1,721,415 research outputs found
Disc machine testing to assess the life of surface-damaged railway track
No full textWheel-rail contacts operate in an arduous and contaminated environment. Railway track running surfaces can become damaged either prior to or during operation. This work is aimed at understanding how that surface damage can affect the life of railway track. Pre-damaged surfaces and track damaged by the entrainment of solid contaminants are considered under both oil and water lubrication. A series of small-scale laboratory experiments has been carried out on a twin-disc rolling-sliding test machine. The test discs are artificially indented and run under typical wheel-rail contact conditions. The experimental results revealed that artificial dents only reduce the fatigue life of the contact under oil, but not water lubrication. With oil lubrication the fatigue failure initiates close to the location of the surface defect. However, with water as the lubricant the whole of the surface undergoes cracking with the defect having no preferential effect. Studies have also been carried out to investigate the damage caused by the entrainment of solid particles into the wheel-rail contact. This kind of damage can accelerate surface fatigue and also lead to excessive wear. An attempt has been made to quantify the wear process and develop a simple empirical model
Influence of grain structure and slip planarity on fatigue crack growth in low alloying artificially aged 2xxx aluminium alloys
Full text linkThe fatigue crack growth behaviour under constant amplitude loading of three low alloying artificially aged 2xxx aluminium alloys with distinct microstructures is analysed. Fatigue crack growth tests show a correlation between fatigue performance and the occurrence of crack closure. Fractography and fracture surface measurements show that rougher surfaces give higher closure levels suggesting a dominating influence of RICC in these alloys. The relationship between the crack path and the microstructure, i.e. grain structure and slip planarity, is assessed semi-quantitatively. A criterion to evaluate the propensity for slip band formation is derived and reasonable correlation is found between the fatigue fracture behaviour of the three alloys and this criterion. <br/
An effective method to investigate short crack growth behaviour by reverse bending testing
No full textA reverse bending rig has the advantage of relatively cheap construction compared with servo-controlled machines, and its robustness and reliability make it ideally suited to long-term testing programmes. In this paper, the details of the mechanical mechanism of a bending rig, the methods of its strain measurement and stress-strain analysis have been presented. A series of tests has been carried out to investigate short crack growth behaviour of AISI type 316 stainless steel under creep-fatigue conditions at 550C. The advantage of this type of test allows a comparison to be made, on one specimen, of the influence of both tensile and compressive hold periods on crack growth behaviour. It has been shown that predominantly intergranular long cracks form on the tensile side and transgranular short cracks on the compressive side and these are a prominent feature between 0.9 – 2.5% strain range
The effects of surface defects on the fatigue of water and oil lubricated contacts
Full text linkA study into effects of surface defects on the rolling contact fatigue of brass and rail steel has been undertaken on a twin-disc rolling-sliding test machine with both oil and water lubrication. Furrows and dents were artificially introduced into the disc surfaces, and surface microcracks and pits were monitored by means of surface replication. The results showed that artificial dents only reduce the fatigue life of the contact with oil, but not water lubrication. With oil lubrication the fatigue failure initiates at the surface defect. However, with water as a lubricant the whole of the surface undergoes cracking with the defect having no preferential effect. The possible mechanisms behind this behaviour are discussed in this pape
Application of uniform design in optimisation of three stage ageing of Al-Cu-Mg alloys
No full textThe hardness variations and precipitation behaviour during the three stage ageing of three Al-Cu-Mg alloys were investigated using micro-hardness testing and differential scanning calorimetry (DSC). To facilitate the determination of an optimised heat treatment, a uniform design method was employed by which the influences of three stage interrupted ageing on the hardness and precipitation can be elucidated with a limited number of experiments. It is found that optimised heat treatment with maximum hardness can be achieved for non-stretched materials by applying the method of three stage ageing, but there is no obvious effect for stretched T351 materials. A long initial Stage I and a suitable Stage II ageing time are beneficial for hardness, and the Stage II ageing at 25C shows more beneficial effect than ageing at 65C. The hardness increase in Stage I and Stage III ageing is closely related to the S phase content
Predicting grain refinement by cold severe plastic deformation in alloys using volume average dislocation generation
No full textThe grain refinement during severe plastic deformation (SPD) is predicted using volume averaged amount of dislocations generated. The model incorporates a new expansion of a model for hardening in the parabolic hardening regime, in which the work hardening depends on the effective dislocation free path related to the presence of non shearable particles and solute-solute nearest neighbour interactions. These two mechanisms give rise to dislocation multiplication in the form of generation of geometrically necessary dislocations and dislocations induced by local bond energies. The model predicts the volume averaged amount of dislocations generated and considers that they distribute to create cell walls and move to existing cell walls/grain boundaries where they increase in the grain boundary misorientation. The model predicts grain sizes of Al alloys subjected to SPD over 2 orders of magnitude. The model correctly predicts the considerable influence of Mg content and content of non-shearable particles on the grain refinement during SPD
Austenite grain growth behavior of microalloyed Al-V-N and Al-V-Ti-N steels
No full textThe austenite grain growth behaviour of microalloyed Al–V–N and Al–V–Ti–N steels has been studied. Estimations of austenite grain size for Al–V–N steels by several different grain growth inhibition models demonstrated that the best match to experimental results can be obtained from Gladman and Rios equations and it is AlN that controls the austenite grain size. The experimental and calculated results indicated that the drag force of plate-shaped AlN particles probably depends on their orientation and austenitising temperature. A modified Gladman model, which considers the effects of complex arrays of different types of particles on the stabilized austenite grain size, can be used to predict the austenite grain size and particle size for an Al–V–Ti–N steel when the combined effect of AlN and TiN is considered
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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