Torsional Fatigue Loading Research Articles

Effects of predeformation on torsional fatigue in R260 rail steel

Rolling contact loading induces severe plastic deformations and initiates cracks near the rail surface. Prevention of such rolling contact fatigue cracks requires a better understanding about the mechanical behavior of the deformed material in this region. Even so, current rail standards do not consider the plasticity-induced changes to mechanical behavior. They only evaluate the mechanical performance of virgin rail steels under uniaxial loading conditions, which is not representative for the material’s performance after years of service. This study proposes a new method for fatigue life evaluation of deformed material under loading conditions similar to rolling contact loading. Both virgin and predeformed test bars with a circumferential notch were subjected to strain-controlled torsional fatigue loading to evaluate the influence of axial loading, predeformation, and torsional loading direction. Superimposed compressive axial loads increase the fatigue life without affecting the torque response. The predeformed test bars exhibited longer lives, an effect we attribute to the combination of different torque responses, hardening, and anisotropy.

Effect of notch on fatigue performance of marine shaft made of 34CrNi3Mo alloy steel under torsional loading

Joint of flange on a marine shaft subjected to torsional loading was more prone to occur fatigue fracture than the other section on the shaft due to stress concentration effect, so torsional fatigue performance in the vicinity of the joint should be payed more attention in terms of safe navigation of ships. The fatigue analysis of 34CrNi3Mo steel as a novel alloy material with a stress concentration factor of 1.45 under cyclic torsional loads was carried out based on the median S-N experimental method by simplifying the flange and shaft joint into 34CrNi3Mo specimens with u-notch subjected to torsional fatigue loading. The S-N curve and fatigue life of 34CrNi3Mo alloy steel were numerically calculated and compared with experimental fatigue life and the plotted S-N curve. It was found that fitting equation of the S-N curve was close to experimental results. Then, the fatigue performance of 34CrNi3Mo specimens with v-notch at angles of 45°, 90° and 135° was compared by means of the validated numerical method. The fracture macrographs and micrographs of the 14 specimens also were provided to explore the effect of notch on fatigue performance of the 34CrNi3Mo materials and to exploit the failure mechanism of fracture.

Mechanical Behavior of Austenitic Steel under Multi-Axial Cyclic Loading.

Low-nickel austenitic steel is subjected to high-pressure torsion fatigue (HPTF) loading, where a constant axial compression is overlaid with a cyclic torsion. The focus of this work lies on investigating whether isotropic J2 plasticity or crystal plasticity can describe the mechanical behavior during HPTF loading, particularly focusing on the axial creep deformation seen in the experiment. The results indicate that a J2 plasticity model with an associated flow rule fails to describe the axial creep behavior. In contrast, a micromechanical model based on an empirical crystal plasticity law with kinematic hardening described by the Ohno-Wang rule can match the HPTF experiments quite accurately. Hence, our results confirm the versatility of crystal plasticity in combination with microstructural models to describe the mechanical behavior of materials under reversing multiaxial loading situations.

A COMPREHENSIVE STUDY OF FATIGUE CRACK INITIATION AND GROWTH UNDER VERY HIGH CYCLE TORSIONAL FATIGUE LOADING

This paper investigates the fatigue behavior of smooth specimens made of VT3-1 titanium alloy under fully reversed loading conditions. Mathematical modeling results are presented for the fatigue fracture of smooth specimens under high cycle torsional fatigue loading. The fatigue quasi-crack initiation and growth are calculated using a multimode two-parameter model of fatigue damage accumulation. The surface and subsurface quasi-crack initiation under torsional loading is studied. The numerical results are in good agreement with experimental data and can be used to predict the change in crack growth mechanisms under complex multiaxial loadings such as torsion.

Microstructural defects governing torsional fatigue failure of additively manufactured as-built and heat-treated Inconel 718

Nickel-based superalloys, such as Inconel 718 (IN718), have the unique properties of high strength, oxidation, and corrosion resistance, hence necessitating their wide use in aircraft engine structural components, power-generation engines, pressure vessels, high performance automobiles, and rocket engines. Additive manufacturing (AM) of these metal superalloys is an emerging technology, which is being investigated in its capability in driving material microstructural development towards enhanced mechanical performance. With torsional fatigue as an often underlying cause for failure of components within these applications, this study investigates the microstructural defects induced through the additive manufacturing process that have driven Inconel 718 samples to failure when subjected to torsional fatigue loading conditions. As-built and heat-treated Inconel 718 torsional fatigue fracture surfaces were compared through use of a variety of material characterization techniques, to show similarities, or lack thereof, in the defects formed due to the AM process that have contributed to torsional fatigue fracture. Results from both as-built and heat-treated direct metal-laser sintered (DMLS) Inconel 718, manufactured using optimized processing parameters reveal that primary torsional fatigue cracks initiated at surface and sub-surface defects where lack of fusion regions and un-melted powder particles are apparent. Through these analyses, a correlation was made between the fracture mechanics response exhibited by each build orientation/post-processing condition and resulting torsional fatigue properties.

