Cycle Fatigue Research Articles

Investigation on the fatigue crack propagation of rock-concrete interface under fatigue loading below the initial cracking load

The fatigue crack propagation of the composite rock-concrete interface under constant-amplitude flexural fatigue loading below the initial cracking load was investigated in the present study. Fatigue pre-crack initiation and propagation tests were first conducted on three types of rock-concrete interfaces under three-point bend loading. It was shown that for the rock-concrete interface, the damage evolution throughout the fatigue loading process can be divided into deceleration and acceleration stages according to the rate curves of flexural stiffness, deformation and crack propagation. The crack propagation rate exhibited two distinct regions when plotted on a log scale, namely the small-crack growth region and the long-crack growth region. The small-crack growth region for the studied rock-concrete interfaces was not particularly pronounced. The long-crack growth region was the Paris’ law region and included both the acceleration and part of the deceleration stages. Based on the experimental results, the fatigue crack propagation rate in the Paris’ law region was then described using the empirical Paris’ law. The exponent m1 in the Paris’ law was found to be approximately constant, with a value of m1 ≈ 21 for the rock-concrete interface. The pre-factor C1 was found to be dependent on both the load ratio R and the type of the rock-concrete interface (represented by an elastic mismatch parameter α). By introducing R and α into the empirical Paris’ law, an adjusted Paris’ law was proposed. The adjusted Paris’ law can describe the fatigue crack propagation rate in a unified way for the same rock-concrete interface of different R and different interfaces in the scope of this research. Based on the adjusted Paris’ law, the fatigue cycles during the crack propagation and fatigue lifetimes of all tested rock-concrete interface specimens were reasonably predicted. For practical applications, an approach was suggested involving a combination of the adjusted Paris’ law and a material coefficient β (approximately β ≈ 0.143 in this study) to estimate the fatigue lifetimes of structures or specimens with existing pre-cracks at the rock-concrete interface.

Fatigue life prediction of metal materials under random loads based on load spectrum extrapolation

The impact of random loading on the fatigue life of mechanical components contains numerous uncertainties. This study aims to enhance the precision of life prediction by developing mean and amplitude distribution models based on the road load spectrum and extrapolating the operational load beyond the threshold value in the time domain. Additionally, it considers the influence of high cycle fatigue (HCF) and low cycle fatigue (LCF) loads on the initiation life of metal cracks. To address this, a load correction factor is introduced, and critical stresses for high and low cycle loads are proposed. Furthermore, a two-dimensional programmed load spectrum is prepared, taking into account the mean and amplitude. The accuracy and rationality of the fatigue life model are validated through examples using 45# steel and 316L, while experiments on engine support are conducted to confirm the effectiveness and accuracy of the over-threshold extrapolation life prediction method under random loading.

The effect of fiber bridging on mode I fatigue delamination propagation—part I: Testing

AbstractThe purpose of this investigation is to assess the effect of fiber bridging on fatigue delamination propagation. Fiber bridging occurs when testing beam type laminates specimens consisting of unidirectional plies. Unidirectional double cantilever beam specimens composed of the carbon fiber reinforced polymer prepreg AS4/8552 were tested by means of fatigue cycling. A Paris relation was determined based on these tests. Fiber bridging in beam specimens composed of unidirectional plies causes the apparent fatigue delamination curves to exhibit slower growth predicting overly conservative results. In Part I of this study, the effect of fiber bridging was eliminated experimentally from the results. In Part II of this study, a cohesive zone model is developed and used to carry out finite element analyses to simulate the experiments, as well as to eliminate the influence of fiber bridging.

A study on comparison of cleaning efficiency of rotary and manually operated endodontic files

: The purpose of this study is comparison of cleaning efficiency of rotary and manual endo files during cleaning and shaping of primary and permanent tooth.: A total of 100 articles were searched in pubmed on cleaning efficiency of rotary and manual files. Articles which had protocol on cleaning efficacy rather than cyclic fatigue and torsional effects were included. A total of 15 articles were assessed out of which 7 were included.: Rotary files were found to have significantly better cleaning efficiency and less time consumption on primary and permanent tooth. However manual endodontic files were also found to serve equivalent cleaning efficiency.: In this study we obtain several articles which stated variable results and conclusion. However, particularly on cleaning efficiency, rotary and manual endodontic files were found to have significantly no differences in primary as well as permanent tooth.

