Combined Axial Tension/Compression and Internal Pressure Testing of Mini-Pipe Specimens in H2S Environment to Determine Three Dimensional (Triaxial) Stress States which Produce Crack Initiation Failure: Explanation of the New Test Fixture, Mini-Pipe Specimen, and Preliminary Test Results

2005 ◽  
Author(s):  
E.P. Cernocky ◽  
V.D. Aaron ◽  
P.R. Paslay ◽  
R.E. Wink
Keyword(s):  
Crack Initiation ◽  
Internal Pressure ◽  
Three Dimensional ◽  
Preliminary Test ◽  
Triaxial Stress ◽  
Test Results ◽  
Test Fixture ◽  
Pressure Testing ◽  
Axial Tension ◽  
Stress States

Influences of Cyclic Pre-Overload on Low Cycle Fatigue Behaviours of Elbow Pipe

2011 ◽  
Author(s):  
Kazuya Matsuo ◽  
Koji Takahashi ◽  
Kyohei Sato
Keyword(s):  
Low Cycle Fatigue ◽  
Three Dimensional ◽  
Preliminary Test ◽  
Growth Direction ◽  
Fatigue Tests ◽  
Test Results ◽  
Cycle Fatigue ◽  
Crack Penetration ◽  
Crack Growth Direction ◽  
Cumulative Fatigue Damage

Low cycle fatigue tests were conducted using sound elbows made of carbon steel (STPT410). The elbows were subjected to cyclic in-plane bending under displacement control with internal pressure of 9 MPa. The preliminary fatigue tests were conducted under constant cyclic displacements. Then, two test conditions were adopted to investigate the influence of cyclic pre-overload on low cycle behavior of elbow on the basis of the preliminary test results. The fatigue test results were evaluated by using the total usage factor UFTotal (= UFpre+UFpost), where the UFpre and UFpost correspond to usage factor for δpre and δpost, respectively. The fatigue lives of overloaded elbow pipes were estimated based on the cumulative fatigue damage rule basically from UFpre = 0.2 to UFpre = 0.6. In addition, three-dimensional elastic-plastic analyses were carried out using the finite element method. The crack penetration area and the crack growth direction were successfully predicted by the analyses.

Low Cycle Fatigue Crack Initiation of Rotating Structures Under Biaxial Stress States

2009 ◽  
Author(s):  
Chao Zhang
Keyword(s):  
Stress State ◽  
Crack Initiation ◽  
Low Cycle Fatigue ◽  
Cyclic Stress ◽  
Biaxial Stress ◽  
Test Results ◽  
Primary Stress ◽  
Biaxial Stress State ◽  
Fatigue Characteristics ◽  
Stress States

Rotating structures can experience biaxial stress states with a wide range of biaxiality ratios on structure surfaces. Low cycle fatigue (LCF) crack initiation in such conditions demonstrates different fatigue characteristics in terms of crack orientation, fatigue life, etc. The biaxial stress states can be categorized into two types: in-phase and out-of-phase under which fatigue characteristics can be significantly different according to rig test results. This paper presents an investigation of LCF crack initiation under in-phase and out-of-phase biaxial stress states based on rig test results of a nickel alloy. The crack orientations are reviewed and discussed at different stress states. Relations of biaxial LCF life debit factor vs biaxiality ratio are derived (the debit factor is defined as a ratio of the LCF life at a biaxial stress state to the LCF life at corresponding uniaxial stress state which has same cyclic and mean stresses as the primary cyclic and mean stressees of the biaxial stress state). The rig test results showed that the crack orientation is usually normal to the primary stress vector under in-phase biaxial stress states but is inclined to the primary stress vector under out-of-phase stress states. As per the derived biaxial LCF life debit factors, the LCF life was found to be slightly reduced with increasing biaxiality ratios under in-phase biaxial stress states but significantly reduced under out-of-phase biaxial stress states compared with corresponding uniaxial primary stress states. The equivalent cyclic stress fatigue criterion is also employed to theoretically model the biaxial LCF life debit factor under in-phase biaxial stress states. The hydrostatic cyclic stress is included in the equivalent cyclic stress in order to take into account the hydrostatic cyclic pressure effects. The equivalent cyclic stress in the criterion can physically reflect the materials’ ductility reduction under in-phase multiaxial stress states.

