Characterisation of a Simplified Aeroengine Casing Subjected to a Radial Loading Condition Using FE and Approximate Methods

2006 ◽  
Author(s):  
Sabesan Rajaratnam ◽  
Tom H. Hyde ◽  
Sean B. Leen
Keyword(s):  
High Reliability ◽  
High Stress ◽  
Bending Moment ◽  
Local Stress ◽  
Load Path ◽  
Approximate Methods ◽  
Loading Mode ◽  
Structure Changes ◽  
Extreme Load ◽  
Radial Loading

In general, aeroegine casings may experience an axial force, a bending-moment and radial loading. Under these loads, the high stress regions of these complex aerongine casings will experience local stress and strain concentrations, with various load combinations. The stiffness will also depend on the loading mode. Hence, careful design is required to avoid the various types of failure such as buckling, crack initiation and propagation must be taken into account when designing an aeroengine casing structure. In addition, aerongine casings require extremely high reliability in service and adequate strength under extreme load conditions, i.e. Fan-Blade-Off (FBO) condition, must be demonstrated. Under radial loading of aeroengine casings, which have spoke to shell connections, these are the most likely sites for plastic deformation to occur and cracks to initiate. Also, the load path for each spoke to shell connection within the casing structure changes during loading. Based on these observations, this paper concentrates on the behavior which occurs in spoke to shell connections, referred to as local joints. The intention is first to characterize the local joint behavior and then to incorporate this into a global casing model. The work reported in this paper includes studies of mesh sensitivity, predictions of load path at each local joint under radial load, FE failure loci, upper bound techniques for predicting limit loads and stresses-strains predictions at local casing notches under elastic-plastic and creep situations using approximate notch methods. Hence, the global responses of a casing structure were predicted by utilizing a “repeated local joint” technique in conjunction with simplified global models.

Investigation of Smooth Pipe Bends Under the Effect of In-Plane Bending

2017 ◽  
Author(s):  
Diana Abdulhameed ◽  
Michael Martens ◽  
J. J. Roger Cheng ◽  
Samer Adeeb
Keyword(s):  
High Stress ◽  
Circular Cross Section ◽  
Bending Moment ◽  
Bend Angle ◽  
Bending Moments ◽  
Bend Radius ◽  
Pipe Bend ◽  
Cross Sectional ◽  
Smooth Pipe ◽  
Plane Bending

Pipe bends are frequently used to change the direction in pipeline systems and they are considered one of the critical components as well. Bending moments acting on the pipe bends result from the surrounding environment, such as thermal expansions, soil deformations, and external loads. As a result of these bending moments, the initially circular cross-section of the pipe bend deforms into an oval shape. This consequently changes the pipe bend’s flexibility leading to higher stresses compared to straight pipes. Past studies considered the case of a closing in-plane bending moment on 90-degree pipe bends and proposed factors that account for the increased flexibility and high-stress levels. These factors are currently presented in the design codes and known as the flexibility and stress intensification factors (SIF). This paper covers the behaviour of an initially circular cross-sectional smooth pipe bend of uniform thickness subjected to in-plane opening/closing bending moment. ABAQUS FEA software is used in this study to model pipe bends with different nominal pipe sizes, bend angles, and various bend radius to cross-sectional pipe radius ratios. A comparison between the CSA-Z662 code and the FEA results is conducted to investigate the applicability of the currently used SIF factor presented in the design code for different loading cases. The study showed that the in-plane bending moment direction acting on the pipe has a significant effect on the stress distribution and the flexibility of the pipe bend. The variation of bend angle and bend radius showed that it affects the maximum stress drastically and should be considered as a parameter in the flexibility and SIF factors. Moreover, the CSA results are found to be un-conservative in some cases depending on the bend angle and direction of the applied bending moment.

Effect of Creep Relaxation on the Delayed Hydride Cracking Behavior of Irradiated Zirconium 2.5%Wt Niobium Pressure Tube Material

2006 ◽  
Author(s):  
Heather Chaput ◽  
Brian W. Leitch ◽  
Don R. Metzger
Keyword(s):  
High Stress ◽  
Local Stress ◽  
Operating Conditions ◽  
Experimental Results ◽  
Pressure Tube ◽  
Experimental Program ◽  
Tube Material ◽  
Cracking Behavior ◽  
Delayed Hydride Cracking ◽  
Hydride Cracking

