This study’s objective was to evaluate repetitive firing cycles’ effects on the translucency, light’s absorption coefficient, and flexural strength of zirconia-reinforced lithium silicate ceramics. Two zirconia-reinforced lithium silicate ceramics and one lithium disilicate glass-ceramic were tested. Blocks of all materials were sectioned into tiles with different thicknesses and subjected to up to five firing cycles using the firing schedule indicated in the manufacturer’s user instructions. Light transmission ratio (T) and absorption coefficients were determined using a spectrophotometer. Further, bars were sectioned from blocks of all materials and tested for three-point-bend flexural strength using a Universal Testing Machine (Instron), and flexural strength was calculated from load at failure. Factorial ANOVA and Tukey’s HSD tests were conducted to analyze light transmission and flexural strength, while regression was used to analyze the absorption coefficient. Weibull parameters and fractographic analysis also were investigated. The results showed that repetitive firing cycles reduced e.max® and Vita Suprinity’s® translucency, but not that of Celtra® Duo, which showed no significant difference. All materials of greater thickness exhibited less translucency, and e.max® CAD had the highest mean light transmission; however, it was not significantly different than Celtra® Duo. Repetitive firing cycles showed more absorption coefficient of light with Vita Suprinity® and e.max®, except for Celtra® Duo, which showed no difference. Vita Suprinity® showed the highest absorption coefficient; however, it was not significantly different than e.max® CAD. Repetitive firing cycles had no significant effect on flexural strength. High and low flexural strength samples for all materials showed similar characteristics with respect to crack propagation patterns, and fracture origins. In conclusion, repetitive firing cycles decreased both e.max® and Vita Suprinity’s® translucency significantly. Repetitive firing cycles increased e.max® and Vita Suprinity’s® absorption coefficient significantly, particularly at shorter wavelengths. Repetitive firing cycles did not increase flexural strength statistically significantly. Vita Suprinity® showed an inherent and more homogeneous flaw-distribution in the first two firing cycles compared to the distribution of flaws in the other two materials.

<p> Flexural vibrations of a shaft mounted at each end on a non - linear spring have been studied. Theoretical analysis is carried out for the cubic non-linear spring. </p> <p> The effect of mountirig of a heavy rotor on the shaft has been considered. The stability analysis of the system is also given in the theoretical analysis.</p> / Thesis / Master of Engineering (ME)

No / This paper presents analytical technique and simplified formulas for the calculations of cracking, yield and ultimate moments of different cases as well as deflections of ECC-concrete composite beams reinforced with steel bars. The technique is based on the simplified constitutive models of materials, strain compatibility, perforce bond of materials and equilibrium of internal forces and moment. Experimental testing of eleven ECC-concrete composite beams reinforced with steel bars is also presented. All beams tested had the same geometrical dimensions but different steel reinforcement strength and ECC thickness. The proposed formulas showed good agreement with the experimental results of various moment values and deflections. A parametric analysis shows that yield and ultimate moments increase with the increase of concrete strength in case of compression failure but, essentially, remain unchanged in case of tensile failure. With increasing the tensile resistance, for example by increasing ECC height replacement ratio, reinforcement ratio, strength of steel reinforcement and ECC, ultimate curvature and energy dissipation increase in case of tensile failure and decrease in case of compressive failure. On the other hand, ductility and energy dissipation ratio decrease with the increase of reinforcement ratio and strength, but, essentially, remain unchanged with increasing the height replacement ratio and strength of ECC. / National Natural Science Foundation of China (51678514, 51308490), the Natural Science Foundation of Jiangsu Province, China (BK20130450), Six Talent Peaks Project of Jiangsu Province (JZ-038, 2016), Graduate Practice Innovation Project of Jiangsu Province (SJCX17-0625) and the Jiangsu Government Scholarship for Overseas Studies.

Yes / Experimental and theoretical investigations on the flexural performance of steel reinforced ECC-concrete composite beams subjected to freeze–thaw cycles are presented in this paper. Four groups of reinforced composite beams with different ECC height replacement ratios subject to 0, 50, 100 and 150 cycles of freeze–thaw were physically tested to failure. Experimental results show that the bending capacity decreases with the increase of freeze–thaw cycles regardless of ECC height replacement ratios. However, the ultimate moment, stiffness and durability of ECC specimens and ECC-concrete composite specimens are greater than those of traditional concrete specimens, owing to the excellent tensile performance of ECC materials. With the increase of ECC height, the crack width and average crack spacing gradually decrease. According to materials’ constitutive models, compatibility and equilibrium conditions, three failure modes with two boundary failure conditions are proposed. Simplified formulas for the moment capacity are also developed. The results predicted by the simplified formulas show good agreement with the experimental moment capacity and failure modes. A parametric analysis is conducted to study the influence of strength and height of ECC, amount of reinforcement, concrete strength and cycles of freeze–thaw on moment capacity and curvature ductility of ECC-concrete composite beams.

