scholarly journals On Modeling of Vibration and Crack Growth in a Rotor for Prognostics

2020 ◽  
Vol 12 (1) ◽  
pp. 9
Author(s):  
Amirhassan Abbasi ◽  
Foad Nazari ◽  
C. Nataraj
Keyword(s):  
Crack Initiation ◽  
Crack Length ◽  
Crack Growth ◽  
Remaining Useful Life ◽  
Operating Conditions ◽  
Crack Initiation And Propagation ◽  
Isolation And Identification ◽  
Critical Crack Length ◽  
Coupled Equations ◽  
Initiation And Propagation

Prognostics and health management (PHM) include comprehensive engineering approaches that evaluate the real-time health condition of an asset and predict its future states under the actual operating conditions. This predictive ability would result in efficient maintenance approaches such as Condition Based Maintenance (CBM) that can set maintenance strategies optimally and reduce the life cycle costs. Diagnostics and Prognostics are two major concepts in PHM. Detection, Isolation and Identification of faults are done by diagnostics while prognostics deals with estimation of future states. Mechanical fatigue phenomenon that causes crack initiation and propagation is considered as a common reason for failure in mechanical parts. Hence, diagnostics and prognostics of the crack initiation and propagation have been the subject of many research papers recently. The current paper presents a diagnostics and prognostics method capable of detecting the crack initiation and propagation in a rotor under cyclic loading. At the first step, the coupled equations of rotor motion and crack growth are obtained. An extended model of Paris–Erdogan equation is used for crack growth modeling. The coupled equations are solved numerically. A set of features are extracted from the dynamic response of the rotor for a range of crack lengths. A dataset is compiled including features of response, operating frequency, crack length and number of cycles remained until reaching the critical crack length. With the objective of generalization of the results, the dataset is used for creating a model using an Artifical Neural Network (ANN). In the trained ANN the inputs are the operating speed and the outputs are the crack length and the remaining useful life (RUL) that address the diagnostics and prognostics objectives, respectively.

Fatigue Crack Growth Behavior of Threaded Pipe Couplings

2011 ◽  
Author(s):  
Jeroen Van Wittenberghe ◽  
Patrick De Baets ◽  
Wim De Waele
Keyword(s):  
Fatigue Crack ◽  
Fracture Surface ◽  
Crack Initiation ◽  
Crack Growth ◽  
Fatigue Behavior ◽  
Crack Opening ◽  
Bending Test ◽  
Crack Initiation And Propagation ◽  
Accurate Knowledge ◽  
Initiation And Propagation

Threaded couplings are used in various applications to connect steel pipes. To maintain a secure connection, such couplings are preloaded and during service additional dynamic loads can act on the connections. The coupling’s threads act as stress raisers, initiating fatigue cracks, which can cause the connection to fail in time. Accurate knowledge of the fatigue behavior, taking into account crack initiation and propagation is necessary to understand the fatigue mechanisms involved. In this study, the fatigue behavior of tapered couplings with NPT threads is studied. This is done by analyzing the results of an experimental four-point bending test. The fatigue crack propagation is monitored using an optical dynamic 3D displacement measurement device and LVDTs to measure the crack opening. At certain times during the test, the load ratio is changed to apply a number of beach marking cycles. This way a fine line is marked in the fracture surface. These marked crack shapes are used as input for a finite element model. The measured deflection and crack opening are compared to the results of the numerical simulations. Using this methodology a distinction is made between fatigue crack initiation and propagation. By analyzing the fracture surface it was observed that once the crack is initiated, it propagates over a wide segment of the pipe’s circumference and subsequently rapidly penetrates the wall of the pipe. The observed crack growth rates are confirmed by a fracture mechanics analysis. Since the appearing long shallow crack is difficult to detect at an early stage the importance is demonstrated of accurate knowledge of the fatigue behavior of threaded connections in order to define acceptable flaw sizes and inspection intervals.

