大鼠皮肤蠕变及循环变形行为研究

发布时间：2018-04-02 23:29

本文选题：皮肤　切入点：粘弹性　出处：《天津大学》2014年硕士论文

【摘要】：皮肤的力学特性对临床皮肤疾病的治疗、发展计算机辅助皮肤疾病治疗技术、评估人工皮肤的综合力学特性以及为研究其它软组织的力学性能提供参考等方面具有十分重要的意义。然而，大量工作都集中在包括拉伸、蠕变、应力松弛和循环加载在内的实验研究上，而很少有考虑加载历史对皮肤力学性能影响方面的研究。本文针对现有研究的不足，，选用大鼠背部皮肤为实验材料，首先开展了不同应力（变）率下的单轴拉伸试验；然后在不同应力下开展了单步蠕变试验和具有3个加载步的多步蠕变实验，重点研究了蠕变及应力松弛历史对蠕变特性的影响。并且，通过石蜡切片技术、HE染色方法，利用光学显微镜，对已完成拉伸、单步或多步蠕变试验的大鼠皮肤进行了微观结构观察和分析。结果表明，皮肤是复杂的非线性粘弹性材料，不论是在单步实验中还是多步实验都表现出应力相关性。而且，蠕变和松弛加载历史都对皮肤的蠕变特性产生重要影响。蠕变加载后纤维束沿受力方向伸直、伸长，并出现聚拢和滑移现象；加载顺序为低应力蠕变-应力松弛-高应力蠕变的多步蠕变加载方式在所进行的蠕变研究中获得的蠕变应变最大，微观结构的空隙率最低。在此基础上，本文还考虑平均应力、应力幅值和应力率等影响因素，开展了单步循环和多步循环实验研究，并对循环实验后大鼠皮肤的微观结构进行了观察和分析。结果表明，循环加载历史对皮肤的循环特性具有重要影响。循环加载后纤维束交变载荷作用而产生变形，表现出因滑移运动和短裂纹（单步循环）或长裂纹（多步平均应力循环）扩展而导致的疲劳断裂；结合Basquin模型和修正的SWT模型可以预测皮肤在单步循环下的低周疲劳寿命；加载历史对循环特性的影响因平均应力或应力幅值的不同而存在差异。
[Abstract]:The mechanical properties of skin in the treatment of clinical skin diseases, the development of computer-assisted skin disease treatment technology,It is of great significance to evaluate the comprehensive mechanical properties of artificial skin and to provide reference for the study of other soft tissue mechanical properties.Then the single-step creep test and the multi-step creep experiment with three loading steps were carried out under different stresses. The influence of creep and stress relaxation history on creep characteristics was studied.The microstructures of the skin of rats with tensile, single or multi-step creep tests were observed and analyzed by means of paraffin section technique and HE staining.The results show that skin is a complex nonlinear viscoelastic material with stress dependence both in one-step and multi-step experiments.Moreover, both creep and relaxation loading history have an important effect on skin creep characteristics.After creep loading, the fiber bundle is straight and elongated along the direction of stress, and the phenomenon of convergence and slippage occurs.The loading sequence is low stress creep, stress relaxation and high stress creep. The creep strain is the largest and the void ratio of microstructure is the lowest.On the basis of this, considering the influence factors of average stress, stress amplitude and stress rate, the experiment of single step cycle and multi step cycle was carried out, and the microstructures of rat skin after cyclic experiment were observed and analyzed.The results show that cyclic loading history plays an important role in the cycling characteristics of skin.After cyclic loading, the fiber bundle is deformed under alternating load, showing fatigue fracture caused by slip motion and short crack (single cycle) or long crack (multistep mean stress cycle) propagation.Combined with the Basquin model and the modified SWT model, the low cycle fatigue life of skin can be predicted under one step cycle, and the effect of loading history on the cycle characteristics is different due to the difference of average stress or stress amplitude.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：R339.11

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