Yes / This paper presents test results of fifteen reinforced engineered cementitious composite (ECC)-concrete beams. The main parameters investigated were the amount and type of reinforcement, and ECC thickness. All reinforced ECC-concrete composite beams tested were classified into four groups according to the amount and type of main longitudinal reinforcement used; three groups were reinforced with FRP, steel and hybrid FRP/steel bars, respectively, having similar tensile capacity, whereas the fourth group had a larger amount of only FRP reinforcement. In each group, four height replacement ratios of ECC to concrete were studied. The test results showed that the moment capacity and stiffness of concrete beams are improved and the crack width can be well controlled when a concrete layer in the tension zone is replaced with an ECC layer of the same thickness. However, the improvement level of ECC-concrete composite beams was controlled by the type and amount of reinforcement used. Based on the simplified constitutive relationships of materials and plane section assumption, three failure modes and their discriminate formulas are developed. Furthermore, simplified formulas for moment capacity calculations are proposed, predicting good agreement with experimental results. / National Natural Science Foundation of China (51678514, 51308490), the Natural Science Foundation of Jiangsu Province, China (BK20130450), Six Talent Peaks Project of Jiangsu Province (JZ-038, 2016), Graduate Practice Innovation Project of Jiangsu Province (SJCX17-0625), the Jiangsu Government Scholarship for Overseas Studies and Top-level Talents Support Project of Yangzhou University.

OBJECTIVES: This in vitro study aims to compare and evaluate the mechanical properties of different 3D-printed resin materials. Determine the impact of 3D printer type on the mechanical properties. Investigate the filler percentage by weight for each resin material. MATERIALS AND METHODS: Eight resin materials were tested for flexural strength, flexural modulus, microhardness, fracture toughness, and wear resistance. Resin materials: Rodin Sculpture (RS), BEGO VarseoSmile Crown Plus (BVS), Desktop Health Flexcera Smile Ultra Plus (DHF), SprintRay Crown (SRC), SprintRay Ceramic Crown (SCC), Saremco Crowntec (SC), Myerson Trusana (MT), PacDent Ceramic Nanohybrid (PAC). 3D printer Asiga Max and Ackuretta SOL were used to print 12 specimens from each material to compare three-point flexural strength in bar-shape, biaxial flexural strength in disc-shape, fracture toughness in single edge V-notched beam, wear resistance in pin-shape. Three discs shape specimens from each material were used to compare the Vickers microhardness. The filler percentage by weight of each material is determined by Ash burning and Solvent extraction. The microstructure of a polished disc from each material was examined under a scanning electron microscope (SEM), and the elemental composition was investigated by Energy Dispersive Spectrometry (EDS). Results were analyzed using ANOVA, regression of least square means (α = 0.05), Tukey HSD test, Pearson correlation coefficient, and Student’s t-test. RESULTS: The flexural strength test results, utilizing the three-point method, reveal significant differences among the materials tested. The highest average was recorded in SCC at 160 MPa, while the lowest was found in SRC at 84.4 MPa. The flexural modulus also exhibited significant differences, with the highest average observed in SCC, BVS, RS, SRC, DHF, SC, and MT, measuring 7.8, 6.2, 6.0, 5.8, 4.9, 4.5, and 3.0 GPa, respectively. The resin materials with the highest biaxial flexural strength were DHF 217 MPa and MT 200 MPa, with no significant distinction between them and different from the remaining materials. SCC demonstrated a notably higher average value in Vickers microhardness 44 HVN, while DHF exhibited a significantly lower value of 15.58. The Fracture toughness test presented no significant differences between DHF, MT, and SCC, with values of 2.28, 2.27, and 2.11 MPa.m0.5, respectively, exceeding the remaining materials. In the wear test, DHF and MT had a significantly higher weight loss rate of 29.25 and 27.18 mg/million cycle, respectively. In contrast, MT's height loss rate of 2.02 mm/million cycle was the only significantly higher difference from other materials. The data indicates that the printer type does not significantly affect biaxial flexural strength. At the same time, Asiga exhibited significantly higher values in three-point flexural strength, flexural modulus and hardness tests. In contrast, the SOL printer demonstrated higher values in fracture toughness than Asiga. The ash and solvent extraction methods revealed that SCC had the highest filler percentage by weight, while MT had the lowest. SEM imaging showed the existence of filler particles in all materials, with PAC containing the largest particles and MT containing the smallest. DHF was the only resin material that contained exclusively spherical shape filler particles. EDS analysis disclosed the elemental composition of each material with a higher percentage in Silica, Oxygen, Barium, Titanium, and Ytterbium. CONCLUSION: The results demonstrate significant differences in the tested materials' flexural strength, flexural modulus, biaxial flexural strength, Vickers microhardness, fracture toughness, and wear rates. Even though there are significant differences in some of the mechanical properties of the printer type, it is small and might not have an effect clinically. A strong correlation exists between filler percentage with flexural modulus r = 0.83, biaxial flexural strength r = 0.60, microhardness r = 0.73, and wear resistance r= 0.82. There is a low correlation between filler percentage with fracture toughness r= 0.41, with no correlation with flexural strength in the three-point test. Filler particle percentage highly affects the mechanical properties of 3D printed resin materials. These findings could be valuable in selecting appropriate materials for specific applications.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23885号 / 工博第4972号 / 新制||工||1776(附属図書館) / 京都大学大学院工学研究科マイクロエンジニアリング専攻 / (主査)教授 横川 隆司, 教授 安達 泰治, 教授 井上 康博 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

