Numerical Analysis of Residual Stress Effects on the Stress Field in a Model of Common Carotid Artery at Wide Range of Transmural Pressure

2013 ◽  
Author(s):  
Adam Piechna ◽  
Krzysztof Cieślicki
Keyword(s):  
Residual Stress ◽  
Numerical Analysis ◽  
Carotid Artery ◽  
Stress Field ◽  
Common Carotid Artery ◽  
Transmural Pressure ◽  
Stress Effects ◽  
Wide Range

ENPOWER: Investigations by Neutron Diffraction and Finite Element Analyses on Residual Stress Formation in Repair Welds Applied to Ferritic Steel Plates

2005 ◽  
Author(s):  
Carsten Ohms ◽  
Robert C. Wimpory ◽  
Dimitar Neov ◽  
Didier Lawrjaniec ◽  
Anastasius G. Youtsos
Keyword(s):  
Experimental Data ◽  
Residual Stress ◽  
Numerical Analysis ◽  
Neutron Diffraction ◽  
Stress Field ◽  
Ferritic Steel ◽  
Maximum Stress ◽  
Steel Plates ◽  
Residual Stress Field ◽  
Welding Procedure

The European collaborative research project ENPOWER (Management of Nuclear Plant Operation by Optimizing Weld Repairs) has as one of its main objectives the development of guidelines for the application of repair welds to safety critical components in nuclear power plants. In this context letter box repair welds applied to thin ferritic steel plates to simulate repair of postulated shallow cracks have been manufactured for the purpose of experimental and numerical analysis of welding residual stresses. Two specimens have been procured, one of them prepared in accordance with a standard welding procedure, while in the second case a different procedure was followed in order to obtain extended martensite formation in the heat affected zone. Residual stresses have been determined in both specimens by neutron diffraction at the High Flux Reactor of the Joint Research Centre in Petten, The Netherlands. In parallel Institut de Soudure in France has performed a full 3-d analysis of the residual stress field for the standard welding case taking into account the materials and phase transformations. The experimental data obtained for both specimens clearly suggest that the non-conventional welding procedure rendered higher maximum stress values. In the case of the standard welding procedure numerical and experimental data show a reasonable qualitative agreement. The maximum stress value was in both cases found in the same region of the material — in the base metal just underneath the weld pool — and in both cases found to be of similar magnitude (∼800 MPa found in neutron diffraction and ∼700 MPa found in numerical analysis). In this paper the experimental and numerical approaches are outlined and the obtained results are presented. In addition an outlook is given to future work to be performed on this part of the ENPOWER project. A main issue pending is the application of an optimized advanced post weld heat treatment in one of the two cases and the subsequent numerical and experimental determination of its impact on the residual stress field. At the same time further evaluation of the materials transformations due to welding is pursued.

Finite Element Analysis of the Effect of Mechanical Stress Improvement Process on Weld Residual Stress and Flaw Growth in a Thick-Walled Pressurizer Safety Nozzle

2017 ◽  
Author(s):  
Giovanni G. Facco ◽  
Patrick A. C. Raynaud ◽  
Michael L. Benson
Keyword(s):  
Residual Stress ◽  
Finite Element Analysis ◽  
Finite Element ◽  
Stress Field ◽  
Mechanical Stress ◽  
Residual Stress Field ◽  
Element Analysis ◽  
Wide Range ◽  
Improvement Process ◽  
Stress Prediction

The Mechanical Stress Improvement Process (MSIP) is generally accepted as an effective method to modify the residual stress field in a given component to mitigate subcritical crack growth in susceptible components [1] [2] [3]. In order to properly utilize MSIP, residual stress prediction is needed to determine the parameters of the MSIP application and the expected final residual stress field in the component afterwards. This paper presents the results of a 2D axisymmetric finite element study to predict weld residual stresses (WRS), and associated flaw growth scenarios, in a thick-walled pressurizer safety nozzle that underwent mitigation by application of MSIP. The authors have developed a finite-element analysis methodology to examine the effect of MSIP application on WRS and flaw growth for various hypothetical welding histories and boundary conditions in a thick-walled pressurizer safety nozzle. In doing so, a wide range of repair scenarios was considered, with the understanding that some bounding scenarios may be impractical for this geometry.

scholarly journals Evaluation of the Impact of Residual Stresses in Crack Initiation with the Application of the Crack Compliance Method Part I, Numerical Analysis

2010 ◽  
Vol 24-25 ◽  
pp. 253-259 ◽  
Author(s):  
G. Urriolagoitia-Sosa ◽  
B. Romero-Ángeles ◽  
Luis Héctor Hernández-Gómez ◽  
G. Urriolagoitia-Calderón ◽  
Juan Alfonso Beltrán-Fernández ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Residual Stress ◽  
Numerical Analysis ◽  
Stress Field ◽  
Crack Initiation ◽  
Residual Stresses ◽  
Main Concern ◽  
Residual Stress Field ◽  
Set Up ◽  
The Impact

