Torsional Fatigue Research Articles

Damage tolerance characterization of carbon fiber composites at a component level: A thermoset carbon fiber composite

This work focuses on the impact damage evaluation of a carbon fiber-reinforced thermoset composite at a component level (beams) as an effort to develop the service strategies for this class of materials. The beams were impact damaged at a variety of energy levels, and the pulse thermography nondestructive evaluation approach was used to characterize the damaged areas. The damaged beams were subjected to compression tests to evaluate their residual properties. As expected, both the beam maximum load and residual stiffness decreased with the increase in damage size. The damage growth rates under different load levels were investigated in fully reversed torsional fatigue tests. The fatigued beams were also characterized for their residual compression properties, which were then compared with those of the unfatigued beams. The results will be used to develop computer-aided engineering models to predict the residual strength and fatigue life of damaged composite components.

Torsional fatigue behavior of wrought and additive manufactured Ti-6Al-4V by powder bed fusion including surface finish effect

Additive manufacturing (AM) is a state of the art technology enabling fabrication of complex geometries, in addition to providing other advantages as compared to the traditional subtractive manufacturing methods. Powder bed fusion (PBF) is one of the most commonly used metal AM processes that uses laser to melt particles on the bed of metallic powder. Ti-6Al-4V is a common alloy made by this process and has applications in many industries, in particular aerospace and medical industries. Understanding mechanical performance of the additively manufactured materials and components for critical load bearing applications is still in early stages. As such components are typically subjected to cyclic loading, fatigue failure is a major consideration in their design. In addition, due to the multiaxial nature of the loading and/or complex geometries manufactured by AM, the state of stress often includes both normal and shear stresses. However, all the studies so far on fatigue behavior of additive manufactured metals have only considered axial loading, resulting in normal stresses. This study is on torsional fatigue behavior producing shear stresses and, therefore, addresses a major gap in understanding the mechanical behavior of additive manufactured metals in general and for PBF Ti-6Al-4V alloy in particular. In this study, thin-walled tubular specimens made of both wrought and AM Ti-6Al-4V were subjected to monotonic as well as cyclic torsional loads to study and compare their shear deformation and fatigue behaviors. Failure mechanisms in different life regimes and the effects of heat treatment and surface finish were also evaluated.

Application of the critical plane approach to the torsional fatigue assessment of welds considering the effect of residual stresses

This study aims to investigate how the welding residual stresses affect the fatigue life of steel tubular joints. A single pass weld with filler material is created on the tubular specimens made of structural steel S355J2H. At first, welding residual stresses are calculated numerically by means of FE simulations. The validity of the results is verified experimentally by means of diffraction measurement techniques. Then, an uncoupled damage model based on the critical plane approach is utilized in order to calculate the fatigue life and the initial crack orientation. The as-welded specimens were subjected to cyclic torsional loading with constant stress amplitudes. The Fatemi-Socie (FS) damage parameter is used which is interpreted as the cyclic shear strain damage modified by the normal stress to include the crack closure effect. The stable portion of welding residual stresses is accounted for by the normal stress term of the model. It was observed that despite the common understandings about the critical weld notches, the crack initiation sites under torsional loading have been shifted from the weld toe and from the surface to the heat affected zone and beneath the surface where high tensile residual stresses exist. Then the initial cracks propagated toward the surface whose orientations were influenced by the presence of compressive residual stresses on the surface.It was generally found that the Fatemi-Socie parameter is capable of torsional fatigue damage assessment of welded tubular specimens which contain residual stresses since this critical plane parameter is based on the maximum shear strain plane.

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.

Effect of HF Welding Process Parameters and Post Heat Treatment in the Development of Micro Alloyed HSLA Steel Tubes for Torsional Applications

