Final Activity Report Summary - SIZEDEPEN (Engineering mechanics based on size-dependent materials properties)
When confined to sub-micrometer dimensions, many materials exhibit unexpected and potentially useful properties that differ from theirs bulk behaviour. This unusual behaviour can be exploited by high-tech industries in small-scale mechanical devices. As conventional continuum theory cannot account for size dependencies there is a need for new material models complying with both description of physical effects and applicability for engineering design.
SIZEDEPEN achieved major breakthroughs in the following areas: Firstly, with respect to a physically-based size dependent continuum theory of plasticity, the basis for a three-dimensional continuum theory of dislocations was laid. This theory was compared to discrete dislocation dynamics simulations, as well as to experiments, and turned out to predict various size effects occurring in small scale plasticity. Furthermore, detailed statistical analyses revealed the intermittent nature of plastic flow on the micron scale which gave rise to intrinsic limitations of forming procedures in small dimensions. The statistical modelling of dislocation-based plasticity was also extended to the treatment of multiple slip processes. New theoretical approaches were developed, which would allow for further generalisations in the future. The discrete dislocation modelling tool was improved in various respects through the implementation of rules for dynamic dislocation motion obtained in atomistic simulations and the treatment of complex boundary conditions. Several columnar grains undergoing plastic deformation were simulated by the discrete dislocation method and the results were compared to finite element simulations. Continuum simulations of the fatigue behaviour of a thin film made up of 250 grains during 1,000 cycles of tensile deformation were performed. Moreover, the development of surface roughness induced by plasticity was predicted in detail. Important progress was achieved towards the understanding of the so-called splitting of drawn tungsten wires, which was a problem of high technological relevance in the lighting industry. The deformation behaviour of tungsten wires was simulated on various scales, ranging from atomistic simulations to macroscopic continuum simulations. The splitting of tungsten wires was found to result from radial tensile stresses in the drawn wire and seemed to be promoted by the special distribution of orientations of the crystallites in such wires.
SIZEDEPEN organised five major events. The first was a scientific workshop on size-dependent mechanical properties in Leiden, the Netherlands, organised in March 2005, which attracted 43 participants from all over Europe. The most important training event of the network was a summer school on multi-scale modelling of plasticity and fracture by means of dislocation mechanics, which took place at the International Centre for Mechanical Sciences (CISM) in Udine in July 2005. The summer school was attended by all members of the project and the total number of participants was 74. A smaller training event was the workshop on experimental characterisation of materials, organised in Budapest in May 2006. A total of 15 young scientists, including all appointed researchers from SIZEDEPEN, attended this workshop. The last training event was an industrial workshop organised in Freiburg in March 2007, which attracted all appointed researchers and 12 external participants. In addition, in August 2007 SIZEDEPEN organised the 17th International Workshop on Computational Mechanics of Materials (IWCMM 17) as the final conference on its subject in Paris. This conference attracted 102 participants from all over Europe and abroad and was the ideal platform to inform the research community about the results achieved in the partial projects.
An intensive exchange programme for the appointed researchers confronted them with different scientific methods and schools of thoughts. The project promoted the build up of new collaborations between the involved partners which would surely exceed the projects duration.
SIZEDEPEN achieved major breakthroughs in the following areas: Firstly, with respect to a physically-based size dependent continuum theory of plasticity, the basis for a three-dimensional continuum theory of dislocations was laid. This theory was compared to discrete dislocation dynamics simulations, as well as to experiments, and turned out to predict various size effects occurring in small scale plasticity. Furthermore, detailed statistical analyses revealed the intermittent nature of plastic flow on the micron scale which gave rise to intrinsic limitations of forming procedures in small dimensions. The statistical modelling of dislocation-based plasticity was also extended to the treatment of multiple slip processes. New theoretical approaches were developed, which would allow for further generalisations in the future. The discrete dislocation modelling tool was improved in various respects through the implementation of rules for dynamic dislocation motion obtained in atomistic simulations and the treatment of complex boundary conditions. Several columnar grains undergoing plastic deformation were simulated by the discrete dislocation method and the results were compared to finite element simulations. Continuum simulations of the fatigue behaviour of a thin film made up of 250 grains during 1,000 cycles of tensile deformation were performed. Moreover, the development of surface roughness induced by plasticity was predicted in detail. Important progress was achieved towards the understanding of the so-called splitting of drawn tungsten wires, which was a problem of high technological relevance in the lighting industry. The deformation behaviour of tungsten wires was simulated on various scales, ranging from atomistic simulations to macroscopic continuum simulations. The splitting of tungsten wires was found to result from radial tensile stresses in the drawn wire and seemed to be promoted by the special distribution of orientations of the crystallites in such wires.
SIZEDEPEN organised five major events. The first was a scientific workshop on size-dependent mechanical properties in Leiden, the Netherlands, organised in March 2005, which attracted 43 participants from all over Europe. The most important training event of the network was a summer school on multi-scale modelling of plasticity and fracture by means of dislocation mechanics, which took place at the International Centre for Mechanical Sciences (CISM) in Udine in July 2005. The summer school was attended by all members of the project and the total number of participants was 74. A smaller training event was the workshop on experimental characterisation of materials, organised in Budapest in May 2006. A total of 15 young scientists, including all appointed researchers from SIZEDEPEN, attended this workshop. The last training event was an industrial workshop organised in Freiburg in March 2007, which attracted all appointed researchers and 12 external participants. In addition, in August 2007 SIZEDEPEN organised the 17th International Workshop on Computational Mechanics of Materials (IWCMM 17) as the final conference on its subject in Paris. This conference attracted 102 participants from all over Europe and abroad and was the ideal platform to inform the research community about the results achieved in the partial projects.
An intensive exchange programme for the appointed researchers confronted them with different scientific methods and schools of thoughts. The project promoted the build up of new collaborations between the involved partners which would surely exceed the projects duration.