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SIZEFFECTS Report Summary

Project ID: 291002
Funded under: FP7-IDEAS-ERC
Country: Italy

Final Report Summary - SIZEFFECTS (Size effects in fracture and plasticity)

The general goal of the SIZEFFECTS project was to understand how materials respond to external mechanical perturbations and in particular how materials strength changes with the sample size. Fracture size effects are a fundamental problem in the design of components, structures and devices that are subject to elastic loads. The straightforward way to control unwanted failure is to perform a test and measure the load that can be carried by the sample without failing. The strength is, however, not deterministic and nominally identical samples can fail at very different loads. Furthermore, when the sample is very large, performing a direct test is not even feasible. This is why a theory of fracture size effects is needed. On the other hand in micro and nanoscale samples, plastic deformation displays not only size effects but also intermittent strain bursts. This in contrast with macroscopic samples where plasticity is a smooth process. Understanding this issue is becoming particularly important in the current miniaturization trend towards nanoscale devices, since the relative amplitude of fluctuations grows as the sample size is reduced. The use of conventional continuum mechanics is, however, problematic and should be complemented by a statistically based approach addressing the complex interplay between defects and long-range elastic interactions.

The SIZEFFECTS project made important progress in understanding the role in fracture size effects of elasticinteractions, strain rate and temperature by numerical studies of disordered lattice models, molecular dynamics simulations of atomistic models
and theoretical calculations. This theoretical understanding was then applied to the study the fracture of nanoscale materials, like graphene or amorphous silica nanowires, and of biological and bio-inspired materials, such as cell membranes and filament networks. Furthermore, numerical and theoretical results obtained during the SIZEFFECTS project for plastically deforming materials have uncovered intriguing statistical properties in the deformation of micro-scale materials with implications for large scale deformation in the geological context. The SIZEFFECTS project achieved a comprehensive understanding of the scale dependent features of plastic deformation in crystalline, polycrystalline and amorphous materials with application in different contexts, from soft colloidal matter to hard metallic materials. Ideas, statistical methods and theoretical tools developed throughout the SIZEFFECTS project have been applied to a wide variety of related phenomena in materials science, physics and biology.

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