LT Specimens Research Articles

Quantitative examination of factors influencing the colour reproduction ability of lithium disilicate glass-ceramics

BackgroundEffects of ceramic translucency, layer thickness, and substrate colour on the shade of lithium disilicate glass-ceramic restorations proved to be significant in several studies, however, quantitative, numerical results on the relationship between the colour difference and these parameters are still lacking. The purpose of this in vitro study was to quantitatively determine how the colour reproduction ability of a lithium disilicate glass-ceramic is affected by its translucency, layer thickness, and substrate colour.MethodsCeramic samples were prepared from A2 shade IPS e.max CAD blocks with high and low translucencies (HT and LT) in a thickness range of 0.5–2.5 mm (+/- 0.05 mm). Layered samples were acquired utilizing composite substrates in 9 shades; transparent try-in paste was used. The spectral reflectance of the specimens was assessed under D65 standard illumination with a Konica Minolta CM-3720d spectrophotometer. The CIEDE2000 colour difference (ΔE00) between two samples was analysed using perceptibility and acceptability thresholds set at 50:50%. Statistical analysis involved linear regression analysis and the Kruskal–Wallis test.ResultsAn increase in the thickness of 0.5 mm reduced the ΔE00 of the HT samples to 72.8%, and that of the T samples to 71.1% (p < 0.0001). 7 substrates with HT and LT specimens had significantly different results from the mean (p < 0.05). A thickness of 0.5 mm is not sufficient to achieve an acceptable result at any level of translucency, while the low translucency ceramic at a thickness of 1.5 mm gave acceptable results, except for severely discoloured substrates (ND8 and ND9).ConclusionsThe colour reproduction ability of lithium disilicate glass-ceramics is significantly affected by their translucency, layer thickness, and 7 substrates out of 9 substrates examined.

In-situ EBSD study of 409 L ferritic stainless steel during tensile testing

Two ferritic stainless steel (FSS) specimens, denoted as loading axis along the rolling direction(LR) and the transverse direction(LT) respectively, were produced to elucidate the mechanical anisotropyof409L FSS at grain scale. This approach was realized by the combination of in situ tensile test and field emission scanning electron microscopy (SEM) with electron backscattering diffraction (EBSD) at room temperature. Microstructure evolution, grain orientation rotation, and crystallographic slip were investigated in the tensile test. During tensile deformation, the tensile axis of LR specimens rotated towards the 〈101〉 direction, which is the stable end orientation of body-centered cubic (BCC) metals. However, the rotation of tensile axis towards 〈101〉 was restrained in LT specimens due to the operation of less favorable slip systems. {110}〈111〉 was the most favorable slip system in both specimens. The mechanical anisotropy in grain scale is due to different slip behaviors of LR and LT specimens.

Evaluation of colour reproduction of CAD/CAM Lithuim-disilicate Evaluation of colour reproduction of CAD/CAM Lithuim-disilicate veneers of different thicknesses and translucency

Background: With the increasing patients’ demand for a perfect smile, the call for highly aesthetic and yet minimally invasive veneers has surmounted. Objective: The aim of this study was to evaluate the colour of CAD/CAM lithium disilicate veneers fabricated in different thicknesses and different translucencies of the lithium disilicate blocks. Materials and Methods: Forty discs of lithium disilicate glass-ceramic (IPS e.max CAD) of shade A1 of both high and low translucency (HT, LT) were tested for their colour reproduction. HT and low LT blocks were cut in the form of plates of dimensions (12 x 14 mm) and of different thicknesses (0.3 mm, 0.5 mm, 0.7 mm, and 0.9 mm). Twenty specimens of each translucency were classified into three sub-groups according to thickness (n=5). Colour reproduction (∆E) was determined using VITA Easyshade Advance against a foundation block and compared with A1 shade tab. Data was collected for statistical analysis. Analysis of Variance (ANOVA), and pair-wise comparison tests were used. Significance level was set to PResults: Two-way ANOVA test showed that the change in both thickness and translucency a well as the interaction between them had a significant effect over (∆E) values. One-way ANOVA and Bonferroni’s tests showed that the low translucency samples showed a statistically significant difference in (∆E) values between all thickness groups except between the 0.3 mm and 0.7 mm as well as between the 0.5 mm and 0.9 mm thickness specimens. High translucency specimens showed a significant difference between all thicknesses. Conclusions: The final colour of laminate veneers could be highly affected by both the thickness and translucency of the ceramic material used. LT specimens produced much better color reproduction with better masking ability than the HT specimens.

