Torsional Fatigue Life Research Articles

Investigating the effects of preliminary overloading and fatigue on the mechanical strength and fractographic characteristics of CuSn7Zn4Pb7 bronze alloy fractures

This study presents the outcomes of experimental research designed to explore the effects of plastic deformation on the tensile strength and torsional fatigue life of the CuSn7Zn4Pb7 bronze alloy. The primary objective was to understand how plastic deformation impacts these critical mechanical properties of the alloy. The study aimed to determine the nature of damages and attempt to systematise them. Various combinations of loads and material microstructure play a decisive role in the propagation of fatigue cracks. Therefore, in the study, the microstructure of the analysed material, the determination of its chemical composition, and its compliance with relevant material standards were presented. Additionally, microscopic images of fracture surfaces, along with fatigue crack analysis and determining the presence of the fatigue and residual zones, were provided.

Fatigue Life Data Fusion Method of Different Stress Ratios Based on Strain Energy Density.

To accurately evaluate the probabilistic characteristics of the fatigue properties of materials with small sample data under different stress ratios, a data fusion method for torsional fatigue life under different stress ratios is proposed based on the energy method. A finite element numerical modeling method is used to calculate the fatigue strain energy density during fatigue damage. Torsional fatigue tests under different stresses and stress ratios are carried out to obtain a database for research. Based on the test data, the Wt-Nf curves under a single stress ratio and different stress ratios are calculated. The reliability of the models is illustrated by the scatter band diagram. More than 85% of points are within ±2 scatter bands, indicating that the fatigue life under different stress ratios can be represented by the same Wt-Nf curve. Furthermore, P-Wt-Nf prediction models are established to consider the probability characteristics. According to the homogeneity of the Wt-Nf model under different stress ratios, we can fuse the fatigue life data under different stress ratios and different strain energy densities. This data fusion method can expand the small sample test data and reduce the dispersion of the test data between different stress ratios. Compared with the pre-fusion data, the standard deviations of the post-fusion data are reduced by a maximum of 21.5% for the smooth specimens and 38.5% for the notched specimens. And more accurate P-Wt-Nf curves can be obtained to respond to the probabilistic properties of the data.

Effect of artificial aging time on torsional fatigue life and cyclic behavior of AA6351 aluminum alloy and evaluation of estimation methods

AbstractThe effects of artificial‐aging time on monotonic properties and torsional fatigue of AA6351 aluminum alloy were studied in this paper. Fatigue tests were carried out by the strain‐controlled condition. Monotonic and cyclic torsional behavior, fatigue life, and estimation methods were verified. Results showed the distance between monotonic and cyclic curves progressively decreased as aging time increased from 1 to 2 and 6 h at 170°C. The yield strength values were subsequently 74.5, 110.7, and 142.5 MPa for monotonic torsion and 127, 145, and 160 MPa for cyclic torsion test (half‐life). Alloy in all aging times showed similar fatigue life in high cycle (N f > 105 cycles), and time 1 h, longer fatigue life in low cycle (Nf < 104 cycles). All specimens presented cyclic hardening at strain amplitudes ranges tested. The estimation methods showed good prediction for the fatigue parameters.

Influence of plastic deformations on both yield strength and torsional fatigue life of non‐ferrous alloys

AbstractThe present paper is aimed to experimentally investigate the influence of a plastic deformation on both yield strength and torsional fatigue life of a CuZn40Pb2 leaded brass alloy and a 6082‐T6 aluminum alloy. Two types of preloading are considered, that is, (i) a cyclic torsion (cyclic preloading) and (ii) a monotonically increasing tension (static preloading). More precisely, for each of the above alloys, different both numbers of loading cycles and maximum values of the static preloading are considered. Moreover, an in‐depth fracture surface analysis on the failed specimens is performed, and fracture mechanisms at different scale lengths summarized.

