Ultimate Torsional Strength Research Articles

Effect of alloy type on the life‐time of torsion‐preloaded nickel‐titanium endodontic instruments

This study was aimed to evaluate the effect of torsional preloads on the cyclic fatigue life of nickel-titanium (NiTi) instruments with different history of heat treatments by manufacturers. WaveOne (Primary) made of M-wire, K3XF (#30/0.06) of R-phase, and ProTaper (F2) of conventional NiTi alloy was used. Each file was preloaded at four conditions (nil, 25, 50, and 75% of their mean ultimate torsional strength) before fatigue testing. The torsional preloads 10-, 30-, or 50-times were applied by securing 5 mm of the file tip, rotating it until the preset torque was attained before returning to the origin. Then, the number of cycles to failure (NCF) was evaluated by rotational bending in a simulated canal. Data were analyzed using multiple linear regression analysis and two-way ANOVA. Fractured instruments were examined under scanning electron microscope (SEM). SEM showed that most WaveOne after 75% preloading, regardless of repetitions, showed some longitudinal cracks parallel to the long axis of the file, which were rare for K3XF. Regression analysis revealed that the brand of instrument was the most critical factor. At up to 75% preloading, ProTaper and K3XF did not show any significant decline in NCF. For 30-repetition groups of WaveOne, the 50 and 25% torsion preloaded groups showed a significantly higher NCF than the 0 and 75% groups. Within the limitations of this study, the alloy type of NiTi instrument have a significant effect on the phenomenon that a certain amount of torsional preload may improve the cyclic fatigue resistance of NiTi rotary instruments.

Effect from surface treatment of nickel-titanium rotary files on the fracture resistance.

This study was aimed to compare the cyclic fatigue resistance and torsional resistance of rotary instruments with and without surface treatment. G6 A2 (Group A2) with and G6 A2 without surface treatment after machining (Group AN) were compared in this study. ProTaper F2 (Group F2) which has similar dimension and shape was also used for comparison. To evaluate the torsional resistance, ultimate torsional strength and distortion angle until fracture were recorded, and the toughness was calculated. The cyclic fatigue resistance was compared by evaluating the number of cycles to failure in a simulated canal. Statistical analysis was performed by one-way analysis of variance and Tukey post hoc test (p = 0.05). After torsional and cyclic fatigue tests, all fracture fragments were observed under a scanning electron microscope. Group A2 showed higher cyclic fatigue resistance than the groups AN and F2 (p < 0.05). Although group A2 demonstrated lower ultimate torsional strength than the others, there were no significant differences in toughness among the groups. While obvious machining grooves were seen in groups AN and F2, group A2 showed smooth surface resulting from the surface treatment. The specimens of fracture fragments showed typical features of cyclic failure such as micro-cracks, overloaded fast fracture zone, and torsional fracture such as unwinding helix, circular abrasion marks and dimples. Under the conditions of this study, the surface treated instruments may improve cyclic fatigue resistance while maintaining the torsional resistances and mechanical properties.

Influence of cyclic torsional preloading on cyclic fatigue resistance of nickel – titanium instruments

To evaluate the effect of different torsional preloads on cyclic fatigue resistance of endodontic rotary instruments constructed from conventional nickel-titanium (NiTi), M-Wire or CM-Wire. Eighty new size 25, 0.06 taper Mtwo instruments (Sweden & Martina), size 25, 0.06 taper HyFlex CM (Coltene/Whaledent, Inc) and X2 ProTaper Next (Dentsply Maillefer) were used. The Torque and distortion angles at failure of new instruments (n = 10) were measured, and 0% (n = 10), 25%, 50% and 75% (n = 20) of the mean ultimate torsional strength as preloading condition were applied according to ISO 3630-1 for each brand. The twenty files tested for every extent of preload were subjected to 20 or 40 torsional cycles (n = 10). After torsional preloading, the number of cycles to failure was evaluated in a simulated canal with 60° angle of curvature and 5 mm of radius of curvature. Data were analysed using two-way analysis of variance. The fracture surface of each fragment was examined with a scanning electron microscope (SEM). Data were analysed by two-way analyses of variance. Preload repetitions did not influence the cyclic fatigue of the three brands; however, the 25%, 50% and 75% torsional preloading significantly reduced the fatigue resistance of all instruments tested (P < 0.01, P < 0.001 and P < 0.0001, respectively) except for the HyFlex CM preloaded with 25% of the maximum torsional strength (P > 0.05). Torsional preloads reduced the cyclic fatigue resistance of conventional and treated (M-wire and CM-wire) NiTi rotary instruments except for size 25, 0.06 taper HyFlex CM instruments with a 25% of torsional preloading.

