Intracoronary stent implantation is a mechanical procedure, the success of which depends to a large degree on the mechanical properties of each vessel component involved and the pressure applied to the balloon. Little is know about the influence of plaque composition on arterial overstretching and the subsequent injury to the vessel wall following stenting. An idealised finite element model was developed to investigate the influence of both plaque type (hypercellular, hypocellular and calcified) and stent inflation pressures (9, 12 and 15 atm) on vessel and plaque stresses during the implantation of a balloon expandable coronary stent into an idealised stenosed artery. The plaque type was found to have a significant influence on the stresses induced within the artery during stenting. Higher stresses were predicted in the artery wall for cellular plaques, while the stiffer calcified plaque appeared to play a protective role by reducing the levels of stress within the arterial tissue for a given inflation pressure. Higher pressures can be applied to calcified plaques with a lower risk of arterial vascular injury which may reduce the stimulus for in-stent restenosis. Results also suggest that the risk of plaque rupture, and any subsequent thrombosis due to platelet deposition at the fissure, is greater for calcified plaques with low fracture stresses. * Manuscript
Due to the significant health and economic impact of blood vessel diseases on modern society, its analysis is becoming of increasing importance for the medical sciences. The complexity of the vascular system, its dynamics and material characteristics all make it an ideal candidate for analysis through fluid-structure interaction (FSI) simulations. FSI is a relatively new approach in numerical analysis and enables the multi-physical analysis of problems, yielding a higher accuracy of results than could be possible when using a single physics code to analyse the same category of problems. This paper introduces the concepts behind the Arbitrary Lagrangian Eulerian (ALE) formulation using the penalty coupling method. It moves on to present a validation case and compares it to available simulation results from the literature using a different FSI method. Results were found to correspond well to the comparison case as well as basic theory.
The human aorta consists of three layers: intima, media and adventitia from the inner to outer layer. Since aortic rupture of victims in vehicle crashes frequently occurs in the intima and the media, latent aortic injuries are difficult to detect at the crash scene or in the emergency room. It is necessary to develop a multi-layer aorta finite element (FE) model to identify and describe the potential mechanisms of injury in various impact modes. In this paper, a novel three-layer FE aortic model was created to study aortic ruptures under impact loading. The orthotropic material model [1] has been implemented into a user-defined material subroutine in the commercial dynamic finite element software LS-DYNA version 970 [2], which was adopted in the aorta FE model. The Arbitrary-Lagrangian Eulerian (ALE) approach was adopted to simulate the interaction between the fluid (blood) and the structure (aorta). Single element verifications for the user-defined subroutine were performed. The mechanical behaviors of aortic tissues under impact loading were simulated by the aorta FE model. The models successfully predicted the rupture of the layers separately. The results provide a basis for a more in-depth investigation of blunt traumatic aortic rupture (BTAR) in vehicle crashes.
This paper examines the capabilities offered by the fluid structure interaction (FSI) algorithms in LS-DYNA for solving problems in vascular biomechanics. In this work a case was examined in which the onset of a pressure pulse was simulated at the entrance of a straight segment of artery. The resulting dynamic response in the form of a propagating pulse wave through the vessel wall was analyzed and compared to both previous numerical results and theory. The results from the three dimensional model compared well to the theoretical description of an idealized thin-walled artery. Results were further compared to those obtained from similar research. The numerical methodologies applied in the three dimensional model were used in the development of an experiment providing a realistic physical model of a carotid artery in its physiological state. The experiment is to be used for further validation of the numerical code.
Various liquids are commonly transported through metal pipes. For reasons of safety it is important to understand the behavior of pipes when subject to an explosive loading from within. This research paper is concerned with examining the expansion and destruction of metal pipes subjected to a high power explosion by high explosive. An experimental study was carried out for this research and visualized using high-speed camera images. Results were then compared to a computer simulation of the same problem. Numerical simulations are performed in three dimensions using the LS-DYNA code. Results obtained numerically compared well to those from experiment.
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