Inverse determination and probability distribution of the mode III strain energy density control radius with an optimized V-notched specimen under torsional fatigue loading

The Strain Energy Density (SED) is a fatigue criterion based on a control volume. This parameter is required for a precise assessment of the fatigue strength of any, especially severely, notched component. A newly developed inverse determination procedure is presented here to precisely determine the mode III (or torsional) control radius. The procedure is then extended to the evaluation of the probability scatter of this length which is properly represented by a skew normal distribution. Experimental results of aluminum alloy 7075-T6 and steel 42CrMo4 + QT are presented, and comparisons are provided between mode I and mode III control radii.

Mixed mode surface crack growth in aluminium alloys under complex stress state

In this study fatigue crack growth tests were carried out on hollow cylindrical specimens, made of D16T and B95AT aluminum alloys (analogue of 2024 and 7075 aluminum), with initial external semi-elliptical surface cracks and undergoing complex stress state. The crack growth behavior of aforementioned materials was studied under cyclic axial tension, pure torsion and combined tension+torsion fatigue loading. Optical microscope measurements and the crack mouth opening displacement (CMOD) method were respectively used to monitor crack length and calculate crack depth. The experimental crack front positions were highlighted by using a beach mark procedure during the tests. The stress strain field along the crack front of semi-elliptical cracks in the cylindrical hollow specimens was assessed by Finite Element Method (FEM) analysis. The stress intensity factors (SIFs) were calculated by the 3D M-integral approach and the distributions of equivalent elastic SIFs along the crack front were used for crack growth rate assessment under mixed mode conditions. As a result, the fracture resistance parameters of aluminum alloys under complex stress state were presented. The simulation of cracks propagation turned out to be consistent with experimental results.

Limited Stress Surface Model for Bending and Torsion Fatigue Loading with the Mean Load Value.

In this study, a linear model of the transformation of the stress amplitude due to the mean value was used. The coefficient of the material sensitivity to cycle asymmetry with consideration of the dependence of this coefficient on the number of fatigue loading cycles is also used. A three-parameter surface model of limited stresses is proposed in this paper. The model is verified using the results of fatigue tests for cyclic bending and torsion under mean loads. The tests are performed for two types of alloy steels—S355J0 and S355J2G1W. Comparison of the allowable stress amplitudes obtained experimentally with those predicted using the proposed model shows errors of no more than 18%, with the area of the surface with the largest error being relatively small.

Estimating the multiaxial fatigue behaviour of C45 steel specimens by using the energy dissipation

Energy-based approaches are adopted in fatigue analysis of materials, components and structures. Several methods consider the thermal energy, which results from energy conversion of the mechanical energy expended by applying cyclic fatigue loadings. By exploiting the self-heating phenomenon, the specific heat energy can be measured during laboratory fatigue tests in a rather simple and efficient way. In previous papers, the specific heat loss has been adopted to correlate fatigue test data relevant to pure axial and pure torsional fatigue loadings. In this paper, it is adopted to correlate successfully the fatigue test data generated under in-phase and out-of-phase axial/torsional multiaxial fatigue loadings.

Cyclic deformation behavior and failure mechanism of S32205 duplex stainless steel under torsional fatigue loadings

Torsional low cycle fatigue tests of ferrite-austenite duplex stainless steel S32205 at various shear strain amplitudes were conducted. The relationship between the evolution of dislocation structures in each constitutive phase and cyclic stress response and cyclic stress-strain curves was thoroughly studied. The surface damage evolution and short cracks nucleation behavior were also discussed. Results show that the cyclic softening occurred at all the strain amplitudes from 0.3% to 1.2% is due to the redistribution and localization of plastic strain and the development of strain transfer between phases, while the formation of regular dislocation cells contributes to achievement of cyclic saturation when the strain amplitude reaches 0.7%. The cyclic stress-strain curves show two-regimes with different cyclic strain hardening rates. As the plastic strain amplitude is smaller than 0.32%, the ferrite and austenite jointly accommodate the plastic strain within material matrix with the coexistence of representative planar slip and incipient wavy slip dislocation configurations in both phases, leading to a low cyclic strain hardening rate. By contrast, the ferrite dominates the plastic deformation with the formation of well-developed low-energy dislocation structures as the plastic strain amplitude is over than 0.32%, resulting in a high cyclic strain hardening rate. Moreover, microstructure observations reveal that the pronounced persistent slip markings in ferrite grains and phase boundaries are the preferential sites for microcrack nucleation and growth.

