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.

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.

Cyclic Plasticity for Nonproportional Paths: Part 2—Comparison With Predictions of Three Incremental Plasticity Models

1978 ◽  
Vol 100 (1) ◽  
pp. 104-111 ◽  
Author(s):  
H. S. Lamba ◽  
O. M. Sidebottom
Keyword(s):  
Cyclic Loading ◽  
Material Property ◽  
Yield Surface ◽  
Strain Path ◽  
Kinematic Hardening ◽  
Cyclic Plasticity ◽  
Limit Surface ◽  
Hardening Rule ◽  
Hardening Models ◽  
Hardening Rules

Experiments that demonstrate the basic quantitative and qualitative aspects of the cyclic plasticity of metals are presented in Part 1. Three incremental plasticity kinematic hardening models of prominence are based on the Prager, Ziegler, and Mroz hardening rules, of which the former two have been more frequently used than the latter. For a specimen previously fully stabilized by out of phase cyclic loading the results of a subsequent cyclic nonproportional strain path experiment are compared to the predictions of the above models. A formulation employing a Tresca yield surface translating inside a Tresca limit surface according to the Mroz hardening rule gives excellent predictions and also demonstrates the erasure of memory material property.

A Comparative Study of the Response of Double Shearing and Hypoplastic Models

2002 ◽  
Author(s):  
Huaning Zhu ◽  
Morteza M. Mehrabadi ◽  
Mehrdad Massoudi
Keyword(s):  
Cyclic Loading ◽  
Mechanical Response ◽  
Constitutive Relations ◽  
Constitutive Models ◽  
Shear Loading ◽  
Biaxial Compression ◽  
Finite Element Program ◽  
Cyclic Shear ◽  
Hypoplastic Model ◽  
Element Program

The principal objective of this paper is to compare the mechanical response of a double shearing model with that of a hypoplastic model under biaxial compression and under cyclic shear loading. As the origins and nature of these two models are completely different, it is interesting to compare the predictions of these two models. The constitutive relations of the double shearing and the hypoplastic models are implemented in the finite element program ABACUS/Explicit. It is found that the hypoplastic and the double shearing constitutive models both show strong capability in capturing the essential behavior of granular materials. In particular, under the condition of non-cyclic loading, the stress ratio and void ratio predictions of the double shearing and the hypoplastic models are relatively close, while under the condition of cyclic loading, the predictions of these models are quite different. It is important to note that in the double shearing model employed in this comparison the shear rates on the two slip systems are assumed to be equal. Hence, the conclusions derived in this comparison pertain only to this particular double shearing model. Similarly, the hypoplasticity model considered here is that proposed by Wu, et al. [30] and the conclusions reached here pertain only to this particular hypoplasticity model.

Simulation of Piping Ratcheting Experiments Using Advanced Plane-Stress Cyclic Elastoplasticity Models

2019 ◽  
Author(s):  
Konstantinos Chatziioannou ◽  
Yuner Huang ◽  
Spyros A. Karamanos
Keyword(s):  
Finite Element ◽  
Numerical Integration ◽  
Plane Stress ◽  
Numerical Scheme ◽  
Large Scale ◽  
Low Cycle Fatigue ◽  
Structural Response ◽  
Material Behavior ◽  
Repeated Loading ◽  
Cycle Fatigue

Abstract Industrial steel piping components are often subjected to severe cyclic loading conditions which introduce large inelastic strains and can lead to low-cycle fatigue. Modeling of their structural response requires the simulation of material behavior under strong repeated loading, associated with large strain amplitudes of alternate sign. Accurate numerical predictions of low-cycle fatigue depend strongly on the selection of cyclic-plasticity model in terms of its ability to predict accurately strain at critical location and its accumulation (referred to as “ratcheting”). It also depends on the efficient numerical integration of the material model within a finite element environment. In the context of von Mises metal plasticity, the implementation of an implicit numerical integration scheme for predicting the cyclic response of piping components is presented herein, suitable for large-scale structural computations. The constitutive model is formulated explicitly for shell-type (plane-stress) components, suitable for efficient analysis of piping components whereas the numerical scheme has been developed in a unified manner, allowing for the consideration of a wide range of hardening rules, which are capable of describing accurately strain ratcheting. The numerical scheme is implemented in a general-purpose finite element software as a material-user subroutine, with the purpose of analyzing a set of large-scale physical experiments on elbow specimens undergoing constant-amplitude in-plane cyclic bending. The accuracy of three advanced constitutive models in predicting the elbow response, in terms of both global structural response and local strain amplitude/accumulation, is validated by direct comparison of numerical results with experimental data, highlighting some key issues associated with the accurate simulation of multiaxial ratcheting phenomena. The very good comparison between numerical and experimental results, indicates that the present numerical methodology and, in particular, its implementation into a finite element environment, can be used for the reliable prediction of mechanical response of industrial piping elbows, under severe inelastic repeated loading.

