고관절 골절 예방 제품의 충격 보호 성능의 유한요소해석

이한수 포항공과대학교 일반대학원 2018 국내석사

Hip fracture due to falls has a great effect on the survival rate and quality of life of the elderly, and is known to be the main cause of lowering the quality of life by increasing the medical expenses of the elderly. In addition, hip fractures due to falls are more frequent in females than in males and as higher the age group. There is a hip protector to prevent hip fracture in the elderly. Impact protection performance evaluation based on impact simulator was performed on the clinical efficacy of current commercial hip protector. However, the existing impact protection performance evaluation by impact simulator is limited by the time and cost limitations. Furthermore, differences have arisen due to experimental limitations that are difficult to account for differences due to biomechanical factors such as differences in evaluation systems and subjects, human shape, stiffness, and trochanteric soft tissue thickness in experimental design. As a result, even in the case of the same subject to be evaluated, there was a difference in the results in the impact protection performance evaluation. In addition, existing commercial products are limited in that they are not manufactured based on the body size of older women aged 60 or older who have the highest hip fracture risk. To supplement the limitations of existing commercial hip protectors, the present study through the usability evaluation research (Jeon et al., 2014) produced a hip protector based on the human scan data (Size Korea, 2004) of the elderly Korean women over 60 years of age. In this study, the optimum hardness of the fabricated hip protector was derived through evaluation of impact protection performance by hardness, and the evaluation method to prove the superiority of the properties was presented. The proposed study consists of the following five steps. (1) Analysis of characteristics and limitations of existing impact protection performance evaluation study and design of impact protection performance evaluation by benchmarking. (2) Designing an evaluation system based on an impact simulator suitable for the hip protector to be evaluated by referring to the impact simulator recommended design presented in the previous study. (3) Establishment of an impact protection performance evaluation protocol based on the human body size data of elderly women, and an impact simulation to determine the optimal hardness of the hip protector to be evaluated. (4) Finite element (FE) modeling is carried out for Finite element analysis (FEA) study to supplement impact protection performance evaluation based on impact simulator. (5) The optimal hardness of the hip protector to be evaluated based on the finite element model (FEM) is determined and compared with the impact simulator results. (6) FEM for verifying the superiority of the properties of the polyurethane material used in the production of the hip protector. First, in design of impact protection performance evaluation step, this study analyzed and benchmarked the characteristics and limitations of previous studies validating the clinical efficacy of the hip protector. In addition, this study referred to Robinovtich et al. (2009) and International Hip Protector Research Group (IHPRG) which established the recommended design guideline, which is an international standard for the design of impact simulator. In addition, this study referred to Robinovtich (2009) and IHPRG which established the recommended design guideline, which is an international standard for the design of impact simulator. Therefore, this study selected the parameters for the design conditions of the impact simulator to evaluate the impact protection performance of the hip protector based on the size data of the elderly Korean women. Second, in design of evaluation system by impact simulator, this study designed the impact simulator based on the parameters of the selected impact simulator, and made of surrogate pelvis parts using the human model (Sawbones, Vashon: WA, USA) for mechanical testing. This study also developed the evaluation system for measuring the total force and femoral neck force required to derive selected the main measures, and selecting measures for quantitative evaluation of the impact protection performance of the hip protector to be evaluated. Third, in design of evaluation protocol development and impact test by impact simulator system, based on the body size data of older Korean women aged 60 years and older, which are major experiment subjects, this study derived theoretical calculation value of total peak force through reference to the rigid model of van Den Kroonenberg et al. (1995). This research validated that total peak force based on the weight and height of Korean elderly woman aged 60 or more, and the total peak force of Bouxsein et al. (2007) based on the rigid model theoretical equation of van Den Kroonenberg et al. (1995), have the similar theoretical value within ± 200 N. The evaluation protocol for the impact test was established by applying the theoretical values, and the femoral neck peak force (N), attenuated peak force (N), force attenuation (%), and fracture risk by hardness of hip protector were analyzed. This regression model shows that the impact protection performance is the most superior at optimal hardness of 44.8 A (R^2= 79.4%, femoral neck peak force = 0.7462x^2-66.9x + 4205). Fourth, in design of FE modeling for finite element analysis of hip protector for the impact protection performance, FE modeling is performed under the same conditions as the impact simulator. Also, based on the human body model used in the impact simulator, FE modeling was performed with reflecting by characteristics of human body of elderly woman (bone shape, bone density, bone mass, trochanteric soft tissue thickness, and femur angle). Also, the properties of hyperelastic materials such as soft tissue and pad were applied to FE modeling through material test evaluation. Finally, 99% of the elements of parts made of elastic or hyperelastic were meshed with aspect ratio < 2 to prevent numerical errors in the analysis and to ensure the reliability of the results. Fifth, in the optimum hardness derivation step for determining impact protection performance of hip protector based FEA, the center of gravity and inertia values are derived from the 35 ° and 0 ° conditions of the model developed through the FEA dedicated tool, and the analysis was carried out by deriving the angular velocities of 2.96 and 2.92 respectively, when wearing and not wearing the pad. The results of hardness analysis for the pad evaluated that the impact protection performance evaluation was superb as in terms of stress and force in order of 40 A> 50 A > 60 A> 70 A pad, and in case of wearing 40 A pad against not wearing pad, contact force attenuation decreased 14.17%, femoral neck force attenuation decreased 25%, and stress decreased 12.5%. Out of pads of target hardness of evaluation, wearing 40 A pad in FEA had the most excellent impact protection performance that was similar to the optimal hardness of 44.8 A pad derived from impact simulation test by impact simulator. Sixth, from the viewpoint of verification of physical properties, polyurethane material, which is the property of hip protector used in this study, was found to have excellent impact protection performance in terms of femoral neck force attenuation and stress as compared with general rubber material. The internal energy absorbed by the pad was found to be superior to the rubber material, but the internal energy absorbed by the bone was lower than that of the rubber material. As a result, when the pad was made of a polyurethane material, it was found that the impact protection performance was superior to that of a pad made of a rubber material. In this study, an impact simulator was developed by referring to the recommended guide line of the impact simulator design presented by IHPRG and Robinovitch et al. (2009), impact simulation test by the impact simulator and FEA were performed to obtain optimal hardness of the hip protector, and the impact protection performance according to the properties of the hip protector was evaluated through impact simulation test by the FEA. Finally, this study can be used as a standard study for the evaluation of the impact protection performance of the hip protector by carrying out the impact simulation test based on the impact simulator and FEA which can complement and replace the limit of impact simulation test based on the impact simulator.

