Prediction of the Fatigue Life of the Vibrational Sieve Supporting Beam

2017 ◽  
Vol 755 ◽  
pp. 274-278
Author(s):  
Jelena M. Djoković ◽  
Ružica R. Nikolić ◽  
Jan Bujnak
Keyword(s):  
Fatigue Life ◽  
Crack Length ◽  
Crack Propagation Rate ◽  
Working Life ◽  
Propagation Rate ◽  
Initial Crack ◽  
Initial Crack Length ◽  
Critical Crack ◽  
Critical Crack Length ◽  
Remaining Fatigue Life

Vibrational sieves are exposed to exceptionally high cyclic loading during their working life and that is the reason why the special attention should be paid to estimates of the fatigue life of their structural elements, as well as to design with respect to fatigue fracture. Any change in the design appearance of the structural component must be carefully analyzed, since even the rearrangement of the components' elements layout, with keeping all the sizes constant, can cause serious consequences to the particular component's fatigue life. The research subject considered in this paper is the remaining fatigue life of the carrying beam, as well as the suggestions for improving the working life of the vibrational sieve. The Paris' law was used for estimates of the average crack propagation rate. From the presented diagram of the initial crack length versus the remaining working life one could see that the fatigue life decreases with the crack length increase. When the initial crack length reaches a value a little less than a half of the critical crack length, the remaining fatigue life starts to drop abruptly.

scholarly journals Behaviour of Damaged B.F.I. Beam Repaired by CFRP Strips under Static or Fatigue Loads Using Finite Element Simulation

2019 ◽  
pp. 1-12
Author(s):  
Hala M. Refat ◽  
Mohamed H. Makhlouf
Keyword(s):  
Crack Length ◽  
Numerical Study ◽  
Initial Crack ◽  
Initial Crack Length ◽  
Load Range ◽  
Critical Crack ◽  
Critical Crack Length ◽  
Reinforced Polymer ◽  
Element Simulation ◽  
Cfrp Strip

This paper presents the numerical study to simulate the fatigue crack growth of artificially damaged steel Broad Flange I- beams section by single edge notched repaired with carbon fiber reinforced polymer CFRP strips. The study is carried out using ANSYS classic modeling approach is suggested to simulate the fatigue response of the beams, based on the cumulative damage theory and strain life method. Experimental test results were compared with FE results obtained. A parametric study was conducted using the validated model. The considered parameters were the number of CFRP strip layers used in the repair, the applied load range, initial crack length at time of strengthening and the thickness of CFRP strip. The numerical results indicated that the CFRP increased the critical crack length at which fracture occurred, and the strengthening was more effective at lower stress ranges. Moreover, the CFRP Strips can substantially delay failure and the results demonstrate the possibility of technique and highlight the importance of early intervention when repairing fatigue critical details. The ultimate load and ductility decreased substantially with increasing initial crack length at the time of installing the strengthening layer. Furthermore, increased capacity was achieved by increase the CFRP thickness and layers.

Fracture Resistance of Ship Longitudinal Members Including Fatigue Crack

2013 ◽  
Author(s):  
Yann Quéméner ◽  
Chien-Hua Huang ◽  
Chi-Fang Lee
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Crack Growth ◽  
Crack Length ◽  
Crack Growth ◽  
Fracture Resistance ◽  
Crack Tip ◽  
Critical Crack ◽  
Critical Crack Length ◽  
Extreme Loads

This study investigates the fracture failure of longitudinal members including cracks. Specifically, this study employs the failure assessment diagram methodology to assess the conditions of failure at the crack tip. Based on various crack configurations, this study establishes the analytical formulations of the crack-tip condition that are validated using finite element analyses. In addition, the material toughness is expressed in terms of crack-tip opening displacement. This study evaluates the failure stress of representative cracked members as a function of the crack length. This enables determining critical crack lengths corresponding to the maximum stresses derived from extreme loads. Finally, this study uses simplified fatigue crack growth analyses to characterize the critical crack length in terms of fatigue life. For members located in the deck and bottom regions, the critical crack lengths correspond to the end of the assessed fatigue life. Therefore, the fracture resistance of the longitudinal members is satisfactory as it will not cause the premature loss of the component. This study also provides analytical formulations for crack-tip conditions that could be employed in a reliability study linking fatigue crack growth and fracture under extreme loads.