Finite element analysis of concrete filled steel tubes subjected to cyclic bending

This study introduces a novel Finite Element (FE) modelling approach for accurately simulating the behaviour of Steel Concrete Filled Tubes (CFTs) subjected to both monotonic and cyclic loads. It comprehensively addresses the challenges of modelling low cyclic fatigue in steel and concrete crushing, a critical aspect often overlooked in previous studies. The methodology is rigorously validated against eight experimental tests on circular CFTs, where it exhibits remarkable precision in capturing the complex interaction between steel and concrete under various loading conditions. The prosed modelling is able to accurately catch the degradation, the number of cycles leading to fracture and the failure modes.

Longevity of different abutments placed on narrow diameter implants: Assessment of structural damage and loosening

ObjectivesTo evaluate structural damage and loosening of abutments placed on narrow diameter implants after cyclic fatigue. MethodsSixty Morse taper narrow diameter implants (Neodent, Brazil) received two types of abutments (1PA- one-piece abutment or 2PA- two-piece abutment), which were randomly divided into 3 fatigue experiments (n = 10). The implants were placed into a customized supporting holder and a software-assisted digital torque wrench secured the manufacturer recommended torque for each abutment. Cone beam computed tomography (CBCT) scans were acquired, before and after fatigue, and post-processed (software e-Vol DX) to assess damage and abutment displacement. The boundary fatigue method was adapted to use 2 × 106 cycles, 2 Hz of frequency and constant peak load of 80 N (first experiment) that varied according to the failure rate of previous specimens (second and third experiments). Failure was evaluated using CBCT scans and removal torque values. Data were used to estimate long-term torque degradation, probability of failure and Weibull modulus (software ALTA PRO9). ResultsAll 2PA specimens became loosen independently of the applied fatigue load, and structural bending was observed in 14 abutments. Eight 1PA got loosen during the fatigue experiment. The Weibull analysis showed a lower modulus (m = 1.0; 0.7, 1.4) for 1PA than for 2PA (m = 2.6; 2, 3.4) resulting in longer predicted lifetimes and slower torque degradation for 1PA than for 2PA specimens. Significance1PA showed greater long-term survival probability than 2PA. Predicting the lifetime and mechanical behavior of implant-abutment systems are useful information to clinicians during the decision-making process of oral rehabilitations.

Assessment of frequency and amplitude dependence on the cyclic degradation of polyurethane foams

AbstractMany energy absorption applications utilize flexible polymeric foams for their viscoelastic properties. It is desired that the material will perform consistently across repeated compression cycles. This study examines the effect of fatigue at low strain rates on the viscoelasticity of open‐cell polyurethane foam. Six polyurethanes of the same base composition with two porosities (70% and 80%) and three chemical indexes (79i, 100i, and 121i) are tested. Large deformation cyclic compression of the foams is conducted on a universal testing system (UTS). These data are then post‐processed leveraging dynamic mechanical analysis Fourier transform rheology to characterize changes in the viscoelasticity of the materials over fatigue cycles. Results show that foams can increase or decrease in stiffness up to 10% over 104 cycles. Specifically, higher chemical index, higher excitation frequency, and larger excitation amplitude correlate with a more pronounced decrease in stiffness. Damping can also change by 15% and correlates with chemical index and excitation frequency. Consequently, the findings suggest that internal foam structure and bulk material properties as well as applied loading parameters affect the viscoelastic fatigue response of flexible polymeric foams.

Polyetherimide in 3D printing: Pioneering non-metallic solutions for personalized orthopedic and traumatology hip prosthetics

Currently, Total Hip Replacement (THR) hip prosthetics are typically made from metallic materials using subtractive manufacturing, and they are not personalized. These materials, with higher densities than trabecular bone, can cause microfractures due to fatigue cycles. This study aims to demonstrate the feasibility of using Polyetherimide (PEI) as a rigid thermoplastic in additive manufacturing, offering a viable alternative for patient-specific prostheses in humans or pets. The starting point was a commercial prosthesis, a similar replica was 3D modelled, and test specimens were printed using ULTEM 1010 material. The PEI prosthesis meets outlined standards and offers an alternative for young, lightweight patients, and various pets. It does so by adapting to specific the patient's anatomical needs. Fatigue life was found to be the limiting factor, as the 392 N applied prosthesis, exceeded the million cycles limitation set for this study, prompting us to focus on the prosthesis' use on children, or small pets.

Microstructure analysis of carbon-fiber-reinforced polymer laminates subjected to self-heating and fatigue strengthening under tension-tension fatigue loading

In this study, tensile-tensile fatigue testing of unidirectional (UD) carbon-fiber-reinforced polymer (CFRP) prepreg laminates was performed. Two types of specimens (open-hole and unopened-hole ones) were examined at different stress levels to elucidate the impact of fatigue damage on their static strength at different numbers of cycles. The effect of internal heat generation during fatigue on the life of unopened-hole CFRP laminates was analyzed by observing the changes in the microstructure of specimens. The results revealed that the difference in fatigue life between unopened specimens with and without cooling at 70% ultimate tension stress (UTS) level was about 88 times. In the open-hole CFRP laminates, the residual tension strength (RTS) after increases and then decreases with the number of fatigue cycles, and the interface debonding was a significant cause of fatigue strengthening. Open-hole specimens were shown to withstand continuous cycling under severe loads at 5% above their ultimate stress levels. Therefore, the fatigue damage extension of the open-hole laminates can be slowed down under intensive cycling at high stress levels, ensuring good fatigue performance of the material.

Prediction of Short- to Long-Term Cyclic Deformation Behavior and Fatigue Life of Polymers.

The prediction of mechanical behavior and fatigue life is of major importance for design and for replacing costly and time-consuming tests. The proposed approach for polymers is a combination of a fatigue model and a governing constitutive model, which is formulated using the Haward-Thackray viscoplastic model (1968) and is capable of capturing large deformations. The fatigue model integrates high- and low-cycle fatigue and is based on the concept of damage evolution and a moving endurance surface in the stress space, therefore memorizing the load history without requesting vague cycle-counting approaches. The proposed approach is applicable for materials in which the fatigue development is ductile, i.e., damage during the formation of microcracks controls most of the fatigue life (up to 90%). Moreover, damage evolution shows a certain asymptote at the ultimate of the low-cycle fatigue, a second asymptote at the ultimate of the high-cycle fatigue (which is near zero), and a curvature of how rapidly the transition between the asymptotes is reached. An interesting matter is that similar to metals, many polymers satisfy these constraints. Therefore, all the model parameters for fatigue can be given in terms of the Basquin and Coffin-Manson model parameters, i.e., satisfying well-defined parameters.

Fatigue and failure mode analyses of glass infiltrated 5Y-PSZ bonded onto dentin analogues

The purpose of this study was to evaluate the fatigue survival of 5Y-PSZ zirconia infiltrated with an experimental glass and bonded onto dentin analogues. Disc-shaped specimens of a 5Y-PSZ (Katana UTML Kuraray Noritake) were cemented onto dentin analogs (NEMA G10) and divided into four groups (n = 15): Zctrl Group (control, without infiltration); Zglz Group (Glaze, compression surface); Zinf-comp Group (Experimental Glass, compression surface); Zinf-tens Group (Experimental Glass, tension surface). Surface treatments were varied. Cyclic fatigue loading, oblique transillumination, stereomicroscope examination, and scanning electron microscopy were performed. Fatigue data were analyzed (failure load and number of cycles) using survival analysis (Kaplan–Meier and Log-Rank Mantel–Cox). There was no statistically significant difference in fatigue survival between the Zglz, Zctrl, and Zinf-comp groups. The Zinf-tens group presented a significantly higher failure load when compared to the other groups and exhibited a different failure mode. The experimental glass effectively infiltrated the zirconia, enhancing structural reliability, altering the failure mode, and improving load-bearing capacity over more cycles, particularly in the group where the glass was infiltrated into the tensile surface of the zirconia. Glass infiltration into 5Y-PSZ zirconia significantly enhanced structural reliability and the ability to withstand loads over an increased number of cycles. This approach has the potential to increase the durability of zirconia restorations, reducing the need for replacements and save time and resources, promoting efficiency in clinical practice.

