• Geomechanics and Engineering
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• 제28권5호
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• pp.493-503
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• 2022

Cavity expansion is a classical problem in the field of solid mechanics with a wide range of applications in geotechnical and petroleum engineering. A drained solution is developed for cylindrical cavity expansion in anisotropic soils under biaxial in-situ stresses using a K0-based anisotropic modified Cam-clay model (K0-AMCC). The problem is formulated by solving differential equations using an auxiliary variable, which provides analytical expressions for the volume and four stress components of the soil around the cylindrical cavity. The solution is validated by comparisons with existing well-developed solutions. The results show that the present solution well captures the cavity expansion responses in anisotropic soils under biaxial in-situ stresses, and removes limiting assumptions that the cylindrical cavity expands under uniform in-situ stress in isotropic soils. The elastic-plastic boundary of the expanding cylindrical cavity in K0-consolidated anisotropic soils under biaxial in-situ stresses is a circle rather than an ellipse in isotropic soils, and the mathematical proof is provided in detail.

• 대한의용생체공학회:의공학회지
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• 제22권4호
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• pp.349-358
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• 2001

A novel electro-mechanical implantable ventricular assist system is developed as a bridge to transplantation or recovery for patients with end-stage heart failure. The developed system is composed of an implanted blood pump, an external monitoring system which stores data, and a wearable system including a portable external driver and a portable power supply system. The blood pump is designed to be implanted into the left upper abdominal space and provides blood flow from the left ventricular apex to the aorta. The pulsatile blood flow is generated by a double cylindrical cam. There was mo excessive heat emission from the blood pump into the temperature-controlled chamber in the heat test and no stagnated flow within the blood sac by the observation in the flow visualization test. Animal experiments were performed using sheep and calves. The maximum assist flow rate reached 7.85L/min in the animal experiment. The evaluation results showed that the developed system was feasible for the implantable ventricular assist system. The long-term in vitro durability test and mid-term in vivo experiments are in progress and mow the modified next model is under development.

• The Journal of Advanced Prosthodontics
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• 제12권5호
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• pp.251-258
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• 2020

PURPOSE. The bond strengths between resin denture teeth with various compositions and denture base resins including conventional and CAD/CAM purposed materials were evaluated to find influence of each material. MATERIALS AND METHODS. Cylindrical rods (6.0 mm diameter × 8.0 mm length) prepared from pre-polymerized CAD/CAM denture base resin blocks (PMMA Block-pink; Huge Dental Material, Vipi Block-Pink; Vipi Industria) were bonded to the basal surface of resin teeth from three different companies (VITA MFT^®; VITA Zahnfabrik, Endura Posterio^®; SHOFU Dental, Duracross Physio^®; Nissin Dental Products Inc.) using resin cement (Super-Bond C&B; SUN MEDICAL). As a control group, rods from a conventional heat-polymerizing denture base resin (Vertex™ Rapid Simplified; Vertex-Dental B.V. Co.) were attached to the resin teeth using the conventional flasking and curing method. Furthermore, the effect of air abrasion was studied with the highly cross-linked resin teeth (VITA MFT^®) groups. The shear bond strengths were measured, and then the fractured surfaces were examined to analyze the mode of failure. RESULTS. The shear bond strengths of the conventional heat-polymerizing PMMA denture resin group and the CAD/CAM denture base resin groups were similar. Air abrasion to VITA MFT^® did not improve shear bond strengths. Interfacial failure was the dominant cause of failure for all specimens. CONCLUSION. Shear bond strengths of CAD/CAM denture base materials and resin denture teeth using resin cement are comparable to those of conventional methods.

• 한국생산제조학회지
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• 제24권2호
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• pp.231-237
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• 2015

The pin-gear drive is a special form of fixed-axle gear mechanism. A large wheel with cylindrical pin teeth is called a pinwheel. As pinwheels are rounded, they have a simple structure, easy processing, low cost, and easy overhaul compared with general gears. They are also suitable for low-speed, heavy-duty mechanical transmission and for occasions with more dust, poor lubrication, etc. This paper introduces a novel slewing ring bearing with an external pinwheel gear set (e-PGS). First, we consider the exact cam pinion profile of the e-PGS with the introduction of a profile shift. Then, the contact stresses are investigated to determine the characteristics of the surface fatigue by varying the shape design parameters. The results show that the contact stresses of the e-PGS can be lowered significantly by increasing the profile shift coefficient.

