A study on the effect of the clearance on the contact stress and kinematics of polymeric composite journal bearings

In this article the effect of the clearance on the contact stress and kinematics of a polymeric composite journal bearing is investigated. To this purpose a test rig is devised, which is capable to measure the tribological characteristics of the large-scale composite bearings. The kinematics of the setup is simulated by a 2D FEM model. Moreover, to evaluate the contact area between the bearing and the shaft, pressure indicator films are used and a simplified 3D model is provided. Simulation results correspond closely to the experimental data, and it is shown that the clearance variation can have a big impact on the contact stress distribution

Wear investigation of wet clutch friction material

Wear of friction plates for wet clutch applications can result in a decreasing transmittable torque and the occurrence of vibrations throughout the entire drive chain causing loss of performance and discomfort. The need for a simple wear model exists to predict the lifetime of the clutch and to give an insight in the combined influence of the operational parameters such as pressure and speed. In this paper wear of paper-based friction material is investigated on a simplified SAE#2 test-rig using only one friction plate and one spacer plate. During engagement torque, applied pressure and sliding velocity are continuously monitored. After a set number of engagement cycles the thickness change of the friction plate is measured and surface topography of the spacer plate is registered. Based on Archard’s wear law a specific wear rate is derived

How design quirks and conditions of use conspire to structural failure : a case study

Sometimes designers introduce a number of quirks in their design, either due to a preference for certain technologies or practices or under the influence of the policies in the companies they work for. While most of the time these quirks are harmless, sometimes they can, either in themselves or in combination with the conditions in which the design is used lead to failure. In this paper a case is discussed in which a designer used a quirky solution of lengthening an existing design of a 40ft. freight container to 45ft.. While the design in itself was not fundamentally flawed, it proved to be incompatible to the handling equipment still in use at most seaports

Polymers in tribology: challenges and opportunities

Seminal characteristics such as good corrosion resistance, self-lubrication ability and acceptable wear resistance have made polymer based materials to become popular in a wide and diverse range of tribological applications. Despite numerous applications and decades of research in polymer tribology, a considerable number of questions remain unsolved both regarding fundamental understanding and engineering design issues. One of the reasons is the vast number of different polymers and polymer based composites that are in use, but also the diversity in applications and the difficulties to observe the governing tribomechanisms. Material and component producers are often the only owners of composition and basic material characteristics. Thus, designers and application engineers are obviously forced to rely on catalogue information and scattered literature data. For that reason prior to application of a chosen material/component functional and tribological tests with scale models or laboratory set-ups are performed to obtain better confidence in the proposed design solutions. Each time again the definition of an adequate test program is of major concern. The present paper discusses some challenges related to the use and testing of polymer based tribocomponents such as bearings, sliders, gears, rollers, etc. Attention is not only given to basic influencing parameters such as contact load, sliding/rolling velocity, environmental conditions, mating surface conditions, etc. Also experimental strategies and advanced measuring techniques that allow to follow the dynamic nature of transfer film formation and wear are considered. Finally, actual trends in reinforcements (e.g. natural fibres) and lubricant additives (nanoparticles) are discussed together with opportunities for improved tribobehaviour

Experimental study and numerical simulation of the large-scale testing of polymeric composite journal bearings: two-dimensional modeling and validation

The self-lubricating properties of some polymeric materials make them very valuable in bearing applications, where the lubrication is difficult or impossible. Composite bearings combine the self-lubricating properties of polymeric materials with better mechanical and thermal properties of the fibers. At present, there are few studies about these bearings and their design is mainly based on manufacturers' experiences. This study includes an experimental and numerical study of the large-scale testing of fiber-reinforced polymeric composite bearings. In the first part of this article, a new tribological test setup for large composite bearings is demonstrated. Besides, a two-dimensional finite-element model is developed in order to study the stress distribution in the composite bearing and kinematics of the test setup. A mixed Lagrangian-Eulerian formulation is used to simulate the rotation of the shaft and the contact between the composite bearing and the shaft. Simulation results correspond closely to the experimental data, and provide careful investigation of the stress distribution in the bearing. In the second part of this article, three-dimensional quasi-static and two-dimensional dynamic models are studied

Tribological behavior of wire-EDM'ed ZrO2-composites and cemented carbides

Five ZrO2-based composites (ZrO2-WC, ZrO2-TiCN and ZrO2-TiN grades) and five WC-Co cemented carbide grades were machined by wire-EDM and tested on a linearly reciprocating sliding pin-on-flat tribometer PLINT TE77 in dry conditions against WC-6wt%Co pins. Measurement of friction coefficient and penetration depth due to wear was performed continuously. The results revealed a strong influence of the secondary phase, surface finish, chemical and mechanical properties on the tribological characteristics of the ZrO2-based composites and cemented carbides. WC10Co(Cr/V) displayed superior wear resistance compared to the other grades. The lowest coefficient of friction was encountered with ZrO2-WC

Fatigue investigation of threaded pipe connections

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 fatigue properties of threaded connections are studied using a combination of finite element modelling and experimental testing. Using 2D axisymmetric FE analysis several connections are compared. It is shown that the load distribution over the engaged threads is an important feature. Experimental tests are carried out on three setups. A small scale four-point bending setup is used to develop S-N curves. An S-N curve for a standard API Line Pipe connection is compared to an S-N curve for a connection that showed an improved load distribution over the engaged threads in the FE analysis. On a medium scale four-point bending setup, strains together with crack opening are measured. The strain measurements are compared with the strains obtained by the numerical model. Finally a full scale resonant bending fatigue setup is presented, which will be used in future testing of pipe connections ranging from 168 mm (6”) to 508 mm (20”) in diameter

Surveillance or metastasis-directed Therapy for OligoMetastatic Prostate cancer recurrence (STOMP): study protocol for a randomized phase II trial

Background: Metastases-directed therapy (MDT) with surgery or stereotactic body radiotherapy (SBRT) is emerging as a new treatment option for prostate cancer (PCa) patients with a limited number of metastases (<= 3) at recurrence - so called "oligometastases". One of the goals of this approach is to delay the start of palliative androgen deprivation therapy (ADT), with its negative impact on quality of life. However, the lack of a control group, selection bias and the use of adjuvant androgen deprivation therapy prevent strong conclusions from published studies. The aim of this multicenter randomized phase II trial is to assess the impact of MTD on the start of palliative ADT compared to patients undergoing active surveillance. Methods/Design: Patients with an oligometastatic recurrence, diagnosed on choline PET/CT after local treatment with curative intent, will be randomised in a 1:1 ratio between arm A: active surveillance only and arm B: MTD followed by active surveillance. Patients will be stratified according to the location of metastasis (node vs. bone metastases) and PSA doubling time ( 3 months). Both surgery and SBRT are allowed as MDT. Active surveillance means 3-monthly PSA testing and re-imaging at PSA progression. The primary endpoint is ADT-free survival. ADT will be started in both arms at time of polymetastatic disease (>3 metastatic lesions), local progression or symptoms. The secondary endpoints include progression-free survival, quality of life, toxicity and prostate-cancer specific survival. Discussion: This is the first randomized phase 2 trial assessing the possibility of deferring palliative ADT with MDT in oligometastatic PCa recurrence