The aim of the present study is to investigate the effect of High frequency (HF) Electric resistance welding process parameters and post heat treatment on the torsional fatigue life of micro alloyed HSLA steel tubes. Micro alloyed grades exhibit higher strength and formability owing to the presence of fine recrystallized ferritic grains due to thermo mechanical treatment and presence of alloying elements like Vanadium, Niobium and Titanium. Welded tubular components made of micro alloyed HSLA steel grades are highly emerging and manufacturing them remains quite challenging. Weld bond width, HAZ width and bond angle are the significant factors that directly influences the Weld quality and strength. The effect of key welding parameters like Heat input, welding temperature, squeeze roll pressure, Vee-angle, Vee-length and Impeder diameter on the above mentioned significant factors was analysed. Narrow bond, Minimum HAZ width with pronounced Hour glass pattern and optimum bond angle resulted in superior bond strength and formability of HSLA tubes. Microstructural characterization of the samples was carried out using Light optical microscopy and Scanning electron microscopy. Residual stress was determined using X-ray diffract meter and tube slitting method. Higher tensile residual stress of magnitude 200 MPa was observed in the weld region. Since such high magnitude of tensile residual stress is detrimental to torsional fatigue life, stress relieving of the tubes was carried out at different subcritical temperatures 650°C and 700°C with soaking time of 45 minutes. Without significant drop in the tensile properties, compressive residual stress of magnitude 129 MPa was observed at a particular stress relieving cycle. As an effect of stress relieving heat treatment below Ac1 temperature, there is a significant improvement in the Torsional fatigue life of the HSLA steel. Thus, High Frequency welded micro alloyed HSLA steel tubes with enhanced torsional fatigue performance were successfully developed.

Study of the influence of ring misalignment in rolling bearings on frictional torque and the fatigue life of supports

The influence of ring misalignments on the torsional characteristics and fatigue life of rolling bearings was investigated. It was shown that ring misalignment increased frictional torque in rolling bearings, especially with the radial and axial forces. Ring misalignment in the radial-thrust bearings has a controversial influence on fatigue life of supports. Fatigue life increases at small misalignments angles and decreases with an increase in the misalignment angle.

Analysis of Stress and Strain of Fatigue Specimens Localised in the Cross-sectional Area of the Gauge Section Testing on Bi-axial Fatigue Machine Loaded in the High-cycle Fatigue Region

Fatigue is a progressive, localized, permanent structural change that occurs in materials subjected to fluctuating stresses and strains that may result in cracks or fracture after a sufficient number of fluctuations. Fatigue fractures are caused by the simultaneous action of cyclic stress, tensile stress and plastic strain. If one of these three acting phenomena is not present, fatigue cracking will not initiate and propagate. Small geometrical changes in the specimens, or specifically, test conditions by invariable angular displacement cannot significantly allow analytical calculation of stresses and strains. Therefore a numerical analysis of stresses generated through bending and torsion fatigue specimens has been performed using available FEM-program ADINA. Computer simulation has been performed on fatigue specimens made of high-strength steel DOMEX 700 MC D.

A Plastic Strain and Stress Analysis of Bending and Torsion Fatigue Specimens in the Low-cycle Fatigue Region Using the Finite Element Methods

The assessment of a reliable S-N curve requires an accurate determination of stresses involved. If the stress state is complicated like in a plastic field of deformation the stress for a neck specimen may not always be calculated using formulae available in standard handbooks. Furthermore, the stress may vary from one point to another in a manner which is difficult to predict. This situation arises for instance during bending, torsion and also combined of fatigue specimens loading. In this article a numerical analysis of stresses generated in bending and torsion fatigue specimens has been performed employing the commercially available FEM program ADINA. Computer simulation has been performed on fatigue specimens from high-strength steel DOMEX 700 MC D.

Quantitative Evaluation of the Flaking Strength of Rolling Bearings with Small Defects: (Part 2: Evaluation of the Flaking Strength of Rolling Bearings with Small Drilled Holes, based on the Stress Intensity Factor)

Rolling contact fatigue (RCF) tests were conducted on rolling bearings, with holes micro-drilled at the mid-point of the tracks. In all of the RCF tests, fatigue cracks initiated at the edge, near the base of the drilled holes, later propagating by shear-mode. Even in the un-flaked specimens tested up to N = 2×108 cycles, short fatigue cracks were discovered at the edges. Using the stress intensity factor (SIF) range, as calculated for the initial defect size, fatigue life data were uniformly gathered inside a narrow band, irrespective of the diameters and depths of the holes. In addition, it was determined that the crack-size dependency of the threshold SIF range, well-known for Mode I fatigue cracks, also exists for Mode II fatigue cracks, as produced after rolling contact. The values of the threshold SIF range obtained by the RCF tests were in good agreement with those obtained in the torsional fatigue tests under static compression.