scholarly journals Numerical Simulation of Hydraulic Fracturing in Earth and Rockfill Dam Using Extended Finite Element Method

2018 ◽  
Vol 2018 ◽  
pp. 1-8
Author(s):  
Enyue Ji ◽  
Zhongzhi Fu ◽  
Shengshui Chen ◽  
Jungao Zhu ◽  
Zhizhou Geng
Keyword(s):  
Hydraulic Fracturing ◽  
Crack Length ◽  
Initial Crack ◽  
Extended Finite Element ◽  
Critical Crack ◽  
Propagation Length ◽  
Critical Crack Length ◽  
The Core ◽  
Rockfill Dam ◽  
Earth And Rockfill Dam

Hydraulic fracturing is one of the most important factors affecting the safety of earth and rockfill dam. In this paper, the extended finite element method (XFEM) is used to simulate the hydraulic fracturing behavior in an actual high earth and rockfill dam. The possibility of hydraulic fracturing occurrence is analyzed, and the critical crack length is obtained when hydraulic fracturing occurs. Then, the crack propagation path and length is obtained by inserting initial crack of different lengths at different elevation. The results indicate that hydraulic fracturing will not occur without the permeable weak surface (initial crack). The critical initial crack length required for hydraulic fracturing is 5.3 m of the calculation model in this paper. The propagation length decreases with the increase of elevation, and the average propagation length decreases from 9.4 m to 3.4 m. Furthermore, it is proved that the direction of crack propagation has a certain angle with the horizontal plane toward the downstream. Considering the up-narrow and down-wide type of the core wall, the possibility of hydraulic fracturing to penetrate the core is extremely high when the upper part of the core wall reaches the critical crack length.

Continuous NDE Monitoring via Web Technology

2008 ◽  
Author(s):  
Pedro V. Marcal ◽  
Jeffrey T. Fong
Keyword(s):  
Life Cycle ◽  
Fatigue Life ◽  
Crack Length ◽  
Crack Growth ◽  
Direct Measurement ◽  
Continuous Monitoring ◽  
Initial Crack ◽  
Pressure Vessels ◽  
Integrity Assessment ◽  
Remaining Fatigue Life

For safe operation of high-consequence structures such as airplanes, ships, trains, chemical plants, electricity-generating units, nuclear reactors, oil and gas pipelines, and pressure vessels, periodic inspection using nondestructive evaluation (NDE) technology and a deterministic approach to modeling fatigue crack growth has been mandated by government in the energy and transportation sectors of the nation’s economy since the 1970s. Recent advances in web-based computing, direct measurement-based NDE, and a stochastic approach to remaining fatigue life cycle prediction model have made it possible to not only enhance the credibility of fatigue life prediction but also shorten the turn-around time between field-based NDE and office-based modeling, analysis, verification and integrity assessment back to the field for decision making. To illustrate this new concept in preventing structural failure and extending useful life of high-consequence systems, we first recount a lesson learned in the history of the deployment of the U.S. nuclear submarine fleet, where the emphasis was on the continuous monitoring of 100% of pipe and vessel welds from their initial placement to the discovery of tangible signs of fatigue damage way before the onset of service disruption. Using two crack length vs. fatigue life cycle plots, one being based on the deterministic and the other a stochastic model, we summarize the contrast between the two models in their ability to deliver a credible prediction of the remaining fatigue life cycle based on a periodic or continuous inspection mode. In conjunction with that summary, we answer an important question in designing an NDE-based inspection strategy, namely, whether the inspection should be periodic or continuous. We show in this paper that the key to the success of a continuous monitoring system for aging structure is an NDE capability in measuring not only the initial crack length and the initial crack growth rate, but also their standard deviations. We conclude with a remark that a continuous direct-measurement-based NDE inspection system, when coupled with a finite element modeling and analysis capability, is capable of monitoring not only surface but also subsurface cracks.

