Friction Fatigue Research Articles

Exploring memory mechanisms for friction fatigue in vibratory pile driving

This paper studies the mechanism that leads to the reduction of frictional soil reaction forces during pile driving, termed friction fatigue. We focus on axial vibratory driving, an environmentally friendly monopile installation method, and examine two friction fatigue formulations, i.e. a penetration-based and a cyclic memory mechanism. Friction fatigue plays a pivotal role in pile drivability and post-installation bearing capacity for piles installed via axial vibratory driving. Through numerical analyses and validation against field data from onshore experiments, the efficacy of these memory mechanisms is assessed. The results reveal that the proposed cyclic memory mechanism provides consistently more accurate predictions than the corresponding penetration-based approach, offering a promising option for modelling friction fatigue in vibratory driving. This study advances our understanding of friction fatigue in the context of vibratory driving for offshore monopile installation, emphasizing the need for further numerical and experimental works in this topic.

Modelling and fatigue reliability investigation on wear prediction of piston/cylinder pair based on friction fatigue mechanism

This paper aims to assess the wear reliability characteristics of the piston/cylinder pair based on the wear failure prediction using numerical and experimental techniques for the water hydraulic state. This is due to the complex forces and contact states acting in the piston, hence, making it difficult to establish a numerical model for wear failure prediction. The Hertzian contact and Elastic-Plastic mechanical equivalence are proposed in numerically modelling the friction fatigue mechanism based on asperity damage for piston/cylinder pair. An experimental analysis is conducted for the reciprocating ceramic peek-2507 steel tribopair to validate the effectiveness of the prediction model. The error between the numerical and experimental models is assessed to be less than 10% with a coefficient of determinant R2 of 0.99. The numerical wear data were scattered within the 10% confidence interval, indicating the high survivability of the predicted data. In addition, the reliability characteristics based on the volume of wear predicting in risk monitoring using the Weibull probability distribution function are proposed to model the reliability and probability of failure for the piston/cylinder pair. From the volume of wear prediction from the computed Mean-Volume-To-Failure (MVTF) = 17.8 mm3, the probability of failure based on the numerical modelling is estimated to be at 0.52. Hence, the proposed numerical model is suitable for predicting the wear volume in the water hydraulic state for various conditions.

Fretting fatigue of cast iron and aluminium – A strength assessment method based on a worst-case assumption

Many components made of cast iron (e.g., in combustion engines) and aluminium (e.g., in aircraft construction) are subject to fretting fatigue. This results in a need for a method for assessing the strengths of the aforementioned materials that takes into account the reduction in fatigue strength due to fretting as well as the accompanying reduction in service life. In a first paper, the authors already presented a calculation method for the fail-safe design of steel–steel contacts subject to fretting fatigue. This enables the engineer or designer to perform a strength assessment for any component connection made of steel. The calculation method is based on a tribological worst-case assumption and can be integrated into the analytical strength assessment of the internationally known FKM Guideline. The strength reduction is taken into account by use of empirically determined fretting factors. The frequent failures of component connections made of cast iron and aluminium in the field made an extension of the calculation method became necessary. This work therefore includes experimental investigations into the materials EN-GJS-700, EN-GJS-400 and EN-GJL-300 (cast iron), as well as EN AW-7075 T651, EN AW-6082 T651 and EN AW-5083 (aluminium). Since the main parameters determining fretting fatigue strength are slip amplitude and contact pressure, the worst-case combinations of these parameters (resulting in the lowest friction fatigue strength) were first determined for each of the two material groups using a laboratory test setup. These parameters could be found at sa=10μm;p=40MPa for cast iron and sa=5μm;p=10MPa for aluminium. Based on these worst-cases, the fretting fatigue limits of the aforementioned materials were determined, as well as the effect of mean stress. The fretting factors of the materials were derived from the experimental results. Additional experimental investigations using a connecting-rod-like geometry served to validate an application typical of the industry. Using the calculation method, the degree of utilisation of the connecting rods could be determined with good accuracy (maximum error: 18.7%).

