Numerical Simulation of CFRP Reinforced Steel Pipe Elbows Subjected to Cyclic Loading

2016 ◽  
Author(s):  
Giannoula Chatzopoulou ◽  
Ioannis Skarakis ◽  
Spyros A. Karamanos ◽  
Nicholas G. Tsouvalis ◽  
Aglaia E. Pournara
Keyword(s):  
Cyclic Loading ◽  
Structural Integrity ◽  
Mechanical Response ◽  
Numerical Models ◽  
Experimental Testing ◽  
Strain Curve ◽  
Steel Pipe ◽  
Cyclic Plasticity ◽  
Loading Conditions ◽  
Piping Systems

Strengthening of pipelines and piping systems under extreme loading conditions increases their operation safety level towards safeguarding their structural integrity. Motivated by the structural integrity of pipelines and piping systems, the present study aims at investigating the effect of Carbon Fiber Reinforced Plastic (CFRP) wrapping on the mechanical response of cyclically-loaded steel pipe elbows. Based on experimental testing results, a finite element model is developed, which simulates reinforced and non-reinforced pipe elbows specimens subjected to low-cyclic fatigue. For the description of the material nonlinearities, an efficient cyclic-plasticity material model is also employed, capable of describing both the yield plateau region of the steel stress-strain curve and the Bauschinger effect that appears under reverse plastic loading conditions. The results from the numerical models are compared successfully with the experimental data. Furthermore, a parametric analysis is conducted in order to examine the effect of internal pressure on the structural behavior of unreinforced and reinforced elbows, subjected to cyclic loading.

scholarly journals CFRP Reinforcement and Repair of Steel Pipe Elbows Subjected to Severe Cyclic Loading

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Ioannis Skarakis ◽  
Giannoula Chatzopoulou ◽  
Spyros A. Karamanos ◽  
Nicholas G. Tsouvalis ◽  
Aglaia E. Pournara
Keyword(s):  
Cyclic Loading ◽  
Structural Integrity ◽  
Mechanical Response ◽  
Low Cycle Fatigue ◽  
Numerical Models ◽  
Strain Curve ◽  
Steel Pipe ◽  
Cyclic Plasticity ◽  
Loading Conditions ◽  
Element Analysis

In order to ensure safe operation and structural integrity of pipelines and piping systems subjected to extreme loading conditions, it is often necessary to strengthen critical pipe components. One method to strengthen pipe components is the use of composite materials. The present study is aimed at investigating the mechanical response of pipe elbows, wrapped with carbon fiber-reinforced plastic (CFRP) material, and subjected to severe cyclic loading that leads to low-cycle fatigue (LCF). In the first part of the paper, a set of LCF experiments on reinforced and nonreinforced pipe bend specimens are described focusing on the effects of CFRP reinforcement on the number of cycles to failure. The experimental work is supported by finite element analysis presented in the second part of the paper, in an attempt to elucidate the failure mechanism. For describing the material nonlinearities of the steel pipe, an efficient cyclic-plasticity material model is employed, capable of describing both the initial yield plateau of the stress–strain curve and the Bauschinger effect characterizing reverse plastic loading conditions. The results from the numerical models are compared with the experimental data, showing an overall good comparison. Furthermore, a parametric numerical analysis is conducted to examine the effect of internal pressure on the structural behavior of nonreinforced and reinforced elbows, subjected to severe cyclic loading.

scholarly journals Simulation of Cyclic Loading on Pipe Elbows Using Advanced Plane-Stress Elastoplasticity Models1

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Konstantinos Chatziioannou ◽  
Yuner Huang ◽  
Spyros A. Karamanos
Keyword(s):  
Cyclic Loading ◽  
Large Scale ◽  
Mechanical Response ◽  
Low Cycle Fatigue ◽  
Constitutive Relations ◽  
Cyclic Plasticity ◽  
Integration Scheme ◽  
Repeated Loading ◽  
Finite Element Software ◽  
Hardening Models

