Dynamic Fatigue Research Articles

Dynamic fatigue resistance and marginal leakage of endocrowns fabricated with two different CAD/CAM ceramic materials.

Dynamic fatigue resistance and marginal leakage of endocrowns fabricated with two different CAD/CAM ceramic materials.

Dynamic Fatigue Reliability Analysis of Transmission Gear Considering Failure Dependence

Multiple failure modes and strength degradation are usually inherent in the gear transmission system, which brings new challenges for conducting fatigue reliability analysis and design. This paper proposes a novel dynamic fatigue reliability analysis method for failure dependence and strength degradation based on the combination of the Copula function and Gamma process. Firstly, the dynamic simulation model of the gear transmission system is established to obtain the dynamic stress-time history. The Gamma process is then used to describe the strength degradation to establish the dynamic stress-strength interference model. The marginal distribution functions of tooth contact fatigue and dedendum bending fatigue are calculated respectively based on the dynamic interference model. Finally, the joint distribution of the two failure modes can be obtained by the t-Copula function to characterize the failure dependence, and so the dynamic fatigue reliability considering failure dependence can be estimated. The effectiveness of the proposed method is illustrated with examples. The results reveal the temporal law of reliability and the effects of failure dependence on dynamic fatigue reliability.

Finite element analysis of MIG welded ERW steel pipe joint

To increase the life of a product/machine, it is vital for the companies to critically examine the product from various aspects. Strength of material and joints is an important aspect, considered by design engineers while working on existing or new design. Fatigue life is an important aspect while working on moving machinery. Bicycle is the machinery of daily use. Many efforts have been made by bicycle industries to check and increase the strength of various joint of bicycle. It has been revealed from literature that Finite Element Analysis (FEA) is less preferred by bicycle industries in India, for examine the fatigue life of various parts of bicycle. Various parts of bicycle are joined by means of welding, brazing and fastening, etc. It has also been revealed from literature that FEA is less used for evaluating the fatigue if of MIG welded pipe joints. An attempt has been made to examine the fatigue life of heat affected zone of MIG welded bicycle fork. FEA has been performed by using ANSYS software was used to performed dynamic fatigue testing machine at innovation Centre for Bicycle and Sewing Machines. Crack initiation of all three forks (F1, F2, F3), as analysed by ANSYS, occursat 25,835, 10,298 and 6182 cycles respectively. It has been revealed that FEA suits well for examining the fatigue life of bicycle fork.

Experimental measurement for dynamic tension fatigue characteristics of HMPE fibre ropes

This paper presents a full-scale experimental investigation for the fatigue properties of HMPE (high-modulus polyethylene) fibre ropes under dynamic loads. Three ropes with different constructions have been tested under various loading averages, amplitudes and periods. The results indicate that the stability of the inner structure plays an important role in fatigue resistance. Therefore, the 2 × 12 braided HMPE rope with more strands of a smaller diameter generally showed a longer fatigue life. An existing empirical equation is validated against the available data and the present experimental results, while a poor agreement is found in the cases of long loading periods. On this account, an equation is further proposed by taking into account the influences of loading period and rope configuration. After setting a proper base for the logarithm of failure time, a good convergence for the iterative fitting in the regression calculation and reasonable agreement against the experimental results have been found.

Dynamic fatigue behavior of lithium hydride at elevated temperatures

The fatigue properties of lithium hydride (LiH) are crucial to its application as neutron shielding and moderating at elevated temperatures. The dynamic fatigue tests of LiH were investigated with the notched 3-point bend (3 PB) specimens over ranges of loading rates at RT up to 400 °C. At RT, the results showed that slow crack growth (SCG) occurred prior to failure as the minor deviation from linearity to nonlinearity in the load-deflection curves. In addition, the fracture strength of LiH decreased with decreasing stress rate and the SCG zone gradually became smaller with higher stress rates, indicating evident dynamic fatigue phenomenon. However, the trends were quite different at 200, 300 and 400 °C due to accumulative creep damage for low stress rates at elevated temperatures. With increasing temperature and decreasing stress rate, there existed a transition of the dominated failure mechanism, from SCG to creep rupture. Evidence of very small SCG zone could also be detected at the notch for the failure dominated by creep rupture.

Influence of short-term cooling on the performance of superelastic and thermally-treated rotary NiTi files tested in dynamic cyclic fatigue model.

