Regional and Layer Distribution of Residual Stresses in an Unloaded Aortic Medial Wall

2020 ◽  
Author(s):  
Atsutaka Tamura ◽  
Koki Matsumoto
Keyword(s):  
Residual Stresses ◽  
Structural Characteristics ◽  
Muscle Layer ◽  
Medial Wall ◽  
Wall Structure ◽  
Aortic Tissue ◽  
Fe Model ◽  
Ring Model ◽  
Unloaded State ◽  
Aortic Media

Abstract The mechanical and structural characteristics of aortic media have profound effects on the physiology and pathophysiology of an aorta. However, many aspects of the aortic tissue remain poorly understood, partly due to the intrinsic layered wall structure and regionally varying residual stresses. Our recent works have demonstrated that a mechanical interaction between the elastic lamina (EL) and smooth muscle layer in the aortic media can be computationally reproduced using a simplified finite element (FE) model. However, it is questionable whether the simplified FE model we created was representative of the structure of a real medial wall and its modeling technique would be applicable to develop a more sophisticated and structure-based aortic FE model. This study aimed to computationally represent EL buckling in the aortic medial ring at an unloaded state and successfully reproduced transmural variation in EL waviness across the aortic wall. We also aimed at confirming the inner and outer layers of the medial wall are subjected to compressive and tensile residual stresses, respectively, at the unloaded state, implying that the ring model will open spontaneously when it is radially cut. Moreover, the computed residual stresses were found to be within the reasonable range of the predicted values, 1–10 kPa, supporting the validity of our modeling approach. Although further study is required, the information obtained here will greatly help improve the understanding of basic aortic physiology and pathophysiology, while simultaneously providing a basis for more sophisticated computational modeling of the aorta.

scholarly journals Residual stresses in thermite welded rails: significance of additional forging

2020 ◽  
Vol 64 (7) ◽  
pp. 1195-1212
Author(s):  
B. Lennart Josefson ◽  
R. Bisschop ◽  
M. Messaadi ◽  
J. Hantusch
Keyword(s):  
Residual Stress ◽  
Stress Field ◽  
Residual Stresses ◽  
Weld Metal ◽  
Welding Process ◽  
Surface Zone ◽  
Fe Model ◽  
Uneven Surface ◽  
Residual Stress Field ◽  
High Dynamic

Abstract The aluminothermic welding (ATW) process is the most commonly used welding process for welding rails (track) in the field. The large amount of weld metal added in the ATW process may result in a wide uneven surface zone on the rail head, which may, in rare cases, lead to irregularities in wear and plastic deformation due to high dynamic wheel-rail forces as wheels pass. The present paper studies the introduction of additional forging to the ATW process, intended to reduce the width of the zone affected by the heat input, while not creating a more detrimental residual stress field. Simulations using a novel thermo-mechanical FE model of the ATW process show that addition of a forging pressure leads to a somewhat smaller width of the zone affected by heat. This is also found in a metallurgical examination, showing that this zone (weld metal and heat-affected zone) is fully pearlitic. Only marginal differences are found in the residual stress field when additional forging is applied. In both cases, large tensile residual stresses are found in the rail web at the weld. Additional forging may increase the risk of hot cracking due to an increase in plastic strains within the welded area.

Evaluation of Residual Stresses in Butt Welded Joint of Dissimilar Material by FEM

2017 ◽  
Vol 754 ◽  
pp. 268-271 ◽  
Author(s):  
Raffaele Sepe ◽  
M. Laiso ◽  
A. de Luca ◽  
Francesco Caputo
Keyword(s):  
Finite Element ◽  
Residual Stresses ◽  
Arc Welding ◽  
Structural Integrity ◽  
Welded Joint ◽  
Dissimilar Material ◽  
Fe Model ◽  
Butt Joints ◽  
Integrity Assessment ◽  
Steel Joints

The study proposed within this paper deals with an application of finite element techniques to the thermo-structural analysis of a dissimilar butt-welded joint. Residual stresses induced by the fusion arc-welding of steel joints in power generation plants are a concern to the industry. Nowadays, the application of finite element method appears to be a very efficient method for the prediction and the investigation of the weld-induced residual stresses, nevertheless the detailed modelling of all phenomena involved in such process is still challenging. The structural integrity assessment of welded structures strongly requires a deep investigation of weld-induced residual stresses in order to be compliant with safety requirement of power plant. The longitudinal and transversal residual stresses in dissimilar material butt joints of 8 mm thick for V-groove shape were studied. The developed thermo-mechanical FE model as well as the simulation procedures are detailed and results are discussed. As a result of such work, it has been found out that residual stresses in the two dissimilar plates are characterized by very different magnitudes and distribution.

scholarly journals Improving the Inner Surface State of Thick-Walled Tubes by Heat Treatments with Internal Quenching Considering a Simulation Based Optimization