Analytical Model for Torsional Response of RC Beams Strengthened With Ferrocement U-Wraps

Wrapping technology is one of the most effective ways of strengthening concrete elements. Several research articles have confirmed the effectiveness of fibre-reinforced polymers (FRP) as wrapping material for enhancing the strength of reinforced concrete (RC) elements. Wrapping three sides of RC members is a convenient method of strengthening the beams that support the slabs. Its cost effectiveness over FRP makes ferrocement a good substitute as a wrapping material for strengthening RC beams. Limited research is reported regarding the torsional strength of ferrocement U-wrapped RC beams subjected to pure torsional loads. In this paper, an analytical model to predict the torsional response of RC beams with ferrocement U-wraps is presented. This analytical model is based on Hsu’s softened membrane model. The analytical model is validated by conducting experimental tests. In this investigation, 12 RC beams wrapped with ferrocement on three sides are tested under pure torsional loading. The different categories of beams tested in this investigation are under-reinforced beams, partially over-reinforced beams (longitudinal and transverse) and completely over-reinforced beams. The variations of U wraps considered in this investigation are three, four and five layers of mesh reinforcement in the ferrocement. The test results indicate that the cracking torque does not depend on the number of mesh layers present in the ferrocement wrapping. Ferrocement wrapping is more effective in the post-cracking stage than in the pre-cracking stage. The increase in the number of mesh layers in the ferrocement increases the ultimate torsional strength of the wrapped beam irrespective of the categories mentioned. The proposed analytical model is capable of predicting the torsional response with reasonable accuracy.

Safety of the Factory Preset Rotation Angle of Reciprocating Instruments

IntroductionThis study aimed to investigate the torsional resistance of 2 reciprocating nickel-titanium instruments (Reciproc [VDW, Munich, Germany] and WaveOne [Dentsply Maillefer, Ballaigues, Switzerland]) operated at the maximum rotating angle in a proprietary motor. MethodsWith the file tip secured at various levels (3, 4, or 5 mm) of Reciproc R25 and WaveOne Primary, the distortion angles and torsional loads were monitored during counterclockwise movement at 2 rpm until fracture (n = 10 at each level) for a load-distortion graph. The rotation angles and loads at the beginning point of the plateau, the ultimate torsional strength, final fracture angle, and toughness were determined. The data were analyzed using 1-way analysis of variance and the Tukey post hoc test at α = .05. The lateral longitudinal aspect and the fracture cross-section of each specimen were examined by scanning electron microscopy after the test. ResultsThe rotation angle at the beginning point of the plateau was significantly greater for a binding site farther away from the tip of the instrument for both systems (P < .05), and all were greater than 170° (preset in the dedicated motor from manufacturer). The ultimate strength and toughness also increased significantly at levels farther away from the instrument tip (P < .05). All specimens showed typical topographic features of torsional fracture, including the circular abrasion marks and fibrous dimples near the rotation center after the test. ConclusionsIt was determined that the 2 brands of reciprocating files are safe when operated at the rotational angle in the proprietary motor.

Simplified Model for the Torsional Strength of Concrete Beams with GFRP Stirrups

An international committee on shear and torsion reported that giving physical significance for the torsion design is an upcoming challenge. The purpose of this paper is to propose a reasonably accurate and relatively simple model capable of predicting the torsional strength of concrete beams reinforced with glass fiber–reinforced polymer (GFRP) stirrups. In this paper, a database for concrete beams reinforced with GFRP stirrups, tested under torsion, is compiled. The implementation of the torsion design provisions of the conventional steel-reinforced-concrete design codes is discussed. A few selected strength models were used to predict the ultimate torsional strength of the tested beams. The predicted strength was compared with that measured during testing. The comparison showed that more improvement is required in calculating the inclination of the diagonal concrete strut and the effective strain in the GFRP stirrups. Two strength models were modified and proposed. The proposed models showed better compliance and consistency with the experimental results compared to the available models and design codes. In addition, the proposed models are noniterative and simple to implement. However, further experimental testing will help refine the proposed models.

강섬유 보강 초고성능 콘크리트 보의 비틀림 거동 특성

Experimental investigation on the structural behavior of steel fiber-reinforced ultra high performance concrete (UHPC) beams subjected to torsion are presented. Six tests carried out on square beams under torsional moment are presented. The experimental parameters were the volume fraction of the fibers and closed-stirrup ratio. The volume fraction of the fibers was 1.0% and 2.0%. The closed-stirrup ratio was 0, 0.35%, and 0.70%. The test results indicated that ultimate torsional strength increased with increasing fiber volume, and that ultimate torsional strength also increased with increasing the closed-stirrup ratio. In addition, predictive equations for evaluating the ultimate torsional strength of UHPC beams were proposed. The comparison between computed values and the experimentally observed values was shown to validate the proposed analytical equations. It was found that predictions by using proposed equation provides good agreement with test results of UHPC beams.

Buckling resistance, bending stiffness, and torsional resistance of various instruments for canal exploration and glide path preparation.

ObjectivesThis study compared the mechanical properties of various instruments for canal exploration and glide-path preparations.Materials and MethodsThe buckling resistance, bending stiffness, ultimate torsional strength, and fracture angle under torsional load were compared for C+ file (CP, Dentsply Maillefer), M access K-file (MA, Dentsply Maillefer), Mani K-file (MN, Mani), and NiTiFlex K-file (NT, Dentsply Maillefer). The files of ISO size #15 and a shaft length of 25 mm were selected. For measuring buckling resistance (n = 10), the files were loaded in the axial direction of the shaft, and the maximum load was measured during the files' deflection. The files (n = 10) were fixed at 3-mm from the tip and then bent 45° with respect to their long axis, while the bending force was recorded by a load cell. For measuring the torsional properties, the files (n = 10) were also fixed at 3-mm, and clockwise rotations (2-rpm) were applied to the files in a straight state. The torsional load and the distortion angle were recorded until the files succumbed to the torque.ResultsThe CP was shown to require the highest load to buckle and bend the files, and the NT showed the least. While MA and MN showed similar buckling resistances, MN showed higher bending stiffness than MA. The NT had the lowest bending stiffness and ultimate torsional strength (p < 0.05).ConclusionsThe tested instruments showed different mechanical properties depending on the evaluated parameters. CP and NT files were revealed to be the stiffest and the most flexible instruments, respectively.

Exploring GFRP bars as reinforcement for rectangular and L-shaped beams subjected to significant torsion: An experimental study

Steel corrosion related problems have been a heavy burden on countries economically and socially for many decades. Therefore, the inevitable quest to find an alternative for steel reinforcements is long overdue. On the other hand, fiber reinforced polymer (FRP) bars have non-corrosive nature and could be the solution for this problem. In this study, the objective is exploring the usage of glass fiber polymer (GFRP) bars as torsion reinforcement for L-shaped beams. New adhesively bonded GFRP stirrups are presented and implemented. Five beams were constructed and tested under significant torsion. The bonded GFRP stirrups were more effective as transversal reinforcement compared with the bent steel stirrups and the bent GFRP stirrups. It improved the ultimate torsional strength and increased the corresponding unit angle of twist and the maximum stirrup strain as well as the major concrete crack width. In addition, the increase in the GFRP transversal reinforcement percentage improved the ultimate torsional strength, the toughness, and the deformability. Moreover, the usage of a stirrup strain value of 0.4% resulted in overly conservative predictions for the ultimate torsional resistance; however, it provided adequate torsional deformability index and toughness.

Effect of Torsional Loading of Nickel-Titanium Instruments on Cyclic Fatigue Resistance

IntroductionThe aim of this study was to evaluate the effect of torsional preload on the cyclic fatigue life of nickel-titanium rotary instruments. MethodsProFile (#25/0.06) (Dentsply Maillefer, Ballaigues, Switzerland) and ProTaper (F1; Dentsply Maillefer) were used. Each file was preloaded at 4 conditions (ie, no preloading and 25%, 50%, and 75% of mean ultimate torsional strength) of torsional prestress before the fatigue test. The torsional preloads were applied by securing 5 mm of the file tip while keeping the file straight, rotating it clockwise until the preset torque, and then returning to the original position. This motion was repeated until a preset number (10, 30, or 50) of repetitions were reached (n = 12). After torsional preloading, the number of cycles to failure was evaluated in a simulated canal. Data were analyzed using 2-way analysis of variance and the Duncan post hoc comparison. The fractured fragment surfaces were examined under a scanning electron microscope for the topographic features of fractured instruments. ResultsFor both instruments, there was a significant effect because of the extent of torsional preloads. The 50% and 75% torsionally preloaded ProFile and all ProTaper preloading groups had a higher number of cycles to failure than the other group(s). There was little difference in the lateral view appearance between new and torsionally preloaded files. After cyclic fatigue testing, all preloaded instruments showed numerous microcracks adjacent to the fracture site on lateral view examination. The microcracks did not seem to follow the machining grooves on the instrument surface but rather ran irregularly. ConclusionsThe torsional preloads within the superelastic limit of the material may improve the cyclic fatigue resistance of nickel-titanium rotary instruments.

Torsional behavior of ultra-high performance concrete squared beams

This paper presents experimental results on the torsional behavior of ultra-high performance concrete (UHPC) beams. Thirteen beam specimens with 300×300-mm cross section were cast from UHPC with the compressive strengths greater than 150MPa. The experimental parameters were the specimens’ volume fraction of steel fibers, transverse reinforcement ratio, and longitudinal reinforcement ratio. The test results indicated that the beams’ initial cracking and ultimate torsional strength increased as the volume fraction of steel fibers increased. The ultimate torsional strength and torsional stiffness after initial cracking increased as the stirrup ratios increased, and ultimate torsional strength increased as the longitudinal rebar ratios increased. The effect of the quantity of transverse and longitudinal reinforcement on the angle of the diagonal compressive stresses was investigated. The results of this study provided valuable data that could be used in future studies to develop computational models of the torsional behavior of UHPC beams and predict their ultimate strength.

Experimental study on ultimate torsional strength of PC composite box-girder with corrugated steel webs under pure torsion

To have a better understanding of the torsional mechanism and influencing factors of PC composite box-girder with corrugated steel webs, ultimate torsional strength of four specimens under pure torsion were analyzed with Model Test Method. Monotonic pure torsion acts on specimens by eccentric concentrated loading. The experimental results show that cracks form at an angle of <TEX>$45^{\circ}$</TEX> to the member's longitudinal axis in the top and bottom concrete slabs. Longitudinal reinforcement located in the center of cross section contributes little to torsional capacity of the specimens. Torsional rigidity is proportional to shape parameter <TEX>${\eta}$</TEX> of corrugation and there is an increase in yielding torque and ultimate torque of specimens as the thickness of corrugated steel webs increases.

Evaluation of Ultimate Torsional Strength of Reinforcement Concrete Beams Using Finite Element Analysis and Artificial Neural Network

Due to lack of theory of elasticity, estimation of ultimate torsional strength of reinforcement concrete beams is a difficult task. Therefore, the finite element methods could be applied for determination of strength of concrete beams. Furthermore, for complicated, highly nonlinear and ambiguous status, artificial neural networks are appropriate tools for prediction of behavior of such states. The main purpose of this paper is evaluation of ultimate torsional strength of rectangular concrete beams using two different approaches: nonlinear finite element modeling and artificial neural network prediction. This aim is achieved by creating a three-dimensional finite element models that employing the brittle failure criterion of concrete and an artificial neural network which training is carried out through experimental data. Numerical modeling is accomplished using the commercial software and its validation is exhibited by selected data from experimental tests. The test specimens were solid rectangular beams that were subjected to pure torsion. All of the experimental data for training of the network has been comprised. Data are divided into three categories: training, testing and validating. Three-layer perceptron network with a back propagation error algorithm is used for training. This study shows that, the results of numerical models are more accurate than neural network models to predict torsional strength of reinforced concrete beams.

Torsional Strength of Ferrocement “U” Wrapped Normal Strength Beams with only Transverse Reinforcement

Structural repair and rehabilitation of concrete structures is necessary for all deteriorated or damaged structures to restore and enhance the load bearing capacity as well as to increase the life span of the structure In the recent past 3Rs of construction Technology (Retrofitting, repair and Rehabilitation) became popular due to the natural calamities or the updates of the codal provisions. Use of FRPs have been gaining world wide acceptance as retrofitting material for their high strength, light weight and good fatigue life. However, from cost benefit point of view ferrocement can be used as wrapping for rehabilitation of deteriorated or damaged reinforced concrete beams. Ferrocement, a thin structural composite material, exhibits better crack arresting capacity, higher tensile strength to weight ratio, ductility and impact resistance. Hence it can be used as an alternative for FRPs in the field of repair and rehabilitation. Very little information is available from literature on the repair and rehabilitation of reinforced concrete beams with ferrocement wrapping especially in resisting pure torsional loads. Repair and rehabilitation of the distressed concrete structures is well addressed by researchers for the basic structural actions such as axial loads, flexure and shear in past few years, but torsional repair and rehabilitation has not attained much importance in research due to its complex nature and its occurrence with other basic structural forces. Circulatory torsion induces shear stresses on all four sides and would be well resisted by closed form reinforcement. But due to monolithic construction of beam and slabs, U wrap retrofitting is the most practical solution. Experimental results and analytical models of previous researchers revealed that wrapping on three sides of the beam also enhance the ultimate torsional strength. An experimental investigation is conducted to address the torsional capacity and twist of reinforced concrete beams with reinforcement only on transverse direction and strengthened with ferrocement “U” wraps (leaving the top side free from wrapping) as this situation is more common in the rehabilitation of concrete structures. The results revealed that single type of reinforcement (only on transverse direction) is not an effective way of enhancing the torsional strength while increase in toughness is found to be marginal

A New Model to Study Healing of a Complex Femur Fracture with Concurrent Soft Tissue Injury in Sheep

High energy bone fractures resulting from impact trauma are often accompanied by subcutaneous soft tissue injuries, even if the skin remains intact. There is evidence that such closed soft tissue injuries affect the healing of bone fractures, and vice versa. Despite this knowledge, most impact trauma studies in animals have focussed on bone fractures or soft tissue trauma in isolation. However, given the simultaneous impact on both tissues a better understanding of the interaction between these two injuries is necessary to optimise clinical treatment. The aim of this study was therefore to develop a new experimental model and characterise, for the first time, the healing of a complex fracture with concurrent closed soft tissue trauma in sheep. A pendulum impact device was designed to deliver a defined and standardised impact to the distal thigh of sheep, causing a reproducible contusion injury to the subcutaneous soft tissues. In a subsequent procedure, a reproducible femoral butterfly fracture (AO C3-type) was created at the sheep’s femur, which was initially stabilised for 5 days by an external fixator construct to allow for soft tissue swelling to recede, and ultimately in a bridging construct using locking plates. The combined injuries were applied to twelve sheep and the healing observed for four or eight weeks (six animals per group) until sacrifice. The pendulum impact led to a moderate to severe circumferential soft tissue injury with significant bruising, haematomas and partial muscle disruptions. Posttraumatic measurements showed elevated intra-compartmental pressure and circulatory tissue breakdown markers, with recovery to normal, pre-injury values within four days. Clinically, no neurovascular deficiencies were observed. Bi-weekly radiological analysis of the healing fractures showed progressive callus healing over time, with the average number of callus bridges increasing from 0.4 at two weeks to 4.2 at eight weeks. Biomechanical testing after sacrifice showed increasing torsional stiffness between four and eight weeks healing time from 10% to 100%, and increasing ultimate torsional strength from 10% to 64% (relative to the contralateral control limb). Our results demonstrate the robust healing of a complex femur fracture in the presence of a severe soft tissue contusion injury in sheep and demonstrate the establishment of a clinically relevant experimental model, for research aimed at improving the treatment of bone fractures accompanied by closed soft tissue injuries.

