Biomechanical Properties of Human Dilated Ascending Aorta

Aneurysms of ascending aorta are dilatation of the first part of the human aorta. They commonly show no clinical symptoms. This condition increases the risk of aorta dissection, which is a life-threatening condition. In this study we attempted to elucidate the changes in the biomechanical properties that occur in the dilated human ascending aorta. Fourteen specimens of ascending aorta wall were mechanically tested under a uniaxial tensile test. Two specimens from each ascending aorta anterior region were cut in longitudinal and circumferential directions. The samples were stretched until rupture of the sample occurred. The obtained experimental data were processed to determine maximal stress, maximal strain and the tangential modulus of elasticity in the linear part of the stress-strain curve. The obtained results showed a remarkable anisotropy of the ascending aorta tissue. We found higher strength of the tissue in the circumferential direction than in the longitudinal direction. There were no statistically significant differences between the strains of the samples. Tangential modulus of elasticity of the aortic samples in the longitudinal direction was significantly lower than the elastic modulus of the samples in the circumferential direction. The tissue in the circumferential direction is stronger and stiffer than in the longitudinal direction.

Hardening Curve Plotting and Determination of the Coating Limiting State Criterion based on the Continuous Indentation Method and Computational Modelling

The article describes the method of determining the parameters of the hardening curve of homogeneous and structured coatings (modulus of elasticity, tangential modulus of elasticity and yield strength) required for the strength analysis of parts with coatings that determine their basic performance and strength characteristics. The dependence for determination of tangential (tangential) modulus of elasticity using the results of nanoindentation is proposed. An algorithm for determining the yield strength of the coating material is developed based on solving the problem of elastic-plastic deformation of the coating during the introduction of the indenter by the finite element method. According to the proposed method, the parameters of the TiN/AlN in coating hardening curve were determined based on the results of indentation of the sample of tool high-speed steel with the appropriate coating.

Scaled Memory Description of Hysteretic Material Behavior

Herein the concept of scaled memory (SM) is proposed to describe hysteretic material behaviors. SM scales the nonlinear variation of tangential modulus during monotonic loadings into a piecewise linear distribution, which can easily be modified to simulate specific characteristics of material behavior during cyclic loadings. As an example, SM is applied to eliminate artificial ratchetting in bounding surface plasticity, and to produce closed stress-strain loops during cyclic loadings, without introducing a single material constant. SM is generalized to six dimensions in the particular case of pressure-independent materials, and is applied to simulate the hysteretic responses of metals.