Xavier Velay

Analysis and Preservation of Pleistocene Human and Animal Footprints: An Example from Toluquilla, Valsequillo Basin (Central Mexico)

Human and animal footprints found in the Valsequillo Basin were formed on the upper bedding planes surfaces of a volcanic ash (Xalnene Ash) deposited by a subaqueous volcano along the shores of a Pleistocene lake. The footprints were made on lake shorelines and the exposed lake floor during low stands associated, either with water displacement during the volcanic eruption, or due to climatically-driven fluctuations in the water balance. The Xalnene Ash has been dated to at least 40 K BP and consequently the human footprints provide evidence for much earlier colonization of the Americas than is often accepted. The methodology used to record, analyze and conserve these footprints used three-dimensional laser scanning, with sub-millimeter precision. This data were used to reproduce polymer models of individual footprints using the application of rapid-prototyping technology. This technology has wide significance for the study of ichnofacies in general. The characteristics of the human footprints and some problems associated with the volcanic ash as a molding medium for the clarity of these characteristics are given. These human footprints and their dating resolve the controversy related to the age of the archaeological and associated megafaunal remains that were reported in the Valsequillo Gravels in the 1960s and 1970s.

Investigation of metal flow in bridge die extrusion of Alloy 6063 and subsequent effect on surface quality and weld seam integrity

Abstract This paper describes a detailed study of tube extrusion by simulation using finite element method (FEM). The finite element model used one-sixth of symmetry. The extrusion load, temperature evolution and metal flow were predicted. Innovative methods, combining both grid and surface tools, were used to define in detail the flow of material. These showed clearly the inner and outer surface formation mechanisms of the tube extrusion. The seam weld, an important quality indicator, was also evaluated by selecting an appropriate criterion.

Materials for Sports

The interplay between materials science and sports equipment takes many forms. Certainly a broad cross section of materials is used in sporting equipment to improve performance and safety, and to reduce cost. The new materials used in sports equipment originate from a long history of innovation, drawing from and contributing to other technologies. Amateurs and professionals play sports, so rules on the use of new technology vary immensely. This allows for a short circuit of new technology into the market-place in some cases and restriction or prohibition of opportunities in others. Also materials selection and development for sports equipment must stretch beyond consideration of the object itself to include the human interface and design of a system that best makes use of the materials. Sports after all are about human capability and interaction. The equipment is just a facilitator. Certainly more efficient ways exist of placing a ball into a hole than hitting it with a long metal stick from hundreds of yards away. This is perhaps the most unique element of materials development for sports. The rules governing materials development are not just laws of science and of government but rules put into place just for “sport.” Because of the connection of sports to the lives of so many people, either as participants or spectators, materials science of sporting equipment is also a great platform for educating students about materials selection and behavior.

On material flow and aspects of structural modification during direct and indirect extrusion of aluminium alloy

Abstract In this paper, both direct and indirect extrusions are simulated using a viscoplastic constitutive model. The simulated velocity fields for both direct and indirect extrusions are discussed and compared with experimental results. Advanced numerical techniques are used to trace backward and forward discrete particles of the billet. The effect of friction on the material flow is discussed. Back-end defects are simulated and practical methodologies are derived to minimise such defects using finite element modelling (FEM). Peak loads, temperatures and strain rate distribution are also compared between direct and indirect extrusions. Numerical subroutines have been developed and integrated into the FEM software in order to introduce the possibility of prediction of microstructural evolution. The results of such numerical simulations to increase productivity within the extrusion industry are currently limited only by the lack of sufficient physical metallurgical detail and by obstacles preventing the FEM simulation to be directly applied. This aspect is discussed in some detail.

Prediction and control of subgrain size in the hot extrusion of aluminum alloys

It is widely recognized that subgrain size has significant influence on the strength and ductility of metals. Modelling of subgrain size evolution is essential for the detailed understanding and control of mechanical properties. In the present paper, the evolutions of subgrain size during hot extrusion of various aluminum alloys are first predicted. A nearly constant distribution of subgrain size is pursued by iso‐subgrain extrusion processes. Substructural strengthening coupled with microstructural evolution is also studied in addition to the normal thermal‐mechanical coupled analysis.

