Friction Fatigue Research Articles

Shakedown upper limit determination of coupled multi-node discrete frictional systems to cyclic loading

Ahn et al. [1] (2009) established that there exists the amplitude of the periodic loading scenarios on which a lower bound below which the system will always shake down and an upper bound above which it cannot shake down. In this paper, we have illustrated that the linear programming method could efficiently identify the upper shakedown limit for the case of an elastic block pressed against a frictional rigid plane. We expect that this method could apply to the frictional fatigue in order to find the loading factor causing the initiation of cyclic microslip behavior.

A Wear Model of Plane Sliding Pairs Based on Fatigue Contact Analysis of Asperities

Wear modeling is essential to predict and improve wear resistance of machine parts. This article presents a fatigue wear model of plane sliding pairs under dry friction. The wear model is constructed through developing a dynamic contact model of surfaces and proposing a mean fatigue damage constant of asperities. It is simpler and more practical than existing fatigue wear models because it describes the quantitative relationship between the wear behaviors of the plane sliding pairs and the main factors including the load and sliding speed, material property, friction property, and surface topography of the pairs. Furthermore, the wear model can predict the wear of each component of the sliding pairs. Reasonability and applicability of the wear model are validated via pin-on-disc wear tests. The wear model is applicable to predict the wear of the plane sliding pairs, which is characterized by friction fatigue of contact surfaces. The wear model can also be used to guide the tribological design of sliding pairs in machinery.

A Dynamic Contact Model of Rough Surfaces Based on the Microscopic Contact Analysis of Asperities

Dynamic contact model of rough surfaces can provide the theoretical basis for analyzing the microscopic damage of surfaces in wear process and constructing the analytical wear model to predict wear. A dynamic contact model of sliding rough surfaces is innovatively constructed based on the characterization of the contact asperities on rough surfaces in this paper. Firstly, an asperity model of rough surface is set up according to the surface topography parameters and the static contact parameters is evaluated in the light of statistics contact theory; Then the contact characteristic of surface topography in sliding is analyzed and a series of equivalent contact models are proposed; Finally, the dynamic contact model of rough surfaces is established and from which the dynamic contact parameter of rough surfaces is formulated. The dynamic contact model can be further improved to analyze the friction fatigue wear of sliding pairs and provide reference for tribology design of mechanical surfaces.

The Effect of Friction Coefficient on Fretting Fatigue Cracks

The riveting is widely used for fitting together two or more components of structure in the same or different materials. And mechanics characteristic is very complex. The paper work focus on study fretting fatigue crack formation with different friction coefficient and fatigue loading, by analyzing the stress field of upper hole edge and outer boundary of contact area. And comparing with the experimental, founding the risk point of single bolt riveted aluminum components.

Centrifuge studies on the effects of existing piles on the end resistance and shaft friction of a newpile

The effects of existing piles on the vertical bearing capacity of piles of a new building were examined using vertical static loading centrifuge tests on a new pile located among existing piles. The results suggest the following conclusions: (1) Existing piles increased the total shaft resistance of the new pile with a rough surface because the existing piles restrained the soil around the new pile and the positive dilatancy of the sand increased the confining pressure of the soil. (2) The shaft resistance of the lower part of the new pile with a rough surface fell rapidly during the loading tests, regardless of whether there were existing piles or not. The diminution of shaft resistance, known as ‘friction fatigue’, was probably caused by sand particle crushing in the vicinity of the pile end. (3) For a new pile with a rough surface, existing piles did not affect the end resistance when the new pile head settlement normalized by the pile diameter, s/Dp, was less than 0.2. (4) Existing piles did not affect the shaft resistance or the end resistance of the new pile with a smooth surface. Dominance of the sliding displacement along the pile–sand contact surface engenders the extremely small variation of the confining pressure of the soil around the new pileshaft.

Piles under cyclic axial loading: study of the friction fatigue and its importance in pile behavior

The main point of this paper is to identify the key features and load transfer mechanisms controlling friction fatigue of piles under cyclic loading. Numerical modeling makes use of an advanced elastoplastic state dependent constitutive model, the ECP model, also known as Hujeux’s model. Therefore, the cyclic loading simulations allowed the identification of three levels of friction degradation, depending on the amplitude of the previous maximum load cycle. Furthermore, the analysis also offers useful insights regarding the modification of the pile static resistance once it has been cyclically loaded. All analyses are carried out considering nondisplacement piles in Toyoura sand.

