Investigation of deformation mechanisms in nanocrystalline metals and alloys by in situ synchrotron X-ray diffraction

In this work, different nanocrystalline metals and alloys were investigated by a synchrotron-based in situ XRD mechanical testing technique in order to investigate the dominant deformation mechanisms. All tested samples show a succession and coexistence of several mechanisms, regardless of grain size, loading condition, or sample geometry. However, the relative shares of the individual mechanisms strongly vary and depend on parameters such as grain size, sample purity, and alloy composition

Investigation of deformation mechanisms in nanocrystalline metals and alloys by in situ synchrotron X-ray diffraction

In this work, different nanocrystalline metals and alloys were investigated by a synchrotron-based in situ XRD mechanical testing technique in order to investigate the dominant deformation mechanisms. All tested samples show a succession and coexistence of several mechanisms, regardless of grain size, loading condition, or sample geometry. However, the relative shares of the individual mechanisms strongly vary and depend on parameters such as grain size, sample purity, and alloy composition

An Approach for Handling Uncertainties Related to Behaviour and Vehicle Mixes in Traffic Simulation Experiments with Automated Vehicles

The introduction of automated vehicles is expected to affect traffic performance. Microscopic traffic simulation offers good possibilities to investigate the potential effects of the introduction of automated vehicles. However, current microscopic traffic simulation models are designed for modelling human-driven vehicles. Thus, modelling the behaviour of automated vehicles requires further development. There are several possible ways to extend the models, but independent of approach a large problem is that the information available on how automated vehicles will behave is limited to todays partly automated vehicles. How future generations of automated vehicles will behave will be unknown for some time. There are also large uncertainties related to what automation functions are technically feasible, allowed, and actually activated by the users, for different road environments and at different stages of the transition from 0 to 100% of automated vehicles. This article presents an approach for handling several of these uncertainties by introducing conceptual descriptions of four different types of driving behaviour of automated vehicles (Rail-safe, Cautious, Normal, and All-knowing) and presents how these driving logics can be implemented in a commonly used traffic simulation program. The driving logics are also linked to assumptions on which logic that could operate in which environment at which part of the transition period. Simulation results for four different types of road facilities are also presented to illustrate potential effects on traffic performance of the driving logics. The simulation results show large variations in throughput, from large decreases to large increases, depending on driving logic and penetration rate.Funding Agencies|European UnionEuropean Union (EU) [H2020-ART-2016-2017, 723201]</p

DEFINITION OF A PYTHON SCRIPT FOR THE MICRO-SIMULATION OF THE TRUCK PLATOONING SYSTEM

Truck platooning is, by now, one of the major topics in transport science and freight transport. The benefits arising from the system explain the growing interest of the involved stakeholders and the many field-tests planned in the next years. This run towards truck platooning saw an abrupt acceleration but there are risks that should be accounted for. Even though field-tests are fundamental for the implementation of a new transport system, they will hardly cover all the traffic scenarios that a platoon of trucks will face on the European network. Therefore, there is the need for many more studies based on traffic simulation and for tools enabling traffic simulation software to reproduce truck platooning. In this framework, the paper has two aims, the first one being to report and describe a Python script to reproduce truck platooning with a common commercial simulation software. The second one is to apply said script to analyse what is the best driving strategy for a platoon of truck to limit the hindrance on the surrounding traffic while approaching a critical highway segment such as the on-ramp one. At the end of the paper, a comparison between three different strategies (driving as usual, dissolution and headway adaptation) is carried out and commented.Peer reviewe

Deformation-induced grain growth and twinning in nanocrystalline palladium thin films

The microstructure and mechanical properties of nanocrystalline Pd films prepared by magnetron sputtering have been investigated as a function of strain. The films were deposited onto polyimide substrates and tested in tensile mode. In order to follow the deformation processes in the material, several samples were strained to defined straining states, up to a maximum engineering strain of 10%, and prepared for post-mortem analysis. The nanocrystalline structure was investigated by quantitative automated crystal orientation mapping (ACOM) in a transmission electron microscope (TEM), identifying grain growth and twinning/detwinning resulting from dislocation activity as two of the mechanisms contributing to the macroscopic deformation. Depending on the initial twin density, the samples behaved differently. For low initial twin densities, an increasing twin density was found during straining. On the other hand, starting from a higher twin density, the twins were depleted with increasing strain. The findings from ACOM-TEM were confirmed by results from molecular dynamics (MD) simulations and from conventional and in-situ synchrotron X-ray diffraction (CXRD, SXRD) experiments

Untangling dislocation and grain boundary mediated plasticity in nanocrystalline nickel

Nanocrystalline (nc) materials possess unique mechanical properties, such as very high strength. However, an understanding of the deformation mechanisms and the succession of related microscopic processes that occur during deformation is still incomplete. We used synchrotron-based in situ compression testing to investigate the sequence of deformation mechanisms emerging in bulk nc nickel with a grain size of 30 nm. The study was accompanied by high-resolution grain size analysis and crystal orientation mapping using transmission electron microscopy. Regardless of the initial microstructure, the deformation behavior of electrodeposited nc Ni is initiated by inhomogeneous elastic lattice straining and its accommodation within the grain boundary network, followed by the onset of dislocation plasticity, which was inferred from texture evolution, and stress-driven grain growth. This observation indicates that deformation in nc metals is governed by a succession of different, partly overlapping mechanisms. It is estimated that intragranular dislocation plasticity contributes only about 40% to the overall deformation. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved