• The Journal of Advanced Prosthodontics
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• 제10권2호
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• pp.113-121
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• 2018

PURPOSE. The aim of this preliminary study was to investigate, for the first time, the effects of addition of titania nanotubes ($n-TiO_2$) to poly methyl methacrylate (PMMA) on mechanical properties of PMMA denture base. MATERIALS AND METHODS. $TiO_2$ nanotubes were prepared using alkaline hydrothermal process. Obtained nanotubes were assessed using FESEM-EDX, XRD, and FT-IR. For 3 experiments of this study (fracture toughness, three-point bending flexural strength, and Vickers microhardness), 135 specimens were prepared according to ISO 20795-1:2013 (n of each experiment=45). For each experiment, PMMA was mixed with 0% (control), 2.5 wt%, and 5 wt% nanotubes. From each $TiO_2$:PMMA ratio, 15 specimens were fabricated for each experiment. Effects of $n-TiO_2$ addition on 3 mechanical properties were assessed using Pearson, ANOVA, and Tukey tests. RESULTS. SEM images of $n-TiO_2$ exhibited the presence of elongated tubular structures. The XRD pattern of synthesized $n-TiO_2$ represented the anatase crystal phase of $TiO_2$. Moderate to very strong significant positive correlations were observed between the concentration of $n-TiO_2$ and each of the 3 physicomechanical properties of PMMA (Pearson's P value ${\leq}.001$, correlation coefficient ranging between 0.5 and 0.9). Flexural strength and hardness values of specimens modified with both 2.5 and 5 wt% $n-TiO_2$ were significantly higher than those of control ($P{\leq}.001$). Fracture toughness of samples reinforced with 5 wt% $n-TiO_2$ (but not those of 2.5% $n-TiO_2$) was higher than control (P=.002). CONCLUSION. Titania nanotubes were successfully introduced for the first time as a means of enhancing the hardness, flexural strength, and fracture toughness of denture base PMMA.

• 대한치과보철학회지
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• 제45권1호
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• pp.21-33
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• 2007

Statement of problem: The esthetic component of dental care has become increasingly more important, while new tooth-colored materials are continually marketed. Various new indirect composite materials have been developed with required advantages. The most recent development in the indirect composites has been the introduction of the second-generation laboratory composite or poly-glass materials. They are processed by different laboratory techniques based on combinations of heat, pressure, vacuum and light polymerization. Although, second generation products became available in 1995, their characteristics and clinical performance have not been adequately investigated. Purpose: The aim of this study was to measure the mechanical properties of the second generation indirect resin system and compare these with an existing universal direct composite resin. Material and method: In this study four indirect composite material (Adoro LC, BelleGlass HP, Tescera, Synfony) were tested for flexural strength, wear resistance, hardness and their degree of conversion against Z250, a light cure direct composite. Results: Within the limitations of this study, the following conclusions were drawn: 1. From the abrasion wear result, Adoro showed the least volume loss while Synfony showed the greatest volume loss. Z250 and BelleGlass HP didn't show significant difference (p>0.05), but they showed significant difference with other groups (p<0.05). From the attrition wear, BelleGlass HP showed the least volume loss and it didn’t show significant difference with Tescera (p>0.05). While Synfony showed the greatest volume loss that it showed significant difference with other groups (p>0.05). 2. Mean values of flexural strength by means of three point bending test was in the order of Z250, Adoro, Belleglass HP, Tescera and Synfony. Mean elastic modulus was in the order of Z250, BelleGlass HP, Tescera, Adoro and Synfony. 3. The result of Vicker‘s microhardness value showed that significantly higher value in Z250 (p<0.05), and is in the order of BelleGlass HP, Tescera, Adoro and Synfony. 4. The degree of conversion measured by FT-IR showed significantly higher value in BelleGlass HP (p<0.05), and is in the order of Adoro, Synfony, Tescera and Z250. Conclusion: Significant differences were found in the flexural strength, wear resistance, hardness and their degree of conversion.

