Torsional Fatigue Research Articles

Torsional Fatigue Performance of a Spot-Welded Structure: An XFEM Analysis

This study delves into the exploration of the fatigue performance of a structure that has been spot-welded and is being loaded with torsional fatigue. The extended finite element method (XFEM) was applied to simulate the intricate interaction of spot welds in response to cyclic loading. The developed model was validated through experiments. The influences of different parameters, such as the number of spot welds used to join the adherends, the diameters of the spot welds, and the load ratio applied, on the fatigue performance of the box were investigated. The first two parameters studied had a significant influence on the extent of the fatigue failure-affected spot welds, where the crack propagation rate can be decreased by more than 700%.

Influence of pre-torsion strengthening on the fatigue properties of 45 CrNiMoVA ultra-high strength steel

Aiming at the demand for fatigue life improvement of 45CrNiMoVA ultra-high strength steel shaft parts, a pre-torsion strengthening process using a combination of two different angles before and after was proposed based on the mechanisms of strain hardening, fine grain strengthening and dislocation strengthening. Through surface integrity measurement, torsional fatigue test and fatigue fracture characterization of the specimens, the main surface integrity factors affecting the fatigue life of the pre-torsion strengthening were analyzed. The results indicated that the grain size was refined and the plastic deformation was increased by the two-angle pre-torsion strengthening compared with the single-angle pre-torsion strengthening. The obtained surface residual compressive stress σx was the main factor affecting the fatigue life of pre-torsion strengthening, and the change in pre-torsion angle results in a significant secondary strengthening layer in the subsurface layer of the material. In summary, the study of the pre-torsion strengthening process with different combinations of angles has a guiding significance for improving the fatigue life of ultra-high strength steel.

Effect of over-ageing on the tensile and torsional fatigue properties of the AlSi7Cu0.5 Mg0.3 precipitation-hardened cast aluminium alloy

The objective of this work is to evaluate the influence of over-ageing on the high cycle fatigue behaviour of the AlSi7Cu0.5Mg0.3 cast aluminium alloy. It is generally accepted that over-ageing has a large influence on the behaviour of these materials, however its effect on the fatigue strength is less understood. This work provides an experimental investigation of the effect of over-ageing on high cycle fatigue strength in both tensile and torsional loading conditions. It is shown that the torsional fatigue strength is more sensitive to over-ageing when compared to the tensile fatigue strength and that the fatigue defect sensitivity is negligible for torsional loads, in contrast to tensile loading conditions. The experimental results indicate that this is due to a change in the crack initiation mechanism, going from initiation in the matrix for torsion loads to initiation from casting defects for tensile loads. An original two-steps approach is proposed to rationalise the effect of over-ageing on the fatigue strength, with particular emphasis on decoupling the respective contributions from defects and the mechanical properties. This approach is used to build normalised Kitagawa-Takahashi diagrams that highlights the reduced defect sensitivity under tensile loads for the most severe over-ageing condition.

Experimental and numerical fatigue evaluation of lightweight crankshafts

The development of lightweight components in the automotive industry is an important aspect in designing of products aiming to reducing fuel consumption, optimal use of material resources and sustainability. The optimization of internal combustion engines (ICE) components can be performed for example by mass subtraction procedure and use of different materials. Optimizing crankshafts is challenging due to the applied bending and torsion loads that increase the stress concentrations in critical regions. In this context, the objective of the present work is to propose a numerical approach for fatigue assessment of crankshafts, which must reduce the number of specimens required in experimental tests and the development costs. The stress distribution of a commercial crankshaft model was determined numerically from harmonic response analysis, and correction factors related to surface treatments and failure criterion were applied for estimating the fatigue strength. The fatigue strength estimated numerically was compared to experimental fatigue tests results, and this methodology was also applied to a lightweight model obtained by means of mass reduction. The fatigue strength estimation showed 2 % and 7 % relative error for the original and lightweight crankshaft models, respectively. In addition, both numerical and experimental results achieved about 10 % of mass reduction for the commercial crankshaft without considerable influence on the bending and torsion fatigue strength. The present work indicates that the proposed numerical approach can predict with good accuracy the fatigue strength of crankshafts during the design stage.