Processes ◽  
2020 ◽  
Vol 8 (10) ◽  
pp. 1303
Author(s):  
Fabian Mühl ◽  
Moritz Klug ◽  
Stefan Dietrich ◽  
Volker Schulze
Keyword(s):  
Heat Treatment ◽  
Residual Stresses ◽  
Surface State ◽  
Treatment Process ◽  
Treatment Method ◽  
Fe Model ◽  
Heat Treatment Process ◽  
Residual Stress State ◽  
Optimization Study ◽  
Inner Surface

Internal Quenching is an innovative heat treatment method for difficult to access component sections. Especially, the microstructure, as well as the residual stress state at inner surfaces, of thick-walled tubes can be adjusted with the presented flexible heat treatment process. Based on multiphysical FE-models of two different steels, a simulative optimization study, considering different internal quenching strategies, was performed in order to find the optimal cooling conditions. The focus hereby was on the adjustment of a martensitic inner surface with high compressive residual stresses. The simulatively determined optimal cooling strategies were carried out experimentally and analyzed. A good agreement of the resulting hardness and residual stresses was achieved, validating the presented Fe-model of the Internal Quenching process. The shown results also indicate that the arising inner surface state is very sensitive to the transformation behavior of the used steel. Furthermore, the presented study shows that a preliminary simulative consideration of the heat treatment process helps to evaluate significant effects, reducing the experimental effort and time.

The Effects of Loadings on Welding Residual Stresses and Assessment of Fracture Parameters in a Welding Residual Stress Field

2011 ◽  
Author(s):  
Liwu Wei ◽  
Weijing He ◽  
Simon Smith
Keyword(s):  
Residual Stress ◽  
Stress Field ◽  
Residual Stresses ◽  
Path Dependence ◽  
Welding Residual Stress ◽  
Assessment Procedure ◽  
Fe Model ◽  
J Integral ◽  
Residual Stress Field ◽  
Growing Crack

The level of welding residual stress is an important consideration in the ECA of a structure or component such as a pipeline girth weld. Such a consideration is further complicated by their variation under load and the complexity involved in the proper assessment of fracture mechanics parameters in a welding residual stress field. In this work, 2D axi-symmetric FEA models for simulation of welding residual stresses in pipe girth welds were first developed. The modelling method was validated using experimental measurements from a 19-pass girth weld. The modeling method was used on a 3-pass pipe girth weld to predict the residual stresses and variation under various static and fatigue loadings. The predicted relaxation in welding residual stress is compared to the solutions recommended in the defect assessment procedure BS 7910. Fully circumferential internal cracks of different sizes were introduced into the FE model of the three-pass girth weld. Two methods were used to introduce a crack. In one method the crack was introduced instantaneously and the other method introduced the crack progressively. Physically, the instantaneously introduced crack represents a crack originated from manufacturing or fabrication processes, while the progressively growing crack simulates a fatigue crack induced during service. The J-integral values for the various cracks in the welding residual stress field were assessed and compared. This analysis was conducted for a welding residual stress field as a result of a welding simulation rather than for a residual stress field due to a prescribed temperature distribution as considered by the majority of previous investigations. The validation with the 19-pass welded pipe demonstrated that the welding residual stress in a pipe girth weld can be predicted reasonably well. The relaxation and redistribution of welding residual stresses in the three-pass weld were found to be significantly affected by the magnitude of applied loads and the strain hardening models. The number of cycles in fatigue loading was shown to have little effect on relaxation of residual stresses, but the range and maximum load together governed the relaxation effect. A significant reduction in residual stresses was induced after first cycle but subsequent cycles had no marked effect. The method of introducing a crack in a FE model, progressively or instantaneously, has a significant effect on J-integral, with a lower value of J obtained for a progressively growing crack. The path-dependence of the J-integral in a welding residual stress field is discussed.

An Analysis of Residual Stress Improvement for a Dissimilar Metal Nozzle-to-Pipe Weld by Using the Heat Sink Method

2008 ◽  
Author(s):  
J.-S. Park ◽  
J.-M. Kim ◽  
G.-H. Sohn ◽  
Y.-H. Kim
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Heat Sink ◽  
Nuclear Power ◽  
Power Plants ◽  
Base Alloy ◽  
Fatigue Cracking ◽  
Hole Drilling ◽  
Fe Model ◽  
Dissimilar Metal

This study is concerned with the mechanics analysis of residual stress improvement by the heat sink method applied to a dissimilar metal weld (DMW) for the use in nuclear power plants. The DMW joint considered here is composed of ferritic low-alloy steel nozzle, austenitic stainless steel safe-end, and nickel-base alloy A52 weld metal. To prepare the DMW joint with a narrow-gap, the gas tungsten arc welding (GTAW) process is utilized, and the heat sink method is employed to control thermal gradients developed in the critical region of work pieces during welding. Weld residual stresses are computed by the non-linear thermal elasto-plastic analysis using the axisymmetric finite element (FE) model, for which temperature-dependent thermal and mechanical properties of the materials are considered. A full-scale mock-up test is conducted to validate analytical solution for the DMW joint, and residual stresses are measured by using the hole-drilling method. Results of the FE modeling and mock-up test for the DMW joint are compared and effects of the heat sink method are discussed. It is found that a significant amount of residual compressive stresses can be developed on the inner surface of the DMW joint by using the heat sink method, which can effectively reduce the susceptibility of the welded materials to stress corrosion or fatigue cracking.