Anisotropy of cold-worked Type-304 austenitic stainless steel: Focus on the hydrogen diffusivity

Anisotropic nature of effective hydrogen diffusivity was investigated on a cold-worked (CW) Type-304 stainless steel. The material was characterized by using disk-shaped specimens sampled from two directions of steel plates with various rolling ratio. The thickness direction of the disks was parallel to the rolling direction for SL specimens and perpendicular for LT ones. Electromagnetic induction (EMI) and electron backscatter diffraction (EBSD) clarified the content and distribution of strain-induced martensite (SIM). The effective diffusivities and solubilities were jointly determined by desorption method and thermal desorption analysis (TDA) in H-charged specimens with high-pressure gas. The increase of SIM with CW ratio and the differences of SIM distribution observed between LT and SL specimens could justify the anisotropic effective diffusivities. Finite element method (FEM) was used to simulate permeation tests based on multiple EBSD maps. Simulations supported the experimental findings: at the CW ratio of 60%, the CW process increased the diffusivity by twenty and the diffusivity was five time greater in the SL specimen than the LT one. The inhomogeneous SIM distribution justified the modifications of diffusion properties by CW in both specimens.

Comparisons of bearing properties for various oriented glulam using digital image correlation

The goal of this study was to analyze the bearing properties of the differently oriented glulam using digital image correlation (DIC). Six differently oriented specimens associated with three anatomical directions including longitudinal (L), radial (R), and tangential (T), and 12-mm drift pins were used to analyze the bearing properties, including yield load and bearing strength. The highest bearing strength of 22.57 MPa from RL was found, whereas the lowest bearing strength of 6.47 MPa from LR was found. Different strain distributions were observed from the differently oriented bearing specimens using DIC. Different failure ratios of the differently oriented specimens were highly related to the strain distributions. Although the bearing properties were found to be different between the differently oriented specimens, for the connection design aspect, the bearing properties of glulam could be grouped as RL and TL specimens, RT and TR specimens, and LR and LT specimens.

지르코니아 블록 종류에 따른 전부도재관의 기계적 특성 비교

Purpose: This study provided the basic data for selecting the zirconia blocks by comparing the mechanical properties of the all ceramic crown between the domestic, import, translucent and shade blocks that were used in clinically. Methods: Currently, the most commercial block of five types(one import and two domestic block which is the translucent and shade) were used. It were elucidated by means of three point bending test, hardness test, FE-SEM observations and EDX analysis. The results were analyzed using a one-way ANOVA and Scheffe post hoc test for significant findings. Results: For flexural strength, LT specimen was the highest as 733.1 MPa, followed by JT specimen(712.0 MPa), ZT specimen(646.0 MPa), LS specimen(553.1 MPa), JS specimen(429.0 MPa). One-way ANOVA showed statistically significant difference between groups for flexural strength(p<0.05). For hardness, ZT specimen was the highest as 1556.5 Hv, followed by JT specimen(1540.3 Hv), LT specimen(1512.3 Hv), JS specimen(1472.0 Hv), LS specimen(1353.3 Hv). One-way ANOVA showed statistically significant difference between groups for hardness(p<0.05). Conclusion: Domestic block was higher than import block for flexural strength, and translucent block was higher than shade block for flexural strength. However, all blocks showed clinically acceptable range. There was no significant difference in hardness between domestic and import blocks. And significant difference was observed in translucent and shade blocks.

