High Frequency Cyclic Loading Research Articles

Rock bolts under cyclic loading: Mechanical performance and damage assessment by acoustic emissions

Rock bolt support is one of the key methods to maintain the stability of underground space. The durability of the rock bolt can be weakened by cyclic loading, resulting in premature failure of the underground structures. A comprehensive understanding of the performance of the bolting system under cyclic loading is essential to assess the safety of the bolting system and underground structures. In this context, this study investigated the mechanical performance of rock bolts installed in simulated soft and medium hard rock and subjected to cyclic loading. The Acoustic Emission (AE) technique was used to monitor internal damage to the bolt system under different loading conditions. A cumulative AE energy slope method has been proposed to determine the onset of the macro crack formation stage. The rock bolt demonstrated an extended fatigue life in soft rock, but its condition worsened when implanted in medium hard rock. The cyclic loading resulted in a slight improvement in the load bearing capacity of the soft rock bolt system and a significant deterioration in the medium hard rock bolt counterpart. The main fatigue failure modes of the rock bolt systems were splitting and shear failure of the surrounding rock, and debonding of the interface. Increasing the amplitude of the cyclic loading reduced the macro crack initiation cycle for both rock bolt systems, whereas increasing the frequency had different effects. The damage variable increased with frequency and amplitude for both rock bolt systems. The toughness of the soft rock bolt degraded during cyclic loading, while the high frequency cyclic loading did not modify the toughness of the medium hard rock bolt.

Influence of high frequency on the fatigue life of metallic single lap joints

Polymer adhesives are known to exhibit time dependent mechanical behaviour, that becomes more and more evident approaching the glass transition temperature, Tg. When subjected to fatigue, bonded joint lifetime can be therefore affected by the loading frequency and amplitude. According to the literature, the influence of the frequency on the fatigue behavior manifests as a rise of the temperature in the adhesive due to the hysteretic heating, which is related in turn to Tg and to the viscoelastic properties of the adhesive. In this paper, cyclic loading was applied to single lap shear joints until failure at frequencies in the range of 70–90 Hz, that are little explored by the existing literature. The aim is twofold: on one side, to investigate the possibility to speed up fatigue tests in comparison to tests performed in the range of 7–9 Hz; on the other side, to explore the possibility to generate stress-life data in a range of number of cycles between 106 and 108, therefore two order of magnitude higher then usual, without exceeding with the time required for the tests. The joints were made with both aluminum and stainless-steel substrates bonded with a structural epoxy adhesive, to manufacture a Single Lap Joint (SLJ). Two loading ratios R (respectively 0.1 and 0.4, defined as the minimum over the maximum force of the fatigue cycle) and different load ranges were applied. Digital Image Correlation (DIC) technique was used to assess the presence of creep strains. A preliminary investigation consisting in a Dynamic Mechanical Analysis (DMA) of bulk adhesive for the range of frequency of interest, and in the measurement of the temperature of the adhesive layer during some selected fatigue tests was carried out. No significant changes of the viscoelastic properties of the adhesive were found for the frequency of interest, and, at the same time, temperature measurements revealed that the temperature increased by a few degrees, remaining in any case far from the glass transition temperature. The test results showed that only small effect due to the application of a high frequency cyclic loading on the fatigue life apparently occurs for tests carried out at the lowest load ratio, in particular when the applied loads were relatively low, and the number of cycles at failure relatively high. On the opposite, the results of tests carried out at the highest load ratio are affected by the loading frequency, and it has been related to the presence of significant creep deformation within the adhesive layer.

A study of the influence of high frequency cyclic loading on the structure and properties of weld connections in process pipelines

Introduction. Pipeline systems are exposed to several conditions that lead to a drastic reduction in their durability, primarily due to variable low-frequency and high-frequency loads arising in a process pipeline due to the operation of compressor units. Hence, fatigue failure occurs, leading to the pipeline failure. As early as at the pipeline installation stage, sections of process pipelines have weld connections, and thermal welding cycles have an adverse effect on the properties of materials exposed to fatigue loading. The study of weld connections in steel pipelines exposed to high-frequency vibrations and effects of weld seam defects on durability characteristics are the focus of this research.
 Materials and methods. Low-carbon pipeline steel St20 was selected for the study. The radiographic inspection method, optical metallography, microhardness of structural phases, and the method of high-frequency fatigue tests were used.
 Results. The results and principal conclusions about the effect of welding defects on durability characteristics of welded samples, made of pipeline steel and exposed to high-frequency fatigue tests, are presented; structural changes in weld connections are analyzed using optical metallography and microhardness methods. Defects of weld seams and their dimensions were identified by means of radiographic inspection. A comparative analysis of durability limits, demonstrated by the parent metal of the model material that has defective weld connections, and the same limits of defect-free samples is provided. The main causes of failure of weld joints, exposed to high-frequency vibrations, are identified.
 Conclusions. Having summarized the research findings, we can argue that high-frequency vibrations have a negative impact on the parent metal of a process pipeline and its weld joints. The weld seam is the point of failure; defects trigger destruction, and their presence has a higher impact on fatigue characteristics than their dimensions or types. Characteristics of durability in case of exposure to high frequency loading applied to a weld joint in the gigacycle range are 67 percent below those of the parent metal.

The Influence of High-Frequency Cyclic Loading on the Mechanical Properties of Steel

The modern development of high-speed transport causes a requirement toughening of the safety requirements for rolling stock and upper track components. Researchers and constructors are actively working towards the creation of more complete and adequate models of constructers and their elements, as well as new materials for their manufacture. The problem of studying traditional materials in various modes of rolling stock operation, including increasing the frequencies of dynamic influences and imposing effects from various loads and oscillations to the high-frequency area, becomes relevant and timely. This work is devoted to modeling the influence of high-frequency loading on a sample made of rail steel, this kind of influence takes place when rolling stock passes through an artificial constructer. It is assumed that the work of the rail within the sleepers step is described by the laws of uniaxial tension-compression. Experimental results and conclusions on ultrasonic high-frequency cyclic tests and structural analysis of the model material - low-carbon steel of the perlite class are presented.

Study of the fatigue behaviour of synthetic nodular cast irons at low and high frequency cyclic loading

The paper presents the results of low and high frequency fatigue tests carried out on nodular cast iron. The specimens of synthetic nodular cast irons from three different melts were studied in the high cycle fatigue region (from 105 to 108 cycles) using fatigue experimental equipments for low and high frequency cyclic loading. Low frequency fatigue tests were carried out at frequency f ≈ 120 Hz using the fatigue experimental machine Zwick/Roell Amsler 150HFP 5100. High frequency fatigue tests were carried out at frequency f ≈ 20 kHz using the ultrasonic fatigue testing device KAUP-ZU. Both of them were carried out at sinusoidal cyclic push-pull loading (stress ratio R = -1) at ambient temperature (T ≈ 20 °C). The relationship σa = f (N) and fatigue strengths were determined experimentally; mechanical properties, microstructures and fracture surfaces were investigated.

Effect of Surface Mechanical Attrition Treatment on the very high cycle fatigue behavior of TC11

As an important engine component material, TC11 (Ti-6.5Al-3.5Mo-1.5Zr-0.3Si) titanium alloy is subjected to high frequency cyclic loading and its failure occurs beyond 109cycles. It is thus essential to investigate the very high cycle fatigue (VHCF) behavior of this alloy. Surface Mechanical Attrition Treatment (SMAT) is a promising surface treatment technique to improve fatigue strength by modifying the surface microstructure. Therefore, it is important to understand the fatigue damage and failure process of SMATed titanium alloy in the VHCF regime. In this work, VHCF tests of TC11 before and after SMAT under fully reversed loading were conducted at room temperature by using an ultrasonic fatigue testing machine at a frequency of 20 kHz. The preliminary results seem to indicate that SMAT can reduce fatigue strength and fatigue life of TC11. Fracture surface analysis of the specimens before and after SMAT was performed using scanning electron microscope (SEM) to investigate the mechanisms of crack initiation and propagation. Particular attention was paid to fatigue crack initiation sites. The effect of SMAT on damage mechanism of SMATed TC11 in the VHCF regime was discussed.

Fatigue Properties of Nodular Cast Iron at Low Frequency Cyclic Loading

Abstract Three melts of ferrite-pearlitic nodular cast iron with different charge composition were used for fatigue tests. Wöhler fatigue curves and fatigue strength were obtained, and microstructure and fracture surfaces were investigated. The aim of the paper is to determine the influence of charge composition on microstructure, mechanical and fatigue properties of synthetic nodular cast irons and their micromechanisms of failure. Fatigue tests were realised at low frequency sinusoidal cyclic push-pull loading (stress ratio R = −1) at ambient temperature (T = 20 ±5°C). They were carried out with using the fatigue experimental machine Zwick/Roell Amsler 150HFP 5100 at frequency f ≈ 120 Hz. The results of fatigue tests at low frequency cyclic loading are compared with fatigue properties at high frequency cyclic loading.