This study is part of a VDOT sponsored project focusing on repair techniques for impact damaged prestressed bridge girders. The investigation included evaluation of the repair installation and flexural strength of four AASHTO Type III girders that were intentionally damaged and repaired. In addition, nonlinear finite element modeling was used to aid in the development of design protocols for each repair method. This report discusses two of the three repair techniques. Three Master of Science students report on the project results: Justin Liesen, Mark Jones, and Michael Gangi. Liesen and Jones (2015) had responsibility for the installation and testing of the repaired girders and Gangi (2015) performed the finite element modeling of the girders. Three repair methods were identified for experimental investigation: strand splice, bonded FRP, and FRCM. During this investigation the repair methods were evaluated by conducting six flexural tests on four AASHTO Type III girders. Flexural tests were conducted instead of shear tests because typical impact damage from overheight vehicles occurs around the mid-span and flexural strength dominated region of bridge girders. The cracking and failure moments for each test were evaluated and compared to predictions of the girder's behavior using AASHTO calculations, a moment-curvature diagram, and non-linear finite element modeling. / Master of Science

Currently, the design model for flexural rupture of an eccentrically loaded bracket plate is based on the material tensile rupture strength times the net elastic section modulus. Different bolt and plate sizes were tested to determine if this model is correct. It was found that the current model is conservative and that the material tensile rupture strength times the net plastic section modulus is a superior design model. Also, limited finite element modeling was performed to predict the elastic stiffness of such connections. The resulting data correlates well with test results, and confirms that most of the connection ductility comes from bolt plowing. These results can be used for splice plate connections in cantilever construction, as well. / Master of Science

Hot-rolled sheet piling has long-been believed to have a better flexural performance than cold-formed sheet piling based on a test conducted by Hartman Engineering twenty years ago. However, cold-formed steel can have similar strength to the hot-rolled steel This experimental program studied the flexural behavior of hot-rolled and cold-formed steel sheet pilings. This program quantified the influence of transverse stresses from soil pressures on the longitudinal flexural strength. Four cross-sections with two pairs of equivalent sectional modulus were investigated. Sheet-piling specimens were subjected to simulated soil pressure from an air bladder loaded transversely to their longitudinal axis. The span lengths were varied, while the loading area remains unchanged to examine the effect of different transverse stresses. Lateral bracings were provided at discrete locations to establish a sheet piling wall behavior and allow the development of transverse stresses. Load-pressure, load-deflection, load-strain, and moment-deflection responses were plotted to demonstrate the behavior of each specimen. The moment-deflection curves were then normalized to the corresponding yield stress from tensile coupon tests to make a meaningful comparison. The results indicate that transverse stresses influence the flexural capacity of the sheet pilings. The longer span length has less amount of transverse strains, resulting in a higher moment capacity. The hot-rolled sheet pilings have better flexural performance also because of less transverse strains. / Master of Science / Sheet piling wall is an essential structure used during the excavation process. Sheet piling can be hot-rolled and cold-formed. Hot-rolled sheet piling has long-been believed to have a better bending performance based on a test conducted by Hartman Engineering twenty years ago. However, cold-formed steel can have similar strength to hot-rolled steel. This experimental program studied the bending behavior of hot-rolled and cold-formed steel sheet pilings. This program quantified the influence of lateral loading from soil pressure on the moment capacity of the sheet piling. Four cross-sections with two pairs of equivalent bending properties were investigated. Sheet-piling specimens were set up as beam members and subjected to simulated soil pressure from an air bladder. The span lengths of the specimens were varied, while the loading area remains unchanged to examine the effect of different amounts of load. Lateral bracings were provided at discrete locations to establish a sheet piling wall behavior and allow local deflection of the cross-section. Load-pressure, load-deflection, load-strain, and moment-deflection responses were plotted to demonstrate the behavior of each specimen. The moment-deflection curves were then normalized to the corresponding material property of each specimen to make a meaningful comparison between different specimens. The results indicate that lateral loading of the soil pressure influences the bending capacity of the sheet pilings. The longer span length has less amount of transverse strains, resulting in a higher bending capacity. The hot-rolled sheet pilings have better bending performance also because of less transverse strains.