Multiphysics Modeling and Reliability Optimization of Power Semiconductor Packages using Finite Element Analysis

최나연 동의대학교 대학원 2025 국내박사

As high efficiency and miniaturization of power conversion systems are required in modern industrial society, ensuring the reliability of power semiconductor packages has become an essential task. In particular, sophisticated analysis and optimization technologies are required to solve complex thermal, mechanical, and electrical problems arising from the introduction of next-generation Wide Bandgap (WBG) devices and the high integration of packages. This thesis proposes an integrated framework that investigates multiphysics phenomena of power semiconductor packages based on Finite Element Analysis (FEA) and evaluates and optimizes reliability by converging experimental verification and machine learning techniques. In addition, to overcome the lack of information on the internal structure and material properties of commercial power semiconductor devices, a methodology for deriving 'Equivalent Chip Properties' was established using reverse engineering-based 3D modeling and experimental data. Based on the established methodology, comprehensive finite element analyses were conducted to evaluate the performance and reliability of power semiconductors under various package types and stress conditions. First, mechanical terminal strength tests (tensile, bending, torque, etc.) based on the MIL-STD-750D standard were simulated for the TO-220 packaged Schottky Barrier Diode (SBD). The analysis results confirmed stress concentration in the lead frame and wire bonding areas, and the validity of the analysis model was verified through comparison with actual tensile tests. Second, an evaluation of the Total Ionizing Dose (TID) effect was performed to ensure reliability in extreme environments such as the aerospace field. By combining Cobalt-60 (Co-60) gamma-ray irradiation experiments on P-Channel MOSFETs with electro-thermal coupled analysis, the degradation behavior of the device's equivalent electrical resistivity and thermal conductivity according to the cumulative radiation dose was quantitatively investigated. Third, the effects of void and fillet shapes in die bonding and wire diameter on thermal characteristics were analyzed for GaN HEMT devices with high-reliability Hermetic packaging. Furthermore, Electric-Thermal-Structural-Electromagnetic multiphysics analysis was performed for the bonding wire design of diode power modules. Through Design of Experiments (DOE), the correlations between wire loop height, diameter, and number on parasitic inductance (ACL), DC resistance (DCR), and thermal/mechanical stress were analyzed, and based on this, a multi-objective optimal design was derived. Finally, a digital design framework incorporating Machine Learning was proposed to overcome the limitations of conventional static material property-based analysis. By training I-V characteristics and heating data of IGBT devices under various bias conditions, dynamic equivalent properties were predicted. By applying this to FEA, it was confirmed that nonlinear behavior in actual operating environments can be simulated with very high accuracy. The evaluation methodology based on multiphysics analysis and the machine learning convergence framework proposed in this study are expected to contribute to reducing costs and time in the early stages of power semiconductor package development and significantly improving device performance and reliability through optimal design.

