scholarly journals Model of the Mechanical Behavior of Cementitious Matrices Reinforced with Nanomaterials

2017 ◽  
Vol 2017 ◽  
pp. 1-10 ◽  
Author(s):  
Victor D. Balopoulos ◽  
Nikolaos Archontas ◽  
Stavroula J. Pantazopoulou
Keyword(s):  
Mechanical Behavior ◽  
Laboratory Tests ◽  
Random Network ◽  
Mechanistic Model ◽  
Cementitious Materials ◽  
Limited Range ◽  
Material Behavior ◽  
Sensitive Material ◽  
Element Approach ◽  
Stress States

CNTs and CNFs have been introduced as a nanoscale reinforcing material to cementitious composites, for stiffening and strengthening the microstructure. This technology is motivated by the need to control crack initiation in the cementitious gel before it propagates into visible crack formations. Experimental evidence supports this concept; however, testing at the nanoscale may only be conducted through nanoindentation, which has a limited range only providing localized results that cannot be extrapolated to general stress states. To evaluate the restraining action of nanomaterials in the gel microstructure, a computational mechanistic model has been developed where the material phases (gel, nanotubes, and pores) are modeled explicitly allowing for natural randomness in their distribution and orientation. Repeated analysis with identical input data reproduces the statistical scatter observed in laboratory tests on identical material samples. The formulation uses a discrete element approach; the gel structure is represented by a random network of hydrates and successfully reproduces the known trends in mechanical behavior of cementitious materials (pressure and restraint sensitive material behavior) and the small ratio of tensile to compressive strength. Simulations illustrate that it is possible to computationally reproduce the measured properties and behavior of fiber-reinforced cement composites using information from simple laboratory tests.

A note on the nonlinear mechanical behavior of planar random network structures subjected to in-plane compression

2011 ◽  
Vol 45 (25) ◽  
pp. 2697-2703 ◽  
Author(s):  
Pär E. Åslund ◽  
Per Isaksson
Keyword(s):  
Mechanical Behavior ◽  
Elastic Material ◽  
Random Network ◽  
Material Model ◽  
Element Model ◽  
Material Behavior ◽  
Fiber Networks ◽  
Damage Models ◽  
Plane Compression ◽  
Random Fiber Networks

The microstructural effect on the mechanical behavior of idealized two-dimensional random fiber networks subjected to in-plane compression is studied. A finite element model utilizing nonlinear beam elements assuming a linearly elastic material is developed. On a macroscopic level, random fiber networks often display an asymmetric material behavior when loaded in tension and compression. In mechanical models, this nonlinearity is traditionally described using continuum elastic-inelastic and/or damage models even though using a continuum approach risks overlooking microstructural effects. It is found that even though a linear elastic material model is used for the individual fibers, the network gives a nonlinear response in compression. The nonlinearity is found to be caused by buckling of individual fibers. This reversible nonlinear mechanism is limited in tensile loading and hence offers an alternative explanation to the global asymmetry of random fibernetworks.

Constitutive modeling for the mechanical behavior of rubber with filler particles

2021 ◽  
Author(s):  
Sankalp Gour ◽  
Deepu Kumar Singh ◽  
Deepak Kumar ◽  
Vinod Yadav
Keyword(s):  
Mechanical Properties ◽  
Carbon Black ◽  
Mechanical Behavior ◽  
Experimental Observation ◽  
Continuum Mechanics ◽  
Constitutive Modeling ◽  
Carbon Nanoparticles ◽  
Material Behavior ◽  
Experimental Results ◽  
Filler Particles

Abstract The present study deals with the constitutive modeling for the mechanical behavior of rubber with filler particles. An analytical model is developed to predict the mechanical properties of rubber with added filler particles based on experimental observation. To develop the same, a continuum mechanics-based hyperelasticity theory is utilized. The model is validated with the experimental results of the chloroprene and nitrile butadiene rubbers filled with different volume fractions of carbon black and carbon nanoparticles, respectively. The findings of the model agree well with the experimental results. In general, the developed model will be helpful to the materialist community working in characterizing the material behavior of tires and other rubber-like materials.