Experimental Analysis of Resilient Characteristics of CRMB – 55 & 60 Grade with Grade-II Aggregates on Pavement

An evaluation of the physical and engineering properties of modified binders was conducted in this paper, namely Crumb Rubber Modified Bitumen (CRMB - 55 grade & CRMB - 60 grade) containing cement as a mineral filler of 2 % and varying binder contents between 4% and 6% for determining the Optimum Binder Content (OBC) for aggregates of nominal size 13.2 mm in Grade-II. As a result of varying stress levels from 10% to 40%, the specimens have been cast for indirect tensile strength (ITS), moisture susceptibility, and fatigue cycles’ estimation. Keywords: Stability, Modified binder, In-direct tensile strength, fatigue cycle of modified binders.

A model on the coupling between cyclic fatigue and microstructure evolution in a metallic glass

Establishing the intrinsic correlation between microstructural heterogeneity and mechanical properties is a challenging issue of metallic glasses. The ratchet behavior was examined in a Zr-based metallic glass under cyclic tensile loading well below the yield point, particularly near the glass transition temperature. It is found that strain evolution during cyclic loading shows heightened sensitivity to temperature and stress rate. Also, creep behavior mirrors the ratchet strain induced by cyclic loading. The proposed constitutive model, integrating the Burgers model with defect concentration based on free volume theory, effectively describes strain evolution during cyclic loading near glass transition temperature. Both macroscopic and microscopic perspectives are included in this model. The results verify that metallic glasses exhibit significant viscous characteristics, displaying noticeable creep deformation under low stress rates and amplitudes, which contributes to ratchet behavior. The fitted parameters show that plastic viscosity decreases with temperature and increases with stress rate, corroborating the decrease of tensile yield stress with temperature increasing; also, the fitted relaxation time increases with loading frequency, reflecting evolution of defect concentration. Structural relaxation competes favorably against stress-driven rejuvenation throughout the cyclic process, suggesting potential in tuning metallic glasses properties through innovation thermos-mechanical processing techniques.

Evaluating and correlating asphalt binder and mixture fatigue properties considering aging conditions

Asphalt fatigue cracking is a critical distress type for flexible pavement. This study utilized the state of practice binder and mixture cracking tests and parameters to investigate how asphalt binders’ and mixtures’ fatigue performance vary between the different mix designs and evaluate their changes with aging. The potential relationships between the measured binder properties and mixture performance were also explored. Five asphalt mixtures with disparate mix designs were evaluated and three different aging conditioning levels were conducted. The binder tests include the traditional time and frequency sweep and linear amplitude sweep test, while the mixture evaluations include the semi-circular bending and cyclic fatigue test. The results indicate that the different fatigue parameters from the tests can evaluate and rank the mixes differently. The correlation analysis using the Spearman correlation coefficient shows that the mixture cracking parameters that are more predominant by asphalt mixture’s flexibility/brittleness show strong correlations (Spearman coefficient larger than 0.8) with binder cracking indices. The LAS fatigue life-related parameters generally do not correlate well with mixture fatigue indices (Spearman coefficient smaller than 0.6). Furthermore, a prediction model to estimate asphalt mixture’s fatigue performance was developed based on linear regression and Artificial Neural Network (ANN) approach, which only requires the mix design info. and binder fatigue property as the inputs, significantly reducing the time and eliminating the effort in preparing and testing the asphalt mixture specimen for mixture fatigue performance measurement.

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.

Visualization of fatigue load cycle numbers using a glass/carbon hybrid composite sensor

A sensor for visualizing the fatigue load cycles was designed, fabricated, and tested. The sensor is made of a glass/carbon hybrid composite and utilizes the delamination length at the glass/carbon interface as an indicator for fatigue cycles. Appropriate design parameters were obtained by performing finite element analysis on the delamination development at the interface between the glass and carbon layers. Hybrid sensors with different carbon layer thicknesses were manufactured, attached to glass/epoxy substrates, and tested under fatigue loading. The predicted results based on the Paris law for crack extensions in one configuration are compared with the experiments for a different configuration to illustrate the efficacy of the approach.

