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

Modelling the fracture behaviour of adhesively-bonded joints as a function of test rate

Tapered-double cantilever-beam joints were manufactured from aluminium-alloy substrates bonded together using a single-part, rubber-toughened, epoxy adhesive. The mode I fracture behaviour of the joints was investigated as a function of loading rate by conducting a series of tests at crosshead speeds ranging from 3.33 × 10−6 m/s to 13.5 m/s. Unstable (i.e. stick–slip crack) growth behaviour was observed at test rates between 0.1 m/s and 6 m/s, whilst stable crack growth occurred at both lower and higher rates of loading. The adhesive fracture energy, GIc, was estimated analytically, and the experiments were simulated numerically employing an implicit finite-volume method together with a cohesive-zone model. Good agreement was achieved between the numerical predictions, analytical results and the experimental observations over the entire range of loading rates investigated. The numerical simulations were able very readily to predict the stable crack growth which was observed, at both the slowest and highest rates of loading. However, the unstable crack propagation that was observed could only be predicted accurately when a particular rate-dependent cohesive-zone model was used. This crack-velocity dependency of GIc was also supported by the predictions of an adiabatic thermal-heating model.Deposited by bulk importAM

Simulation of fracture tests on notched composite plates

Size effects influence the behavior of composites and have a great effect on their properties such as strength, type of failure, etc. The effects of size of the specimen on the behavior of composite laminates were studied based on numerical analyses of sharp and blunt notched [45/90/-45/0] 4s carbon/epoxy composite laminates. Five different numerical models in each notch case with in-plane dimensions scaled up to a factor 16 were analyzed. The computational framework adopted in the study uses phantom node method for modelling matrix cracks, continuum damage model for fibre failure and interface elements for de- lamination. The capability of the framework to capture the size effects in the failure load and failure mechanisms of composite laminates with both sharp and blunt notches was assessed. The damage zone properties captured through CT images from interrupted tests were compared with the results obtained from numerical simulations. Parametric studies were carried out on the numerical models to match the simulation and the experimental results. The observations from the study revealed that there is a good correlation between the experimental and simulation results. The computational framework used in the study predicts the strengths of composite laminates, replicates size effects in the laminates and the failure mechanisms accurately.Civil Engineering | Structural Mechanic

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

Cohesive zone modelling of wafer bonding and fracture: effect of patterning and toughness variations

Direct wafer bonding has increasingly become popular in the manufacture of microelectromechanical systems and semiconductor microelectronics components. The success of the bonding process is controlled by variables such as wafer flatness and surface preparation. In order to understand the effects of these variables, spontaneous planar crack propagation simulations were performed using the spectral scheme in conjunction with a cohesive zone model. The fracture-toughness on the bond interface is varied to simulate the effect of surface roughness (nanotopography) and patterning. Our analysis indicated that the energetics of crack propagation is sensitive to the local surface property variations. The patterned wafers are tougher (well bonded) than the unpatterned ones of the same average fracture-toughness