Mathematical Modelling of Materials Behavior Under Creep Conditions

2001 ◽  
Vol 54 (2) ◽  
pp. 107-132 ◽  
Author(s):  
J. Betten
Keyword(s):  
Experimental Data ◽  
Mathematical Modelling ◽  
Mechanical Behavior ◽  
Review Article ◽  
Material Behavior ◽  
Experimental Investigations ◽  
Rational Basis ◽  
Complex Material ◽  
Interpolation Methods ◽  
Materials Behavior

This article will provide a short survey of some recent advances in the mathematical modelling of materials behavior under creep conditions. The mechanical behavior of anisotropic solids requires a suitable mathematical modelling. The properties of tensor functions with several argument tensors constitute a rational basis for a consistent mathematical modelling of complex material behavior. This article presents certain principles, methods, and recent successful applications of tensor functions in creep mechanics. The rules for specifying irreducible sets of tensor invariants and tensor generators for material tensors of rank two and four are also discussed. Furthermore, it is very important that the scalar coefficients in constitutive and evolutional equations are determined as functions of the integrity basis and experimental data. It is explained in detail that these coefficients can be determined by using tensorial interpolation methods. Some examples for practical use are discussed. Finally, we have carried out our own experiments to examine the validity of the mathematical modelling. Furthermore, an overview of some important experimental investigations in creep mechanics of other scientists has been provided. There are 243 references cited in this review article.

Investigation of the effect of stress states on hydro-mechanical behaviors of reservoir rock under fluid injection

2021 ◽  
Author(s):  
Qi Li ◽  
Miao He ◽  
Michael Kühn ◽  
Xiaying Li ◽  
Liang Xu
Keyword(s):  
Stress State ◽  
Mechanical Behavior ◽  
Triaxial Compression ◽  
Reservoir Rock ◽  
Fluid Injection ◽  
Differential Stress ◽  
Mechanical Coupling ◽  
Injection Process ◽  
The Difference ◽  
Stress States

<p>Injecting fluid into the formation is an effective solution for improving the permeability and production of a target reservoir. The evaluation of economy and safety of injection process is a challenging issue faced in reservoir engineering [1-2]. As known, the relative magnitude and direction of the principal stresses significantly influence the hydro-mechanical behavior of reservoir rock during fluid injection. However, due to the limitations of current testing techniques, it is still difficult to comprehensively conduct laboratory injection tests under various stress conditions, e.g. triaxial extension stress states [3]. To this end, a series of numerical simulations were carried out on reservoir rock to study the hydro-mechanical changes under different stress states during fluid injection. In this modelling, the saturated rock is first loaded to the target stress state under drainage conditions, and then the stress state is maintained and water is injected from the top end to simulate the reservoir injection process. Particular attention is paid to the difference in hydro-mechanical changes under triaxial compression and extension stresses. This includes the difference of the pore pressure propagation, mean effective stress, volumetric strain, and stress-induced permeability. The numerical results demonstrate that the differential stress will significantly affect the hydro-mechanical behavior of target rock, but the degree of influence is different under the two triaxial stress states. The hydro-mechanical changes caused by the triaxial compression stress states are generally greater than that of extension, but the difference decreases with increasing differential stress, indicating that the increase of the differential stress will weaken the impact of the stress state on the hydro-mechanical response. This study can deepen our understanding of the stress-induced hydro-mechanical coupling process in reservoir injection engineering.</p><p>Keywords: Reservoir injection; Subsurface flow; Hydro-mechanical coupling; Stress state; Triaxial experiment modelling</p><p>[1] Li, X., Lei, X. & Li, Q. 2016. Injection-induced fracturing process in a tight sandstone under different saturation conditions. Environmental Earth Sciences, 75, 1466, http://doi.org/10.1007/s12665-016-6265-2</p><p>[2] Yang, D., Li, Q. & Zhang, L. 2016. Propagation of pore pressure diffusion waves in saturated dual-porosity media (II). Journal of Applied Physics, 119, 154901, http://doi.org/10.1063/1.4946832</p><p>[3] Xu, L., Li, Q., Myers, M., Tan, Y., He, M., Umeobi, H.I. & Li, X. 2021. The effects of porosity and permeability changes on simulated supercritical CO<sub>2</sub> migration front in tight glutenite under different effective confining pressures from 1.5 MPa to 21.5 MPa. Greenhouse Gases: Science and Technology, http://doi.org/10.1002/ghg.2043</p>

