Difference In Fatigue Life Research Articles

Fatigue testing of Chilean asphalt mixtures and data fitting with phenomenological models

Thirteen hot asphalt mixtures were tested for fatigue in four-point beam configuration. Theresults were analysed using the MEPDG fatigue model and a modified version of it, which included binders’ thermal susceptibility as an additional forecasting variable. Seven mixtures were dense-graded, three were stone mastic asphalts and three were semi-open. Three mixtures used unmodified asphalt binders UB, while the rest had SBS polymer modified binders PMB. The fatigue lives of PMB mixtures were one order of magnitude higher than UB ones. The results indicated that the higher the degree of modification in the binder, the higher the fatigue life. No significant differences in fatigue life were observed between the three aggregate gradations. The MEPDG fatigue model parameters were calibrated using the test results. The predictions showed very low accuracy. When including the binders’ thermal susceptibility as an additional forecasting variable, significant improvements were achieved in the accuracy of the predictions.

Requirements for stress gradient‐based fatigue assessment of notched structures according to theory of critical distance

AbstractNotches, local stress raisers within structural components, are one of the most important locations for fatigue crack initiation. It is well known that fatigue is governed by the effective stresses in the vicinity of notches. Within this study, differences in prediction accuracy between different types of theory of critical distance methods, that is, point and line methods, are systematically investigated in conjunction with a sensitivity study regarding mesh refinement, assumed strength hypothesis and material behaviour. For this purpose, a finite element analysis parameter study on notched structures is performed and recommendations for the application of stress gradient methods are presented. Difference in effective stress of up to 30%, and hence a significant difference in fatigue life (e.g., 185% for a slope of S‐N curve of k = 4), is found for typical notch shapes, for example, in welded joints.

Fatigue curve of microscale single-crystal copper: An in situ SEM tension-compression study

A series of quantitative in situ tension-compression fatigue experiments in SEM are performed to investigate the fatigue curve of microscale single-crystal copper specimens with a test part of 1 × 1 × 2 μm under various strain amplitudes. The variation of resolved shear stress on the primary slip plane (τB4) and the corresponding evolution of crystallographic slips in each cycle are analyzed and in situ observed, respectively. The variation of τB4 during fatigue shows that, (i) the variation of τB4 clearly includes the early stage, the saturation stage, and the final fracture of the specimen; (ii) apparent cyclic hardening and softening appear in the early stage of all specimens; (iii) τB4 shows a strain-dependent variation in the saturation stage. Continuous cyclic softening and secondary cyclic hardening occur in specimens with relatively higher strain, while only slight cyclic hardening emerges in the specimen with the minimum strain. Based on in situ SEM observations, the variation trend of τB4 is interpreted from the evolution of geometrical characteristics of slip traces. Finally, we obtain the fatigue curve of microscale single-crystal coppers. The fatigue life is apparently dependent on the strain amplitude, while insensitive to the frequency of cyclic loading. Moreover, the fatigue lives of microscale single-crystal Cu are much shorter than those of bulks, indicating a significant size effect. The difference in fatigue lives of microscale and bulk ones reduces from about 360 to only 7 times with the decrease of applied strain, revealing the strain-dependence of size effect of fatigue life for microscale single-crystal coppers.

The Effect of Temper, Grain Orientation, and Composition on the Fatigue Properties of Forged Aluminum-Lithium 2195 Alloy

The AA2195 alloy was designed for aerospace applications. Fatigue failures are among the major causes of aircraft failures. However, there exist limited studies on fatigue behavior of forged AA2195 alloy. Samples of AA2195 alloys were taken from an aircraft wheel and an open-die hand-forged billet. A total of 44 aircraft wheel samples and 67 hand-forged samples were tested. Aircraft wheel samples taken from the hub and tubewell were prepared in two tempers: T6 (peak aged) and T8 (cold worked and aged). The hand-forged samples were prepared in three temper conditions (T6, T8-4% strain, and T8-8% strain) and cut in the transverse (T) direction, short-transverse (S) direction and 45° between these directions (ST45). The study revealed that T8 temper, while providing higher strength, showed longer fatigue life compared to T6 temper. The anisotropic behavior of AA2195 hand forgings showed the trend NT > NS > NST45. The forged aircraft wheels at different locations and tempers showed similar fatigue life at high stresses. At low stresses, different locations showed significant differences in fatigue lives. The reason may be related to the variance of manufacturing and thermomechanical processes experienced by different locations on a complex-shaped wheel. The AA2195 aircraft wheel samples were also compared with samples taken from a similar aircraft wheel but made of AA2014 alloy. The results revealed that the addition of lithium significantly improved fatigue life.

Evaluation of the effect of temperature on cyclic fatigue resistance of three types of Nickel-Titanium rotary files with various alloy properties: An in vitro study

Background and objectives: the fracturing of nickel-titanium rotary instruments during endodontic treatment because of the cyclic fatigue remains a common incidence. This study evaluated the effect of temperature on the cyclic fatigue of various nickel-titanium rotary files and compare between them. Methods: Three types of rotary instruments with tip size 0.25 were used: HyFlex EDM (OneFile, variable taper, Colten/Whaledent), ProTaper Gold (F2, 0.08 taper, Dentsply) and 2Shape (TS2, 0.06 taper, Micro-Mega). Twenty files for each instrument were tested for cyclic fatigue at (20°C and 37°C) temperatures and rotated until fracture occurred in a simulated canal with an angle curvature of about 60°, a radius curvature of 5 mm, and a canal width of 1.5 mm. Six groups were formed for all instruments (total number = 60), with ten files in each group. The number of cycles to fracture was recorded, and statistical analysis was completed using analysis of variance and independent t-test with significance at a (P<0.05). Results: HyFlex EDM OneFile registered no differences in fatigue life between the 2 temperatures tested (P > .05), whereas ProTaper Gold F2 and 2Shape TS2 showed a statistically significant reduction in fatigue life at body temperature compared with room temperature ( P <0.05). HyFlex EDM OneFile exhibited statistically higher resistance to cyclic fatigue than ProTaper Gold F2 and 2Shape TS2 both at room and body temperatures (P<0.05). Conclusions: Within the limitations of this study, body temperature influenced the cyclic fatigue resistance of ProTaper Gold F2 and 2Shape TS2 files, whereas it did not influence the fatigue life of HyFlex EDM OneFile. The HyFlex EDM OneFile was more resistant to cyclic fatigue than the ProTaper Gold F2 and 2Shape TS2 files at room and body temperatures.

Stochastic Traffic-Based Fatigue Life Assessment of Rib-to-Deck Welding Joints in Orthotropic Steel Decks with Thickened Edge U-Ribs

Rib-to-deck (RD) joints in orthotropic steel decks (OSDs) are highly prone to fatigue cracking under heavy traffic. An innovative longitudinal rib, named the thickened edge U-rib (TEU), has been proposed to enhance the fatigue strength of RD joints and validated through model tests. However, more studies are still required on the effect of TEUs in real engineering applications. To this end, a typical OSD bridge in China has been investigated, based on the experimental results. In the analysis, a stochastic traffic model is employed to simulate the vehicle-induced fatigue actions comprehensively. The framework of the stochastic model is proposed by considering the randomness in both the vehicles and their lateral distribution. Then the traffic model is instantiated using standard truck models in conjunction with the codes of practice as well as the observed data. A multi-scale finite element model is later established to determine the stochastic stress responses, whereas the influence surface method is used to improve computational efficiency. In this study, Monte Carlo simulations have been carried out to derive the stress spectra for the RD joints at different critical locations. Based on the test data and the derived spectra, an engineering assessment has been performed to obtain the fatigue life of RD joints in OSDs with and without TEUs, respectively. The new findings show that the position of joints has a remarkable influence on the stress spectra of RD joints, which results in the notable difference in fatigue life of the joints. Further, the fatigue life of RD joints can be significantly prolonged by using TEUs, and the prolongation rates are varied from 141% to 161% depending on the calculation methods and traffic models used.

Thermomechanical Characterization of SiC/SiC Ceramic Matrix Composites in a Combustion Facility

A combustion facility which includes uniaxial mechanical loading was implemented that enables environmental conditions more akin to jet engine environments compared to conventional static environment tests. Two types of woven SiC/SiC ceramic matrix composites (CMCs), melt-infiltrated (MI) and chemical vapor infiltrated (CVI), were subjected to fatigue loading in the combustion facility and under isothermal furnace conditions. Some CVI test coupons were coated with a multilayer environmental barrier coating (EBC) of mullite + ytterbium monosilicate using slurry infiltration process to demonstrate the performance with a coating. Combustion conditions were applied using a high velocity oxy fuel gun on the front side of the specimen and mechanical loading was applied using a horizontal hydraulic MTS machine. All the specimens considered were subjected to tension-tension fatigue loading at 100 MPa, stress ratio of 0.1 and specimen front-side surface temperature of 1200 ± 20 °C. Nondestructive evaluation (NDE) methods, such as electrical resistance (ER), was used as an in-situ health monitoring technique. Similar fatigue tests were performed in an isothermal furnace for comparison. A much lower fatigue life was observed for the uncoated specimens tested under combustion conditions in comparison to isothermal furnace condition. This difference in fatigue life was attributed to damage associated with added thermal stress due to the thermal gradient and higher rate of oxidative embrittlement due to the presence of high velocity combustion gases in the combustion environment. EBC coating increased the fatigue life in combustion environment. However, EBC coated specimens experienced spallation in the high-velocity flame due to the presence of micro cracks in the coating surface. Fracture surfaces of the failed specimens were investigated under the scanning electron microscope (SEM) to determine the extent of oxidation and damage.

Compressive fatigue behavior of compound concrete containing demolished concrete lumps

This research focused on the uniaxial compressive fatigue behavior of compound concrete (CC) made of fresh concrete (FC) and demolished concrete lumps (DCLs) distinctly larger than conventional recycled aggregates. Sixty cylindrical and three planar specimens were tested under constant-amplitude sinusoidal loading. Digital image correlation was employed to monitor the initiation and propagation of cracks on the specimens. The variances in the dissipated energy, Poisson’s ratio, fatigue modulus and longitudinal residual strain of the cylindrical specimens with the number of cycles are discussed. Linear formulas describing the relationship between secondary strain rate and fatigue life are presented. The results indicate that there is no distinct difference in fatigue life between CC and conventional concrete, though the lateral expansion of CC under such loading is greater. The replacement ratio of DCLs can hardly influence the secondary strain rate of CC. The interfaces between DCLs and FC are not evident weak zones in CC.

Thickness effect in laser shock processing for test specimens with a small hole under smaller laser power density

In order to consider the influence of the thickness difference of the small hole sample or member on the effect of laser shock processing and the optimization of the process parameters, the differences in residual stress distribution, fatigue source location, fracture characteristics and crack growth rate and their correlations were investigated by simulation and experimental methods after laser shock processing of small hole specimens with different thicknesses under certain power densities. There was a significant difference in fatigue life after laser shock of small hole specimens with different thickness. And there were differences of the fatigue crack initiation and growth mechanism of the laser shocked specimens with different thickness, indicating the small hole specimens after laser shock processing had a thickness effect. This thickness effect was closely related to the distribution of the residual stress due to the difference in plate thickness.

Inferomedial cortical bone contact and fixation with calcar screws on the dynamic and static mechanical stability of proximal humerus fractures

BackgroundThis study aimed to explore the effect of retaining inferomedial cortical bone contact and fixation with calcar screws on the dynamic and static mechanical stability of proximal humerus fractures treated with a locking plate.MethodsTwelve Synbone prosthetic humeri (SYNBONE-AG, Switzerland) were used for a wedge osteotomy model at the proximal humerus, in four groups. In the cortex contact + screw fixation group and cortex contact group, the inferomedial cortical bone contact was retained. In the screw fixation group and control group, the inferomedial cortical bone contact was not retained. Calcar screw fixation was implemented only in the screw fixation groups. The dynamic and static mechanical stability of the models were tested with dynamic fatigue mechanics testing, quasi-static axial compression, three-point bending, and torsion testing.ResultsThe cortex contact + screw fixation group showed the longest fatigue life and the best stability. There was 35% difference in fatigue life between the cortex contact + screw fixation group and the cortex contact group, 43%between the cortex contact + screw fixation group and screw fixation group, and 63% between the cortex contact + screw fixation group and screw fixation group (P < 0.01). The cortex contact + screw fixation group showed the best axial compressive stiffness, bending stiffness, and torsion stiffness; these were successively decreased in the other three groups (P < 0.01).ConclusionRetaining inferomedial cortical bone contact and fixation with two calcar screws maintained fracture stability with the highest strength and minimum deformation. Of the two methods, restoration of the inferomedial cortical bone support showed better dynamic and static biomechanical properties than placement of calcar screws alone.

Fatigue Life Properties of Stainless Steels in Wide Ranged Biaxial Stress States using a Hollow Cylinder Specimen

Stress controlled multiaxial fatigue tests were carried out using hollow cylinder specimens of type 430 and 316 stainless steels at room temperature. A newly developed fatigue testing machine which can apply push-pull loading and inner pressure to the specimen was used. For inner pressure, oil was put inside of the specimen. 7 types of cyclic loading paths were employed by combining axial and hoop stresses; a Pull, an Inner-pressure, a Push-pull, an Equi-biaxial, a Square-shape, a LT-shape and a LC-shape. Fatigue lives vary depending on the loading path when those were evaluated by the maximum Mises’ equivalent stress range on inner surface of the specimen. The fatigue lives of both the steels showed a similar tendency. However, the following difference was identified. Specifically, differences in fatigue lives of type 430 stainless steel between the uniaxial loading and the multiaxial tests were large, while those of type 316 stainless steel were small. To discuss difference in fatigue life properties between both steels, this study investigates the effect of the shear stress range, mean stress and additional hardening and which leads to evaluate the lives suitably.

Investigation of the fatigue properties of asphalt mixture designed using vertical vibration method

In this work, the flexural tensile fatigue behaviours of AC-20 asphalt mixtures were studied using beams, which were designed by the vertical vibration method (VVTM) and Marshall method. Then an analysis of variance (ANOVA) was used to examine the differences in fatigue lives, and the Weibull distribution was used to analyze the fatigue lives and establish the fatigue equations of the mixtures. Subsequently, the fatigue lives were compared and analyzed under the same stress level and repeated load force. The results showed that the test accuracy of specimens produced using the vertical vibration compaction method (VVCM) exceeds 92%. Compared to the Marshall design, the asphalt mixture fabricated with the VVTM design improved crack resistance and rutting resistance by at least 40% and 30%, respectively. The ratio of the slopes (the values of the regression coefficient b) of fatigue equations of asphalt mixtures designed by the VVTM to that of Marshall method ranges from 0.883 to 0.965, and the ratio of the intercepts (the values of the regression coefficient a) ranges from 1.278 to 1.284. The results also showed that compared to the Marshall design, asphalt mixtures fabricated with VVTM design exhibited improved fatigue lives by at least 61% (at a stress level of 0.45) and 356% (with a repeated load force of 0.378 kN).

Study on the Role of Casting Defects and Surface Finish on Fatigue Life in Die-cast AM60B Magnesium Alloy Using X-Ray Computed Tomography

Abstract Magnesium alloy has attracted considerable attention from the automotive industry because of its low density and high specific strength combined with excellent casting capabilities. However, the role of casting defects and surface finish on the fatigue life emerges as a major concern. To study the role of surface finish, the die-cast skin was removed from the selected test specimens by hand polishing. No major difference in surface roughness was observed between the die-cast and polished surface. To characterize the casting defects in each test specimen, prior to the fatigue test, X-ray computed tomography (XCT) scans were performed on a desktop micro-XCT scanner. The preliminary XCT scans revealed a large number of gas and shrinkage pores concentrated in the center sections of the test specimens and a few scattered close to the free surface. In addition to gas and shrinkage pores, in unpolished specimens, small microcracks and notch-like surface imperfections were also observed on the edge of the test specimens. Strain controlled fatigue tests were performed on polished and unpolished test specimens at a 0.3 % strain amplitude. After every 2,000 fatigue cycles, the test was interrupted and XCT was performed to study the crack initiation and propagation in the respective test specimens. The fatigue test exhibited no major difference in fatigue life between the unpolished and polished specimens. However, XCT scans revealed the dominant fatigue crack initiated from the surface imperfections in unpolished specimens and from casting pores closer to the free surface in polished specimens. The fatigue test results and spatial distribution of casting pores were compared with the specimens extracted from a die-cast shock-tower structure from a previous study. Although a difference in spatial distribution of the casting pores was observed, it had no major impact on the fatigue life between the two sets of specimens.

Effect of specimen configuration on fatigue properties of dissimilar aluminum to steel resistance spot welds

General Motors (GM) has developed a proprietary resistance spot welding process using a Multi-Ring, Domed (MRD) electrode geometry that is capable of producing welds between aluminum alloys and steel materials with acceptable joint strength. This work presents fatigue properties of resistance spot welds (RSWs) produced between dissimilar 1.2-mm thick wrought aluminum AA6022-T4 and 2.0-mm thick IF steel RSWs in tensile-shear and coach-peel configurations. The results were compared to those of spot welds made of 1.2-mm thick and 2.00-mm thick AA6022-T4. The tensile-shear and coach-peel spot welds exhibited limited scatter in fatigue life for both stack-ups. The overall fatigue life of the tensile-shear AA6022-T4 to IF stack-ups was much greater than that of the AA6022-T4 to AA6022-T4 stack-ups. However, in coach-peel, there was no significant difference in fatigue life between the two stack-ups. In both tensile-shear and coach-peel fatigue tests the fracture mode for both stack-ups was primarily crack growth through the 1.2-mm thick AA6022-T4 sheet. The superior performance of the tensile-shear AA6022-T4 to IF steel RSWs was most likely a result of larger weld nugget size along with microstructural features that improved performance. These included more favourable notch root openings as well as columnar grain growth and alloying of the aluminum nugget with iron that could retard fatigue crack propagation.

Fatigue life of additively manufactured Ti6Al4V scaffolds under tension-tension, tension-compression and compression-compression fatigue load

Mechanical performance of additively manufactured (AM) Ti6Al4V scaffolds has mostly been studied in uniaxial compression. However, in real-life applications, more complex load conditions occur. To address this, a novel sample geometry was designed, tested and analyzed in this work. The new scaffold geometry, with porosity gradient between the solid ends and scaffold middle, was successfully used for quasi-static tension, tension-tension (R = 0.1), tension-compression (R = −1) and compression-compression (R = 10) fatigue tests. Results show that global loading in tension-tension leads to a decreased fatigue performance compared to global loading in compression-compression. This difference in fatigue life can be understood fairly well by approximating the local tensile stress amplitudes in the struts near the nodes. Local stress based Haigh diagrams were constructed to provide more insight in the fatigue behavior. When fatigue life is interpreted in terms of local stresses, the behavior of single struts is shown to be qualitatively the same as bulk Ti6Al4V. Compression-compression and tension-tension fatigue regimes lead to a shorter fatigue life than fully reversed loading due to the presence of a mean local tensile stress. Fractographic analysis showed that most fracture sites were located close to the nodes, where the highest tensile stresses are located.

Correlating Scatter in Fatigue Life with Fracture Mechanisms in Forged Ti-6242Si Alloy

Unlike the quasi-static mechanical properties, such as strength and ductility, fatigue life can vary significantly (by an order of magnitude or more) for nominally identical material and test conditions in many materials, including Ti-alloys. This makes life prediction and management more challenging for components that are subjected to cyclic loading in service. The differences in fracture mechanisms can cause the scatter in fatigue life. In this study, the fatigue fracture mechanisms were investigated in a forged near-α titanium alloy, Ti-6Al-2Sn-4Zr-2Mo-0.1Si, which had been tested under a condition that resulted in life variations by more than an order of magnitude. The crack-initiation and small crack growth processes, including their contributions to fatigue life variability, were elucidated via quantitative characterization of fatigue fracture surfaces. Combining the results from quantitative tilt fractography and electron backscatter diffraction, crystallography of crack-initiating and neighboring facets on the fracture surface was determined. Cracks initiated on the surface for both the shortest and the longest life specimens. The facet plane in the crack-initiating grain was aligned with the basal plane of a primary α grain for both the specimens. The facet planes in grains neighboring the crack-initiating grain were also closely aligned with the basal plane for the shortest life specimen, whereas the facet planes in the neighboring grains were significantly misoriented from the basal plane for the longest life specimen. The difference in the extent of cracking along the basal plane can explain the difference in fatigue life of specimens at the opposite ends of scatter band.

Comparison in surface integrity and fatigue performance for hardened steel ball-end milled with different milling speeds

This paper aims at comparing the surface integrity and fatigue performance of hardened AISI D2 steel ball-end milled with different milling speeds. Results show that the milling speed has a significant effect on surface topography, surface roughness, microhardness and residual stress. The fatigue life for samples with hard milled surface was raised at least 83% compared with that of polished samples. This is ascribed to the high surface residual compressive stress and the enhanced microhardness induced by the hard milling process. The maximum difference in fatigue life is about 12.2% for samples milled with spindle speed N ranging from 3000 r/min to 8000 r/min. Samples milled with a low or high spindle speed have a longer fatigue life than those samples milled with a middle spindle speed condition (N=6000 r/min). Moreover, excessive surface strain hardening will increase surface brittleness which is detrimental to fatigue resistance. The increase of spindle speed can decrease the degree of strain hardening to some extent. Based on this, selecting a relatively high spindle speed can obtain a satisfying combination of surface residual stress and microhardness during the ball-end milling process of hardened AISI D2 steel, which is feasible and prospective from high fatigue performance of ball-end milled surface and the machining efficiency point of view.

09.17: Fatigue life of marked steel components

ABSTRACTSteel components have to be identifiable and traceable during the whole manufacturing chain. The choice of the identification method is not specified consistently in international rules and standards. The European standard for the execution of steel structures EN 1090‐2 specifies that the use of durable marks may not result in producing damages without saying which damages are meant. Hard stamped marks are only permitted for steel grades up to S355 and only in areas where no effect on the fatigue life is expected. Otherwise the use of soft stamps should be verified. In other international standards hard stamped marks are explicitly required. These contradictions should be resolved.In terms of durability and liability, markings should be resistant against particular manufacturing processes such as sandblasting, hot‐dip galvanizing or coating. For this reason, the following marking methods are used in practical applications: hard stamping, scribing, plasma marking and needling.Nowadays the machinery manufacturers have developed machines in which the marking process can be automatically integrated in the manufacturing process of steel components so that manual layout scribing is not required anymore and components can be marked on the fly. However, the effect of the installed notch due to the marking process on the fatigue strength of the components has not been investigated yet. As a result, a classification of the resulting notched details according to the European detail categories of EN 1993‐1‐9 is in principle not possible.For these reasons, the influence of durable marking methods on the fatigue strength of steel components needs to be clarified by experimental fatigue tests and numerical calculations which have been performed at the Institute for Metal and Lightweight Structures of the University of Duisburg‐Essen. Within these investigations the different marking methods hard stamped, scribed, plasma marked and needled as well as unmarked structural details have been examined. The experimental investigations have been carried out considering three different steel plate thicknesses 15 mm, 25 mm and 40 mm and two different steel grades S355J2 and S460N.As expected the marked specimens show a decrease of the loading cycles until failure even though there are differences in fatigue life due to the different markings and their characteristic notch geometries.

Microstructure and fatigue properties of linear friction welded TC4 titanium alloy joints

The welded joints are often subjected to cyclic stresses and high-strain-rate deformation resulting in worrisome fatigue failure. Therefore, it is necessary to evaluate the fatigue resistance and cyclic deformation characteristics of these weldments. Ti–6Al–4V–0.3Fe–0.1C–0.05N–0.015H–0.2O (TC4) titanium alloy joints were produced via linear friction welding and a sound joint was obtained. It was observed that fine subgrains formed in the weld zone where the hardness became higher. The strain ratio had a strong effect on the cyclic deformation characteristics of the joint, with hysteresis loops being different at different strain ratios. However, the difference of fatigue life of the joint was small with varying strain ratios. The stress amplitude of linear friction welded TC4 joint showed essentially cyclic softening until failure at all strain ratios. Fatigue cracks initiated from the near-surface of base metal and propagated by the formation of fatigue striations together with secondary cracks.

Influence of Temperature on Cyclic Fatigue Resistance of ProTaper Gold and ProTaper Universal Rotary Files

IntroductionThe aim of this study was to evaluate the cyclic fatigue resistance of ProTaper Universal (PTU; Dentsply Maillefer, Baillagues, Switzerland) and ProTaper Gold (PTG, Dentsply Maillefer) nickel-titanium rotary files at room and intracanal temperatures. MethodsA total of 120 files were used to test the cyclic fatigue resistance of PTU (S1 and F2) and PTG (S1 and F2) in an artificial canal at room temperature (20°C) and at intracanal temperature (35°C). The number of cycles to failure and the fracture length of the fragment were recorded, and data were subjected to statistical analysis. ResultsPTG registered no differences in fatigue life between the 2 temperatures tested (P > .05), whereas PTU showed a statistically significant reduction in fatigue life at intracanal temperature compared with room temperature (P < .05). PTG instruments exhibited a statistically higher resistance to cyclic fatigue than PTU instruments both at room and intracanal temperatures (P < .05). There were no statistically significant differences among the fracture length of separated instruments (P > .05). ConclusionsIntracanal temperature influenced the cyclic fatigue resistance of instruments produced with traditional nickel-titanium, whereas it did not influence the fatigue life of instruments produced with gold heat treatment. Gold heating treatment enhances the resistance to cyclic fatigue of ProTaper instruments.