Investigation of the similarity between physical tests and fatigue simulation of flange yoke made of C45 E material used in cardan shafts

AbstractThis study is focused on experimental and numerical estimation of the fatigue life of a flange yoke. The material's stress‐life (fatigue) curve (S−N curve) for axial loading is constructed using specimens extracted from actual flange yokes. The torsional fatigue lives of components are determined by torsional fatigue tests of the complete cardan shafts. Simulation of the cardan shaft model including the flange yoke is carried out in Catia V5 R6 2016 software, which is then transferred to Altair Hyperworks 2017 software for the stress analyses. To predict the number of cycles to failure, the results are transferred into nCode 2018 DesignLife analysis module. An aim is to employ the stress‐life curves as input in numerical calculations and finite element analyses to minimize the costly and time‐consuming experimental work. The results show that physical testing and analysis results are in accordance when S−N curve of actual component material, as well as surface roughness factors measured from real component surface affecting fatigue life are incorporated into the analysis.

Optimal Design and Research on the Structure of Tripod Constant Velocity Universal Joint

In order to reduce the problems of wear between the internal structures of the universal joints and short service life, a new track contact structure was designed based on the original type of universal joint structure, and a mechanical model of the structure was established. In the ANSYS Workbench, the material properties, contact pair settings, universal joint force and other parameters are analyzed, the contact stress changes between the original structure and the optimized structure are studied, and the torsional fatigue life experiment is carried out in conjunction with the experimental workbench. The results show that the optimized new structure can effectively reduce wear and increase durability in the service process, thus extending its service life.

A plastic strain energy method exploration between machined surface integrity evolution and torsion fatigue behaviour of low alloy steel

To explore the evolution mechanism of multistage machining processes and torsional fatigue behaviour based on strain energy for the first time and provide process optimization of axis parts of low alloy steel for service performance, four multistage machining processes were applied to the 45CrNiMoVA steel, including the Rough Turning process (RT), RT+ the Finish Turning process (FRT), FRT+ the Grinding process (GFRT) and RT+ the Finish Turning process on dry cutting condition (FRT0). The result showed that the FRT process’s average low-cycle torsional fatigue life increased by 50% when it evolved from the RT process. The lower surface roughness of Ra 1.3 μm caused the total strain energy to increase by 163.8 Pa mm/mm instead of the unchanged strain energy density, and the crack feature evolved from some specific bulges to flat shear plane characteristics. When the GFRT process evolved from the FRT process, its average fatigue life increased by 1.45 times, compared with the RT process. Plastic strain amplitude decreased by 21%, and the strain energy density decreased by 4% due to more considerable compressive residual stress (−249 MPa). Plastic deformation layer depth had a consistent tendency with surface roughness. In this paper, surface integrity evolutions on cyclic characteristics and fatigue behaviour have also been explained. A fatigue life prediction model based on the energy method for machined surface integrity is proposed.

Torsional Fatigue Life Prediction of 30CrMnSiNi2A Based on Meso-Inhomogeneous Deformation.

In this paper, torsional fatigue failure of 30CrMnSiNi2A steel which exhibited non-Masing behavior was studied under different constant shear strain amplitudes, using thin-walled tubular specimens. The relationship between shear fatigue and the evolution of meso-deformation inhomogeneity and the prediction method of the torsional fatigue life curve were investigated. Shear fatigue of the material under constant amplitude was researched by numerical simulation with reference to tests, by using crystal plasticity of polycrystalline representative volume element (RVE) as the material model. Considering the non-Masing behavior of material, when determining the parameter values of the crystal plasticity model the correlation between these parameters and strain amplitude was taken into account. The meso-deformation inhomogeneity with increments in the number of cycles was characterized by using the statistical shear strain standard deviation of RVE as the basic parameter. Considering the effect of strain amplitude on fatigue damage, ratio cycle peak stress/yield stress was taken as the weight to measure the torsional fatigue damage and an improved fatigue indicator parameter (FIP) to measure the inhomogeneous deformation of the material was proposed. The torsional fatigue life curve of 30CrMnSiNi2A steel was predicted by the critical value of the FIP and then the result was confirmed.

