Micromechanical behavior of damaged composites subjected to dynamic loading will be investigated. For this purpose, a novel efficient analytical-numerical tool based on the boundary integral equation method (BIEM) or the boundary element method (BEM) will be developed and applied to the micromechanical investigations of particulate, layered and fiber-reinforced composites with micro-damages like interior, surface and interface cracks as well as imperfect bonding conditions. Both impact and time-harmonic dynamic loadings will be considered. By using the dynamic Greens functions, boundary integral equations will be formulated for analysis of crack and inclusion problems without any strong restrictions on their geometrical configuration and loading conditions. Particulate and disk-shaped elastic inclusions as well as elastic fibers will be considered as the reinforcements of the composites, while interior or interface cracks, thin interphase layers, and imperfect bonding between the material constituents will be taken as the micro-damages in the composites. The interfacial displacements and tractions for the volumetric inclusions, jumps of these quantities across thin-walled inclusions and interphases, and crack-opening-displacements are the unknown functions in the equations. Moreover, BIEM/BEM for cracked anisotropic solids under dynamic loading will be developed, which is suitable for dynamic analysis of fiber-reinforced composites with cracks. The boundary integral equations will be solved numerically by adopting efficient regularization and discretization procedures both in the time and frequency domain. With the tool to be developed in this project, a wide class of dynamic problems in damaged composites will be analyzed, in particular:
Particulate composites with cracks;
Layered composites or laminates with cracks;
Fiber-reinforced composites with cracks or cracked anisotropic solids;
Interactions between reinforcing particles or fibers and cracks with different shapes, sizes and orientations;
Interior, sub-surface, surface-breaking and interface cracks under dynamic loading;
Effects of imperfect bonding conditions between the materials constituents.
The influences of the inertial effects on the near-field (stress concentration factors and stress intensity factors), the far-field (scattered displacements and scattering cross sections), and the macroscopic or effective material properties (dynamic elastic constants, dynamic stiffness, phase velocities and attenuation of elastic waves) will be analyzed for dynamic pulses of different shapes and propagation directions. The reinforcing properties of dispersed material phases, resonance phenomena, failure pattern, and flaw detection parameters by using ultrasonics will be studied in details. The proposed project has direct engineering applications in material sciences, fracture and damage mechanics, structural and nanomechanics, geomechanics, and nondestructive material testing.