The influence of non-metallic inclusions upon the properties of linepipe steels

The principal aim of this work was to determine the role of non-metallic inclusions in the process of hydrogen stepwise cracking (SWC). Additionally, the influence of inclusions upon the notch ductility of hydrogen charged (HC) and uncharged (UN) tensile specimens was examined. To obtain a basis for experiment a series of low carbon-manganese steels were prepared by induction melting. In order to produce variations in the composition, morphology, volume fraction, size and distribution of the inclusions the steel chemistry was adjusted prior to casting by additions of deoxidiser and Ca-Si injection. Sections of each ingot were hot rolled. Metallography, image analysis, mechanical tests and hydrogen SWC tests were then carried out. The volume fraction, morphology, and shape of inclusions influenced the tensile ductility of the steels. Marked anisotropy was found in the steels containing type II MnS inclusions at all rolling temperatures, whereas the fully Ca treated steel was isotropic. It was found that several inclusion parameters (projected length PL, mean free distance MFD, nearest-neighbour distance NND) correlated with fracture strain. An increase in inclusion volume fraction and/or the dimension of inclusions on a plane parallel to the plane of fracture led to a decrease in fracture strain. The inclusion parameters did not correlate with the fracture strains for the HC tensile specimens. However, large or clusters of inclusions acted as the principal sites for crack initiation. `Fisheyes' or areas of `flat' fracture were often found on these fracture surfaces. The criteria for SWC initiation was found to be either large inclusions or clusters of inclusions. As the PL of inclusions increased the probability of large SWCs occurring increased. SWC initiation at inclusions was believed to occur at a critical concentration of hydrogen. Factors which assisted the concentration of hydrogen at inclusions were discussed. None of the proposed mechanisms of hydrogen embrittlement could be identified as the single cause of SWC.

Computer simulation of form-roll design

Changes in modern structural design have created a demand for products which are light but possess high strength. The objective is a reduction in fuel consumption and weight of materials to satisfy both economic and environmental criteria. Cold roll forming has the potential to fulfil this requirement. The bending process is controlled by the shape of the profile machined on the periphery of the rolls. A CNC lathe can machine complicated profiles to a high standard of precision, but the expertise of a numerical control programmer is required. A computer program was developed during this project, using the expert system concept, to calculate tool paths and consequently to expedite the procurement of the machine control tapes whilst removing the need for a skilled programmer. Codifying the expertise of a human and the encapsulation of knowledge within a computer memory, destroys the dependency on highly trained people whose services can be costly, inconsistent and unreliable. A successful cold roll forming operation, where the product is geometrically correct and free from visual defects, is not easy to attain. The geometry of the sheet after travelling through the rolling mill depends on the residual strains generated by the elastic-plastic deformation. Accurate evaluation of the residual strains can provide the basis for predicting the geometry of the section. A study of geometric and material non-linearity, yield criteria, material hardening and stress-strain relationships was undertaken in this research project. The finite element method was chosen to provide a mathematical model of the bending process and, to ensure an efficient manipulation of the large stiffness matrices, the frontal solution was applied. A series of experimental investigations provided data to compare with corresponding values obtained from the theoretical modelling. A computer simulation, capable of predicting that a design will be satisfactory prior to the manufacture of the rolls, would allow effort to be concentrated into devising an optimum design where costs are minimised.

Some aspects of system design for production management in the rolling-mill industry

Case studies in copper-alloy rolling mill companies showed that existing planning systems suffer from numerous shortcomings. Where computerised systems are in use, these tend to simply emulate older manual systems and still rely heavily on modification by experienced planners on the shopfloor. As the size and number of orders increase, the task of process planners, while seeking to optimise the manufacturing objectives and keep within the production constraints, becomes extremely complicated because of the number of options for mixing or splitting the orders into batches. This thesis develops a modular approach to computerisation of the production management and planning functions. The full functional specification of each module is discussed, together with practical problems associated with their phased implementation. By adapting the Distributed Bill of Material concept from Material Requirements Planning (MRP) philosophy, the production routes generated by the planning system are broken down to identify the rolling stages required. Then to optimise the use of material at each rolling stage, the system generates an optimal cutting pattern using a new algorithm that produces practical solutions to the cutting stock problem. It is shown that the proposed system can be accommodated on a micro-computer, which brings it into the reach of typical companies in the copper-alloy rolling industry, where profit margins are traditionally low and the cost of widespread use of mainframe computers would be prohibitive.