HBI 제작용 롤러 소재의 고온물성 연구

권대우 연세대학교 일반대학원 2026 국내석사

During the high-temperature and high-pressure compaction of Direct Reduced Iron (DRI) into Hot Briquetted Iron (HBI), the briquetting roll plays a critical role in determining briquette quality and process stability. Because the roll is simultaneously subjected to wear, plastic deformation, and fracture, an integrated evaluation of wear resistance, plastic deformation resistance, and fracture resistance is required. This study systematically evaluated the high-temperature properties of SKH51 in hot-rolled [R] and cast [C] forms through microstructural analysis, high-temperature hardness testing, V-bending–based yield load and fracture load measurements, and finite element analysis (FEA). Hot-rolled specimens exhibited uniformly dispersed spheroidized primary carbides, whereas cast specimens contained grain-boundary network carbides and abundant fine secondary carbides, resulting in a higher overall carbide fraction. In particular, the cast material showed superior resistance to high-temperature softening due to its rich population of fine carbides. Hot hardness and carbide fraction were used as indicators of wear resistance, while yield load and fracture load obtained from V-bending were applied as indicators of plastic deformation resistance and fracture resistance, respectively. At 200 °C, hot-rolled specimens showed ductile behavior, whereas cast specimens exhibited brittle response associated with network carbides. A combined evaluation incorporating these indicators identified 9 h[R] and 12 h[C] as the most favorable conditions for rolled and cast materials. Subsequent V-bending at 280 °C revealed that 12 h[C] experienced a temporary reduction in both YL and FL due to stress concentration at sharp-edged carbides, while 9 h[R] maintained relatively stable load responses. However, above 370 °C, the 12 h[C] condition converged to levels comparable to the hot-rolled material, and the overall integrated evaluation confirmed that 12 h[C], supported by its high carbide fraction and stable load indicators, is more suitable for HBI rolls. Fracture surface analysis showed ductile dimples and carbide–matrix decohesion in 9 h[R], whereas 12 h[C] exhibited intergranular brittle fracture at 200 °C and shear–quasi-cleavage fracture above 280 °C due to stress concentration near sharp-edged carbides, providing critical insight into the structural behavior of cast-based HBI roll materials. Finite element analysis confirmed similar stress concentration at the tip edge between V bending specimens and an actual HBI roll model, verifying that the V-bending test effectively simulates roll deformation behavior. This integrated evaluation framework offers foundational guidance for determining optimal SKH51 conditions for HBI rolls and for future alloy design and process optimization. 직접환원철(Direct Reduced Iron, DRI)을 고온·고압에서 HBI(Hot Briquetted Iron)로 성형할 때 HBI roll은 성형체의 품질과 공정 안정성에 직접적인 영향을 주는 핵심 부품이다. 그러나 roll은 마모와 압하력에 의한 변형에 지속적으로 노출되므로, 내마모성·소성변형저항성·파단저항성을 동시에 고려한 소재 종합 평가가 요구된다. 본 연구는 SKH51을 대상으로, 열연재(Hot-rolled, R)와 주조재(Cast, C)의 열처리(다중 템퍼링) 조건에 따른 미세조직, 고온 경도, 그리고 V-bending과 유한요소해석(Finite Element Analysis, FEA)을 연계하여 고온물성을 체계적으로 평가하였다. 열연재는 구상화된 1차 카바이드가 균일 분포된 반면, 주조재는 입계 네트워크형 카바이드와 풍부한 미세 2차 카바이드가 특징적이었으며 전체 카바이드 분율도 더 높았다. 특히 주조재는 미세 카바이드가 풍부하여 고온 경도 연화 저항성이 우수하였다. 본 연구에서는 경도와 카바이드 분율을 내마모성 지표로 적용하였다. V-bending에서는 항복·파단하중을 각각 소성·파단저항성의 지표로 적용하였다. 200 ℃에서 열연재는 연성적 거동을, 주조재는 입계 네트워크형 카바이드 기인 취성적 거동을 보였다. 세 지표의 곱으로 소재 종합 평가 결과 열연재는 9 h[R], 주조재는 12 h[C] 조건이 가장 우수하였다. 이후 200-450 ℃ 범위에서 두 조건을 비교한 결과 주조재는 280 ℃에서 항복하중과 파단하중의 일시적인 저하가 있었으나, 370 ℃ 이상에서 열연재와 유사 수준으로 수렴하였다. 소재 종합 평가 결과 12 h[C]는 높은 카바이드 분율과 우수한 하중 지표를 바탕으로 HBI roll에 더 적합한 소재임을 확인하였다. 파단면 분석 결과, 열연재 9 h[R]은 카바이드-기지 계면 탈착과 국부 딤플(dimple)이 동반된 안정적인 연성적 파단 양상을 보였으며, 이는 균일한 구상 카바이드 분포가 기지의 파단 지연에 기여한 것으로 판단된다. 반면, 주조재 12 h[C]는 200 ℃ 에서 네트워크형 카바이드를 따라 입계 취성 파단을 보였으나, 경질 카바이드의 균열 성장 지연 효과로 인해 비교적 높은 하중 지표를 나타냈다. 280 ℃ 이상에서는 입내 전단 및 quasi-cleavage 파단이 관찰되었으며, 이는 sharp-edged 카바이드에서의 응력 집중과 연관된 것으로 해석된다. 이러한 파단면 특성은 주조재 기반 HBI roll의 구조적 거동 이해에 중요한 근거를 제공한다. 또한 FEA로 V-bending 시편과 실제 HBI roll 모델의 응력 분포를 비교해, tip edge 부의 응력 집중 양상이 유사한 양상을 보임을 확인함으로써, V-bending 시험법이 roll 소재의 변형 거동을 효과적으로 모사함을 검증하였다. 나아가 본 연구의 소재 종합 평가 방안은 HBI용 SKH51의 최적 조건 도출과 향후 합금 설계·공정 최적화의 기초 자료로 활용될 수 있다.

Human-centered research of a transfer assist system to assist nursing care of patients with lower extermities physical disabilities

박철제 과학기술연합대학원대학교(UST) 2015 국내박사

본 연구에서는 스스로 거동이 힘든 환자를 위해 침대, 휠체어 및 변기 상호간 쉽고 편하게 이승하는 것을 목적으로 하는 효과적인 이승시스템을 제안하며 인간과 이승시스템 상호간에 안정적인 이승방안과 안전하게 이승을 하기 위한 연구방법론을 고려한 인간중심적 연구방법을 제시한다. 제안한 이승시스템은 사고나 질병 및 고령으로 인한 하지 지체장애 환자 등의 타인의 도움을 받아야만 거동이 가능한 신체기능이 저하된 사람에게 사용된다. 사람을 이승하는 방법적(안기, 부축하기, 업기) 분석을 통해서 효과적인 이승동작인 업는 방법을 적용한 이승시스템의 개발을 위해 인간과 기구 장치간에 상호작용 하는 기구학과 생체역학적 분석 및 유한요소해석(FEA)을 통한 업는 형태의 간병보조용 이승시스템을 개발하였다. 업는 방법의 이승시스템의 개발을 위해 실제 사람을 업는 동작의 특징 분석절차를 통해 사람을 업는 효과를 주며 신체하중을 들어올려 지지하기 위한 최소한의 구동모듈을 가진 모바일 리프트 구조로 설계하였고 시스템 제작비용도 절감을 하였다. 또한 사람이 이승시스템에 업힐 때 신체하중을 고루 분산하여 지지할 수 있는 구조로 상체지지 쿠션과 허벅지 및 등 체결패드 형태도 개발하여 1분 이내 신속착용 가능한 기구적 디자인을 적용하였다. FEA와 생체역학적 시뮬레이션을 통해 사람을 업는 동작에서 상체 굽힘각도 변화에 따라 신체와 기구 사이에 상호 작용하며 가감되는 응력을 분석하여 신체에 최소한의 체압을 받고 하중을 고루 분산시키는 안정된 이승시스템의 체결위치를 분석한다. 이 분석데이터를 통해 상체 굽힘 각도에 따라 사람의 무게중심이 바뀌는 특징을 고려해 허벅지 및 등 체결패드는 가변 하여 사람의 하중을 지지할 수 있도록 하였다. 역학적 분석으로 얻은 데이터를 통해 간병인이 힘들이지 않고 신속하게 침대에서 사람을 이승시스템에 탑승시켜 변기로 이승하는 일련의 과정 및 절차를 제시하여 업는 형태의 이승시스템이 간병인 입장에서 누구나 쉽게 이용 가능하도록 사용절차가 간단하게 기구적 편의성을 주며 신체적 부담을 줄여주고 환자입장에서 기구압박에 의한 고통을 최소화하여 편안함과 안정성을 주는 것을 실험 및 검증하였다. 본 연구를 통해 제안한 이승 시스템을 사용함으로써 간병인 입장에서는 육체적, 정신적 스트레스를 최소화 할 수 있고 환자입장에서 편안함과 안정감을 줄 수 있어 각 병원 및 노인 요양병원 및 가정 등에서 환자 이승을 위한 간병 보조하는데 많은 기여를 하리라 생각하며 파급효과가 클 것으로 기대된다. In this thesis, an effective transfer assist system for patients who are unable to move themselves is proposed for transferring them conveniently and comfortably wherever between their bed, wheelchair, and toilet bowl. In addition, the method of human-centered research presented about how to stable transferring and investigation methodology for safe transfer between human and the system. The proposed transfer assist system aims to help those who have impaired bodily functions and can only move with assistance, such as patients with lower extremity physical disabilities due to accident, disease, or age. Through the analysis of carrying persons (Lifting Hug, Holding Arms, Piggybacking), the transfer assist system that applies piggybacking as the effective transfer method was developed by means of the kinematics that show the interaction between human and the system, biomechanical analysis and finite element analysis (FEA). To develop a transfer assist system that uses a piggyback method, a mobile lift structure with an actuator module that supplies the least force required to have a piggybacking effect and to lift and support body-weight loads was designed through analyzing the characteristics of piggybacking persons, thereby reducing the system manufacturing cost. In addition, a mechanical design that can be worn rapidly (within one minute) was applied, as it also developed an upper body support cushion, and thighs- and back-attached pads with a structure that supports and distributes a body weight load uniformly, while piggybacking using the transfer assist system. Through FEA and biomechanical simulation, stresses that are added or removed between human bodies and the system depending on the upper body bending angle in the piggybacking action were analyzed, thereby determining the stable attachment position of the transfer assist system that can distribute loads uniformly and give the least body pressure to the human body. Through this analysis data, we adapted the transfer assist system’s thigh- and back-attached pads according to the characteristics of the change to the center of mass, depending on the upper body bending angle. This thesis also provides an experiment to verify the comfort and reliability of the transfer assist system that applies piggybacking, to minimize the pain caused by the pressure of the device from a patient’s viewpoint. The transfer assist system also reduces the physical burden of the caregivers and provides the simplicity of the mechanical convenience with procedures that are easy-to-use by any caregiver. This is achieved by providing a series of processes and procedures that allow transfer patients from a bed, to the transfer-assist system, and to toilet bowl rapidly without difficulty for the caregiver through mechanical analysis. As using the proposed transfer assist system through this thesis that the system can minimize the physical- and mental-stress from caregiver’s viewpoint. Also it provides the comfort and stability from patient’s viewpoint. So we expect that the system will have a great ripple effect and contribute to caregiving for patient transfer at hospitals, in aged care facilities, and homes.

