Material Fatigue Research Articles

Turbulence-induced vibrations prediction through use of an anisotropic pressure fluctuation model

In nuclear fuel rod bundles, turbulence-induced pressure fluctuations caused by an axial flow can create small but significant vibrations in the fuel rods, which in turn can cause structural effects such as material fatigue and fretting wear. Fluid-structure interaction simulations can be used to model these vibrations, but for affordable simulations based on the URANS approach, a model for the pressure fluctuations must be utilised. Driven by the goal to improve the current state-of-the-art pressure fluctuation model, AniPFM (Anisotropic Pressure Fluctuation Model) was developed. AniPFM can model velocity fluctuations based on anisotropic Reynolds stress tensors, with temporal correlation through the convection and decorrelation of turbulence. From these velocity fluctuations and the mean flow properties, the pressure fluctuations are calculated. The model was applied to several test cases and shows promising results in terms of reproducing qualitatively similar flow structures, as well as predicting the root-mean-squared pressure fluctuations. While further validation is being performed, the AniPFM has already demonstrated its potential for affordable simulations of turbulence-induced vibrations in industrial nuclear applications.

Fatigue life prediction of aluminum 6061 alloy through experimental and numerical analysis under various stress ratios in axial tension-tension loading condition

Aluminum alloy 6061 is a versatile material widely used in aerospace, automotive, marine, and structural applications due to its mechanical strength, weldability, and corrosion resistance. Understanding and addressing fatigue is crucial for ensuring the reliable and safe performance of components made from this alloy. This study focused on predicting the fatigue life of aluminum 6061 at room temperature under axial loading conditions and evaluating the fatigue life at various stress ratios. The experimental S-N curve, derived from tension-tension fatigue loading tests, was instrumental in characterizing the material's fatigue behaviour under constant amplitude loading condition. The data obtained from these tests were then imported into ANSYS software, a widely recognized tool for finite element analysis and simulation. ANSYS was used to conduct a detailed numerical analysis to predict the fatigue life of aluminum 6061 at different stress ratios. The results from the experimental and numerical analyses exhibited good agreement, validating the accuracy of ANSYS software in predicting fatigue life at different stress ratios. This study demonstrated the effectiveness of employing a combined experimental and numerical approach for understanding fatigue behaviour in materials, particularly in terms of its applicability to different loading scenarios. The findings from this research provide valuable insights into the fatigue life of aluminum 6061 under diverse stress ratios, with the goal of enhancing material design and engineering processes. By leveraging the capabilities of ANSYS software in conjunction with experimental data, the study established a reliable methodology for predicting fatigue life, which is crucial for optimizing the performance and longevity of components subjected to cyclic loading in various industries.

A contribution to the theoretical-experimental investigation of transverse vibrations of the controlling lever of a commercial motor vehicle

During exploitation, commercial motor vehicles are exposed to various types of loads, among which vibrations are of particular importance. Vibrations lead to fatigue of vehicle users and materials of their components. Therefore, they must be studied in the earliest stages of design, using mathematical models, experiments, or their combinations. In theoretical considerations, vibrations of concentrated masses are usually observed, although recently, with the development of numerical methods (especially finite element methods), attention has also been paid to the vibrations of elastic systems of these vehicles. In such cases, simplifications are usually made, especially regarding exploitation conditions and interconnections of vehicle components. This paper attempts to develop a method for identifying vibrational loads on the controlling lever under exploitation conditions, using a two-parameter frequency analysis with the use of 2 D Fourier transform. The applicability of the procedure is illustrated on an idealized model of the controlling lever, and the conducted research has shown that the two-parameter frequency analysis can also be used to generate transverse vibrations in laboratory conditions.

Effect of acidic media on flexural strength and fatigue of CAD-CAM dental materials.

