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Abrasive particle wear in corrosive environments is very common in offshore industry, e.g., dredging. The synergy or mutual effects between the abrasive and corrosive wear on material degradation cannot be quantified with standard tribological test equipment. A novel test rig has been developed, which couples pin abrasion test set-up (ASTM G132) along with three-electrode electrochemical system that allows to quantify experimentally the synergy between two-body multiple asperity abrasion and corrosion of metallic materials. The present article explains in detail the design and construction of this novel tribocorrosion test rig and discusses the results of investigation on an abrasion resistant martensitic steel in the presence and absence of corrosive medium resulting in higher wear in the latter condition.

Polymers are frequently considered as a candidate material for heavy duty tribological applications. Standard tribological testing for such applications may result in unrealistic tribological properties in terms of wear mechanism, transfer film formation and friction coefficient etc. Thus the present research aims to explore the tribological behaviour of currently available neat polymers under heavy duty loading condition. In this background, nine different polymers (PAI, PEI, PC, PPSU, PA6, PET, PPS, PVDF, and UHMWPE) of amorphous and semi-crystalline groups were chosen from engineering and high performance grades. Large scale reciprocating sliding wear tests with 50×50 mm contact area were used. Considering heavy duty loading condition, the operational parameter were idealised at 10 kN normal force and 50 mm/s sliding speed. From the test results the polymers are classified into three groups based on the wear mechanisms and the transfer layer characteristics observed from the counterface. Group 1 did not persist any transfer layer (PC and PEI), whereas Group 2 materials (PET, PPS, PPSU and PAI) has lumpy discontinuous transfer layer and finally Group 3 materials evidenced uniform thin transfer layer. Clear signs of three body abrasion were evidenced in Group 1 material which is due to the absence of transfer layer and also from the large loose debris. Poor adhesion of inhomogeneous lumpy transfer layer in Group 2 showed an intermediate wear rate. Based on the wear and friction performance, the Group 3 materials (PVDF, UHMWPE and PA6) are proposed as the candidate materials for heavy duty tribological application. In regards to the transfer layer thickness and wear mechanisms at large scale testing, the present observations showed incomparable results with the literature. This research concludes that the revisit to polymer tribology at high load condition has indicated the difference in wear mechanism and the corresponding tribological characteristics in large scale testing. As a future work multi-scale testing is an absolute must for the complete understanding of tribological characteristics w.r.t a specific material.

A fretting fatigue failure scenario can be explained by accumulation of damage, which leads to formation of initial macro-cracks at the contact interface and propagation of macro-cracks to sudden rupture of bulk material. The main aim of this study is estimating these two portions by means of a numerical modelling approach. For this purpose, an uncoupled damage model based on a thermodynamic potential function is used to model the crack initiation lifetime. In order to model crack propagation part a linear-elastic fracture mechanics approach under mixed-mode loading conditions has been considered. The crack propagation direction is defined based on experimental observation and compared with some available criteria in the literature, which are usually used for proportional loading conditions. The estimated results are compared with observed experimental lifetime and show good agreement.

To ensure a reliable connection between two pipe sections, an initial make-up is applied to the threaded connections to induce a favorable stress state. Using finite element analysis techniques, it is possible to predict the internal strains and stresses of the connection when torque is applied. This article presents the outline of an experimental setup, which allows to directly validate the occurring strains together with the torque versus turn diagram and indirectly the contact pressures. The strains are measured by means of digital image correlation and strain gages. Both methods provide similar results and comply with the predicted finite element analysis strains when taper mismatch is taken into account. In an effort to qualitatively validate the simulated contact pressures, the temperature of the box is measured during make-up by means of infrared monitoring. The maximum temperature increase occurs near the vanishing threads where contact pressures are larger. Despite promising results, no decisive validation for the contact pressures could be obtained.

This paper studies the contact mechanics in a line contact during fretting fatigue conditions. Inliterature one can find numerical and analytical solutions of normal and tangential stresses for a variety ofloading cases. However, a unified solution valid for all loading cases during fretting fatigue conditions is notavailable. We present in this paper a strategy to combine existing contact mechanics theories into a unifiedcalculation procedure. Therefore, the relevant contact mechanics theories for an idealized cylinder-on-flatcontact are selected and bundled. Two clear flowcharts group the existing theories, which results in aunified strategy that can easily be implemented in a programming language. A Matlab script wasprogrammed and calculates the normal and tangential stress distribution based on the applied forces, thegeometry of the contact, the coefficient of friction and the material properties. The present theory can beused to automate the calculation of the stress distributions, or as validation of new numerical techniques.The script is modular and can be extended to calculate the lifetime of a component, by adding lifetimecriteria.

In the transportation industry every vehicle that makes contact with the road and propels itself, is subjected to roll-slip in the wheel-road interface. Therefore a good understanding of this phenomenon is important. This article describes roll-slip contacts in general, with extra attention for the wheel-rail contact which is commonly used. Firstly the contact area and the pressure distribution that occur when a normal load is applied between two bodies is discussed. On this base, the traction mechanisms for static and rolling configurations are shown. Lastly, wear mechanisms and two different wear maps are shown which are very useful and commonly used in wear mapping of roll-slip contacts. A good agreement with field measurements can be obtained.

