在体轴向伸长比条件下血管壁的周向应力分布

本文通过检测在体轴向伸长比条件下血管段的压力－容积数据,利用应变能密度函数,求得血管壁周向应力沿壁厚的分布。文章的正常大鼠腹主动脉为例进行计算,结果发现,在生理压力作用下（例如ｐ＝１３．３ｋＰａ）,不考虑残余应力确实出现在血管内壁处的周向应力集中,血管内、外壁处的应力值之比可达１５左右,而存在于实际动脉管中的残余应力会使血管壁中的周向应力沿壁厚的分布明显趋于均匀,血管处的周向应力之比差不多只有２左     

动脉压对静脉血管壁周向应力分布的影响

自体静脉是病变动脉管段常用的替代物。移植后因承受压力急剧升高引起的静脉管壁应力改变是影响移植手术的主要因素之一。为了比较移植前(静脉压作用下)和移植后(动脉压作用下)静脉管壁的周向应力分布，本文通过检测一定轴向伸长比条件下静脉管的p(压力)——V(容积)试验数据，利用3参数的应变能密度函数对实验数据进行拟合，进而求得静脉管壁的残余应力和沿血管壁的周向应力分布。对狗的股静脉和颈静脉的分析结果表明，在动脉压作用下静脉管壁周向应力将急剧增大。与处于静脉压环境相比，处于动脉压环境中的颈静脉管周向应力将增大差不多2个数量级。计算结果还显示，静脉管壁残余应力的数值虽然比动脉管壁的相应值小很多，但是与动脉管相同，血管壁残余应力依然对静脉管壁上的周向应力分布影响显著，残余应力的存在将大大削弱在静脉管内壁处的周向应力集中，使周向应力沿静脉管壁厚的变化梯度明显减小。     

用p-V指数关系确定血管壁的周向应力

通过检测，得到在体轴向伸长比条件下血管段的压力－容积（p-V)数据，利用指数函数关系，求得在一定内压作用下血管壁周向应力沿壁厚的分布。并以正常大鼠腹主动脉为例进行计算，结果表明，在生理压力作用下，残余应力对血管壁周向应力的分布有很大影响，不考虑残余应力将使血管内壁处出现明显的周向应力集中，当考虑存在于血管壁内的残余应力后，周向应力沿壁厚的分布将变得较均匀，例如当内压p=10kPa时，血管内、外壁周向应力值之比，对前者将达10以上，而对后者差不多只有2左右。所得结果与用Fung提出的应变能密度函数的计算结果作比较，发现二者符合得相当好。     

脉动血压对在体轴向极限强约束血管壁应力分布的影响

本文详细分析正弦脉动压力载荷对动脉管壁应力分布的影响。结果表明,对某确定时刻,包含在运动方程中的惯性项对血管壁应力的影响很小,可忽略不计;在体轴向极限强约束下,血管壁周向应力随时间的变化曲线与压力曲线同相位和同周期,而且振幅不随频率的快慢而改变。一个心动周期内,血管内、外壁处周向应力随时间变化的平均值只与脉动压力载荷的平均值有关,而振幅主要与脉压有关,在内壁处随平均压的改变有一定变化,但在外壁处受平均压的影响很小。     

脉动流条件下血管壁的应力分布

为了分析血液-血管耦合运动所产生血液脉动压力载荷对血管壁应力分布的影响,利用线性化的血液-血管耦合运动方程的Womersley解,导得血液脉动压力载荷下的血管壁Green应变,同时利用Fung的血管壁应变能密度函数,导得相应血管壁应力分布的一般表达式.数值结果表明,在脉动流条件下,当考虑血液-血管耦合运动时,血管壁中周向应力最大,轴向应力居中,径向应力最小;血管壁的残余应力将明显减小血管内壁的应力集中;脉动压力载荷将导致血管壁周向应力在一个心动周期中随时间的脉动,而且随着Womersley数α和血管轴向约束参数K*的增大,血管壁周向应力的脉动将明显加剧,提示在分析动脉重建时必须计及血液-血管耦合运动对血管壁应力分布的影响.     

