Han H C, Fung Y C
Department of Engineering Mechanics, Xi'an Jiaotong University, China.
Am J Physiol. 1996 Feb;270(2 Pt 2):H750-9. doi: 10.1152/ajpheart.1996.270.2.H750.
Residual strains were measured in the porcine aorta. Segments were cut from the aorta perpendicular to its longitudinal axis. Microdots of water-insoluble black ink were sprinkled onto the transverse sectional surface of the segments in the no-load state. The segments were then cut radially, and sectional zero-stress states were approached. The coordinates of selected microdots (2-20 microns) were digitized from photographs taken in the no-load state and the zero-stress state. Residual strains in the transverse section were calculated from the displacement of the microdots. The circumferential residual strains on the inner wall and outer wall were calculated from the circumferential lengths in the no-load state and the zero-stress state. Results show that the circumferential residual strain is negative (compressive) in the inner layer of the aortic wall and positive (tensile) in the outer layer, whereas the radial residual strain is tensile in the inner layer and compressive in the outer layer. This residual strain distribution reduces the stress concentration in the aorta under physiological load. The experimental results compared well with theoretical estimations of a cylindrical model. Regional difference of the residual strain exists and is significant (P < 0.01), e.g., the circumferential residual strains on the inner wall of the ascending, descending thoracic, and abdominal regions of the aorta are -0.133 +/- 0.019, -0.074 +/- 0.020, and -0.046 +/- 0.017 (mean +/- SD), respectively. More radial cuts of a segment produced no significant additional strains. This means that an aortic segment after one radial cut can be considered as the zero-stress state.
在猪主动脉中测量了残余应变。从主动脉上垂直于其纵轴切取节段。在无负载状态下，将水不溶性黑色墨水的微点洒在节段的横截面上。然后将节段径向切割，使其接近截面零应力状态。从在无负载状态和零应力状态下拍摄的照片中数字化选定微点（2 - 20微米）的坐标。根据微点的位移计算横截面上的残余应变。根据无负载状态和零应力状态下的圆周长度计算内壁和外壁上的圆周残余应变。结果表明，主动脉壁内层的圆周残余应变是负的（压缩性的），外层是正的（拉伸性的），而径向残余应变在内层是拉伸性的，外层是压缩性的。这种残余应变分布降低了生理负荷下主动脉中的应力集中。实验结果与圆柱形模型的理论估计值比较吻合。残余应变存在区域差异且具有显著性（P < 0.01），例如，主动脉升部、胸降部和腹部区域内壁上的圆周残余应变分别为-0.133±0.019、-0.074±0.020和-0.046±0.017（平均值±标准差）。对一个节段进行更多的径向切割不会产生显著的额外应变。这意味着经过一次径向切割后的主动脉节段可被视为零应力状态。