The understanding of how materials fail is still today a fundamental research problem for scientist and engineers. The main concern is the assessment of the necessary conditions to propagate a crack that will eventually lead to failure. Nevertheless, this kind of analysis tends to be more complicated, when a prior history in the material is taken into consideration and it will be extremely important to recognize all the factors involved in this process. In this work, a numerical simulation of the introduction of residual stresses, which change the crack initiation conditions, in a modified compact tensile specimen to change the condition of crack initiation is presented. Four numerical analyses were carried out; an initial evaluation was performed in a specimen without a crack and it was used for the estimation of a residual stress field produced by an overload; three more cases were simulated and a crack was introduced in each specimen (1 mm, 5 mm and 10 mm, respectively). The overload was then applied to set up a residual stress field into the component; furthermore, in each case the crack compliance method (CCM) was applied to measure the induced residual stress field. By performing this numerical simulation, the accuracy of the crack compliance method can be evaluated. On the other hand, elastic-plastic finite element analysis was utilized for the residual stress estimation. The numerical analysis was based on the mechanical properties of a biocompatible material (AISI 316L). The obtained results provided significant data about diverse factors, like; the manner in which a residual stress field could modify the crack initiation conditions, the convenient set up for induction of a beneficial residual stresses field, as well as useful information that can be applied for the experimental implementation of this research.

Influence of Material Model on Tensile Loaded Joint

2010 ◽  
Vol 165 ◽  
pp. 394-399 ◽  
Author(s):  
E. Szymczyk ◽  
Grzegorz Slawinski
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Numerical Analysis ◽  
Stress Field ◽  
Material Model ◽  
Finite Element Simulations ◽  
Residual Stress Field ◽  
Material Models ◽  
Riveted Joint ◽  
Load Conditions

The paper deals with the numerical analysis of a tensile loaded riveted joint. Finite element simulations of the upsetting process were carried out with the use of Marc code to determine the residual stress field. The contact with friction is defined between the mating parts of the joint. The computations were performed for four cases of material and load conditions and a comparison was performed on the basis of results obtained for standard elasto plastic and Gurson material models. Moreover, the influence of material model and residual stress on the tensile loaded joint was analyzed.

Simple Model of Lu¨ders Behaviour in a Novel Compact Tension Specimen for Investigation of Residual Stress Effects

2006 ◽  
Author(s):  
Mark R. Wenman ◽  
Robert D. Plant
Keyword(s):  
Residual Stress ◽  
Stress Field ◽  
Tensile Test ◽  
Crack Growth ◽  
Yield Point ◽  
Compact Tension ◽  
Uniaxial Tensile ◽  
Tensile Behaviour ◽  
Fe Model ◽  
Stress Effects

Residual stress effects on defects have been investigated by the use of a novel compact tension (CT) specimen. Mild steel CT specimens have been preloaded in compression to generate a plastic zone around the notch prior to precracking. Upon unloading, the specimen contains a residual tensile stress, around the notch tip, into which a defect such as a prefatigue crack can be introduced. The effect of the residual stress on fatigue crack growth and final fracture is then investigated. Here, the uniaxial tensile behaviour of the steel used shows Piobert-Lu¨ders behaviour typical of certain ferritic pressure vessel steels. The mechanical preloading process has been modelled via a finite element (FE) analysis. The plastic deformation behaviour, taken from tensile test data, has been incorporated into the CT specimen model, first ignoring the Lu¨ders behaviour and then including it via a simple plastic model of the phenomenon. The model of Lu¨ders behaviour was tested on a FE model, of an uniaxial tensile test, before it was applied to the CT specimen. The result of this test was the generation of a realistic propagating band of plastic instability along the gauge length of the tensile specimen. Results for FE models of CT specimens, with and without the Lu¨ders behaviour, were then compared to real preloaded CT specimens. The models using only a lower yield point and ignoring Lu¨ders behaviour under predict the deformation of real specimens. The incorporation of plastic data containing an upper yield point predicts with reasonable accuracy the preloading cycle and as a result the shape of the residual stress field generated. Hardness maps have been made, by the use of scanning indentation mechanical microprobe (SIMM), of the free surface, of preloaded specimens. These maps reveal the strain profile of the surface and Lu¨ders bands emanating from the notch region are clearly visible. The FE model of the CT specimen, including Lu¨ders behaviour, shows Von Mises stress contours in a similar pattern to the Lu¨ders bands in the real specimen. Finally, some specimens were precracked, using cyclic compression, and then fractured at lower shelf temperatures (-140°C) to reveal the precrack shape; this matched the predicted shape of the maximum principal stress field responsible for driving crack growth. The lower shelf fracture toughness of preloaded specimens was found to be considerably reduced from reference toughness specimens with no preload. This suggests that the tensile residual stress was dominant over any benefit gained from warm pre-stressing the material.

