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Yichun Zhou - One of the best experts on this subject based on the ideXlab platform.
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fracture characteristics of thermal barrier coatings after tensile and Bending Tests
Surface & Coatings Technology, 2002Co-Authors: Yichun Zhou, Tetsuro Tonomori, A Yoshida, Lihui Liu, G Bignall, Toshiyuki HashidaAbstract:Uniaxial tension and four-point Bending Tests were conducted on two-layer (non-functionally graded material) plasma-sprayed rectangular specimens, boasting a new, functionally graded material (FGM) layer. The top coat layer was composed of stabilized yttria-zirconia (YSZ), and the bond coat layer was NiCrAlY. The FGM was composed of five layers: 100% YSZ; 80% YSZ+20% NiCrAlY; 60% YSZ+40% NiCrAlY; 40% YSZ+60% NiCrAlY; and 20% YSZ+80% NiCrAlY. Fracture in the thermal barrier coating (TBC) system was examined by scanning electron microscopy (SEM), which showed that vertical multiple cracking first occurred in the top coat, followed by propagation of interface cracking between the top and bond coats. Spallation of non-FGM coatings occurred in tensile/Bending experiments, but not for the FGM-coated specimens, with only localized delamination observed along the interface between FGM layers and the substrate. For specimens prepared with a gun–substrate distance of approximately 120 mm and gun operating power of approximately 32.5 kW, the interface fracture toughness, evaluated by a shear lag model for the uniaxial tensile test, was 0.94 and 0.67 MPa m1/2 for type-A and -B coatings, respectively. Here, types A and B correspond to an average roughness of the bond coat surface of 12.8 μm and 6.8 μm, respectively. The interface fracture toughness evaluated by the Suo–Hutchinson model was 1.05–1.27 and 1.0–1.17 MPa m1/2 for type-A and -B coatings, respectively. The results are very close to data obtained by the blister test method. For specimens prepared with a gun–substrate distance of 125–130 mm and gun operating power of approximately 38.5 kW, the interface fracture toughness, evaluated by the Suo–Hutchinson model for four-point Bending, was 4.26–7.21 MPa m1/2.
Marco Tatullo - One of the best experts on this subject based on the ideXlab platform.
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Three-Point Bending Tests of Zirconia Core/Veneer Ceramics for Dental Restorations
International Journal of Dentistry, 2013Co-Authors: Massimo Marrelli, Carmine Maletta, Francesco Inchingolo, Marco Alfano, Marco TatulloAbstract:Introduction. The mechanical strength and the surface hardness of commercially available yttrium-doped zirconia were investigated. Furthermore, a comparative study of eight different ceramic veneers, to be used for the production of two-layered all-ceramic restorative systems, was carried out. Materials and Methods. Four types of zirconia specimens were analyzed, according to a standard ISO procedure (ISO 6872). Besides, two-layered zirconia-veneer specimens were prepared for three-point Bending Tests. Results. A strong effect of the surface roughness on the mechanical strength of zirconia specimens was observed. Finally, a comparative study of eight commercially available veneering ceramics shows different modes of failure between the selected veneers. Conclusion. The results indicate that close attention should be paid to the preparation of zirconia-based crowns and bridges by CAD/CAM process, because surface roughness has an important effect on the mechanical strength of the material. Finally, the results of the mechanical Tests on two-layered specimens represent an important support to the choice of the veneering ceramic.
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three point Bending Tests of zirconia core veneer ceramics for dental restorations
International Journal of Dentistry, 2013Co-Authors: Massimo Marrelli, Carmine Maletta, Francesco Inchingolo, Marco Alfano, Marco TatulloAbstract:Introduction. The mechanical strength and the surface hardness of commercially available yttrium-doped zirconia were investigated. Furthermore, a comparative study of eight different ceramic veneers, to be used for the production of two-layered all-ceramic restorative systems, was carried out. Materials and Methods. Four types of zirconia specimens were analyzed, according to a standard ISO procedure (ISO 6872). Besides, two-layered zirconia-veneer specimens were prepared for three-point Bending Tests. Results. A strong effect of the surface roughness on the mechanical strength of zirconia specimens was observed. Finally, a comparative study of eight commercially available veneering ceramics shows different modes of failure between the selected veneers. Conclusion. The results indicate that close attention should be paid to the preparation of zirconia-based crowns and bridges by CAD/CAM process, because surface roughness has an important effect on the mechanical strength of the material. Finally, the results of the mechanical Tests on two-layered specimens represent an important support to the choice of the veneering ceramic.
Toshiyuki Hashida - One of the best experts on this subject based on the ideXlab platform.
