Fatigue Failure Location Research Articles

Fatigue strength improvement factors for high strength steel welded joints treated by high frequency mechanical impact

Numerous studies have observed that the fatigue strength of improved welds increases with material yield strength. This paper provides a comprehensive evaluation of published data for high frequency mechanical impact treated welds. In total, 228 experimental results for three weld geometries subject to R=0.1 axial loading have been reviewed. A design recommendation including one fatigue class increase in strength (about 12.5%) for every 200MPa increase in static yield strength is proposed and are shown to be conservative with respect to all available data. Special cautions are given for high R-ratio or variable amplitude fatigue and potential alternate failure locations.

ねじ山らせんモデルによるボルト締結体の疲労強度評価

Fatigue failures of bolted joints frequently lead to serious accidents of machines and structures. It is well known that fatigue failure is likely to occur around the first thread root of bolt adjacent to the nut loaded surface and the run-out of bolt thread. That is because high stress amplitudes are generated there due to alternating external forces. Accordingly, it is significantly important to evaluate the stress amplitudes along the thread root in order to better define the fatigue failure mechanism of bolted joints. In this study, stress amplitude distributions along the thread helix including the thread run-out are analyzed by three-dimensional finite element analysis, where the numerical models of bolted joints are constructed so as to accurately take account of the effect of thread helical geometry, using the modeling scheme proposed in the previous paper. The analytical objectives are bolted joints with axi-symmetric geometry except for the helical-shaped threaded portions, and are subjected to axi-symmetric external forces. It has been substantiated, based on the stress amplitude distributions along the thread helix, that the fatigue failures are likely to originate from the first bolt thread, as in the case of the maximum stress, and the run-out of threads. Also shown is that the fatigue failure location varies depending on the distance between the target bolt and the loading position and whether or not there is a separation at the plate interface.Copyright © 2009 by ASME

Numerical Simulation on Rolling Contact Fatigue with Dent at Rolling Surface

This work has investigated the effect of spherical dent on rolling contact fatigue (RCF). A 3-D finite element simulation model of bearing rolling contact incorporating critical plane approach has been developed to study the fatigue failure location. It was found that the fatigue failure locations were significantly influenced by the dent. The calculation results are in good agreement with the experimental results and comparable with the results from the published literatures in which 2-D models were generally used.

Premium-Connection Design

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper OTC 17221, "Premium & Semi-Premium Drilling-With-Casing Applications," by N.J. Santi and G.E. Carcagno, SPE, Tenaris, and R. Toscano, Centro Investigation Industrial, prepared for the 2005 Offshore Technology Conference, Houston, 2-5 May. High resistance to fatigue loading together with high torque and compression capacities is necessary for connections used for drilling with casing. On the other hand, cost-effective solutions must be found to provide connections for shallow wells for which sophisticated premium connections are not economical. The full-length paper describes the development and evaluation of premium and semipremium connections for tubing/casing. Introduction Drilling with casing originally was used for nondemanding vertical wells where, in almost all cases, American Petroleum Inst. (API) connections (sometimes with modifications to improve torque capacity) were used. As drilling with casing was used in more demanding and critical applications such as horizontal, deviated, and offshore wells where most wells are drilled directionally, new connection types were needed. Requirements for these connections include reliability, sealability, high overtorque capacity, and ultrahigh fatigue resistance because the stresses produced by bending and vibrations while rotating can reduce connection life. Considerations Use of oil-country-tubular-goods (OCTG) connections for drilling began as an attempt to reduce costs. Standard OCTG casing connections are designed to withstand static loads of tension and compression, internal and external pressure, and bending. Torque requirements for these connections are low. However, for drilling with casing, some critical issues that become important for drilling directional and deviated wells include the following.Wear protection.High torque and compression resistance.High fatigue resistance.Cost effectiveness. Wear protection is provided by means of centralizers or other hardened surfaces located close to the pipe end to avoid damage to the connection. Higher torque and compression requirements are met by designs that include robust torque shoulders, thread interferences, and reduced gaps between mating threads. Fatigue resistance is a very important issue for drilling with casing and perhaps the most difficult challenge to address. Fatigue Response of OCTG Connections. Fatigue is a complex process that affects mechanical components subjected to cyclic loads. Fatigue failure is not a sudden crack, instead it involves different failure phases that occur until component failure becomes evident. This failure occurs at stress levels much less than the elastic limit of the material. When subjected to cyclic loading, ordinary OCTG connections are weaker than drillpipe connectors that are designed to work with alternating stresses. The fatigue-failure location of threaded connections is in the area with the highest stress-concentration factor (SCF). Location of the SCF can be estimated with finite-element analysis (FEA), which also can yield a numerical value of the SCF. For standard premium OCTG connections with loads expected in drilling with casing applications, the SCF normally is greater than 2. However, from a fatigue perspective, it is desirable that the SCF be as low as possible. Threaded-connection response to fatigue loads can be plotted as a stress vs. number-of-cycles-to-failure curve.

The Effect of Dent Size on the Pressure Distribution and Failure Location in Dry Point Frictionless Rolling Contacts

Finite element simulation is performed for rolling contact over four different size spherical dents. Two rolling contacts are simulated using a portion of a sphere as a counter-face to the dented half-space. The effect of dent size on the pressure distribution and fatigue failure location for dry point contact is studied. The material model used was adjusted to match both the stress amplitude versus strain range curve and ratchetting experimental data for 52100 bearing steel.

Prediction of fatigue failure location on a component using a critical distance method

The prediction of fatigue failure from notches and other stress concentrators is complicated by factors relating to the local notch geometry and stress field. One problem which has received little attention is the fact that for a component containing several stress concentrating features, failure may occur from a feature which is not the one causing the highest stress. This paper reports the analysis of an automotive suspension component which demonstrates this phenomenon. Commercial software for fatigue life prediction was unable to predict systematically the correct failure location, taking stress-concentration effects into account. A critical distance approach gave a successful prediction, and a good estimate of the fatigue life. It is recommended that this approach be adopted in future predictive software.

Fatigue behaviour of oblique nozzles on cylindrical shells submitted to internal pressure and axial forces

In detailed analytical checks against fatigue failure, the local notch stress approach can be considered as one of the most advanced methods for predicting the fatigue behaviour of a mechanical structure. However, it is based on a detailed strength analysis, including macroscopic notch effects, of the real structure, e.g., at weld seams. In this paper, the fatigue behaviour of oblique nozzles on cylindrical shells submitted to internal pressure, axial force and combined loading is analysed according to these principles. Detailed three-dimensional, parametric, finite element models based on brick elements are applied to describe the mechanical behaviour of the structure for a wide range of relevant geometrical parameters. The results of the serial finite element analyses are approximated analytically and thus can be offered to potential users to determine the stresses at arbitrary points of the nozzle-to-vessel junction and to predict the most probable location of fatigue failure.

Fatigue Behavior and Connection Efficiency of Pultruded GFRP Beams

This study describes the fatigue performance of pultruded glass fiber reinforced plastic (GFRP) box and wide flange (WF) beams without and with flexural connections. A total of 51 tests were conducted under cyclic bending loads to monitor stiffness degradation, failure progression, failure patterns, and fatigue performance. The test data revealed that sections showed no stiffness reduction till they reached 70–80% of their fatigue life. Fatigue performance of GFRP sections versus steel has been presented. The effect of load application mode (uniform across flange and over a part of flange) on the fatigue performance of box sections is described. The WF sections showed better fatigue performance than the box sections. Failure modes revealed that the web-flange junction on the compression side was the principal location of fatigue failure. A total of 35 tests were conducted on sections with connections to study the performance and efficiency of sections with splice connection as compared to those sections without any connection.

On-farm service loading on a rotary cultivator

Service loading data are required by agricultural implement manufacturers to design against failure due to overload and to ensure an adequate fatigue life. Long term on-farm data are the most realistic but also the most difficult to collect, and more often data are obtained in short duration field tests in severe conditions using an arbitrary range of machine settings. In this investigation, long term on-farm data for a p.t.o. (power take off) driven rotary cultivator were collected and compared with data from short tests to establish whether a laboratory fatigue endurance test based on short duration test results alone would produce the optimum cultivator design for farm usage. On-farm recordings were made of p.t.o. torque and the structural strain at a potential fatigue failure location on the cultivator. The records were taken during transport and field manoeuvring as well as cultivation on nine farms, and covered periods ranging from 20 min to 12.5 h. The short duration field test data were obtained in a separate and earlier study using the same cultivator and included the same data measurements. These short tests lasted 2 or 3 min only and did not include transport and field manoeuvring. Torque records from the p.t.o. were analysed to give histograms of the proportion of time spent at different torque levels, and the strain records were analysed in accordance with BS 5400 to calculate fatigue damage and fatigue life. The productive working time from the on-farm tests, which was taken to be the time spent above the zero torque level, was in most cases 60–70% of the total but could be as low as 40%. Maximum p.t.o. torque was similar in both short and long term tests. The severity of loading between short and long term tests was compared using the mean fatigue life calculated for the two groups of tests. On this basis on-farm usage was one-sixth of the severity of the short duration tests. A laboratory endurance test based on short duration test data alone, without regard to their relationship with on-farm data, would lead to an unnecessarily heavy and costly machine.

On-farm service loading on a rotary cultivator

Service loading data are required by agricultural implement manufacturers to design against failure due to overload and to ensure an adequate fatigue life. Long term on-farm data are the most realistic but also the most difficult to collect, and more often data are obtained in short duration field tests in severe conditions using an arbitrary range of machine settings. In this investigation, long term on-farm data for a p.t.o. (power take off) driven rotary cultivator were collected and compared with data from short tests to establish whether a laboratory fatigue endurance test based on short duration test results alone would produce the optimum cultivator design for farm usage. On-farm recordings were made of p.t.o. torque and the structural strain at a potential fatigue failure location on the cultivator. The records were taken during transport and field manoeuvring as well as cultivation on nine farms, and covered periods ranging from 20 min to 12.5 h. The short duration field test data were obtained in a separate and earlier study using the same cultivator and included the same data measurements. These short tests lasted 2 or 3 min only and did not include transport and field manoeuvring. Torque records from the p.t.o. were analysed to give histograms of the proportion of time spent at different torque levels, and the strain records were analysed in accordance with BS 5400 to calculate fatigue damage and fatigue life. The productive working time from the on-farm tests, which was taken to be the time spent above the zero torque level, was in most cases 60–70% of the total but could be as low as 40%. Maximum p.t.o. torque was similar in both short and long term tests. The severity of loading between short and long term tests was compared using the mean fatigue life calculated for the two groups of tests. On this basis on-farm usage was one-sixth of the severity of the short duration tests. A laboratory endurance test based on short duration test data alone, without regard to their relationship with on-farm data, would lead to an unnecessarily heavy and costly machine.

Influence of water on fatigue failure location and surface alteration during rolling-contact lubrication: Schatzberg, P., Felsen, I. M. Transactions of the American Society of Mechanical Engineers, Journal of Lubrication Technology, Vol 91, Series F, No 2 (April 1969) pp 301–319

Influence of water on fatigue failure location and surface alteration during rolling-contact lubrication: Schatzberg, P., Felsen, I. M. Transactions of the American Society of Mechanical Engineers, Journal of Lubrication Technology, Vol 91, Series F, No 2 (April 1969) pp 301–319

Closure to “Discussions of ‘Influence of Water on Fatigue-Failure Location and Surface Alteration During Rolling-Contact Lubrication’” (1969, ASME J. Lubr. Technol., 91, pp. 581–583)

Closure to “Discussions of ‘Influence of Water on Fatigue-Failure Location and Surface Alteration During Rolling-Contact Lubrication’” (1969, ASME J. Lubr. Technol., 91, pp. 581–583)

Influence of Water on Fatigue-Failure Location and Surface Alteration During Rolling-Contact Lubrication

The influence of dissolved water in the lubricant on fatigue-failure location and surface alteration was determined from experiments conducted with a planetary four-ball machine in the range of 925 to 1300 ksi maximum Hertz compressive stress. The distribution of fatigue spalls on the bearing ball surfaces was influenced by small amounts of water in the hydrocarbon lubricant. In the presence of 0.01 precent water an increase in fatigue-failures occurred on the chemically more reactive portion of the bearing balls. An increase in wear during rolling contact was observed due to the presence of water. This was demonstrated by weight determinations, surface profile measurements and light microscopy.