Penetration Characteristics of Suction Caisson for Offshore Wind Power: A Field Study

Suction caisson is a new offshore wind power foundation structure developed in recent years. Understanding its penetration characteristics is crucial to the successful application. A field test was conducted in the eastern waters of Rudong, Jiangsu Province, China, to investigate the penetration process of suction caisson. The test results demonstrate that suction caisson can penetrate smoothly to a predetermined elevation of seabed soil under the complex environmental loads, such as natural wind and wave currents. The inclination of the caisson is only 0.018° once the penetration process is complete. The pore water pressure at the outer skirt is primarily influenced by the tide level and drainage conditions of the contact soil layer during penetration, and the peak effective interface pressure at the skirt-soil interface decreases by about 46.7% due to negative pressure inside the skirt. Frictional fatigue effects are found at the skirt-soil interfaces. Meanwhile, the seepage reduction and squeezing induced resistance effects at the skirt-soil interface are the leading causes for the different distributions of effective interface pressure between the inner and outer skirts of the caisson. The findings of this study can guide the future penetration of suction caisson under challenging geological circumstances.

Structural and functional regularities of the damage accumulation and failure in metals under dynamic loading and wear

The effect of damage caused by friction and wear on the accumulation of fatigue damage in the near-surface layers of the material used in technical systems operating under dynamic loading is studied. A comparative study of the samples of carbonized Cr – Mn – Si steel under ultrasonic loading in the range up to 109 cycles and the samples of steel 45 loaded at a permanent frequency of 100 Hz to simulate conditions of tribological tests for frictional fatigue revealed the same types of damage occurring in the characteristic frequency ranges of loading. To assess the effect of friction fatigue on damage accumulation and the probability of operational failures the authors have supposed that the processes of structural damage accumulation in cyclic and frictional fatigue are similar. The analysis of experimental data on the behavior of the friction coefficients and the magnitudes of broadening X-ray lines which characterize changes in the dislocation structure of the metallic structural materials (steels and titanium alloys) upon friction and the friction fatigue curves confirmed that the process of friction fatigue failure occurs via the mechanisms of low and high cycle fatigue that proves the validity of the proposed approach. The calculation results for the probability of the compressor failure are presented as an example. The calculations are based on the friction fatigue curves in a wide range of loading cycles obtained upon testing the crankshaft neck. The use of friction fatigue curves thus obtained provided assessment of the effects of combined action of the dynamic loading and friction, resulting in increased gaps and the dynamic loads (due to the wear of contacting parts) on the fatigue damage accumulation, durability and the reliability of the mechanical systems during operation.

Numerical Investigations of Tribological Characteristics of Biomimetic-Textured Surfaces

Rail transportation has dramatically improved travel convenience, but it has also led to environmental pollution and energy consumption issues. These challenges can be partially addressed by reducing friction loss in the mechanical transmission of rail systems. This paper examines the tribological properties of bionic-textured surfaces inspired by snake- and sharkskin. This study focuses on generating bionic textured surfaces with randomly distributed peaks through numerical simulation and connecting them to a transient Reynolds equation and friction fatigue model. The bionic surface wear lubrication model considers the lubricating film’s thickness and contact pressure obtained from the GT model. The results reveal that the existence of a bionic texture can reduce the friction coefficient and wear amount on the contact surface. The findings of this study not only offer a potential solution for reducing energy consumption and emissions in intelligent rail transit systems but also hold promise for providing further insights into the numerical simulation of bionic weaving and the investigation of tribological characteristics.

ARTIFICIAL INTELLIGENCE TECHNIQUES FOR IMPROVING CYLINDRICAL SHRINK-FIT SHAFT-HUB COUPLINGS

AbstractDue to the continuous progress in information technology, complex problems of machine elements can be investigated using numerical methods. The focus of these investigations and optimizations often aims to reduce the stresses that occur or to increase the forces and torques that can be transmitted. Interference fit connections are an essential machine element for drive technology applications and are characterized by their economical fabrication. The transmission of external loads over a large contact surface between the shaft and hub makes it less vulnerable to impact loads. These advantages contrast with disadvantages such as the limited transmittable power, the risk of friction fatigue, and stress peaks at the hub edges, which can lead to undesirable and sudden failure, especially in the case of brittle hub materials. Analytical approaches already exist for optimizing these connections, which are expensive, time-consuming, and complex, so a high degree of expert knowledge is required to apply these methods in practice successfully. This paper presents a novel method using the example of optimizing the pressure distribution in the interface of a shrink-fit connection.