Surface scratches and flaws encountered in CANDU nuclear pressure tubes must be evaluated to ensure that a cracking mechanism, called delayed hydride cracking (DHC), is not initiated. The stress concentration due to a flaw can cause diffusion of hydrogen and precipitation of zirconium hydride at the flaw tip. The presence of a hydride results in reduced fracture resistance in a local region where high stress prevails. In many cases, flaws exist for an extended period of time before the hydrogen content in the base material is sufficient to form a hydride. In this situation high stress creep can significantly relax the local stress at the flaw tip. The assessment of flaws on the basis of local stress distribution not considering creep is expected to be overly conservative, and may result in unnecessary remedial action in reactor operation and maintenance procedures. An experimental program has been developed to isolate and quantify the effect of creep on DHC in irradiated Zr-2.5%Nb pressure tube material. As part of this program, the thermal and load histories relevant to reactor operating conditions have been considered, and initial experimental results indicate that the action of creep increases the threshold load for crack initiation. Finite element analysis of creep relaxation around a hydride also supports the experimental results, and a fracture initiation model is applied to the experimental conditions in order to establish an analytical trend for the effect of creep. The quantitative effect predicted by the model is in reasonable agreement with the experimental results, and an improved, less conservative assessment procedure that accounts for creep is deemed to be practical.

FATIGUE CRACK STATISTICS IN FASTENER HOLES

2010 ◽  
Vol 17 (06) ◽  
pp. 543-553
Author(s):  
D. GARY HARLOW
Keyword(s):  
Life Cycle ◽  
Residual Life ◽  
High Reliability ◽  
Fatigue Cracks ◽  
High Stress ◽  
Life Cycle Management ◽  
Distribution Functions ◽  
Cumulative Distribution ◽  
Original Design ◽  
Geometrical Properties

Structural components in aircraft are often required to be operative beyond their original design service objectives (DSO). Vital issues for aging infrastructures are estimation and prediction, with confidence, of residual life, reliability, and availability, given the service history. Uncertainty increasingly is considered to be a major factor. Demanding high reliability exacerbates the role of uncertainty. One aspect of life cycle management for aging aircraft was investigated by replicating laboratory specimens subjected to fatigue loading that is typical for a class of military aircraft wing skins. Samples were fabricated from 7075-T6 plate aluminum alloy similar to that used for wing panels. A total of 15 specimens were tested. Tests were terminated when the fatigue life expended (FLE) reached a prescribed value of 100%, 150%, or 200% of the component DSO. Then, microscopy was used to quantify the size of fatigue cracks within high stress regions of simulated fastener holes in laboratory specimens. Cumulative distribution functions (cdfs) for geometrical properties of cracks and constituent particles in the alloy were characterized statistically as input for residual life estimations and for life cycle management analyses. Insights into crack initiation and growth are also provided.

Predicting the Long Term Distribution of Extreme Loads From Limited Duration Data: Comparing Full Integration and Approximate Methods

2002 ◽  
Author(s):  
LeRoy M. Fitzwater ◽  
Steven R. Winterstein ◽  
C. Allin Cornell
Keyword(s):  
Load Distribution ◽  
Robust Methods ◽  
Short Term ◽  
Approximate Methods ◽  
Wind Speeds ◽  
Extreme Loads ◽  
Long Run ◽  
Extreme Load ◽  
Limited Duration

In this paper we present a methodology for proceeding from the short-term observations of extreme loads to the long-run load distribution of these extreme events, for both flap and edge loading in both operating and parked wind turbine conditions. First a general approach utilizing full integration, where numerical routines are used to directly integrate the conditional short-term load distribution over the annual occurrence of wind speeds and turbulence intensities, is presented. Then starting from this general approach, a qualitative analysis is undertaken to explore the extent of the contribution of each of the three variables, in the governing equation, to the variability in the long-term extreme load distribution. From this analysis, lower order models are considered, where instead of using the entire distribution of the variables, a constant fractile of the short-term extreme load distribution, turbulence intensity distribution, or both are used. Finally recommendations are given to guide the analyst to decide when simpler, yet robust, methods which account for sufficient variability in extreme load event may be employed with confidence.

The Influence of the Bourdon Effect on Pipe Elbow

2016 ◽  
Author(s):  
Diana Abdulhameed ◽  
Samer Adeeb ◽  
Roger Cheng ◽  
Michael Martens
Keyword(s):  
Internal Pressure ◽  
Cross Section ◽  
High Stress ◽  
Bending Moment ◽  
Design Parameters ◽  
Pipeline System ◽  
Pipe Elbow ◽  
Stress Levels ◽  
Current Design ◽  
Thrust Forces