A novel thin-film image binarization method to detect nanofiller dispersibility for improving the mechanical performance of epoxy/polybenzoxazine laminate nanocomposites

Developing novel methods to detect and enhance the dispersibility of graphene nanofillers is critical for overcoming the limitations of polybenzoxazine (PBZ) resins, including difficulties in processing, the requirement of large amounts of solvents during sample preparation, and low fracture toughness. In this study, an epoxy resin was used to replace the solvents in PBZ preparation. Methylene-diphenyl-diisocyanate-grafted graphene nanosheets or multi-walled carbon nanotubes were incorporated to improve the mechanical strength and torsional fatigue life of carbon-fiber-reinforced polymer (CFRP) based on the PBZ resin. A novel thin-film image binarization method was developed to easily measure and assess the dispersibility of nanofillers in the nanocomposites at the macroscale. The effect of nanofiller dispersibility on the mechanical properties was systemically discussed. The results indicated that the dispersibility of the nanofillers and mechanical properties can be significantly improved by (1) taking advantage of the low viscosity and high toughness of Epoxy and (2) adjusting the sequence of sample preparation based on changes in the rheological behavior. These improvements ultimately extend the torsional fatigue life of CFRP and thus its applicability.

Influence of pre-torsion angles on torsion fatigue properties of 45CrMoVA steel bars

45CrMoVA steel bar specimens were pre-twisted at different angles (θpre) ranging from 8.3° to 16.3°. Torsion fatigue properties of the pre-torsion specimens were investigated. The results indicate that the torsion fatigue life of the specimens increases first, and then decreases with increasing θpre. A model was established to predict torsion fatigue life for the pre-torsion shaft components, and the desired θpre of 11.4° corresponding to the longest fatigue life for the pre-torsion 45CrMoVA steel bars was obtained. It is expected that the model may provide a guideline for the pre-torsion process of the steel shaft parts.

Effect of Surface Condition on the Torsional Fatigue Behaviour of 20MnCr5 Steel

Torsional fatigue behaviour of steel is influenced by various significant factors on the surface of steel such as the stress state, the metallurgical conditions and the surface roughness etc. This research presents the results of the studies conducted on the torsional fatigue life of steel for different surface stresses, conditions and microstructures. Based on the results, inferences were derived out of the factors and conditions which are instrumental in increasing the fatigue performance. This research is done with the purpose of increasing the fatigue performance of power train shafts processed through vacuum carburizing followed by second tempering. The fatigue tests were conducted using a bi-directional torsional cyclic loading in a MTS make torque testing machine. Various researches has been conducted in this paper to find out the impact of surface roughness, second tempering, inter granular oxidation and carbon case depth on the transmission shafts. The existence of surface retained austenite has not yielded a notable enhancement in fatigue performance in the power train shaft whereas existence of martensite with minimum fraction of retained austenite enhanced the fatigue performance significantly from 12,000 to 35,000 cycles on ± 3100 N m torque load.

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.

Comparative and assessment study of torsional fatigue life for different types of steel

Different types of steel specimens were tested using low cycle torsional fatigue tests to evaluate the torsional behavior. During previous years many authors have developed empirical relationships related to stress amplitude with the life of failure in many types of steel materials. Studies continue to find the best experimental relationships for different subjects. In this study two main problems were considered: torsional fatigue study and comparing the behavior of different steel materials under the influence of torsional fatigue. The effect of temperature on the properties of these substances was also studied. A comparison and evaluation of torsional fatigue for different types of steel were found in this study. Three groups of steel specimen were selected for the present investigation, these included low carbon steel AISI 1020, stainless steel AISI 316L, and cold worked stainless steel AISI 304H. The tests were carried out for each group of the steel specimen using a fatigue machine under fully reversed low cycle at ambient temperature and 100 °C. The temperature range was chosen from room temperature to 100° C because the low carbon steel AISI 1020 material showed high ductility above 100 °C. The shear strain amplitude applied was selected between the max. and min. values of 0.18 and 0.02 respectively. A comparison was carried out between the three steel groups at ambient temperature, it was noticed that the ratio of life to failure for both AISI steels 316L and AISI 304H with respect to AISI 1020 showed an increase of 4 and 2.3 times respectively. Also, the ratio of life to failure showed an increase of 4 and 3.5 times respectively at 100 °C. That is mean the ratio of life to failure for AISI steel 316L with respect to AISI 1020 has no effect with the temperature change because their cycles of life have been affected in the same manner. AISI 304H showed a good withstand to the temperature change because the ratio of life to failure with respect to AISI 1020 has been increased.