Comparing the impact of various sterilization methods on the cyclic fatigue resistance, bending strength, and torsional fatigue properties of NiTi rotary files

This study aimed to evaluate the influence of various sterilization techniques on the cyclic fatigue resistance, bending strength, and torsional fatigue resistance of Tornado Blue and Race Evo rotary endodontic file systems. Both the file systems underwent a series of 15 cycles of sterilization according to the following study groups: control group (G1; i.e., without treatment), chemical sterilization with 5.25% sodium hypochlorite (G2), dry heat sterilization (G3), glass beads sterilization (G4), and steam autoclaving (G5). Each group consisted of 8 samples (n = 8/group). Statistical analysis was performed using a two-way ANOVA and Tukey’s tests (p ≤ 0.05). Mean values for the number of cycles between both files were 1291 ± 52.79 rpm and 2095 ± 52.91 rpm for Tornado Blue and Race Evo, respectively. The torsional fatigue resistance was 8.00 ± 0.85 NCF and 10.70 ± 0.85 NCF and the bending strength was 486.94 ± 20.97 gf and 564.17 ± 20.97 gf for Tornado Blue and Race Evo, respectively. The results showed no significant difference in the mechanical properties followed by different sterilization protocols. However, a significant difference was observed in tested properties between the two file systems (p ≤ 0.05). The outcome is reassuring for clinicians that the essential process of routine sterilization at clinics seems safe with regards to mechanical integrity of the endodontic files.

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.

Experimental investigation on the fatigue life and damage mechanism of plain weave composites under biaxial tension–torsion combined fatigue loading

In this paper, the fatigue life and damage mechanism of plain weave composites under biaxial tension–torsion combined fatigue loading (TTF) are experimentally investigated. A biaxial TTF loading spectrum is designed to consider different fatigue frequencies and amplitudes, and an automated multi-module loading method with synchronized acquisition of the digital image correlation (DIC) and the testing machine is proposed. A comprehensive analysis of the experimental results, including fatigue lives, strain distribution, temperature variation, stiffness degradation, and typical damage morphologies at different fatigue cycles, has been conducted by utilizing DIC, infrared thermography (IRT) and computed tomography (CT). It is observed that the superimposed torsional fatigue load results in a rapid reduction in fatigue lives of plain weave composites, accompanied by more significant residual strain, energy dissipation, temperature rise and stiffness degradation. Particularly, the superimposed torsional fatigue loads mainly promote matrix cracking and debonding around the fiber/matrix interfaces, which then accelerates the damage initiations and accumulations of fiber yarns, ultimately leading to a rapid reduction in TTF fatigue lives. This study can provide valuable references for the design and safe application of plain weave composites under TTF loading.

Effect of Mean Torsional Stress on Very High Cycle Torsional Fatigue Strength of High Strength Steel

Effect of Mean Torsional Stress on Very High Cycle Torsional Fatigue Strength of High Strength Steel

Temperature effects on the lifetime reinforcement due to strain-induced crystallization in carbon black filled natural rubber under non-relaxing torsion: comparison with non-relaxing tensile loadings

This paper investigates the lifetime reinforcement at different temperatures of carbon black filled natural rubber under non-relaxing torsion. Torsion fatigue tests with different angle ratios have been carried out with axisymmetric-shaped specimens. Finite element analysis was used to predict the local mechanical state by taking into account temperature effects and stress softening heterogeneities. It has been shown that when the temperature of the test is increased, the mechanical response does no longer stabilize, contrary to what is observed when the test is carried out at ambient temperature. A strategy has been proposed to evaluate an equivalent loading ratio, in order to compute the minimum loading as the Cauchy stress normal to the crack plane for the minimum torsion angle applied and to represent the results in the Haigh diagram. It was found that the lifetime reinforcement under torsion loading decreases when the temperature is increased to 90 °C, but is still observed. The lifetime reinforcement under torsion at 90 °C was of the same amplitude as the one obtained with the same material under uniaxial tension at the same temperature. The study has been completed by post-mortem analysis at the macro- and the microscale in order to characterize damage mechanisms at 90 °C.