Analysis of cyclic thermal stress on restored tooth using finite element analysis : 유한요소분석을 통한 수복치아의 주기적 열응력 분석

한우람 서울대학교 대학원 2015 국내석사

Introduction The intake of hot and cold substance in daily life generates cyclic thermal stress to tooth and this repeated stress may result in fatigue failure. The purpose of this study was to analyze the relationship between cyclic thermal stress and tooth crack formation using finite element analysis. Methods A maxillary first molar with class I or class II restoration was modeled via CAD-FEM procedure. Thermal load based on in vivo experimental data was applied to class I/II prepared natural tooth without filling material (control) and class I/II gold restored tooth. Stress generated in tooth structure was examined. Predicted fatigue life based on stress analysis was calculated using Basquin's equation. Results Calculated fatigue life was shorter in gold restored group than in controlled group and class II restored group showed shorter fatigue life than class I restored group. The shortest fatigue life was shown in class II gold restored tooth (3 X 107 years). For all cases, maximum stress was held in cold stimulation. Conclusions The cyclic thermal stress is a contributing factor of tooth crack formation and the presence of restoration facilitates the fatigue failure caused by cyclic thermal stress.

Stability Evaluation of Femur-Implant Structures according to Lateral Wall Thickness Classification in Femoral Intertrochanteric Fractures

김경림 부산대학교 대학원 2025 국내석사

In pertrochanteric fractures, the measurement of lateral wall thickness is essential, especially when considered alongside the size of the posteromedial defect, which is closely linked to fracture instability. This study proposes a novel approach for quantifying lateral wall thickness relative to posteromedial defect dimensions. Additionally, it explores the clinical significance of lateral wall thickness within the AO classification by using finite element analysis to validate biomechanical variations at the fracture site and implant in response to changes in lateral wall thickness. In this study, a femoral model representative of a 50 kg female was subjected to an initial load equivalent to 300% of the hip joint reaction force. To account for varying loads during different phases of gait, the applied force was systematically increased from one to four times the baseline, depending on the requirements of each simulation. The static simulations, which evaluated stress and displacement in the cortical bone and femoral implant under loads from one to three times the femoral load, demonstrated that reductions in lateral wall thickness led to increases in both stress and displacement. Further fatigue simulations, involving forces of 3, 3.5, and 4 times the fatigue failure threshold, indicated a significant decrease in the number of fatigue life cycles with higher applied forces, particularly in models where the lateral wall thickness measured 17.08 mm. These findings suggest that, in the context of pertrochanteric fractures, measuring lateral wall thickness from the posterior region of the proximal femur could provide a more accurate assessment of fracture stability. Consequently, this study highlights the importance of reconsidering the role of lateral wall thickness within the AO classification to better reflect fracture stability in clinical practice.