Prediction of Low-Cycle Fatigue Lives of Elbow and Tee Pipes Using Revised Universal Slope Method

2016 ◽  
Author(s):  
Hiun Nagamori ◽  
Koji Takahashi
Keyword(s):  
Finite Element ◽  
Crack Initiation ◽  
Internal Pressure ◽  
Low Cycle Fatigue ◽  
Growth Direction ◽  
Cycle Fatigue ◽  
Finite Element Analyses ◽  
Slope Method ◽  
Crack Growth Direction ◽  
Stress States

The stress states of elbow and tee pipes are complex and different from those of straight pipes. Several researchers have reported the low-cycle fatigue lives of elbows and tees under cyclic bending with internal pressure conditions. In this work, finite element analyses were carried out to simulate the reported experimental results of elbows and tees. The crack initiation area and the crack growth direction were successfully predicted by the analyses. The analytical results showed that the revised universal slope method can accurately predict the low-cycle fatigue lives of elbow and tee pipes under internal pressure conditions regardless of differences in shape and dimensions.

Overload Fracture of Hydrided Region at Simulated Blunt Flaws in Zr-2.5Nb Pressure Tube Material

2005 ◽  
Author(s):  
Jun Cui ◽  
Gordon K. Shek
Keyword(s):  
Crack Initiation ◽  
Hydrogen Diffusion ◽  
Preliminary Test ◽  
Pressure Tube ◽  
Test Results ◽  
Hydride Formation ◽  
Repetitive Process ◽  
Pressure Tubes ◽  
Reactor Operating ◽  
Increasing Load

Flaws in Zr-2.5Nb alloy pressure tubes in CANDU nuclear reactors are susceptible to a crack initiation and growth mechanism known as Delayed Hydride Cracking (DHC), which is a repetitive process that involves hydrogen diffusion, hydride precipitation, growth of the hydrided region and fracture of the hydrided region at the flaw-tip. An overload occurs when the hydrided region at a flaw is loaded to a stress higher than that at which this region is formed. Flaw disposition requires justification that the hydrided region overload from normal reactor operating and transient loading conditions will not fracture the hydrided region, and will not initiate DHC. Some preliminary test results on the effect of hydrided region overload on DHC initiation were presented in Reference [1]. In the present work, several series of more systematically designed monotonically increasing load experiments were performed on specimens prepared from an unirradiated pressure tube with hydrided region formed at flaws with a root radius of 0.1 or 0.3 mm under different hydride formation stresses and thermal histories. Crack initiation in the overload tests was detected by the acoustic emission technique. Test results indicate that the resistance to overload fracture is dependent on a variety of parameters including hydride formation stress, thermal history, flaw geometry and hydrogen concentration.

Validation of a Belt Model for Prediction of Hub Forces from a Rolling Tire4

2009 ◽  
Vol 37 (2) ◽  
pp. 62-102 ◽  
Author(s):  
C. Lecomte ◽  
W. R. Graham ◽  
D. J. O’Boy
Keyword(s):  
Internal Pressure ◽  
Equations Of Motion ◽  
Three Dimensional ◽  
Prediction Method ◽  
Analytical Models ◽  
Beam Model ◽  
Impedance Boundary ◽  
Bending Waves ◽  
Tire Rotation ◽  
Three Dimensional Models

Abstract An integrated model is under development which will be able to predict the interior noise due to the vibrations of a rolling tire structurally transmitted to the hub of a vehicle. Here, the tire belt model used as part of this prediction method is first briefly presented and discussed, and it is then compared to other models available in the literature. This component will be linked to the tread blocks through normal and tangential forces and to the sidewalls through impedance boundary conditions. The tire belt is modeled as an orthotropic cylindrical ring of negligible thickness with rotational effects, internal pressure, and prestresses included. The associated equations of motion are derived by a variational approach and are investigated for both unforced and forced motions. The model supports extensional and bending waves, which are believed to be the important features to correctly predict the hub forces in the midfrequency (50–500 Hz) range of interest. The predicted waves and forced responses of a benchmark structure are compared to the predictions of several alternative analytical models: two three dimensional models that can support multiple isotropic layers, one of these models include curvature and the other one is flat; a one-dimensional beam model which does not consider axial variations; and several shell models. Finally, the effects of internal pressure, prestress, curvature, and tire rotation on free waves are discussed.

To the theory analysis of tightness of tank of pressure testing

2019 ◽  
Vol 5 (4) ◽  
pp. 129-142
Author(s):  
Vladislav Sh. Shagapov ◽  
Ismagilyan G. Khusainov ◽  
Emiliya V. Galiakbarova ◽  
Zulfya R. Khakimova
Keyword(s):  
Relaxation Time ◽  
Three Dimensional ◽  
Petroleum Products ◽  
Technical Condition ◽  
Excess Pressure ◽  
Soil Parameters ◽  
Theory Analysis ◽  
Pressure Testing ◽  
Tank Pressure ◽  
Over Time