Laboratory Test Study on Pile Jacking Penetration Mechanism Considering Different Diameter and Length Based on Photoelectric Integration Technology

Model tests are carried out on the jacked single piles of different diameters and pile lengths under the model pile of different diameters and pile lengths in clayey soil, which aims to investigate the penetration mechanical mechanism. How to accurately test the pile end resistance and pile side resistance during jacked pile sinking is particularly important. In this paper, a full-section spoke-type pressure sensor, a double diaphragm temperature self-compensating fiber Bragg grating (FBG) earth pressure sensor and a sensitized miniature FBG strain sensor are jointly applied to a single pile penetration model test to test a single pile driving force, pile end resistance and pile body stress during penetration. The test results show that the load transfer performance of test piles will be affected by different diameters, and the axial force transfer capability of a large diameter in the depth direction is better than that of a small diameter since the compacting effect is more obvious. The unit skin friction of the pile increases gradually as the depth increases, which is larger due to the lateral extrusion force increasing as the diameter increases. At the same depth, the unit skin friction of two different diameter piles demonstrates “friction fatigue”, which also decreases obviously as the depth increases. Under the conditions of this test, the maximum frictional resistance of the pile TP1 pile side is about 27.7% higher than that of the test pile TP2. In the static pile sinking process of three test piles in cohesive soil, 50% is end bearing; therefore, there is 50% friction, and the diameter influences the end bearing and the length influences the friction.

Experimental Study and Analysis of Fretting Wear and its Influence on Functionality of Mechanical Components

Fretting occurs when there is tangentially low-amplitude vibrational motion (range tens of nanometres to tens of micrometers) between nominally stationary contact surfaces. This is a common occurrence as most machines are exposed to vibration both in transit and in operation. Contacts that appear to have no relative movement, such as press-fit, can actually slide on a scale of 1 μm with alternating pendulum loads. It is very difficult to eliminate such movements and the resulting friction. Fretting wear and frictional fatigue occur on almost every machine and otherwise cause a total failure of robust components. Studies have shown that, in contrast to other forms of wear, the frequency of machine fit problems has not diminished in the last few decades. Experiments were conducted on a fretting wear testing machine of amplitude range 10–200 μm, frequency range 4–120 Hz and surface roughness were recorded for both polished and unpolished condition. The correlation was made between changing parameters and variation in surface roughness. Friction fatigue is an important but almost unknown factor when load-bearing components are damaged at very low loads. Therefore, we will conduct an experimental study of fretting and its control parameters. For unpolished specimen, the variation of amplitude with respect to the coefficient of friction (COF) increases to 0.5, then it becomes linear. For semi-polished specimen, it increases to COF 0.45 and then it starts decreasing. For a fully polished specimen, there is no change in COF to 75 μm and then it starts increasing. According to the experimental data, for all specimens’ COF constantly decrease with increasing the load.

Analytical method for predicting pile running during driving

Most offshore structures, such as conventional oil and gas jacket platforms or wind turbines, are typically supported by driven large-diameter steel piles. The piles resist the loads of the superstructure and environmental wind and wave forces. Pile running is a major hazard associated with the installation of driven piles in a layered seabed. An analytical method based on Newton's second law of motion is proposed to predict pile running. Two methods are used to calculate the soil resistance to dynamic penetration: (1) the conventional American Petroleum Institute (API) method, where the strain rate dependency and remoulding of the surrounding soil are considered, and (2) the Cone Penetration Test (CPT)-based method, which accounts for friction fatigue. The drag resistance in the context of fluid mechanics has also been considered for pile running. The velocity at the start of pile running was determined by the energy delivered by the piling hammer. A numerical programme was implemented and validated, and then used for three case studies; the results obtained were in good agreement with field measurements. The method presented in this study is dependable for analysing pile running and can provide significant support for pile installation assessment and risk management in offshore engineering design.

On the dynamic wear behavior of misaligned journal bearing with profile modification under mixed lubrication

In this paper, we introduce a method of one-side profile modification for the misaligned journal bearing to reduce the edge wear caused by the journal defection under the external load. To predict the bearing wear behavior, a dynamic wear model considering mixed lubrication based on friction fatigue mechanism is applied. The positive role of the one-side profile modification in mitigating the negative effects caused by journal misalignment is confirmed by numerical calculations. The optimal modification parameter setting is determined with the calculation results, and the dependence of the optimal modification parameters on the different operating conditions, including external force and shaft length, are explored. The results indicate that the reasonable design of one-sided profile modification can effectively increase the minimum film thickness at the edge of the bearing and reduce the rough contact, thereby improve the anti-wear performance of the misaligned journal bearing under mixed lubrication. The present study could provide an engineering approach for the anti-wear optimal design in misaligned journal bearing applications.

