降温速率和低温保护剂浓度对主动脉血管在冻结相变温区热应力的影响

Effects of Cooling Rates and Cryoprotective Agent Concentrations on Thermal Stress Distributions of Artery During Freezing Phase Change

根据实测物性参数,利用ANSYS计算软件,研究了降温速率以及低温保护剂浓度对冻结相变温区兔主动脉血管热应力分布的影响,并进一步考察了血管有微裂纹存在时的应力集中现象。研究结果表明,血管壁外表面所受的应力值最大,内表面次之,中心处的应力值略小于内表面的应力绝对值,这说明血管外表面是最先出现裂纹的。降温速率越大,血管内部最大温差也越大,引起血管内部热应力增大。在没有添加二甲基亚砜(DMSO)的情况下,最大热应力值出现在热膨胀系数突变点(-32～-35℃温区),热膨胀系数和弹性模量是影响热应力分布的最主要因素;而一旦添加较高浓度DMSO后(如10%v/v),血管冻结过程产生的热应力显著减小,血管冻结过程产生的最大应力值出现在最大温差所对应的温度(如-4℃)附近,这种情况下,温差是影响热应力分布的最主要因素。血管存在微裂纹时,应力集中始终出现在裂尖点,且裂纹越小,其应力值越大,这是受血管材料断裂韧性因子KIC制约的,这个结果也表明,血管中存在微小裂纹,对于血管低温保存时的裂纹成核与扩展是非常危险的,尤其降温速率越大时,这种潜在的危险也就越大。

This article used the finite element software of ANSYS to perform thermal stress analysis of rabbit artery during freezing phase change.Results show that： 1） The fracture in frozen artery will originate from the outer surface due to the fact that the highest value of the maximum principal stress occurs at the outer surface of artery;2） A higher thermal stress in frozen artery was induced by the larger the maximum temperature difference as a result of the higher cooling rate;3） The peak value of maximum principal stress of the sample without dimethyl sulfoxide（DMSO） present at the turning point of thermal expansion coefficient（i.e.-32 ～-35℃）,which means that thermal expansion coefficient and elastic modulus are main factors effecting thermal stress distributions;However,the maximum principal stress decreases significantly when higher concentrations DMSO（i.e.10% v /v） were added to the samples.In this situation,the peak value occurred at the largest temperature differences point（e.g.-4℃） and the temperature difference is the major factor effecting thermal stress distribution;4） for pre-existing model,stress concentration always forms at the crack tip;the smaller the crack or the higher the cooling rate,the larger the maximum principal stress occurs,which also directs that micro-crack is very dangerous for the cryo-preservation of artery.