Comparison of low and high frequency fatigue tests

Abstract The paper presents the results of low and high frequency fatigue tests carried out on nodular cast iron. The specimens of synthetic nodular cast irons from three different melts were studied in the high cycle fatigue region (from 105 to 108 cycles) using fatigue experimental equipments for low and high frequency cyclic loading. Low frequency fatigue tests were carried out at frequency f ≈ 120 Hz using the fatigue experimental machine Zwick/Roell Amsler 150HFP 5100; high frequency fatigue tests were carried out at frequency f ≈ 20 kHz using the ultrasonic fatigue testing device KAUP-ZU. Both fatigue tests were realised at sinusoidal cyclic push-pull loading (stress ratio R = −1) at ambient temperature (T = 20 ± 5 °C).

Fatigue tests of nodular cast iron at low and high frequency cyclic loading

The paper presents the results of fatigue tests of nodular cast iron at low and high frequency cyclic loading. For comparison of fatigue properties, the specimens from three melts of nodular cast iron with different microstructure and mechanical properties were used. Fatigue tests were carried out at low and high frequency sinusoidal cyclic push-pull loading (stress ratio R = –1) at ambient temperature (T = 20 ± 5°C). Low frequency fatigue tests were carried out at frequency f ≈ 120 Hz; high frequency fatigue tests were carried out at frequency f ≈ 20 kHz.

Comparison of Fatigue Properties of Nodular Cast Iron at Low and High Frequency Cyclic Loading

The paper deals with comparison of the fatigue properties of nodular cast iron at low and high frequency fatigue testing. The specimens from three melts of nodular cast iron with different microstructure and mechanical properties were used for experiments. Fatigue tests were carried out at low and high frequency sinusoidal cyclic push-pull loading (stress ratio R = –1) at ambient temperature (T = 20 ± 5°C). Low frequency fatigue tests were carried out using the fatigue experimental machine Zwick/Roell Amsler 150HFP 5100 at frequency f≈ 120 Hz; high frequency fatigue tests were carried out using the ultrasonic fatigue testing device KAUP-ZU at frequency f≈ 20 kHz.

High frequency cycling behaviour of three AZ magnesium alloys – microstructural characterisation

Abstract Three Mg–Al–Zn alloys, namely AZ31, AZ63 and AZ91, were subjected to high frequency cyclic loading with the aim of revealing their fatigue behaviour. AZ63 and AZ91 alloys contained discontinuous and continuous precipitates and also the intermetallic compound Mg17Al12. Samples were loaded step by step at increasing stress amplitudes at room temperature. Three characteristics of the cycled samples were investigated: the sample surface, the fatigue fracture surface and the fracture surface after the static fracture of samples. Details of the fatigue and fracture behaviour were examined using scanning electron microscopy. The significant roles of twinning and dislocation movement during the high frequency cycling are discussed. The limited plasticity of alloys estimated during the high frequency cycling is due to a decrease in the moving dislocation density entering into the thermally activated process.

Deformation and Degradation Mechanisms of Railway Ballast under High Frequency Cyclic Loading

AbstractThe increased demand for higher speeds and increased freight capacity in railroad transportation exacerbates the rate of ballast degradation that leads to unacceptable track deformation and frequent maintenance. In response, a series of large-scale cyclic triaxial tests was performed to investigate the combined effect of train speed (frequency), axle load, and confinement on the deformation and degradation of ballast. In these tests, the load frequency f was varied from 5 to 60 Hz to simulate train speeds of 40–400 km/h. Two sets of deviator stress magnitude qmax,cyc (230 and 370 kPa) were applied to resemble axle loads of 25 and 40 t, respectively, and the effect of three levels of confining pressure σ3′ (10, 30, and 60 kPa) was examined. The results indicate that three distinct categories of permanent deformation mechanisms exist at various levels of f, qmax,cyc, and σ3′. Ballast degradation was more pronounced at higher f, and it had a more profound effect on cyclic densification. The resilien...