자동차 와이퍼의 부상특성을 고려한 누름압 해석

홍윤화 인하대학교 대학원 2015 국내석사

The wiping performance which is performance of wiping a windshield of the automobile wiper depending on the operating direction, the wiper position and the speed of the automobile. The wiping performance of a automobile wiper is a ability to wipe the windshield for secure a clear view of a driver. This performance can be decided by contact pressure of a wiper in contacting to a windshield. Contact pressure of a wiper is increased by increasing speed of car. But a wiper can be lifted locally when a car is driving in high speed. This lifting phenomenon of a wiper called the wind lift has a bad influence for the wiping performance. As a result, view of a driver is not cleared by problems the remaining water on a windshield and the chattering of a blade. For prevent this problems and maintain the performance of a wiper, use the FEA analysis as structural analysis and flow analysis when designing a wiper. But, this way can't confirm the wind lift effects on a contact pressure, because these analysis are considering a one thing which is wind lift or contact pressure by a shape of wiper. In this study, confirm a contact pressure by the wind lift using FSI analysis for overcome the limitation of a existing way of a analysis. This study found the extreme condition, about the problem of the wiper performance, from comparing results of a analysis with variables of a analysis which are speed of a car, a location of a wiper and a operating direction of a wiper. This study expect to save a time and a cost using the result of extreme condition when designing a wiper.

Diffusion of Designerly Finite Element Analysis

Peterson, Jerrod Paul ProQuest Dissertations & Theses Stanford Universit 2015 해외박사(DDOD)

To address a variety of difficulties surrounding the use of finite element analysis (FEA) in product development at Sandia National Laboratories, this research explored a 'designerly' insertion of FEA into the design-build-test product development cycle. Designerly FEA is characterized by the use of simplified FEA models, designer-friendly FEA software, an FEA analyst embedded in the product design team, relative comparisons of design options, and a deliberate leveraging of routine prototype testing to collect model validation data. Two case study projects were used to explore the impact of this approach on the product development teams' thinking and perceptions of FEA. The case study data was collected using a variety of methods and analyzed using a theory-building approach. The results were synthesized into a framework that describes how the use of FEA to build confidence in a product design is related to the process by which product development teams gain or lose confidence in FEA itself. The implications may extend to other organizations that desire to increase the impact of FEA or other simulation technologies in their product development process.