Torsional fatigue behaviour and damage mechanisms of martensitic spring steel in the HCF regime

This study investigates the fatigue behaviour and damage mechanisms of the martensitic spring steel SAE 9254, with emphasis on short crack propagation. Shear stress-controlled torsional fatigue tests are performed at stress ratio R = -1 and test frequency f = 79 Hz using structure-sensitive measurement techniques to detect the relevant damage mechanisms. An in-situ torsional fatigue testing device is applied for shear-controlled fatigue tests at two amplitudes of the torsion angle using R = –1 and f = 5 Hz, and the microstructural-dependent short crack propagation path is documented by means of confocal laser microscopy and electron backscattering analysis. It is found that the early development of fatigue damage is characterised by the formation of slip bands, which serve as crack initiation sites. In this process, crack initiation occurs preferentially at or near prior austenite grain boundaries. Furthermore, prior austenite grain boundaries were identified as obstacles for the propagation of short cracks, because of the change of the crystallographic orientation leading to an oscillating propagation rate of short cracks. The short crack density ρCD, which is an important parameter for fatigue damage, is rapidly growing with increasing shear stress amplitude ΔτT/2 and reveals a stress type specific behaviour.

Mathematical Modelling for Failure Analysis of Composite Drive Shaft Using Modal Flexibility and Curvature Method

Early damage identification in composite structures has attracted a lot of attention in post-failure examinations in recent years. In the research, torsional fatigue test of composite drive shafts has been done and numerical methodologies have been employed for the validation for premature failure using modal flexibility and modal curvature methods. Initially, the eigenvalue and eigenvectors of healthy and fractured drive shafts are evaluated using a numerical model and verified by fatigue experimental approach. Flexibility variance and the absolute curvature difference between the drive shafts that are fractured and those that are healthy are evaluated after mass normalization. Variations in absolute modal curvatures and variations in local flexibilities that are utilized to identify the existence, location, and severity of a drive shaft fracture. The position and severity of the fracture are predicted more precisely by the modal curvature approach than by the modal flexibility approach.

Evaluation of mechanical properties of an original and a replica-like reciprocating instruments.

This study assessed the mechanical properties of the Only One File Blue and the Reciproc Blue instruments. A total of 80 new 25 mm reciprocating NiTi instruments (25/.08v) were evaluated for their mechanical performance (n = 40 per group). Cyclic fatigue resistance, torsional fatigue, flexural resistance and buckling resistance tests were conducted. Statistical analysis was employed with a significance level set at 5%. The results indicated no statistically significant differences in resistance to cyclic fatigue neither in the fragment length between the instruments (p > 0.05). However, the Reciproc Blue instrument exhibited greater torque to fracture and a larger rotation angle than the Only One File Blue instrument (p < 0.05). The Only One File Blue instrument demonstrated higher flexibility but lower resistance to buckling compared to the Reciproc Blue instrument (p < 0.05). In conclusion, the tested instruments exhibit differences in mechanical properties, with the Reciproc Blue instrument generally presenting greater advantages than the Only One File Blue.

A continuum approach to multiaxial high-cycle fatigue modeling for ductile metallic materials

In this work we propose a generalization of the endurance function employed in the continuum approach to high-cycle fatigue modeling by Ottosen et al. (2008). The von Mises-type backstress-modified effective stress term of the original formulation is replaced by the non-quadratic Hershey-Hosford function, which introduces flexibility with respect to the predicted fatigue limit in pure shear. While the original model assumes a fixed ratio between the fatigue limits in fully reversed torsion and fully reversed bending of 0.5774 for all materials, the modification enables the ratio to take on values on the interval from 0.5 to 0.5852 by calibration to experimental data that is readily available in the literature. Like the original formulation simplifies to the invariant-based Mises-Sines fatigue limit criterion for proportional stress histories, the current proposal can be written as a Hershey-Hosford-Sines criterion. A systematic validation to experimental multiaxial infinite fatigue life data from eight different mild and semi-hard metals with fully reversed torsion and bending fatigue limit ratios lower than 0.6 demonstrates that the proposed modification increases the accuracy and reduces the number of non-conservative predictions.