To assemble pipelines and tubular structures, threaded couplings can be used. In service these couplings are often subjected to dynamic loads. To maintain a secure connection, they are generally preloaded. The combination of preload and external dynamic loads results in a multiaxial stress distribution over the connection, where the coupling’s threads act as stress raisers, initiating fatigue cracks. The fatigue life of the connection depends on its global geometry, local thread geometry, interface and material properties. In this study the fatigue life of standard API Line Pipe couplings and two modified coupling configurations is determined experimentally. The influence of the coupling’s global geometry on the connection’s fatigue life was studied. Threaded pipe samples with a nominal size of 1” were tested on a four-point bending fatigue test setup. A sample was considered to be failed when a through thickness crack appeared. This was detected by pressurizing the tube samples. When a pressure drop was recorded, the test was stopped. The number of elapsed load cycles defines the fatigue life of the connection. Using this methodology, S-N curves were obtained for the standard API Line Pipe connection and two modified coupling configurations. Both configurations exhibited an improved fatigue life relative to the standard connection. In the final part of this paper, these experimental observations are explained by a combination of a damage evolution law and a finite element model.

The automotive industry uses ball joints in the suspension systems of cars. These ball joints are subject to various forces and relative displacements which inevitably invoke wear. The same happens in other applications that use ball joints, for example human hip joints. Nowadays there are only a few test rigs that can correctly simulate wear in these joints or test the joints according to a realistic loading cycle. This paper focuses on the design of a test rig that allows parametric research on these ball joints in order to increase the performance.

Polymer-metal pairs are found in many engineering applications, especially in rolling/sliding conditions. Transfer layer formation is imperative in friction and wear investigations on using these tribo-pairs. In the existing literature quantitative description was given for the formation of protective layer from the post mortem analysis (preferentially for sliding configurations). Since there is a dynamicity involved in the transfer layer the straight forward answer from the quantitative postmortem responses is rather uncertain. In the current research, rolling/sliding tests were performed for polymer and it’s composite against metal to explore the underlying mechanisms using both qualitative and quantitative approaches. The tests were performed with intermediate pauses to observe the surface changes where characterization based on surface morphology and roughness (Ra) are used. The results show that the transfer layer deposition occurs in four stages which are explained from the view point of change in Surface roughness Ra in correspondence to its micrographs of the surface topography. The four stages can be categorized as 1. Scouring 2. Running-in 3. Transition and 4. Steady stage. Results show that in polymers the Ra increases during the scouring stage subsequently it decreases on reaching the steady stage. In steel counter parts the Ra does not change significantly during the scouring period. However, the Ra increases in the running-in period followed by a transition region leading to a steady state. Among the polymer and its composites the pure polymer shows significant change in roughness due to the difference in strength. The change in Ra for steel in the steady region also depends upon the contact materials, the mechanical and tribological properties of the polymer. Thus the stages can be used to study the transfer layer behaviour and understand the underlying mechanism in segregating the wear mechanisms both quantitatively and qualitatively.

In this paper, four-point bending experiments are performed to determine the fatigue life of several threaded pipe couplings. It is shown that fatigue life of these couplings can be improved by designing them with more uniform load distribution in the threads, achieved through reducing the global and local stiffness of the coupling. Finite element simulations of a 2D axisymmetric model show consistence between experimental observation and analytical modeling. A 3D finite element simulation, which includes nonlinear material behavior, elaborate contact properties and represents the coupling geometry more accurately, is also performed to evaluate the 2D axisymmetric finite element model.

There is no standard or generally accepted test rig for fretting fatigue experiments. Therefore,researchers adopt an existing concept, or build a new test rig that meets their specific requirements.However, too many different test rigs may be disadvantageous because the results of two different test rigsare hard to compare. The increasing amount of diversity is mainly caused by the lack of a recent literaturesurvey on fretting fatigue test rigs. In 1994, Hills and Nowell described a few test rigs in Mechanics OfFretting Fatigue. In this study, the authors made a classification of test rigs based on the contact geometry,which is determined by the test specimens, not by the test rig itself.Ghent University, Laboratory Soete, BelgiumThe authors of this article present a review of the available literature, and present a classification based onthe properties of test rigs. Fretting fatigue test rigs are first divided in two categories based on the geometryof the test specimen: full scale and coupon scale test rigs. The latter are mostly used to perform researchand are subdivided in categories based on increasing functionalities. This is the ability to apply a fatigueload, a constant normal force, and an alternating slip in the range of some micrometers. In time, from thefifties until now, progress has been seen in the design of fretting fatigue test rigs. More parameters can becontrolled during experiments and more measuring techniques are incorporated. State of the art test rigsare classified in the last category with most functionalities, but still have imperfections. Future designerscan use this article to classify their needs, or help to design a better test rig knowing the imperfections ofthe state of the art test rigs.

Threaded pipe connections are used to connect well casing, well tubing, drill pipes and risers.For many of these applications fatigue resistance plays an important role. In this study the fatigueproperties of threaded connections are studied using a combination of finite element modelling andexperimental testing. Using 2D axisymmetric FE analysis several connections are compared. It is shownthat the load distribution over the engaged threads is an important feature. Experimental tests are carriedout on three setups. A small scale four-point bending setup is used to develop S-N curves. An S-N curve fora standard API Line Pipe connection is compared to an S-N curve for a connection that showed animproved load distribution over the engaged threads in the FE analysis. On a medium scale four-pointbending setup, strains together with crack opening are measured. The strain measurements are comparedwith the strains obtained by the numerical model. Finally a full scale resonant bending fatigue setup ispresented, which will be used in future testing of pipe connections ranging from 168 mm (6”) to 508 mm(20”) in diameter.