Experimental Study on Thermo-Elastic Behavior of Automotive Disk Brake

조호준 인하대학교 일반대학원 2008 국내박사

디스크 브레이크 시스템은 제동 시 극심한 마찰 접촉에 의해 발생되는 진동 과 소음 문제들을 유발시킨다. 특히, 저더와 스퀼은 브레이크 NVH 문제들 중 가장 주된 진동, 소음 문제이다. 저더는 브레이크 시스템에서 저주파 진동 (10~30Hz) 현상을 의미한다. 일반적으로 디스크와 패드 간에는 불균일 마찰 접 촉 압력이 발생하여 이로 인한 불균일 열변형이 발생된다. (열적 불균일). 그러 나 어떤 임계 조건들은 (특히 고속에서 제동 시) 이러한 불안정한 불균일 열변 형을 열섬으로 더욱 성장시킬 수 있다. 결국 불안정한 열적 불균일은 다시 차량 의 제어를 어렵게 만드는 저더를 발생시킨다. 불안정성 조건은 시스템의 기하학 적인 조건, 마찰재와 피마찰재 재료의 조합 그리고 작동되는 조건에 따라 변화 한다. 반면, 스퀼은 고속에서의 제동 시 보다 저속에서의 제동 시에 보다 쉽게 발생하는 고주파 제동 소음이다. 저더와 유사하게 스퀼 현상은 브레이크 시스템 의 기하학적 형상, 재료, 조작 조건을 포함하여 여러 설계 인자들에 영향을 받 는다. 이는 저더와 스퀼을 동시에 고려한 브레이크 NVH의 최적 설계가 이루어 져야 함을 의미한다. 본 논문에서는 자동차 디스크 브레이크에서의 열적-기계적 거동을 보다 잘 이해하기 위해 세 가지 주제로 연구를 수행하였다. 첫째로, 열탄성 불안정성 (TEI) 실험 (새시 다이나모미터와 고속 적외선 카메라 이용)과 유한요소해석을 (HOTSPOTTER 및 ABAQUS를 이용) 비교하여 상관관계를 분석하였다. 상관 분 석 방법은 열섬 성장에 높은 영향을 주는 인자로 획득한 브레이크 압력에 초점 을 두었다. 브레이크 압력 변화로부터 얻어낸 실험 결과를 바탕으로 회귀분석과 보간법이 수행되었다. 둘째로, 열섬 발생에 따른 진동 변화를 실험적으로 연구 하였다. TEI 이론에 따르면 비대칭 열적 모드는 열탄성 불안정성을 발생시킬 수 있는 가장 작은 임계 속도에서 가장 먼저 발생되며 그보다 높은 속도에서는 대 칭 열적 모드가 발생된다. 대칭 열적 모드와 디스크의 면외 방향 모드와의 관계 를 연구하기 위해 열섬 발생 시 브레이크 디스크의 동적 거동을 자세히 관찰하 고 측정하였다. 제동 초기부터 열섬이 완전히 발생되었을 때까지 천이 온도 분 포와 진동을 시간에 따라 측정하였다. 그 결과를 토대로 자동차 디스크의 열탄 성 거동에 높은 연관성을 보이기 위한 열섬 이동과 진동 변화 관계를 연구하였 다. 마지막으로 저더와 스퀼에 대한 연계 디자인을 위해 자동차 디스크 브레이 크의 최적 설계 방안을 제시하였다. 보다 정확한 해석 수행을 위해 모달 분석을 통해 실제 모델과 유한요소 모델 간의 보정을 수행했다. 디스크와 패드 간의 압 력은 TEI와 스퀼에 높은 관계가 있으므로 가압 방식과 형상에 따른 압력 분포 와 열변형 분석을 수행하였다. 또한 ABAQUS를 이용하여 스퀼 특성을 평가하 기 위해 복소 고유치 분석이 수행되었다. 본 연구로부터 얻은 결론은 다음과 같다. 일반적인 제동 성능과 특히 저더를 발생시키는 f_(0) 회전 차수 성분, 1/2f0 분수 조화 진동 성분을 증가시키는 불균일 접촉뿐만 아니라 브레이크 접촉 압력 특성 또한 브레이크 NVH에 높은 영향을 준다. 패드의 길이 및 압력 경계 조건에 의한 구속 조건이 열탄성 불안정성과 동적 불안정성에 높은 영향을 준다. 열탄성 불안정성에 높은 저항 성능을 갖도 록 설계된 브레이크 시스템일지라도 동적 불안정성은 더욱 심각하게 나타날 수 있다. Disk brake systems are vulnerable to noise and vibration problems arising from severe inherent sliding contact on their operation. Major brake NVH (Noise, Vibration and Harshness) is notorious for judder and squeal. Judder is a phenomenon of low frequency vibration in brake systems. The non-uniform frictional contact pressure commonly exists between a disk and pads and hence causes nonuniform thermal deformation (i.e. hot roughness) on disk surface. However, some critical conditions (especially, high speed brake) can grow this non-uniform thermal deformation unstably to hot spots. Finally, the unstable hot roughness, in turn, induces the judder which makes the vehicle control difficult. The conditions of the instability depend on the system dimensions, material combination, and operating conditions. On the other hand, squeal is a high frequency brake noise experiencing easier at brake of low vehicle speeds than at brake of high speeds. Like the case of judder, the squeal phenomena are related to variety of design factors partially including dimensions, materials, and operating conditions in the brake system. This implies that an optimal design of brake NVH should consider both judder and squeal phenomena simultaneously. In this dissertation, three subjects in automotive disk brakes are mainly studied for better understanding thermo-mechanical behavior. Firstly, thermo-elastic instability (TEI) is analyzed by comparing experiments (through using chassis dynamometer and infrared camera) and finite element analyses (through commercialized softwares, HOTSPOTTER and ABAQUS) to correlate each other. A correlation method focuses on a brake pressure factor which is found to influence greatly on hot spot development. The regression and interpolation are employed to reflect experimental results from brake pressure changes. Secondly, vibration changes due to hot spot development are experimentally investigated. According to the TEI theory, an anti-symmetric thermal mode develops first beyond a critical speed which is a minimum sliding speed enabling the thermo-elastic instability, followed by a symmetric thermal mode at the higher speed. To investigate relationship between the symmetric thermal mode and the out-of-plane modes of a disk, dynamic behaviors of the disk on hot spot occurrence are closely monitored and measured. Transient temperature distribution and vibration from brake initiation to the fully grown hot spots are recorded with time. As results, a relationship between hot spot migration and vibration change is investigated to show a close relation with the thermo-elastic behavior of the automotive disk. Finally, the optimal design methodology of an automotive disk brake is suggested for coupled design about judder and squeal. For achieving more accurate simulation of complex eigenvalue analysis, the correlation of a real model to a finite element model is performed through modal analysis. Since uniformity of pressure distribution between brake disk and pads highly affects TEI and squeal, pressure distribution and thermal deformation analysis is performed. Besides, complex eigenvalue analysis is conducted to evaluate a squeal characteristic by using ABAQUS. It is concluded from this study that brake contact pressure characteristics highly affects brake NVH as well as conventional braking performance, and uneven contact on hot spots increases the amplitude of broad frequency band, especially f0 rotation order component and 1/2f0 sub-harmonic component which leads to the judder. Constraints due to pad arc length and pressure boundary conditions highly affects thermo-elastic instability and dynamic instability. In spite of high resistance shown by optimized brake systems against thermo-elastic instability, severe dynamic instability can still occur.