To investigate the effect of acidic media, including beverages and gastric fluids on flexural strength and fatigue of CAD-CAM materials. Four CAD-CAM materials (high-translucency zirconia (Ceramill Zolid HT+), lithium disilicate (IPS e-max CAD), hybrid ceramic (Vita Enamic), and nanohybrid resin composite (Grandio Blocs) were prepared and immersed in one of five media (gastric HCl, white wine, Coca-Cola, orange juice, and artificial saliva) in an incubator (37℃, 24h). Surface topography and roughness were obtained using a scanning electron microscope (SEM) and a stylus contact profilometer, respectively. Initial 3-point flexural strength was measured for half of the bars (n=20/gp) using a universal testing machine (0.5mm/min). The other bars underwent 106 cyclic fatigue loadings before measurement of residual 3-point flexural strength. Data were statistically analyzed (two-way and three-way ANOVA, Tukey's post-hoc, p<0.05). Weibull distributions were plotted for reliability analysis. Zirconia bars has the highest initial flexural strengths followed by lithium disilicate, while resin composite and hybrid ceramic groups had the lowest strength regardless of the erosive medium. Cyclic fatigue significantly reduced initial flexural strengths for all materials except for hybrid ceramic and resin composite. Weibull moduli were the highest for zirconia, lithium disilicate and resin composite and lowest for hybrid ceramic. Erosive media significantly changed surface roughness of CAD-CAM materials except for zirconia and resin composite without jeopardizing the flexural strength of the CAD-CAM materials. Despite the higher flexural strengths for zirconia and lithium disilicate, resin composite and hybrid ceramic were more resistant to cyclic fatigue.

Contribution to the research of the possibility of application of two-parameter frequency analysis in the experimental identification of torsional vibration parameters of elastic shafts in vehicles power transmissions

During exploitation, motor vehicles are exposed to vibrational loads that lead to fatigue of users and materials of their aggregates. Therefore, vibrations must be studied even in the earliest stages of design, using mathematical models, experiments, or their combinations. In theoretical considerations, vibrations of concentrated masses are usually observed , although, with the recent development of numerical methods (especially finite element methods), attention is also being paid to vibrations of vehicle elastic systems. This usually involves idealizations, especially regarding exploitation conditions and interconnections of motor vehicle aggregates. In this paper, an attempt has been made to develop a method for identifying real vibrational loads of elastic power transmission shafts in vehicles (engine, rail, etc.) under exploitation conditions. Namely, 2D Fourier transformation was used for two-parameter frequency analysis. The possibilities of applying the procedure were illustrated on an idealized elastic torsionally loaded shaft. The conducted research showed that two-parameter frequency analysis can be used in generating torsional vibrations of elastic shafts of vehicles in laboratory conditions.

NUMERICAL ANALYSIS OF THE DURABILITY OF STRUCTURAL ELEMENTS UNDER THERMAL CYCLIC LOADING

The methodological aspects of assessing the service life of new equipment (elements of gas turbine engines), the operating modes of which lead to non-stationary thermomechanical loads, are considered. The associated thermoviscoplastic processes of deformation and damage states of the degradable continuum are modeled. A model of thermal fatigue in polycrystalline structural alloys for arbitrary complex deformation trajectories is described, consisting of relationships that determine cyclic thermoviscoplastic deformation; evolutionary equations for damage accumulation and strength criteria for damaged material. Kinetic equations take into account the effects of nonlinear damage accumulation, are based on the introduction of a scalar damage parameter, and are based on energy principles. The related formulation of the kinetic equations for damage accumulation under low-cycle fatigue and long-term strength describes the nonlinear nature of damage accumulation. The criterion for the strength of damaged material is the condition that the damage reaches a critical value. Using the developed original methodological, algorithmic and software that allows for end-to-end numerical modeling of thermal cyclic processes, the problem of assessing the thermal cyclic durability of models of elements and components of gas turbine engines during thermal pulsations has been solved. The results of an analysis of the influence of the angle of inclination of cooling channels in a model of combustion chamber pipes on the thermal cyclic durability are presented. The issues of the influence of complex thermal cyclic deformation, accumulation of fatigue damage, plastic deformations and creep deformations on the thermal fatigue of structural elements are considered. A comparative analysis of numerical results with experimental data was carried out. The efficiency of the model for describing the process of thermal fatigue of materials and structures under multiaxial disproportionate paths of thermal cyclic loading has been confirmed.

Numerical study of a centred crack on an elastoplastic material by the FEM method

The numerical study of crack propagation is a very complex and important problem for knowing the lifetime of a structure. Nowadays, the modelling of crack propagation by various numerical methods plays a beneficial part in solving problems in fracture mechanics. Significantly used in biomechanics, biomaterials and structural calculation, it also makes it possible to deal with certain problems of fatigue of materials. In this article, a numerical study based on the finite element method (FEM) was used for a two-dimensional model, of an elastoplastic material, containing a central crack. The article is also based on the study of different cracking factors, such as stress intensity factors KI and KII, J-integral and strain energy. On the other hand, the contrast of these parameters was precisely centred on the five contours of the crack front. In addition, Abaqus computer code was used to obtain different results, moreover, CPS4R elements were used for modelling.