Abstract This work investigates the response of industrial steel pipe elbows subjected to severe cyclic loading (e.g., seismic or shutdown/startup conditions), associated with the development of significant inelastic strain amplitudes of alternate sign, which may lead to low-cycle fatigue. To model this response, three cyclic-plasticity hardening models are employed for the numerical analysis of large-scale experiments on elbows reported elsewhere. The constitutive relations of the material model follow the context of von Mises cyclic elasto-plasticity, and the hardening models are implemented in a user subroutine, developed by the authors, which employs a robust numerical integration scheme, and is inserted in a general-purpose finite element software. The three hardening models are evaluated in terms of their ability to predict the strain range at critical locations, and in particular, strain accumulation over the load cycles, a phenomenon called “ratcheting.” The overall good comparison between numerical and experimental results demonstrates that the proposed numerical methodology can be used for simulating accurately the mechanical response of pipe elbows under severe inelastic repeated loading. Finally, this paper highlights some limitations of conventional hardening rules in simulating multi-axial material ratcheting.

Finite Element Investigation on the Tensile Armor Wire Response of Flexible Pipe for Axisymmetric Loading Conditions Using an Implicit Solver

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Alireza Ebrahimi ◽  
Shawn Kenny ◽  
Amgad Hussein
Keyword(s):  
Finite Element ◽  
Oil And Gas ◽  
Mechanical Response ◽  
Numerical Models ◽  
Oil And Gas Industry ◽  
Parameter Study ◽  
Loading Conditions ◽  
Flexible Pipe ◽  
Axisymmetric Loading ◽  
Implicit Solver

Composite flexible pipe is used in the offshore oil and gas industry for the transport of hydrocarbons, jumpers connecting subsea infrastructure, and risers with surface platforms and facilities. Although the material fabrication costs are high, there are technical advantages with respect to installation and performance envelope (e.g., fatigue). Flexible pipe has a complex, composite section with each layer addressing a specific function (e.g., pressure containment, and axial load). Continuum finite element modeling (FEM) procedures are developed to examine the mechanical response of an unbonded flexible pipe subject to axisymmetric loading conditions. A parameter study examined the effects of: (1) pure torsion, (2) interlayer friction factor, (3) axial tension, and (4) external and internal pressure on the pipe mechanical response. The results demonstrated a coupled global-local mechanism with a bifurcation path for positive angles of twist relative to the tensile armor wire pitch angle. These results indicated that idealized analytical- and structural-based numerical models may be incomplete or may provide an accurate prediction of the pipe mechanical response. The importance of using an implicit solver to predict the bifurcation response and simulate contact mechanics between layers was highlighted.

A Phenomenological Model for Cyclic Plasticity

1997 ◽  
Vol 119 (1) ◽  
pp. 7-11 ◽  
Author(s):  
Dar-Yun Chiang
Keyword(s):  
Cyclic Loading ◽  
Phenomenological Model ◽  
Material Properties ◽  
Experimental Studies ◽  
Cyclic Hardening ◽  
Analytical Models ◽  
Cyclic Plasticity ◽  
Loading Conditions ◽  
Microstructural Behavior ◽  
Distributed Elements

A phenomenological model is proposed for cyclic plasticity based on the concept of distributed elements, which is capable of reflecting microstructural behavior of real materials under multiaxial cyclic loading conditions. By investigating the detailed behavior of the model, various important phenomena and effects of materials in cyclic plasticity can be elucidated. Generalization of the model is also done to include cyclic hardening effects. A thorough understanding of these complicated response mechanisms and material properties provides useful insight and guidelines for validating analytical models and for performing experimental studies in the related areas of cyclic plasticity.

scholarly journals Dynamic Behavior and Fatigue Damage Evolution of Sandstone under Uniaxial Cyclic Loading

2020 ◽  
Vol 2020 ◽  
pp. 1-9 ◽  
Author(s):  
Yidan Sun ◽  
Yu Yang ◽  
Min Li
Keyword(s):  
Cyclic Loading ◽  
Fatigue Damage ◽  
Mechanical Response ◽  
Compressive Strain ◽  
Damage Model ◽  
Testing Machine ◽  
Strain Curve ◽  
Peak Stress ◽  
Creep Theory ◽  
Cycle Number

