High speed tooling

Creating tooling for a new product can be a long and expensive process. The authors explore the use of rapid prototyping technology for producing metal tools     

Symmetry aspects of pretransformation behavior in metallic alloys

This paper deals with pretransformation behavior in both mineral and alloy systems. Theory that has previously been developed on the existence of local structural variants in incommensurate structures is reviewed and later applied to the study of local interactions in pretransformation phenomena. A review of the pretransformation behavior in both potassium feldspar and the mineral cordierite shows that the important feature in both cases is a very strong interaction between two orthogonal transverse acoustical waves to create a local shear structure. In the case of potassium feldspar this shear structure is the required product in the transformation, but in cordierite the first shear structure to appear in the pretransformation mechanism is not the correct one. Why this should be is explained in detail from a group theoretical analysis of the situation. Ultimately in cordierite this initial structure gives way to the correct structure with the appearance of twinning. The theory developed from the study of the mineralogical examples is then applied to the familiar cubic to tetragonal martensitic transformation in alloys such as In Tl with satisfactory results. Formerly with Schlumberger Cambridge Research, P.O. Box 153, Cambridge CB2 OHG This paper is based on a presentation made in the symposium “Pre-transformation Behavior Related to Displacive Transformations in Alloys≓ presented at the 1986 annual AIME meeting in New Orleans, March 2-6, 1986, under the auspices of the ASM-MSD Structures Committee.     

Interdependence of Phase Chemistry, Microstructure, and Oxygen Fugacity in Titanate Nuclear Waste Ceramics

Titanate ceramic waste forms were prepared using several combinations of calcination atmosphere (N₂, N₂-3.5% H₂, H₂) and metallic redox buffers (Ni, Fe, Ti, Al) to examine the dependence of microstructure and durability upon oxygen activity. It was found that the microstructures and phase assemblages were mostly insensitive to the fabrication method, although in detail systematic changes were recognized. The correlation of aqueous durability with oxygen fugacity was not straightforward, because of density variations in the hot-pressed ceramics. These fluctuations in density dominated the dissolution characteristics of the waste forms and sometimes obscured the more subtle changes associated with redox potential. It is concluded that although the best durability is achieved at lower fugacities (i.e., Ti metal buffer and H₂ calcination atmosphere), a satisfactory product can be produced using any of the preparative routes examined, provided the material is completely densified.     

Non-stationarity,heterogeneity, scale effects,and anisotropy investigations on natural rock joint roughness using the variogram method

Bulletin of Engineering Geology and the Environment - The variogram method is used to investigate the effect of non-stationarity, heterogeneity, scale-related parameters and anisotropy on roughness...     

Environmental impact assessment and strategic environmental assessment in the UK after leaving the European Union

Abstract

The United Kingdom has voted to leave the European Union and, until the terms of the ‘Brexit’ are negotiated, this has led to considerable uncertainty over the future practice of environmental impact assessment (EIA) and strategic environmental assessment (SEA) in the UK. Here we show that multiple obligations exist outside the scope of the EU which mean that EIA and SEA will continue to be required in the long term, but that their future compliance with the Directives remains unclear. We consider three scenarios for Brexit and present the implications of each; these are: signing up to the European Economic Area (EEA) Agreement; membership of the European Free Trade Association, but not EEA, or negotiate a separate agreement. The implications of no longer being subjected to the obligations of the Directives under some scenarios are discussed and include opening the door for increasing diversity of application across the regions of the UK, and the probability of raised screening thresholds so as to reduce the burden of assessment on developers.     

Modeling and optimization of cold extrusion process by using response surface methodology and metaheuristic approaches

Obtaining the optimal extrusion process parameters by integration of optimization techniques was crucial and continuous engineering task in which it attempted to minimize the tool load. The tool load should be minimized as higher extrusion forces required greater capacity and energy. It may lead to increase the chance of part defects, die wear and die breakage. Besides, optimization may help to save the time and cost of producing the final product, in addition to produce better formability of work material and better quality of the finishing product. In this regard, this study aimed to determine the optimal extrusion process parameters. The minimization of punch load was the main concern, in such a way that the structurally sound product at minimum load can be achieved. Minimization of punch load during the extrusion process was first formulated as a nonlinear programming model using response surface methodology in this study. The established extrusion force model was then taken as the fitness function. Subsequently, the analytical approach and metaheuristic algorithms, specifically the particle swarm optimization, cuckoo search algorithm (CSA) and flower pollination algorithm, were applied to optimize the extrusion process parameters. Performance assessment demonstrated the promising results of all presented techniques in minimizing the tool loading. The CSA, however, gave more persistent optimization results, which was validated through statistical analysis.

     

On the Relationship between Two Fatigue-Life Models

The relationship between two fatigue life distributions, namely the Birnbaum-Saunders and the Inverse Gaussian, is further investigated. An intimate connection exists between the two models, viz, the Birnbaum-Saunders is a mixture of two probability distributions: 1) an Inverse Gaussian random variable, and 2) the reciprocal of an Inverse Gaussian random variable. Advantages and disadvantages of the two distributions are discussed. The arguments favour the Birnbaum-Saunders distribution from a stochastic modeling point of view, whereas the Inverse Gaussian distribution seems to be the more attractive of the two with respect to statistical analysis and analysis of censored data.     

Modeling Particle-Size Distribution Dynamics during Precipitative Softening

A population balance model was developed to simulate simultaneous precipitation and flocculation during precipitative softening. Rate coefficients for nucleation, crystal growth, and flocculation were extracted from experimental particle-size distribution (PSD) data based on changes in the total number and total volume of particles. Three models of flocculation were evaluated: rectilinear, curvilinear, and an empirical size-independent model. Model simulations were compared with experimental PSD data to test which model was most appropriate. The curvilinear precipitative flocculation model was superior when seeded precipitation occurred at moderate mixing intensities (G = 50–100?s?1). However, the curvilinear model overpredicts the formation of very large particles and requires values of the collision efficiency greater than 1.0, suggesting a more complicated dependence of the PSD dynamics on mixing intensity and saturation ratio than presently included in the model. At higher mixing intensities (G = 300?s?1), flocculation exhibited size-independent behavior, indicating that physical/chemical aspects of the precipitation process are altering or overshadowing the physics described in the curvilinear flocculation model.