Prediction of the Fatigue Life of Tires Using CED and VCCT

2005 ◽  
Vol 297-300 ◽  
pp. 102-107 ◽  
Author(s):  
T.W. Kim ◽  
H.Y. Jeong ◽  
J.H. Choe ◽  
Y.H. Kim
Keyword(s):  
Fatigue Life ◽  
Crack Length ◽  
Test Data ◽  
Fem Simulation ◽  
Strain Energy Release ◽  
Initial Crack ◽  
Tire Model ◽  
Initial Crack Length ◽  
Paris Law ◽  
Final Crack

A new simulation methodology using the finite element method (FEM) was proposed to predict the fatigue life of tires. In the FEM simulation the cracking energy density (CED) was calculated, and the virtual crack closure technique (VCCT) was used to calculate the strain energy release rate (SERR) for a crack. First, a plane in an element on which CED had its maximum was determined, and a crack was created on the plane. Once a crack was introduced, another plane on which CED had its maximum was again determined, and the crack was further elongated along the plane. In addition, SERR was calculated for every crack increment by using VCCT, and it was represented as a function of the crack length. Then, the fatigue life of a tire was determined using Paris law. For Paris law, the initial crack length and the final crack length as well as the material constants should be known. In this paper, the initial crack length was set in a way that the fatigue life predicted by using Paris law became the same as the test data for a tire model (Tire A), and the final crack length was determined from the cross-section views of failed tires which showed cracks grown about halfway toward the carcass from the carcass turn-up edge. Finally, the fatigue life for another tire model (Tire B) was predicted by using Paris law, and the predicted fatigue life was compared with the test data.

scholarly journals Probability of the Critical Length of a Fatigue Crack Occurring at the Tooth Foot of Cylindrical Geared Wheels of the Drive System of a Fiomax 2000 Ring Spinner

2017 ◽  
Vol 25 (0) ◽  
pp. 0-0 ◽  
Author(s):  
Jacek Rysiński ◽  
Robert Drobina ◽  
Jerzy Tomaszewski
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Crack Length ◽  
Technical Specification ◽  
Critical Length ◽  
Drive System ◽  
Test Machine ◽  
Tooth Root ◽  
Critical Crack ◽  
Critical Crack Length

In the present paper, we describe a method of determination of the probability of reaching the critical crack length at the tooth root of the cylindrical geared wheels of the drive system of the Fiomax 2000 ring spinner. The Paris-Erdogan formula was utilised for calculations of the fatigue crack length depending on the number of load cycles. Experimental investigations were performed on cylindrical geared wheels. The wheel specimens were manufactured from 1.6523 steel (UE) according to a technical specification relevant to the drive system of the ring spinner. The experiments were performed using a professional pulsator (pulsating test machine). Based upon the experiments (series of 12 tests), material constants and were calculated. These parameters were utilised in the Paris law of crack propagation for further calculations. Moreover it was also ascertained that these unknowns are related via the deterministic relationship. Therefore a function allowing for approximation of constant in dependence on exponent m was derived. In the next step, for the values of parameter chosen – belonging to the variability interval, established from experimental data – we determined the times of reaching the critical length of the fatigue crack. It was stated that the best approximation distribution describing the simulated random values of times of reaching the critical length of the tooth crack for the drive system of the ring spinner is the asymptotic Gumbel’s distribution. Knowing the distribution and number of cycles until reaching the critical crack length at the tooth root, one can evaluate the fatigue life of the damaged wheel in the ring spinner (Fiomax) drive system for the assumed probability. The goal of the present paper is evaluation of the working time of the elements of the drive system of a ring spinner until the occurrence of damage. The highest fatigue life of geared wheels was achieved within the interval (4.3 – 4.5)x 105 cycles. However, it is recommended to change of the geared wheel in case of the spotting of early symptoms of defect. For the stretching apparatus, the authors of the present paper suggest the exchange of the idler geared wheels at least once per year.

A LIFE PREDICTION MODEL OF THERMAL BARRIER COATINGS

2010 ◽  
Vol 24 (15n16) ◽  
pp. 3161-3166 ◽  
Author(s):  
LIYONG NI ◽  
CHAO LIU ◽  
CHUNGEN ZHOU
Keyword(s):  
Crack Propagation ◽  
Prediction Model ◽  
Thermal Barrier Coatings ◽  
Life Prediction ◽  
Crack Propagation Rate ◽  
Thermal Barrier ◽  
Critical Crack ◽  
Critical Crack Length ◽  
Barrier Coatings ◽  
Life Prediction Model

The durability and reliability of thermal barrier coatings(TBCs) have become a major concern of hot-section components due to lack of a reliable life prediction model. In this paper, it is found that the failure location of TBCs is at the TBC/TGO interface by a sequence of crack propagation and coalescence process. The critical crack length of failure samples is 8.8mm. The crack propagation rate is 3-10µm/cycle at the beginning and increases largely to 40µm/cycle near coating failure. A life prediction model based a simple fracture mechanics approach is proposed.