Fatigue crack propagation in a helicopter component subjected to impact damage

Damage tolerant methodology is increasingly used in aeronautical components, especially due the fact that the Aviation Regulation requires such an assessment in case an accidental damage occurs. At present, there is a strong and actual interest in applying such procedures to helicopter components that are subjected to high frequency cyclic loads. In this paper, an investigation on a damaged transmission shaft for a tail rotor transmission of an actual helicopter has been carried out focusing on the fatigue crack propagation. A complete sequence of experimental tests was performed in order to create an actual ballistic damage and to subsequently check the damage tolerant behaviour. The shaft was damaged by oblique ballistic impact and was subsequently subjected to torsional fatigue loading. During the fatigue cycles several cracks propagated from the ballistic damages. Both of these steps (impact and fatigue loading) were also simulated by a complex modelling approach based on Finite Element Models and fracture mechanics theory. The comparison between the experimental and numerical results shows a good agreement but it underlines the need for a very refined modelling technique capable to replicate all the features associated with the damage in order to reliably simulate the subsequent propagation phase.

Torsional fatigue in bamboo fibers reinforced epoxy resin composites

Natural fibers are low-priced, abundant and renewable. The application of natural fiber to reinforced polymers materials can reduce cost, decrease weight and increase the mechanical properties of the composites. Many studies were carried out in natural fibers reinforced polymer composites using different natural fibers, one of those is bamboo fibers. Nevertheless, torsional fatigue tests have not been applied to predict the mechanical behavior of the bamboo fibers reinforced polymer composites. In this study, bamboo fiber reinforced epoxy resin composites were molded by compression in a rectangular mold. These specimens were machined according to the schematic of thin-walled tubular specimen suggested by ASTM-2207–15 and tested in torsional fatigue loading with R = −1. A mechanical torsion fatigue testing machine was constructed to perform torsion test with constant amplitude of the twist angle. An angle measuring device was constructed to measure the angular displacement in the useful region of the specimens (gage length). Torsional fatigue life curves were plotted for pure epoxy resin, unidirectional and discontinuous bamboo fibers reinforced epoxy resin composites. Pure epoxy resin specimens presented the longest torsional fatigue life and the poorest results were found in discontinuous bamboo fibers composites. The experimental results suggest that the epoxy resin is strongly related to the torsional fatigue behavior of the composite materials. The fracture surface of test specimens often showed that cracks occurred in the interfacial region of the composites.

Numerical study of the effect of torsional fatigue loading on the energy absorption of composite tubes

AbstractA three‐dimensional finite element model is developed to predict the effect of torsional fatigue loading on the energy absorption of unidirectional carbon/epoxy (AS4/3501‐6) composite tubes. Progressive fatigue damage model for fatigue loading and progressive failure model for axial velocity impact are implemented separately in the Abaqus software through user subroutine VUMAT. Each model is validated by the experimental data available in literature and good agreement is observed between the simulation results and experimental data. Then, these two models are sequentially applied to the composite tube with three different layups. The tube is first placed under torsional fatigue loading and a number of predefined loading cycles is applied. During this loading, the mechanical properties of the material are degraded based on sudden and gradual material properties degradation rules. Next, the fatigued tube is placed under axial impact loading. The results show that by increasing the number of fatigue cycles, the tube's ability to absorb energy is first reduced uniformly but in a particular cycle, due to the sudden drop in the shear mechanical properties of the material, the amount of energy absorption drops sharply and the tube loses its ability to absorb energy before it's catastrophic fatigue failure.

Analysis of Fatigue Strain, Fatigue Modulus and Fatigue Damage for the Model Formulation of Concrete Based on Strain Life Approach

Analysis of fatigue strain, fatigue modulus and fatigue damage for the modeling of concrete plays a vital role in the evolution material behaviour which is heterogeneous and anisotropic in nature. The Level-S nonlinear fatigue strain curve, fatigue modulus curve, residual strain curve of concrete in compression, tension, flexure and torsional fatigue loading were proposed using strain life approach. The parameters such as physical meaning, the ranges, and the impact on the shape of the curve were discussed. Then, the evolution model of fatigue modulus was established based on the fatigue strain, fatigue modulus, residual strain and secondary strain evolution model. The hypothesis of fatigue modulus is inversely related with the fatigue strain amplitude. The fatigue evolution of concrete damages the bond between material grains, changed the orientation of structure of molecules and affects the elastic properties resulting in the reduction of material stiffness and modulus by formation of microcracking, macro cracking, cracking and finally damage. This paper presents the fatigue strain life model and analysis of fatigue strain, fatigue modulus and damage parameters of concrete which is capable of predicting stiffness degradation, inelastic deformation, and strength reduction under fatigue loading and experimental results were employed for the validation of the theoretical model.

