최소 침습 수술과 척추의 거동 안정화를 위한 척추 인공삽입물 설계

허민혁(Minhyuk Heo),윤지환(Jihwan Yun),박성훈(Seonghun Park) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11

The purpose of the present study is to design a novel lumbar spine implant that allows a minimally invasive surgery that can avoid soft tissue removal as much as possible in the device installation procedure and that makes the lumbar behavior similar to normal lumbar behavior even after the procedure, so that the drawbacks of conventional lumbar spine implants may be overcome. The lumbar spine implant developed in this study was designed to include spike and ratchet elements in the fixed part of the device in order to minimize removal of soft tissue. Also, the part that connects the interspinous process was designed as a spring element to enable normal lumbar movement after the lumbar support installation process. In order to analyze the structural stability of the device, a load of 250 N was applied to the lumbar spine implant. As a result of the analysis, it was evaluated that the lumbar spine implant was structurally stable. When the lumbar spine implant was inserted, the disc pressure decreased by 80 - 92% compared to the defect model and the flexion movement was also recovered to the normal behavior range reported in previous studies. These results suggest that the currently designed the lumbar spine implant could provide the minimization degenerative diseases at the adjacent lumbar segment.

디스크 수핵 대체 재료 개발을 위하여 혼합체 이론을 적용하여 유체-고체 혼합체 구조에서의 PVA-H의 기계적 거동

허민혁(Minhyuk Heo),김한종(Hanjong Kim),박성훈(Seonghun Park) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.11

Polyvinyl Alcohol-Hydrogel (PVA-H) is well known as a biomaterial. Previous studies have also shown that PVA-H shows hydrophilic elastic nature and excellent biocompatibility. The objective of this study was to determine mechanical properties of PVA-H at different ratios of polyvinyl alcohol (PVA) and phosphate buffered saline (PVA) to determine the possible use of PVA-H as an alternative material to nucleus pulposus of the intervertebral disc. PVA-H specimens were made by changing the ratio of PVA and PBS compositions (PVA-H1: 3 wt% PVA and 97 wt% PBS; PVA-H2:5 wt% PVA and 95 wt% PBS; PVA-H3: 7 wt% PVA and 93 wt% PBS). Unconfined and confined tests were carried out to measure the mechanical properties of PVA-H1, -H2, and -H3 within PBS solution. The mixture theory was applied to the results of unconfined and confined tests to investigate the mechanical properties reflecting the structural characteristics of fluid-solid mixture structure of nucleus pulposus in intervertebral disc. We used finite element analysis (FE-bio) with mixture theory to determine the composition of pva-h that is suitable to replace the intervertebral disc.

차량용 웨더스트립 고무의 초탄성 물성 모델 연구

최병규(Byounggyu Choi),허민혁(Minhyuk Heo),서창만(Changman Seo),권혜린(Hyerin Kwon),김광훈(Kwanghoon Kim),박성훈(Seonghun Park) 한국자동차공학회 2017 한국자동차공학회 학술대회 및 전시회 Vol.2017 No.11

Automotive weatherstrips are made of rubber with nonlinear hyperelastic properties, and it is difficult to express properties by a mathematical model. Therefore, in order to design the door weatherstrip, it is necessary to accurately identify the properties of the rubber and find a suitable mathematical model. The purpose of this study is to select a hyperelastic mathematical model suitable for automotive weatherstrip rubber to improve the accuracy and reliability of the design. A hyperelastic mathematical model was constructed using uniaxial tensile and compression test data of rubber and applied to nonlinear finite element analysis. A 100 mm weatherstrip compression test was performed and compared with the finite element analysis results. There is a difference in the accuracy of the hyperelastic model depending on the strain range, and the strain range should be considered when selecting the model. The weatherstrip used in the analysis showed a strain of 0.5 or less, and the Yeoh model is the most suitable model at low strain.