The purpose of the present study was to investigate the effects of various short-term cooling durations on the performance of both superelastic and thermally treated nickel titanium (NiTi) files, tested in a dynamic cyclic fatigue model. Superelastic RaCe (FKG, La Chaux-de-Fonds, Switzerland) and thermally treated RaCe EVO (FKG, La Chaux-de-Fonds, Switzerland) files of the same size and taper (25, 0.06) (n = 45 each) were tested using a dynamic cyclic fatigue model, where the number of cycles to failure (Nf) was measured at simulated body temperature. In each group, the samples were tested as received, after 5 seconds of cooling treatment, and after 15 seconds of cooling treatment (n = 15 each). Fractured file surfaces were investigated via scanning electron microscopy. Statistical analysis was performed using a one-way ANOVA with Scheffe's post hoc test at a significance level of 0.05. Significant differences in the Nf between the tested groups were found (p < 0.05) at each testing condition, where RaCe Evo files showed overall improved cyclic fatigue resistance. Only the RaCe groups at 5 second cooling showed significantly higher Nf than the control subgroup (p < 0.05). RaCe EVO group, showed no significant difference between the 3 subgroups (p > 0.05). Scanning Electron Microscope (SEM) images revealed typical features of cyclic fatigue behavior in both groups. Short-term cooling application for 5 seconds on superelastic NiTi files showed an enhanced cyclic fatigue resistance.

Influence of Sodium Hypochlorite and Chlorhexidine on the Dynamic Cyclic Fatigue Resistance of XP Endo Shaper Instruments

Objective This study evaluated the dynamic cyclic fatigue resistance of the XP-Endo Shaper (XPS), associated with chlorhexidine digluconate (CHX) or sodium hypochlorite (NaOCl) in two different formulations: gel (G) or liquid (L). Materials and Methods Sixty XPS were used in an artificial stainless-steel canal, and the files were fully immersed in the irrigating solution throughout the experiment until the fracture. The files were divided into six groups ( n = 10) based on the irrigation solution used: NaOCl(L), NaOCl(G), CHX(L), CHX(G), natrosol gel (NAT) (control), and lubricating oil (LO) (control). The artificial canal was manufactured 1.5 mm wide, 20 mm long, and, 3.5 mm deep with a straight cervical segment measuring 14.29 mm; an apical segment of 4.71 mm with 3 mm radius; and 90 degrees of curvature apical 1 mm long straight segment. Resistance to cyclic fatigue was determined by recording the number of cycles to fracture (NCF). Results The CHX(G), CHX(L), and OIL (LO) groups showed no significant difference between them and presented longer time to fracture ( p > 0.05). NaOCl(L) shows the lowest NCF without significant differences between NaOCl(G) and NAT. The NCF of the NaOCl(G) was statistically similar to the CHX(L) and statistically lower than the CHX(G) and OIL groups. NAT did not present a statistical difference of the NaOCl(L), NaOCl(G), and presented a significantly lower NCF than the CHX(G) ( p < 0.01). Conclusion The use of CHX(G) resulted in increased cyclic fatigue resistance of the XPS instruments compared to NaOCl or LO.

Effect of laboratory aging on the stiffness and fatigue cracking of asphalt mixture containing bamboo fiber

Bamboo fiber is a kind of environmentally friendly fiber, which exhibits low pollution, biodegradable, and renewable characteristics. Thus, bamboo fiber as a natural fiber used to replace other synthetic fibers in asphalt mixtures can not only enhance the road performance of the asphalt mixture, but also save resources and reduce environmental pollution. Fiber-reinforced asphalt mixture can enhance the cracking resistance performance of asphalt pavement in long-term service life. In this study, the stiffness and fatigue performance of fiber-reinforced asphalt mixture (bamboo fiber and polyester fiber) subjected to different aging conditions were investigated. Short-term aging and long-term aging procedure were carried out in accordance with AASHTO R30 and the NCHRP 09–54 project research (0, 4, and 7 days of treatment at 95 °C), respectively. Dynamic modulus and uniaxial fatigue tests were then performed to investigate the stiffness and cracking properties of specimens after different aging durations. Finally, the viscoelastic characterization and fatigue life were analyzed with the simplified viscoelastic continuum damage (S-VECD) theory. The test results indicated that the dynamic modulus values of the asphalt mixtures increased with aging levels and the observed difference after aging in the modulus of fiber-reinforced asphalt mixture is more noticeable. Furthermore, fiber addition increased the dynamic modulus values of the asphalt mixture, and the modulus change trend of bamboo fiber asphalt mixture (BAM) was similar to that of polyester fiber asphalt mixture (PAM). The fatigue life of the asphalt mixture decreased with an increase in aging levels, but the inclusion of fiber enhanced the fatigue resistance performance compared with hot mix asphalt (HMA). BAM exhibits stiffness and cracking performances similar to PAM after long-term aging. Hence, the renewable bamboo fiber could be used as a viable alternative fiber in the asphalt mixture to enhance the fatigue life of the asphalt mixture and realize green development.