Anisotropy in Mechanical Properties and Fracture Behavior of an Oxide Dispersion Fe20Cr5Al Alloy

Anisotropy of fracture toughness and fracture behavior of Fe20Cr5Al oxide dispersion-strengthened alloy has been investigated by means of compression tests, hardness tests, and wedge splitting test. The results show a small effect of the compression direction on yield strength (YS) and strain hardening. The YS is minimum for longitudinal direction and maximum for the tangential direction. The transverse plastic strain ratio is similar for tangential and longitudinal directions but very different from that in normal direction. Hardness depends on the indentation plane; it is lower for any plane parallel to the L-T plane and of similar magnitude for the other orthogonal planes, i.e., the L-S and T-S planes. Macroscopically, two failure modes have been observed after wedge-splitting tests, those of LS and TS specimens in which fracture deviates along one or two branches normal to the notch plane, and those of LT, TL, SL, and ST specimens in which fracture propagates along the notch plane. Besides LT and TL specimens present delaminations parallel to L-T plane. Both, the fracture surface of branching cracks and that of the delaminations, show an intergranular brittle fracture appearance. It is proposed that the main cause of the delamination and crack branching is the alignment in the mesoscopic scale of the ultrafine grains structure which is enhanced by the 〈110〉-texture of the material and by the presence in the grain boundaries of both yttria dispersoids and impurity contaminations. An elastoplastic finite element analysis was performed to study what stress state is the cause of the branches and delaminations. It is concluded that the normal to the crack branches and/or the shear stress components could determine the crack bifurcation mechanism, whereas the delamination it seems that it is controlled by the magnitude of the stress component normal to the delamination plane.

마찰교반용접된 7075-T651 알루미늄 합금 용접부의 피로균열전파율의 공간적 변동성에 미치는 균열 방향의 영향

Abstract: In this investigation, the effect of crack orientation on spatial randomness of fatigue crack growth rate (FCGR) in friction stir welded (FSWed) 7075-T651 aluminum alloy joints has been statistically analyzed by Weibull distribution. The fatigue crack growth tests are conducted under three different constant stress intensity factor range (SIFR) control at room temperature with R = 0.1 and frequency 10Hz on compact tension (CT) specimen machined at base metal (BM) and weld metal (WM). The experimental fatigue crack growth rate data were obtained for two types of specimens having LT and TL orientations. LT specimens both base metal and weld metal showed higher fatigue crack growth rate as compared to TL specimens. In the lower SIFR region, FCGR were found to be almost 3 times higher in higher SIFR region. The shape parameter of Weibull both LT and TL orientation for FCGR was increased with increasing SIFR, the scale parameter was also increased with increasing SIFR. The smallest value of the shape parameter was shown in weld metal specimens having LT orientation at lower SIFR region.

Notch Impact Behavior of Oxide-Dispersion-Strengthened (ODS) Fe20Cr5Al Alloy

In this article, tensile tests as well as LS and LT notched Charpy impact tests were performed at the temperature range between 77 K (−196 °C) and 473 K (200 °C) on an oxide-dispersion-strengthened (ODS) Fe20Cr6Al0.5Y2O3 hot-rolled tube. The absorbed energy values in the range of high temperatures of LS notched specimens are considerably higher than those of LT notched specimens; however, such values tend to converge as temperature increases. Ductile fracture on the normal planes to RD with delaminations parallel to the tube surface was observed in the temperature range between room temperature (RT) and 473 K (200 °C). Delaminations of crack divider type were observed in LT specimens, whereas delaminations of crack arrester type were observed in LS specimens. The yttria particles in the grain boundaries and the transverse plastic anisotropy are the possible reasons why the delaminations were parallel to the tube surface.

일정 응력확대계수범위 제어 시험하의 마찰교반용접된 7075-T651 알루미늄 합금 용접부의 피로균열전파 거동의 실험적 고찰 (LT 방향의 시험편에 대하여)

본 연구에서는 마찰교반용접재의 피로균열전파 거동의 공간적 불규칙성을 고찰하기 위한 연구의 일환으로써, 최적의 조건에서 마찰교반용접된 7075-T651 알루미늄 합금 용접부의 LT-방향의 각각 5개의 피로균열전파 시험편에 대하여 일정 응력확대계수범위 제어하의 피로균열전파 실험을 수행하여 마찰교반용접부의 교반용접부재(WM)와 열영향부재(HAZ) 그리고 모재(BM)에 대한 피로균열전파 거동을 실험적으로 고찰하였다. WM재의 피로균열전파율이 가장 빠르게 나타났으며, 그 다음 HAZ재와 WM재 순으로 나타났다. 게다가 시험편간 피로균열전파율의 변동성은 WM시험편에서 가장 높았고, 반면 BM재에서 가장 낮게 나타났다.

