Mechanical properties of heterogeneous systems based on carbon black (CB) filled semi-crystalline ethylene butyl acrylate (EBA) copolymer nanocomposites are characterized using nano-indentation technique. The size effect and CB content dependence on the deformation behavior at room temperature were investigated. The phenomenology for hardness response (H) indicates a typical enhancement of the H when the indentation depth (h) decreases as for the usual elastomeric materials. All H-h curves, fitted according to the Meyer's empirical power law and Franck elasticity model, highlight the so-called length-scale-dependent deformation. Similar trend is observed for the elastic modulus. Furthermore, it is evidenced that the increases of CB content increases the mechanical properties of composites, that is, hardness and elastic modulus. This behavior can be mainly related, on the one hand, to the change of the meso-structure, formed by the interconnected network of polymer and the aggregates of CB particles and to the nature of the polymer matrix, on the other hand. The mechanical properties characterized from micro and submicron indentations were compared to that characterized at macroscopic scale to highlight the possible correlations between the two scales. This investigation can interest many applications of polymer composites for rubber technology such as tires industry, soft robotic, and adhesives.
Numerous methods have been proposed to estimate the indentation fracture toughness Kic for brittle materials. These methods generally uses formulae established from empirical correlations between critical applied force, or average crack length, and classical fracture mechanics tests. This study compares several models of fracture toughness calculation obtained by using Vickers indenters. Two optical glasses (Crown and Flint), one vitroceramic (Zerodur) and one ceramic (hydroxyapatite) are tested. Fracture toughness and hardness are obtained by using instrumented Vickers indentation at micrometer scale. Young's moduli are obtained by instrumented Berkovich indentation at nanometer scale. Fracture toughness is calculated with models involving crack length measurements, and by models free of crack length measurements by considering critical force, chipping, pop-in. Finally, method based on the cracking energy, commonly employed for coated materials is also used. The aim of this work is to compare seven methods, which enable the facture toughness determination, on four brittle materials. To do so, it was necessary to determine some specific constant in the case of Vickers tip use. On the one hand, results show that methods using crack length, critical force, edge chipping or pop-in lead to comparable results, and the advantages and drawbacks are highlighted. On the other hand, the indentation energy method leads to underestimated results of about 20%.
This work presents a study of crack propagation with a new 2D finite element method with the stretching of the mesh. This method affects at each propagation step new coordinates of each element node of the mesh. The structure is divided to areas and each area has its own coordinate formulas. A program in FORTRAN allows us to create a parametric mesh, which keeps the same number of nodes and elements during different steps of crack propagation. The nodes are stretched using the criterion of maximum circumferential stress (MCS). The fracture parameters such as stress intensity factors in modes I and II and the orientation angles are calculated by solving the problem by the finite element code ABAQUS.
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