脉劝流条件下血管壁的应力分布

为了分析血液-血管耦合运动所产生血液脉动压力载荷对血管壁应力分布的影响,利用线性化的血液-血管耦合运动方程的Womersley解,导得血液脉动压力载荷下的血管壁Green应变,同时利用Fung的血管壁应变能密度函数,导得相应血管壁应力分布的一般表达式.数值结果表明,在脉动流条件下,当考虑血液-血管耦合运动时,血管壁中周向应力最大,轴向应力居中,径向应力最小;血管壁的残余应力将明显减小血管内壁的应力集中;脉动压力载荷将导致血管壁周向应力在一个心动周期中随时间的脉动,而且随着Womersley数α和血管轴向约束参数K～＊的增大,血管壁周向应力的脉动将明显加剧,提示在分析动脉重建时必须计及血液-血管耦合运动对血管壁应力分布的影响.     

局部扩张动脉管血液振荡流的切应力分布

本文求解局部缓慢扩张动脉管中血液振荡流的基本方程，得到血管内血液的流速与压力梯度的关系。通过导出压力梯度沿局部扩张管轴向的变化特性。建立利用扩张段上游血管均匀段中心流速波形确定局部扩张管中血液流的速度和切应力分布的方法，文章以人体颈动脉余弦扩张为例进行分析。详细讨论了局部扩张对血管壁切应力及其梯度分布的影响。数值结果表明，在与刚性均匀管中管壁切应力沿轴向保持不变不同，在局部扩张段，管壁切应力将随着血管半径的增大而减小，因而管壁切应力梯度一般不为零，甚至在某些位置达到相当大的数值。另外，随着血管扩张程度的增加，管壁切应力还将进一步减小，而且管壁切应力梯度也将进一步增大，血管扩张导致管壁切应力的这些变化将直接影响血管壁的结构和功能，使其产生适应性的变化。     

非稳态纯滚动接触弹塑性分析

建立了二维弹塑性非稳态循环纯滚动接触有限元模型.材料本构采用一种较好的循环塑性模型,并通过材料用户子程序在通用有限元软件ABAQUS中自定义该本构模型.通过在弹塑性无限半空间表面上重复移动随时间按简谐规律变化的赫兹法向载荷来模拟非稳态循环纯滚动接触过程.通过数值模拟,得到接触表面附近的残余累积变形、应变和残余应力.不同的最大赫兹接触压力对残余应力和残余应变影响较大.在简谐变化的法向接触载荷作用下接触表面的变形呈波浪形,随着滚动次数的增加,该波状表面沿载荷移动相反方向逐渐移动,但移动速率要衰减.波状表面波谷处的残余应力、应变和变形大于波峰处.随滚动次数的增加,残余应力增大但很快趋于稳定,残余应变也增大但增大速率衰减.     

循环接触下安定状态问题的研究

基于线性随动强化理论,运用算子分离技术,研究将弹塑性问题转换为弹性问题和残余问题的分析方法,且针对循环载荷接触安定状态,建立了计算机分析程序,该研究能够分析计算弹塑性接触载荷在安定状态下的应力、残余累积应变及残余应力,分析计算了不同载荷的安定状态,并探讨其残余应力场的分析方法。     

不同爆炸载荷下TA2钛合金圆管膨胀破坏过程

金属柱壳破坏过程与材料、结构及载荷等相关,断裂结果呈现多种形式,采用有限元结合实验对不同爆炸载荷作用下,TA2钛合金圆管的破坏机制开展研究。有限元结果显示:对于理想均质柱壳,由于冲击波传播使壁厚中间形成二次塑性区,圆管壁厚中部的等效塑性应变总是大于内、外壁。在较高爆压下,裂纹在加载阶段从试样壁厚中部起始,沿45°或135°向内外壁剪切扩展;而在较低爆压下,破坏发生在自由膨胀阶段,断裂从内壁起始向外壁剪切扩展,两者破坏过程和机制不同,总体来说,与实验现象符合较好。相关实验中出现的一些外壁拉伸断裂现象,可能与试样的几何、材料缺陷等因素相关,其对金属圆管爆炸破坏的影响值得进一步关注。     

