Role of the Crystallographic Phase of NiTi Rotary Instruments in Determining Their Torsional Resistance during Different Bending Conditions

The aim of this study was to assess the role of the crystallographic phase of Nickel-titanium (NiTi) rotary instruments in determining their torsional resistance during different bending conditions, such as different degrees and angles of curvature. 200 F-One 20.04 instruments (Fanta Dental, Shanghai, China) were used, 100 austenitic instruments and 100 martensitic instruments. Each group was divided in 5 subgroups according to the different bending conditions (straight canal, 90° or 60° of curvature degrees and 3 mm or 5 mm of radius of curvature). The static torsional test was performed by using a device composed of an electric motor capable of recording torque values (N·cm); a vice used to secure the instruments at 3 mm from the tip; and artificial canals, which allow instruments to remain flexed during test. Each instrument was rotated at 500 rpm with a torque limit set to 5.5 Ncm until its fracture. Torque at Fracture (TtF) was registered. A scanning electron microscopy (SEM) observation was conducted. The collected data confirm that an increase in the angle of curvature and a decrease in the radius of curvature of the artificial canals lead to an increase of TtF values with a statistically significant difference (p < 0.05), both in the austenitic and martensitic groups. Regarding the comparison between austenitic and martensitic groups in the same bending condition, a statistically significant difference was found only when the torsional test was performed in the canals with the degrees of curvature of 90° and the radius of curvature of 3 mm and 5 mm, with the austenitic instruments showing a higher TtF than the martensitic ones. In conclusion, it can be stated that the crystallographic phase influences the maximum torque at fracture when the instruments are subjected to severe bending and that the radius of curvature significantly influences their torsional resistance.

In Vitro Evaluation of a Recently Developed Rotary File: AF Rotary

Objective: Aim of the present study is to evaluate mechanical properties of a newly developed rotary file, AF Rotary (Fanta Dental, Shanghai, China), and to compare these features with a worldwide spread rotary file, Protaper Gold F2 (PTG F2; Dentsply Maillefer, Ballaigues, Switzerland). Material and Methods: 60 AF Rotary 25.06 and 60 PTG F2 were divided in three groups of 20 files each. A group underwent to cyclic fatigue resistance tests, second group underwent to torsional resistance tests, third group underwent to bending tests. The statistical analysis was performed using t student test with significance level set at 95% (p < 0.05). Results: AF Rotary showed significantly higher torsional resistance and cyclic fatigue resistance (p < 0.05) when compared to the PTG F2. AF Rotary also showed significantly lower bending resistance (p < 0.05) when compared to the PTG F2. Conclusion: Therefore, within the limitations of this study, the results show better performances for AF Rotary compared to PTG F2 regarding the cyclic fatigue test, the torsional test and the bending test. Since the PTG F2 is a commonly used and widely investigated instrument it could be possible to state that the AF Rotary exhibits remarkable in vitro performances. Keywords AF Rotary; Protaper gold; NiTi rotary instruments; Cyclic fatigue; Torsional resistance.

Study of the Stiffness Characteristics of Waist Type Laminated Membrane Coupling Considering Flange Elasticity

Studies show that the systematic study of the stiffness characteristics of the laminated membrane coupling is helpful to analyze the vibration status of the shaft system deeply and accurately. Moreover, such an investigation can provide a reliable guarantee for the safe operation of the power plant. Therefore, establishing an accurate expression for the stiffness and analyzing its characteristics have great significance. In the present study, a finite element model of the waist type laminated membrane coupling is established which considers the influence of the contact between laminations. In order to evaluate the performance of the proposed method, four stiffness characteristics of the coupling are analyzed, including torsional, axial, radial and angular stiffness. The torsional stiffness is verified by the static torsional test. The influence of the flange elasticity and the friction coefficient between the laminations on the stiffness characteristics of the coupling is studied. In the present study, variations of the flange stiffness, the pre-tightening force of the bolt and the friction coefficient between the laminations are studied based on the results obtained from the finite element method. It is expected that the present study can provide a reference for designing and application of the lamination coupling.

Influence of Different Heat Treatments on Torsional and Cyclic Fatigue Resistance of Nickel–Titanium Rotary Files: A Comparative Study

Protaper Universal (PTU), Protaper Gold (PTG) (Maillefer, Ballaigues, CH), EdgeTaper (ET), and EdgeTaper Platinum (ETP) (Albuquerque, NM, USA) were tested for both torsional and flexural resistance. The aim of the present study was to evaluate the influence of proprietary heat treatment on the metallurgical properties of the aforementioned instruments. Four groups of 30 different instruments (size 20.07) were tested, then divided into two subgroups of 15 instruments—one for the cyclic fatigue test in a curved canal (90°—2 mm radius) at 300 rpm and 2.5 Ncm. The time to fracture (TtF) and fragment length (FL) were recorded. The other subgroup was subjected to the torsional test (300 rpm, 5.5 Ncm). The torque to fracture and TtF were recorded. All the instruments underwent a SEM analysis. The heat-treated instruments showed a significantly higher fatigue resistance than the non-heat-treated instruments (p < 0.05). No significant differences were found in the torsional resistance between the ET and PTU, and the ETP and PTG. However, when comparing all the groups, the heat-treated instruments showed less torsional resistance. The improvement from heat treatment was mainly found in the cyclic fatigue resistance.