Pipe elbows are frequently used in a pipeline system to change the directions. Thermal expansion and internal pressure results in bending moments on the bends causing ovalization of the initial circular cross-section. The ability of the bend to ovalize will result in an increase in the bend flexibility when compared to straight pipes [1]. In case of bends subjected to internal pressure, the pipe will start to straighten out due to the difference between the intrados and extrados surface areas. The internal pressure causes unbalanced thrust forces tending to open up the elbow depending on its stiffness and surrounding constraints. These forces tending to cause ovalization of the cross section and causing the tendency of pipe bends to open up are termed the “Bourdon effect”. If these unbalanced thrust forces are not taken into consideration, unanticipated deformations and high stress levels could occur at the elbow location that may not be accounted for in traditional stress analysis [2]. A better understanding of the influence of the Bourdon effect on the elbow design parameters is required. Past studies have investigated the behaviour of pipe elbows under closing bending moment and proposed factors that account for the increased flexibility and high stress levels resulted from ovalization. These factors are used in the current design codes [3],[4] &[5] and known as the flexibility factor and stress intensification factor. In this investigation, pipe elbows with different nominal pipe size and various bend radiuses to internal pipe radius ratios (R/r) are studied to get a better understanding of the Bourdon effect and its influence on the pipe stresses and deformations. Differential equilibrium equations are solved to derive a mathematical model to evaluate the unbalanced thrust forces resulted from the Bourdon effect on a pipe elbow. The forces evaluated from the derived model are compared to finite element model results and showed excellent agreement. A comparison between the CSA-Z662 code and the FEA results is conducted to investigate the applicability of the stress intensification factors used in the current design code for different loading cases. The study showed that the external bending moment direction acting on the pipe has a significant effect on the distribution of stresses on the pipe elbow and significantly depending on the level of applied internal pressure.

Effect of Mechanical Model on Limit Load Analysis of High Pressure Heater Tubesheet

2017 ◽  
Author(s):  
Yan-Nan Du ◽  
Xiao-Ying Tang ◽  
Jia-huan Wang ◽  
Zhi-Gang Yang ◽  
Yi-Feng Ren ◽  
...  
Keyword(s):  
High Pressure ◽  
Mechanical Model ◽  
High Stress ◽  
Local Stress ◽  
Limit Load ◽  
Element Model ◽  
Plastic Collapse ◽  
Analysis Design ◽  
Load Analysis ◽  
Collapse Assessment

Tubesheet is the main part of high pressure heater, which is very thick based on chinese code GB151 for the design of heat exchangers. Increased tubesheet with large thermal stress are not conducive to manufacture, heat transmission and detection. The stress and structure of tubesheet are so complex that the time costs too large during the analysis design, and stress classification exists uncertainty. Limit load method contributes to tubesheet lightweight. 3-D finite element model used for analysis design should be simplified reasonably. In this paper, the effect of mechanical model on limit load analysis of high pressure heater tubesheet conforming to the design-by-analysis code is researched. It is found that the tubesheet could pass the plastic collapse assessment, and the thickness of tubesheet could be decreased. The difference between the equivalent sold tubesheet model and the whole tubesheet model exists during plastic collapse assessment. Though the local stress distribution is different, the limit load results occurred plastic collapse by the equivalent sold tubesheet model is close to that by the whole tubesheet model. The limit load occurred plastic collapse is influenced by max circular diameter of tube layout little. The reason is attributed to original tubesheet owning enough rigidity related to thickness, and high stress appeares on the inner wall of jointing of tubesheet with head. The equivalent sold tubesheet model could be used for primary evaluation of limit load, and the whole tubesheet model is suited for partial analysis. The results provide some reference for the design-by-analysis of high pressure heater tubesheet.

scholarly journals Pyroxene low-temperature plasticity and fragmentation as a record of seismic stress evolution in the lower crust

2020 ◽  
Author(s):  
Lucy Campbell ◽  
Luca Menegon
Keyword(s):  
Low Temperature ◽  
Shear Zone ◽  
Lower Crust ◽  
Damage Zone ◽  
High Stress ◽  
Local Stress ◽  
Stress Evolution ◽  
Short Term ◽  
Viscous Shear ◽  
Lower Crustal

<p>Seismic rupture of the lower continental crust requires a high failure stress, given large lithostatic stresses and potentially strong rheologies. Several mechanisms have been proposed to generate high stresses at depth, including local amplification of stress heterogeneities driven by the geometry and rheological contrast within a shear zone network. High dynamic stresses are additionally associated with the subsequent slip event, driven by propagation of the rupture tips. In the brittle upper crust, fracturing of the damage zone is the typical response to high stress, but in the lower crust, the evolution of combined crystal plastic and brittle deformation may be used to constrain in more detail the stress history of rupture, as well as  additonal parameters of the deformation environment. It is crucial to understand these deep crustal seismic deformation mechanisms both along the fault and in the wall rock, as coseismic damage is an important (and sometimes the only) method of significantly weakening anhydrous and metastable lower crust, whether by grain size reduction or by fluid redistribution.</p><p>A detailed study of pyroxene microstructures are used here to characterise the short-term evolution of high stress deformation experienced on the initiation of lower crustal earthquake rupture. These pyroxenes are sampled from the pseudotachylyte-bearing fault planes and damage zones of lower crustal earthquakes linked to local stress amplifications within a viscous shear zone network, recorded in an exhumed granulite-facies section in Lofoten, northern Norway. In orthopyroxene, initial low-temperature plasticity is overtaken by pulverisation-style fragmentation, generating potential pathways for hydration and reaction. In clinopyroxene, low-temperature plasticity remains dominant throughout but the microstructural style changes rapidly through the pre- and co-seismic periods from twinning to undulose extinction and finally the formation of low angle boundaries. We present here an important record of lower crustal short-term stress evolution along seismogenic faults.</p>

scholarly journals Stress Heterogeneity and Slip Weakening of Faults under Various Stress and Slip