차량용 웨더스트립 고무의 초탄성 및 점탄성 거동

최병규(Byounggyu Choi),허민혁(Minhyuk Heo),서창만(Changman Seo),권혜린(Hyerin Kwon),김광훈(Kwanghoon Kim),박성훈(Seonghun Park) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11

Automotive weatherstrips made of rubber material have nonlinear hyperelastic/viscoelastic properties and it is difficult to design accurately reflecting their properties. Therefore, it is necessary to present a mathematical model suitable for accurate rubber behavior to design the weatherstrip. The purpose of this study is to find the hyperelastic/viscoelastic mathematical model for the rubber material of automotive weatherstrips and to apply this model to the computational analysis in order to improve the accuracy and reliability of the static and dynamic analyses during door closing. Uniaxial tensile/compressive tests and DMA (Dynamic Mechanical Analysis) tests were used to construct a mathematical model. Compression tests using a 100 mm weatherstrip sample were also carried out to verify the computational results. The maximum strain of the automotive door weatherstrip was found to be as low as 0.5 or less through the finite element analysis when the automotive door was closed. Computational compressive load deflection (CLD) results of the weatherstrip using several hyperelastic models were compared with weatherstrip test results and an accurate material model for low strain range was selected. The viscoelastic model was also added to the selected model to confirm the stress relaxation over time. When only uniaxial tensile test data were used, the Form model combined with the viscoelastic Prony series was the most suitable model to express the nonlinear viscoelastic behavior of the rubber at low strain range.

항공기용 열교환기 매니폴드의 위상최적화 설계

김한종(Hanjong Kim),허민혁(Minhyuk Heo),한창완(Changwan Han),박성훈(Seonghun Park) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11

The heat exchanger manifold of the aircraft serves to evenly distribute the fluid coming in through the inlet and then out to the heat transfer unit. To meet this requirement, the manifold must be designed to be lightweight and to withstand high internal pressures. Therefore, this study aims at minimizing the weight of the heat exchanger manifold through topology optimization. To optimize the topology, the initial design space was first determined considering the inner surface of the existing manifold model with the outer surface shaped by a solid cube. A finite element model of the initial design space was created in ANSYS Workbench. Upper side of the manifold was then fixed to represent the welding joints of the manifold and an inner pressure of 5.5 MPa was applied on the inner surface of the manifold as boundary conditions. Six case studies were performed with different weight targets to obtain a minimized shape with maximum stiffness at a given volume, resulting in the key structure of the manifold being identified. By observing the change in manifold structure due to weight reduction, we were able to select the key structure to distribute the load on the manifold. Currently, we further simply the shape of the topology optimised manifold reflecting the key structure identified in the case study results and we also plan to use the 3D metal printing process to manufacture the manifold optimised and simplified.

SCM440강으로 제작된 센터링크 체인의 표면거칠기가 피로수명에 미치는 영향

한창완(Changwan Han),김한종(Hanjong Kim),허민혁(Minhyuk Heo),박성훈(Seonghun Park) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11

The purpose of the present study is to analyze the effect of surface roughness on fatigue life of center-link chain made by SCM440 steel. Two groups of specimens were made from SCM440 steel with and without surface polished after forging process and resulted in different values of surface roughness. The difference of the surface roughness between two groups was clearly distinguished even to the naked eye. The surface roughness of both groups of the specimens was quantitatively measured by a roughness measuring device, Talysurf series2 (Taylor-Hobson Co., USA). Average roughness (R<SUB>a</SUB>) values were obtained by scanning 45 mm with a speed of 0.25 mm/s. Fatigue tests were conducted using a three-point bending method with a cyclic sinusoidal profile of 5 Hz, stress ratio of R = 0.1 and reference life for fatigue limit of 1 × 10<SUP>6</SUP> cycles. Ra without surface machining was 10.5 ± 1.7 μm, respectively while those values with surface machining were 0.9 ± 0.5 μm. It was found that the average roughness decreased approximately 12 times compared to the testing specimens without surface machining. The results of the fatigue test using the specimen with reduced surface roughness (from Ra = 10.5 to 0.9 μm) by surface machining demonstrated reduced scattering and increased fatigue limit (from 746.7 to 920.3 MPa). The results showed that an increase in surface roughness values led to a decrease in fatigue lives.