scholarly journals Finite-Element-Based Multiple Normal Loading-Unloading of an Elastic-Plastic Spherical Stick Contact

2013 ◽  
Vol 2013 ◽  
pp. 1-13 ◽  
Author(s):  
Biplab Chatterjee ◽  
Prasanta Sahoo
Keyword(s):  
Finite Element ◽  
Strain Hardening ◽  
Tangent Modulus ◽  
Repeated Loading ◽  
Normal Loading ◽  
Elastic Plastic ◽  
Finite Element Software ◽  
Hardening Models ◽  
Hardening Rules ◽  
Contact Parameters

The repeated normal elastic plastic contact problem of a deformable sphere against a rigid flat under full stick contact condition is investigated with a commercial finite element software ANSYS. Emphasis is placed on the effect of strain hardening and hardening model with the maximum interference of load ranging from elastic to fully plastic, which has not yet been reported. Different values of tangent modulus coupled with isotropic and kinematic hardening models are considered to study their influence on contact parameters. Up to ten normal loading-unloading cycles are applied with a maximum interference of 200 times the interference required to initiate yielding. Results for the variation of mean contact pressure, contact load, residual interference, and contact area with the increasing number of loading unloading cycles at high hardening parameter as well as for low tangent modulus with two different hardening models are presented. Results are compared with available finite element simulations and in situ results reported in the literature. It is found that small variation of tangent modulus results in same shakedown behavior and similar interfacial parameters in repeated loading-unloading with both the hardening rules. However at high tangent modulus, the strain hardening and hardening rules have strong influence on contact parameters.

Dented Externally-Pressurised Pipes Subjected to Cyclic Axial Loading

2019 ◽  
Author(s):  
Konstantinos Chatziioannou ◽  
Yuner Huang ◽  
Spyros A. Karamanos
Keyword(s):  
Numerical Simulation ◽  
Stainless Steel ◽  
Cyclic Loading ◽  
Large Scale ◽  
Mechanical Response ◽  
Axial Loading ◽  
External Pressure ◽  
Nonlinear Material ◽  
Steel Pipes ◽  
Cycles To Failure

Abstract The present paper describes a numerical investigation of the mechanical response of externally-pressurized dented stainless-steel pipes, subjected to reverse cyclic axial loading. This is the first part of a large-scale project, between The University of Edinburgh and Tianjin University, and is motivated by the mechanical response of offshore pipelines, which are often subjected to cyclic loading during installation or operation. Under those cyclic loading conditions, the pipe may collapse because of accumulation of plastic deformations at the dent area. The paper describes a numerical simulation of the above physical problem, in an attempt to support experiments on 50mm-diameter stainless steel pipes, which are being performed at the laboratory facilities of Tianjin University. Pipe segments are subjected to reverse cyclic axial loading (tension and compression), in the presence of external pressure. Prior to the application of external pressure and axial load, the pipes are locally dented, in the form of “smooth dent” or “local ovalization”, so that collapse initiates at the dent area. The numerical simulation is aimed at examining some aspects of pipeline behavior to support and complement the experimental observations. The simulation is conducted using rigorous finite element tools, which account for large displacement and nonlinear material. Towards this purpose, an advanced material model is employed, capable of describing the phenomenological aspects of material response under cyclic loading, such as the accumulation of plastic strain and ratcheting. In the first part of the analysis, the local ovalization (denting) process is simulated. Subsequently, the pipes are subjected to uniform constant external pressure and, keeping the pressure level constant, monotonic or cyclic axial loading is applied until collapse. The numerical results are aimed at identifying the interrelation between the magnitude of the applied loading and the number of loading cycles to failure. The results are presented in diagrams of axial displacement, ovalization and local strain versus the corresponding number of cycles to failure, for specific levels of external pressure.

scholarly journals Mechanical Behavior of Steel Pipes With Local Wall Distortions Under Cyclic Loading

