Crack propagation computer simulation

A pecuhar sohd phase, which has been discovered not too long ago [172], is the quasi-crystalline phase. Quasi-crystals are characterized by a fivefold or icosahedral symmetry which is not of crystallographic type and therefore was assumed to be forbidden. In addition to dislocations which also exist in normal crystals, quasi-crystals show new types of defects called phasons. Computer simulations of the growth of quasicrystals [173] are still somewhat scarce, but an increasing number of quasi-crystalline details are studied by simulations, including dislocations and phasons, anomalous self-diffusion, and crack propagation [174,175]. 

Rowe RC, Roberts RJ. The effect of some formulation variables on crack propagation in pigmented tablet film coatings using computer simulation. Int J Pharm 1992 86 49-58. 

Fig. 3.18. Computer simulation results for fracture growth in perfect lattice. Transition from smoothly advancing crack to violent propagation and branching instabilities occurs with larger pulling stresses (from Marder and Fineberg 1996).

By definition, the crack will propagate only when h > ha. This is not only a consequence of the CRC concept but also supported by the molecular dynamics computer simulations [50,51] showing that a crossover exists from the force field region dominated by chain relaxation to one in which crack propagation occurs. 

Every theory makes certain assumptions. Computer simulations of polymers provide us with information inaccessible experimentally (17) the section Fractiu-e Mechanics and Crack Propagation deals more on this subject. The simulations also make possible testing theoretical models. If there is a disagreement between the behavior of a computer-generated material and the prediction, one cannot blame it on errors of the experiment. 

Computer Simulation of Crack Propagation. A typical experimental procedure for investigating fracture consists in looking at the fracture surface with a scanning electron microscope (SEM) or a transmission electron microscope (TEM) (49,50). This provides us with the morphology at the time of fracture, which is useful information. However, the microscopic techniques do not tell us where and how the crack(s) which eventually led to fracture had started. 

An example of the answer is shown in Figure 13 (51). A large crack which is going to cause fracture is formed at the interfaces on the matrix side. The beauty of computer simulations is that we can watch the cracks form and propagate imtil fracture. Animations of this process are made for added perspicuity. 

Computer analysis of crack propagation through finite element grids was developed by several authors. Cracks are represented by discontinuities of the finite element mesh, and smeared crack models were also applied. Cement-based matrices were considered as linear elastic bodies up to the point where cracks open and later their behaviour becomes highly non-linear. Various methods are applied to represent non-linear and heterogeneous materials and to simulate their behaviour under load (cf. Petersson 1981). In discrete models, cracks are represented as discontinuities in the finite element mesh. This is also where smeared crack models are introduced. 

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