Effect of annual rings on transmission of 100 GHz millimeter waves through wood

For the application of millimeter wave (MMW) technique to nondestructive evaluation of wood, the effect of annual rings on the behavior of a 100 GHz MMW transmitted through wood was examined. The complex amplitude was measured for 2 mm thick flat- (LT) and quarter-sawn (LR) specimens of several species with different annual ring structures at 11 % moisture content, of which the density distribution was measured using X-ray radiography. For the LT specimens of all species and the LR specimens with small density fluctuation or with earlywood width smaller than the wavelength of the MMW (=3 mm), the amplitude and phase of the transmitted wave were similar to those of the wave without a specimen. For the LR specimen with large density fluctuation and with earlywood width close to or larger than the wavelength, the amplitude and phase were different from those of the wave without a specimen. All the measured complex amplitudes were well expressed using a diffraction model. It was concluded that the MMW is deformed by the density distribution, and then its components with periods shorter than the wavelength by diffraction are attenuated.

S0305-2-2 SPC270材のスポット溶接における疲労寿命解析([S0305-2]継手・切欠き)

The "FLARP" numerical fatigue crack initiation and propagation simulation code has been applied to the fatigue test of spot-welded SPC270 steel TS and LT specimen. To obtain accurate stress range and residual stress along the assumed crack path, finite element analyses are employed, in which the variation of the yield stress for base, HAZ, and nugget material is considered in detail. The finite element models are also contributed to obtain the relation between crack depth and stress intensity factor of a surface crack propagating along the spot nugget and one that appears on the back surface. The simulation results with well-identified input parameters using measurement value are compatible with the real fatigue test result, which shows that the simulation code is valid for predicting S-N curve of the given specimens.

Wood Fracture Pattern during the Water Adsorption Process

Summary A research program was conducted to investigate the effect of water transition on wood fracture properties, focusing on fracture behavior and patterns with different crack orientations of Betula platyphylla Suk. and Pinus bungeana in three different moisture adsorption processes. At a constant temperature of 20°C, three levels of relative humidity were considered: 66%, 82% and 100%. The results indicated that moisture content did not influence the crack propagation path, while specimen crack orientation did. With longer moisture adsorption times, the time needed to reach the maximum load from the critical load also grew; this is because below the fiber saturation point, from excessive dryness to a certain moisture content, the cell wall becomes less brittle and the toughness is enhanced. At 20°C constant temperature, the fracture toughness gradually increased from oven-dry state adsorbing moisture to 82% relative humidity, but decreased from 82% to 100% relative humidity. Within a tree species, fracture toughness depended on specimen type. The fracture toughness of LT specimens was by far higher than that of TL and TR specimens. The LT specimen fracture toughness of Betula platyphylla Suk. was comparable to that of Pinus bungeana.

Phase Transition in Cs2KMnF6: Crystal Structures of Low- and High-Temperature Modifications