Subcritical Crack Growth Parameters for Glass under Different Environmental Conditions

In the present work, subcritical crack growth in soda‐lime silicate glass is investigated under different environmental conditions. Crack growth parameters as a function of temperature and humidity were determined by dynamic fatigue tests. The specimens were pre‐damaged for constant initial crack lengths in all specimens using the Vickers indenter. The initial flaw size induced by the Vickers indenter was obtained by a scanning electron microscope picture of the fracture surface, which could also show the initial flaw geometry. Furthermore, the influence of humidity and temperature on the failure stress of specimens with a constant initial crack length was simulated and the deviations are shown. A comprehensive version of this investigation is currently (16.03.2021) under review in the Journal for Glass Structures and Engineering.

Research Method of Fatigue Performance of Surgically Implanted Heart Valve Stent

The aim of this study was to evaluate the fatigue property in vitro of a domestic surgically implanted heart valve stent (SIHVS). The domestic SIHVS was used as a testing sample, and a protocol was developed according to the standards GB 12279-2008 and ISO 5840-2:2015. A dynamic fatigue testing machine was used to apply for a 0.365 mm cyclic radial displacement at the end of the SIHVS. The SIHVS were observed after 400 million cycles by a scanning electron microscope. The observed results show that the structure of SIHVS is intact. There are no fracture, no obvious wear, and no loosening of the wire and casing. In the tested stents, no structural distortion, no cracks and obvious pits were observed. This study demonstrated that SIHVS structure meets the expected fatigue performance requirements.

Determination of critical testing frequency of the short fiber‐reinforced plastics for efficient fatigue test

AbstractHeat generated by viscous energy dissipation and friction during high‐frequency fatigue testing can reduce the fatigue life of short fiber‐reinforced plastics. Herein, we proposed new method of determining an appropriate testing frequency, taking into consideration the temperature increase in SFRPs during fatigue testing. An experimental procedure was developed to obtain viscoelastic and thermal parameters in a theoretical model using dynamic mechanical analyses and fatigue tests with an infrared camera. Then, according to the stress levels under tension in fatigue tests, a critical frequency was calculated to allow a temperature increase within 10°C. Finally, experimental fatigue tests at low stress levels and high frequencies were performed, demonstrating the applicability of the current method to design fatigue tests that take into account stress levels at a given frequency and a limited temperature rise.

Parametric Analyses of the Dynamic Response and Fatigue Life of a Compliant Vertical Access Riser with Internal Flow

Subsea interventions on wellheads can be directly performed from a platform using a compliant vertical access riser (CVAR), thereby incurring tremendous economic benefits. The dynamic response and the fatigue damage of a CVAR subjected to regular waves are important for assessing its application feasibility. Therefore, a reasonable numerical model is presented for assessing the damage to a CVAR considering the internal flow using the slender rod theory. The finite element method combined with a Newmark-β scheme is employed to discretize the equations and update the time integration. The Palmgren-Miner rule is applied for fatigue life prediction, focusing on the wave-induced dynamic response and fatigue life of a CVAR with various parameters, including the wave height and period, internal flow, and external current. The results demonstrate that the dynamic response and the fatigue life of the CVAR are relatively sensitive to the wave height and the external current. The tension and the displacement decrease with the increasing excitation frequency, but the opposite is true for the fatigue life. In addition, the internal flow has a weak influence on the CVAR.

