26 research outputs found
Recommended from our members
Maximum Height to Width Ratio of Freestanding Structures Built Using Ultrasonic Consolidation
Ultrasonic consolidation (UC) is a process whereby metal foils can be metallurgically
bonded at or near room temperature. The UC process works by inducing high-speed differential
motion (~20kHz) between a newly deposited layer and a substrate (which consists of a base plate
and any previously deposited layers of material). This differential motion causes plastic
deformation at the interface, which breaks up surface oxides and deforms surface asperities,
bringing clean metal surfaces into intimate contact, where bonding occurs. If the substrate is not
stiff enough to resist deflection during ultrasonic excitation of newly deposited layers, then it
deflects along with the newly deposited layer, resulting in no differential motion and lack of
bonding. Geometric issues which control substrate stiffness and deflection were investigated at
Utah State University by building a number of free-standing rib structures with varying
dimensions and orientations. Each structure was built to a height where lack of bonding between
the previously deposited layers and the newly deposited layer caused the building process to fail,
a height to width ratio (H/W) of approximately 1:1. The parts were then cut, polished, and
viewed under a microscope. An ANSYS model was created to investigate analytically the cause
of this failure. It appears build failure is due to excessive deflection of the ribs around a 1:1 H/W,
resulting in insufficient differential motion and deformation to achieve bonding. Preliminary
results show, when the H/W reaches 1:1, the von Mises stress is found to be tensile along
portions of the bonding interface, which eliminates the compressive frictional forces necessary
for plastic deformation and formation of a metallurgical bond. These tensile stresses are shown
to be concentrated at regions near the edges of the newly deposited foil layer.Mechanical Engineerin
Hybrid additive manufacturing of 3D electronic systems
A novel hybrid additive manufacturing (AM) technology combining digital light projection (DLP) stereolithography (SL) with 3D micro-dispensing alongside conventional surface mount packaging is presented in this work. This technology overcomes the inherent limitations of individual AM processes and integrates seamlessly with conventional packaging processes to enable the deposition of multiple materials. This facilitates the creation of bespoke end-use products with complex 3D geometry and multi-layer embedded electronic systems. Through a combination of four-point probe measurement and non-contact focus variation microscopy, it was identified that there was no obvious adverse effect of DLP SL embedding process on the electrical conductivity of printed conductors. The resistivity maintained to be less than 4 × 10−4 Ω centerdot cm before and after DLP SL embedding when cured at 100 °C for 1 h. The mechanical strength of SL specimens with thick polymerized layers was also identified through tensile testing. It was found that the polymerization thickness should be minimised (less than 2 mm) to maximise the bonding strength. As a demonstrator a polymer pyramid with embedded triple-layer 555 LED blinking circuitry was successfully fabricated to prove the technical viability
Shells and humans: molluscs and other coastal resources from the earliest human occupations at the Mesolithic shell midden of El Mazo (Asturias, Northern Spain)
Human populations exploited coastal areas with intensity during the Mesolithic in Atlantic Europe, resulting in the accumulation of large shell middens. Northern Spain is one of the most prolific regions, and especially the so-called Asturian area. Large accumulations of shellfish led some scholars to propose the existence of intensification in the exploitation of coastal resources in the region during the Mesolithic. In this paper, shell remains (molluscs, crustaceans and echinoderms) from stratigraphic units 114 and 115 (dated to the early Mesolithic c. 9 kys cal BP) at El Mazo cave (Asturias, northern Spain) were studied in order to establish resource exploitation patterns and environmental conditions. Species representation showed that limpets, top shells and sea urchins were preferentially exploited. One-millimetre mesh screens were crucial in establishing an accurate minimum number of individuals for sea urchins and to determine their importance in exploitation patterns. Environmental conditions deduced from shell assemblages indicated that temperate conditions prevailed at the time of the occupation and the morphology of the coastline was similar to today (rocky exposed shores). Information recovered relating to species representation, collection areas and shell biometry reflected some evidence of intensification (reduced shell size, collection in lower areas of exposed shores, no size selection in some units and species) in the exploitation of coastal resources through time. However, the results suggested the existence of changes in collection strategies and resource management, and periods of intense shell collection may have alternated with times of shell stock recovery throughout the Mesolithic.This research was performed as part of the project “The human response to the global climatic change in a littoral zone: the case of the transition to the Holocene in the Cantabrian coast (10,000–5000 cal BC) (HAR2010-22115-C02-01)” funded by the Spanish Ministry of Economy and Competitiveness. AGE was funded by the University of Cantabria through a predoctoral grant and IGZ was funded by the Spanish Ministry of Economy and Competitiveness through a Juan de la Cierva grant. We also would like to thank the University of Cantabria and the IIIPC for providing support, David Cuenca-Solana, Alejandro García Moreno and Lucia Agudo Pérez for their help. We also thank Jennifer Jones for correcting the English. Comments from two anonymous reviewers helped to improve the paper