• 대한치과보철학회지
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• 제33권4호
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• pp.780-806
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• 1995

The purpose of this study was to describe the application of 3D finite element analysis to determine resultant stresses on the bone anchored fixed prosthesis, implants and supporting bone of the mandible according to fixture numbers and load conditions. 4 or 6 fixtures and the bone anchored fixed prosthesis were placed in 3D finite element mandibular arch model which represents an actual mandibular skull. A $45^{\circ}$ diagonal load of 10㎏ was labiolingually applied in the center of the prosthesis(P1). A $45^{\circ}$ diagonal load of 20㎏ was buccolingually applied at the location of the 10mm or 20mm cantilever posterior to the most distal implant(P2 or P3). The vertical distribution loads were applied to the superior surfaces of both the right and the left 20mm cantilevers(P4). In order that the boundary conditions of the structure were located to the mandibular ramus and angle, the distal bone plane was to totally fixed to prevent rigid body motion of the entire model. 3D finite element analysis was perfomed for stress distribution and deflection on implants and supporting bone using commercial software(ABAQUS program. for Sun-SPARC Workstation. The results were as follows : 1. In all conditions of load, the hightest tensile stresses were observed at the metal lates of prostheses. 2. The higher tensile stresses were observed at the diagonal loads rather than the vertical loads 3. 6-implants cases were more stable than 4-implants cases for decreasing bending and torque under diagonal load on the anterior of prosthesis. 4. From a biomechanical perspective, high stress developed at the metal plate of cantilever-to-the most distal implant junctions as a consequence of loads applied to the cantilever extension. 5. Under diagonal load on cantilever extension, the 6-implants cases had a tendency to reduce displacement and to increase the reaction force of supporting point due to increasing the bendign stiffness of the prosthesis than 4-implants cases. 6. Under diagonal load on cantilever extension, the case of 10mm long cantilever was more stable than that of 20mm long cnatilever in respect of stress distribution and displacement. 7. When the ends of 10mm or 20mm long cantilever were loaded, the higher tensile stress was observed at the second most distal implant rather than the first most distal implant. 8. The 6-implants cases were more favorable about prevention of screw loosening under repeated loadings because 6-implants cases had smaller deformation and 4-implants cases had larger deformation.

• 한국강구조학회 논문집
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• 제20권6호
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• pp.731-740
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• 2008

본 연구는 하부 절곡강판과 T형강을 D16mm 스터드 전단연결재를 이용하여 콘크리트와 일체화시킨 교량용 강합성 바닥판의 피로 거동 및 피로성능을 평가하기 위한 것이다. 제안된 강합성 바닥판의 피로성능 평가를 위하여 총 8본의 시험체가 제작되었으며, 각각의 시험체에 3 종류의 일정진폭을 가진 피로하중이 재하되었다. 피로실험결과, 피로균열은 강합성 바닥판 하부 절곡강판의 절곡점에서 발생하여 상부 T형강으로 진전되는 것으로 나타났으며, 피로하중에 따라 시험체의 변위 및 변형률이 증가하고 피로균열발생 후 변위와 변형률이 급격히 변화하였다. 제안된 강합성 바닥판의 피로강도는 도로교설계기준 및 도로교설계기준 피로상세 범주의 자료가 된 NCHRP 102와 NCHRP 147 보고서의 피로실험결 과와 비교하여 평가한 결과 대상 강합성 바닥판은 피로상세 범주 C에 해당하는 것으로 평가되었다.

• 치위생과학회지
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• 제10권6호
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• pp.445-450
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• 2010

본 연구에서는 열중합 의치상 레진에 유리 섬유, 아라미드 섬유, 폴리에틸렌 섬유를 2.6%, 5.3% 부피비로 첨가하여 섬유의 종류에 따른 강화효과를 평가하고, 각 섬유를 두 가지로 조합한 hybrid FRC를 제작하여 동일 함량의 단독 섬유 FRC보다 굴곡성질이 더 우수한지 평가하고자 하였다. 단독 섬유 FRC에서는 5.3% 부피비의 GL, PE 섬유군의 굴곡강도가 높게 나타났다. 두 가지 섬유 조합FRC의 굴곡강도는 단독 섬유 FRC보다 증가하는 양상을 보였으나, 5.3% GL, PE 섬유군과 유의한 차이가 없었다. 단독 섬유 FRC의 굴곡계수는 5.3% 부피비의 GL 섬유군이 가장 높게 나타났다. 두 가지 섬유 조합FRC의 굴곡계수는 단독 섬유 FRC의 5.3% GL 섬유군보다 높게 나타나 유의한 차이를 보였다. 열중합 의치상 레진의 강화를 위해 섬유를 단독으로 이용할 경우 5.3% 부피비로 첨가한 유리 섬유가 굴곡강도와 굴곡계수 면에서 효과적으로 적용될 수 있을 것으로 본다. 두 가지 섬유 조합FRC의 경우 굴곡강도 면에서는 강화효과가 크지 않았지만, 굴곡계수 면에서 볼 때 유리섬유를 하방에 아라미드 섬유를 그 상방에 위치 시킨 조합을 의치상의 강화에 효과적으로 적용할 수 있을 것으로 본다.