Finite element analysis on the zone of the center of resistance in the mandibular posterior teeth segment

오문비 Graduate School, Yonsei University 2019 국내박사

이 연구의 목적은 하악 구치부 치아군(제1대구치 단독, 제1,2대구치, 제1,2대구치와 제2소구치, 제1,2대구치와 제1,2소구치)의 저항중심의 위치를 3차원 유한요소분석을 통해 알아내고자 함이다. 최근 3차원적인 공간에서 저항중심이 유한소수인 한 점이 아니라 작은 체적(volume)으로 존재하여 힘의 적용방향에 따라 2차원적 저항중심이 달라진다고 알려져, 본 연구에서는 “저항중심 영역(Zone of Center of Resistance, ZCR)” 이라는 용어를 도입하고 이를 검증하였다. 성인의 정상교합 표본 치아모형의 하악 치열을 3차원 레이저 스캐닝하여 치아, 치근막, 치조골로 구성된 3차원 유한요소 모델을 제작하고 각각의 치아군을 형성하여 세가지 방향(근원심적, 수직적, 협설적)으로 치아군에 힘을 적용하였으며, 이 때 치아군이 치체이동하는 힘의 적용 지점을 저항중심 영역으로 해석하였다. 또한 힘의 적용방향에 따른 2차원적 저항중심의 위치 차이를 분석하였다. 힘의 적용방향에 따른 2차원적 저항중심의 위치 차이는 본 연구에서 0.1 ~ 0.2mm로 임상적으로 힘을 적용할 때 고려하기에 미미한 차이였다. 이는 하악 구치부 치아군의 3차원 저항중심 영역(ZCR)은 임상적으로 한 점으로 간주될 수 있음을 보여주며, 각 치아군의 3차원 저항중심 영역(ZCR)의 위치는 다음과 같다. 1. 하악 제1대구치 : 저항중심 영역은 수직적으로 치조골 높이로부터 치근단 방향으로 제1대구치 치근 길이의 48%, 교합면에서 보았을 때 제1대구치 근원심 폭경에 대하여 2:3, 협설측 폭경에 대하여 2:1.5의 비율로 제1대구치의 원심 협측에 위치하였다. 2. 하악 제1,2대구치 : 저항중심 영역은 수직적으로 치조골 높이로부터 치근단 방향으로 제1대구치 치근 길이의 46%, 교합면에서 보았을 때 치아군 장경(sectional arch length)에 대하여 2:2.3, 제1대구치 협설측 폭경에 대하여 2:1.1의 비율로 제1대구치의 원심 협측에 위치하였다. 3. 하악 제1,2대구치, 제2소구치 : 저항중심 영역은 수직적으로 치조골 높이로부터 치근단 방향으로 제1대구치 치근 길이의 50%, 교합면에서 보았을 때 치아군 장경(sectional arch length)에 대하여 2:2.4, 제1대구치 협설측 폭경에 대하여 2:1.6의 비율로 제1대구치의 원심 협측에 위치하였다. 4. 하악 제1,2대구치, 제1,2소구치 : 저항중심 영역은 수직적으로 치조골 높이로부터 치근단 방향으로 제1대구치 치근 길이의 53%, 교합면에서 보았을 때 치아군 장경(sectional arch length)에 대하여 2:2.5, 제1대구치 협설측 폭경에 대하여 2:2.4의 비율로 제1대구치의 중심소와(central pit)에 가깝게 위치하였다. 이상의 결과는 하악 구치부 개개 치아나 치아군을 교정적으로 이동시킬 때 더 정확한 3차원 힘체계(3D load system)를 적용하여 치체이동(translation)을 도모하기 위한 좋은 참고가 된다는 임상적 의의를 지닌다. Introduction: We sought the 3-dimensional (3D) zone of the center of resistance (ZCR) of mandibular posterior teeth groups (Group 1: first molar; Group 2: both molars; Group 3: both molars, and second premolar; Group 4: both molars, and both premolars) using 3D-finite-element analysis. Methods: 3D-finite-element models comprised the mandibular posterior teeth, periodontal ligament, and alveolar bone. In the symmetric bilateral model, a 100-g midline force was applied on a median sagittal plane at 0.1-mm intervals, to determine the anteroposterior and vertical positions of the ZCR (where the applied force induced translation). The most reliable buccolingual position of the ZCR was then determined in the unilateral model. The combination of the anteroposterior, vertical, and buccolingual positions was defined as the ZCR. Results: The ZCRs of Group 1/Group 2/Group 3/Group 4 were 0.48, 0.46, 0.5, and 0.53 of the mandibular first molar root length from the alveolar crest level, and located slightly distobuccally, at anteroposterior ratios of 2:3, 2:2.3, 2:2.4, and 2:2.5 to each sectional arch length and at buccolingual ratios of 2:1.5, 2:1.1, 2:1.6, and 2:2.4 to the first molar’s buccolingual width, respectively. Conclusions: The ZCR can be a useful reference for 3D-movement planning of mandibular posterior teeth or segments.