Résumé
Objective Based on interface damage, a numerical simulation method for in-plane propagation of false lumen (FL) was proposed to explore the regular pattern of in-plane propagation of the initial cavity. Methods Three interface damage modes were characterized by bi-linear traction separation law, and the damage parameters were calibrated by simulating peeling and shearing tests. The damage interface was introduced into the ideal double-layer cylindrical tube aortic model by means of cohesive zone model (CZM) to simulate the in-plane propagation of FL. The control variable method was used to establish several computational models to investigate the influence of cavity geometric parameters on propagation direction, critical pressure and interface damage mode. Results The interface damage was mainly opening mode (Mode I) in axial propagation and sliding mode (Mode II) in circumferential propagation. With radial depth of the initial cavity increasing, the propagation of the FL changed from circumferential direction to axial direction, the critical pressure decreased, and the axial damage tended to be pure opening mode. With circumferential angle and axial length of the initial cavity increasing, the critical pressure decreased and the circumferential damage tended to be pure sliding mode. The critical pressure of single damage was lower than that of mixed damage. Conclusions The CZM can effectively characterize interface damage behavior of elastic lamellae within the media, and it applies to numerical simulation of in-plane propagation of the FL. The results of this study is helpful to understand the complex pathophysiological process of dissection crack propagation.
Résumé
Objective To study the effect of non-self-similar hierarchy on fracture mechanical properties and crack propagation of the biocomposite. Methods The numerical models were established by using ABAQUS, and the stiffness and crack initiation and propagation in the biocomposite with the inclination angles between the axis of the prism and mineralized collagen fibrils θ=0°,20°,40°,60°,80° were simulated by extended finite element method. Results The inclination angle θ had limited influences on biocomposite stiffness at θ≤40°, while biocomposite stiffness decreased with θ at θ>40°. The ultimate tensile strain also increased at θ>40°. Asymmetry in the crack was also found during propagation of matrix surrounded-enhanced phases at θ>0°. The crack propagatation on one side of the long axis of the mineral crystal was relatively easier than that on the other side at θ>0°. Conclusions The non-uniform distributions of cracks were found in biological hard tissues arisen from the non-self-similar hierarchy. The non-uniform crystal arrangement in the biocomposite would result in local damage rather than catastrophic fracture. The findings of this study can provide theoretical support for material design.
Résumé
Objective To cross-link the porous biological ceramics and PVA hydrogel to form a double layer construction between the artificial cartilage and hard joint, and to analyze its morphologies and mechanical properties. Methods With hydroxyl apatite (HA) as the substrate, the porous hydroxyl apatite biological ceramics with different porosities were prepared by using NH4HCO3 crystal grains as the pore-formed material. The poly vinyl alcohol (PVA) and epoxypropane were used as the primary material and cross-linking agent, respectively. The PVA hydrogel with double layer construction was cross-linked and prepared on the porous biological ceramics surface. The fracture appearances of the test specimen section were characterized. The performances of anti tensile strength and anti-shear strength for PVA hydrogel were analyzed. Results The cross-linked PVA hydrogel could permeate in the biological ceramics substrate, and the union between ceramic substrate and PVA hydrogel performed well. With the porosity of the porous biological ceramics increasing, the tension load and shear load of the PVA hydrogel samples both increased, and with the average porosity of 70%, the samples’ biggest tension load and shear load were 153.61 N and 64.46 N, respectively. But the corresponding tensile strength and shear strength both decreased and with the average porsity of 70%, the samples’ biggest tensile strength and shear strength were 2.12 MPa and 1.13 MPa, respectively. The failure mode of both tension and shear tests for PVA hydrogel samples was due to the crack propagation, and the fracture morphologies showed that obvious cracks and internal defects appeared on the fracture surface, while the source of the crack and the direction of the crack propagation could be observed. Conclusions Considering the compression strength of porous biological ceramics, the permeation effect on the porous biological ceramic substrate with the average porosity of 50% is moderate to be used, which ensures the appropriate shear and tensile strength of PVA hydrogel samples and the compression strength of porous biological ceramic.