Crystalline <I>γ</I>-Al<SUB>2</SUB>O<SUB>3</SUB> Physical Vapour Deposition-Coating for Steel Thixoforging Tools

The process of thixoforming, which has been part of many researches during the last decades, combines the advantages of forging and casting for the shaping of metallic components. But due to the high temperatures of semi-solid steel alloys high demands on the tools are requested. To resists the thermal and mechanical loads (wear, friction, thermal and thermomechanical fatigue) protecting thin films are necessary. In this regard crystalline gamma-Al2O3 deposited via Physical Vapour Deposition (PVD) is a promising candidate: It exhibits high thermal stability, high oxidation resistance and high hot hardness. In the present work the application of a (Ti, Al)N/gamma-Al2O3 coating deposited by means of Magnetron Sputter Ion Plating in an industrial coating unit is presented. The coating was analysed by means of Rockwell test, nanoindentation, and Scanning Electron Microscopy (SEM). The coated tool was tested in thixoforging experiments with steel grade X210CrW12 (AlSI D6). The surface of the coated dies was examined with Scanning Electron Microscope (SEM) after 22, 42, 90 and 170 forging cycles.

Improved Evaluation of Interface Friction on Steel Pipe Pile in Sand

AbstractOpen-ended steel pipe piles are now widely used as the foundations for offshore structures. The pile-soil interface behavior is of particular interest in sands where shaft friction plays an important role in resisting the applied load. The rational design of the shaft capacity depends on a good understanding of the mechanisms of interface friction during pile installation and static loading. There are two new methods on the basis of the cone penetration test results that take into account the effect of friction fatigue arising from pile installation. An improvement is made in this study to account for the influence of plugging degree, which is a key issue for open-ended piles. The significance of the modified design framework lies in that it allows for the role of plugging in a more rational way by using the soil-squeezing ratio that is closely related to the radial effective stress and, consequently, the shaft capacity. The performance of the improved method is assessed against the existing metho...

The Wear Mechanism of DLC Films at Variable Working Conditions

The Diamond-like carbon coating (DLC) was derived by the PVCD method on the 45 steel surfaces. The frictional properties and fatigue failure of 45 steel with the DLC films were investigated under three different conditions including full contact condition, horizontal reciprocating movements and vertical reciprocating movements. It was found that (a) at full contact conditions: the increase in the load leads to the initial decrease in the frictional coefficient and then increase, and a lowest frictional coefficient of 0.205 appears at 250N; (b) at horizontal reciprocating conditions: the slow decrease in the frictional coefficient was caused by the increase in load, and frictional coefficients of 0.213 and 0.178 appears at 100N and 300N, respectively; (c) at vertical reciprocating conditions: the frictional coefficient was initially enhanced and then followed by a decrease trend; the highest frictional coefficients of 0.640 appears at load of 200N. The wear rate was slightly enhanced as the load is lower than 200N, and was sharply increased with the further increase in the load. The lowest wear rate was 1.55 mg/10000r, and the highest wear rate was 15.6mg/10000r.

The Shaft Capacity of Displacement Piles in Clay: A State of the Art Review

The rapid expansion of the offshore wind sector, coupled with increasing demand for high rise structures, has placed renewed demand on the driven piling market. In light of this industry growth, this paper reviews the evolution of design approaches for calculating the shaft capacity of displacement piles installed in cohesive soils. The transition from traditional total stress design towards effective stress methods is described. Complex stress–strain changes occur during pile installation, equalisation and load testing and as a consequence, the selection of parameters for use in conventional earth-pressure type effective stress approaches is not straight-forward. These problems have led to the development of empirical correlations between shaft resistance and in situ tests, such as the cone penetration tests. However, many of these approaches are limited because they were developed for specific geological conditions. Significant insight into pile behaviour has been obtained from recent model pile tests, which included reliable measurements of radial effective stresses. These tests have allowed factors such as friction fatigue and interface friction to be included explicitly in design methods. Whilst analytical methods have been developed to investigate pile response, these techniques cannot yet fully describe the complete stress–strain history experienced by driven piles. The use of analytical methods in examining features of pile behaviour, such as the development of pore pressure during installation and the effects of pile end geometry on pile capacity, is discussed.

