Macroscopic pitting is a common gear flank failure mode. The determination of pitting life is done experimentally and the formation of macropit is typically followed by regular visual inspections and ...photographing of tooth flanks, which is time consuming and gives limited information about progression of failure. In this study, the progression of gear macropitting was detected with on-line particle monitoring from lubricating oil together with vibration monitoring and visual inspections. The tests were carried out with case-hardened gears under heavy loading condition. The results show that the concentration of metallic particles in oil correlate well with the severity of macropitting obtained from the visual inspection. Vibration acceleration descriptors indicating peaked signal correlate also with the wear of gear contact.
•Pitting tests with FZG gears were carried out.•Visually seen pitting was compared with particle and vibration monitoring results.•Progression of pitting was detected successfully with on-line particle monitoring.•Vibration acceleration descriptors can be related to wear of gear contact.
A large-scale fatigue testing machine based on the rotating beam method in a four-point bending configuration was designed and built. With the device, high-strength metal specimens with a 32-mm gauge ...diameter and a 100-mm gauge length can be tested at a cyclic frequency of up to 48 Hz. In this work, particular attention was paid to evaluating the spatial and temporal uniformity of the loading within the large specimen; methods for quantitative evaluation of these effects were developed. The developed test methodology allows for the fatigue testing of specimens with size, microstructure, and surface conditions that are similar to actual machine parts.
A simulation method to predict the reliability of clamped metal contacts under cyclic loading is presented. The main idea is to predict the development of contact condition of a joint by simulating a ...spatially variable coefficient of friction (COF) and wear. Frictional energy dissipation drives the COF evolution rule, and classic Archard's equation is employed as the evolution rule for wear depth. As both the COF and wear evolution are considered, the presented approach is capable of predicting changes in the contact condition over time. The approach is based on the Finite Element Method (FEM) and is generally applicable to industrial cases. The method is implemented as a subroutine to a FEM solver Abaqus to define a contact formulation in both normal and tangential directions. The subroutine allows full coupling between normal and tangential contact variables, which makes the approach robust also in complex industrial applications. As the effect of wear is described in the contact pressure calculation, there is no need for mesh modification. The presented approach was validated by simulating cylinder-on-plane configuration. The presented method provides similar results obtained with a simulation where geometry is updated due to wear. The results of the case study were qualitatively verified against a bolted joint type fretting experiment. The area of slip after stabilized COF distribution corresponds well with the experimental fretting scars. However, Archard's wear law seems to be limited, at least in partial slip cases, as it overestimates the amount of wear without considering entrapment of wear debris in the contact. A case study of medium speed combustion engine component is presented to show how the simulation method can be used in engine development to ensure reliable contact interfaces.
•Novel local coefficient of friction and wear simulation methodology for finite element method.•A new approach to simulate changing contact condition.•Surface damage criterion for fretting damage is introduced.•Method is applicable to real industrial size problems.
Running experiments with full-size gearboxes from the actual application has the advantage of giving realistic results in terms of power losses. The drawback is extensive costs, lengthy testing, and ...the difficulty in differentiating between load dependent and load independent losses, and which losses are coming from the gears, seals, bearings or synchronizers. In this work, the correlation between friction measurements conducted in a ball-on-disc machine and friction measurements conducted in a back-to-back gear rig is investigated. The correlation between the gear tests and the ball-on-disc tests was reasonably good in terms of absolute values, and the shape of the friction curves was similar, indicating that the ball-on-disc measurements to a large extent are capturing the behavior of the gear contact.
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•Friction is measured with three oils in a gear test rig, and in a ball-on-disc rig.•Test conditions in both rigs are as similar as possible.•The ranking of the three oils is the same in both rigs at both temperatures.•Ball-on-disc tests could be used as a cheaper alternative to gear tests.•Friction mapping gives information of several arbitrary gears in one test.
Leaded tin bronze alloys are widely used in heavy machinery bearings operating in boundary and mixed lubrication regions due to the excellent dry lubrication properties of lead. However, restrictions ...on the use of lead have created an increasing demand for lead-free or low-lead bearing materials. In the present study, suitability of a novel bismuth bronze bimetal material for possible substitution of leaded tin bronze was studied with a special thrust bearing test device, which simulates the contact conditions in the main thrust bearing of mineral crushers. The oil-lubricated test bearings have a flat-on-flat type contact with oil grooves and a constant eccentric motion against a case hardened steel counter plate under a periodically increased axial pressure. The test was continued until a sudden rise in friction, which indicates bearing failure and risk of an imminent seizure. The bismuth bronze showed a load capacity of the same level with the reference material, continuously cast CuSn10Pb10. Characterization by electron microscopy showed that the dry-lubricating bismuth precipitations had a fine grain size and an even distribution, which explains the good load carrying capacity. It was concluded that the bismuth bronze has potential for substituting the leaded tin bronzes in the studied operating conditions.
