Fine-grain process modelling

In this paper, we propose the use of fine-grain process modelling as an aid to software development. We suggest the use of two levels of granularity, one at the level of the individual developer and another at the level of the representation scheme used by that developer. The advantages of modelling the software development process at these two levels, we argue, include respectively: (1) the production of models that better reflect actual development processes because they are oriented towards the actors who enact them, and (2) models that are vehicles for providing guidance because they may be expressed in terms of the actual representation schemes employed by those actors. We suggest that our previously published approach of using multiple “ViewPoints” to model software development participants, the perspectives that they hold, the representation schemes that they deploy and the process models that they maintain, is one way of supporting the fine-grain modelling we advocate. We point to some simple, tool-based experiments we have performed that support our proposition

Fine-grain process modelling

In this paper, we propose the use of fine-grain processmodelling as an aid to software development. We suggestthe use of two levels of granularity, one at the level of theindividual developer and another at the level of therepresentation scheme used by that developer. Theadvantages of modelling the software development processat these two levels, we argue, include respectively: (1) theproduction of models that better reflect actualdevelopment processes because they are oriented towardsthe actors who enact them, and (2) models that arevehicles for providing guidance because they may beexpressed in terms of the actual representation schemesemployed by those actors. We suggest that our previouslypublished approach of using multiple ?ViewPoints? tomodel software development participants, the perspectivesthat they hold, the representation schemes that theydeploy and the process models that they maintain, is oneway of supporting the fine-grain modelling we advocate.We point to some simple, tool-based experiments we haveperformed that support our proposition

Continuous extrusion of a commercially pure titanium powder via the Conform process

It is shown for the first time that cold commercially pure titanium powder can be extruded through a standard Conform machine into fully dense wire with a fine recrystallised microstructure. The grain size has been shown to decrease with increasing wheel speed with an associated increase in tensile strength. The macrostructure of the wire extrudate exhibits a characteristic flow pattern with several regions defined by differences in average grain size and distribution. Finite-element modelling of the process shows the formation of the characteristic macrostructure from powder fed Conform. The process is continuous, utilises standard equipment and does not require powder preheating or inert gas shrouding providing a footing for a true cost reduction in longsection titanium mill product

Development of a novel differential velocity sideways extrusion process for forming curved profiles with fine grains and high strength

The aim of this study is to develop a novel process, differential velocity sideways extrusion (DVSE), for forming curved profiles with fine grains and high strength. In this new forming-bending-refining process, billets are used as the work-piece material to directly form curved profiles with certain cross-sections in order to increase the manufacturing efficiency and decrease the bending defects in conventional bending process. The DVSE process has been studied in this thesis by using forming experiments, microstructure characterisation experiments, finite element (FE) modelling and theoretical modelling. A tool set enabling sideways extrusion to be performed using opposing punches moving with different velocities was designed and manufactured. Plasticine was used as a model work-piece material and a series of compression tests were undertaken, to determine its constitutive properties and gain an estimate of work-piece die friction for use in process simulation. Feasibility studies for the DVSE process were carried out through a series of designed experimental programmes on plasticine, in which punch/extrusion velocity ratio, extrusion ratio and die land length were process parameters. Ultimately, trial tests using AA1050 at room temperature and AZ31 at elevated temperatures were conducted. Effects of extrusion velocity ratio, extrusion ratio, die land length, forming temperature and strain rate on profile curvature were studied. The microstructure evolution of the formed curved AA1050 bar by DVSE at room temperature was studied through EBSD. The evolution of grain structure and texture of formed curved AZ31 bars at different DVSE process conditions (temperature and strain rate) was investigated through optical microscopy and EBSD, and the optimum temperature and strain rate condition for obtaining fine equiaxed and homogeneous microstructure was identified. The different grain refinement mechanisms of AA1050 and AZ31 during the DVSE process were revealed. Micro-hardness of formed curved AA1050 and AZ31 bars was examined. Process mechanics of DVSE were modelled using FE modelling and upper bound theorem. The extent of work-piece flow velocity gradient across the die exit orifice, which causes curvature, was identified. A dead zone of roughly triangular shape, which exists on the chamber wall opposite the die exit orifice, was determined. The effective strain of the formed curved profiles was studied to confirm the rise of severe plastic deformation (SPD). The effective strain rate in the intersection regions of the channels was investigated to identify the source of severe plastic deformation. An analytical upper-bound-based model has been developed with the consideration of the determined dead zone. The extrusion force and curvature predicted by the analytical method agreed reasonably well with results from experiments and FE modelling. Discussions were made about the correlations between experimental and modelling approaches and results. The relationships between mechanical properties (yield strength, ultimate tensile strength, and elongation to failure) and microstructures (grain size, micro-texture) of formed curved profiles were correlated. From the experimental and modelling work, it has been demonstrated that the DVSE process proposed in this thesis is an effective way to efficiently form curved aluminium and magnesium profiles with controlled curvature and improved properties.Open Acces

Dispersion strengthening in vanadium microalloyed steels processed by simulated thin slab casting and direct charging: Part I - Processing parameters, mechanical properties and microstructure