• Geomechanics and Engineering
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• 제20권2호
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• pp.147-154
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• 2020

A novel approach for predicting lateral displacement caused by pile installation in anisotropic clay is presented, on the basis of the cylindrical and spherical cavities expansion theory. The K₀-based modified Cam-clay (K₀-MCC) model is adopted for the K₀-consolidated clay and the process of pile installation is taken as the cavity expansion problem in undrained condition. The radial displacement of plastic region is obtained by combining the cavity wall boundary and the elastic-plastic (EP) boundary conditions. The predicted equations of lateral displacement during single pile and multi-pile installation are proposed, and the hydraulic fracture problem in the vicinity of the pile tip is investigated. The comparison between the lateral displacement obtained from the presented approach and the measured data from Chai et al. (2005) is carried out and shows a good agreement. It is suggested that the presented approach is a useful tool for the design of soft subsoil improvement resulting from the pile installation.

• 문화기술의 융합
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• 제8권5호
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• pp.591-596
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• 2022

다양한 산업분야에서 사용되는 4절 링크기구는 링크 길이가 고정되어 있으므로 기구의 움직임을 변경하기 위해서는 독립적인 링크기구나 제어장치를 추가해야 하는 불편함이 있다. 따라서 본 논문에서는 상황에 따라 링크기구의 운동을 선택적으로 제어할 수 있도록 링크 길이가 조절되는 가변형 4절 링크기구를 설계하였으며 링크기구에 의해 구동되는 제품인 선풍기에 적용하여 그 타당성을 검증하였다. 바람 범위의 효율성을 고려하여 선풍기 회전각도를3단계로 분할하였으며 각 구간에 필요한 링크 길이를 계산하였다. 또한, 원통캠을 이용하여 링크 길이를 조절하였으며 선풍기의 회전각도 조절 작동 여부를 실제 제작 및 측정을 통해 확인하였다. 본 논문에서 제시한 가변형 링크기구는 산업용 로봇이나 연료 밸브 시스템 등과 같은 4절링크 적용 제품의 효율성을 향상시킬 수 있을 것으로 기대된다.

• 대한치과교정학회지
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• 제53권1호
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• pp.45-53
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• 2023

Objective: This study aimed to evaluate the shear bond strength (SBS) of orthodontic brackets bonded to three-dimensionally (3D)-printed materials after various surface treatments and artificial aging compared with that bonded to computer-aided design/computer-aided manufacturing (CAD-CAM) polymethyl methacrylate (PMMA)-milled materials. Methods: Eighty cylindrical specimens were 3D printed and divided into the following four subgroups (n = 20 each) according to the surface treatment and artificial aging procedure. Group A, sandblasted with 50 ㎛ aluminum oxide particles (SA) and aging; group B, sandblasted with 30 ㎛ silica-coated alumina particles (CO) and aging; group C, SA without aging; and group D, CO without aging. For the control group, 20 CAD-CAM PMMA-milled cylindrical specimens were sandblasted with SA and aged. The SBS was measured using a universal testing machine (0.25 mm/min), examined at ×2.5 magnification for failure mode classification, and statistically analyzed (p = 0.05). Results: The retention obtained with the 3D-printed materials (groups A-D) was higher than that obtained with the PMMA-milled materials (control group). However, no significant difference was found between the study and control groups, except for group C (SA without aging), which showed significantly higher retention than the control group (PMMA-SA and thermocycling) (p = 0.037). Study groups A-D predominantly exhibited a cohesive specimen mode, indicating specimen fracture. Conclusions: Orthodontic brackets bonded to 3D-printed materials exhibit acceptable bonding strengths. However, 3D-printed materials are prone to cohesive failure, which may result in crown fractures.

