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.

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.

Inertial Effects on Void Growth in Porous Viscoplastic Materials

1995 ◽  
Vol 62 (3) ◽  
pp. 633-639 ◽  
Author(s):  
W. Tong ◽  
G. Ravichandran
Keyword(s):  
Void Growth ◽  
Constitutive Models ◽  
Rate Sensitivity ◽  
High Rate ◽  
Dynamic Crack ◽  
Inertial Effects ◽  
Loading Conditions ◽  
Viscoplastic Material ◽  
Dynamic Loading Conditions ◽  
Very High

The present work examines the inertial effects on void growth in viscoplastic materials which have been largely neglected in analyses of dynamic crack growth and spallation phenomena using existing continuum porous material models. The dynamic void growth in porous materials is investigated by analyzing the finite deformation of an elastic/viscoplastic spherical shell under intense hydrostatic tensile loading. Under typical dynamic loading conditions, inertia is found to have a strong stabilizing effect on void growth process and consequently to delay coalescence even when the high rate-sensitivity of materials at very high strain rates is taken into account. Effects of strain hardening and thermal softening are found to be relatively small. Approximate relations are suggested to incorporate inertial effects and rate sensitivity of matrix materials into the porous viscoplastic material constitutive models for dynamic ductile fracture analyses for certain loading conditions.

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 How the Thermomechanical Processing Can Modify the High Strain Rate Mechanical Response of a Microalloyed Steel

Materials ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 6062
Author(s):  
Remigiusz Błoniarz ◽  
Janusz Majta ◽  
Bogdan Rutkowski ◽  
Grzegorz Korpała ◽  
Ulrich Prahl ◽  
...  
Keyword(s):  
Dynamic Loading ◽  
Mechanical Response ◽  
Split Hopkinson Pressure Bar ◽  
Thermomechanical Processing ◽  
Microstructural Analysis ◽  
Image Correlation ◽  
Microalloyed Steels ◽  
Loading Conditions ◽  
Hopkinson Pressure Bar ◽  
Dynamic Loading Conditions

The effects of thermomechanical processing (TMP) on the mechanical response of microalloyed steels subjected to dynamic loading conditions were examined. The deformation conditions in the thermomechanical laboratory rolling processes were selected on the basis of dilatometric tests. It allowed (with a constant value of total deformation) us to obtain microstructures with different compositions and morphology of the particular components. Several samples characterized by a particularly complex and unexpected representation of the obtained microstructures were selected for further research. Plastometric tests, i.e., compression and tensile tests, were performed under quasi-static loading with digital image correlation (DIC) analysis, and under dynamic loading on the Split Hopkinson Pressure Bar (SHPB) apparatus with strain rates of 1400 and 2000 s−1. Samples deformed in such conditions were subjected to microstructural analysis and hardness measurements. It has been observed that the use of various combinations of TMP parameters can result in the formation of specific microstructures, which in turn are the source of an attractive mechanical response under dynamic loading conditions. This opens up new possible areas of application for such popular structural materials which are microalloyed steels.

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 Thermo-Hydro-Mechanical Coupled Modeling of Methane Hydrate-Bearing Sediments: Formulation and Application

Energies ◽  
2019 ◽  
Vol 12 (11) ◽  
pp. 2178 ◽  
Author(s):  
Maria De La Fuente ◽  
Jean Vaunat ◽  
Héctor Marín-Moreno
Keyword(s):  
Methane Hydrate ◽  
Mechanical Response ◽  
Solid Phase ◽  
Production Method ◽  
Triaxial Tests ◽  
Coupled Modeling ◽  
Mechanical Formulation ◽  
Hydrate Saturation ◽  
Sediment Deformation ◽  
Hydrate Bearing Sediments