Rate-dependent transformation ratcheting-fatigue interaction of super-elastic NiTi alloy under uniaxial and torsional loadings: Experimental observation

To investigate the interaction between the rate-dependent transformation ratcheting and fatigue failure of super-elastic NiTi shape memory alloy (SMA) thin-walled tubes, uniaxial and torsional stress-controlled fatigue tests were conducted at various loading rates. The experimental results show that the uniaxial transformation ratcheting is more obvious than the torsional one and the torsional fatigue lives are significantly longer than the uniaxial ones, which imply that a more obvious transformation ratcheting leads to a shorter fatigue life. The rate-dependent transformation ratcheting and fatigue failure of super-elastic NiTi SMA can be attributed to the significant thermo-mechanical coupling effect.

Analysis of loading history influence on fatigue and fracture surface parameters using the method of induction trees

In fatigue life testing under various loading conditions, researchers observe the profile, surface and morphology of materials. In this study authors research the fatigue life of material and the surface fracture geometry. Areal field and fractal based characterisation are evaluated for the whole fracture surfaces. Results of this test were correlated to notch geometry and loading conditions. It was confirmed, for notched specimens, that the change from torsion to proportional bending with torsion fatigue life increase significantly, the same as changing loading from bending with torsion to bending. The measurement device was equipped with a motorised nosepiece using five dedicated microscopic objective lenses from 2.5× to 100× magnification. This paper presents the application of the induction tree method for analysis of loading history influence on fatigue and fracture surface parameters. In a decision tree, nodes store tests checking values of example attributes and leaves store categories assigned to them. For each of possible test results, there is one branch coming from a node to a subtree. In this way, it is possible to represent any attributes of the hypothesis admissible for a given set. Analysis of selected parameters will estimate their impact on the surface structure.

Preparation of CFRP with modified MWCNT to improve the mechanical properties and torsional fatigue of epoxy/polybenzoxazine copolymer

This study proposes a novel method for preparing a high-performance laminated nanocomposite that simultaneously offers low weight, high strength, long material life, high weatherability, and high environmental friendliness. 4,4-Methylene diphenyl diisocyanate (MDI) was grafted onto multiwall carbon nanotube (MWCNT) surfaces, and hot-compression exhaust method was used to prepare nanocomposites and carbon-fiber-reinforced polymer (CFRP) composites, to improve the dispersivity of MWCNTs in the matrix while reducing interlaminar defects in CFRP, and thereby, enhance the mechanical strength and torsional fatigue life of the material. The experimental results showed 11% increase in storage modulus, with the glass transition temperature increasing from 102 °C to 158 °C. The drop-weight impact test and C-scan results indicated that the hot-compression exhaust method effectively constricted the expansion caused by delamination and damage through denser and tighter bonding between laminates of prepreg cloth. The torsional fatigue strength was also enhanced, with the average fatigue life increased more than 20 times.

