There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Thermomechanics of shape memory polymers: Uniaxial experiments and constitutive modeling

Dual-phase (DP) steel is the flagship of advanced high-strength steels, which were the first among various candidate alloy systems to find application in weight-reduced automotive components. On the one hand, this is a metallurgical success story: Lean alloying and simple thermomechanical treatment enable use of less material to accomplish more performance while complying with demanding environmental and economic constraints. On the other hand, the enormous literature on DP steels demonstrates the immense complexity of microstructure physics in multiphase alloys: Roughly 50 years after the first reports on ferrite-martensite steels, there are still various open scientific questions. Fortunately, the last decades witnessed enormous advances in the development of enabling experimental and simulation techniques, significantly improving the understanding of DP steels. This review provides a detailed account of these improvements, focusing specifically on (a) microstructure evolution during processing, (b) exp...

An Overview of Dual-Phase Steels: Advances in Microstructure-Oriented Processing and Micromechanically Guided Design

DAMASK – The Düsseldorf Advanced Material Simulation Kit for modeling multi-physics crystal plasticity, thermal, and damage phenomena from the single crystal up to the component scale

Shape memory alloys (SMAs) exhibit peculiar thermomechanical, thermoelectrical and thermochemical behaviors under mechanical, thermal, electrical and chemical conditions. Examples of these materials are Cu-based SMAs, NiTi SMAs, ferrous SMAs, shape memory ceramics and shape memory polymers. NiTi SMAs in particular, have unique thermomechanical behaviors such as shape memory effect and pseudoelasticity, which have made them attractive candidates for structural vibration control applications. Numerous studies have been conducted in modeling and applications of NiTi SMAs in structural vibration control. Several active, passive and hybrid energy absorption and vibration isolation devices have been developed utilizing NiTi SMAs. In this paper we present an overview of NiTi behaviors, modeling and applications as well as their limitations for structural vibration control and seismic isolation.

/pdf/an-overview-of-vibration-and-seismic-applications-of-niti-4uy9khvvr0.pdf

An overview of vibration and seismic applications of NiTi shape memory alloy

Shape memory behaviour: modelling within continuum thermomechanics

Tension and torsion as well as combined tension-torsion tests on NiTi Tubes are presented in this article. Two different specimens are used in the experiments: one is austenitic and the other is martensitic at room temperature. The experiments are performed at nearly isothermal conditions. However, non-isothermal effects occur as well because of the self-heating of the material during the phase transitions and the detwinning of the martensite. These effects can be excluded applying very small deformation rates. In contrast to this, the influence of the self- heating on the material behavior is investigated in other experiments, where temperature fields are measured by means of infrared thermography. This allows detailed observations of the temperature field on the surface of the specimen and leads to additional insight into the thermomechanical behavior of shape memory alloys. In simple tension and pure torsion experiments the various effects of the material behavior can be decoupled. In particular, relaxation and creep processes are observed as a result of self-heating, but also as a consequence of the viscosity of the material. The combined tension-torsion experiments make it possible to analyze coupling effects of the biaxial behavior. In this context, a proportional and non-proportional deformation path is carried out.

Thermomechanical behavior of shape memory alloys

Stress computation in finite thermoviscoplasticity

Aiming for an integrated approach to computational materials engineering in an industrial context poses big challenges in the development of suitable materials descriptions for the different steps along the processing chain. The first key component is to correctly describe the microstructural changes during the thermal and mechanical processing of the base material into a semi-finished product. Explicit representations of the microstructure are most suitable there. The final processing steps and particularly component assessment then has to describe the entire component which requires homogenized continuum mechanical representations. A key challenge is the step in between, the determination of the (macroscopic) materials descriptions from microscopic structures. This article describes methods to include microstructure into descriptions of the deformation of metal, and demonstrates the central steps of the simulation along the processing chain of an automotive component manufactured from a dual phase steel.

Dirk Helm

Papers

Shape memory behaviour: modelling within continuum thermomechanics

Thermomechanical behavior of shape memory alloys

Stress computation in finite thermoviscoplasticity

Microstructure-based description of the deformation of metals: Theory and application

Material behavior of steel : Modeling of complex phenomena and thermodynamic consistency