The effect of mean axial and torsional stresses on the fatigue strength of 34CrNiMo6 high strength steel

The present study consists of a theoretical, experimental and fractographic investigation of the effect of superimposed static axial and shear stresses on the high cycle fatigue behavior of a 34CrNiMo6 high strength steel in quenched and tempered condition (UTS = 1210 MPa), commonly employed in highly stressed mechanical components. The Haigh diagrams for the axial and torsional cases under different values of mean stress were obtained. In both cases, experimental results showed that increasing the mean stress gradually reduces the stress amplitude that the material can withstand without failure. The results of the present tests are compared with the theoretical predictions from Findley, based on the maximum damage critical plane; and the methods of Marin and Froustey, which are energetic based criterions. Froustey’s method shows the best agreement with experimental results for torsional fatigue with mean shear stresses, showing a non-conservative behaviour for the axial fatigue loading case. Macro-analyses and micro-analyses of specimen fracture appearance were conducted in order to obtain the fracture characteristics for different mean shear stress values under torsion fatigue loading.

Influence of mean shear stress on the torsional fatigue behaviour of 34CrNiMo6 steel

This study provides a theoretical and experimental investigation of the effect of static shear stresses on the high-cycle fatigue behaviour of a 34CrNiMo6 high-strength steel under quenched and tempered conditions. Torsion S–N curves under different mean shear stresses were obtained. Experimental results show that an increase in mean shear stress yields a gradual reduction in shear-stress amplitude that the material can withstand without failure. The results for this steel agree well with the Smith’s hypothesis for ductile steels, which states that the effect of the torsional mean stresses on the torsional fatigue limit is negligible as long as the maximum shear stress is within the torsional yield strength. Taking into account the results collected from the literature and the experimental results on torsional fatigue of 34CrNiMo6 steel, an extension of the theory of Crossland is proposed to include the mean-shear-stress effect. Its application to the torsional fatigue case with mean shear stresses can be interpreted in terms of a balance of the energy of distortion. Macro-analyses of the specimen fracture appearance were conducted to obtain the fracture characteristics for different mean-shear-stress values under torsion fatigue loading.

Influence of small defects on the uniaxial and torsional fatigue strength of 17-4PH stainless steel

The influences of small defects on the fatigue properties of 17-4PH stainless steel under uniaxial and torsional loading are investigated. Experiments were performed with different testing techniques (rotating bending, servohydraulic and ultrasonic fatigue testing) in the high cycle and very high cycle fatigue regime. Fatigue limits under cyclic torsional loading, τa, and cyclic axial loading, σa, were determined. The ratio of τa/σa for smooth specimens is in good accordance with the von Mises criterion. This ratio increases in the presence of defects and becomes close to 1 for defects with area larger than 80 µm. The experimental data are evaluated to determine a predictive approach for the fatigue strength under uniaxial and torsional fatigue loadings.

Influences of small defects on torsional fatigue limit of 17-4PH stainless steel

The sensitivity of 17-4PH stainless steel to small defects under torsional fatigue loading condition at a stress ratio of R=−1 is examined in the high-cycle fatigue regime. Fatigue crack initiation and growth behaviors are observed, and fractographic investigations are performed. As a key geometric parameter, area is used to investigate the influence of small defects on torsional fatigue limit. Further, the results are compared to the data obtained in the uniaxial fatigue tests, which allows the effect of biaxial stresses on the surface of the material to be discussed.

High cycle torsional fatigue properties of 17-4PH stainless steel

Sensitivity to small defects under torsional fatigue loading condition is examined in the high cycle fatigue regime. Fatigue crack initiation and small crack growth behaviors were observed during fatigue testing and fractographic investigations were performed. The results are compared to the data obtained in the uniaxial fatigue tests, which allows the effect of biaxial stresses on the surface of material to be discussed. Finally, an approach for predicting the fatigue limit of 17-4PH stainless steel under torsional and tension-compression fatigue loadings is presented.

Determination of the Mechanical Properties of Friction Welded Tube Yoke and Tube Joint

This paper deals with the friction welding of the tube yoke and the tube of the drive shaft used in light commercial vehicles. Tube yoke made from hot forged microalloyed steel and the tube made from cold drawn steel, with a ratio (thickness/outside diameter ratio) of less than 0.1, were successfully welded by friction welding method. Hardness distributions on both sides of the welded joint across the welding interface were determined and the microstructure of the joint was investigated. Furthermore, joint strength was tested under tensile, static torsional, and torsional fatigue loadings. The tested data were analyzed by Weibull distribution. The maximum hardness value along the welded joint was detected as 553 Hv1. The lowest detected tensile strength of the joint was 13% less than the base materials’ tensile strength. The torsional load carrying capacity of the friction welded thin walled tubular joint without any damage was obtained as 4.252,5 Nm in 95% confidence interval. After conducting fully reversed torsional fatigue tests, the fatigue life of friction welded tubular joints was detected as 220.066,3 cycles.