An extension research on the theory of critical distances for multiaxial notch fatigue finite life prediction

Based on the theory of critical distances (TCD), a new multiaxial notch fatigue life prediction method is proposed in this paper. Firstly, inspired by the means for determining the critical distance of fatigue limit shown in Kitagawa and Takahashi’s diagram, a new measure is proposed to extend the means to the finite life interval. Then, by combining this new measure and the Sih et al. mixed mode fracture criterion, the relationship between axial and torsional notch fatigue lives can be established. Thus, torsional fatigue life can be calculated based on the axial data. Furthermore, on the basis of these obtained data and the modified wöhler curve method (MWCM), the multiaxial notch fatigue life can be estimated. As with the original TCD method, the present method preserves the advantage of effective computation through the so-called point method (PM) and linear elastic stress analysis. However, the new method can more fully takes into account the multiaxiality effect by considering both axial and torsional fatigue damage contribution, which is consistent with the thought of MWCM for plain fatigue assessment.

Torsional fatigue with axial constant stress of oligo‐crystalline 316L stainless steel thin wire

AbstractA series of symmetric torsional fatigue with axial constant stress tests, a kind of multiaxial fatigue test, was conducted on oligo‐crystalline 316L stainless steel thin wire, which was less than 3.5 grains across diameter of 200 μm. The material presents significant cyclic hardening under symmetric torsion cycling, and hardening is more obvious with the increasing shear strain amplitude. However, symmetric torsional cycle with constant axial stresses tests characterize rapid initial hardening and then gradually softening until fatigue failure. The axial stress has a great effect on torsional fatigue life. Fractography observation shows a mixed failure mode combined torsional fatigue with tensile strain because of axial tensile stress. A newly proposed model with axial stress damage parameter is used to predict the torsional fatigue life with constant axial stress of small scale thin wire.

Axial-torsional high-cycle fatigue of both coarse-grained and nanostructured metals: A 3D cohesive finite element model with uncertainty characteristics

In this study the combined axial–torsional fatigue life and damage evolution of both coarse-grained (CG) and nanostructured metals are modeled by a 3D cohesive finite element method with uncertainty characteristics. To account for the random nature of metal fatigue, we combine the Monte Carlo simulation with the three-parameter Weibull statistical distribution function. For both CG and nanostructured metals, we find that the axial load levels have greater effects than random fields on the amplitude of specimen rotation. Compared with the CG metals, the nanostructured metals are found to exhibit an improved fatigue resistance, for the reason that their damage process initiates from the subsurface beneath the nanograined layer and then extends to the exterior surface. Good agreements between the numerical results and experimental data are also observed. It shows the applicability of the 3D cohesive finite element method for the analysis of damage evolution and prediction of fatigue life in these two classes of metals.

Design of an ultra-high torque double shoulder drill-pipe tool joint for extended reach wells

Drill-pipe tool joints in extended reach wells often suffer a shear failure. In view of this, an ultra-high torque double-shoulder pipe joint was designed according to the deformation compatibility relation of the drill-pipe tool joint under torque. It is structurally characterized by long primary and secondary shoulders, small thread taper and large fillet radius of bottom tooth. First, a 3D numerical simulation model was established for this type of joint, named the XSJ joint here, based on the principle of virtual work, the Von Mises yield criterion and the nonlinear contact theory. Second, orthogonal optimization was performed on its key structural parameters by means of the orthogonal optimization method. The optimal combination of key structural parameters of the XSJ joint is taper 1:16, thread pitch 6.55 mm, guiding surface angle 29°, bearing surface angle 28°, and tooth height 3.755 mm. Finally, the bearing performance and fatigue performance of this tool joint and the API tool joint were calculated and compared using the Simulia Abaqus fe-safe software. Compared with the API tool joint, the XSJ joint is better, and its tensile strength, torsion strength, bending strength and compression strength increase by 10.65%, 62.5%, 2.75% and 52%, respectively. Its tension compression fatigue life, bending fatigue life, torsion fatigue life and composite fatigue life increase by 1.19 times, 1.74 times, 550 times and 28.79%, respectively. It is concluded that the designed XSJ joint is significantly improved in term of torsion capacity while its tension strength, bending strength and compression strength are not decreased, so it can better meet the drilling conditions of extended reach wells.