The mechanical response characteristics of sandstone specimens under different stress amplitudes and loading frequencies were tested by a TAW-2000 rock triaxial testing machine. The characteristics of the stress-strain curve and the evolution process of strain damage under cyclic loading are analyzed. Based on creep theory and the disturbance state concept, a theoretical model between the axial compressive strain, axial compressive stress, and cycle number is established. The results show that there exists an upper threshold value of stress in cyclic loading above which the specimen will be damaged. As peak stress increases, the energy loss and irreversible deformation caused by damage gradually increase. When loading to an unstable peak stress under cyclic loading, the fatigue damage of sandstone under cyclic loading undergoes three characteristic stages: the initial stage; the stable stage; and the accelerated failure stage. The parameters of the strain damage model based on the disturbance state concept of sandstone are identified by test data, and the rationality of the model is validated by comparing theoretical values with experimental measurements.

Status of Research on Environmentally Assisted Cracking in LWR Pressure Vessel Steels

1988 ◽  
Vol 110 (2) ◽  
pp. 113-128 ◽  
Author(s):  
F. P. Ford
Keyword(s):  
Cyclic Loading ◽  
Crack Growth ◽  
Structural Integrity ◽  
Reaction Rates ◽  
Pressure Vessels ◽  
Crack Advance ◽  
Loading Conditions ◽  
Film Rupture ◽  
Life Evaluation ◽  
Environmentally Assisted Cracking

This paper reviews collaborative work that has the objective of defining, from first principles, the environmentally assisted crack growth rates in the Type A533B or A508 low-alloy steel/water system at 288°C under static and cyclic loading conditions. These theoretical rates are then used to assess the validity of the current ASME XI life evaluation code. The investigations, which were conducted by members of the International Cyclic Crack Growth Rate Group, have centered around (a) defining a working hypothesis for environmentally assisted cracking, (b) determining the nature and magnitude of crack tip environments and reaction rates that are pertinent to the crack advance hypotheses, (c) quantitatively validating a hypothesis by comparing observed and theoretical values, and (d) using the qualified mechanism to evalute the validity of current life-evaluation codes for environmentally assisted crack propagation. It is concluded that, on the basis of the bulk of present data, the slip dissolution (film rupture) model seems to be quantitatively the most valid crack advance mechanism for this system at 288°C. However, under certain system conditions, it is possible that an additional advance component due to environmentally assisted cleavage may become significant. Regardless of these nuances, however, it is apparent that the current ASME XI code is probably conservative for extended cyclic loading conditions, and that a time-based (rather than a cyclic-base) code would give a more realistic assessment of the structural integrity for the expected range of load/time histories in pressure vessels.

On the Modeling of Nonproportional Cyclic Plasticity of Waspaloy

1994 ◽  
Vol 116 (1) ◽  
pp. 35-44 ◽  
Author(s):  
A. Abdul-Latif ◽  
M. Clavel ◽  
V. Ferney ◽  
K. Saanouni
Keyword(s):  
Cyclic Loading ◽  
Kinematic Hardening ◽  
Experimental Tests ◽  
Point Of View ◽  
Cyclic Plasticity ◽  
Loading Path ◽  
Isotropic Hardening ◽  
Loading Conditions ◽  
Effective Role ◽  
Deformation Modes

The isotropic hardening is known to play an effective role in the overhardening of materials under nonproportional cyclic loading. However, the behavior of the two states of Waspaloy (namely overaged and underaged states) under these loading conditions, shows that the kinematic hardening has also a considerable role in the overhardening. Experimental tests were carried out on these two states under various proportional and nonproportional cyclic loading conditions at room temperature. The effect of loading paths on micro-mechanisms of deformation was studied. From a microstructural point of view, it was shown that the deformation modes (quantitatively and qualitatively) depend on the loading path and the heat treatment. A constitutive model is proposed to describe the effect of overhardening, under the nonproportional loading conditions, on the kinematic hardening. The predicted responses are in good agreement with experimental results.

scholarly journals Factors affecting the response of steel columns to close-in detonations

2018 ◽  
Author(s):  
Ioan Marginean ◽  
Florea Dinu ◽  
Dan Dubina ◽  
Ahmed Amir Khalil ◽  
Emiliano De Iuliis
Keyword(s):  
Urban Areas ◽  
Structural Integrity ◽  
Numerical Models ◽  
Experimental Testing ◽  
Frame Structure ◽  
Building Structures ◽  
Injury Death ◽  
Factors Affecting ◽  
Steel Columns ◽  
Residual Capacity

