Open Science Seminar, March 28

Abstracts

 

Reflecting on failure theories for composite delamination – a physics perspective

René Alderliesten, Delft University of Technology    

In engineering strength and fatigue assessment generally stress based failure theories are adopted that link induced stresses to a critical state of failure. For delamination growth, usually fracture mechanics concepts are adopted where strain energy relates rates (as equivalent to stress intensity factors) are related in a phenomenological fashion to delamination growth rates. An increasing amount of versions of these methodologies are presented in literature indicating a lack of consensus on how to converge to a unified theory.

This presentation takes recent studies on quasi-static and fatigue delamination growth under mode I, mode II and mixed mode opening, in which a more physics based concept was adopted. In the tests, the strain energy applied was quantified and correlated to the strain energy dissipation required for delamination growth. Aside from providing better insight in the phenomenon of delamination growth, it will be indicated how future theories could be based on tis physical concepts.

 

Liquid metal catalysis: role of liquid copper in high-quality graphene synthesis

Mie Andersen, Theoretical Chemistry, Technical University of Munich, Germany

Chemical vapor deposition on (solid) metal surfaces has been established as an important and efficient graphene synthesis method, but often the samples produced suffer from defects and impurities. Recent experimental evidence suggests that using liquid metal catalysts (LMCats) instead of solid ones bears the prospect of a continuous production of graphene with unprecedented quality and production speed [1,2]. However, the current knowledge about the catalytic properties of LMCats is extremely poor, as they had no technological significance in the past. In the LMCat project [3] we study the growth mechanisms of two-dimensional materials on metal catalysts that are in the liquid state during the growth process. We particularly focus on in situ experiments (simultaneous synchrotron X-ray scattering, Raman spectroscopy and optical microscopy techniques) and theoretical modeling (density functional theory, molecular dynamics simulations) of the growth of graphene on a liquid copper substrate. In my talk, I will give an overview of recent progress on the growth and in situ characterization of graphene samples, as well as theoretical modeling focusing on the initial steps of graphene nucleation and the role of the liquid copper substrate for the growth and the experimentally observed self-alignment of growing flakes on the liquid catalyst [1,4].

[1] D. Geng et al. PNAS 109, 7992 (2012).

[2] L. Tan, M. Zeng, T. Zhang, L. Fu, Nanoscale 7, 9105 (2015).

[3] www.lmcat.eu

[4] M. Zeng et al., J. Am. Chem. Soc., 138, 7812 (2016)

 

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