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Research Papers

Fatigue Crack Propagation Analysis of Plaque Rupture

[+] Author and Article Information
Xuan Pei

School of Biological Science and
Medical Engineering,
Southeast University,
Nanjing 210096, China

Baijian Wu

Department of Engineering Mechanics,
Southeast University,
Nanjing 210096, China

Zhi-Yong Li

School of Biological Science and
Medical Engineering,
Southeast University,
Nanjing 210096, China;
University Department of Radiology,
University of Cambridge,
Cambridge CB2 0QQ, UK
e-mail: ZYL22@cam.ac.uk

1Corresponding author.

Contributed by the Bioengineering Division of ASME for publication in the Journal of Biomechanical Engineering. Manuscript received December 31, 2012; final manuscript received June 27, 2013; accepted manuscript posted July 29, 2013; published online September 13, 2013. Assoc. Editor: Jeffrey W. Holmes.

J Biomech Eng 135(10), 101003 (Sep 13, 2013) (9 pages) Paper No: BIO-12-1640; doi: 10.1115/1.4025106 History: Received December 31, 2012; Revised June 27, 2013; Accepted July 03, 2013

Rupture of atheromatous plaque is the major cause of stroke or heart attack. Considering that the cardiovascular system is a classic fatigue environment, plaque rupture was treated as a chronic fatigue crack growth process in this study. Fracture mechanics theory was introduced to describe the stress status at the crack tip and Paris' law was used to calculate the crack growth rate. The effect of anatomical variation of an idealized plaque cross-section model was investigated. The crack initiation was considered to be either at the maximum circumferential stress location or at any other possible locations around the lumen. Although the crack automatically initialized at the maximum circumferential stress location usually propagated faster than others, it was not necessarily the most critical location where the fatigue life reached its minimum. We found that the fatigue life was minimum for cracks initialized in the following three regions: the midcap zone, the shoulder zone, and the backside zone. The anatomical variation has a significant influence on the fatigue life. Either a decrease in cap thickness or an increase in lipid pool size resulted in a significant decrease in fatigue life. Comparing to the previously used stress analysis, this fatigue model provides some possible explanations of plaque rupture at a low stress level in a pulsatile cardiovascular environment, and the method proposed here may be useful for further investigation of the mechanism of plaque rupture based on in vivo patient data.

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Figures

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Fig. 1

The idealized plaque model. The cross section consists of three parts contributed to different materials—the arterial wall, the plaque, and the lipid pool. The controlling parameters are rwi, rwo, rl, el, tc, αp, and tp.

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Fig. 2

The anatomical variations of the arterial cross-section model with different cap thicknesses, lipid thicknesses, and lipid lengths. The lipid angle in group (A) is constant as 45 deg, while the cap thickness and lipid thickness are fixed as 10 and 10 mm, respectively, in group (B).

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Fig. 3

Finite element model for a cracked TC5-TP15-AP45 cross section, a case on the eve of rupture: (a) The geometry and (b) the model was meshed by eight-node quadrilateral elements except for those around the crack tip; it has 6533 elements totally and 20,21 nodes. (c) A detailed mesh in the neighborhood of the crack tip. The first four layers of highly regular elements around the tip are generated by the sweeping operation; while the first layer around the tip consists of collapsed triangle elements. (d) The Mises stress contour for this case.

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Fig. 4

The calculated results for the model of baseline (TC10-TP10-AP45): (a) cycles versus crack length, (b) the fatigue life corresponding to each crack initiation location, and (c) propagation paths for selected initial crack locations. The blue lines are for those specified initial locations and the red line or red circle marker is for the automatically generated cracks.

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Fig. 5

A complete list of results for all cross sections arranged in the same order as Fig. 2. The blue lines are for those specified initial locations and the red line or red circle marker is for the automatically generated cracks.

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Fig. 6

The critical zones for crack initiation. The plaque is divided into three regions—the center region (in dark blue), the shoulder region (in blue), and the back region (in green). The following critical zones were found: the midcap zone (MZ), the shoulder zone (SZ), and the backside zone (BZ). The zones were marked in red circles and the maximum stress locations were marked in purple circles.

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Fig. 7

The changes of the fatigue life when cap thickness increases. (a) For cases of which the pool thicknesses and the pool angles are consistent as 5 mm and 45 deg, respectively, corresponding to the first column in group (A) in Fig. 2. (b) For cases of which the pool thicknesses and the pool angles are consistent as 10 mm and 45 deg, respectively, corresponding to the second column in group (A) in Fig. 2.

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Fig. 8

The changes of the average crack growth rate when cap thickness increases. (a) For cases of which the pool thicknesses and the pool angles are consistent as 5 mm and 45 deg, respectively, corresponding to the first column in group (A) in Fig. 2. (b) For cases of which the pool thicknesses and the pool angles are consistent as 10 mm and 45 deg, respectively, corresponding to the second column in group (A) in Fig. 2.

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Fig. 9

The changes of the fatigue life when pool thickness increases. (a) For cases of which the cap thicknesses and the pool angles are consistent as 5 mm and 45 deg, respectively, corresponding to the first row in group (A) in Fig. 2. (b) For cases of which the pool thicknesses and the pool angles are consistent as 10 mm and 45 deg, respectively, corresponding to the second row in group (A) in Fig. 2.

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Fig. 10

The changes of the fatigue life when pool angle increases for cases of which the cap thicknesses and the pool thickness are consistent as 10 and 10 mm, respectively, corresponding to group (B) in Fig. 2

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