2012 ◽  
Author(s):  
Aglaia E. Pournara ◽  
Spyros A. Karamanos
Keyword(s):  
Cyclic Loading ◽  
Large Scale ◽  
Structural Integrity ◽  
Oil And Gas ◽  
Pipe Wall ◽  
Local Stress ◽  
Local Strain ◽  
Design Guidelines ◽  
Repeated Loading ◽  
Steel Pipes

Evaluating the severity of pipe wall distortions is a crucial step towards safeguarding the structural integrity of aging hydrocarbon pipeline infrastructure. The present research refers to the remaining life of oil and gas transmission steel pipelines with local wall distortions (i.e. dents and buckles) under repeated loading. The research described in this paper constitutes the first part of a large numerical/experimental research project, aimed at developing methodologies and relevant design guidelines towards assessing and repairing structural pipeline damages in the form of local wall distortions. The paper describes numerical research aimed at investigating the residual structural integrity of smooth dented and buckled steel pipes, with respect to repeated loading that causes fatigue, with the purpose of designing large-scale experiments. Finite element models are developed to simulate the formation of dents and buckles on the pipe wall at various sizes (depths). The deformed steel pipes are further subjected to cyclic pressure or cyclic bending loading in order to estimate the remaining fatigue life of the deformed pipe. The local stress and strain variations due to cyclic loading application are calculated numerically at the deformed area of the pipe wall. In addition, the local strain variations are expressed in terms of strain concentration factors (SNCF) at the critical region of the pipe.

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.

The Mechanical Response Analysis of the Airport Asphalt Pavement Considering Horizontal Load

2013 ◽  
Vol 645 ◽  
pp. 471-475
Author(s):  
Jian Jiao ◽  
Shu Dong Meng ◽  
Qiang Jiao ◽  
Nan Li
Keyword(s):  
Shear Stress ◽  
Surface Layer ◽  
Tensile Stress ◽  
Large Scale ◽  
Mechanical Response ◽  
Asphalt Pavement ◽  
Response Analysis ◽  
Horizontal Load ◽  
Horizontal Shear ◽  
Finite Element Software

In order to research the mechanical response of asphalt pavement under horizontal load which produced by the large aircraft braking process, large-scale finite element software is used in this paper. The model of main landing gear load is established to analyze the change of principal mechanics indexes of airfield pavement when the aircraft has different landing distance. The results show that: the horizontal load has a significant influence on the normal stress of landing direction, but the influence area is concentrated in the rear of the wheel. The horizontal load has more effect on horizontal shear stress and longitudinal shear stress, while has less effect on tensile stress of surface layer bottom, tensile tress of base course bottom and transverse shear stress. The tensile stress of surface layer will increase significantly when the braking distance is less than 2000m. Meanwhile, thickening surface layer could decrease the tensile stress and increase the fatigue lifetime apparently.

Experimental and Numerical Investigation of Pipe T-Junctions Under Strong Cyclic Loading

2013 ◽  
Author(s):  
Theocharis Papatheocharis ◽  
Kalliopi Diamanti ◽  
George E. Varelis ◽  
Philip C. Perdikaris ◽  
Spyros A. Karamanos
Keyword(s):  
Experimental Investigation ◽  
Structural Integrity ◽  
Low Cycle Fatigue ◽  
Testing Procedure ◽  
Cyclic Plasticity ◽  
Repeated Loading ◽  
Performance Tests ◽  
Local Strains ◽  
Numerical Effort ◽  
Out Of Plane

Tee pipe junctions are piping components widely used in industrial and pipeline applications. Their performance under severe loading conditions may be critical for the structural integrity of an industrial facility. When these components are subjected to repeated loading associated with cyclic plasticity, failure is possible. The present work is a combined experimental and numerical effort which examines the behavior of piping branch T-junctions subjected to strong cyclic out-of-plane bending. The first part of this paper describes the experimental investigation of the junction performance. Tests are conducted in a constant and varying amplitude displacement-controlled mode resulting to failure in the low-cycle fatigue range. The overall behavior of each specimen in terms of fatigue life, as well as the evolution and concentration of local strains are monitored throughout the testing procedure. The experimental investigation is supported by finite element modeling, developed to simulate the experiments. Advanced cyclic plasticity material models are employed and emphasis is given on the local strains developed at the critical part of the T-junctions where first cracking occurs.

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