Tensile Mean Stress Research Articles

Effect of high mean tensile stress on the fretting fatigue life of an Ibis steel reinforced aluminium conductor

The aim of this work is to evaluate the effect of a high mean tensile pre-load on the fatigue life of an Ibis type of steel reinforced aluminium conductor (ACSR) mounted on a monoarticulated cast aluminium suspension clamp. To carry out the tests a new and enhanced version of a fretting fatigue rig for overhead conductors was built. Based on the obtained S–N curves for this assembly it was shown that an increase of the Everyday stress (EDS) from 20% to 30% of the cable rated tensile strength (RTS) caused an average reduction of 50% in life. Failure analysis revealed that cracks always initiated at contact interfaces within the cable/clamp assembly, at the fretting marks.

Notch effect on torsional fatigue of austenitic stainless steel: Comparison with low carbon steel

Notch effect in austenitic stainless steel under cyclic torsion is quite different depending on the superposition of static tension. In pure torsion, the rubbing of the serrated factory-roof type crack faces delays the crack growth along the notch root. Thus, the lifetime in notched specimen becomes longer than in smooth specimen. However, in cyclic torsion with static tension, the flat crack path and mean tensile stress reduce the influence of the crack face contact. Accordingly, shorter lifetime resulted from higher strain concentration at the notch root. Crack growth in low carbon steel under cyclic torsion is highly affected by the ferrite/pearlite banded microstructure besides the addition of static tension. Because of a small amount of the crack face contact, the reduction of lifetime in notched specimen is revealed irrespective of superposition of static tension.

Low-Cycle Fatigue Deformation Behavior and Evaluation of Fatigue Life on Extruded Magnesium Alloys

Extruded magnesium alloy shows a strong anisotropy of mechanical properties, which is caused by both of a crystallographic nature in hexagonal close packed lattice structure and a fiber texture with basal plane aligned parallel to the extruded direction by mechanical processing. To evaluate fatigue deformation behavior and fatigue life of extruded magnesium alloys, total strain-controlled and stress-controlled low-cycle fatigue test of three extruded magnesium alloys, AZ31, AZ61 and AZ80, were performed in ambient atmosphere at room temperature using smooth round bar specimen. Mean tensile stress during the total strain-controlled fatigue process and mean compressive strain during the stress-controlled fatigue process appeared due to the difference between tensile yield stress and compressive one, which resulted in mechanical twinning in the compressive phase. Fatigue criteria proposed previously considering the mean stress effect were evaluated in terms of fatigue life predictions based on the experimental results. Also, an energy-based model taken into account of plastic and elastic energy density was discussed to predict the fatigue lives obtained from the total strain- and the stress-controlled fatigue experiments.

OS2018 マグネシウム合金押出し材の応力及びひずみ制御低サイクル疲労変形挙動と疲労寿命評価(OS20-4 疲労と強度,OS-20 HCP金属の実験力学と計算力学)

Extruded magnesium alloy shows a strong anisotropy of mechanical properties, which is caused by both of a crystallographic nature in hexagonal close packed lattice structure and a fiber texture with basal plane aligned parallel to the extruded direction by mechanical processing. To evaluate fatigue deformation behavior and fatigue life of extruded magnesium alloys, total strain-controlled and stress-controlled low-cycle fatigue test of three extruded magnesium alloys, AZ31, AZ61 and AZ80, were performed in ambient atmosphere at room temperature using smooth round bar specimen. Mean tensile stress during total strain-controlled fatigue process and mean compressive strain during stress-controlled fatigue process appeared due to the difference between tensile yield stress and compressive one, which resulted in mechanical twinning in the compressive phase. Fatigue criteria proposed previously considering the mean stress effect were evaluated in terms of fatigue life predictions based on the experimental results. Also, an energy-based model taken into account of plastic and elastic energy density was discussed to predict the fatigue lives obtained from total strain- and stress-controlled fatigue experiments.

Low-Cycle Fatigue Deformation Behavior and Evaluation of Fatigue Life on Extruded Magnesium Alloys

To evaluate fatigue deformation behavior and fatigue life of extruded magnesium alloy, total strain-controlled and stress-controlled low-cycle fatigue test of three extruded magnesium alloys, AZ31, AZ61 and AZ80, were performed in ambient atmosphere at room temperature using smooth round bar specimen. Mean tensile stress during total strain-controlled fatigue process and mean compressive strain during stress-controlled fatigue process appeared due to asymmetry of yield stress between tension and compression. The values of mean stress and mean strain appeared on three alloys were associated with the ratio of compressive yield stress to tensile one, which resulted in mechanical twinning in the compressive phase. Fatigue criteria proposed previously considering the mean stress effect were evaluated in terms of fatigue life predictions based on the experimental results. Also, an energy-based model taken into account of plastic and elastic energy density was discussed to predict the fatigue lives obtained from total strain- and stress-controlled fatigue experiments.

Low-Cycle Fatigue Properties of Extruded AZ31 Magnesium Alloy

Fully reversed tension-compression low-cycle fatigue tests controlled by both of total strain and stress were conducted on extruded AZ31 magnesium alloy using smooth round bar specimens in ambient atmosphere at room temperature. The stress-strain hysteresis loops exhibited a characteristic asymmetric shape with a positive mean stress during total strain-controlled fatigue cycle, in comparison with those with a compressive mean strain under stress-controlled fatigue test. The mean stress was associated with the ratio of compressive yield stress and tensile one in the material, which resulted in mechanical twinning in the compressive phase. The fatigue lives obtained from both controlled experiments were nicely described by the Coffin-Manson relationship. From the plastic strain range-life curves, fatigue life under total strain-controlled fatigue test was shorter than that under stress-controlled one because of an effect of tensile mean stress. Fatigue criteria considering the mean stress effect previously proposed were evaluated in terms of fatigue life predictions based on the experimental results. Also, an energy-based model taken into account of plastic and elastic energy density was discussed to predict the fatigue lives obtained from total strain- and stress-controlled fatigue experiments.

Low Cycle Fatigue Life Threshold for Titanium Aluminides

AbstractAlthough there exists a good understanding of dislocation glide mechanisms during fatigue of titanium aluminides,1 fatigue life prediction remains a crucial issue because of the low amount of macroscopic plastic strain and the existence of microstructural inhomogeneities. The concept proposed here aims at a threshold value, allowing a reasonable low cycle fatigue life for isothermal and thermomechanical fatigue conditions. It can be stated that under isothermal testing conditions a maximum strain amplitude of Δε/2 = 0.35% (corresponding to a stress amplitude of about Δσ/2 = 500 MPa) for temperatures up to 750 °C is feasible for TNB‐V2 in order to reliably reach a sufficient LCF life. Concerning satisfactory thermomechanical fatigue life the proposed concept suggests that the acting combination of mean stress and strain amplitude needs to be located below the Goodman line. It can be concluded that with increase in maximum cyclic temperature and temperature range, the tolerable strain amplitude decreases. Because of the well‐documented unfavorable combination of tensile mean stresses and environmental attack during OP‐TMF, an acceptable strain amplitude for TMF conditions is significantly lower than under isothermal conditions.

Experimental study on uniaxial time-dependent ratcheting of a polyetherimide polymer

The uniaxial ratcheting behavior of a polyetherimide (PEI) polymer ‘TECAPEI’ was studied using stress-controlled cyclic loading at room temperature, including both cyclic tension-compression with non-zero tensile mean stress and tension-unloading tests. The experimental observations were focused on the time-dependent ratcheting of the PEI polymer revealed in cyclic tests at diverse stress rates and with different peak stress holding times. The results showed that the PEI polymer shows obvious ratcheting deformation; i.e., the ratcheting strain accumulates progressively in the tensile direction during stress-controlled cyclic tests with non-zero mean stress. The ratcheting is highly dependent on the applied mean stress and stress amplitude, and is also characterized by a strong time-dependency during the cyclic stressing at diverse stress rates and with different peak stress holding times. The time-dependent ratcheting of the PEI polymer is caused mainly by its remarkable viscosity. A comparison of the ratcheting occurring before and beyond the ultimate stress point of the PEI polymer showed that the ratcheting beyond the ultimate stress point is more significant than that occurring before that point.