Prediction Scheme of Torsional Strength of Reinforced Concrete Beam

This study proposes a artificial neural network with genetic algorithm (GA-ANN) for predicting the torsional strength of reinforced concrete beam. Genetic algorithm is used to the optimal network structure and parameters. A database of the torsional failure of reinforced concrete beams with a rectangular section subjected to pure torsion was obtained from existing literature for analysis. This study compare the predictions of the GA-ANN model with the ACI 318 code used for analyzing the torsional strength of reinforced concrete beam. The results show that the proposed model provides reasonable predictions of the ultimate torsional strength of reinforced concrete beams and offers superior torsion accuracy compared to that of the ACI 318-89 equation.

Fusion welding of nickel–titanium and 304 stainless steel tubes: Part II: tungsten inert gas welding

Shape memory nickel–titanium is attractive for lightweight actuators as it can generate large blocking stresses and high recovery strains through solid-state operation. A key challenge is the integration of the nickel–titanium components into systems; this alloy is difficult and expensive to machine and challenging to weld to itself and other materials. In this research, we join nickel–titanium and 304 stainless steel tubes of 9.53 mm (0.375 in) in diameter through tungsten inert gas welding. By joining nickel–titanium to a common structural material that is easily machined and readily welded to other materials, the system integration challenges are greatly reduced. The joints prepared in this study were subjected to optical microscopic inspection, hardness mapping, energy dispersive X-ray spectroscopy, mechanical testing, and failure surface analysis via scanning electron microscopy. The affected zone from welding is approximately 125 µm (0.005 in) wide including partially mixed zones with a maximum hardness of 817 HV and a possible heat-affected zone of 1–2 µm (39–79 µin) wide. The maximum average ultimate torsional strength is 415 MPa (60.2 x 103 lbf/in2). Implementation of this joining method is demonstrated in the construction of a solid-state torsional actuator that can lift a weight of 2.3 kg (5 lb) to a distance of 610 mm (24 in). The laser and TIG welding processes are compared.

Using a Hybrid Neural Network to Predict the Torsional Strength of Reinforced Concrete Beams

This study proposes a multilayer perceptrons neural network with genetic algorithm (GA-MLP) for predicting the torsional strength of reinforced concrete beams. Genetic algorithm is used to determine the optimum number of inputs and hidden nodes of a feedforward neural network, the optimum slope of the activation function, and the optimum values of the learning rates and momentum coefficients. A database of the torsional failure of reinforced concrete (including normal-strength and high-strength concrete) beams with a rectangular section subjected to pure torsion was obtained from existing literature for analysis. We compare the predictions of the GA-MLP model with the ACI 318 code used for analyzing the torsional strength of reinforced concrete beams. We found that the proposed model provides reasonable predictions of the ultimate torsional strength of reinforced concrete beams and offers superior torsion accuracy compared to that of the ACI 318-02 equation considering both the correlation coefficient and absolute relative error.

Determining the shear fracture properties of HIP joints of reduced-activation ferritic/martensitic steel by a torsion test

Hot isostatic pressing (HIP) is a key technology used to fabricate a first wall with cooling channels for the fusion blanket system utilizing a reduced-activation ferritic/martensitic steel. To qualify the HIPped components, small specimen test techniques are beneficial not only to evaluate the thin-wall cooling channels containing the HIP joint but also to use in neutron irradiation studies. This study aims to develop the torsion test method with special emphasis on providing a reasonable and comprehensive method to determine interfacial shear properties of HIP joints during the torsional fracture process. Torsion test results identified that the torsion process shows yield of the base metal followed by non-elastic deformation due to work hardening of the base metal. By considering this work hardening issue, we propose a reasonable and realistic solution to determine the torsional yield shear stress and the ultimate torsional shear strength of the HIPped interface. Finally, a representative torsion fracture process was identified.

Nonlinear analysis for PC box-girder with corrugated steel webs under pure torsion

A three dimensional finite element model of PC box-girder with corrugated steel webs taking material nonlinearity into consideration is established to investigate the behavior under pure torsion. The torque–twist curves and ultimate torsional strength predicted by FEM show good agreement with test data. Results obtained from finite element model indicate that specimens go through three stages subjected to pure torsion and the shear flow in concrete top or bottom flange is not equal to that in corrugated steel webs. Parametric study is carried out including effect of corrugation, effect of thickness of web, effect of strength of concrete, and effect of prestressed tendons. It is shown that the ultimate torsional strength of specimens is in linear proportion to shear modulus and thickness of corrugated steel webs and to compressive strength of concrete.