The effects of submerged laser peening, cavitation peening, and shot peening on the improvement of the torsional fatigue strength of powder bed fused Ti6Al4V produced through laser sintering

This study demonstrates the improvement in the fatigue strength of additive manufacturing (AM) metals such as laser-based powder bed fusion of metals by post-processing. Titanium alloy samples manufactured by powder bed fused (PBF) Ti6Al4V produced through laser sintering (LS), treated by submerged laser peening (SLP), cavitation peening (CP), and shot peening accelerated via a water jet (SPwj), were subjected to torsional fatigue testing and compared with the as-built specimen. At SLP, the samples were treated by laser ablation (LA) and laser cavitation (LC) which was developed following LA. A cavitating jet was used for CP. For comparison, conventional post-processing using SPwj was also performed. To characterize the microstructural modification caused by the three post-processing methods, the cross-section of the treated surface was observed by electron backscatter diffraction. The fatigue strengths at 107 cycles were found to be 217, 361, 313, and 285 MPa for the as-built, SLP, CP, and SPwj specimens, respectively. The primary factors contributing to fatigue strength improvement by post-processing were surface smoothing and the introduction of compressive residual stress. The experimental observations were used to derive correlation formulas to estimate the fatigue life improvement due to post-processing as the function of the surface roughness and surface residual stress.

Mechanical Behavior and Life Prediction of a Low Nickel/High Nitrogen Austenitic Steel under Pure Torsion, Uniaxial Tension-Compression, and Multiaxial Fatigue

Abstract Fatigue life prediction, crack growth, and propagation mechanisms are important details to consider for a structure to be used in service without fear of early failure. This is especially important for a new material for which very limited information is available. In this study, austenitic stainless steel P558 with low nickel content and high nitrogen content was subjected to fatigue testing at room temperature in multiaxial (static compression and cyclic torsion), pure torsion, and uniaxial tension-compression modes. The material generally depicts cyclic softening in the three loading conditions; although the multiaxial experiments experienced some initial hardening, those with a high shear stress and axial stress combination furthermore experienced a secondary hardening before softening. The Fatemi-Socie model predicts the pure torsion and multiaxial fatigue well but fails to predict fatigue lives for uniaxial tension-compression. On the other hand, the Smith-Watson-Topper model predicts fatigue lives for the uniaxial fatigue and pure torsion sufficiently but is poor in predicting fatigue lives for the multiaxial fatigue loading conditions. The cracking behavior was observed to be dependent on the loading condition and the strain amplitude with Mode II cracks or shear-oriented cracks observed for the high strain amplitudes (resulting in shorter lives) whereas Mode I cracks, or tensile-oriented cracks, were observed from low strain amplitudes (resulting in higher lives). A mixed mode was also observed for specimens in the midrange strain amplitudes, which exhibited a branching from shear to tensile cracks. The static compressive stress is believed to have a negative influence on the cracking behavior and the fatigue life by the rubbing of the crack surfaces, which in turn reduces the load-holding capability of the material. The same friction at the crack tip could also be the reason for the heating up of the specimens.