Prilog istraživanju oscilatornih opterećenja oslonjene i neoslonjenih masa radi stvaranja uslova za laboratorijska ispitivanja teretnih motornih vozila

Introduction/purpose: Motor vehicles are complex dynamic systems due to spatial displacements, changes in the characteristics of components during their lifetime, a large number of influences and disturbances, the appearance of backlash, friction, hysteresis, etc. The aforementioned dynamic phenomena, especially vibrations, cause driver and passenger fatigue, reduce the lifetime of the vehicle and its systems, etc. Methods: In general, the movement of vehicles is carried out on uneven roads and curvilinear paths in the road. Not only do oscillatory movements cause material fatigue of vehicle parts, but they also have a negative effect on people's health. That is why special attention must be paid to the coordination of the mutual movement of the subsystems, and in particular, the vehicle suspension system, even at the stage of the motor vehicle design. For these purposes, theoretical, experimental or combined methods can be used. Therefore, it is very useful to have the experimental results of the oscillations of the vehicle subsystem in operating conditions, so the aim of this work was to use the movement of the 4x4 drive FAP 1118 vehicle in operating conditions (due to higher speeds - in road conditions) to define the conditions for testing oscillatory loads in laboratory conditions. Results: This is made possible by registering and identifying statistical parameters of registered quantities. Conclusion: Based on the measured data, the research can be programmed on shakers in laboratory conditions, and, at the same time, the size to be reproduced can be chosen as well.

Thin-walled shell service life under variable thermomechanical load

A method is proposed for determining the service life of a metal shell structure under variable thermomechanical loading. The operating stresses are determined by solving a nonlinear boundary value problem for a thin-walled shell of revolution. The service life of a metal structure under variable thermomechanical loads and taking into account contact with an aggressive environment is determined using the equations of low-cycle material fatigue. The method is demonstrated on the design of a muffle intended for high temperature annealing of electrolytic steel.

An analysis regarding train derailments caused by cracked wheelsets

The wheelset is a critical component of a bogie's rolling equipment, and safety requirements necessitate both static and fatigue analysis of wheelset axles. This paper proposes a comparative analysis of derailments and accidents caused by cracked wheelsets, a topic that is extensively debated among wheelset manufacturers and railway administrations. The central issue under discussion is whether the cause of wheelset axle cracking is attributed to failure in complying with wagon or locomotive loading requirements, leading to increased static stress, or to material fatigue. The answer to this debate may be found through technical expertise that involves analyzing the cross-section of the cracking, stress levels, and the impact of dynamic conditions.

Defect-based fatigue model for additive manufacturing

A novel defect-based fatigue model for the prediction of S–N (stress versus number of cycles) data points and curves is proposed in this paper. The model is capable of predicting the material fatigue performance based on defect size and location from the surface. A defect factor was introduced and obtained based on notch theory, which considers the notch sensitivity of the material as well as the stress concentration obtained using the finite element method. A newly developed equation was applied to represent the relationship between the defect factor, defect size and defect location from the surface. AlSi10Mg samples were manufactured using laser powder bed fusion, and then machined. The samples were tested under rotational bending cyclic loading until failure. The failed samples were analysed using scanning electron microscopy and it was found that cracks initiated from defects located at the surface. The measured defect size and location were used to predict the number of cycles for an applied stress using the proposed defect-based fatigue model. This model was validated by comparing the predicted and experimentally obtained S–N data. The proposed model has the potential to be applied to component-level fatigue assessment and integrated into industrial quality assurance workflows. For instance, defects can be measured for each produced industrial component and directly assessed against fatigue performance using the developed defect-based fatigue model. This could enable the rapid approval and certification of future additively manufactured industrial components, which can unleash the commercial potential of additive manufacturing for light-weight multi-functional component designs.

Machine learning-based predictions of fatigue life for multi-principal element alloys

Compared to conventional alloys, multi-principal element alloys (MPEAs) offer attractive and tunable fatigue properties. With the advancement of machine learning (ML) in material science, it is perceived as an effective tool for predicting materials fatigue life. Therefore, in this work, we aim to predict the room temperature fatigue lives of two classes of MPEAs, the single-phase CoaCrbFecMndNie system and the multi-phase AlfCogCrhFeiMnjNik system, using four different ML algorithms. Popular ML algorithms viz., Random Forest (RF), Support Vector Machine (SVM), and boosting algorithms such as GBOOST and XGBOOST were employed. Three pairs of test and training datasets were utilized to generalize the employed ML models. Input variables selection procedure was also carried out for possible improvement of algorithms’ performance. SVM and boosting algorithms predicted fatigue lives of both classes of MPEAs within the band of the factor of two. Overall, all algorithms performed reasonably well, despite several hindering factors, such as the data's inherent scatter and limited datasets, which were acquired using different testing standards.