• Geomechanics and Engineering
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• 제25권4호
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• pp.303-315
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• 2021

A rigorous and generic similarity solution is developed for assessment of the undrained expansion responses of a cylindrical cavity expansion in K₀-consolidated anisotropic soils. A K₀-consolidated anisotropic modified Cam-clay (K₀-AMCC) model that can represent the initial stress anisotropy and the effects of stress-induced anisotropy is used to model the soil behaviors during cavity expansion. All the seven basic unknowns, the three stress components, the pore water pressure, the particle velocity, the specific volume and the hardening parameter, are reduced to the functions of a dimensionless radial coordinate and are taken as coupled variables to formulate the problem. The governing equations are formulated by making use of the equilibrium equation, the constitutive equation, the consistency condition, the continuity condition and the undrained condition, which are then solved as an initial value problem. The proposed rigorous similarity solution is compared with some well-documented rigorous solutions to validate the solution and to highlight the special expansion responses in anisotropic soils. The results reveal that the present solution can yield more predictions for cavity expansion problems in soils with initial anisotropic stresses.

• Restorative Dentistry and Endodontics
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• 제23권1호
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• pp.487-501
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• 1998

In the case of CAD/CAM ceramic inlay restorations, if isthmus width is widened too much, it may cause fracture of remaining tooth structure or loss of bonding at the luting interface because of excessive displacement of buccal or lingual cusps under occlusal loads. So to clarify the criterior of widening isthmus width, this study was designed to test the tensile bond strength and bond failure mode between dentin and ceramic cemented with luting composite resin cements. Cylindrical ceramic blocks(Vita Cerec Mark II, d=4mm) were bonded to buccal dentin of 40 freshly extracted third molars with 4 luting composite resin cements(group1 : Scotchbond Resin Cement/Scotchbond Multi-Purpose, group2 : Duolink Resin Cement/ All-Bond 2, group3: Bistite Resin Cement/Ceramics Primer, and group4:Superbond C&B). Tensile bond test was done under universal testing machine using bonding and measuring alignment blocks(${\phi}ilo$ & Urn, 1992). After immersion of fractured samples into 1 % methylene blue for 24 hours, failure mode was analysed under stereomicroscope and SEM. Results: The tensile bond strength of goup 1, 2 & 4 was $13.97{\pm}2.90$ MPa, $16.49{\pm}3.90$ MPa and $16.l7{\pm}4.32$ MPa, respectively. There was no statistical differences(p>0.05). But, group 3 showed significantly lower bond stregnth($5.98{\pm}1.l7$ MPa, p<0.05). In almost all samples, adhesive fractures between dentin and resin cements were observed. But, in group 1, 2 & 4, as bond strength increased, cohesive fracture within resin cement was observed simultaneously. And, in group 3, as bond strength decreased, cohesive fracture between hybrid layer and composite resin cement was also observed. Cohesive fracture within dentin and porcelain adhesive fracture were not observed. In conclusion, although adhesive cements were used in CAD/CAM -fabricated ceramic inlay restorations, the conservative priciples of cavity preparation must be obligated.

• 한국지반공학회논문집
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• 제22권11호
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• pp.75-87
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• 2006

본 논문에서는 과압밀된 점토에서 피에조콘 관입으로 인한 과잉간극수압의 공간적인 분포를 알아내기 위한 대형 토조시험을 실시하고 분석결과를 제시하였다. 시험결과에 의하면 콘 주변의 전단영역에서 과잉간극수압은 콘 표면으로부터 전단영역의 경계까지 직선적으로 증가하며, 소성영역에서는 대수적으로 감소하여 소성영역 경계에서 영으로 접근하였다. 또한 전단영역의 크기는 콘 반경의 2.2-1.5배 정도이며 과압밀비 증가 시 전단영역의 크기는 감소하는 반면 소성영역의 크기는 과압밀비에 상관없이 콘 반경의 약 11배로 일정하였다. 본 연구에서는 변형률 속도와 응력이 방성 효과를 고려하여 MCC(Modified Cam Clay) 모델과 공동확장이론으로부터 피에조콘 위치에서의 과잉간극수압을 예측하였으며, 전단영역에서 ${\Delta}u_{shear}$의 선형증가와 전단 및 소성영역에서 ${\Delta}u_{oct}$의 대수적 감소를 가정하여 과잉간극수압의 공간적 분포를 예측하기 위한 방법을 제시하였다. 이러한 방법으로 예측된 간극수압의 분포는 대형 토조시험에서의 콘 관입시험 결과와 비교를 통해 검증되었다.