, 5, 10, 20, 50 and 100 years. The effect of number of dampers, fluid-structure interaction, added mass effects and actuator saturation has been simultaneously implemented in the current study. A total of six performance indices based on maximum and root mean square (RMS) of responses (inter-story displacement, velocity and acceleration) are used to assess the efficiency of the control method for waves with different intensities and return periods. Results of current analyses provide a comprehensive overview of the performance of the MR damper for the semi-active control of the Ressalat jacket platform under different wave loads with different return periods and show an acceptable performance for all the considered wave loads, with the goal of enhanced safety and increased service life.

The Operational Technique of Increasing Service Life Time of the Major Components of the Fighter Aircraft Engine Rotors

Abstract The operational technique for the major components of the fighter aircraft engine rotors has been introduced basing on the real conditions of their cyclic loading in each flight or ground test and a priori information on their previous operation. It has been confirmed that the obtained technical solutions not only conform to the current methods of accounting for the depletion of the life cycle of the Afterburning Turbofan Engine (ATE) but also introduce additional opportunities to consider individual characteristics and conditions of their cyclic loading throughout the overall operating time. A method for estimating the depletion of the life cycle in accordance with the Total Accumulated Cycle (TAC) has been proposed. It allows us to compare the actual operating time of the ATE in hours and the accumulated value of cyclic damage to the engine and its major components (within the TAC parameter) during the previous operation.

Metabolism of bioactive compounds and antioxidant activity in bananas during ripening

The study aimed to characterize bananas in their different stages of ripeness, to determine the variables that demonstrate higher levels at each moment. The fruits were analyzed according to physical parameters: weight, texture, and diameter of the fruits; as well as physicochemical parameters: pH, titratable acidity, soluble solids, and Ratio; and also biochemical parameters: total sugars, phenolic compounds, ascorbic acid, pigments, antioxidant activity by DPPH and FRAP methods. The used samples were collected at the following maturation stages: 2, 4, 6, and 7 and determined according to the Von Loesecke Maturation Scale. In relation to the behavior of the parameters evaluated, the fruits showed significant reductions in relation to the physical parameters, while there were increases in relation to pH, titratable acidity, and soluble solids. The antioxidant and phenolic activities also showed reductions, which shows that the degradative process caused by ripening also causes reductions in these compounds. Novelty impact statement The main parameters and metabolites evaluated in the present study showed optimum values at the stages in which the consumption of fresh fruits is recommended. As the banana is a climacteric fruit, the obtained results showed interesting correlations, with emphasis on the physical parameters, which showed a reduction during ripening, and the physicochemical parameters, that increased, displaying a negative correlation between these groups. It becomes necessary to understand the physiology of the fruit, with emphasis, such as it has been done in this work, on the reactions of synthesis and degradation of primary and secondary metabolites in the ripening and senescence of the fruits, as well as their correlations between the evaluated parameters. Such study is necessary to have an understanding of the regulatory process and possible manipulation of the fruit, to increase service life and reduce losses.

Method of continuous non-destructive observation of profiles made of polymer fibre composite materials for the registration of crack formation

The relevance of the study is conditioned by the absence of the necessary devices and structures made of composite materials such as stingers with holes for registering cracks. The purpose of the study is to develop the design and manufacturing technology of stringer-type profiles made of composite materials with micro-holes in the cross-section or inside which hollow polymer fibres are laid, while the holes did not significantly affect the strength of the product and the specified strength properties of the product are preserved. The task of manufacturing products from a polymer composite material is solved by a method that includes pre-laying hollow longitudinal fibres or introducing bundles coated with anti-adhesive lubricant at specified cross-section points of stringers with subsequent pressing when laying pre-cut layers of composite material in a mould (polymerisation of the binder). After cooling, decompressing, removing the bundles with anti-adhesive grease (the second option) and stripping the product, special sensors are installed, a vacuum is created inside the holes or pressure is applied within 0.1-0.2 atm. At the same time, the holes do not significantly affect the strength of the product and the specified properties of the product are preserved. The study suggests a method for continuous and autonomous monitoring of the integrity of profiles made of polymer fibre composite materials for registering the formation of cracks based on the introduction of longitudinal micro-holes or hollow fibres under pressure or vacuum into their structure, followed by recording changes in the pressure value. The advantage of the proposed method is that it allows making a product from composite materials with increased physical and mechanical properties, increasing operational safety, increasing service life, and reducing the cost of routine inspections due to continuous monitoring of the occurrence and development of damage in real time. At the same time, the reliability of the design significantly increases, which leads to an improvement in the quality of the product