•Thrust bearing performance and structure of a bimetal bismuth bronze was studied.•The bimetal shows equal bearing load capacity to the reference bronze CuSn10Pb10.•The bimetal bismuth bronze shows an even distribution of fine bismuth precipitations.•The fine distribution of dry-lubricating bismuth enables the good load capacity.•The bismuth bimetal shows potential for substituting leaded tin bronzes in bearings.
A severe oxygen deficit induced a fish kill in the eutrophicated two-basin Lake Äimäjärvi in southern Finland during winter 2002–2003, resulting in cascading effects on the lower trophic levels of ...the lake. Pikeperch disappeared from the lake and bleak and white bream decreased to low numbers. The recovery of the populations of other species started immediately when strong year-classes of roach and perch appeared in summer 2003 and onwards. A sharp increase in the growth of perch and roach was recorded, and perch became the dominant fish species during 2004–2006. Consequent responses after the fish kill included increased Secchi depth, expansion of submerged macrophytes, decreased nutrient concentrations and reduction of Cyanophyta from the more eutrophic northern basin of the lake, and a temporary increase in the size of
Daphnia
in the early summer 2003. However, the ecosystem of the lake returned gradually to the earlier structure and level of eutrophication. Bluegreen algae have returned since 2005, the water has become more turbid, macrophytes declined in 2007 and the fish community was again dominated by small cyprinid fishes in 2008.
One of the most common challenges in gear drive design is to determine the best combination of gear geometry parameters. These parameters should be capable of being varied effectively and related to ...gear mesh stiffness variation in advanced excitation and vibration analysis. Accurate prediction of gear mesh stiffness and transmission error requires an efficient numerical method. The parameterized numerical model was developed for the evaluation of excitation induced by mesh stiffness variation for helical gear design purposes. The model uses linear finite-element (FE) method to calculate tooth deflections, including tooth foundation flexibility. The model combines Hertzian contact analysis with structural analysis to avoid large FE meshes. Thus, mesh stiffness variation was obtained in the time and frequency domains, which gives flexibility if comparison is made with measured spectrums. Calculations showed that a fairly low number of elements suffice for the estimation of mesh stiffness variation. A reasonable compromise was achieved between design trends and calculation time.
Heavy steel plates are used in demanding applications that require both high strength and hardness. An important step in the production of such components is cutting the plates with a cost-effective ...thermal cutting method such as flame cutting. Flame cutting is performed with a controlled flame and oxygen jet, which burns the steel and forms a cutting edge. However, the thermal cutting of heavy steel plates causes several problems. A heat-affected zone (HAZ) is generated at the cut edge due to the steep temperature gradient. Consequently, volume changes, hardness variations, and microstructural changes occur in the HAZ. In addition, residual stresses are formed at the cut edge during the process. In the worst case, unsuitable flame cutting practices generate cracks at the cut edge. The flame cutting of thick steel plate was modeled using the commercial finite element software ABAQUS. The results of modeling were verified by X-ray diffraction-based residual stress measurements and microstructural analysis. The model provides several outcomes, such as obtaining more information related to the formation of residual stresses and the temperature history during the flame cutting process. In addition, an extensive series of flame cut samples was designed with the assistance of the model.
Phenotypic and molecular methods were used to identify and compare the strain composition of three industrial dairy starters used for the manufacture of viili. Preliminary differentiation was made by ...phenotypic methods. Genotypic differentiation was carried out using polymerase chain reaction (PCR) and further characterization at strain level by pulsed-field gel electrophoresis (PFGE). The isolates could be assigned as acid-producing Lactococcus lactis strains of both lactis and cremoris subspecies, and aroma producers, identified as L. lactis subsp. lactis biovar diacetylactis and Leuconostoc mesenteroides. PCR analysis discriminated between the lactococcal subspecies, and cluster analysis of the digestion patterns of PFGE analysis revealed different genotypes in each subspecies. Each Leuconostoc-genotype seemed to be specific to only a single starter mix. The work proved that in addition to L. lactis subsp. lactis biovar diacetylactis and Leuc. mesenteroides subsp. cremoris, commercial viili starters of traditional origin may contain (i) only L. lactis subsp. cremoris, (ii) both L. lactis subsp. cremoris and L. lactis subsp. lactis as a minority, and - as a new discovery - (iii) only L. lactis subsp. lactis. The results obtained give an overview of the microbial population of viili starters and can be exploited in the development of optimized starter cultures for industrial-scale manufacture of viili.
A numerical model for the calculation of fretting fatigue crack initiation is presented and compared with experiments. The model is focused on smooth sphere-on-plane contact in partial and gross slip ...conditions. It is based on Hamilton’s explicit stress equations and the multi-axial Dang Van and Findley fatigue criteria enhanced with a statistical size factor concept. Promising correlation was found between the model and the experimental results with quenched and tempered steel 34CrNiMo6. The model assumptions, limitations and general application are also discussed.
► Promising correlation was found between the model and the experimental results. ► The statistical size factor related to Findley fatigue criteria is of the order of 1.2–1.3. ► The highest friction coefficient and tangential force values at the beginning of the test dominate crack initiation. ►A higher tangential force is needed for cracking at high normal force levels than at a low normal force level.
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