Installation and aging effects on the capacity of small displacement piles

Pile setup is not fully understood, despite its high potential for cost saving and risk mitigation in onshore and offshore constructions. Studies indicate that the pile installation process has important influence on initial pile capacity and the subsequent setup. However, only few studies considered a wide range of installation methods (e.g., jacking, vibratory pile driving) when quantifying both initial capacity and setup characteristics. This study presents data of 88 static tension load tests conducted on 44 small piles at 1, 2, 10, and 100 days after their installation by four different methods. Piles made from mild and stainless steel exhibit strongly divergent setup characteristics, being a result of their different resistance to corrosion. Additional factors governing setup are the number of shear cycles induced during pile installation and the elapsed time after end of driving. We suggest a new approach considering the setup as a multidimensional effect, enabling the prediction of the initial capacity of a pile and its temporal development for the tested boundary conditions. This study provides a significant contribution to the understanding of the mechanisms governing setup by combining existing conceptual models, as friction fatigue and stress re-equilibration, together with corrosion under a time perspective.

Effects of solid friction modifier on friction and rolling contact fatigue damage of wheel-rail surfaces

In railway network, friction is an important factor to consider in terms of the service behaviors of wheel-rail system. The objective of this study was to investigate the effect of a solid friction modifier (FM) in a railway environment. This was achieved by studying the friction, wear, and rolling contact fatigue (RCF) damage on the wheel-rail materials at different slip ratios. The results showed that when a solid FM was applied, the friction coefficient decreased. After the solid FM was separated from the wheel-rail interface, the friction coefficient gradually increased to its original level. With the application of the solid FM, the wear rates of the wheel-rail decreased. In addition, the thickness and hardness of the plastic deformation layers of the wheel-rail materials were reduced. The worn surfaces of the wheel-rail were dominated by pits and RCF cracks. Without the FM, RCF cracks ranged from 84 to 120 µm, and subsurface cracks were generated. However, with the FM, RCF cracks ranged from 17 to 97 µm and no subsurface cracks were generated. These findings indicate possible methods of improving the performance of railway rolling stock by managing friction, and reducing wear and permanent RCF damage affecting both the wheels and rails.

Some Regularities of Life Time and Damage for the New Structural Material MoNiCa during Sliding Friction and Mechano-Sliding Fatigue

The results of an experimental study of damage for the structural material MoNiCa (it is high-strength cast iron VCHTG – patent of the Republic of Belarus № 15617) on sliding friction and mechano-sliding fatigue are analyzed in the report. Tests of the mechanical system shaft (a sample with a working part diameter of 10 mm made of 0.45 % carbon steel) - an insert (a prismatic counter sample with a cross section of 10 ´ 10 mm made of MoNiCa) were carried out. The kinetics of the change in average wear at 8 local points along the perimeter of the dangerous area of the sample is given for contact loads FN from 20 to 92 N of the mechanical system under study with MoNiCa inserts without heat treatment and with heat treatment. The test results of the system under study are also presented in the form of sliding friction and mechano-sliding fatigue curves in coordinates of the contact load FN – the number of cycles N until the limit state.

ДОСЛІДЖЕННЯ ЗАКОНОМІРНОСТЕЙ ЗНОШУВАННЯ ПОВЕРХОНЬ З'ЄДНАННЯ "ПІДШИПНИК КОВЗАННЯ ВАЛ"

Problem statement and its connection with important scientific or practical tasks. The search for technical solutions aimed at improving the reliability of connections of parts of ship's technical means (STM) is a topical issue in the design and operation of ship systems. The necessary level of safety and reliability is laid down at creation of ship knots and units, in the course of operation only support of the parameters set at designing due to the correct maintenance and repair that is connected with time and financial expenses is possible. One of the ways to increase the reliability of joints of STM parts is to increase their service life by increasing their wear resistance. There is a lot of research work aimed at improving the anti-wear properties of the surfaces of the connection "sliding bearing", their geometry, materials and technologies of their manufacture. Design experience shows that changing the profile of the contact surfaces several hundredths of a millimeter changes the contact planes and pressures by 2 ÷ 5 times and significantly affects the distribution of internal force factors. The purpose of this study is to determine the patterns of wear of the surfaces of the connection "shaft-sliding bearing". [1] Key words: ship technical means, microgeometry of a surface, frictional fatigue, connection "shaft-sliding bearing", radius of curvature of a wave.