FE Modeling of the Three-Layer Human Carotid Artery Under Impact Loadings

2007 ◽  
Author(s):  
Aihong Zhao ◽  
Ken Digges ◽  
Mark Field ◽  
David Richens
Keyword(s):  
Finite Element ◽  
Carotid Artery ◽  
Model Simulation ◽  
Material Model ◽  
Element Model ◽  
Traumatic Rupture ◽  
Aortic Tissue ◽  
Fe Model ◽  
Arbitrary Lagrangian Eulerian ◽  
The Impact

Blunt traumatic rupture of the carotid artery is a rare but life threatening injury. The histology of the artery is key to understanding the aetiology of this injury. The carotid artery is composed of three layers known as the tunica intima, media, and adventitia, with distinct biomechanical properties. In order to examine the behaviour of the carotid artery under external load we have developed a three layer finite element model of this vessel. A rubber-like material model from LS-DYNA was selected for the FE model. The Arbitrary-Lagrangian Eulerian (ALE) approach was adopted to simulate the interaction between the fluid (blood) and the structure (carotid). To verify the FE model, the impact bending tests are simulated using this FE model. Simulation results agree with tests results well. Furthermore, the mechanical behaviour of carotid artery tissues under impact loading were revealed by the simulations. The results provide a basis for a more in-depth investigation of the carotid artery in vehicle crashes. In addition, it provides a basis for further work on aortic tissue finite element modeling.

Effect of Coating Process Parameters on the Development of Residual Stresses in Ceramic Coatings

2019 ◽  
Author(s):  
Ali Gadelmoula ◽  
Khaled Al-Athel
Keyword(s):  
Residual Stresses ◽  
Process Parameters ◽  
Elevated Temperatures ◽  
Ceramic Coatings ◽  
Interface Roughness ◽  
Fe Model ◽  
Computational Framework ◽  
Scientists And Engineers ◽  
Coating Layers

Abstract Ceramic coatings are widely used in many engineering applications, especially applications related to components operating at elevated temperatures. One of the main issues relates to ceramic coatings is the development of residual stresses due to quenching and the thermal mismatch between the deposited coating layers and the substrate. In this work, a computational framework is developed to investigate the effect of various process parameters on the development of the residual stresses. The geometry of the coating layers and the interface roughness between the layers is first generated using SimCoat, a Monte Carlo based statistical algorithm that determines the effect of process parameters (droplet size, spraying speed, etc.) on the characteristics of the developed coating (coating thickness, porosity, etc.). An in-house code is used to convert the statistical data into a finite element (FE) model. Various FE models are generated with different process parameters, and the development of residual stresses is compared between them. The developed framework can be used by material scientists and engineers to predict the quality of the coating and optimize the process parameters to any specific application.

scholarly journals Epicardial prestrained confinement and residual stresses: a newly observed heart ventricle confinement interface

2019 ◽  
Vol 16 (152) ◽  
pp. 20190028 ◽  
Author(s):  
Xiaodan Shi ◽  
Yue Liu ◽  
Katherine M. Copeland ◽  
Sara R. McMahan ◽  
Song Zhang ◽  
...  
Keyword(s):  
Residual Stresses ◽  
Resistance Mechanism ◽  
Mechanical Effect ◽  
Fe Model ◽  
Prosthetic Devices ◽  
Dominant Component ◽  
Myocardial Stress ◽  
Epicardial Layer ◽  
Additional Resistance ◽  
Biaxial Mechanical Testing

The heart epicardial layer, with elastin as the dominant component, has not been well investigated, specifically on how it contributes to ventricular biomechanics. In this study, we revealed and quantitatively assessed the overall status of prestraining and residual stresses exerted by the epicardial layer on the heart left ventricle (LV). During porcine heart wall dissection, we discovered that bi-layered LV surface strips, consisting of an epicardial layer and cardiac muscle, always curled towards the epicardial side due to epicardial residual stresses. We hence developed a curling angle characterization technique to intuitively and qualitatively reveal the location-dependency and direction-dependency of epicardial residual stresses. Moreover, by combining prestrain measurement and biaxial mechanical testing, we were able to quantify the epicardial prestrains and residual stresses on the unpressurized intact LV. To investigate the potential mechanical effect of epicardial prestraining, a finite-element (FE) model has been constructed, and we demonstrate that it is the prestraining of the epicardial layer, not the epicardial layer alone, providing an additional resistance mechanism during LV diastolic expansion and ventricular wall protection by reducing myocardial stress. In short, our study on healthy, native porcine hearts has revealed an important phenomenon—the epicardial layer, rich in elastin, acts like a prestrained ‘balloon’ that wraps around the heart and functions as an extra confinement and protection interface. The obtained knowledge fills a gap in ventricular biomechanics and will help design novel biomimicking materials or prosthetic devices to target the maintenance/recreation of this ventricle confinement interface.

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