Effects of aircraft operating fluids and environmental thermal fatigue on fly ash and steel slag based cementitious composites

This paper investigates the performance of concrete incorporating high-volume fly ash (HVFA) and steel slag aggregates against the detrimental effects of combined cycles of environmental thermal fatigue and exposure to leaked aircraft fluids. A total of 128 cubes and 90 prisms were cast for five mixes and exposed to 60, 120, 180, 240 and 300 combined cycles. The results demonstrate the positive effect of utilization of HVFA which reduces the total amount of portlandite available in the system. The SS aggregates demonstrate a strong interlocking with the surrounding matrix and supply the necessary portlandite for continued pozzolanic reaction. However, their reaction with aircraft fluids causes significant degradation to flexural strength initially, which is redeemed by pozzolanic reaction at a later stage. Hybrid basalt and polypropylene fibres were successful in enhancing the flexural strength and reducing the cracking. The mercury intrusion porosimetry revealed a reduction in pore volume because of HVFA. Scanning electron microscopy and differential scanning calorimetry were also employed to uncover the underlying mechanisms of damage and assess the performance of the cementitious composite.

Comparison of the effectiveness of the endodontic treatment using Reciproc Blue instrument with or without glide path preparation

Background: To overcome file fracture due to torsional stress and cyclic fatigue during root canal preparation, the Reciproc Blue endodontic file system with reciprocating motion helps to shape the canal with only one instrument. Objective: To compare the time of root canal shaping and the results of endodontic treatment of first molars with Reciproc Blue files with and without glide path preparation. Materials and Methods: A controlled clinical trial on 78 first molars with irreversible pulpitis in patients visiting Hue University of Medicine and Pharmacy Hospital from July 2020 to October 2022. Group 1 and Group 2 (n = 36 each) were respectively prepared with a Reciproc Blue file with and without a glide path preparation. Comparison of preparation time and treatment outcome based on clinical and radiographic characteristics at 1 week, 3 months, and 6 months. Results: Endodontic treatment using Reciproc Blue file without glide path preparation recorded a shorter time consumption (p < 0.05) and no complications. However, the treatment results after 1 week, 3 months, and 6 months were not different between the two groups regards to glide path preparation (p > 0.05). Conclusion: Shaping root canals with Reciproc Blue without creating a glide path reduces shaping time, simplifies the procedure, and does not adversely affect treatment outcomes compared to the group with glide path creation. Key words: First molar, glide path, Reciproc Blue, root canal preparation.

Grain size sensitive modelling of the nonlinear behaviour and fatigue damage of Inconel 718 superalloy

Fatigue tests conducted on various types of materials often exhibit significant scatter, particularly in High Cycle Fatigue tests, attributed to imperfections located at the scale of the microstructure. In metallic materials, one contributor to this dispersion, but not the only one, is the variation in grain size, which cannot be uniform in a structure that has undergone a complex thermal history during its manufacturing process. This paper introduces a new model for predicting the evolution of the grain size in the nickel-based superalloy Inconel® 718 based on the applied thermal load and explores its impact on cyclic elasto-viscoplastic behaviour and fatigue life predictions. The proposed approach is applied to a complete numerical life analysis of an aircraft turbine disk.

Study on the corrosion fatigue properties of ultrasonic surface strengthened axle steel

Owing to fatigue damage and environmental erosion, locomotive axles are prone to premature failure during service. It is therefore very important to improve the corrosion fatigue properties of axles. In this paper, the fatigue behavior of ultrasonic surface strengthened axle steel under corrosive environment was studied. The surface integrity of ultrasonic strengthened axle steel was characterized by microscopic analysis and hardness test. The fatigue data and fatigue fracture of axle steel under corrosion environment were compared. Also, the mechanism of the corrosion environment on fatigue crack initiation and propagation was analyzed. Results show that serious plastic deformation is generated in the surface of axle steel after ultrasonic strengthening. The grains in surface layer are obviously refined and get coarse gradually as deep into the matrix. The hardness of surface layer is greatly improved as well. The maximum value is located on the outermost surface, about 2 times of the matrix. Under the same fatigue load, the fatigue cycle number for ultrasonic strengthened axle steel is more than that of original sample. This is due to grain refinement, work hardening, and residual compressive stress induced by ultrasonic strengthening, which inhibits fatigue crack initiation in corrosion environment.