Development of ultrasonic torsional fatigue testing machine with mean torsional stress

Development of ultrasonic torsional fatigue testing machine with mean torsional stress

The influence of static crack-opening stress on the threshold level for shear-mode fatigue crack growth in bearing steels

An investigation was conducted into the influence of statically-applied, mode I, crack-opening load on the threshold condition for propagation of a shear-mode fatigue crack in a bearing steel. Torsional fatigue test was carried out at an R of −1 using a hollow cylindrical specimen into which a semi-elliptical, small slit was axially introduced. A static axial compressive stress was simultaneously applied to suppress crack branching. A coplanar, shear-mode, non-propagating fatigue crack emanating from the slit was attained by appropriate control of shear stress amplitude. Internal pressure was then applied to generate a hoop stress as a static crack-opening stress, σθ static. Consequently, the threshold shear-mode stress intensity factor range, ΔKτth, was significantly decreased with increase of the static mode I stress intensity factor. To further understand the contribution of σθ static to the reduction in ΔKτth, microstructural observations for the cross-sections of a non-propagating crack were conducted using a scanning electron microscope in conjunction with the electron backscatter diffraction analysis. The results revealed that the excess loading of σθ static accounts for the change in the crack-path, resulting in a further reduction in ΔKτth.

Cyclic deformation and fatigue behavior of carburized automotive gear steel and predictions including multiaxial stress states

The fatigue behavior of carburized components such as automotive transmission gears is very complex due to hardness and microstructure difference, residual stresses and multi-axial stress states developed between the case and the core and/or at stress concentrations. In addition, automotive gears in service, commonly used in helical type, are actually subjected to complex stress conditions such as bending, torsion, and contact stress states. This study presents experimental and analytical results on deformation behavior of carburized steels, widely used in automotive gears, under cyclic stress conditions including axial, torsional and combined axial-torsion loadings. Axial fatigue and rotating bending fatigue, as well as torsional fatigue and in-phase axial-torsional fatigue tests are also included. Predictions of cyclic deformation and fatigue behaviors of the carburized steel with two-layer model are compared with experimental results. Predicted results with simple two-layer model for the cyclic deformation and fatigue behaviors were comparatively similar to the experimental data.

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.

Crack initiation life in notched steel bars under torsional fatigue: Synthesis based on the averaged strain energy density approach

In a recent contribution by Tanaka, the fatigue behaviour of notched bars made of austenitic stainless steel, SUS 316L, and carbon steel, SGV 410, characterized by different values of the notch tip radius was investigated under torsion loading. Tanaka monitored both fatigue crack initiation and propagation phases by means of the potential drop technique. The crack initiation life is correlated here to the depth of the initiated fatigue crack by means of calibration curves derived from electrical finite element (FE) analyses. In the present contribution, the approach based on the strain energy density (SED) averaged over a structural volume embracing the notch tip is employed to re-analyse the original experimental results of each material, by taking into account the crack initiation life, in order to exclude all extrinsic mechanisms acting during the crack propagation phase, i.e. sliding contact, friction and meshing between crack mating surfaces.

Discussion: “A New Approach for Fatigue Damage Modeling of Subsurface-Initiated Spalling in Large Rolling Contacts” (Walvekar, A. A., Paulson, N., Sadeghi, F., Weinzapfel, N., Correns, M., and Dinkel, M., 2016, ASME J. Tribol. 139(1), p. 011101)