Zur Ermüdungsfestigkeit hochfester großer Schrauben

StahlbauVolume 79, Issue 9 p. 703-703 Dissertation Zur Ermüdungsfestigkeit hochfester großer Schrauben Frithjof Marten Dr.-Ing., Frithjof Marten Dr.-Ing.Search for more papers by this author Frithjof Marten Dr.-Ing., Frithjof Marten Dr.-Ing.Search for more papers by this author First published: 06 September 2010 https://doi.org/10.1002/stab.201090101Citations: 4AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume79, Issue9September 2010Pages 703-703 RelatedInformation

Dynamic tensile response of Zr-based bulk amorphous alloys: Fracture morphologies and mechanisms

Plate impact experiments were conducted to examine the dynamic tensile response of Zr-based bulk amorphous alloys (BAAs) having a nominal composition of Zr56.7Cu15.3Ni12.5Nb5.0Al10.0Y0.5. The experimental configuration used in our work permitted soft recovery of the samples to allow a careful examination of the fractured samples along with real-time measurements of the sample free-surface velocity (FSV) histories. Tensile loading was preceded by elastic compressive loading to peak stresses in the 3.6 to 6.0 GPa range. Tensile damage in the recovered samples was examined using optical and electron microscopy. The microscopy results showed that the BAA samples exhibit a brittle behavior (as a glass) at the macroscopic level and a ductile behavior (as a metal) at the microscopic level; in addition, corrugations and bumps are observed at the nanoscale. The observed fracture morphologies are related to three key features present in our spall experiments: preceding compressive stress (3.6–6.0 GPa), high tensile loading rate (∼106/s), high mean tensile stress (∼2.3 GPa); and are intrinsically related to the amorphous glassy structure of the BAAs (free volume content). We propose that the compressive stress depletes the free volume content. With increasing compressive stress, the available free volume decreases causing a suppression of shear stresses during tension. Thus, the mean tensile component becomes more dominant at higher stresses. Consequently, the observed surface morphology results from brittle cleavage, causing an increased damage localization in the recovered samples spalled at higher stresses. These observations support the inferences made from measurements of FSV histories. The high tensile loading rate is proposed to be responsible for cracking by multiple shear band propagation and interception, rendering the observed serrated surface morphology. Finally, we proposed that the corrugations are created due to a succession of arrest and propagation of mode I cracks. A subsequent dilatation, due to the effect of the tensile mean stress, caused the corrugations to evolve to bump-type features with sizes in the range of 10–100 nm. Our proposed mechanisms, although qualitative, constitute a systematic attempt to provide an explanation for the fracture morphologies observed in spalled BAA samples.

Stability of Microstructure of Ultrafine-Grained Copper Under Fatigue and Thermal Exposition

Abstract: Effect of cyclic loading and thermal exposition on microstructure of bulk ultrafine-grained Cu prepared by equal channel angular pressing was experimentally investigated by means of electron backscattering diffraction and by transmission electron microscopy. Stability of the microstructure under stress-controlled cyclic loading with a tensile mean stress of 200 MPa was shown to be high. Neither dynamic grain coarsening nor development of bimodal microstructure was observed. However, annealing at 250 °C for 30 min resulted in formation of bimodal microstructure. Consequently, fatigue strength of annealed specimens was low.

Enhancing the fatigue property of rolled AZ31 magnesium alloy by controlling {10-12} twinning-detwinning characteristics

An improvement of the fatigue resistance of rolled AZ31 magnesium alloy was attempted by reducing the tensile mean stress developed during fatigue deformation, which was achievable by tailoring the {10-12} twinning-detwinning characteristics of the material through the precompression process. The modification of the {10-12} twinning-detwinning characteristics made it possible to control the plastic deformation mechanisms activated during fatigue deformation so that the imposed tensile strain could be fully accommodated by detwinning alone, which led to a significant reduction of tensile flow stress, finally resulting in the reduction of mean stress.

Applicability of Rain Flow Method to Fatigue Life Span Estimation of Overhead Contact Wire

The rain flow method has been put forward as a method for waveform counting to estimate what the fatigue life span would be under actual waveform stress. The authors carried out experiments to test its applicability to hard drawn copper contact wire. In order to consider the effect of mean tensile stress when applying the rain flow method it is first necessary to define the fatigue life span properties for the various mean tensile stresses. The authors confirmed that these estimations can be found using fatigue test results from hard drawn copper contact wire placed under two types of mean tensile stress condition. The authors then conducted six fatigue tests to investigate the applicability of the rain flow method. The actual measured fatigue life span in tests generally exceeded estimations. The rain flow method may therefore conceivably be used to derive a method for safe estimation of fatigue life.