Increasing Service Life of a Railway Wheel with Surface Hardening Technology

The article presents surface hardening technology as applied to solid-rolled wheels of rolling stock. The obtained results of the theoretical study on the process of strengthening the metal of the wheel will make it possible to develop scientifically grounded technological and technical solutions to prevent formation and development of defects on the rolling surface, as well as to eliminate them during maintenance.The objective of this work is to identify the optimal method for surface hardening of a railway wheel with defects.At present, the issue of extending service life of elements and critical parts of rolling stock is becoming increasingly acute. Due to the limited economic feasibility and limited availability of existing production technologies, it becomes necessary to create a new material modified with nanoclusters and hardened with surfactants.Nanoclusters have high plasticity and hardness values. To determine the hardness value of nanomaterials, the Vickers hardness test method is used, in which hardness is determined by the size of the area of the indentation after removing the load from the pyramid shaped diamond.Superplasticity is observed in nanostructures. For nickel and nickel-aluminium alloy NiAl3, low-temperature superplasticity is observed in the temperature range 450–470°C, which is three times lower than their melting point.

Evaluation of increasing service life of epoxy zinc-rich coating on 3 wt.% Ni-advanced low-alloy steel in marine atmospheric environment

Evaluation of increasing service life of epoxy zinc-rich coating on 3 wt.% Ni-advanced low-alloy steel in marine atmospheric environment

Study of Corrosion and Mechanical Resistance of Structural Pipe Steels of Long-Term Operation in Hydrogen Sulfur Containing Environments

Analysis of literature sources, as well as practical data indicate that the existing scientific, technical and technological developments to ensure reliable corrosion-mechanical resistance and durability of oil and gas pipelines and other shell metal structures of critical use and subordinate to the State Service for Mining Supervision and Industrial Safety of Ukraine largely find contradictions and uncertainty; there are no quantitatively substantiated recommendations for practical application in order to ensure corrosion and mechanical resistance of pipelines operating in technologically aggressive environments under alternating temperature and barometric conditions and loads; there is a need for a systematic study of the causes, conditions and mechanisms of corrosion and mechanical damage of long-term equipment, which will significantly increase the operational reliability of industrial equipment. Experimental studies have established the causes and substantiated the mechanisms of metal softening with increasing service life (from 0 to 25 years) that leads to its degradation, especially during long-term operation in corrosive environments. A method for forecasting the residual working (accident-free) life of pipeline metal structures has been developed, which makes it possible to purposefully regulate their operational condition. This allows the timely use of technical, design and technological measures to improve the performance of such structures. Numerous and diverse results of experimental tests of metal samples for various purposes have been obtained, which provide an opportunity to create a base for comparative analysis of steels in many parameters of crack resistance, which will become a reliable basis for scientific and practical substantiation of the equivalent replacement of some steel grades with other grades, taking into account technological loads, corrosive environments and others.

Understanding the influence of anti‐reversion agent and metal oxide dose on natural rubber–carbon black system

AbstractSulfidic linkages that are formed during the vulcanization process of natural rubber (NR) are unstable at a higher temperature and can be reversed into conjugated diene. To overcome such issue and to build a compound that is hostile to inversion and with increasing service life, anti‐reversion agent (ARA), for example, N,N′‐4,4′‐diphenylmethyene bismaleimide (BMDM), is added into the formulation. This work explains the conjugation reaction mechanism of conjugated diene and BMDM by means of gas chromatography–mass spectrometry and Fourier transform infrared spectroscopy. The first phase of this study is associated with the change in ARA dosage keeping ZnO dosage the same. It is observed that 5 phr of BMDM and 2 phr ZnO combination (ARA4) shows lowest reversion at 160°C. The modulus value at 300% elongation increased 12% by the incorporation of BMDM as compared to the compound of no BMDM (ARA1). The second part is all about keeping BMDM dosage the same at 5 phr level and varying ZnO phr by 3, 4, and 5. From the overall results, it is observed that at a suitable dosage of BMDM and ZnO (5 phr BMDM and 3 phr ZnO combination [ARA5]), least reversion can be achieved and vulcanizates containing optimized BMDM and ZnO show better retention properties after aerobic aging as compared to ARA1.