Stress Analysis of SS316L Tube Die Expansion for High Pressure Gas Coolers

2020 ◽  
Author(s):  
Zijian Zhao ◽  
Abdel-Hakim Bouzid
Keyword(s):  
Residual Stress ◽  
High Pressure ◽  
Plastic Material ◽  
Research Work ◽  
Material Behavior ◽  
Isotropic Hardening ◽  
Plastic Behavior ◽  
Expansion Process ◽  
Elastic Plastic ◽  
Stress States

Abstract SS316L finned tubes are becoming very popular in high-pressure gas exchangers and particularly in CO2 cooler applications. Due to the high-pressure requirement during operation, these tubes require an accurate residual stress evaluation during the expansion process. Indeed, die expansion of SS tubes creates not only high stresses when combined with operation stresses but also micro-cracks during expansion when the expansion process is not very well controlled. This research work aims at studying the elastic-plastic behavior and estimating the residual stress states by modeling the die expansion process. The stresses and deformations of the joint are analyzed numerically using the finite element method. The expansion and contraction process is modeled considering elastic-plastic material behavior for different die sizes. The maximum longitudinal, tangential and contact stresses are evaluated to verify the critical stress state of the joint during the expansion process. The importance of the material behavior in evaluating the residual stresses using kinematic and isotropic hardening is addressed.

Computational Approach of the Cortical Bone Mechanical Behavior Based on an Elastic Viscoplastic Damageable Constitutive Model

2020 ◽  
Vol 12 (07) ◽  
pp. 2050081
Author(s):  
Tesnim Kraiem ◽  
Abdelwahed Barkaoui ◽  
Tarek Merzouki ◽  
Moez Chafra
Keyword(s):  
Mechanical Behavior ◽  
Bone Quality ◽  
Damage Evolution ◽  
Sensitivity Study ◽  
Computational Approach ◽  
Material Behavior ◽  
The Finite Element Method ◽  
Non Invasive ◽  
Applied Loading ◽  
Good Agreement

Bone mechanical behavior varies according to the mechanical loading to which it is subjected, and its response effectiveness mainly depends on its quality. Thus, measuring the indicators controlling the bone quality is required to assess its strength. Indeed, the Finite Element Method (FEM) provides a non-invasive tool to interpret bone quality. Therefore, this work coupled the FEM with a micromechanical law, aiming to provide an exhaustive description of the human bone mechanical behavior. Anisotropy, viscoplasticity and damage were introduced in the material behavior law and the damage evolution was plotted based on the applied loading. Then a sensitivity study was conducted to evaluate the effects of viscoplasticity and damage parameters on bone behavior. The obtained numerical results were in a good agreement with the previously reported experimental data and allowed to distinguish key parameters from non-significant ones. This new computational model provided a better understanding of the main parameters affecting bone behavior.

