Simulation of Low-velocity Impact Damage in Layered Composites using a Cohesive-based Finite Element Technique

The mechanism of damage initiation and growth in layered composites subjected to low- velocity impact is simulated using a cohesive-based finite element technique. The numerical technique used comprises cohesive elements sandwiched between the regular finite elements. The basic structure of the formulation is presented, followed by the results of the simulation. The success of this numerical technique is dependent on the cohesive model used. The cohesive model is a thermodynamic all^-based phenomenological model, describing the damage ahead of a crack tip. Details of the rate-independent cohesive model used in this study are also presented

Cohesive Modeling of Dynamic Fracture: Rate Dependence and Intersonic Crack Motion

167 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2001.The second dynamic fracture problem addressed in this thesis is concerned with the issue of intersonic crack propagation, a topic of great interest in the fracture mechanics and geophysics community with the recent first direct observations of shear cracks exceeding the shear wave speed in homogeneous brittle specimen. Special interest is placed in this study on the possibility of steady-state and transient intersonic crack motion under mixed-mode conditions. Results show that exclusive shear damage in the cohesive zone is responsible for intersonic crack propagation even though the external load comprises of both shear and tensile components. The situation is very different in the subsonic regime, where crack motion is a result of combined shear and tensile damage inside the cohesive zone. The study also provides information on the effect of mode mixity on the length of the cohesive failure zone.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD

Simulation of Low-velocity Impact Damage in Layered Composites using a Cohesive-based Finite Element Technique

The mechanism of damage initiation and growth in layered composites subjected to low- velocity impact is simulated using a cohesive-based finite element technique. The numerical technique used comprises cohesive elements sandwiched between the regular finite elements. The basic structure of the formulation is presented, followed by the results of the simulation. The success of this numerical technique is dependent on the cohesive model used. The cohesive model is a thermodynamically-based phenomenological model, describing the damage ahead of a crack tip. Details of the rate-independent cohesive model used in this study are also presented

Asymptotic Analysis of a Mode III Stationary Crack in a Ductile Functionally Graded Material

The dominant and higher-order asymptotic stress and displacement fields surrounding a stationary crack embedded in a ductile functionally graded material subjected to anti-plane shear loading are derived. The plastic material gradient is assumed to be in the radial direction only and elastic effects are neglected. As in the elastic case, the leading (most singular) term in the asymptotic expansion is the same in the graded material as in the homogeneous one with the properties evaluated at the crack tip location. Assuming a power law for the plastic strains and another power law for the material spatial gradient, we derive the next term in the asymptotic expansion for the near-tip fields. The second term in the series may or may not differ from that of the homogeneous case depending on the particular material property variation. This result is a consequence of the interaction between the plasticity effects associated with a loading dependent length scale (the plas-tic zone size) and the inhomogeneity effects, which are also characterized by a separate length scale (the property gradient variation)