生物組織壓痕試驗之剪應力分析及圓柱形壓頭圓角曲率之最佳化研究

Shear Stress Analysis and Fillet Curvature Optimization of Cylindrical Indenter in Indentation Test of Bio-Tissue

蘇翰飛(Hans Su)

指導教授 ： 吳文方

共同指導教授 ： 林哲宇(Che-Yu Lin)

國立臺灣大學/工學院/機械工程學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201902994

摘要

現今，器官捐贈數目遠遠無法滿足社會需求，所以只能透過再生醫學以仿生材料重建器官或其他人體組織。此時，就必須選用具有與人體組織相似的材料。就材料機械性質而言，唯有了解人體組織的機械性質，再生醫學才有用武之地。由於人體組織是由大量蛋白質構成，人體組織尤其是軟組織對剪應力的抵抗性低，值得我們特別留意。當我們對人體組織或仿生材料進行壓痕試驗想瞭解其機械性質時，壓頭形狀與其彈性模數會影響受試組織的剪應力；我們需避免試驗產生過大剪應力，致破壞受試組織或材料。就此，本論文欲找出在同樣受力下，對受試材料產生最小剪應力的壓頭形狀，並探討壓頭材料彈性模數與受試材料剪應力間的關係。本論文先以有限元素法模擬球形壓頭與圓柱形壓頭的壓痕試驗，將其結果與具理論解之Hertz接觸力學分析結果比對，藉以找出有限元素模型之適當幾何與網格大小。而後，模擬在同樣受力下，具不同曲率導圓角圓柱形壓頭之壓痕試驗，一一獲得受試材料的剪應力分佈，並比較其結果，以找出產生最小剪應力圓柱形壓頭的圓角曲率。本論文並改變壓頭彈性模數，模擬並獲知前述剪應力與彈性模數間的關係。本論文最後將前述模擬過程與結果無因次化，以利爾後研究者應用。本論文研究發現，就圓柱形壓頭而言，以具曲率半徑0.1 mm導圓角的圓柱形壓頭作壓痕試驗，對受試材料產生的剪應力最小；而壓頭彈性模數越小，受試材料產生的剪應力也越小，其間具有非線性遞減的關係。

關鍵字

人體軟組織 ； 壓痕試驗 ； 接觸力學 ； 有限元素法 ； 剪應力

並列摘要

The supply of organ donation is far below its demand now. Only with the help of regenerative medicine to reconstruct organs or body tissues can the demand be satisfied. The reconstruction, in general, requires the appropriate selection of material that has similar mechanical properties to human tissues. Before that, the mechanical properties of human tissues must be understood and studied in advance. Since a large portion of human tissues is made of protein, it is worth paying attention to the fact that human soft tissues have low resistance against shear stress. Large shear stress could damage tissues of the specimen and should be avoided. It has been pointed out that shear stress distribution of a tested specimen is influenced by both the geometry and the elastic modulus of the indenter, and so using indentation to test human tissues or equivalent biomaterials to understand their mechanical properties is necessary. Therefore, the relation between the elastic modulus of the indenter and shear stress of the specimen had better be known beforehand. Based on the above considerations, this thesis intends to find the appropriate shape of an indenter that results in small shear stress in specimens during indentation test. The relation between the elastic modulus of the indenter and shear stress of the specimen will also be investigated. The study begins with the finite element simulation of the indentation test carried out by a spherical and a cylindrical indenter, respectively. The results are compared with those obtained directly from the Hertz contact theory for justifying the simulation model including its mesh size. By using the same model, the best fillet curvature of a cylindrical indenter leading to the smallest shear stress in tested specimens is found. The relation of elastic modulus of the indenter and shear stress of the tested specimen is also found. All results are nondimensionalized for future use by other researchers. The major findings of this study are that, for cylindrical indenters used in indentation test of biomaterials, a fillet having 0.1 mm radius of curvature would result in the least shear stress in specimens; and the shear stress decreases along with the decrease of elastic modulus of the indenter.

並列關鍵字

human soft tissue ； indentation test ； contact mechanics ； finite element analysis (FEA) ； shear stress

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