This article studies the process of relaxation of the pressure in a tank with the damaged area of the wall after pressure-testing. The authors use different methods for the diagnosis of the technical condition of objects of petroleum products storage. Pressure testing is one of nondestructive methods. The rate of pressure decrease is characteristic of the system tightness. This article studies the cases of ground and underground location of the tank. Pressure testing involves excess pressure inside of a tank and observing its decrease. Over time, one can assess the integrity of the system. This has required creating mathematical models to account the filtration of the liquid depending on the location of the tank. The results include the analytical solution of the task and the formulas for describing the dependence of the relaxation time of pressure in the tank from the liquid and soil parameters, geometry of the tank, and the damaged portion of the wall. The two- and three-dimensional cases of liquids filtration for the case of underground location of the tank were considered. The results of some numerical calculations of the dependence of reduction time and the time of half-life pressure from the area of the damaged portion of the wall were shown. The obtained solutions allow assessing the extent of the damaged area by the pressure testing with known values of tank, liquid, and soil.

scholarly journals Mesoscale Modelling of Concretes Subjected to Triaxial Loadings: Mechanical Properties and Fracture Behaviour

Materials ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1099
Author(s):  
Qingqing Chen ◽  
Yuhang Zhang ◽  
Tingting Zhao ◽  
Zhiyong Wang ◽  
Zhihua Wang
Keyword(s):  
Mechanical Properties ◽  
Tensile Stress ◽  
Failure Criterion ◽  
Mesoscale Model ◽  
Fracture Behaviour ◽  
Descent Method ◽  
Triaxial Stress ◽  
Gradient Descent Method ◽  
Stress States ◽  
Shear Failures

The mechanical properties and fracture behaviour of concretes under different triaxial stress states were investigated based on a 3D mesoscale model. The quasistatic triaxial loadings, namely, compression–compression–compression (C–C–C), compression–tension–tension (C–T–T) and compression–compression–tension (C–C–T), were simulated using an implicit solver. The mesoscopic modelling with good robustness gave reliable and detailed damage evolution processes under different triaxial stress states. The lateral tensile stress significantly influenced the multiaxial mechanical behaviour of the concretes, accelerating the concrete failure. With low lateral pressures or tensile stress, axial cleavage was the main failure mode of the specimens. Furthermore, the concretes presented shear failures under medium lateral pressures. The concretes experienced a transition from brittle fracture to plastic failure under high lateral pressures. The Ottosen parameters were modified by the gradient descent method and then the failure criterion of the concretes in the principal stress space was given. The failure criterion could describe the strength characteristics of concrete materials well by being fitted with experimental data under different triaxial stress states.

scholarly journals Precise point positioning with GPS and Galileo broadcast ephemerides

GPS Solutions ◽  
2021 ◽  
Vol 25 (2) ◽  
Author(s):  
Luca Carlin ◽  
André Hauschild ◽  
Oliver Montenbruck
Keyword(s):  
Precise Point Positioning ◽  
Three Dimensional ◽  
Test Results ◽  
Process Noise ◽  
Functional Models ◽  
Ambiguity Estimation ◽  
Point Positioning ◽  
And Performance ◽  
Range Error ◽  
Space Range

AbstractFor more than 20 years, precise point positioning (PPP) has been a well-established technique for carrier phase-based navigation. Traditionally, it relies on precise orbit and clock products to achieve accuracies in the order of centimeters. With the modernization of legacy GNSS constellations and the introduction of new systems such as Galileo, a continued reduction in the signal-in-space range error (SISRE) can be observed. Supported by this fact, we analyze the feasibility and performance of PPP with broadcast ephemerides and observations of Galileo and GPS. Two different functional models for compensation of SISREs are assessed: process noise in the ambiguity states and the explicit estimation of a SISRE state for each channel. Tests performed with permanent reference stations show that the position can be estimated in kinematic conditions with an average three-dimensional (3D) root mean square (RMS) error of 29 cm for Galileo and 63 cm for GPS. Dual-constellation solutions can further improve the accuracy to 25 cm. Compared to standard algorithms without SISRE compensation, the proposed PPP approaches offer a 40% performance improvement for Galileo and 70% for GPS when working with broadcast ephemerides. An additional test with observations taken on a boat ride yielded 3D RMS accuracy of 39 cm for Galileo, 41 cm for GPS, and 27 cm for dual-constellation processing compared to a real-time kinematic reference solution. Compared to the use of process noise in the phase ambiguity estimation, the explicit estimation of SISRE states yields a slightly improved robustness and accuracy at the expense of increased algorithmic complexity. Overall, the test results demonstrate that the application of broadcast ephemerides in a PPP model is feasible with modern GNSS constellations and able to reach accuracies in the order of few decimeters when using proper SISRE compensation techniques.

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