Study on Compression-Torsion Deformation Behavior and Recrystallization Grain Size of Mg13Gd4Y2Zn0.5Zr Alloy

In this paper, the compression-torsion composite deformation of homogenized Mg-13Gd-4Y-2Zn-0.5Zr alloy with strain rate of 0.001 s-1-0.5 s-1 during the temperature interval of 350 °C-480 °C was studied by the torsional test using the equipment of Gleeble3500 unique to North University of Chain. The effects of temperature and strain rate on the flow behavior of the alloy during compression-torsion deformation were investigated. And the compression-torsion constitutive equation of the high temperature flow stress of the alloy was constructed by introducing the temperature compensation factor Z, providing a theoretical basis for subsequent finite element analysis. The results showed that the flow stress increased with the increase of strain when the flow curves of the alloy were 350 °C and 400 °C. When the deformation temperatures were 450 °C and 480 °C, the flow stress was a typical recrystallization type. The influence of temperature and strain rate on dynamic recrystallization behavior was investigated by OM observation. The results showed that the number and size of recrystallized grains increased with the increase of temperature at the same strain rate, and the number and size of recrystallized grains increased with the decrease of strain rate at the same temperature.

Reliability design of relief groove for torque shaft of shearer

On cutting coal, the cutting resistance of a shearer may change suddenly due to uneven coal quality. It can lead to sudden acceleration of the cutting motor, deceleration, overload shutdown, and even burnout of the motor. We studied the dynamic, static, and working characteristics of the torque shaft of a typical shearer to ensure that the torque shaft of the cutting unit can transfer the torque from the cutting motor to the gear reducer in the rocker under rated conditions and be turned off immediately to protect the motor in case of overload. A method of radial size design of the relief groove of torque shaft based on combining positive, reverse reliability with unloading coefficient has been presented, and the flow chart using this design method has been provided. The positive and reverse reliability torsional test of strength of the experimental torque shafts without relief grooves using three different materials and the measurement test of unloading coefficient of various types of relief grooves were performed. The experimental results obtained through our investigation achieve and even surpass the design purpose. More importantly, to serve the industry it is designed for, the torque shaft designed using this method has high reliability.

Analysis of a Methodology for Torsional Test under Normal Stress and Shear Performance for Asphalt Mixtures

Insufficient shear performance in an asphalt mixture is a primary reason for rutting deformation and pavement surface longitudinal cracking. Thus, it is important to choose a suitable shear test method to evaluate shear performance in an asphalt mixture. Current testing methods mainly evaluate the bonding strength between asphalt layers, and the current shear test method for an asphalt mixture is disadvantaged by high equipment cost and complicated procedures. Our study proposes a torsional test method under normal stress condition, and evaluation was done for four types of asphalt mixture under different temperature conditions. Through the mechanical analysis, the calculation formulas for shear strength and shear parameters (cohesion and internal friction angle) for the torsional test under a normal stress condition were obtained. Testing results were also obtained for shear strength, shear modulus, and cohesion and internal friction angle of the asphalt mixtures. Experimental testing indicated that the method was able to provide repeatable results for the shear resistance of asphalt mixtures at different temperatures and also reflected the difference in shear performance of the various asphalt mixtures and the influence of temperature on shear performance. The failure mode of the specimen was the appearance of an oblique crack of about 45° from the vertical axis after the specimen was destroyed, which accorded with shear failure characteristics. A shear fatigue model was obtained considering different shear stress levels. The torsional test method under normal stress formed a compression-shear action on the specimen by applying torque and normal stress and was used to evaluate the shear performance of the asphalt mixtures.

Comparative Study on Torsional Shear and Triaxial Test of Asphalt Mixtures

In order to verify the reliability and effectiveness of the torsional shear test method, a comparative study of the torsional test under normal stress conditions and triaxial test was carried out with two different asphalt types (unmodified asphalt and SBS-modified asphalt) for asphalt mixtures of AC-13 and AC-20 at three temperatures of 20°C, 40°C, and 60°C. The results showed that the crack spreading routine and the spreading angle were different between the two test methods. The cohesion of the torsional test was slightly larger than that of the triaxial test for different mixtures, asphalts, and temperatures. The main cause of this result is the difference of loading mode. The internal friction angle was basically equivalent in the two methods for different mixtures, asphalts, and temperatures, which indicated that the internal friction angle was mainly related to the spatial distribution of the aggregates or the mutual interlock and had little to do with the test method and external conditions. The results of the ANOVA and regression analysis indicated that the two test methods have a good correlation, and the torsional shear test is a reliable and effective laboratory test method for evaluating the shear performance of asphalt mixtures.