Effect of cyclic jacking on sand-pile interface shear behaviour

Pile jacking is a kind of competitive method for pile installation due to its less noise and vibration pollution. In this paper, the pile jacking process has been numerically simulated by considering the friction fatigue, and the characteristics of sand-pile interface shear paths at different depths were thoroughly investigated. It is found that during the cyclic jacking process, the interface shear path at a specified depth tends to transform from one-way shear to two-way shear, especially for the shallow to middle depth. But for the deep soil layer, one-way cyclic shear is still the dominated loading mode. Focusing the effects of different paths on the sand-pile interface shear behaviours, a series of cyclic interface shear tests have been conducted, in which two types of sands and four typical shear paths were adopted. It has been revealed that during continuous jacking process, the sample volume response changes significantly with different interface shear paths. The previous shear path also plays a key role in the cyclic degradation of interface strength with CNS (constant normal stiffness) condition. If the sample contraction is small during jacking process, the cyclic degradation of interface strength is obvious. But, when the sample contraction during jacking process is significant, the interface strength degradation is largely suppressed. This is mainly because the abundant broken fine particles along the pile shaft will fill into the voids and make the sand sample near the interface much denser. It is shown that the changes of pile-soil interface characteristics will affect the pile responses.

Tribological properties of structural alloys for the heat exchange equipment parts subjected to fretting

Trobological characteristics of sliding friction in stainless steel and titanium alloys in dry and water lubricated conditions have been determined. The character of the coefficient of friction variation with load and the duration of tests have confi rmed the prevailing wear mechanism in these materials to be frictional fatigue fracture that in the case of titanium alloys is accompanied with adhesive interaction and plastic plowing. The frictional fatigue curves built in a result of this investigation make possible to estimate the materials tribological longevity.

Empirical Shaft Resistance of Driven Piles Penetrating Weak Rock

In this paper, an empirical relationship between the Unconfined Compressive Strength (UCS) of intact rock and the unit shaft resistance of piles penetrating rock is investigated. A growing number of civil engineering projects are utilizing steel piles driven into rock where a significant portion of the pile capacity is derived from the shaft resistance. Despite the growing number of projects utilizing the technology, little to no guidance is offered in the literature as to how the shaft resistance is to be calculated for such piles. A database has been created for driven piles that penetrate bedrock. The database consists of 42 pile load tests of which a majority are steel H-piles. The friction fatigue model is applied to seven of the pile load tests for which sufficient UCS data exists in order to develop an empirical relation. The focus of this paper is on case histories that include driven pipe piles with at least 2 m penetration into rock.

A lubricated wear model for determining wear surface geometry on journal-bearing surfaces

In this study, the friction fatigue mechanism is employed to describe the quantitative information concerning characterization of the steady-state wear process in journal bearings, which combined with the load sharing notion in mixed lubrication. For this approach, the asperity stress cycle number is estimated by combining the statistical dynamic contact model with the mixed elasto-hydrodynamic lubrication (EHL) simulation model. The maximum shear stress theory is applied together with the subsurface stress distribution of contact asperities to predict the average volume of wear fragment for asperity. Quantitative analysis of steady-state wear profiles for the bearing reveals that the maximum wear depth appears at both ends of the bearing. With the increase of running time, the wear gradually extends to the bearing centre, and the wear rate rapidly decreases to a certain value and then tends to be stable. With this lubricated wear model, the influences of surface roughness, external load, and shaft speed are also discussed. The proposed wear simulation method is based on the interdisciplinary theory, which includes the description of surface micro-morphology (Gaussian rough surfaces), the friction fatigue theory for explaining the generation of wear debris, and the coupling effect of wear and lubrication that is expressed by considering the wear surface geometry in oil film thickness equation. Additionally, the simulation results and available experiment data are compared to demonstrate the fatigue wear modeling scheme.

Fretting & friction induced fatigue failure: damage criterion of polytetrafluoroethylene

Biomedical implants like the hip joint with cup work under continuous friction and wear phenomena where soft materials are suitable for the low coefficient of friction. As continuous, joints go under dynamic fatigue that should be accelerated by the fretting action generated from contact pairs and the inclination angle of the femur. In this research, the fatigue behavior of PTFE has been studied and compared under friction along with fretting action. A FE based Numerical model justified the experimental results. It showed that fretting and friction influence the fatigue life of PTFE by various angles. Fretting pressure optimization was identified as the determinant factor, while the loading point ratio was remarked as an effective parameter for both fretting and friction fatigue. Penetration depths proportionality to corresponding stress observed the effect of fretting fatigue where friction acts in different degrees depending on the geometry (collar/notch)-loading (friction) position. The fractographical demonstration revealed a relation between crack orientation and fretting action. Predefined loading action on test samples justified the singularity of fretting-friction fatigue characteristics on the damage mechanism of PTFE.