Influence of Reinforcement Geometry on the Very High-Cycle Fatigue Behavior of Aluminium-Matrix-Composites

During technical operation, high performance materials are partially exposed to high frequency cyclic loading conditions. Furthermore, the small strains in the very high cycle fatigue (VHCF)-regime lead to accumulative damage which causes crack initiation related to an appropriate local deformation leading to final fatal fracture. At the same time, quite high requirements with regard to high number of cycles without any damage are demanded for many applications. Fields of application of these light-weight, but expensive materials, are e.g. in the automobile industry (e.g. engine blocks, cylinder heads, brakes).The fatigue behavior of Al-matrix composites (Al-MMCs) reinforced by alumina particles (15 vol.% Al2O3) or short fibers (20 vol.% Saffil), respectively, was already intensively studied in the LCF and HCF range. The present study is focusing on investigations in the very high cycle fatigue regime at stress amplitudes up to 140 MPa to reach fatigue life of about 1010 cycles. All experiments were carried out using an ultrasonic fatigue testing device under symmetric loading conditions (R=-1). Fatigue tests were accompanied by in situ thermography measurements to record the temperature of the whole specimen and to find “hot spots” indicating changes in microstructure and therefore the initiation or growth of cracks. Moreover, the resonant frequency as well as the damage parameter were evaluated to determine the beginning of damage. For a better understanding of the damage mechanism (matrix decohesion, matrix failure or failure of reinforcement) all fractured surfaces were investigated by scanning electron microscopy. The combination of these methods contributes to a better understanding of the underlying mechanism of damage in aluminum-matrix-composites.

Repeated Loading of Cohesive Soil – Shakedown Theory in Undrained Conditions

Abstract The development of industry and application of new production techniques could bring about extraordinary problems that have been neglected. One of these challenges in terms of soil mechanics is high frequency cyclic loading. Well constructed foundation may reduce this troublesome phenomenon but excluding it is usually uneconomic. In this paper, shakedown theory assumptions were studied. Cyclically loaded soils behave in various ways depending on the applied stress rate. Common cohesive soils in Poland, i.e., sandy-silty clays are problematic and understanding of their behaviour in various conditions is desired. In order to study repeated loading of this material, cyclic triaxial test were carried out. Cyclic loading tests were conducted also in one way compression. These methods in small strain regime allow permanent strain increment analysis with resilient response after numerous cycles. This behaviour was subsequently exploited in the study of shakedown theory. This paper contains some conclusions concerning the above-mentioned theory.

Effect of Temperature on the Subsurface Microstructure and Mechanical Properties of AA 7075-T6 in Machining

Machining processes such as turning are known for generating high strains, strain rates and temperatures. These mechanical and thermal loadings combined on the workpiece can affect the surface microstructure in the context of average grain sizes, texture … etc. Therefore a thorough understanding of these two competing phenomenon on the surface should be investigated to predict the surface microstructure and therefore mechanical properties. However more and more specific parts used in high frequency cyclic loading applications require not only an understanding of the surface but also the subsurface microstructure evolution in the context of deformation resistance and fatigue failure. The main scope of this paper is to investigate the thermal effects of a machining process on the subsurface grain size and hardness through a modelling approach. In this work, a physics-driven model to predict temperature profiles in turning is proposed. Based on the predicted results, a diffusion-based model to predict the average grain size growth in the subsurface is developed, subsequently the Hall-Petch phenomenological equation was used to predict the hardness evolution in the subsurface. To validate the predicted results, machining experiments were conducted for aerospace aluminum alloy AA-7075-T6.

Li-Ion Battery

Ultrasonic welding is a solid-state welding process that can be used for multi-layered thin structures of lithium-ion battery. This welding methodology provides a good solution, using high frequency cyclic loading and transferring frictional energy into weld areas. To take advantage of the benefits of ultrasonic metal welding, it needs to understand the relationship between manufacturing factors(amplitude, pressure, weld time). This paper presents preliminary results for the effect of welding parameters on multi-layered thin structure. The welding strength.is determined to explore the weldability of the structure