Development and performance analysis of hemispherical piezoelectric transducer for road applications

Following the extensive research on piezoelectric technology and the increasing popularity of intelligent transportation during the past few years, the harvesting of pavement vibration energy has attracted increased research attention. At present, most innovations in the direction of the road piezoelectric energy are focused on the materials and structures of the transducers. However, few transducers meet the road requirements. Therefore, in this study, a hemispherical piezoelectric transducer was developed for road applications. We also analyzed the effects of different sizes and structures of transducers on energy harvesting efficiency based on laboratory tests, and the outcomes were compared with those from plane transducers. Under the excitation frequency of 10 Hz and the load of 0.7 MPa, the maximum output power of the planar transducer was 0.422 mW, while the power of the hemispherical transducer at the same load was 0.765 mW. Based on the dynamic load test, the ultimate load of the hemispheric transducer was 1900 N, which was 2.66 times that under standard axial load. Subsequently, a dynamic fatigue test was conducted for 24 h at the excitation conditions of 10 Hz and 0.7 MPa, wherein the voltage attenuation of the plane transducer exceeded 60%, while that of the hemispheric transducer was <20%. The experimental results show that the structure had a stable performance and good durability, and its strength and acquisition efficiency met the requirements of road transducers.

Influence of particle size selection methods on asphalt mixtures produced with lateritic aggregates

The aggregates of asphalt mixtures provide resistance to most of the load applied to the pavement, so it is important to evaluate the physical and mechanical properties of the aggregates. In some regions of Brazil, the availability of traditional aggregates (granitic) is becoming scarce due to the rapid increase in infrastructure projects and the longer distance of deposit to the paving works. To address the above issues, we tried to find substitutes for granitic aggregates in asphalt mixtures. Laterite is a tropical or sub-tropical weathering product, abundant material in the North and Northeast of Brazil. The study aimed to evaluate the performance of asphalt mixtures produced with lateritic and granitic aggregates and verify the influence of National Department of Transport Infrastructure (DNIT), Bailey, and French particle size selection methods in the mixtures, through mechanical tests. The Dominant Aggregates Range (DAR) technique was used to evaluate the behavior of the mixtures in terms of permanent deformation. The asphalt mixtures were analyzed through dynamic modulus, flow number, fatigue test, resilience modulus, and Modified Lottman test. The analysis of the mixtures by the DAR method showed results that did not corroborate the results of the mechanical tests. However, all the analyzed mixtures showed good performance regarding permanent deformation, especially the mixtures with lateritic aggregates. The asphalt mixtures produced with lateritic aggregates present better mechanical performance, enabling their use mainly in countries with a tropical climate and low rainfall, such as the northeast region of Brazil. The French method showed equivalent mechanical performance and even superior to the DNIT method, commonly used in Brazil.

Research on Dynamic Response Characteristics for Basement Structure of Heavy Haul Railway Tunnel with Defects

Based on the basic principle of thermodynamics, an elastoplastic damage constitutive model of concrete is constructed in this paper. The model is realized and verified in FLAC3D, which provides a solid foundation for the study of dynamic response and fatigue damage to the base structure of a heavy haul railway tunnel. The dynamic response and damage distribution of the base structure of a heavy-duty railway tunnel with defects were numerically simulated by the concrete elastic-plastic damage constitutive model. Then, by analyzing the response characteristics of the tunnel basement structure under different surrounding rock softening degrees, different foundation suspension range and different foundation structure damage degree are determined. The results show the following: (1) The elastoplastic damage constitutive model of concrete can well describe the stress–strain relationship of materials, especially with the simulation results of post peak softening being in good agreement with the test results, and the simulation effect of the unloading–reloading process of the cyclic loading and unloading test also meet the requirements. (2) The initial stress field and dynamic response of the tunnel basement structure under the action of train vibration load are very different from the ideal state of the structure design when the surrounding rock of the base is softened, the base is suspended, or the basement structure is damaged. With the surrounding rock softening, basement hanging, or basement structure damage developing to a certain extent, the basement structure will be damaged. (3) The horizontal dynamic stress amplitude increases with the increase in the softening degree of the basement surrounding rock. The horizontal dynamic stress of the measuring point increases with the increase in the width of the hanging out area when the hanging out area is located directly below the loading line. When the degree of damage to the basement structure is aggravated, the horizontal dynamic tensile stress of each measuring point gradually decreases. (4) The maximum principal stress increment increases with the increase in the fracture degree of the basement structure, while the minimum principal stress increment decreases with the increase in the fracture degree of the basement structure, but the variation range of the large and minimum principal stress increments is small. The research results have important theoretical and practical significance for further analysis of the damage mechanism and control technology of the foundation structure of a heavy haul railway tunnel with defects.

