Micromechanics

About: Micromechanics is a research topic. Over the lifetime, 6000 publications have been published within this topic receiving 162635 citations.

Micromechanics of deformation in particle-toughened polyamides

Abstract: It is now well appreciated that a number of semicrystalline polymers can be effectively toughened by the addition of a well-dispersed secondary phase, when the average interparticle matrix ligament thickness, Λ, of the blend is reduced below a critical length parameter, Λc. This critical parameter is a specific material characteristic of the base polymer and can be achieved by various combinations of filler particle volume fraction and particle size. Recently, the significant improvements in toughness achieved when Λ≤Λc were attributed to a morphological transition taking place when interface-induced crystallization of characteristic thickness Λc/2 successfully percolates through the primary phase. These transcrystallized layers are highly anisotropic in their mechanical response and, as a result, change the preferred modes of plastic deformation in the material, enabling the large plastic strains, which provide the high toughness. This study aims to elucidate the micromechanics and micromechanisms responsible for the high toughness exhibited by these morphologically altered heterogeneous systems via a series of micromechanical models. The case of polyamide-6 modified with cavitating spherical elastomeric particles treated as voids is modeled. It is found that the mechanical response and local modes of plastic deformation of these systems depend strongly on the morphology of the primary phase, the volume fraction of filler particles and the level of applied stress triaxiality. In particular, when Λ<Λc and highly textured material percolates through the matrix, the material is found to deform by multiple shear banding along crystallographic planes of low shear resistance in the matrix ligaments diagonally bridging particles. This mode of plastic deformation is found to be robust to increases in triaxiality and, indeed, the textured material acts to resist void growth while promoting shear along the preferentially oriented crystallographic planes.

Energy dissipation due to interfacial slip in nanocomposites reinforced with aligned carbon nanotubes.

Abstract: Interfacial slip mechanisms of strain energy dissipation and vibration damping of highly aligned carbon nanotube (CNT) reinforced polymer composites were studied through experimentation and complementary micromechanics modeling. Experimentally, we have developed CNT-polystyrene (PS) composites with a high degree of CNT alignment via a combination of twin-screw extrusion and hot-drawing. The aligned nanocomposites enabled a focused study of the interfacial slip mechanics associated with shear stress concentrations along the CNT-PS interface induced by the elastic mismatch between the filler and matrix. The variation of storage and loss modulus suggests the initiation of the interfacial slip occurs at axial strains as low as 0.028%, primarily due to shear stress concentration along the CNT-PS interface. Through micromechanics modeling and by matching the model with the experimental results at the onset of slip, the interfacial shear strength was evaluated. The model was then used to provide additional insig...