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-12 ◽  
Author(s):  
Longjun Dong ◽  
Qiaomu Luo
Keyword(s):  
Slip Surface ◽  
Water Pressure ◽  
High Stress ◽  
Local Stress ◽  
Seismic Source ◽  
High Water ◽  
Fault Slip ◽  
Underground Engineering ◽  
Finite Element Software ◽  
Stress Heterogeneity

The rock mass of deep underground engineering is in the complex geological environment of high stress, high temperature, and high water pressure. In the process of deep mining and underground space development, the fault-slip seismic source may cause engineering accidents with strong destructive capacity. An in-depth study of fault slip characteristics is very important in the engineering disaster prevention and control. In this paper, a slip model was established based on the finite element software ABAQUS. A total of 20 loading ways are set for various stress and slip, which include the possible slip conditions of fast slip, slow slip, and critical state. By comparing the simulation diagrams and collecting the data of representative grid elements on the loading surface and slip surface, the slip characteristics such as stress heterogeneity under different loads are analyzed. The results show that the increase of slip velocity will make the slip unstable, and the local stress and deformation will become irregular. The spatial stress heterogeneity and the resulting local high working rate will lead to the decrease of the friction strength and the slip weakening. These results can provide some useful suggestions for the research of seismic activities caused by fault slip.

Extreme load estimation of the wind turbine tower during power production

2019 ◽  
pp. 0309524X1987276
Author(s):  
Atsushi Yamaguchi ◽  
Prasanti Widyasih Sarli ◽  
Takeshi Ishihara
Keyword(s):  
Bending Moment ◽  
Power Production ◽  
Data Sets ◽  
Bending Moments ◽  
Recurrence Period ◽  
Wind Turbine Tower ◽  
Extreme Load ◽  
Predicted Values ◽  
New Criterion ◽  
Good Agreement

Wind turbines have to be designed against extreme load during power production with the recurrence period of 50 years. This extreme load is usually calculated through statistical extrapolation. However, large uncertainties exist in the estimation of the extreme load. This study aims to reduce these uncertainties in the statistical extrapolation by using systematic simulations. First, a new criterion is proposed for the data sets to be used for the statistical extrapolation and the resulting uncertainty satisfies the requirement in the standard for prediction of wind load. Then, a new extrapolation factor for load extrapolation is proposed and the predicted maximum tower bending moments at all the heights show favorable agreement with measurement. Finally, empirical formulae are proposed to estimate the expected value of the maximum tower bending moment and the predicted values show good agreement with the numerical simulations.

The Effect of Microstructure Heterogeneity on Fatigue Property of Powder Metallurgy Steels

2008 ◽  
Vol 273-276 ◽  
pp. 348-353 ◽  
Author(s):  
H. Abdoos ◽  
H. Khorsand ◽  
A.R. Shahani ◽  
M. Arjomandi
Keyword(s):  
Powder Metallurgy ◽  
Fatigue Behavior ◽  
Local Stress ◽  
Fatigue Property ◽  
Fatigue Performance ◽  
Loading Mode ◽  
Stress Risers ◽  
High Fatigue ◽  
Different Response ◽  
Effect Of Microstructure

Powder metallurgy is a new method for mass production of precision components with appropriate mechanical properties, but in this kind of materials (PM parts) with special microstructures (pores act as local stress risers), fracture due to fatigue is expected as an important destructive factor. Various microstructures in powder metallurgy steels, depending on alloying methods, have different response against cyclic loading. diffusion bonding is an effective method to obtain high fatigue performance in PM steels. The main characteristic of this materials consists of well-organized phases distribution due to incomplete diffusion of alloying elements. In this study fatigue behavior of diffusion-bonded, distaloy AE, steel with two carbon contents under different periodic loading are investigated. The effect of carbon content and various loading mode upon fatigue performance is analyzed. Metallugraphy and fractography examination on fatigue loaded samples revealed the positive effect of microstructure heterogeneity on fatigue crack behavior and this concept is a reason for increasing of diffusion-bonded powders application to manufacturing of components that are subjected to cyclic stresses.

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