Piezoelectric Generators as Battery Chargers in Mobile Devices

This paper presents a design idea for an electric charging device designed to sit underneath the keypad of various mobile devices using piezoelectric and similar effect materials. It discusses the benefits of such a device and the current problems associated with developing one. The basis for the device is that multiple piezoelectric materials placed under the keypad are subjected to repeated loading from activities such as ‘texting’ or ‘menu browsing’. This causes a variable voltage generation which can assist in charging or other suitable function of the device. The paper shows the ways to achieve this goal and examine current piezoelectric generators.Copyright

Innovative Methodologies for the Simulation of Static Recrystallisation during the Solution Soaking Process of Shape Extrusion

Materials which form the surface and subcutaneous layers of an extrudate experience large deformations when they traverse the die land. This, when added to the inhomogeneity caused by the dead metal zone, leads to considerable modifications to the deformation parameters when compared to the remainder of the extrusion. The distribution of structure is therefore greatly inhomogeneous. Reference to both empirical and physical models of the recrystallisation process indicates that nucleation and growth will differ at these locations in those aluminium alloys that are usually solution treated and aged subsequent to the deformation process. Since static recrystallisation has a significant influence on many of the properties of the extrudate, it is therefore essential to provide the methodology to predict these variations. In the work presented, a physical model, for AA2024, based on dislocation density, subgrain size and misorientation is modified and integrated into the commercial finite element method (FEM) code, FORGE, to study the microstructure changes. Axi-symmetrical and shape extrusion are presented as examples. The evolution of the substructure influencing static recrystallisation is studied. The predicted results show an agreement with the experimental measurement. The distribution of equivalent strain, temperature compensated strain rate and temperatures are also presented to aid interpretation. Importantly the properties of hard alloys improve as the temperature of the extrusion is raised. This phenomenon is discussed and theoretically justified. This paper also presents some innovative work where the physically based models, and the Cellular Automata (CA) method, are combined to simulate the static recrystallisation process. The FEM is adopted to provide the initial morphology and state variables for the structure models, such as the equivalent strain, the temperature and the equivalent strain rate. The subgrain size, and dislocation densities are calculated from physically based models and are transferred to CA models to construct the data required to define the initial state for recrystallisation. Simulation results are compared with experimental measurements. It is demonstrated that CA integrated with the physically based models is effective in predicting the structural changes by selecting a suitable neighbourhood and reasonable transition rules.

VICARIA: An e-learning tool for risk assessment and management

This paper is based on research carried out as part of the VICARIA project, an interactive tool which was developed from an EC Leonardo grant, to provide distance learning and virtual classrooms in the field of risk management and control. Companies are responsible to provide appropriate training especially in sensitive and critical areas such as risk assessment and management; unfortunately many consider, risk analysis training to be expensive, costly and time consuming. VICARIA allows flexibility in training time, it is cost-effective i.e. reduced travel and subsistence expenses, it enables managers to attend and assist in courses, allowing them to judge the relevancy and quality of training provided and also VICARIA offers specialised and the latest knowledge in the specific field of risk analysis. This system includes accessibility, interoperability, durability and re-usability aspects and uses open standards with respect to platform and content. English, French and Greek are the languages used.

A discussion of the scaling effect in numerical simulation of the extrusion process

Abstract The main objective of the work of this paper is to study the possibility of using a small scale geometrical model in the numerical simulation of aluminium extrusion. The advantages and shortcomings of the application of the geometrically similar model in FEM simulation are discussed. Thermal – mechanical and metallurgical combined simulations are performed within two tests using geometrically similar models and assessment is made in terms of mechanical and material properties. It was found that small scale simulation could not reproduce most of the important forming parameters of the original process, although it could help to bring about significant savings in computation time.

Simulating the operation of a novel variable camber hydrofoil

Small marine vehicles such as boats and particularly windsurfers, employ winglike lifting surfaces, such as daggerboards, rudders and fins, on the underside of the hull to resist the sideways force of the sail and also for directional control. Because these lifting surfaces must operate on both tacks, a geometrically symmetrical cross-section is normally used, which inhibits the maximum values of lift that can be generated by a given surface area. To improve the performance it is proposed to develop a cross-section with camber, even though this presents a problem for a lifting surface which has to operate on both tacks. This paper discusses the process and reasoning behind the development of a cambered lifting section for marine vehicles and the way in which aerodynamic data, theory and computational techniques are being applied in this process.