• 한국해양공학회지
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• 제27권5호
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• pp.22-27
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• 2013

The present work dealt with the high temperature thermal shock properties of 316 stainless steels, in conjunction with a detailed analysis of their microstructures. In particular, the effects of the thermal shock temperature difference and thermal shock cycle number on the properties of 316 stainless steels were investigated. A thermal shock test for 316 stainless steel was carried out at thermal shock temperature differences from $300^{\circ}C$ to $1000^{\circ}C$. The cyclic thermal shock test for the 316 stainless steel was performed at a thermal shock temperature difference of $700^{\circ}C$ up to 100 cycles. The characterization of 316 stainless steels was evaluated using an optical microscope and a three-point bending test. Both the microstructure and flexural strength of 316 stainless steels were affected by the high-temperature thermal shock. The flexural strength of 316 stainless steels gradually increased with an increase in the thermal shock temperature difference, accompanied by a growth in the grain size of the microstructure. However, a thermal shock temperature difference of $800^{\circ}C$ produced a decrease in the flexural strength of the 316 stainless steel because of damage to the material surface. The properties of 316 stainless steels greatly depended on the thermal shock cycle number. In other words, the flexural strength of 316 stainless steels decreased with an increase in the thermal shock cycle number, accompanied by a linear growth in the grain size of the microstructure. In particular, the 316 stainless steel had a flexural strength of about 500 MPa at 100 thermal-shock cycles, which corresponded to about 80% of the strength of the as-received materials.

• Advances in concrete construction
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• 제5권5호
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• pp.513-537
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• 2017

In this study, the fracture toughness $K_{IC}$ of high performance concrete (HPC) was investigated by conducting three-point bending tests on a total of 240 notched beams of $500mm{\times}100mm{\times}100mm$ subjected to heating temperatures up to $450^{\circ}C$ with exposure times up to 16 hours and various heating and cooling rates. For a heating rate of $3^{\circ}C/min$, $K_{IC}$ for the hot concrete sustained a monotonic decrease trend with the increasing heating temperature and exposure time, from $1.389MN/m^{1.5}$ at room temperature to $0.942MN/m^{1.5}$ at $450^{\circ}C$ for 4-hour exposure time, $0.906MN/m^{1.5}$ for 8-hour exposure time and $0.866MN/m^{1.5}$ for 16-hour exposure time. For the cold concrete, $K_{IC}$ sustained a two-stage decrease trend, dropping slowly with the heating temperature up to $150^{\circ}C$ and then rapidly down to $0.869MN/m^{1.5}$ at $450^{\circ}C$ for 4-hour exposure time, $0.812MN/m^{1.5}$ for 8-hour exposure time and $0.771MN/m^{1.5}$ for 16-hour exposure time. In general, the $K_{IC}$ values for the hot concrete up to $200^{\circ}C$ were larger than those for the cold concrete, and an inverse trend was observed thereafter. The increase in heating rate slightly decreased $K_{IC}$, and at $450^{\circ}C$ $K_{IC}$ decreased from $0.893MN/m^{1.5}$ for $1^{\circ}C/min$ to $0.839MN/m^{1.5}$ for $10^{\circ}C/min$ for the hot concrete and from $0.792MN/m^{1.5}$ for $1^{\circ}C/min$ to $0.743MN/m^{1.5}$ for $10^{\circ}C/min$ for the cold concrete after an exposure time of 16 hours. The increase in cooling rate also slightly decreased $K_{IC}$, and at $450^{\circ}C$ $K_{IC}$ decreased from $0.771MN/m^{1.5}$ for slow cooling to $0.739MN/m^{1.5}$ for fast cooling after an exposure time of 16 hours. The fracture energy-based fracture toughness $K_{IC}$' was also assessed, and similar decrease trends with the heating temperature and exposure time existed for both hot and cold concretes. The relationships of two fracture toughness parameters with the weight loss and the modulus of rapture were also evaluated.