Towards a Better Understanding of Crack Growth in Nickel-Cast Alloys Under Creep-Fatigue and Thermo-Mechanical Fatigue Conditions

2019 ◽  
Author(s):  
Karl Michael Kraemer ◽  
Falk Mueller ◽  
Christian Kontermann ◽  
Matthias Oechsner
Keyword(s):  
Crack Initiation ◽  
Crack Growth ◽  
Load Cycle ◽  
Crack Initiation And Propagation ◽  
Mechanical Fatigue ◽  
Initiation And Propagation ◽  
Creep Fatigue ◽  
Cast Alloys ◽  
Crack Growth Rates

Abstract To ensure the feasibility of gas turbines, despite rising commodity prices and emission restrictions, an enhancement of both their efficiency and flexibility is necessary. The consequential higher loading of components at high temperature conditions calls for an increased use of damage tolerant design approaches. To still guarantee a safe operation, a sound understanding and reliable estimations for crack growth under service conditions is indispensable. In this paper, the results from several projects in this field conducted at the TU Darmstadt and involved partners are summarized to identify and describe the various influences on crack growth under creep-fatigue and thermo-mechanical fatigue (TMF) loading. The activation of damage mechanisms under TMF loading and interactions between them are dependent of the temperature cycle and the respective load phasing. Depending on the type of loading (force- vs. strain-control), contrary influences of the phase shift on the TMF crack growth rates are found. This can partially be attributed to the differences in mean stress evolution. Crack initiation and propagation under creep-fatigue and TMF conditions are also often connected with significant scattering of initiation sites and crack growth rates. One reason for this non-uniform behaviour is the interaction of geometric discontinuities with the microstructure. To investigate the role of the local grain structure for crack initiation and propagation, in-situ observation techniques for crack tip movement and local strain fields were applied. Harsh gradients in the local deformation behaviour were identified as origins of secondary crack initiation. To describe crack growth under creep-fatigue and TMF conditions, the linear accumulation model “O.C.F.” was developed. It is based on the contributions of fatigue, creep and oxidation to crack growth per load cycle. This model is capable to reproduce the effects of time-dependent damage, different load ratios and TMF phase shifts, as well as component geometry. Substantial advantages of this method are its independence from empiric correction factors to assess changing load cycle forms and the possibility to give analytic estimations without the need of extensive data processing. The model is currently validated for three nickel cast alloys, also including single crystalline (SX) and directionally solidified (DS) cast variants, different creep-fatigue and TMF loading scenarios and crack geometries. The model’s linear formulation allows assessing the dominant driver of crack growth at each stage of an experiment. These predictions are compared with fractographic investigations and in-situ observations of crack paths to identify the mechanisms of crack growth under different TMF load cycle forms.

Rubber Oxidation and Tire Aging - A Review

2008 ◽  
Vol 81 (2) ◽  
pp. 338-358 ◽  
Author(s):  
John M. Baldwin ◽  
David R. Bauer
Keyword(s):  
Crack Initiation ◽  
Crack Growth ◽  
Crack Growth Resistance ◽  
Crack Initiation And Propagation ◽  
Initiation And Propagation ◽  
Different Climates

Abstract While a new tire may have excellent resistance to crack initiation and propagation between the steel belts, an aged tire of the exact same construction can exhibit dramatically reduced crack growth resistance, which in some cases may contribute to tire failure. This article will review the research that has gone into quantifying the rate of oxidation the steel belt rubber oxidizes in different climates from tire samples retrieved from consumers' vehicles. The information obtained from the field is then compared to data collected from various resources attempting to develop accelerated tire aging protocols. Finally, methods for potentially improving tire aging are reviewed.

scholarly journals Modelling the Crack Initiation and Propagation of Notched Rock Beam under the Three-Point Bending Load

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Xun Xi ◽  
Xu Wu ◽  
Qifeng Guo ◽  
Meifeng Cai
Keyword(s):  
Crack Initiation ◽  
Crack Length ◽  
Numerical Method ◽  
Rock Fracture ◽  
Peak Load ◽  
Crack Pattern ◽  
Crack Initiation And Propagation ◽  
Three Point Bending ◽  
Initiation And Propagation ◽  
Rock Beam