We present a fully coupled thermo-hydro-mechanical formulation for the simulation of sediment deformation, fluid and heat transport and fluid/solid phase transformations occurring in methane hydrate geological systems. We reformulate the governing equations of energy and mass balance of the Code_Bright simulator to incorporate hydrate as a new pore phase. The formulation also integrates the constitutive model Hydrate-CASM to capture the effect of hydrate saturation in the mechanical response of the sediment. The thermo-hydraulic capabilities of the formulation are validated against the results from a series of state-of-the-art simulators involved in the first international gas hydrate code comparison study developed by the NETL-USGS. The coupling with the mechanical formulation is investigated by modeling synthetic dissociation tests and validated by reproducing published experimental data from triaxial tests performed in hydrate-bearing sands dissociated via depressurization. Our results show that the formulation captures the dominant mass and heat transfer phenomena occurring during hydrate dissociation and reproduces the stress release and volumetric deformation associated with this process. They also show that the hydrate production method has a strong influence on sediment deformation.

scholarly journals Discrete element analysis of the punching behaviour of a secured drapery system: from laboratory characterization to idealized in situ conditions

2021 ◽  
Author(s):  
Antonio Pol ◽  
Fabio Gabrieli ◽  
Lorenzo Brezzi
Keyword(s):  
Mechanical Response ◽  
Steel Wire ◽  
Discrete Element ◽  
Wire Mesh ◽  
Steel Plates ◽  
Loading Conditions ◽  
Element Analysis ◽  
In Situ Conditions ◽  
Wire Meshes

AbstractIn this work, the mechanical response of a steel wire mesh panel against a punching load is studied starting from laboratory test conditions and extending the results to field applications. Wire meshes anchored with bolts and steel plates are extensively used in rockfall protection and slope stabilization. Their performances are evaluated through laboratory tests, but the mechanical constraints, the geometry and the loading conditions may strongly differ from the in situ conditions leading to incorrect estimations of the strength of the mesh. In this work, the discrete element method is used to simulate a wire mesh. After validation of the numerical mesh model against experimental data, the punching behaviour of an anchored mesh panel is investigated in order to obtain a more realistic characterization of the mesh mechanical response in field conditions. The dimension of the punching element, its position, the anchor plate size and the anchor spacing are varied, providing analytical relationships able to predict the panel response in different loading conditions. Furthermore, the mesh panel aspect ratio is analysed showing the existence of an optimal value. The results of this study can provide useful information to practitioners for designing secured drapery systems, as well as for the assessment of their safety conditions.

scholarly journals Ability of Constitutive Models to Characterize the Temperature Dependence of Rubber Hyperelasticity and to Predict the Stress-Strain Behavior of Filled Rubber under Different Defor Mation States

Polymers ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 369
Author(s):  
Xintao Fu ◽  
Zepeng Wang ◽  
Lianxiang Ma
Keyword(s):  
Experimental Data ◽  
Temperature Dependence ◽  
Mechanical Response ◽  
Constitutive Models ◽  
Uniaxial Tensile ◽  
Uniaxial Tensile Test ◽  
Chain Model ◽  
Stress Strain ◽  
Filled Rubber ◽  
Yeoh Model

In this paper, some representative hyperelastic constitutive models of rubber materials were reviewed from the perspectives of molecular chain network statistical mechanics and continuum mechanics. Based on the advantages of existing models, an improved constitutive model was developed, and the stress–strain relationship was derived. Uniaxial tensile tests were performed on two types of filled tire compounds at different temperatures. The physical phenomena related to rubber deformation were analyzed, and the temperature dependence of the mechanical behavior of filled rubber in a larger deformation range (150% strain) was revealed from multiple angles. Based on the experimental data, the ability of several models to describe the stress–strain mechanical response of carbon black filled compound was studied, and the application limitations of some constitutive models were revealed. Combined with the experimental data, the ability of Yeoh model, Ogden model (n = 3), and improved eight-chain model to characterize the temperature dependence was studied, and the laws of temperature dependence of their parameters were revealed. By fitting the uniaxial tensile test data and comparing it with the Yeoh model, the improved eight-chain model was proved to have a better ability to predict the hyperelastic behavior of rubber materials under different deformation states. Finally, the improved eight-chain model was successfully applied to finite element analysis (FEA) and compared with the experimental data. It was found that the improved eight-chain model can accurately describe the stress–strain characteristics of filled rubber.

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