Finite Element Modeling of Biodegradable Stents

2013 ◽  
Author(s):  
Nic Debusschere ◽  
Matthieu De Beule ◽  
Peter Dubruel ◽  
Patrick Segers ◽  
Benedict Verhegghe
Keyword(s):  
Finite Element ◽  
Mechanical Behavior ◽  
Mechanical Performance ◽  
Cost Effective ◽  
Minimal Invasive ◽  
Material Behavior ◽  
Element Analysis ◽  
Design And Optimization ◽  
Stent Restenosis ◽  
Biodegradable Stents

Biodegradable stents, which temporarily support a stenotic blood vessel and afterwards fully disappear, have recently gained a lot of interest. They avoid long-term complications associated with conventional stents such as late stent thrombosis and in-stent restenosis. Moreover, degradable stents allow for a restoration of vasomotion and vessel growth which makes them particularly suitable for pediatric applications [1]. Finite element simulations have proven to be an efficient and cost-effective tool to investigate and optimize the mechanical performance of minimal invasive devices such as stents [2]. Biodegradable stents have however created new challenges in their design and optimization via finite element analysis because of their complex time-varying material behavior. To correctly simulate the mechanical behavior of biodegradable stents, a model should be developed that incorporates the effect of degradation upon all material characteristics. By combining existing constitutive material models based on continuum damage theory we were able to create such a virtual environment in which the transitional mechanical behavior of biodegradable stents can be investigated.

Experimental and Numerical Evaluation of Fracture Toughness on Electron Beam Welded Joint in Al6061-T6

2016 ◽  
Author(s):  
W. Rekik ◽  
O. Ancelet ◽  
C. Gardin ◽  
F. Hamon
Keyword(s):  
Electron Beam ◽  
Mechanical Behavior ◽  
Yield Stress ◽  
Base Metal ◽  
Heat Affected Zone ◽  
Welded Joint ◽  
Material Behavior ◽  
Failure Assessment ◽  
Tearing Resistance ◽  
Alloy 6061

In order to ensure the integrity of structures, failure assessment is required. In this context, the fracture behavior of an electron beam (EB) welded joint on thick plate of aluminum alloy 6061-T6 used for structural components of experimental nuclear reactors was investigated. In the particular case of welded structures, the tearing resistance is strongly dependent on the mismatch of the welded joint and the local behavior of each metallurgical zone. For a reliable analysis, the tensile mechanical behavior of each position of the welded joint was precisely determined by the use of a new measurement prototype. The toughness behavior under different configurations was then evaluated on CT specimens. From these experimental results a mechanical behavior contrast was highlighted. In fact, the fusion zone presents the lowest yield stress and a gradient is observed in the heat affected zone until the material behavior reaches of the base metal yield stress. On the contrary, the toughness of the welded zone is the highest and decreases strongly in the heat affected zone according to an exponential function until the base metal toughness is reached.

Effect of the Load Eccentricity on Fracture Behaviour of Cementitious Materials Subjected to the Modified Compact Tension Test

2016 ◽  
Vol 258 ◽  
pp. 518-521 ◽  
Author(s):  
Stanislav Seitl ◽  
José D. Ríos ◽  
Héctor Cifuentes ◽  
Václav Veselý
Keyword(s):  
Fracture Behaviour ◽  
Tensile Load ◽  
Experimental Tests ◽  
Compact Tension ◽  
Cementitious Materials ◽  
Direct Tension ◽  
Dog Bone ◽  
Fracture Models ◽  
Stress States ◽  
Stress And Deformation

Fracture properties of quasi-brittle cementitious composites are typically determined from the load–displacement response recorded during a fracture test by using the work-of-fracture method or possibly other relevant fracture models. Our contribution is focused on a set of experimental tests which are used to study the fracture behaviour on notched dog-bone-shaped specimens made of cementitious materials. These specimens are subjected to modified compact tension (ModCT) test under a specific range of eccentricity of the tensile load. This type of test generates a stress state in the specimen ligament which combines a direct tension with a defined level of bending due to eccentricity of the tensile load. Several values of relative notch length are also considered. While the crack propagates, a variety of stress states, resulting in variations in the crack-tip stress and deformation constraint, appears in the ligament zone because of the changes in the eccentricity of the applied load, which influences the fracture behaviour of the investigated specimens. The K-calibration, T-stress, CMOD and COD curves for ModCT specimens are introduced and variations of these curves with varying load eccentricity are discussed.

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