Prediction of cumulative fatigue damage

Electrical resistivity of an incrementally fatigued lead alloy: Lawson, L. and Meshii, M. Scr. Metall. Mater. July 1991 25, (7), 1713–1717

On some basic problems of fatigue research in engineering

In view of non-conservative prediction of cumulative fatigue life calculated by Miner's and Haibach's methods, the authors proposed in a previous paper a new model providing better and conservative prediction, although it was limited in application to only the bi-linear fatigue diagram in high cycle fatigue regime. If a fatigue diagram will be required to be expressed for a wide range of fatigue life from very low cycle to high cycle regimes, it is a convenient way to express the diagram by Stromeyer's expression.The previously proposed model is developed in the present paper so as to be applicable to Stromeyer's as well as hi-linear expressions of a basic fatigue diagram in undamaged condition. The newly proposed model in this paper is based on a concept consisting of two assumptions ; (i) Fatigue damage will be accumulated as a power function of cycle ratio, and (ii) Fatigue strength at infinite fatigue life or at 107 cycles will decrease functionally according as accumulation of fatigue damage.

Developing a full range S–N curve and estimating cumulative fatigue damage of steel elements

A stochastic theory for the cumulative fatigue damage of structural component with random fatigue strength under random loading is proposed on the basis of Stratonovich — Khasminskii theorem. The analytical solutions for the probability densities of the cumulative fatigue damage and fatigue life and for the reliability function are given for steel and reinforced concrete components with constant fatigue strength subject to narrow band stationary Gaussian stress process with zero mean. The results agree very well with those of digital simulation. It is noted that the theory can be applied, in principle, to metallic and some non-metallic materials, to both narrow band and wide band stress process, and can be adapted to a sequence of n stationary stress processes or quasi-stationary stress process. The scatter and degradation of fatigue strength can also be incorporated into the theory.

This paper describes the fundamental behaviour about cumulative damages of nonstructural members such as glass window sashes under destructive cyclic wind disturbances.The analysis consists of wind modelling for fatigue damages and the formulation to obtain the cumulative damage analysis.First, in modelling the observed strong wind information, three steps of wind action in the long period are selected to discuss the fatigue damage properties.The fist wind model is to present the simple strong wind continuing normally during 20 to 30 hours from annual average about 4 5 m/s to the extreme maximum wind velocity.Next step is to represent the whole annual wind actions using the meteorologically obseved wind velocity per hour.Finally, the return period concept is utilized to the overall fatigue damage of a life time of the structure or members.Accordingly, the damage responses of nonstructural members are presented in three parts.The basic concept to give a quantitative expression of a cumulative fatigue damage is proposed when the simple strong wind is subjected to nonstructural member. The annual cumulative damages and fatigue behaviour in the return period are also discussed on the basis of computed results.One of the most important results is to evaluate the cyclic repeated wind action to structural safety rather than the most large extreme value in the previously observed data.

Dynamic analysis, finite element analysis and fatigue life analysis of transmission gear of Self-Propelled Gun is achieved in this paper according to the theory of multi-body dynamics, finite element and cumulative fatigue damage, and the well-known software Pro/E, ADAMS, PATRAN and FE-Fatigue are integrated in the research. The virtual prototyping model of self-propelled gun’s transmission box is built by ADAMS software. The dynamic load spectrum of transmission gear is achieved by virtual driving of Self-Propelled Gun. The finite element model of the gear is built by using PATRAN software, after defining reasonable boundary conditions, material and element properties, according to the load and the fatigue failure criterion of the gear, the stress-strain state of gear on load is studied. The dynamic load spectrum and the stress-strain state of the gear are considered as basic input data, the fatigue life of the gear is calculated by using FE-fatigue software. The road haul of gear without fault is predicted when the self-propelled gun drives on the second-class load surface at low speed. This method offers a new idea to the fatigue life prediction. It can predict fatigue life without experiments, and save cost and time. It has the great significance to the optimization design of the self-propelled gun.

Fatigue is a damage accumulation process in which material properties are continuously deteriorated and degraded under cyclic loading. Damage accumulation analysis plays a key role in preventing the occurrence of fatigue failure, and the damage evolution mechanism is an important parameter of interest for fatigue behavior. The fatigue cumulative damage life prediction model is established by focusing on the damage evolution mechanism, and an improved Manson–Harford cumulative damage nonlinear model is developed to calculate fatigue damage life by considering the effect of load ratio of multi-stage loading on fatigue life. A fatigue life prediction method considering high-low cycles and multi-stage mixed loads is proposed. The fatigue life prediction accuracy of the model is verified by fatigue tests on structural samples. The accuracy of the fatigue life prediction error is the highest among similar models under the same test, the model proposed in this paper.

This paper introduces a hybrid approach for obtaining S-N curves with reduced number of tests associated to statistically simulated data. In order to validate the proposal, two validation process were developed. One using a methodology to generate S-N curves based on Monte Carlo simulations and other using actual data according Zhao et al. (1998), allowing to compare the hybrid approach with the experimental curve S-N obtained with high replication. In both validation process, a good accuracy was verified. Subsequently, the fatigue analysis of a fillet welded joint was carried out using finite element analysis to evaluate the cumulative damage and fatigue life, enabling comparison between the proposed method and standard NBR 8800 (2008). The results obtained with the proposed methodology allowed more accuracy results and less conservative than standard for the same weld detail class, both for fatigue life and for cumulative fatigue damage evaluations.

In this paper, fundamental experiments are carried out to examine the occurrence of slip-bands (flecks) in copper electroplating foil under variable stresses. The following conclusions are drawn: (1) Miner's rule holds for the occurrence of slip-bands under two-level single block stressing; (2) The appearance of slip-bands is dominated by the amplitude of the primary stressing; (3) When different kinds of stresses act continuously on the plating foil, cumulative fatigue damage that causes the slip-initiation and the grain growth in the foil is not dominated by Miner's rule; (4) Both overstressing and understressing reduce the heating duration for the recrystallization of the copper plating foil and then promote the occurrence of slip-bands.

In order to predict the fatigue life under two-stage loading by formulating a cumulative fatigue damage rule for composite materials, the fatigue process in SiC–Al and glass-fibre reinforced plastics were investigated. A microcrack occurred within the composites which resulted in cumulative fatigue damage that increased linearly with the number of cycles. The mechanical conditions of damage growth and failure were determined by characterizing the microdamage governing the fatigue. The ultimate failure is shown to occur when the product of the stress amplitude ratio and microdamage density is beyond a critical value and an expression for the remaining fatigue life is derived.

Industry advances continue to enable pursuit of more challenging drilling targets with complex well bore trajectories. Many of these targets are in costly deepwater and/or remote operating areas. Demand for a practical, field-proven drill pipe fatigue management system has grown as drill string failures due to fatigue contribute to a significant amount of non-productive time and cost. The response to this demand has been the development of an engineered approach that combines pipe section positioning and inspection scheduling based on estimated fatigue damage rather than rotating hours or footage drilled. Successful real-time field implementation with ongoing drilling programs demonstrates that the cumulative fatigue damage technique is a valuable and proven tool for risk mitigation and cost reduction. The cumulative fatigue damage technique and its implementation have been introduced in previous literature [1,3,8,10]. This method of monitoring fatigue damage due to rotary operations allows the pipe to be evaluated under real-time operating conditions along a specific section or the entire length of the drill pipe. Monitoring begins at spud and is performed on each joint of drill pipe as it traverses along the well path to total depth (TD). This not only allows a quantitative measure of the relative fatigue damage accumulated joint by joint for the drill pipe, but also provides the opportunity to manage logistics, forecast pipe inspections and position pipe sections to minimize cumulative drill string fatigue damage. The cumulative fatigue damage technique has been successfully applied in the field[1,10]. Hind casting, pre-drill planning and real-time analyses have been utilized for assessing drill string design as well as pipe management. The current case study further demonstrates the methodology introduced in the previous literature and illustrates the modeling and management of fatigue damage over a three well project. The subject operator originally anticipated that pipe inspection may be required before each well to mitigate costly historical drill pipe failures. However, the cost and logistical challenges of mid-program pipe inspection in remote operations could not be ignored. Described is the pipe management strategy employed to complete the drilling program without drill pipe failures and without the need for any mid-program inspections. In addition, the inspection results post TD of the third programmed well have been evaluated and correlated back to expected pipe damage, making this an excellent case study for the further deployment of this technology.

Fatigue damage of damper increases with applied load cycles in a cumulative manner. Cumulative fatigue damage analysis plays a key role in life prediction of components and structure of dumpers subjected to field load histories. In order to investigate the fracture reasons of some components of coal dumper installed at Qinhuangdao Port, some field measurements of strain and stress were carried out. The field measurement data shows that the first principal stress of structure is less than limited strength of applied material and stress concentration problem has distinct affection to stress distribution for some components. The loading spectrums acted on dumpers are created according to measured strain data in field. The finite element model is meshed for assessing and calculating stress distribution and strength characteristics of dumpers. The stress distribution and stress concentration factors of main components of dumper at different loading cases are numerically simulated. A fatigue damage model is developed for evaluating accumulative fatigue damage of dumpers. The Ramberg-Osgood equation is used for constructing cyclic stress-strain relation. Fatigue damage indexes and service life are calculated by a modified Palmgren-Miner rule and finite element model. The investigation shows that fatigue notch factor and stress concentration factor have a significant influence on the calculation of fatigue damage of dumpers. The numerical simulation for fatigue calculation of dumper shows that prediction results of fatigue life agreed good with practical life.

This paper consists of six sections of original contributions to the theory of cumulative fatigue damage of airframe structures and a section which consists of extensive bibliography of important papers in cumulative fatigue damage. Classical models for predicting the average number of cycles-to-failure, using basically one form or another of the so-called Miner’s rule, are known to be inadequate, in the sense that they either underestimate or overestimate, in some cases, the average number of cycles-to-failure. This is because they do not take into consideration, or even do not know how to take into consideration, the various co-occurring or concomitant factors, other than the various types of loads themselves, and incorporate them into the formula for predicting the expected number of cycles-to-failure. We believe that, in this paper we have suggested methods to circumvent the drawbacks from which the classical Miner’s rule suffers, and we have also offered models, in the more difficult and realistic situation, in which the additional increments in the propagation of the dominant crack form a dependent sequence of chance variables. It is the fond hope of the authors that they and other workers in the field will have the opportunity of applying the realistic approach to predicting the average number of cycles of a large airframe, based on actual flight test data, and to compare its performance with that of methods advanced in a follow-up effort.

Study on a novel type of metallic damper