Structural integrity assessment for a component of the bucket-wheel excavator

2014 ◽  
Vol 5 (2) ◽  
pp. 129-140 ◽  
Author(s):  
Anghel Cernescu ◽  
Liviu Marsavina ◽  
Ion Dumitru
Keyword(s):  
Risk Factor ◽  
Fatigue Life ◽  
Crack Length ◽  
Structural Integrity ◽  
Evaluation Procedure ◽  
Content Type ◽  
Integrity Assessment ◽  
Material Component ◽  
High Level ◽  
Remaining Fatigue Life

Purpose – The purpose of this paper is to present a methodology for assessing the structural integrity of a tie member from a bucket-wheel excavator, ESRC 470 model, which was in operation for about 20 years. The tie member is made of S355J2N structural steel. Following the period of operation, the occurrence of microcracks which can propagate by fatigue is almost inevitable. It is therefore necessary to analyze the structural integrity and the remaining life of the component analyzed. Design/methodology/approach – In principle, the assessment methodology is based on three steps: first, the evaluation of mechanical properties of the material component; second, a BEM analysis using FRANC 3D software package to estimate the evolution of the stress intensity factor based on crack length and applied stress; third, risk factor estimation and remaining fatigue life predictions based on failure assessment diagram and fatigue damage tolerance concept. Findings – Following the evaluation procedure were made predictions of failure risk factor and remaining fatigue life function of crack length and variable stress range, for a high level of confidence. Originality/value – As results of this analysis was implemented a program for verification and inspection of the tie member for the loading state and development of small cracks during operation.

Impact of PWSCC and Current Leak Detection on Leak-Before-Break Acceptance

2005 ◽  
Author(s):  
Gery Wilkowski ◽  
Rick Wolterman ◽  
Dave Rudland
Keyword(s):  
Fatigue Crack ◽  
Crack Length ◽  
Flow Path ◽  
Critical Crack ◽  
Cracking Behavior ◽  
Critical Crack Length ◽  
Crack Morphology ◽  
Actual Flow ◽  
The Difference ◽  
Morphology Parameters

This paper assesses the effect of using primary water stress corrosion cracking (PWSCC) crack morphology parameters (roughness, number of turns, and actual flow path/pipe thickness) in determining the difference in the leakage crack length, and how the difference in the leaking crack lengths changes typical margins from past LBB submittals and published reports. Several past LBB submittal cases were selected; in addition, cases from generic LBB reports published by EPRI were also selected. The results of the analyses showed that the past submittals by nuclear steam system supply (NSSS) companies frequently used the surface roughness comparable to an air-fatigue crack with no turns and the actual flow path equal to the thickness of the pipe. This condition would give the shortest possible leakage flaw length. The roughness, number of turns, and actual flow path to thickness ratio for PWSCC cracks were determined from photomicrographs of service-removed cracks. When using the PWSCC crack morphology parameters that corresponded to the crack growing parallel to the long direction of the dendritic grains (V.C. Summer and Ringhals cases), then the leakage flaw length increased 69 percent over the air-fatigue crack length at the same leak rate. Using the same critical crack length as was used in the initial LBB submittals and the published documents, the margins on the crack length changed from 1.77 to 6.0 for the initial submittals (which we also reproduced) to 0.88 to 2.74 from our calculations for a PWSCC crack. If the crack grew in the buttered region of the bimetallic weld, then based on metallographic sections from service-removed flaws, there would be a more tortuous flow path. For this crack condition, in all but one case, the margins on the normal operating versus N+SSE crack lengths were below the safety factor of two required for LBB approval. The average margin decreased from 3.39 for the air-fatigue crack to 1.55 for the PWSCC crack growing transverse to the long direction of the dendritic grains. This was about an additional 20 percent decrease in the margin from the case of having the PWSCC grow parallel to the long direction of the dendritic grains. These results show that LBB is difficult to satisfy for PWSCC susceptible pipe using the current SRP 3.6.3 LBB approach. This LBB assessment did not consider the possible development of a long circumferential surface crack, which would be more detrimental to LBB behavior. Such cracking behavior would violate the LBB screening criterion.

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