Molecular & Cellular Biomechanics

on the onset of cracks in arteries

Konstantin Volokh — 2020-02-27

We present a theoretical approach to study the onset of failure localization into cracks
in arterial wall. The arterial wall is a soft composite comprising hydrated ground matrix
of proteoglycans reinforced by spatially dispersed elastin and collagen ?bers. As any mate-
rial, the arterial tissue cannot accumulate and dissipate strain energy beyond a critical value.
This critical value is enforced in the constitutive theory via energy limiters. The limiters
automatically bound reachable stresses and allow examining the mathematical condition of
strong ellipticity. Loss of the strong ellipticity physically means inability of material to propa-
gate superimposed waves. The waves cannot propagate because material failure localizes into
cracks perpendicular to a possible wave direction. Thus, not only the onset of a crack can be
analyzed but also its direction.
We use the recently developed constitutive theories of the arterial wall including 8 and
16 structure tensors to account for the ?ber dispersion. We enhance these theories with
energy limiters. We examine the loss of strong ellipticity in uniaxial tension and pure shear in
circumferential and axial directions of the arterial wall. We ?nd that the vanishing longitudinal
wave speed predicts the appearance of cracks in the direction perpendicular to tension. We
also ?nd that the vanishing transverse wave speed predicts the appearance of cracks in the the
direction inclined (non-perpendicular) to tension. The latter result is counter-intuitive yet it
is supported by recent experimental observations.

Kinematic and Dynamic Characteristics of Pulsating Flow in 180 Degree Tube

Tin-Kan Hung — 2020-02-27

Kinematic and dynamic characteristics of pulsating flow in a model of human aortic arch are obtained by a computational analysis. Three-dimensional flow processes are summarized by pressure distributions on the symmetric plane together with velocity and pressure contours on a few cross sections for systolic acceleration and deceleration. Without considering the effects of aortic tapering and the carotid arteries, the development of tubular boundary layer with centrifugal forces and pulsation are also analyzed for flow separation and backflow during systolic deceleration.

A A Study on the Finite Element Model for Head Injury in Facial Collision Accident

Bin Yang — 2020-02-27

This paper aims at predicting and evaluating the biomechanical response of the facial impact on head injury in a crash accident. With the combination of CT/MRI medical imaging technique, the 50th percentile head biomechanical model with detailed cranio-facial structure is established. After which the validity of the model based on the classical experimental data from Nahum and Trosseille is verified. Based on the analysis of nine typical facial collision scenes, this work studies the propagation path of stress wave in the skull, then brain, von Mises stress and shear stress distribution are achieved. It is proved that facial structure can absorb a large amount of impact energy to protect the brain. The propagation path and distribution of stress wave in the skull and brain determine the mechanism of brain impact injury, which provides a theoretic basis for the diagnosis, treatment and protection of craniocerebral injury caused by facial impact.

Multifrequency Microwave Imaging for Brain Stroke Detection

LULU WANG — 2020-02-26

This paper describes the feasibility of the use of a multifrequency holographic microwave imaging (HMI) algorithm for brain stroke detection. A numerical system, including HMI data collection model and a realistic head model, was developed to demonstrate the proposed method for imaging of brain tissues. Various experiments were carried out to evaluate the performance of the proposed method. The multifrequency HMI was also compared with the previously developed single frequency HMI. Results suggest that the multifrequency HMI could clearly identify stroke with more correct information on location and size than the single frequency HMI.