Prediction of rock fracture is essential to understand the rock failure mechanism. The three-point bending test has been one of the most popular experiments for the determination of rock fracture parameters. However, the crack initiation and propagation of rock beam with the center notch and offset notch have not been fully understood. This paper develops a numerical method for modelling the notched beam cracking based on nonlocal extended finite element method (i.e., XFEM) and mixed mode rock fracture model. An example is worked out to demonstrate the application of the numerical method and verified with experimental results. The crack length development, crack pattern, crack opening and slipping displacements, and the load-crack mouth of displacement (P-CMOD) curve are obtained. The effects of offset notch location and mechanical properties on the crack length development, P-CMOD curve, and crack pattern are investigated and discussed. It has been found that the peak load of the notched beam nearly linearly increases with the increase of the notch offset ratio. The cracking of rock beam with offset notch is dominated by mode I fracture, but mode II fracture contributes more when crack deflection occurs. The fracture energy significantly affects the peak load, while it has little effect on the prepeak and postpeak slopes in the P-CMOD curve.

Toward a Better Understanding of Crack Growth in Nickel-Cast Alloys Under Creep-Fatigue and Thermo-Mechanical Fatigue Conditions

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Karl Michael Kraemer ◽  
Falk Mueller ◽  
Christian Kontermann ◽  
Matthias Oechsner
Keyword(s):  
Crack Initiation ◽  
Crack Growth ◽  
Load Cycle ◽  
Crack Initiation And Propagation ◽  
Mechanical Fatigue ◽  
Initiation And Propagation ◽  
Creep Fatigue ◽  
Cast Alloys ◽  
Crack Growth Rates

Abstract To ensure the feasibility of gas turbines, despite rising commodity prices and emission restrictions, an enhancement of both their efficiency and flexibility is necessary. The consequential higher loading of components at high temperature conditions calls for an increased use of damage tolerant design approaches. To still guarantee a safe operation, a sound understanding and reliable estimations for crack growth under service conditions are indispensable. In this paper, the results from several projects in this field conducted at the TU Darmstadt and involved partners are summarized to identify and describe the various influences on crack growth under creep-fatigue and thermo-mechanical fatigue (TMF) loading. The activation of damage mechanisms under TMF loading and interactions between them is dependent on the temperature cycle and the respective load phasing. Depending on the type of loading (force versus strain control), contrary influences of the phase shift on the TMF crack growth rates are found. This can partially be attributed to the differences in mean stress evolution. Crack initiation and propagation under creep-fatigue and TMF conditions are also often connected with significant scattering of initiation sites and crack growth rates. One reason for this nonuniform behavior is the interaction of geometric discontinuities with the microstructure. To investigate the role of the local grain structure for crack initiation and propagation, in situ observation techniques for crack tip movement and local strain fields were applied. Harsh gradients in the local deformation behavior were identified as origins of secondary crack initiation. To describe crack growth under creep-fatigue and TMF conditions, the linear accumulation model “O.C.F.” was developed. It is based on the contributions of fatigue, creep, and oxidation to crack growth per load cycle. This model is capable of reproducing the effects of time-dependent damage, different load ratios, TMF phase shifts, as well as component geometry. Substantial advantages of this method are its independence from empiric correction factors to assess changing load cycle forms and the possibility to give analytic estimations without the need of extensive data processing. The model is currently validated for three nickel cast alloys, also including single-crystalline and directionally solidified cast variants, different creep-fatigue and TMF loading scenarios, and crack geometries. The model's linear formulation allows assessing the dominant driver of crack growth at each stage of an experiment. These predictions are compared with fractographic investigations and in situ observations of crack paths to identify the mechanisms of crack growth under different TMF load cycle forms.