Professor Sadeghi and his coworkers have been developing a method to estimate the rolling contact fatigue life of rolling bearings in recent years using a continuum damage mechanics (CDM) approach. Development of the method has involved progression from a defect-free and inclusion-free model to ones incorporating grain boundary cracks and inclusions.The most recent paper on this topic is authored by Walvekar et al. [1]. In Sec. 2.2, the authors stated “It was hypothesised that failure mechanism for torsional fatigue and rolling contact fatigue are equivalent because the mechanism for damage accumulation is similar for both types of fatigue phenomena.” It is necessary to verify whether such a hypothesis is correct or not but this has not been carried out within the paper.This hypothesis was postulated by Raje and Sadeghi in 2009 in a paper published in the IMechE Journal of Engineering Tribology entitled “Statistical Numerical Modelling of Sub-Surface Initiated Spalling in Bearing Contacts” [2]. In Sec. 3, the authors stated “It is hypothesised that since fatigue damage under rolling contact conditions is caused purely by the action of shear stresses, the mechanism of failure is similar to that prevalent in torsional fatigue. Thus, by knowing the stress-life relationship for a material in torsional fatigue, the fatigue damage parameters can be extracted.”Torsional fatigue data on SAE 52100 bearing steel from Styri were used to provide the shear stress to failure [3], but Styri stated that in about 90% of cases, failures start below the surface, presumably at inclusions or other defects that act as stress concentrating features. However, the model being validated by Raje and Sadeghi is for a material free of defects, voids, or inclusions, while the steel used by Styri would be of 1940 s pedigree but with no statement of its cleanliness.Would the authors comment upon this observation, particularly as, intuitively, the torsional fatigue life of a pristine steel would be expected to be much longer than the one containing defects or inclusions while failures would be surface-initiated?Furthermore, results from the CDM model of pristine steel are compared to L10 bearing lives measured by Lundberg and Palmgren for NU 209 cylindrical roller bearings. The authors present a method in Sec. 4.3 for the conversion of L10 life in shaft revolutions to inner race stress cycles. A comparison of the model results and the bearing lives of Lundberg–Palmgren is then presented. The authors stated that “Stress-life results for this bearing are shown in Fig. 7 and are found to be in good agreement with stress-life results from the current model.”Would the authors comment upon this conclusion, taking into account that the results from the CDM model of pristine steel are being compared to bearings of 1940 s pedigree with no statement of cleanliness?In Sec. 4.2, the authors claim that the model is found to fit within the range of experimental data for cylindrical roller bearings reported by Harris and Barnsby [4]. Reference to this data appears to suggest that shaft revolutions have been plotted as opposed to stress cycles in Fig. 7. Would the authors confirm whether this is the case or not?Intuitively, a defect-free and inclusion-free model should predict lives that are much longer than both the experimental data from Harris–Barnsby and Lundberg–Palmgren. Once defects such as inclusions are introduced into the model, comparisons may then be made with the experimental data. It is necessary to model the size, number, shape, and composition of the inclusions (and other defects, such as carbide stringers) within the steels tested by Harris–Barnsby (1980 s/1990 s pedigree) and Lundberg–Palmgren (1940 s pedigree) in order to carry out such a comparison. Only at this point the claims can be made for validation (or otherwise) of the model. Would the authors comment upon this observation?It also appears that the CDM model has not been validated at lower contact stresses. It may be difficult to validate the model at contact stresses below 2200 MPa (the main region of interest for industrial machines) for the following reasons:Would the authors comment upon validation of the model at lower contact stresses?

Rolling contact fatigue of case carburized steels

Case carburized steels are widely used in high performance ball and rolling element bearings. They are characterized by the hardened exterior and gradient in the material properties as a function of depth. In this investigation, an elastic-plastic finite element model based on micro-indentation tests was developed to investigate the rolling contact fatigue of case carburized steels. A series of micro-indentation tests were conducted to obtain the hardness gradient in the case carburized 8620 steel. The results demonstrated that the hardness varies linearly from the surface to the core of the material. The finite element modeling approach employs Mises based plasticity model with kinematic hardening to incorporate the effect of material plasticity. The hardness gradient in the material was modeled by changing the yield strength as a function of depth. Linear relationship between hardness and yield strength was assumed. The FE model was coupled with continuum damage mechanics approach to capture material degradation due to fatigue damage. It considers both; stress and accumulated plastic strain based damage evolution laws for fatigue failure initiation and propagation. The residual stress distribution due to carburization process was modeled by modifying the damage evolution law. Material dependent parameters used in the damage evolution laws were determined using the SN results for torsional fatigue of the bearing steel. The effects of topological randomness in the material microstructure are accounted in the model through the use of Voronoi tessellations.The model was used to compare the rolling contact fatigue (RCF) lives of through hardened and case carburized bearing steel with different case depths at contact pressures ranging from 2 to 3.5GPa. The effect of residual stress distribution on RCF lives was also investigated. The results show that there is an optimum case depth for which maximum RCF lives can be attained. The spall shapes and the depth below the surface where damage initiates were found to be dependent on the case depth. The model was also used to study the effect of initial material imperfections. The fatigue lives and their dispersion quantified by Weibull slopes obtained from the model correlate well with the experiments.

Averaged strain energy density-based synthesis of crack initiation life in notched steel bars under torsional fatigue

The torsional fatigue behaviour of circumferentially notched specimens made of austenitic stainless steel, SUS316L, and carbon steel, SGV410, characterized by different notch root radii has been recently investigated by Tanaka. In that contribution, it was observed that the total fatigue life of the austenitic stainless steel increases with increasing stress concentration factor for a given applied nominal shear stress amplitude. By using the electrical potential drop method, Tanaka observed that the crack nucleation life was reduced with increasing stress concentration, on the other hand the crack propagation life increased. The experimental fatigue results, originally expressed in terms of nominal shear stress amplitude, have been reanalysed by means of the local strain energy density (SED) averaged over a control volume having radius R0 surrounding the notch tip. To exclude all extrinsic effects acting during the fatigue crack propagation phase, such as sliding contact and/or friction between fracture surfaces, crack initiation life has been considered in the present work. In the original paper, initiation life was defined in correspondence of a 0.1÷0.4-mm-deep crack. The control radius R0 for fatigue strength assessment of notched components, thought of as a material property, has been estimated by imposing the constancy of the averaged SED for both smooth and cracked specimens at NA = 2 million loading cycles.