Examining slow crack growth metrics and competing failure modes in IM7/5320-1 carbon fiber reinforced polymer laminates with pre-existing damage states

The growing use of composites in aircraft structures has necessitated a slow growth criteria to assess the life of these materials and an appropriate similitude parameter. Due to the simplified stress state and inherent interactions of intralaminar and interlaminar damage progression in multi-directional ply layups, there have been questions about the applicability of double cantilever beam specimens to aerospace applications. This study examines these interconnected damage growth mechanisms in [±453]s and [±452/902]s layups via compact tension specimen geometries, with and without pre-existing damage, in order to examine the efficacy of proposed similitude parameters in capturing slow crack growth. The change in stored potential strain energy per cycle provided the most unified results across the 18 tests under different loading and pre-existing damage conditions. Via microscopy of the specimens after damage progression, the similitude parameters were connected to overall trends in the damage mechanisms. The fatigue results, coupled with the microscopy of the interactions amongst the complex damage mechanisms, demonstrates the need to analyze proposed similitude parameters across various sample geometries and stress states, which will be more enable an understanding of composite material fatigue performance in aerospace applications.

Atmospheric Drivers of Wind Turbine Blade Leading Edge Erosion: Review and Recommendations for Future Research

Leading edge erosion (LEE) of wind turbine blades causes decreased aerodynamic performance leading to lower power production and revenue and increased operations and maintenance costs. LEE is caused primarily by materials stresses when hydrometeors (rain and hail) impact on rotating blades. The kinetic energy transferred by these impacts is a function of the precipitation intensity, droplet size distributions (DSD), hydrometeor phase and the wind turbine rotational speed which in turn depends on the wind speed at hub-height. Hence, there is a need to better understand the hydrometeor properties and the joint probability distributions of precipitation and wind speeds at prospective and operating wind farms in order to quantify the potential for LEE and the financial efficacy of LEE mitigation measures. However, there are relatively few observational datasets of hydrometeor DSD available for such locations. Here, we analyze six observational datasets from spatially dispersed locations and compare them with existing literature and assumed DSD used in laboratory experiments of material fatigue. We show that the so-called Best DSD being recommended for use in whirling arm experiments does not represent the observational data. Neither does the Marshall Palmer approximation. We also use these data to derive and compare joint probability distributions of drivers of LEE; precipitation intensity (and phase) and wind speed. We further review and summarize observational metrologies for hydrometeor DSD, provide information regarding measurement uncertainty in the parameters of critical importance to kinetic energy transfer and closure of data sets from different instruments. A series of recommendations are made about research needed to evolve towards the required fidelity for a priori estimates of LEE potential.

A new procedure for fatigue life prediction of CFRP relying on the first amplitude harmonic of the temperature signal

The use of thermal indexes assessed by monitoring rapid fatigue tests with infrared detectors as reliable damage parameters to reconstruct S/N curve is a topic still presenting open points. First of all, the selection of the proper thermal index representing damage is a topic to be explored and also the relationship between the damage from rapid stepwise test and constant amplitude test is another a point of discussion.In the present work, we deal with such an issue by investigating the First Amplitude Harmonic (FAH) of thermal signal related to thermoelastic phenomena and dissipative effects too. It has been demonstrated that FAH is related to stiffness degradation and stress induced effects. Moreover, it provides a local analysis of the specific effect related to the material fatigue damage without artifacts.The results show that due to relationship between stiffness degradation and FAH, and specific material properties it is possible to reconstruct S/N curve by carrying out just one constant amplitude test and stepwise rapid tests. Moreover, the capability of temperature FAH to study fatigue behaviour and detect damage during any loading procedure, are also presented.

Quantitative characterization of material uniformity and fatigue life reliability based on the initial damage discreteness

A quantitative characterization method for scattering behaviors of experimental fatigue lives has been developed based on the probabilistic distribution of material’s initial damage. The zero initial damage corresponds to the typical micro-defect state of material and results in the average (statistical expectation) fatigue life. While a minus initial damage corresponds to a less micro-defect state and results in longer life, a plus one corresponds to a more micro-defect state and results in shorter life. The reliability induced by material’s nonuniformity can be evaluated quantitatively from the probabilistic distribution of initial damage, which is a characteristic property of structural material.

