The present study focuses on constitutive relations, toughening mechanisms and fracture characterization of polymeric materials. At first the progress on these three aspects is reviewed comprehensively. Then we study the deformation behavior of particulate-modified polymers and in situ composites by the two-scale method for inhomogeneous media....[ Read more ]

The present study focuses on constitutive relations, toughening mechanisms and fracture characterization of polymeric materials. At first the progress on these three aspects is reviewed comprehensively. Then we study the deformation behavior of particulate-modified polymers and in situ composites by the two-scale method for inhomogeneous media.

A face-centered cubic cell model and a particle-crack tip interaction model are presented to account for full inter-particle interaction and particle-crack tip interaction in rubber-toughened polymers. The face-centered cubic cell model is also adopted to study the deformation and toughening mechanisms for rigid-rigid polymer blends containing one particulate phase. The aligned and staggered periodic cell models are provided for in-situ composites containing ellipsoidal liquid crystalline polymer (LCP) phase, which can be reduced to the simple regular cubic cell model and the face-centered cubic cell model for spherical particles.

The local stress and strain distributions are obtained by three-dimensional elastoplastic finite element analysis to explore the rubber-toughening mechanisms and the rigid-rigid polymer toughening mechanisms at different stress triaxiality. The effective elastoplastic constitutive relations for rubbery and plastic particulate-toughened polymers are derived by the homogenization method. The effects of the volume fraction, the aspect ratio, the fiber spacing as well as the fiber arrangement of the LCP phase on the effective longitudinal Young modulus, transverse Young modulus and shear modulus of in-situ composites are also investigated by two-dimensional finite element analysis.

Then, a generalized fracture criterion based upon the essential fracture work concept is developed to describe crack propagation under small-scale yielding (SSY) and large-scale yielding (LSY) including stable crack growth (SCG). The applicability of the generalized fracture mechanics principles to the toughness prediction for brittle and ductile fracture is investigated, which provides a consistent and unified clarification of various fracture characterization techniques.

Finally, the essential fracture work method is simulated numerically for the first time using the crack-tip opening angle (CTOA) fracture criterion and the true stress-strain relation of the material under consideration. The load-displacement curves and the J[subscritp R]-curves for samples with different ligament lengths can be calculated for any given specimen geometry. The finite element analysis is carried out for deep double-edge notched tension (DENT), deep center notched tension (DCNT), single-edge notched tension (SENT) and center-lined ligament loading (CLLL) samples. Numerical results for a selection of DENT and DCNT specimens of PE thin sheets are in good comparison with experimental data.