Effects of Second-Order Hydrodynamics on the Dynamic Responses and Fatigue Damage of a 15 MW Floating Offshore Wind Turbine

In order to investigate the effects of second-order hydrodynamic loads on a 15 MW floating offshore wind turbine (FOWT), this study employs a tool that integrates AQWA and OpenFAST to conduct fully coupled simulations of the FOWT subjected to wind and wave loadings. The load cases covering normal and extreme conditions are defined based on the met-ocean data observed at a specific site. The results indicate that the second-order wave excitations activate the surge mode of the platform. As a result, the surge motion is increased for each of the examined load case. In addition, the pitch, heave, and yaw motions are underestimated when neglecting the second-order hydrodynamics under the extreme condition. First-order wave excitation is the major contributor to the tower-base bending moments. The fatigue damage of the tower-base under the extreme condition is underestimated by 57.1% if the effect of second-order hydrodynamics is ignored. In addition, the accumulative fatigue damage over 25 years at the tower-base is overestimated by 16.92%. Therefore, it is suggested to consider the effects of second-order wave excitations of the floating platform for the design of the tower to reduce the cost of the FOWT.

Life-Limiting Aspects of an Melt-Infiltrated Silicon Carbide Fiber-Reinforced Silicon Carbide Matrix Ceramic Matrix Composite in Interlaminar Shear at Elevated Temperature

Abstract Life-limiting behavior of a melt-infiltrated (MI) silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC) ceramic matrix composite (CMC) was determined under interlaminar shear at 1316 °C in air using double-notch-shear test specimens. The three different shear loading configurations of dynamic fatigue, static fatigue, and cyclic fatigue were employed to assess their individual respective lives. The MI SiC/SiC CMC exhibited low susceptibility to fatigue (“slow crack growth”) regardless of loading configuration. A life prediction model for interlaminar shear in cyclic fatigue was developed based on the fracture mechanics framework. The newly developed cyclic fatigue model as well as the previously developed dynamic and static fatigue models were all in good agreement with the experimental data, indicating that the governing failure mechanism under interlaminar shear was consistent, independent of fatigue loading configuration.

Enhancing bending fatigue resistance of the CoCrFeMnNi high-entropy alloy thin foils by Al addition

Fatigue behaviors of the CoCrFeMnNi-based high-entropy alloy thin foils with different Al addition were investigated under dynamical bending fatigue loading. The results reveal that the Al addition can effectively decrease the cyclic strain localization and improve the fatigue resistance, which is associated with the reduced cyclic slip irreversibility. The physical reasons for such reduction can be attributed to the enhanced planar-slip ability induced by Al addition. Furthermore, the formation of BCC phases caused by 10 at.% Al addition also leads to a delay in the fatigue crack propagation.

Implementing a robust wrist dynamic fatigue task: repeatability and investigation of the features involved.

In this study, we implemented a protocol for the robotic assessment of the effects of forearm muscle fatigue on wrist dynamics. The potential of robotic devices lies in the possibility to control and measure a wide variety of kinematic and physiological variables, both in repeated sessions over time and during real-time assessments. The implemented fatigue task is tailored to the robotically assessed single-subject maximal force and based on a real-time evaluation of muscle activity. The protocol resulted to be repeatable across sessions evaluated on the same subject and a preliminary step toward a better understanding of which features should be monitored to design a robust and strongly controlled dynamic fatiguing task.

Laboratory Characterization of Geosynthetics-Reinforced Asphalt Mixture.

In order to improve the mechanical properties of asphalt pavement, geosynthetics can be employed in asphalt mixture. This research designed 12 reinforced schemes based on the types of geosynthetics, bonding layers and reinforced position. For the relative tests carried out, reinforced specimens were prepared according to each individual scheme. Moreover, rutting tests, bending creep tests and split fatigue tests were carried out on reinforced specimens in the laboratory. The results obtained in this investigation showed that the dynamic stability, bending creep rate and fatigue life of geocell-reinforced specimens are better than those of geogrid-reinforced specimens. The bonding layer of Styrene-Butadiene-Styrene (SBS) modified asphalt is better than epoxy modified asphalt. The dynamic stability and fatigue life of middle reinforcement are better than those of the lower reinforcement, while the bending creep rate of the lower reinforcement is better than middle reinforcement. In addition, reinforced scheme (9) has the largest increase in dynamic stability and fatigue life by 103 and 137%, respectively, and reinforced scheme (12) has the largest reduction in bending creep rate by 46%. However, scheme (9) improved dynamic stability and fatigue life by 43 and 29% higher than scheme (12), while the reduction of flexural creep rate of scheme (12) is only 7% higher than that of scheme (9).