Low Cycle Fatigue Behavior of Plastically Pre-Strained HSLA S355MC and S460MC Steels.

Cold roll forming used in the manufacturing of lightweight steel profiles for racking storage systems is associated with localized, non-uniform plastic deformations in the corner sections of the profiles, which act as fatigue damage initiation sites. In order to obtain a clearer insight on the role of existing plastic deformation on material fatigue performance, the effect of plastic pre-straining on the low cycle fatigue behavior of S355MC and S460MC steels was investigated. The steels were plastically deformed at different pre-strain levels under tension, and subsequently subjected to cyclic strain-controlled testing. Plastic pre-straining was found to increase cyclic yield strength, decrease ductility, and induce cyclic softening, which, in S460MC, degrades fatigue resistance compared to the unstrained material. In unstrained conditions, the materials present a cyclic softening to hardening transition with increasing plastic strain amplitude, which in S355MC occurs at lower strain amplitudes and degrades its fatigue resistance with regard to the pre-strained material. Pre-straining also leads to a reduction in transition life from low to high cycle fatigue. SEM fractography, performed following the onset of crack initiation, revealed that plastic pre-straining reduces the fatigue fracture section as well as striation spacing, predominantly in the S355MC steel.

Multiaxial fatigue behavior of a 2198-T8 Al–Li alloy under proportional and nonproportional loading

Abstract 2198-T8 Al–Li alloy was examined under different loading path. Uniaxial and multiaxial proportional and nonproportional loading tests were conducted to determine the material fatigue constant, and to study the multiaxial fatigue behavior, respectively. The multiaxial fatigue life was estimated by various criteria. The results show that, the torsional fatigue performance is better than the tension–compression fatigue performance. The fatigue life of nonproportional loading increases firstly and then decreases with the increase of phase difference from 0° to 90°. Shear Findley model and SWT model were modified by introducing shear damage parameters. The modified models provide fine results which are all within a factor of two.

Magnetic Barkhausen Noise Technique for Fatigue Detection and Classification in Martensitic Stainless-Steel

Abstract Stainless steel is used in many applications because of its excellent mechanical properties at elevated temperatures. Material fatigue is a major problem in steel structures and can cause catastrophic damage resulting in significant economic consequences. Conventional nondestructive evaluation techniques can detect macro defects but do not perform well when it comes to material degradation due to fatigue, which happens at a microstructure level. It is well known that stress applied on a material will have an impact on the microstructure and produces a change in the magnetic properties of the material. Hence, magnetic nondestructive evaluation techniques that are sensitive to changes in magnetic properties play a major role in the early-stage fatigue detection, i.e., before the macro crack initiates. This paper introduces the magnetic Barkhausen noise technique to garner information about fatigue state of the material under test. K-medoids clustering algorithm and genetic optimization algorithm are used to classify the stainless-samples into fatigue categories. The results prove that martensitic grade stainless-steel samples in different stages of fatigue can be classified into broad fatigue categories, i.e., low fatigue, mid fatigue, and high fatigue based on the remaining useful life of the sample.

Experimental study of temperature effect on the mechanical tensile fatigue of hydrated lime modified asphalt concrete and case application for the analysis of climatic effect on constructed pavement

Previous experimental studies have suggested that hot mixed asphalt (HMA) concrete using hydrated lime (HL) to partially replace the conventional limestone dust filler at 2.5% by the total weight of all aggregates showed an optimum improvement on several key mechanical properties, fatigue life span and moisture susceptibility. However, so far, the knowledge of the thermal response of the modified asphalt concrete and thermal influence on the durability of the pavement constructed are still relatively limited but important to inform pavement design. This paper, at first, reports an experimental study of the tensile fatigue life of HMA concrete mixes designed for wearing layer application. Tests were conducted under three different temperatures for five mixes of different HL contents and one with no use of HL. On the experimental data, temperature effect on material fatigue was characterized in terms of the S-N curve modelling parameters. At last, numerical modelling, set at a climatic scenario in the UK, was performed to analyse and compare the seasonal climatic thermal influence on the fatigue life of two pavement structures using and not using the HL modified HMA concrete. Both the experiment and modelling have demonstrated that the 2.5% HL HMA concrete largely enhances the fatigue life of the material and the constructed pavement.