Narrow Results

Two hypotheses for the mechanism of anode break excitation in cardiac tissue are electrotonic interaction between adjacent regions of depolarization and hyperpolarization, and a hyperpolarization-activated membrane current, i_f. We incorporate membrane kinetics proposed for i_f into the bidomain model with unequal anisotropy ratios. During unipolar stimulation, we find that:

(1) The mechanisms of cathode make, cathode break, and anode make excitation are insensitive to i_f.

(2) Both electrotonic interactions and i_f contribute to anode break excitation. In our simulations, i_f makes the dominant contribution.

(3) Electrotonic interactions cause the "dip" in the anodal strength-interval curve.

(4) Following anode break excitation, the wave front propagates in the direction perpendicular to the fibers.

(5) i_f improves the agreement between the measured and calculated strength-interval curves.

We suggest three experiments to determine the mechanism of anode break excitation: measure the site and timing of initial excitation, or use drugs to suppress i_f.

The anisotropy affected fatigue cracks that propagate on the rolling direction as mixed mode I-II cracks in CCT-specimens of pure aluminum sheets were predicted using Finite Element Method. The crack growth paths were estimated based on the value of mode I, II, total stress intensity factor range, and the ratio of mode II and mode I energy release rate of the crack. The predictions of crack propagation paths in no-hole specimens and 6-type holed specimens with 0, 30, 45 and 60 degrees of rolling direction towards loading direction were performed and the results were coincided with experimental results.

Numerical implementation of an anisotropic constitutive model for clays (SANICLAY) is presented. Moreover, a case study in which a soil embankment is placed on a K₀-consolidated over-consolidated clay is analyzed by conducting an elastoplastic fully-coupled finite element analysis. It is shown that anisotropy has significant impact on the ground settlement caused by the placement of soil embankment and on the pore pressure generation and dissipation within the foundation soil. The simulations using SANICLAY favorably compare with the field measurements of ground settlement and pore pressure. The drawbacks of the use of an isotropic elastoplastic model (Cam Clay) are also demonstrated.

Hyperelastic models are of particular interest in modeling biomaterials. In order to implement them, one must derive the stress and elasticity tensors from the given potential energy function explicitly. However, it is often cumbersome to do so because researchers in biomechanics may not be well-exposed to systematic approaches to derive the stress and elasticity tensors as it is vaguely addressed in literature. To resolve this, we present a framework of a general approach to derive the stress and elasticity tensors for hyperelastic models. Throughout the derivation we carefully elaborate the differences between formulas used in the displacement-based formulation and the displacement/pressure mixed formulation. Three hyperelastic models, Mooney–Rivlin, Yeoh and Holzapfel–Gasser–Ogden models that span from first-order to higher order and from isotropic to anisotropic materials, are served as examples. These detailed derivations are validated with numerical experiments that demonstrate excellent agreements with analytical and other computational solutions. Following this framework, one could implement with ease any hyperelastic model as user-defined functions in software packages or develop as an original source code from scratch.