長嶋 利夫

Development of a low-invasive microneedle is currently desired in the medical field to mitigate the patients’ stress and pain. We have paid attention to mosquitoes that puncture the skin without giving humans no feelings of pain. We have observed mosquitoes and found that when their proboscis punctures human skin, they make the following three behaviors: apply tension to human skin; rotate their proboscis; vibrate their proboscis. In our previous studies, we developed a bundled set of three microneedle imitating the mosquito’s proboscis and experimentally proved the usefulness of their alternate vibrations, which is one of the mosquito’s puncturing behaviors. However, the setting of three needles with proper clearances from each other was difficult, making their driving system too complex to practically use it. Therefore, we have developed a simplified microneedle by reducing the number of needles from three to two or one. This paper has focused on the effects of the rotations of a single needle. Using our developed microneedle with a diameter of 90 µm and the thinnest commercial microneedle with a diameter of 180 µm, we evaluated the effect of reciprocating rotation, one of the mosquitoes’ puncturing behaviors, by puncture experiments using artificial skin and nonlinear finite element method (FEM) analysis. As a result, it was found that the reciprocating rotation suppresses the puncture resistance force and the skin deflection.

<title>Abstract</title> To predict fracture behavior for ductile materials, some ductile fracture simulation methods different from classical approaches have been investigated based on appropriate models of ductile fracture. For the future use of the methods to overcome restrictions of classical approaches, the applicability to the actual components is of concern. In this study, two benchmark problems on the fracture tests supposing actual components were provided to investigate prediction ability of simulation methods containing parameter decisions. One was the circumferentially through-wall and surface cracked pipes subjected to monotonic bending, and the other was the circumferentially through-wall cracked pipes subjected to cyclic bending. Participants predicted the ductile crack propagation behavior by their own approaches, including FEM employed GTN yielding function with void ratio criterion, are FEM employed GTN yielding function, FEM with fracture strain or energy criterion modified by stress triaxiality, XFEM with J or ?J criterion, FEM with stress triaxiality and plastic strain based ductile crack propagation using FEM, and elastic-plastic peridynamics. Both the deformation and the crack propagation behaviors for monotonic bending were well reproduced, while few participants reproduced those for cyclic bending. To reproduce pipe deformation and fracture behaviors, most of groups needed parameters which were determined to reproduce pipe deformation and fracture behaviors in benchmark problems themselves and it is still difficult to reproduce them by using parameters only from basic materials tests.

注射の際のストレスを低減可能な低侵襲性の微細針の開発にあたっては，針の性能評価が必要となる．筆者らは，以前から単純な形状の1本針を人工皮膚に穿刺する場合についての穿刺実験とそれに対応する有限要素法解析を行い，抵抗力等の評価を行ってきた．本研究では，複数本の針を穿刺する場合や針を振動させながら穿刺する場合について，LS-DYNAを用いた非線形有限要素法解析を実施し，穿刺抵抗力の低減効果等を検討した．

近年，注射の際の患者へのストレスを軽減可能な低侵襲性の注射針が求められているが，このような微細針の開発には針の穿刺時の抵抗力などの評価が必要となる．そこで，本研究ではLS-DYNAを用いた非線形有限要素法解析を行い，微細針を皮膚モデルに穿刺した場合の穿刺抵抗力を評価することで，針の最適な形状や穿刺速度などの条件について考察した．また，FEM解析と対応する条件での穿刺実験を行い，結果を比較した．

低侵襲な検査・治療を目的として，我々はこれまでに様々な微細針を作製してきた．本報では，画像解析による穿刺対象のひずみ分布の可視化を行った．この結果とロードセルで測定した穿刺時の荷重に基づき，最適な針の先端形状，穿刺モード（振動の有無等），穿刺速度について実験的に検討した．また，穿刺実験と対応するFEM解析を行い，結果の比較を行った．

蚊は3本の口針（上唇および一対の小顎）を協調振動させながら人間の皮膚に穿刺している．本研究では，これらの口針を模倣した3D-CADモデルを作成し，LS-DYNAを用いて針を皮膚モデルに穿刺する場合についてのFEM解析を行うことにより，協調振動の効果を確認した．また，3本針で穿刺した場合と1本針（上唇のみ）で穿刺した場合の穿刺抵抗力の比較を行うことにより，3本針での穿刺の効果を検討した．

拡張有限要素法による二次元亀裂進展解析について、従来の漸近解基底を拡充した方法と、拡充しない方法の差異について比較した結果を比較考察した．

The extended finite element method (XFEM) using a crack tip element (TIP element), which is enriched through only the Heaviside function, is applied to crack and its propagation analysis in two-dimensional elastic problems. In the proposed method, two-kind of signed distance functions are utilized in order to express crack geometry implicitly and finite elements, which has interaction with crack, are appropriately partitioned according to the level set values and then integrated numerically for derivation of stiffness matrix. The results by XFEM using TIP elements were compared with those by the conventional XFEM using both the asymptotic bases and the Heaviside function. It was shown that the TIP element provides appropriate stress intensity factors and crack propagation path.

Conventional finite element method is continually used for the flaw evaluation of pipe structures to investigate the fitness-for-service for power plant components, however, it is generally time consuming to make a model of specific crack configuration. The consideration of a propagating surface crack is further accentuated since the crack propagation behavior along the crack front is implicitly affected by the distribution of the crack driving force along the crack front. The authors developed a system to conduct crack propagation analysis by use of the three-dimensional elastic-plastic extended finite element method. It was applied to simulate ductile crack propagation of circumferentially surface cracks in pipe structures and could realize the simultaneous calculation of the J-integral and the consequent ductile crack propagation. Both the crack extension and the possible change of crack shape were evaluated by the developed system.

The extended finite element method (X-FEM), which can model the domain without explicitly meshing the crack surface, can be used to perform stress analyses for solving fracture mechanics problems efficiently. In the present study, the principle of superposition is used to solve crack problems in conjunction with the X-FEM. In the proposed method, the surface load distributed on the crack surface, which is modeled implicitly by the interpolation functions with enrichment terms, is introduced to X-FEM analysis. Moreover, the energy release rate at the crack front is evaluated by the domain integral method with boundary integral terms for the surface load. The proposed method is verified through numerical analyses of two- and three-dimensional crack problems in linear fracture mechanics.