A study simulating thin slab continuous casting followed by direct charging into an equalisation furnace has been undertaken based on six low carbon (0.06wt-%) vanadium microalloyed steels. Mechanical and impact test data showed properties were similar or better than those obtained from similar microalloyed conventional thick cast as rolled slabs. The dispersion plus dislocation strengthening was estimated to be in the range 80-250MPa.A detailed TEM/EELS analysis of the dispersion sized sub-15nm particles showed that in all the steels, they were essentially nitrides with little crystalline carbon detected. In the Steels V-Nb, V-Ti and V-Nb-Ti, mixed transition metal nitrides were present. Modelling of equilibrium precipitates in these steels, based on a modified version of ChemSage, predicted that only vanadium rich nitrides would precipitate in austenite but that the C/N ratio would increase through the two phase field and in ferrite. The experimental analytical data clearly points to the thin slab direct charging process, which has substantially higher cooling rates than conventional casting, nucleating non-equilibrium particles in ferrite which are close to stoichiometric nitrides. These did not coarsen during the final stages of processing, but retained their highly stable average size of ~7nm resulting in substantial dispersion strengthening. The results are considered in conjunction with pertinent published literature

Intergranular stress distributions in polycrystalline aggregates of irradiated stainless steel

In order to predict InterGranular Stress Corrosion Cracking (IGSCC) of post-irradiated austenitic stainless steel in Light Water Reactor (LWR) environment, reliable predictions of intergranular stresses are required. Finite elements simulations have been performed on realistic polycrystalline aggregate with a recently proposed physically-based crystal plasticity constitutive equations validated for neutron-irradiated austenitic stainless steel. Intergranular normal stress probability density functions are found with respect to plastic strain and irradiation level, for uniaxial loading conditions. In addition, plastic slip activity jumps at grain boundaries are also presented. Intergranular normal stress distributions describe, from a statistical point of view, the potential increase of intergranular stress with respect to the macroscopic stress due to grain-grain interactions. The distributions are shown to be well described by a master curve once rescaled by the macroscopic stress, in the range of irradiation level and strain considered in this study. The upper tail of this master curve is shown to be insensitive to free surface effect, which is relevant for IGSC

Microembossing of ultrafine grained Al: microstructural analysis and finite element modelling

Ultra fine grained (UFG) Al-1050 processed by equal channel angular pressing (ECAP) and UFG Al-Mg-Cu-Mn processed by high pressure torsion (HPT) were embossed at both room temperature and 300 °C, with the aim of producing micro-channels. The behaviour of Al alloys during the embossing process was analysed using finite element (FE) modelling. The cold embossing of both Al alloys is characterised by a partial pattern transfer, a large embossing force, channels with oblique sidewalls and a large failure rate of the mould. The hot embossing is characterised by straight channel sidewalls, fully transferred patterns and reduced loads which decrease the failure rate of the mould. Hot embossing of UFG Al-Mg-Cu-Mn produced by HPT shows a potential of fabrication of microelectromechanical system (MEMS) components with micro channels

Sedimentological characterization of Antarctic moraines using UAVs and Structure-from-Motion photogrammetry

In glacial environments particle-size analysis of moraines provides insights into clast origin, transport history, depositional mechanism and processes of reworking. Traditional methods for grain-size classification are labour-intensive, physically intrusive and are limited to patch-scale (1m2) observation. We develop emerging, high-resolution ground- and unmanned aerial vehicle-based ‘Structure-from-Motion’ (UAV-SfM) photogrammetry to recover grain-size information across an moraine surface in the Heritage Range, Antarctica. SfM data products were benchmarked against equivalent datasets acquired using terrestrial laser scanning, and were found to be accurate to within 1.7 and 50mm for patch- and site-scale modelling, respectively. Grain-size distributions were obtained through digital grain classification, or ‘photo-sieving’, of patch-scale SfM orthoimagery. Photo-sieved distributions were accurate to <2mm compared to control distributions derived from dry sieving. A relationship between patch-scale median grain size and the standard deviation of local surface elevations was applied to a site-scale UAV-SfM model to facilitate upscaling and the production of a spatially continuous map of the median grain size across a 0.3 km2 area of moraine. This highly automated workflow for site scale sedimentological characterization eliminates much of the subjectivity associated with traditional methods and forms a sound basis for subsequent glaciological process interpretation and analysis

Developments in modelling of backward erosion piping

One of the failure mechanisms that can affect the safety of a dyke or another water-retaining structure is backward erosion piping, a phenomenon that results in the formation of shallow pipes at the interface of a sandyor silty foundation and a cohesive cover layer. Themodels available for predicting the critical head at which the pipe progresses to the upstreamside have been validated and adapted on the basis of experiments with two-dimensional (2D) configurations. However, the experimental base for backward erosion in three-dimensional (3D) configurations in which the flow concentrates towards one point, a situation that is commonly encountered in the field, is limited. This paper presents additional 3D configuration experiments at two scales with a range of sand types. The critical gradients, the formed pipes and the erosion mechanism were analysed for the available experiments, indicating that the erosion mechanism is more complex than previously assumed, as both erosion at the tip of the pipe (primary erosion) and in the pipe (secondary erosion) are relevant. In addition, a 3D configuration was found to result in significantly lower critical gradients than those predicted by an accepted calculation model calibrated on the basis of 2D experiments, a finding that is essential for the application of the model in the field