Failure Processes in Embedded Monolayer Graphene under Axial Compression

Exfoliated monolayer graphene flakes were embedded in a polymer matrix and loaded under axial compression. By monitoring the shifts of the 2D Raman phonons of rectangular flakes of various sizes under load, the critical strain to failure was determined. Prior to loading care was taken for the examined area of the flake to be free of residual stresses. The critical strain values for first failure were found to be independent of flake size at a mean value of -0.60 % corresponding to a yield stress of -6 GPa. By combining Euler mechanics with a Winkler approach, we show that unlike buckling in air, the presence of the polymer constraint results in graphene buckling at a fixed value of strain with an estimated wrinkle wavelength of the order of 1-2 nm. These results were compared with DFT computations performed on analogue coronene/ PMMA oligomers and a reasonable agreement was obtained.Comment: 28 pages. Manuscript 20 pages, 8 figures. Supporting information 10 pages, 6 figure

Failure Processes in Embedded Monolayer Graphene under Axial Compression

Exfoliated monolayer graphene flakes were embedded in a polymer matrix and loaded under axial compression. By monitoring the shifts of the 2D Raman phonons of rectangular flakes of various sizes under load, the critical strain to failure was determined. Prior to loading care was taken for the examined area of the flake to be free of residual stresses. The critical strain values for first failure were found to be independent of flake size at a mean value of –0.60% corresponding to a yield stress up to -6 GPa. By combining Euler mechanics with a Winkler approach, we show that unlike buckling in air, the presence of the polymer constraint results in graphene buckling at a fixed value of strain with an estimated wrinkle wavelength of the order of 1–2 nm. These results were compared with DFT computations performed on analogue coronene/PMMA oligomers and a reasonable agreement was obtained

Transforming Students’ Knowledge about Democracy and Citizenship through Art and the Use of Educational Media

Democracy and citizenship are two values that are closely linked to the education of each individual. Most education systems seek to transform attitudes and enhance individuals’ knowledge by offering courses related to citizenship and democracy. In Greece until the school year 2019-2020, the course “Modern World, Citizenship and Democracy” was taught to 11th grade students. In a sample of 76 students, research was conducted to explore how different works of art can contribute to the expected transformation. Students were given a digital list of concepts related to “Democracy” and “Citizenship and Rights” and were asked to choose a concept and link it to a work of art by submitting their project to a digital repository. The concepts that students mostly chose were racism, democracy, and rights (individual, political, social). In addition, projects were recorded, in which the selected work of art referred to two concepts. The works of art they chose were mainly: painting, cinema, photography, and sketch/comics. The use of the internet as a source of artwork was limited. There seems to be a strong correlation between the choice of concepts and socio-economic reality. In addition, the operation of the digital classroom and the dialogue developed in relation to their projects, strengthened the educational framework, created a variety of perspectives, and contributed to the expected transformation

An analytical solution of the Reynolds Equation for the finite journal bearing and evaluation of the lubricant pressure

The Reynolds equation for the pressure distribution of the lubricant in a journal bearing with finite length is solved analytically. Using the method of the separation of variables in an additive and in a multiplicative form a set of particular solutions of the Reynolds equation is added in the general solution of the homogenous Reynolds equation and a closed form expression for the definition of the lubricant pressure is presented. The Reynolds equation is split in four linear ordinary differential equations of second order with non constant coefficients and together with the boundary conditions they form four Sturm-Liouville problems with the three of them to have direct forms of solution and one of them to be confronted using the method of power series. In this part of the work, the mathematical procedure is presented up to the point that the application of the boundaries for the pressure distribution yield the final definition of the solution with the calculation of the constants. The distributions of the pressure given from the particular solution and the solution of the homogeneous Reynolds equation are presented together with the resulting pressure. Also, the results of an approximate analytical solution using Bessels functions and linearization of the fluid film thickness function are also presented together with the results of the numerical solution using the finite differences method. Diagrams for the pressure profiles under the current study are compared with those from the approximate analytical and the numerical solution. The locations in which the maximum, the zero, and the minimum pressure are presented are given as a function of eccentricity rate with closed form expressions