A comparative study of finite element methodologies for the prediction of torsional response of bladed rotors

The prevention of torsional vibration-induced fatigue damage to turbo-generators requires determining natural frequencies by either field testing or mathematical modelling. Torsional excitation methods, measurement techniques and mathematical modelling are active fields of research. However, these aspects are mostly considered in isolation and often without experimental verification. The objective of this work is to compare one dimensional (1D), full three dimensional (3D) and 3D cyclic symmetric (3DCS) Finite element (FE) methodologies for torsional vibration response. Results are compared to experimental results for a small-scale test rotor. It is concluded that 3D approaches are feasible given the current computing technology and require less simplification with potentially increased accuracy. Accuracy of 1D models may be reduced due to simplifications but faster solution times are obtained. For high levels of accuracy model updating using field test results is recommended.

Development of Bending and Torsion Fatigue Testing Machine for Multiaxial Non-Proportional Loading

This study presents a newly developed multiaxial high cycle fatigue testing machine which can load a cyclic bending loading and a reversed torsion loading onto an hour-glass shaped solid bar specimen. This testing machine can perform the fatigue tests with a high frequency under a proportional and a non-proportional loading conditions. In the non-proportional loading, principal directions of stress and strain are changed in a cycle. In the testing machine, the loading is generated by centrifugal force caused by the revolving weights attached to rotational wheels. The maximum frequency of the testing machine is 50Hz. A material tested was a type 304 stainless steel. In the test, two types of loading paths are employed, a proportional loading and a non-proportional loading. The former is a cyclic bending loading and the latter a combining cyclic bending and reversed torsion loading in the developed testing machine. In this study, an applicability of the testing machine is evaluated by carrying out the tests under these loading conditions.

Biomechanical Study of the Fixation Strength of Anteromedial Plating for Humeral Shaft Fractures.

Background:Open reduction and internal fixation with plate and screws are the gold standard for the surgical treatment of humeral shaft fractures, this study was to compare the mechanical properties of anteromedial, anterolateral, and posterior plating for humeral shaft fractures.Methods:A distal third humeral shaft fracture model was constructed using fourth-generation sawbones (#3404, composite bone). A total of 24 sawbones with a distal third humeral shaft fracture was randomly divided into three Groups: A, B, and C (n = 8 in each group) for anteromedial, anterolateral, and posterior plating, respectively. All sawbones were subjected to horizontal torsional fatigue tests, horizontal torsional and axial compressive fatigue tests, four-point bending fatigue tests in anteroposterior (AP) and mediolateral (ML) directions and horizontal torsional destructive tests.Results:In the horizontal torsional fatigue tests, the mean torsional angle amplitude in Groups A, B, and C were 6.12°, 6.53°, and 6.81°. In horizontal torsional and axial compressive fatigue tests, the mean torsional angle amplitude in Groups A, B, and C were 5.66°, 5.67°, and 6.36°. The mean plate displacement amplitude was 0.05 mm, 0.08 mm, and 0.10 mm. Group A was smaller than Group C (P < 0.05). In AP four-point bending fatigue tests, the mean plate displacement amplitude was 0.16 mm, 0.13 mm, and 0.20 mm. Group B was smaller than Group C (P < 0.05). In ML four-point bending fatigue tests, the mean plate displacement amplitude were 0.16 mm, 0.19 mm, and 0.17 mm. In horizontal torsional destructive tests, the mean torsional rigidity in Groups A, B, and C was 0.82, 0.75, and 0.76 N·m/deg. The yielding torsional angle was 24.50°, 25.70°, and 23.86°. The mean yielding torque was 18.46, 18.05, and 16.83 N·m, respectively.Conclusions:Anteromedial plating was superior to anterolateral or posterior plating in all mechanical tests except in AP four-point bending fatigue tests compared to the anterolateral plating group. We can suggest that anteromedial plating is a clinically safe and effective way for humeral shaft fractures.