Uniaxial ratchetting of polymer and polymer matrix composites: Time-dependent experimental observations

The uniaxial time-dependent ratchetting of polyester resin and glass fiber reinforced polyester resin matrix composites was observed by the stress-controlled cyclic tension–compression with non-zero tensile mean stress and tension–tension tests at room temperature. After the ratchetting of the polyester resin had been observed by the cyclic tests with different loading conditions including some time-related factors, such as stress rate and peak stress hold, the ratchetting evolutions of the continuous and short glass fiber reinforced resin matrix composites were also investigated by the stress-controlled cyclic tests, respectively. It is concluded that: both the polyester resin and its composites present apparent ratchetting deformation, i.e., the ratchetting strain accumulates progressively in the tensile direction during the cyclic tension–compression with non-zero tensile mean stress and tension–tension tests; the ratchetting depends on the applied stress amplitude, mean stress, stress rate and peak stress hold, and the time-dependent ratchetting is obvious even for the continuous glass fiber reinforced resin matrix composites with high fiber volume fraction (such as 40% and 50%); the time-dependent ratchetting of the polyester resin and its composites mainly stems from the viscosity of the polyester resin, while the addition of glass fiber into the resin matrix improves the resistance of the composites to the ratchetting deformation and lowers the time-dependence of the ratchetting simultaneously.

Thermomechanical Fatigue of the TiAl Intermetallic Alloy TNB-V2

TiAl is supposed to substitute Ni or Ti alloys in energy conversion systems, such as aero engines. These components are subjected to thermomechanical fatigue (TMF), whereas this mechanical behaviour may substantially differ from isothermal low cycle fatigue (LCF). Therefore, it is necessary to assess TMF properties, in order to establish a reliable and precise lifetime prediction model. In this study the γ-base TiAl intermetallic alloy TNB-V2 was subjected to fully-reversed TMF tests under total strain control at strain amplitude of 0.7%, accompanied by LCF tests in air and vacuum. Temperature ranged from 550°C to 850°C. In TMF tests a continuous built-up of compressive (in-phase) or tensile (out-of-phase) mean stresses is observed. The lifetime ratio between IP and OP is 30–200, depending on temperature range. Substantially longer lifetimes of OP-TMF tests in vacuum are observed. Fracture always occurs in a transcrystalline mode. A lifetime description at 550°C based on the Basquin-Coffin-Manson equation reveals that the fatigue behaviour is governed by the amount of elastic strain even at low cycles, and the transition lifetime was found to be at 5 cycles. A damage parameter based on the equation of Smith, Watson and Topper is able to describe LCF and in-phase TMF lifetimes reasonably.

Ratcheting and fatigue properties of the high-nitrogen steel X13CrMnMoN18-14-3 under cyclic loading

Abstract High-nitrogen steel X13CrMnMoN18-14-3 has been used in manufacturing expanding metallic stents with 0.1 mm diameter, and such medical implant is subjected to complicated and asymmetrical cyclic loading during service. But there is no test data published for the thin wire of the material under cyclic loading. In this study, a series of tests were conducted on X13CrMnMoN18-14-3 stainless steel under uniaxial cyclic loading with mean tensile stress. The yield stress and ultimate strength were higher than that of large size specimen with diameters of 5 mm and 7 mm. The effects of stress amplitude, mean stress, loading history and stress rate on the ratcheting behavior of high-nitrogen steel were analyzed, respectively. It can be concluded that the ratcheting strain amplitude and ratcheting strain rate of X13CrMnMoN18-14-3 steel increases with increasing stress amplitude or mean stress correspondingly. At the meantime, experimental results reveal that the material exhibits a strong memory of the previous loading history, the stress cycling with higher stress amplitude or mean stress greatly restrains the ratcheting of subsequent stress cycling with lower ones. The ratcheting strain rate was very sensitive to the applied cyclic stress rate, and the accumulation of ratcheting strain under stress rate of 21.2 MPa/s is much faster than that under stress rate of 106 MPa/s. In addition, comparison of the fatigue life between bulk specimen and thin wire indicates that the size effect has significant influence on fatigue properties of the material. In the case of the test conducted under stress amplitude of 400 MPa, the fatigue life of small specimen is approximately ten times longer than that of bulk specimen under the same loading conditions.

