Christopher L. Magee

The Deformation of aluminum foams

The compressive flow behavior of Al, Al−7 pct Mg and 7075 Al alloy foams has been determined in structures whose void fraction varies from 0.80 to 0.95 of the total volume. In all cases, a greater than linear increase in flow strength with increase in density was exhibited, indicating that bending stresses within the foam structure are an important feature of the collapse mode. The flow strength did not follow proportionately changes in bulk flow strength in comparisons of either alloy or of heat-treatment conditions. Ancillary tensile and metallographic observations show that this lack of correlation arises because the different foams collapse by different modes with localized fracture becoming dominant in the higher strength 7075 alloy. The energy absorbing efficiency was found to be independent of foam density for all the materials. However, the efficiency was found to be a strong function of the alloy and heat treatment increasing from about 30 pct in Al, to 43 pct in Al−7 pct Mg and to 50 pct in the solution heat treated and aged 7075 alloy. The increase in efficiency occurs because of an increase in the propensity to fracture in the higher strength alloys which introduces the potential for a propagating constant-stress collapse process.

The kinetics of martensite formation in small particles

The kinetics of martensite nucleation in “atomized” particles of Fe-24.2 Ni-3.6 Mn and Fe-22 Ni-0.49 C have been investigated as a function of particle size (10 to 140 μ) and reaction temperature. The dependence of particle fraction transformed on particle size indicates that martensite nucleates at surface or near-surface sites for the Fe−Ni−C powder and throughout the bulk for the Fe−Ni−Mn powder. It is shown that, in contrast to kinetic measurements on bulk samples where autocatalysis predominates, the present technique measures reaction rate due solely to the sites present initially. The measurements show that there is no detectable incubation time for nucleation and that the nucleation sites have a specific distribution of activation energies. A method for extracting the distribution from experimental measurements is given and the result is used to develop a revised equation for describing isothermal martensite formation. The isothermal kinetics of martensite formation in Fe-22 Ni-0.49 C are investigated despite the fact that such measurements are not possible in bulk samples because the alloy transforms by “bursting”. It is found that the apparent activation entropy for martensite nucleation is significantly higher for this alloy than for Fe-24.2 Ni-3.6 Mn. This suggests that the dislocation-dislocation interactions at the critical nucleation step are longer-range in the Fe−Ni−C alloy than in the Fe−Ni−Mn alloy.

Deformation characteristics of zinc foam

The temperature dependence of the yield stress and energy absorbing capacity of zinc foam, having a density between 0.05 and 0.07 of that of zinc, was determined over a range of temperatures from 0.1 Tm to 0.7 Tm approximately. With increase in temperature over this temperature range, the yield stress and energy absorbing capacity of the foam at first increased, and then subsequently decreased, above room temperature. At low temperatures,e.g. 0.1 Tm, the foam disintegrated into powder, and the energy absorbing efficiency parameters were high and independent of the foam density. In contrast, at the highest temperatures,e.g. 0.7 Tm, the energy absorbing efficiency parameters were lower and decreased with increase in density. The results are interpreted on the basis of the change in deformation mode which occurs in the zinc matrix of the foam over this temperature range,i.e. the transition from cleavage at the low temperature to plastic flow at the high temperature of deformation.

Design Considerations in Energy Absorption by Structural Collapse

A general treatment of the absorption of mechanical energy by the axial collapse of a variety of structural shapes, including tubes, honeycombs and foams is developed which encompasses both the geometry of the structure and also the material properties. The use of the method in the design of load bearing structures in which energy absorption is an additional design function is illustrated. High strength-to-weight ratio materials offer a significant weight saving for energy absorbing components, although such materials may have a reduced tensile ductility. The implications to situations in vehicle crashworthiness are discussed. /SAE/

Research agenda for an integrated approach to infrastructure planning, design and management

Building on broad discussions between many universities, this paper presents a research agenda based on a holistic, comprehensive view of the issues. It proposes that our infrastructure is a system of systems involving different technical manifestations and social organisations. The implication is that we need a fundamental reconsideration of how we look at system design, away from traditional disciplinary considerations and toward a multi-domain, multi-disciplinary effort. To this end, it proposes an agenda of: comparative analyses across infrastructures and political structures, that would identify commonalities and larger lessons; creation of integrated socio-technical models that usefully describe the interactions between the technical infrastructure and its social context; methodological efforts, aimed largely at capturing the network characteristics, both technical and social, of the infrastructure system of systems; explicit testing and evaluation of the research through programs of collaboration with practitioners and governmental organisations.