HIGH-CYCLE FATIGUE BEHAVIOR OF AM3 NICKEL-BASE SINGLE CRYSTAL SUPERALLOY AT HIGH TEMPERATURE

A single crystal nickel-base superalloy with ‹001› orientation was subjected to high cycle fatigue loading at temperature of 700°C and 870°C. The tests were performed in ambient atmosphere under load control at a stress ratio R =σ min /σ max =0.1 and a frequency of 83.3 Hz on smooth specimens. In this paper, the premature initiation and rapid propagation of cracks to failure due to high frequency cyclic loading were explored. The dislocation characteristics and fracture surface observation were evaluated through scanning electron microscopy and transmission electron microscopy, respectively. The results showed that the fatigue strength at 700°C was higher than that at 870°C. At 700°C the interaction of cyclic stress with high temperature induced the precipitation of homogeneous hyperfine secondary γ′ particles, that is beneficial to fatigue strength. At 870°C, the cyclic stress led to the formation of persistent slip bands moving through the γ matrix channels and the γ′ precipitates. The morphology change of γ′ phase was not notable during the deformation at high frequency cyclic loading.

Two-time scale fatigue modelling: application to damage

A temporal multiscale modelling applied to fatigue damage evolution in cortical bone is presented. Microdamage accumulation in cortical bone, ensued from daily activities, leads to impaired mechanical properties, in particular by reducing the bone stiffness and inducing fatigue. However, bone damage is also known as a stimulus to bone remodelling, whose aim is to repair and generate new bone, adapted to its environment. This biological process by removing fatigue damage seems essential to the skeleton lifetime. As daily activities induce high frequency cycles (about 10,000 cycles a day), identifying two-time scale is very fruitful: a fast one connected with the high frequency cyclic loading and a slow one related to a quasi-static loading. A scaling parameter is defined between the intrinsic time (bone lifetime of several years) and the high frequency loading (few seconds). An asymptotic approach allows to decouple the two scales and to take into account history effects (Guennouni and Aubry in CR Acad Sci Paris Ser II 20:1765–1767, 1986). The method is here applied to a simple case of fatigue damage and a real cortical bone microstructure. A significant reduction in the amount of computation time in addition to a small computational error between time homogenized and non homogenized models are obtained. This method seems thus to give new perspectives to assess fatigue damage and, with regard to bone, to give a better understanding of bone remodelling.

Synthesis, characterization, and cyclic stress‐influenced degradation of a poly(ethylene glycol)‐based poly(beta‐amino ester)

This study aims to fundamentally understand the polymer network formed by poly(ethylene glycol) diacrylate (PEGDA) MW 700 and 3-methoxypropylamine (3MOPA) as well as to characterize the degradation response of this material with and without applied cyclic stress. Macromer reaction chemistry was confirmed by (1)H NMR measurements. UV calorimetry analysis revealed conditions of network formation were dependent on molecular weight of the PEGDA monomer and light intensity. The glass transition temperature of all networks PEGDA MW 258, 575, and 700 were measured and found to be in the range of -40 to -30 degrees C with a rubbery moduli ranging from 4 to 10 MPa by DMA. Degradation studies were performed with and without applied cyclical stress, and in most cases, elastic modulus decrease and mass loss occurred steadily over a 24-h period. Unexpected partial crystallization was discovered to occur in the networks containing higher molecular weight PEGDA in the presence of humidity and high frequency cyclic loading. In all materials, high frequency applied cyclic loading during in situ degradation resulted in catastrophic fracture of the material prior to an appreciable decrease in modulus.

Reliability Evaluation of Piezoelectric Micro-Actuators With Application in Hard Disk Drives

Piezoelectric micro-actuators have been extensively studied and used in hard disk drive head positioning systems. In these cases, piezoelectric micro-actuators/sensors experience high frequency cyclic loading during their operations. The fatigue failure and the lifespan of such micro-actuators become a concern of researchers and engineers. However, the probability and statistics based reliability theory has not been well developed for piezoelectric micro actuators. In this paper, a probabilistic approach is presented to evaluate the reliability of piezoelectric micro-actuators. Based on the relationship between the lifetime degradation mechanism of piezoelectric actuators and the electric field strength, an interference model of electric load and strength is introduced for the reliability study of piezoelectric micro-actuators. Furthermore the reliability model is expanded into a 2-D case to take into account the effects of both driving voltage and temperature. A 2-D interference model incorporating the 2-D strength and load is proposed to obtain the relationship among the reliability, usage cycles, driving voltage and temperature. A case study of a piezoelectric micro-actuator used in a disk drive head positioning system demonstrates the application of the proposed approach.