Rolling bearing vibrations: the effects of varying compliance, manufacturing tolerances and wear

In this study some common types of Rolling Bearing vibrations are analysed in depth both theoretically and experimentally. The study is restricted to vibrations in the radial direction of bearings having pure radial load and a positive radial clearance. The general vibrational behaviour of such bearings has been investigated with respect to the effects of varying compliance, manufacturing tolerances and the interaction between the bearing and the machine structure into which it is fitted. The equations of motion for a rotor supported by a bearing in which the stiffness varies with cage position has been set up and examples of solutions,obtained by digital simulation. is given. A method to calculate amplitudes and frequencies of vibration components due to out of roundness of the inner ring and varying roller diameters has been developed. The results from these investigations have been combined with a theory for bearing/machine frame interaction using mechanical impedance technique, thereby facilitating prediction of the vibrational behaviour of the whole set up. Finally. the effects of bearing fatigue and wear have been studied with particular emphasis on the use of vibration analysis for condition monitoring purposes. A number of monitoring methods have been tried and their effectiveness discussed. The experimental investigation was carried out using two purpose built rigs. For the purpose of analysis of the experimental measurements a digital mini computer was adapted for signal processing and a suite of programs was written. The program package performs several of the commonly used signal analysis processes and :include all necessary input and output functions.

Implementation of vectorial bend sensors using long-period gratings UV-inscribed in special shape fibres

We report the implementation of vector bending sensors using long-period gratings (LPGs) UV-inscribed in flat-clad, four-core and D-shaped fibres. Our experiments reveal a strong fibre-orientation dependence of the spectral response when such LPGs are subjected to dynamic bending, which provided an opportunity to realize curvature measurement with direction recognition.

Shape of the posterior vitreous chamber in human emmetropia and myopia

PURPOSE - To compare posterior vitreous chamber shape in myopia to that in emmetropia. METHODS - Both eyes of 55 adult subjects were studied, 27 with emmetropia (MSE =-0.55; <+0.75D; mean +0.09 ±0.36D) and 28 with myopia (MSE -5.87 ±2.31D). Cycloplegic refraction was measured with a Shin Nippon autorefractor and anterior chamber depth and axial length with a Zeiss IOLMaster. Posterior vitreous chamber shapes were determined from T2-weighted MRI (3-Tesla) using procedures previously reported by our laboratory. 3-D surface model coordinates were assigned to nasal, temporal, superior and inferior quadrants and plotted in 2-D to illustrate the composite shape of respective quadrants posterior to the second nodal point. Spherical analogues of chamber shape were constructed to compare relative sphericity between refractive groups and quadrants. RESULTS - Differences in shape occurred in the region posterior to points of maximum globe width and were thus in general accord with an equatorial model of myopic expansion. Shape in emmetropia is categorised distinctly as that of an oblate ellipse and in myopia as an oblate ellipse of significantly less degree such that it approximates to a sphere. There was concordance between shape and retinotopic projection of respective quadrants into right, left, superior and inferior visual fields. CONCLUSIONS - The transition in shape from oblate ellipse to sphere with axial elongation supports the hypothesis that myopia may be a consequence of equatorial restriction associated with biomechanical anomalies of the ciliary apparatus. The synchronisation of quadrant shapes with retinotopic projection suggests that binocular growth is coordinated by processes that operate beyond the optic chiasm.

A micro-compression study of shape-memory deformation in U-13 at.% Nb

Microcompression specimens, 10–15 µm in diameter by 20–30 µm in height, were produced from individual parent grains in a polycrystalline U–13 at.%Nb shape-memory alloy using the focused ion beam technique. The specimens were tested in a nanoindentation instrument with a flat diamond tip to investigate stress–strain behavior as a function of crystallographic orientation. The results are in qualitative agreement with a single-crystal accommodation strain (Bain strain) model of the shape-memory effect for this alloy.

Impact of FBGs reflectivity shape on spectra of radiation in 10 km Raman fibre laser

We study the impact of the shape of fibre Bragg gratings spectral reflectivity on spectral broadening in a 10 km Raman fibre laser. We show that, at high powers, spectral characteristics are determined by intra-cavity processes rather than by the gratings profile.