Crystalline Cs2KMnF6, when prepared below 500°C, adopts a tetragonal elpasolite structure type. Differential scanning calorimetric investigations indicated that Cs2KMnF6 undergoes a phase transition from the low-temperature tetragonal phase (LT) to a high-temperature phase (HT) at about 530°C. Single crystals of the new HT phase could be obtained by annealing a crystalline LT specimen at 600°C followed by rapid quenching to room temperature. In the present study the structures of both phases have been studied by single-crystal X-ray diffraction techniques. The LT phase has the tetragonal space group symmetry I4/mmm, with unit-cell parameters a=6.319(1) (a·2=8.936) and c=9.257(2) Å, and Z=2. The HT phase has the cubic symmetry Fm3m, with the cell parameter a=9.067 Å and Z=4. Structural models of the LT and HT phases have been refined vs collected single-crystal X-ray reflection data to R values of 0.034 and 0.022, respectively. The uneven Mn–F bond distance distribution in the LT form, four bonds of 1.860(6) two of 2.034(9) Å, are typical for an octahedrally coordinated high-spin Mn3+ ion affected by Jahn–Teller effects. Due to symmetry constraints, all six octahedral Mn–F bonds in the HT form are equal to 1.931(5) Å. However, the mean square atomic displacement parameters of the fluorine atoms increases significantly from about 0.022 Å2 for the LT phase to 0.042 Å2 for the HT phase. The increased displacement parameters indicate that the phase transition from the LT to the HT form is associated with a directional disorder of the Jahn–Teller distortions around the Mn3+ ions.

真空中および空気中におけるチタニウム材の疲労変形挙動異方性

To study the fatigue behavior of the cold-rolled titanium plate (KS40) with the texture of the major orientation of (0001) [1010]±30°, the plane bending fatigue tests have been carried out on the specimens (0.3mm thick) cut out parallel (LT) and perpendicular (TL) to the rolling direction, respectively. The tests were conducted in vacuum (1.33×10-3Pa) and in air at the resonant frequency of about 600Hz for the second-order mode of oscillation. Comparison of the TL with the LT specimens showed that in air the anisotropy was discernible in S-N curves and fatigue crack growth behavior, but hardly in vacuum. In air, the TL specimen had fatigue strength and fatigue crack growth properties greater than the LT specimen and the fracture surfaces appeared more brittle in the TL specimen. It seemed that the character of fatigue behavior in air could be connected with the crystallographic conditions for deformation: the ease of slipping or twinning shear. In vacuum, the specimens raised temperature in themselves up to 45K above room temperature, when cyclically stressed at σ=±201MPa, and fractured in ductile modes. Common microstructure around fatigue cracks was characterized by cell structure both in vacuum and in air, although numerous twins were contained in the specimen prior to fatigue tests. The cells were developed more in vacuum than in air. The results obtained were discussed in connection with the plastic deformability enhanced by internal heating during fatigue testing from the crystallographic points of view.

高力アルミニウム合金の食塩水中腐食疲労き裂進展挙動に及ぼす電位と異方性の影響

Fatigue crack growth tests were made in air and in 3.5% saltwater on 7075-T6 aluminum alloy specimens extructed in LT and TL directions. The testing in saltwater was made under the application of anodic and cathodic potentials. The test results showed that the crack growth rate in saltwater was higher than that in air under all the conditions tested, regardless of the applied potential and the specimen orientation. Although an appreciable effect of the applied potential was observed in the lower ΔKI range of the da/dN-ΔKI relation for LT specimen, almost no effect of potential was observed in both the da/dN-ΔKI relation for TL specimen and the da/dN-ΔKIeff relations for LT and TL specimens. Intergranular fracture and secondary cracking of intergranular type were observed quite often in the LT and TL specimens fatigued under free corrosion.

５０８３アルミニウム合金板の引裂き強さに及ぼす温度の影響

Tear fracture strength of 5083 aluminum alloy plate was studied experimentally for the test temperatures ranging from 4K to 473K. The total absorbed energy during the tear fracture shows N-letter type changes with respect to the test temperatures indicating the presence of three distinct temperature regions. In the higher and lower temperature regions, the temperature dependences of the total absorbed energy are negative, while they are positive in the medium temperature region. The temperature dependence of the absorbed energy for the crack propagation is substantially the same as that of the total absorbed energy. The total absorbed energy of the specimen L in which the crack propagation direction was vertical to the rolling direction, is higher by about 10 to 20% than that of LT specimen in which the crack propagation direction was parallel to the rolling direction. The tear fracture strength increases linearly with 0.2% proof stress measured by tensile test. No clear linearlity is observed, however, between the ultimate tensile strength and tear fracture strength. A laminated fracture in the tear fractured surface is observed only at 4K.