Advanced power transformer with improved parameters for rural electrical networks

The problem of power quality supply is relevant for rural electrical networks, due to long distance and branching, as well as connection of a large number of single-phase and non-linear loads. Asymmetry of electrical loads causes voltage asymmetry, which adversely affects the operation of all elements of the electrical system, causing additional power losses, reducing the service life of electrical equipment and its economic performance, as well as reliability of operation of individual electrical equipment and power supply system as a whole. Reduction of voltage asymmetry can be ensured by rational construction of electrical network circuit and use of special correcting devices. The authors consider it reasonable to use relatively simple and reliable by design and inexpensive power transformers with a “star - double zigzag with a zero wire” (Y/2Zн) winding connection circuit with a neutral winding connection group. The paper deals with design and processes of converting electrical energy in a transformer. It has been proved that phase EMF of the secondary winding coincides in phase with the same EMF of the primary winding, i.e. the proposed circuit has a neutral windings’ connection group. Results of theoretical studies of transformer operation with an asymmetric and non-linear load are presented. Decrease in voltage asymmetry is due to the neutral sequence components compensation. Decrease of the higher harmonic voltage components level occurs due to the compensation of the higher harmonics multiplied three times. It is theoretically substantiated that transformer will not emit higher harmonic components of zero sequence voltages into the supply network. Experimental studies have confirmed the theoretical conclusions that a transformer with Y/2Zн winding connection circuit allows obtaining the highest level of voltage symmetry with an asymmetric load. In single-phase load mode, the values of voltage unbalance factor in reverse sequence do not exceed 1.7 %, in neutral sequence - 2.9 %. The transformer allows obtaining 1.2-1.5 times lower value of total harmonic components factor at non-linear load, which is the best result among circuits studied. This power transformer is resistant to load effects that distort voltage quality and is capable to provide a high level of symmetry and sinusoidal voltage as well as parallel operation with commercially available transformers. This makes it possible to use it in rural electrical networks to reduce power losses, increase service life and efficiency of electrical equipment, and increase reliability of the power supply system.

Increasing Service Life and System Efficiency of Parallel Pumps Using Combined Pump Regulation

The paper discusses the use of the combined control for a system of two parallel pumps to increase its service life. Using the combined control, the pumping system is controlled together by change the speed, throttling, and bypass. The power consumption of the pumping system is calculated for three methods of flow control: with minimum energy consumption, with maximum reliability, and control with a trade-off between efficiency and reliability. In the case of control with maximum reliability, the energy consumption of the pumping system is higher than in the case of control with minimum energy consumption by 29.2%. In the case of the proposed trade-off control, which provides acceptable reliability, the power consumption is higher than with the minimum energy consumption control by only 7.3%.

Amorphous Carbon Coatings for Total Knee Replacements-Part I: Deposition, Cytocompatibility, Chemical and Mechanical Properties.

Diamond-like carbon (DLC) coatings have the potential to reduce implant wear and thus to contribute to avoiding premature failure and increase service life of total knee replacements (TKAs). This two-part study addresses the development of such coatings for ultrahigh molecular weight polyethylene (UHMWPE) tibial inlays as well as cobalt–chromium–molybdenum (CoCr) and titanium (Ti64) alloy femoral components. While a detailed characterization of the tribological behavior is the subject of part II, part I focusses on the deposition of pure (a-C:H) and tungsten-doped hydrogen-containing amorphous carbon coatings (a-C:H:W) and the detailed characterization of their chemical, cytological, mechanical and adhesion behavior. The coatings are fabricated by physical vapor deposition (PVD) and display typical DLC morphology and composition, as verified by focused ion beam scanning electron microscopy and Raman spectroscopy. Their roughness is higher than that of the plain substrates. Initial screening with contact angle and surface tension as well as in vitro testing by indirect and direct application indicate favorable cytocompatibility. The DLC coatings feature excellent mechanical properties with a substantial enhancement of indentation hardness and elastic modulus ratios. The adhesion of the coatings as determined in modified scratch tests can be considered as sufficient for the use in TKAs.