A Comprehensive Investigation of Linear and Nonlinear Beam Models on Flexible Wind Turbine Blade Load Calculations

This study was performed to investigate the effects of structural nonlinearity and large deformations on the aeroelastic loads of flexible wind turbine blades. First, a blade structural analysis model was established using the geometrically exact beam (GEB) theory. Subsequently, the blade element momentum (BEM) theory was corrected using the geometrically exact method leading to the development of a geometrically exact blade element momentum (GE-BEM) model. The results from the GE-BEM model indicated that flapwise deformations always reduce blade fatigue loads, while torsional deformations decrease fatigue loads under low wind speeds but increase them under high wind speeds. Finally, the linear Euler–Bernoulli beam and the GEB were compared to explore the influence of geometric nonlinearity on the blade aeroelastic loads, which revealed that the Euler beam model underestimates the blade loads. The simulations that used the GEB model produced torsional root twist fatigue loads that were 57.49% greater than those generated when the Euler beam model was used. Furthermore, the flapwise bending moment fatigue loads at the root were 8.24% greater than those obtained by the Euler beam model. The smallest discrepancy between the results of the two models was 7.26%, and it corresponded to the edgewise fatigue load.

Comprehensive Characterization of Blue Wire NiTi File Failure: A Comparative Analysis of Cyclic Fatigue and Torsional Resistance Properties

This study compared the fatigue resistance and elemental composition of two blue heat-treated nickel–titanium (NiTi) files used in root canal preparation as follows: Tia Tornado Blue (TTB) and Race Evo (RE) file systems. For cyclic fatigue testing, the two systems were tested where each file was rotated inside an artificial metal canal submerged in either sodium hypochlorite or saline solution until fracture. Time to fracture was recorded. For torsional fatigue testing, the file tip was secured while the file was allowed to rotate at a fixed rate until fracture. Torque at failure was recorded. The two experiments were performed at simulated body temperature and the length of fractured segments was measured. Statistical analysis was carried out with a significance level (p-value) set at 5%. The mean cycles to fracture for RE were superior to that of TTB irrespective of the solution used (p &lt; 0.05). TTB’s cyclic fatigue resistance decreased in NaOCl (p &lt; 0.0001). RE demonstrated lower torque at failure (p = 0.002). All files were fractured at comparable lengths (p = 0.218). Although RE is considered more resistant to cyclic fatigue, it showed inferior torsional resistance compared with TTB. The NaOCl negatively affected the TTB’s cyclic fatigue resistance.

Fatigue life reinforcement of carbon black filled natural rubber under non‐relaxing torsion loadings and comparison with non‐relaxing tension loadings

AbstractIn this paper, the effect of non‐relaxing torsion loadings on the fatigue lifetime reinforcement of carbon black filled natural rubber is fully addressed. Torsion fatigue tests with different loading ratios have been performed with highly notched axisymmetric‐shaped specimens. Finite element analysis is used to predict the mechanical state at any point in the specimens. The prediction is significantly improved by taking into account the heterogeneous accommodation. The first Haigh diagram under fatigue torsion is built and analyzed by calculating the minimum loading in terms of the Cauchy stress as the normal stress to the crack for the minimum angle prescribed during the cycle. A strong lifetime reinforcement has been observed, which is found to be of the same amplitude to the one obtained under uniaxial tension with the same material. This has been confirmed by specific tests that combined non‐relaxing torsion and non‐relaxing tension loadings. Post‐mortem analysis carried out at the macroscopic and the microscopic scales enabled us to identify damage mechanisms, especially in the cases where the lifetime reinforcement was observed.

Torsional Fatigue and Static Torsion Strength and Test Validations of Composite Tube Hybrid Drive Shafts

Drive shafts are the transmission components which transfer power from power source to required location. The connection may be between steering wheel and rack &amp; pinion mechanism or gearbox to differential. As in gearbox to differential connection, operational conditions are harsh and high loads are generated, steel materials are mainly preferred to be used. Though steels have such advantages in cost, performance and durability, it is heavier compared to other engineering materials. Since international regulations dictate to decrease the carbon emissions rates due to global concerns, weight decrement of automobile components plays an important role in solving such problem. Considering the operational requirements and boundary conditions, weight reduction in steel parts might be tough. For this reason, alternative materials must be deeply investigated and implemented into the traditional technologies. In the scope of this study, fatigue and torsional strength of propeller shaft with composite tube and aluminum subcomponents were investigated.