Advancement of Mechanical Properties of Nickel-Titanium Rotary Endodontic Instruments by Spring Machining on the File Shaft

Nickel-titanium (NiTi) endodontic rotary instruments are used extensively in root canal procedures by both general dentists and specialists. However, their vulnerability to fracture is the major reason for clinicians’ concern regarding their use. The objective of this study was to investigate the potential effects of spring machining of the file shaft on the fatigue and torsional resistances of NiTi rotary instruments. Three types of NiTi rotary systems with (S) and without (NS) spring machining were used in this study (n = 15 each): a spring file (SPR; #25/.06, SPR-S, SPR-NS), a ProTaper Next X2 (PTN; #25/variable taper, PTN-S, PTN-NS), and a ProTaper Gold F2 (PTG; #25/variable taper, PTG-S, PTG-NS). Spring machining was adjusted on the 6 mm of each file system’s shaft via a laser cutting process. The number of rotation cycles until fracture (i.e., cyclic fatigue resistance), ultimate torsional strength, the distortion angle, and the toughness of each subgroup were estimated with specially designed devices. The results were analyzed using a paired t-test at a significance level of 95%. NiTi rotary instruments with spring machining exhibited a higher cyclic fatigue resistance than instruments without spring machining. The groups with spring machining exhibited a higher toughness and larger distortion angle than the groups without it (p < 0.05). In conclusion, spring machining on the shank of NiTi instruments may provide a stress-bearing area and attenuate the torsional and cyclic fatigue of NiTi rotary instruments.

KARAKTERISASI PENGARUH KECEPATAN LAS PADA PENGELASAN MIG AA5083H116 DENGAN ELEKTRODA ER5356

Indonesia is a maritime country where 2/3 of its territory is ocean. Therefore, many ships are needed for transportation from one island to the nother within NKRI region. The AA5083H116 materials are widely used in maritime transportation vehicle due to its low density and high weldability. The research propose is to characterize the influence of welding speed of Metal Inert Gas (MIG) of AA5083H116 using ER5356 electrode on the welded joint properties. The AA5083H116 materials of 3 mm x 1200 mm x 2400 mm dimension were cut into welding specimens of 3 mm x 75 mm x 300 mm size. Any pair of specimens was welded using electrode of 0.8 mm diameter. The welding parameters being used are 19 volts of electrical voltage, 120 amperes of electrical current, and 8, 10, 12 mm/s of welding speeds. The characterization were carried out on angle distortion that measured using dial indicator on a milling machine table, X-ray radiography test, as well as physical and mechanical properties tests i.e. microstructure, Vickers micro hardness, tensile and bending strength. The research results show that the smallest distortion angle was found at welding speed of 12 mm/s, all of the welding results satisfy the distortion angle of < 5o, and the radiographic results satisfy the DEPNAKER RI regulation standard. The microstructure exhibits Al2Mg3 precipitation, Vickers hardness distributions, while the highest tensile and bending strength were obtained at welding speed of 10 mm/s.

INFLUENCE OF THE SLOPE FOR THE DISTORTION EFFECT OF PRE-STRESSED SKEWED BOX-SECTION GIRDER BRIDGE

In order to analyze the distortion effects of the skewed PC box-section girder bridge, a simply-supported and three-span continuous skewed PC box-section girder bridge models are built by using the finite element analysis software ANSYS in this paper. First of all, the distortion effects in the longitudinal direction are analyzed for the bridge models and the most disadvantage section are found. Then the longitudinal distortion effects how to vary with the slope is discussed. The results show that the influence of slope is remarkable, with the increase of slope, distortion is becoming more and more large, and it is proportional to the slope degree, the distortion angle of 1/4 span and 3/4 cross section of the bridge is the largest. Therefore, in the process of design, construction and maintenance, the deformation of unfavorable cross section should be paid special attention.

Theoretical Studies of the Local Structures and EPR Parameters for the Rhombic Cu2+ Center in Cu0.5Zr2(PO4)3 Phosphate

The local structure of the rhombic Cu2+ center in Cu0.5Zr2(PO4)3 phosphate is investigated by using the high-order perturbation formulas of electron paramagnetic resonance (EPR) parameters, g-factors gi (i=x, y, z), and hyperfine structure constants Ai for 3d9 ions in rhombically elongated octahedral symmetry. According to the studies, the local axial distortion angle Δα (≈ 5.1°) and the planar bond angle θ (≈ 83.8°) in [CuO6]10- cluster was obtained. The theoretical EPR parameters based on the aforementioned local structure parameters show good agreement with the observed values, and some improvement have been made as compared with the previous studies.

Phase Structure and Piezoelectric Properties of (K0.5Nb0.5)NbO3 - CaZrO3 Ceramics

Lead-free piezoelectric ceramics of (1-x)(K0.5Na0.5)NbO3-xCaZrO3(abbreviated as KNN-CZ,x= 0 ~ 0.04) were synthesized by the conventional solid state method. Their phase structures and piezoelectric properties were investigated with x-ray diffraction (XRD), Scanning Electron Microscope (SEM), d33meter and Impedance Analyzer. KNN-CZ samples exhibit only pure perovskite phases with a small monoclinic distortion. It was observed that the lattice parameter b has a maximum atx= 0.02 but the monoclinic distortion angle β shows a minimum at the same composition. From the dependence of the lattice parameters (a, b, c, β) and cell volume on the content of CZ, it is considered that the intermediate phase transition exists near atx= 0.02. Piezoelectric properties show the maximum value of d33 = 121 pC/N and kp = 0.35 for the sample withx= 0.02, which seems to be due to the co-existence of the two different phases.

CALCULATION OF THE PHOTOLUMINESCENCE SPECTRA FOR Yb3+-DOPED CuInS2 CRYSTAL

Six crystal field energy levels obtained from the photoluminescence spectra of Yb 3+-doped CuInS 2 semiconductor crystal are calculated from the diagonalization (of energy matrix) method. The root-mean-square (r.m.s) deviation σ is 4.5 cm-1 and so the calculated results are in good agreement with the experimental values. The local tetragonal distortion angle θ for the Yb 3+ center in CuInS 2 (which is different from the corresponding angle θh in the host crystal) is obtained from the calculation.

Investigation on Twist of Asymmetric Flanging of Wheel Cowling Tail of Fender and its Influencing Factors

The flanging on both sides of wheel cowling tail of front fender is stretch flanging. An asymmetric flanging model is built according to the asymmetric twist defect in flanging. The strain distribution of the flanging regions, which is analyzed through finite element method (FEM), is in reasonable agreement with related theories. The result shows that the built model is appropriate to investigate the flanging twist defect of the fender. The accuracy of the model is proved by the comparison of the simulation result with the practical production. Also it shows that the severity of the distortion mainly relies on the asymmetry of the fender and some suggestions are proposed on distortion control through the analysis of the factors influencing laws on the distortion angle, which is define to measure the twist, like radius ratio of the two sides of the fender, flanging height, the clearance between the die and punch of the flanging tools, the fillet radius of the flanging die.