Physical metallurgy of automotive high-strength steels

This paper briefly reviews the various available types of high-strength steels — conventional, recovery-annealed, and dual-phase steels. A judgmental analysis of a large number of stamped automotive components shows that dual-phase steels, with their superior strength at a given elongation (formability), offer the best potential for weight savings. The rest of the paper concerns the physical metallurgy and mechanical response of dual-phase steels. It is shown that strength is a function of the percent martensite in the structure, although the strength is less than predicted by a simple rule of mixtures. The enhanced ductility of dual-phase steels is shown to be a consequence of the high s train-hardening rate observed in these steels, the reason for which is not well understood but probably reflects the properties of the ferrite matrix. The strain-rate sensitivity of dual-phase steels is found to be higher than that of conventional high-strength steels of comparable tensile strengths. Fatigue studies of dual-phase steels show them to be comparable to conventional high-strength steels in the notched condition; energy absorption during the axial collapse of tubes is shown to be solely a function of tensile strength. Also included are data on the temperature dependence of tensile strength in both the notched and unnotched conditions; high-strength dual-phase steels exhibit notch sensitivity even at room temperature. A study of formability (springback) shows that high-strength dual-phase steel is slightly worse than SAE 950X but much better than SAE 980X steel.

Detecting evolving patterns of self-organizing networks by flow hierarchy measurement

Hierarchies occur widely in evolving self-organizing ecological, biological, technological, and social networks, but detecting and comparing hierarchies is difficult. Here we present a metric and technique to quantitatively assess the extent to which self-organizing directed networks exhibit a flow hierarchy. Flow hierarchy is a commonly observed but theoretically overlooked form of hierarchy in networks. We show that the ecological, neurobiological, economic, and information processing networks are generally more hierarchical than their comparable random networks. We further discovered that hierarchy degree has increased over the course of the evolution of Linux kernels. Taken together, our results suggest that hierarchy is a central organizing feature of real-world evolving networks, and the measurement of hierarchy opens the way to understand the structural regimes and evolutionary patterns of self-organizing networks. Our measurement technique makes it possible to objectively compare hierarchies of different networks and of different evolutionary stages of a single network, and compare evolving patterns of different networks. It can be applied to various complex systems, which can be represented as directed networks.

Quantitative Determination of Technological Improvement from Patent Data

The results in this paper establish that information contained in patents in a technological domain is strongly correlated with the rate of technological progress in that domain. The importance of patents in a domain, the recency of patents in a domain and the immediacy of patents in a domain are all strongly correlated with increases in the rate of performance improvement in the domain of interest. A patent metric that combines both importance and immediacy is not only highly correlated (r = 0.76, p = 2.6*10-6) with the performance improvement rate but the correlation is also very robust to domain selection and appears to have good predictive power for more than ten years into the future. Linear regressions with all three causal concepts indicate realistic value in practical use to estimate the important performance improvement rate of a technological domain.

Development of an extended Kansei engineering method to incorporate experience requirements in product–service system design

The customer experience is important for adding value to firms’ offerings but two challenges arise: the customer experience is increasingly created through interactions with product–service systems (PSSs) and it is formed through all moments of interaction with multiple firms. Incorporating customer experience requirements (ERs) into the design of PSSs is therefore a complex task. To address this challenge, this paper presents an extension of the Kansei engineering method consisting of two components. First, the extension includes an in-depth study of the customer experience from a holistic perspective that informs the design process. Second, it involves the active participation of multidisciplinary experts from the different partner companies that together enable the PSS offering. An application of this new extension is presented for mid-distance bus trips, involving passengers, a vehicle manufacturing and a transport provider company. The research followed design-science guidelines using an action research approach to develop new public transportation PSS concepts by involving a multidisciplinary design team. The customer experience study enables the team adequately incorporate ERs along the development process, and the joint work of the intercompany team of experts enables integration of the different PSS elements into a solution that enhances the travel experience from a holistic perspective.

The effect of interstitial solutes on the twinning stress of b.c.c. metals

Abstract Flow stress measurements at −196°C on Fe-4.8 at. % Sn-C alloys demonstrate that the presence of interstitial carbon markedly increases the stress for deformation by twinning. The flow stress for an alloy with 0.09 at. % carbon is 12.6 Kg/mm2 higher than the flow stress for a carbon-free alloy. This behaviour, which is an exception to the rule that twinning stresses are relatively invariant to solute content, was anticipated because the normal twinning mode in ferrite does not shear all interstitial atoms to proper octahedral sites. In confirmation of this viewpoint, the experimental results were found to be in reasonable agreement with a theoretical estimate of the change in twinning stress that should result from this crystallographic restraint.