A Model of Arterial Adaptation to Alterations in Blood Flow

Mechanisms of arterial adaptation to changes in blood flow rates were tested by comparing the predictions of a proposed theoretical model with available experimental data. The artery was modeled as an elastic membrane made of a nonlinear, incompressible, elastic material. Stimulation of the vascular smooth muscle was modeled through the generation of an active component of circumferential stress. The muscular tone was modulated by flow-induced shear stress sensed by the arterial endothelium, and is responsible for the vasomotor adjustment of the deformed arterial diameter in response to changes in blood flow. This study addresses the hypothesis that the synthetic and proliferative activity of smooth muscle cells, leading to a change in arterial dimensions, is shear stress dependent and is associated with changes in the contractile state of the smooth muscle cells and changes in the circumferential wall stress. Remodeling to a step change in flow was formulated as an initial-value problem for a system of first order autonomous differential equations for the evolution of muscular tone and evolution of arterial geometry. The governing equations were solved numerically for model parameters identified from experimental data available in the literature. The model predictions for the time variation of the geometrical dimensions and their asymptotic values were found to be in qualitative agreement with available experimental data. Experiments for validating the introduced hypotheses and further generalizations of the model were discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

An analysis model of pulsatile blood flow in arteries

IntroductionTheperiodicallypulsatilebloodflowinthearterycausesthecircumferentialandaxialmotionoftheelasticbloodvesselandinturntheoscillationofthevesselaffectsthatofthebloodflow .Womersley[1]resolvedsuccessfullythisfluid_solidcouplingproblembysolvingbothlinearNavier_Stokesequationsandthemotionequationsofthethin_walledelastictubeandgainedtheexpressionsofthebloodflowvelocitiesandthevasculardisplacements.Histheoryhasbeenthebasisforthequantitativeanalysisoftherelationshipofthearterialstructureandi…     

爆炸处理消除大型柱壳结构环焊缝残余应力实验研究

为探讨大型耐压柱壳结构对接环焊缝焊接残余应力消除方法,根据耐压柱壳结构环焊缝焊接工艺,设计并制作了大型耐压柱壳结构对接环焊缝模拟焊接模型,并采用沿焊缝条状布药,分别进行了单、双面布药爆炸处理消除大型耐压柱壳结构对接环焊缝焊接残余应力模型实验。结果表明:大型耐压柱壳结构对接环焊缝存在较大的焊接残余应力;单、双面爆炸处理均能有效调整、消除焊接残余应力,残余应力分布明显均匀化;焊后残余应力越大,爆炸处理效果越明显,当焊接残余应力大于0.5s时,单面爆炸处理后残余应力m下降幅度在40%以上,双面爆炸处理后残余应力m下降幅度在60%以上;采用沿焊缝条状布药,爆炸处理能有效消除沿焊缝的纵向残余应力;双面爆炸处理效果优于单面爆炸处理效果。     

Measurement of Torsionally Induced Shear Stresses in Shrink-Fit Assemblies

Shear stresses along the shaft/hub interface in shrink-fit components, generated by torsional loads, can drive premature failure through fretting mechanisms. It is difficult to numerically predict these shear stresses, and the associated circumferential slip along the shaft/hub interface, due to uncertainties in frictional behaviour and the presence of steep stress gradients which can cause meshing problems. This paper attempts to provide validation of a numerical modelling methodology, based on finite element analysis, so the procedure may be used with confidence in fitness-for-purpose cases. Very few experimental techniques offer the potential to make measurements of stress and residual stress interior to metallic components. Even fewer techniques provide the possibility of measuring shear stresses. This paper reports the results of neutron diffraction measurements of shear stress and residual shear stress in a bespoke test specimen containing a shrink-fit. One set of measurements was made with a torsional load ‘locked-in’. A second set of measurements was made to determine the residual shear stress when the torsional load had been applied and removed. Overall, measurement results were consistent with numerical models, but the necessity for a small test specimen to allow penetration of the neutron beam to the measurement locations meant the magnitude of shear stresses was at the limits of what could be measured experimentally.     

Constitutive function,residual stress,and state of uniform stress in arteries

Fung (1983) has conjectured that the residual stress in an artery distributes itself in such a way to assure that the circumferential stress is uniform across the artery wall under physiological conditions. In this work, we identify the entire class of constitutive functions for which the circumferential stress is uniform across the artery wall when it is subjected to an internal pressure. It is found that these constitutive functions do not necessarily endow residual stresses. Furthermore, a subset of the class of the constitutive functions is identified for which the circumferential stresses are uniform for the entire range of internal pressures. The constitutive functions in this sub-class are found to have zero residual stress. It is the inhomogeneity, rather than residual stress, that assures uniform circumferential stresses. We also examine the possibility of utilizing these constitutive functions in the design and fabrication of an engineered blood vessel with optimal mechanical properties.