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fracture characteristics of thermal barrier coatings after tensile and Bending Tests
Surface & Coatings Technology, 2002Co-Authors: Yichun Zhou, Tetsuro Tonomori, A Yoshida, Lihui Liu, G Bignall, Toshiyuki HashidaAbstract:Uniaxial tension and four-point Bending Tests were conducted on two-layer (non-functionally graded material) plasma-sprayed rectangular specimens, boasting a new, functionally graded material (FGM) layer. The top coat layer was composed of stabilized yttria-zirconia (YSZ), and the bond coat layer was NiCrAlY. The FGM was composed of five layers: 100% YSZ; 80% YSZ+20% NiCrAlY; 60% YSZ+40% NiCrAlY; 40% YSZ+60% NiCrAlY; and 20% YSZ+80% NiCrAlY. Fracture in the thermal barrier coating (TBC) system was examined by scanning electron microscopy (SEM), which showed that vertical multiple cracking first occurred in the top coat, followed by propagation of interface cracking between the top and bond coats. Spallation of non-FGM coatings occurred in tensile/Bending experiments, but not for the FGM-coated specimens, with only localized delamination observed along the interface between FGM layers and the substrate. For specimens prepared with a gun–substrate distance of approximately 120 mm and gun operating power of approximately 32.5 kW, the interface fracture toughness, evaluated by a shear lag model for the uniaxial tensile test, was 0.94 and 0.67 MPa m1/2 for type-A and -B coatings, respectively. Here, types A and B correspond to an average roughness of the bond coat surface of 12.8 μm and 6.8 μm, respectively. The interface fracture toughness evaluated by the Suo–Hutchinson model was 1.05–1.27 and 1.0–1.17 MPa m1/2 for type-A and -B coatings, respectively. The results are very close to data obtained by the blister test method. For specimens prepared with a gun–substrate distance of 125–130 mm and gun operating power of approximately 38.5 kW, the interface fracture toughness, evaluated by the Suo–Hutchinson model for four-point Bending, was 4.26–7.21 MPa m1/2.
Alfred Scholz - One of the best experts on this subject based on the ideXlab platform.
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the determination of the delamination resistance in thermal barrier coating system by four point Bending Tests
Surface & Coatings Technology, 2006Co-Authors: Y. Yamazaki, Andreas Schmidt, Alfred ScholzAbstract:Abstract The delamination resistance in a plasma-sprayed thermal barrier coating (TBC) system was evaluated by means of a modified four-point Bending test. In this work, in order to study the effect of the interface roughness between the bond coating (BC) and the top coating (TC), two kinds of the powder with the different particle size were used for spraying the BC material. In addition, the influence of the isothermal aging on the delamination resistance was also investigated. The experimental results indicate that the effect of the TC/BC interface roughness wasn't significant. The energy release rate G c , which was estimated by the modified four-point Bending Tests, increased with increasing aging time at 1000 °C, on the other hand, the scatter of it decreased with increasing aging time. The crack mainly propagated in the top coating for as-sprayed condition and at the top-coating/bond-coating interface after thermal aging for 2000 h. The energy release rate G c was correlated with the fracture strength of the weakest parts of the TBC specimen. The energy release rate G c increased with thermal aging until a critical time due to the sintering of the top-coating expired. It can be expected that G c will decrease with the thermal aging after the critical aging time because the top-coating/bond-coating interfacial strength decreases by the TGO growth. The critical aging time in this work is approximately 2000 h.
Ralph Müller - One of the best experts on this subject based on the ideXlab platform.
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tissue modulus calculated from beam theory is biased by bone size and geometry implications for the use of three point Bending Tests to determine bone tissue modulus
Bone, 2008Co-Authors: Harry G Van Lenthe, R Voide, Steven K Boyd, Ralph MüllerAbstract:Current practice to determine bone tissue modulus of murine cortical bone is to estimate it from three-point Bending Tests, using Euler-Bernoulli beam theory. However, murine femora are not perfect beams; hence, results can be inaccurate. Our aim was to assess the accuracy of beam theory, which we tested for two commonly used inbred strains of mice, C57BL/6 (B6) and C3H/He (C3H). We measured the three-dimensional structure of male and female B6 and C3H femora (N=20/group) by means of micro-computed tomography. For each femur five micro-finite element (micro-FE) models were created that simulated three-point Bending Tests with varying distances between the supports. Tissue modulus was calculated from beam theory using micro-FE results. The accuracy of beam theory was assessed by comparing the beam theory-derived moduli with the modulus as used in the micro-FE analyses. An additional set of fresh-frozen femora (10 B6 and 12 C3H) was biomechanically tested and subjected to the same micro-FE analyses. These combined experimental-computational analyses enabled an unbiased assessment of specimen-specific tissue modulus. We found that by using beam theory, tissue modulus was underestimated for all femora. Femoral geometry and size had strong effects on beam theory-derived tissue moduli. Owing to their relatively thin cortex, underestimation was markedly higher for B6 than for C3H. Underestimation was dependent on support width in a strain-specific manner. From our combined experimental-computational approach we calculated tissue moduli of 12.0+/-1.3 GPa and 13.4+/-2.1 GPa for B6 and C3H, respectively. We conclude that tissue moduli in murine femora are strongly underestimated when calculated from beam theory. Using image-based micro-FE analyses we could precisely quantify this underestimation. We showed that previously reported murine inbred strain-specific differences in tissue modulus are largely an effect of geometric differences, not accounted for by beam theory. We suggest a re-evaluation of the tissue properties obtained from three-point Bending Tests, especially in mouse genetics.
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Bone tissue properties as derived from three-point Bending Tests are severely underestimated in a murine model of mouse genetics
2006Co-Authors: Harry Van Lenthe, Romain Voide, Leah Rae Donahue, Ralph MüllerAbstract:INTRODUCTION strain Sex N Cortical thickn. [mm] Wallthickness ratio Aspect ratio Osteoporosis is a disease of decreased bone strength, leading to an increased risk of fracture. Many factors influence bone strength, such as bone volume, geometry, and intrinsic material properties. In mice, up to three-fold differences in bone tissue modulus (E) have been reported [1], and identified as factors influencing bone strength [2]. In these, and other, studies E was derived from three-point Bending Tests using EulerBernoulli beam theory, as:
