► The non-local damage parameter history under variable amplitude bending was computed. ► The computation includes the application of the elastic–plastic material behavior with the kinematic ...hardening. ► The computed history of damage parameter is used by the well known damage accumulation algorithm to estimate fatigue lives.
The paper presents a non-local damage parameter successfully applied to fatigue life assessment of the smooth specimens subjected to variable amplitude bending. The parameter is based on averaging the stresses over the critical plane in the material using weight function in the exponential form. Parameter of the considered weight function is identified using fatigue lives of specimens subjected to sinusoidal plane bending. The stress fields in specimens are computed taking into account non-linear kinematic hardening of the material implemented in Matlab-based algorithm. It is shown that the kinematic hardening of the material has considerable influence on the histograms of stress amplitudes under the analyzed variable loading. The stress field on the critical plane is reduced to effective stress (the non-local damage parameter) for every time variable
t by the weighted averaging process. The computed history of effective stress is used by the well known damage accumulation algorithm along with two damage accumulation hypotheses (Palmgren–Miner and Serensen–Kogayev) to estimate fatigue lives. For comparison purposes, the local concept is also applied for which the calculated fatigue lives are underestimated.
The objective of this work is to present the cyclic internal pressure behaviors and generated reasons of different long distance transmission pipelines, considering transported fluid, in-service ...period, and pressure data sampling methods. Rainflow counting method is adopted to obtain pressure cycles, and the analysis results indicate that pipelines pressure show variously in respects of cycle number and amplitude value, and pressure cycling reasons and suggestions are specially discussed. The authors argue that suitable operation scheme should be carried out to avoid unnecessary pipeline damage according to the oil or gas pipelines' special pressure fluctuation characteristics and generated reasons.
The cycle counting procedure is a fundamental step in the fatigue analysis of structures. This paper is devoted to cycle counting methods, starting from the spectral properties of the loading ...process. Cycle counting methods for stationary Gaussian narrow-band and broad-band processes proposed in literature are discussed. Focusing attention on bi-modal processes, which are usual in dynamic response of structures, the cycles histograms obtained by the Peak and Peak-Valley Counting methods are expressed in closed form. From these, a couple of upper and lower bounds for the mean total damage and for the mean fatigue life are obtained. Then, an advanced formulation of the cycle counting is developed, obtaining a new closed form solution of the cycles histogram which better approximate the Rainflow Counting results. The proposed method is finally applied to several different bi-modal processes, comparing the results with other criteria and with solutions based on simulated time-histories.
A modeller was developed that simulates random load histories by considering a statistical distribution and a sequence of load cycles that correspond to a rainflow algorithm. The random load ...histories are generated stepwise by putting together series of load cycles, successively predicted by the modeller. The core of the modeller is a conditional probability density function of load cycles, which is modelled by a multilayer perceptron. The theoretical foundations of the modeller and three examples of its application for the simulation of random load histories are presented in the paper. We concluded from the examples that it is possible to simulate new random load histories on the basis of the load cycles, extracted from the original load history with the rainflow method, so that the statistical distribution and the sequence of load cycles from the original load history are preserved in simulated load histories.