• 한국전산구조공학회논문집
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• 제35권2호
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• pp.73-82
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• 2022

이 논문은 72m 초고강도 콘크리트 섬유보강 콘크리트 프리스트레스트 박스거더의 비선형 거동을 해석하는 3차원 해석방법을 제시하였다. UHPC재료의 비선형 거동을 나타내기 위해 콘크리트 손상소성(CDP)모델을 채택하였다. 제시된 응력-변형률 관계 곡선에 근거한 수치해석 모델은 50m UHPC 프리스트레스트 박스 거더 휨실험결과로 검증하였다. 검증된 해석모델을 사용하여 72m UHPC 프리스트레스트 박스거더의 휨거동을 파악하는데 적용하였다. 각 하중단계에 따른 하중 변위관계, 응력상태 및 연결부분 상세를 해석하였다. 하중-변위관계 곡선과 설계하중 및 극한하중 비교 결과는 UHPC 박스거더 휨거동을 해석하는 적절한 수단으로써 비선형 유한요소법의 적용성을 입증하고 있다.

• 한국결정성장학회지
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• 제32권5호
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• pp.212-217
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• 2022

고온의 탄화규소 단결정성장공정에서는 탄화규소-흑연간의 열팽창계수의 차이로 인한 열응력이 크게 발생할 수 있어 흑연부재로부터 탄화규소 종자정이 분리되어 성장 중에 종자정이 떨어지는 문제가 발생할 수 있다. 그러나 이러한 탄화규소 종자정 모듈의 접합특성에 대한 연구는 현재까지 거의 보고된 바가 없다. 본 연구에서는 탄화규소-흑연 간의 접합특성을 평가하기 위해 3점 굽힘시험법을 응용한 복합모드꺾임시험(Mixed-Mode Flexure Test)을 통해 탄화규소-흑연을 서로 다른 접합제를 적용하여 접합한 시편의 접합 특성을 확인하고, 흑연 접착제의 미세구조를 분석하기 위해 라만분광법(Raman spectroscopy), X선 광전자분광법(X-ray Photoelectron Spectroscopy) 및 X선 전산화 단층촬영법(X-ray Computed Tomography)을 활용하였다. 이러한 일련의 과정을 통하여 선별한 접착성이 우수한 접착제를 적용하여 직경 50 mm급의 탄화규소 종자결정모듈을 제작하고, 이를 적용하여 고온의 상부종자용액성장 공정을 이용하여 공정 중 종자정의 탈락없이 성공적으로 직경 50 mm급의 탄화규소 단결정을 성장시켰다.

• The Journal of Advanced Prosthodontics
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• 제13권4호
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• pp.226-236
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• 2021

PURPOSE. This study aimed to evaluate the effect of incorporating zirconium oxide nanoparticles (nano-ZrO₂) in polymethylmethacrylate (PMMA) denture base resin on flexural properties at different material thicknesses. MATERIALS AND METHODS. Heat polymerized acrylic resin specimens (N = 120) were fabricated and divided into 4 groups according to denture base thickness (2.5 mm, 2.0 mm, 1.5 mm, 1.0 mm). Each group was subdivided into 3 subgroups (n = 10) according to nano-ZrO₂ concentration (0%, 2.5%, and 5%). Flexural strength and elastic modulus were evaluated using a three-point bending test. One-way ANOVA, Tukey's post hoc, and two-way ANOVA were used for data analysis (α = .05). Scanning electron microscopy (SEM) was used for fracture surface analysis and nanoparticles distributions. RESULTS. Groups with 0% nano-ZrO₂ showed no significant difference in the flexural strength as thickness decreased (P = .153). The addition of nano-zirconia significantly increased the flexural strength (P < .001). The highest value was with 5% nano-ZrO₂ and 2 mm-thickness (125.4 ± 18.3 MPa), followed by 5% nano-ZrO₂ and 1.5 mm-thickness (110.3 ± 8.5 MPa). Moreover, the effect of various concentration levels on elastic modulus was statistically significant for 2 mm thickness (P = .001), but the combined effect of thickness and concentration on elastic modulus was insignificant (P = .10). CONCLUSION. Reinforcement of denture base material with nano-ZrO₂ significantly increased flexural strength and modulus of elasticity. Reducing material thickness did not decrease flexural strength when nano-ZrO₂ was incorporated. In clinical practice, when low thickness of denture base material is indicated, PMMA/nano-ZrO₂ could be used with minimum acceptable thickness of 1.5 mm.