Durability Assessment of Cylinder Block for Two Stroke Free Piston Linear Engine using Random Loading

This research presents the durability assessment of cylinder block for a two-stroke free piston engine using narrow band approach. The life prediction results are worthy for improving the component design at the very early developing stage. This approach is adequate for periodic loading, however, requires very large time records to accurately describe random loading processes. Fatigue damage in conventionally determined from time signals of the loading, frequently in the form of stress and strain. However, there are scenarios when a spectral form of loading is more appropriate. In this case the loading is defined in terms of its magnitude at different frequencies in the form of a Power Spectral Density (PSD) plot. The vibration fatigue calculation can be utilized where the random loading and response are categorized using power spectral density functions and the dynamic structure is modeled as a linear transfer function. This research also investigates the effect of the mean stress on the fatigue life prediction using the random loading. The acquired results indicate that the Goodman mean stress correction method gives the most conservative results with the Gerber and no (zero) mean stress method. It is observed that the compressive mean stresses are beneficial while the tensile mean stresses are detrimental to the fatigue life. The proposed technique is capable of determining premature products failure phenomena. Therefore, this technique is able to reduce cost, time to market, improve the product reliability and finally the user confidence.

FATIGUE LIFE PREDICTION OF ROLLED AZ31 MAGNESIUM ALLOY USING AN ENERGY-BASED MODEL

Fatigue behavior of rolled AZ31 magnesium alloy, which shows an anisotropic deformation behavior due to the direction dependent formation of deformation twins, was investigated by carrying out stress and strain controlled fatigue tests. The anisotropy in deformation behavior introduced asymmetric stress-strain hysteresis hoops, which make it difficult to use common fatigue life prediction models, such as stress and strain-based models, and induced mean stress and/or strain even under fully-reversed conditions; the tensile mean stress and strain were found to have a harmful effect on the fatigue resistance. An energy-based model was used to describe the fatigue life behavior as strain energy density was stabilized at the early stage of fatigue life and nearly invariant through entire life. To account for the mean stress and strain effects, an elastic energy related to the mean stress and a plastic strain energy consumed by the mean strain were appropriately considered in the model. The results showed that there is good agreement between the prediction and the experimental data.

A new on-chip test structure for real time fatigue analysis in polysilicon MEMS

Fatigue test results on 15 μm thick polysilicon specimens are presented and discussed, both quantitatively and qualitatively. The test structure is a newly designed, electrostatically actuated, MEMS device that allows the execution of on-chip fatigue and fracture tests on polysilicon specimens. The experiments have been carried out through a new analog, low-noise and low-perturbing electrostatic position measurement system for capacitive MEMS sensors. The setup allows for a real time monitoring of MEMS position, from which a macroscopic quantity, the elastic stiffness of the specimen, can be continuously evaluated, provided that the applied force is known. The results obtained in the present research put in evidence the decrease of the elastic stiffness during fatigue life before rupture. In addition, the stress amplitude during the load cycles plays a role on the lifetime of the test devices: larger stress amplitudes around a tensile mean stress reduce the fatigue resistance, mainly when a compressive stress is also present, in good agreement with a Wöhler curve.

Influence of hold time on low cycle fatigue behaviour of near alpha titanium alloy IMI 834 at 873K

In the present work, IMI 834, a near α titanium alloy was evaluated for tensile and low cycle fatigue (LCF, with and without hold time) behavior at 873K. Tensile tests were performed at the initial strain rate of 4 × 10−3 s−1 at 873K. Fully reversed, total strain control LCF tests were conducted at total strain amplitude of ± 1.0% at constant strain rate of 4 × 10−3 s−1 at 873K. For LCF tests with dwell, hold time were imposed in tension, compression and tension — compression mode with varied hold times of 60 sec, 120 sec, 180 secs. In LCF tests without dwell, the Coffin-Manson plot showed dual slope behavior at 873K. In LCF tests with dwell, at 873K, tensile, compressive and tensile — compressive hold time tests have shown lower LCF resistance than that of the tests without hold time. Among the three modes of hold times employed, the tensile hold has exhibited the highest LCF resistance followed by tensile — compressive and compressive hold time tests. In the present study, tensile hold introduces compressive mean stresses while the compressive hold introduces tensile mean stresses. Further, the creep effect of stress relaxation was examined at 873K in order to explain the hold time effects.