On the Methodology of Numerical Etching

1999 ◽  
Vol 563 ◽  
Author(s):  
X. H. Wang ◽  
K. Shyu ◽  
C.-T. Chang ◽  
D. W. Zheng ◽  
Weijia Wen
Keyword(s):  
Thin Film ◽  
Residual Stress ◽  
Stress State ◽  
Numerical Analysis ◽  
Stress Distribution ◽  
Stress Field ◽  
Initial Stress ◽  
Silicon Wafer ◽  
Initial Stress Field ◽  
Actual Stress

AbstractA methodology to study the stress distribution of a patterned thin film residing on a silicon wafer was developed. Si underlying the pattern was thinned down through etching so that the deformation caused by residual stress in the microstructure could be detected by a Twyman- Green interferometer. A procedure called "numerical etching" was implemented to simulate the etching process, which linked the stress state of the microstructure on a regular wafer to that on a Si diaphragm. An initial stress field on the pattern was assumed, and its effect on the deformation of the Si diaphragm beneath was calculated and compared with experimental results. The discrepancy between them was used to modify the initially assumed stress field and repeated until a satisfactory match was achieved. The stress field from numerical analysis accurately predicts the actual stress distribution in and around the patterned structure under investigation. The stress distribution in a Ti pad on a Si3N4/ SiO2/Si composite diaphragm is used as an example.

scholarly journals Numerical Analysis of Longitudinal Residual Stresses and Deflections in a T-joint Welded Structure Using a Local Preheating Technique

Energies ◽  
2018 ◽  
Vol 11 (12) ◽  
pp. 3487 ◽  
Author(s):  
Mato Perić ◽  
Ivica Garašić ◽  
Sandro Nižetić ◽  
Hrvoje Dedić-Jandrek
Keyword(s):  
Residual Stress ◽  
Numerical Analysis ◽  
Stress Field ◽  
Numerical Models ◽  
Preheat Temperature ◽  
Residual Stress Field ◽  
Residual Stress State ◽  
Welded Structure ◽  
Longitudinal Residual Stress ◽  
Interpass Time

In this paper a numerical analysis of a T-joint fillet weld is performed to investigate the influences of different preheat temperatures and the interpass time on the longitudinal residual stress fields and structure deflections. In the frame of the numerical investigations, two thermo-mechanical finite element models, denoted M2 and M3, were analyzed and the results obtained were then compared with the model M1, where the preheating technique was not applied. It is concluded that by applying the preheat temperature prior to the start of welding the post-welding deformations of welded structures can be significantly reduced. The increase of the preheat temperature increased the longitudinal residual stress field at the ends of the plates. The influence of the interpass time between two weld passes on the longitudinal residual stress state and plate deflection was investigated on two preheated numerical models, M4 and M5, with an interpass time of 60 s and 120 s, respectively. The results obtained were then compared with the preheated model M3, where there was no time gap between the two weld passes. It can be concluded that with the increase of interpass time, the plate deflections significantly increase, while the influence of the interpass time on the longitudinal residual stress field can be neglected.

Prediction of cerebral blood flow in fetal lambs by carotid artery ultrasonic flow transducer

1996 ◽  
Vol 8 (1) ◽  
pp. 157 ◽  
Author(s):  
RF Covert ◽  
MD Schreiber ◽  
LJ Torgerson ◽  
RW Torgerson ◽  
DJ Miletich
Keyword(s):  
Blood Flow ◽  
Carotid Artery ◽  
Common Carotid Artery ◽  
Fetal Sheep ◽  
Flow Transducer ◽  
Blood Flows ◽  
Total Brain ◽  
Wide Range ◽  
Highly Correlated ◽  
Artery Flow

To determine whether common carotid artery blood flow measured with an ultrasonic flow transducer would predict brain blood flow in fetal sheep, we measured unilateral common carotid artery blood flow and compared this to simultaneous measurements of total brain blood flows made by radioisotope-labelled microsphere techniques. We studied anaesthetized, exteriorized fetal sheep with intact umbilical circulation after ligation of extracranial, extracerebral arteries and placement of a common carotid artery flow transducer; five fetuses at 120 d gestation had 19 total comparison measurements. As measured by microsphere technique, mean basal blood flow during undisturbed conditions to regional brain areas were similar to normal values reported for the exteriorized ovine fetus; these flows were highly correlated to fetal PaCO2 and successfully varied over a wide range (total brain 9.1-200.4 ml/min/100g and total cortex 6.1-153.1 ml/min/100g) in subsequent experimental conditions of hypercapnia or occluded blood flow. Blood flow as measured by flow transducer significantly correlated (P < or = 0.01) with microsphere measurements of blood flow to total brain (r = 0.56) and total cortex (r = 0.62); regional flow to cerebellum (r = 0.70) and thalamus (r = 0.60) also correlated to transducer measurements. Stronger correlations were observed at low-flow conditions to total brain (r = 0.83) and to total cortex (r = 0.90). As measured by microsphere technique, right and left cortical blood flows were highly correlated (P = 0.0001, r = 0.97), indicating that the flow transducer or surgical manipulation did not disturb the distribution of cerebral blood flow. The mean values for zero flow reference of the transducer were < 1.5% of mean basal flow values. It is concluded that the common carotid artery flow transducer technique developed in this study provides an accurate prediction of blood flow to total brain and total cortex over a wide range of values in fetal sheep. This technique provides a methodologic advantage to sequential experimental interventions and may prove advantageous to studies of fetal sheep cerebral circulation.

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