Fatigue Life Estimates for Bluntly Notched Members

1980 ◽  
Vol 102 (1) ◽  
pp. 153-158 ◽  
Author(s):  
D. F. Socie
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Crack Growth ◽  
Crack Formation ◽  
Growth Stages ◽  
Crack Initiation And Propagation ◽  
Test Program ◽  
Initiation And Propagation ◽  
Cumulative Fatigue Damage ◽  
Total Life

Methods for estimating the total fatigue lives of bluntly notched members are presented. Analytical estimates are compared to experimental data generated in the Society of Automotive Engineers Cumulative Fatigue Damage Test Program. The crack initiation lives were predicted using strain life concepts and fracture mechanics methods were employed to predict the fatigue crack growth stages. The methods used highlighted the proportions of the total fatigue life spent in crack initiation and propagation. These were found to depend on load amplitude and level of mean load. For the bluntly notched member investigated the initiation and early stages of crack formation formed the major part of the total life, when the loading was predominantly tensile. Conversely for a loading history where most of the cycles were compressive the majority of the fatigue life was expended in crack growth away from the notch.

Crack Initiation and Propagation Under Hydrogen-Enhanced Fatigue of a Cr-Mo Steel for Gaseous Hydrogen Storage

2014 ◽  
Author(s):  
Laurent Briottet ◽  
Marielle Escot ◽  
Isabelle Moro ◽  
Gian Marco Tamponi ◽  
Jader Furtado ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Hydrogen Storage ◽  
Crack Growth ◽  
Hydrogen Pressure ◽  
Pressure Vessels ◽  
Gaseous Hydrogen ◽  
Crack Initiation And Propagation ◽  
High Hydrogen ◽  
Initiation And Propagation

The current international standards and codes dedicated to the design of pressure vessels do not properly ensure fitness for service of such vessel used for gaseous hydrogen storage and subjected to hydrogen enhanced fatigue. Yet, hydrogen can reduce the fatigue life in two ways: by decreasing the crack initiation period and by increasing the fatigue crack growth rate. The European project MATHRYCE aims are to propose an easy to implement vessel design methodology based on lab-scale tests and taking into account hydrogen enhanced fatigue. The study is focused on a low alloy Cr-Mo steel, exhibiting a tempered bainitic and martensitic microstructure, and classically used to store hydrogen gas up to 45 MPa. Due to hydrogen diffusion at room temperature in such steel, tests have to be performed under hydrogen pressure to avoid outgassing. In the present work, experimental procedures have been developed to study both crack initiation and crack growth. The specimens and tests instrumentation have been specifically designed to quantitatively measure in-situ these two stages under high hydrogen pressure. We developed and tested crack gages located close to a small drilled notch. This notch simulates the presence of steel nonmetallic inclusions and other microstructural features that can affect fatigue crack initiation and propagation. The experimental results addressing the effects of the testing conditions, such as stress ratio, frequency and hydrogen pressure will be compared to the local strain and stress fields obtained by Finite Element Method and correlated to the possible hydrogen enhanced fatigue mechanisms involved.

A Finite Element Analysis of Crack Initiation and Propagation in a Notched Disk Submitted to Rolling Contact Fatigue

1998 ◽  
Vol 120 (3) ◽  
pp. 436-441 ◽  
Author(s):  
V. Bordi ◽  
Ch. Dorier ◽  
B. Villechaise
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Crack Initiation ◽  
Crack Growth ◽  
Rolling Contact Fatigue ◽  
Contact Fatigue ◽  
Rolling Contact ◽  
Crack Initiation And Propagation ◽  
Element Analysis ◽  
Initiation And Propagation

A finite element model has been developed to predict crack initiation and propagation in a notched disk submitted to rolling contact fatigue. The aim of this study is to validate the model with experimental results obtained by tests carried out on a two-disk machine. First, a three-dimensional finite element analysis is performed. A unidimensional equivalent damage stress is calculated by applying a plastic criterion in an attempt to estimate the damage location and the time necessary to initiate cracks from the notches. Then a two-dimensional calculation based on linear fracture mechanics is conducted to determine mixed mode stress intensity factors at the tip of a crack initiated from the notch. Several crack growth criteria are used to evaluate crack growth direction and rate. Numerical results are in good agreement with experimental ones.

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