Review and classification of fretting fatigue test rigs

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 rigs are hard to compare. The increasing amount of diversity is mainly caused by the lack of a recent literature survey on fretting fatigue test rigs. In 1994, Hills and Nowell described a few test rigs in Mechanics Of Fretting 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. The authors of this article present a review of the available literature, and present a classification based on the properties of test rigs. Fretting fatigue test rigs are first divided in two categories based on the geometry of the test specimen: full scale and coupon scale test rigs. The latter are mostly used to perform research and are subdivided in categories based on increasing functionalities. This is the ability to apply a fatigue load, a constant normal force, and an alternating slip in the range of some micrometers. In time, from the fifties until now, progress has been seen in the design of fretting fatigue test rigs. More parameters can be controlled during experiments and more measuring techniques are incorporated. State of the art test rigs are classified in the last category with mostffunctionalities, but still have imperfections. Future designers can use this article to classify their needs, or help to design a better test rig knowing the imperfections of the state of the art test rigs

Modeling of preloaded threaded pipe connections

In this paper a modeling method to perform parametric studies on preloaded threaded connections is presented. The method uses a non-linear 2D axisymmetric finite element model, and is illustrated by a parametric study of an API Line Pipe connection. The method was used to quantify the influence of the coefficient of friction, the wall thickness of pin and box and the box recess length of the connection

Design of a tribological ball joint tester

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.</jats:p

Analysis of API 5C3 failure prediction formulae for casing and tubing

Due to the increasing demand for oil and gas, coupled with the fact that oil reserves are becoming rather scarce, the petroleum industry is pushed to drill and complete deeper wells. Threaded connections are often the weakest link in this process and are therefore the subject of research and optimization. At first, this paper presents a brief overview of the design characteristics of today’s premium connections. Secondly, the failure mechanisms of Oil Country Tubular Goods (OCTG) are discussed. At last, an in-depth analysis of the API 5C3 formulae is given. Four formulas for collapse are given in API 5C3, each valid for a specific D/t range. With increasing yield strength of the steel, the difference between the yield strength collapse and the plastic collapse gets larger. Also, the elastic collapse zone gets bigger, so stronger materials with relatively large D/t ratios will collapse in the elastic zone instead of the plastic or transition zone. These four formulas can be approached by a third-order polynomial equation that is valid for all D/t ratios

Design of a fretting fatigue test rig with compliant springs

Fretting is a small amplitude oscillatory movement which occurs between contacting bodies who are subjected to cyclic loading or vibrations. In the contact area arise stresses -normal and tangential- causing stress concentrations and surface degradation. Fretting in combination with ordinary fatigue will reduce the plain fatigue lifetime due to the additional stresses and surface degradation. Applications susceptible to fretting fatigue are for instance connections techniques. By nature they have contacting bodies and transfer loads or vibrations. Connection techniques commonly seen in the field of fretting fatigue are lap-joints, dovetail connections and spline connections. Although mitigating or managing fretting fatigue is industrially relevant, academic research is confined and only revealed basic insights. Therefore, we developed a fretting fatigue test rig at Soete Laboratory. The paper describes the design of the test rig and points out some important features. To study the general phenomenon of fretting fatigue we selected a coupon scale test rig rather than a full scale test rig where only one application can be studied. The specimens used are one dog bone specimen and two indentation pads which make contact with the dog bone specimen. The normal force FN between the specimen and the pads is close loop controlled with a hydraulic actuator. A second hydraulic actuator controls the dynamic force Ffat in the dog bone specimen. A third force FT is introduced during dynamic loading between the dog bone specimen and the pads by means of compliant springs. The combination of these three forces: FN, Ffat, FT in the contact area gives rise to the fretting fatigue phenomenon. The test rig at Soete laboratory can be used to study fretting fatigue and examine mitigations such as surface texturing, surface work hardening, etc

Characterisation of a resonant bending fatigue setup for pipes

This paper discusses the resonant bending fatigue test setup designed at laboratory Soete for full-scale fatigue tests on pipes. Following an enumeration of other types of fatigue test setups an attempt is made to characterise the resonant bending machine. The characterisation is obtained by conducting different tests on a steel pipe of grade API X65. Concordance between measured and calculated stresses and influence of excentre position on stress amplitude is discussed. High frequencies and small power input make this test setup very effective. The analytical model correctly predicts the measured stresses and a stress versus excentre curve is obtained. However not yet fully defined, it gives a first indication for the excentre position when preparing for a fatigue test

Review of current knee biomechanical modeling techniques

In this paper we are going to present an essential modification of an existing analytical model. The model creation normally starts with a simplified, less complex analytical model, where the phenomena can be easily interpreted, checked and controlled. If this model is available and valid – with its certain simplifications – then as a following step, it can be either extended by taking into account earlier neglected factors or a similar but more advanced computational model has to be created in order to broaden the investigated factors. The accent will be set on a neglected factor, the moving center of gravity (COG), in this paper, and the obtained results will be compared with some external data from other authors