Analyzing Drivability of Open Ended Piles in Very Dense Sands

AbstractThe successful installation of long piles driven into very dense sands relies on the occurrence of the reduction in local friction with increased pile embedment, a phenomenon known as ‘friction fatigue’. The underlying mechanisms controlling friction fatigue are poorly understood, with some design methods including an adjustment for the influence of pile diameter while others do not. This paper back calculates the installation resistance of 0.356m to 2m (14in to 78in) diameter open ended piles driven into very dense sands using wave equation analyses. Cone penetration test data are used to link soil properties to installation resistance. The study illustrates consistent interpretation of a variety of case histories of open ended piles driven in very dense sands using newly developed analysis techniques and normalized parameters. Results provide information on methods for incorporating friction fatigue into drivability studies as well as a discussion of mechanisms related to pipe pile installation ...

Axial resistance of CFA piles in Dublin Boulder Clay

This paper describes the results of static compression and tension load tests performed on three-instrumented large-diameter continuous flight auger piles installed in Dublin Boulder Clay. The piles developed very high shaft resistance and, in contrast to piles driven into Boulder Clay that exhibit friction fatigue, the shaft distribution was uniform along the pile shaft. This resulted in the normalised average shear resistance being mobilised by a bored pile exceeding that of a pile driven in similar ground conditions. In contrast, the base resistance of the test piles was significantly lower than that of a pile driven in similar ground conditions.

Frictional Wear and Thermal Fatigue Behaviours of Biomimetic Coupling Materials for Brake Drums

In order to enhance frictional wear resistance and thermal fatigue resistance of brake drums, two kinds of biomimetic coupling materials are prepared by laser surface melting and laser coating technology respectively. These materials are all compounded by base metal and biomimetic coupling units, and have different coupling characteristics, such as the variation of the unit shape, different microstructures and hardness, different chemical compositions of units. The frictional wear resistance and thermal fatigue resistance of biomimetic coupling materials and gray cast iron used for brake drum are compared. The results indicate that frictional wear resistance and thermal fatigue resistance of biomimetic coupling sample is better than that of untreated sample, and among the biomimetic samples, laser coating treated sample has superior resistance to wear and thermal fatigue comparing with laser melting treated sample.

Effect of Friction Fatigue on Pile Capacity in Dense Sand

The paper presents the results of a series of field tests performed to study the causes of friction fatigue experienced by displacement piles. Four instrumented model piles were installed at a dense sand test-bed site. The test series was designed to impose different levels of cyclic loading during pile installation. Static and cyclic load tests were subsequently performed to study the differences in the axial capacities developed for ostensibly monotonic and cyclic installations. The test results indicated that the mobilized horizontal effective stress regime that controls pile side friction primarily depends on the in situ sand state, as reflected by the cone penetration test (CPT) qc resistance. A zone of highly stressed sand that produced a concentration of high shear resistance was mobilized in the vicinity of the pile base. The horizontal effective stress that acted on the pile shaft reduced in response to cyclic loading, with the largest reductions occurring for high-intensity cyclic loading or when the pile had experienced only a few load cycles during installation. Although cyclic loading caused a reduction in the horizontal effective stress that acted on the pile shaft, the elevated stress built up in the vicinity of the pile base during installation remained higher than that remote from the base. The elevated stress in the vicinity of the pile base only dissipated after cyclic tension loading had been applied.

Microscale Observation and Modeling of Soil-Structure Interface Behavior Using Particle Image Velocimetry

The shearing behavior of a soil-structure interface governs the response of many geotechnical systems, in particular piled foundations. The shaft resistance of piled foundations is known to degrade with cyclic loading, although the governing mechanism is not well understood. This paper presents the results of a laboratory soil-structure investigation in which internal specimen deformations were obtained using particle image velocimetry (PIV) and the normal confining stress was permitted to vary according to a constant normal stiffness (CNS) condition. The PIV measurements showed the shear deformation and volume change to be concentrated within a shear band with a thickness of 5-7 particle diameters adjacent to the interface. During a single cycle the volume change within the shear band began with an initial contraction, followed by dilation to the failure envelop. For the cycling amplitude investigated this response led to a net specimen contraction. The benefit of quantifying the thickness and contraction of the shear band using PIV is that the progressive decrease in void ratio of the shear band can be linked to the limiting value imposed by the minimum void ratio. This provides a framework in which the contraction of the specimen depends on the potential contraction expressed as the difference between the current and minimum void ratio. A model for this contraction is presented, and linked to the decay in normal stress and the limiting loss of interface friction. This framework clarifies the mechanism of friction fatigue during installation and loading of displacement piles in sand.