Explosions produced in urban areas by the detonation of explosives are low-probability but high-impact events. When they occur in the immediate vicinity of buildings, the explosions can pose a high risk to the structural integrity (local/global failures) and to the occupants (risk of injury, death). Therefore, the design and the construction of the buildings should contain preventive measures to increase the robustness of the structures. The paper presents the results of recent research carried out on the safety of building structures under extreme actions. Blast tests performed on two identical 3D specimen extracted from a typical moment resisting steel frame structure, allow to calibrate the numerical models of a full scale building structural frame system and evaluate the consequences of close-in detonations on the structural elements. The data of the experimental testing, combined with the numerical modelling, allow to investigate different factors, such as dynamic factors that affect the local failure mechanism and the residual capacity of steel columns under different blast scenarios. 

MECHANICAL CHARACTERIZATION OF ANIMAL DERIVED GRAFTS FOR SURGICAL IMPLANTATION

2016 ◽  
Vol 16 (03) ◽  
pp. 1650023 ◽  
Author(s):  
PIERO GIOVANNI PAVAN ◽  
PAOLA PACHERA ◽  
SILVIA TODROS ◽  
CESARE TIENGO ◽  
ARTURO NICOLA NATALI
Keyword(s):  
Stress Relaxation ◽  
Constitutive Model ◽  
Relaxation Process ◽  
Mechanical Response ◽  
Numerical Models ◽  
Experimental Testing ◽  
Axial Stress ◽  
Experimental Tests ◽  
Tissue Samples

Bioprostheses obtained from animal models are often adopted in abdominal surgery for repair and reconstruction. The functionality of these prosthetic implants is related also to their mechanical characteristics that are analyzed here. This work illustrates a constitutive model to describe the short-term mechanical response of Permacol[Formula: see text] bioprostheses. Experimental tests were developed on tissue samples to highlight mechanical non-linear characteristics and viscoelastic phenomena. Uni-axial tensile tests were developed to evaluate the strength and strain stiffening. Incremental uni-axial stress relaxation tests were carried out at nominal strain ranging from 10% to 20% and to monitor the stress relaxation process up to 400[Formula: see text]s. The constitutive model effectively describes the mechanical behavior found in experimental testing. The mechanical response appears to be independent on the loading direction, showing that the tissue can be considered as isotropic. The viscoelastic response of the tissue shows a strong decay of the stress in the first seconds of the relaxation process. The investigation performed is aimed at a general characterization of the biomechanical response and addresses the development of numerical models to evaluate the biomechanical performance of the graft with surrounding host tissues.

scholarly journals The Distinct Elemental Analysis of the Microstructural Evolution of a Methane Hydrate Specimen under Cyclic Loading Conditions

Energies ◽  
2019 ◽  
Vol 12 (19) ◽  
pp. 3694 ◽  
Author(s):  
Dong Wang ◽  
Bin Gong ◽  
Yujing Jiang
Keyword(s):  
Cyclic Loading ◽  
Methane Hydrate ◽  
Mechanical Response ◽  
Distinct Element ◽  
Constitutive Models ◽  
Slope Instability ◽  
Loading Conditions ◽  
Shear Process ◽  
Hydrate Saturation ◽  
Dynamic Loading Conditions

Submarine slope instability may be triggered by earthquakes and tsunamis. Methane hydrate sediments (MHS) are commonly buried under submarine slopes. Submarine slides would probably be triggered once the MHS are damaged under cyclic loading conditions. For this reason, it is essential to research the mechanical response of MHSs under dynamic loading conditions. In this study, a series of drained cyclic biaxial compressive tests with constant stress amplitudes were numerically carried out with the distinct element method (DEM). The cyclic loading number decreased as the hydrate saturation (Sh) increased when the MHS were damaged. The failure mode of the MHS was shown to be dependent on the dynamic stress amplitude and hydrate saturation. The microstructure of MHS during the cyclic loading shear process was also analyzed. The results can help us to understand the mechanical behavior of MHS during the cyclic loading process and develop micromechanical-based constitutive models.

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