Modelling load–displacement response of driven piles in cohesionless soils under tensile loading

A new methodology for deriving the uplift load–displacement response of long driven piles in cohesionless soils is proposed. This method accounts for the effects of the friction fatigue processes during pile driving and the existence of locked-in residual stresses at the end of pile driving before commencing the pile load test. A hyperbolic formulation is utilized to simulate the nonlinear load transfer curves (the so-called t– z curves). The utility of this technique is demonstrated for a field pullout load test on a driven pile in sand. Predicted and measured load–displacement curves showed good agreement, indicating that this approach yields reasonable results as long as representative input parameters are employed.

Friction fatigue on displacement piles in sand

Experiments with instrumented displacement piles have shown that the ultimate shaft friction that can develop in a given sand horizon decreases as the pile tip penetrates to deeper levels. This phenomenon, which is now commonly referred to as friction fatigue, is investigated here using centrifuge model piles equipped with lateral stress sensors, and by drawing on other experimental data from the laboratory and the field. It is shown that the primary mechanism controlling friction fatigue is the cyclic history imparted during pile installation to soil elements at the pile–sand interface. For a given installation method the stationary lateral stress acting at any given level on a displacement pile can be described as a relatively unique function of the cone penetration test end resistance and the number of cycles imposed during installation. The strong influence of cycling, which is also seen in cyclic constant normal stiffness interface shear tests, is attributed to contraction of a narrow shear zone at the shaft–soil interface that is surrounded by soil with a relatively high lateral stiffness.

Friction fatigue on displacement piles in sand

Experiments with instrumented displacement piles have shown that the ultimate shaft friction that can develop in a given sand horizon decreases as the pile tip penetrates to deeper levels. This phenomenon, which is now commonly referred to as friction fatigue, is investigated here using centrifuge model piles equipped with lateral stress sensors, and by drawing on other experimental data from the laboratory and the field. It is shown that the primary mechanism controlling friction fatigue is the cyclic history imparted during pile installation to soil elements at the pile–sand interface. For a given installation method the stationary lateral stress acting at any given level on a displacement pile can be described as a relatively unique function of the cone penetration test end resistance and the number of cycles imposed during installation. The strong influence of cycling, which is also seen in cyclic constant normal stiffness interface shear tests, is attributed to contraction of a narrow shear zone at the shaft–soil interface that is surrounded by soil with a relatively high lateral stiffness.

Displacement and strain paths during plane-strain model pile installation in sand

The underlying mechanisms governing the behaviour of displacement piles in sand are not well understood, leading to unreliability in design methods. A series of plane-strain calibration chamber tests has been conducted in order to quantify the penetration mechanism around the pile tip, and the response of the interface layer adjacent to the shaft during further penetration. A series of eight tests is reported, examining the influence of soil type, initial state, pile breadth and the use of a driving shoe. A novel image-based deformation measurement technique has been used to observe the displacement and strain paths, which are found to be relatively independent of soil type. The measured strain paths are similar to predictions made by the strain path method, and contrast sharply with assumptions implicit in cavity expansion solutions. An interface zone adjacent to the pile shaft comprising fine broken soil particles was observed to contract while shearing along the pile–soil interface. This mechanism offers an explanation for the degradation of shaft friction at a given soil horizon with increased pile penetration (‘friction fatigue’), and a subsequent recovery of capacity over time (‘set-up’).

Displacement and strain paths during plane-strain model pile installation in sand

The underlying mechanisms governing the behaviour of displacement piles in sand are not well understood, leading to unreliability in design methods. A series of plane-strain calibration chamber tests has been conducted in order to quantify the penetration mechanism around the pile tip, and the response of the interface layer adjacent to the shaft during further penetration. A series of eight tests is reported, examining the influence of soil type, initial state, pile breadth and the use of a driving shoe. A novel image-based deformation measurement technique has been used to observe the displacement and strain paths, which are found to be relatively independent of soil type. The measured strain paths are similar to predictions made by the strain path method, and contrast sharply with assumptions implicit in cavity expansion solutions. An interface zone adjacent to the pile shaft comprising fine broken soil particles was observed to contract while shearing along the pile–soil interface. This mechanism offers an explanation for the degradation of shaft friction at a given soil horizon with increased pile penetration (‘friction fatigue’), and a subsequent recovery of capacity over time (‘set-up’).