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.

Analysis of crush-damaged carbon-fiber-reinforced-polymer (CFRP) composites with optimization-assisted post-peak-stress modeling

2020 ◽  
pp. 002199832095770
Author(s):  
Sheng Dong ◽  
Lars Gräning ◽  
Kelly Carney ◽  
Allen Sheldon
Keyword(s):  
Cross Sections ◽  
Peak Stress ◽  
Material Model ◽  
Material Behavior ◽  
Engineering Practice ◽  
Model Parameters ◽  
Optimization Strategy ◽  
Damage Models ◽  
Cfrp Composites ◽  
Force Time

In the presented effort, layered CFRP composites samples with differing thicknesses and cross-sections are manufactured and crushed under quasi-static loading conditions. Simulation of the crushes are conducted using traditional continuum mechanics damage models. Parameters are proposed to represent the post peak-stress material behavior including the residual strengths of the fiber and matrix, as well the ultimate strain for deletion of composite elements. This paper presents a systematic approach to identify optimal values for these post peak-stress parameters based on a methodology incorporating CAE models and numerical optimization. An adaptive meta-model based global optimization strategy, with the objective of matching the force-time characteristics of multiple crush experiments simultaneously, has been established to quantify the values of the CFRP’s post peak-stress degradation and erosion material model parameters through calibration. Using two separate test configurations for optimization, a set of values for those parameters are determined. This parameter set is shown to successfully predict the response of additional test cases, including matching of force-displacement curves and crushing modes. The resulting composite crush simulations show a good quantitative as well as qualitative agreement between simulations and experiments to a degree that is difficult to be achieved solely with previous engineering practice.

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 Study of the Dynamic Behavior of Elastomeric Materials Using Finite Elements

1996 ◽  
Vol 118 (4) ◽  
pp. 503-508 ◽  
Author(s):  
G. E. Vallee ◽  
Arun Shukla
Keyword(s):  
Finite Element ◽  
Dynamic Behavior ◽  
Split Hopkinson Pressure Bar ◽  
Material Model ◽  
Element Model ◽  
Material Behavior ◽  
Hopkinson Pressure Bar ◽  
Material Models ◽  
Finite Element Program ◽  
Elastomeric Materials

A numerical method is described for determining a dynamic finite element material model for elastomeric materials loaded primarily in compression. The method employs data obtained using the Split Hopkinson Pressure Bar (SHPB) technique to define a molecular constitutive model for elastomers. The molecular theory is then used to predict dynamic material behavior in several additional deformation modes used by the ABAQUS/Explicit (Hibbitt, Karlsson, and Sorenson, 1993a) commercial finite element program to define hyperelastic material behavior. The resulting dynamic material models are used to create a finite element model of the SHPB system, yielding insights into both the accuracy of the material models and the SHPB technique itself when used to determine the dynamic behavior of elastomeric materials. Impact loading of larger elastomeric specimens whose size prohibits examination by the SHPB technique are examined and compared to the results of dynamic load-deflection experiments to further verify the dynamic material models.

Evaluation of the out-of-plane response of fiber networks with a representative volume element model

TAPPI Journal ◽  
2018 ◽  
Vol 17 (06) ◽  
pp. 329-339 ◽  
Author(s):  
Yujun Li ◽  
Zengzhi Yu ◽  
Stefanie Reese ◽  
Jaan-Willem Simon
Keyword(s):  
Mechanical Behavior ◽  
Representative Volume Element ◽  
Mechanical Response ◽  
Volume Fraction ◽  
Volume Element ◽  
Specimen Thickness ◽  
Fiber Networks ◽  
Representative Volume ◽  
Out Of Plane ◽  
Plane Compression

Many natural and synthetic materials have fibrous microstructures, including nonwoven fabrics, paper, and fiberboard. Experimentally evaluating their out-of-plane mechanical behavior can be difficult because of the small thickness compared with the in-plane dimension. To properly predict such properties, network-scale models are required to obtain homogenized material mechanics by considering fiber-scale mechanisms. We demonstrate a three-dimensional representative volume element (RVE) for fiber networks using the finite element method. We first adopted the classical deposition procedure to generate fiber networks with random or preferential fiber orientations and then an artificial compression to achieve the practical fiber volume fraction. The hollow fibers, described with elastic-plastic brick elements, were joined by interface-based cohesive zone elements introduced in all fiber-fiber contact areas. Thereafter, the fiber networks were subjected to displacement boundary conditions, and their apparent mechanical response was evaluated by a homogenized stress. To determine the RVE dimension, we further conducted an RVE size convergence study for the out-of-plane compression and tension (varying specimen length while keeping the specimen thickness constant). Finally, we evaluated the apparent out-of-plane response of the obtained RVE for four loading cases: out-of-plane compression, tension, simple shear, and pure shear. The results show a quite different mechanical behavior of fiber networks between all these out-of-plane loading cases, particularly between tension and compression.

scholarly journals Adaptive, Small-Rotation-Based, Corotational Technique for Analysis of 2D Nonlinear Elastic Frames

2014 ◽  
Vol 2014 ◽  
pp. 1-15 ◽  
Author(s):  
Jaroon Rungamornrat ◽  
Saethapoom Sihanartkatakul ◽  
Pattawee Kanchanakitcharoen
Keyword(s):  
Elastic Material ◽  
Numerical Technique ◽  
Body Movement ◽  
Material Model ◽  
Material Behavior ◽  
Algebraic Equations ◽  
Nonlinear Elastic Material ◽  
Computational Performance ◽  
Nonlinear Elastic ◽  
Small Rotation

This paper presents an efficient and accurate numerical technique for analysis of two-dimensional frames accounted for both geometric nonlinearity and nonlinear elastic material behavior. An adaptive remeshing scheme is utilized to optimally discretize a structure into a set of elements where the total displacement can be decomposed into the rigid body movement and one possessing small rotations. This, therefore, allows the force-deformation relationship for the latter part to be established based on small-rotation-based kinematics. Nonlinear elastic material model is integrated into such relation via the prescribed nonlinear moment-curvature relationship. The global force-displacement relation for each element can be derived subsequently using corotational formulations. A final system of nonlinear algebraic equations along with its associated gradient matrix for the whole structure is obtained by a standard assembly procedure and then solved numerically by Newton-Raphson algorithm. A selected set of results is then reported to demonstrate and discuss the computational performance including the accuracy and convergence of the proposed technique.

scholarly journals Nonlinear-Elastic Orthotropic Material Modeling of an Epoxy-Based Polymer for Predicting the Material Behavior of Transversely Loaded Fiber-Reinforced Composites

2020 ◽  
Vol 4 (2) ◽  
pp. 46
Author(s):  
Caroline Lüders
Keyword(s):  
Elastic Material ◽  
Orthotropic Material ◽  
Material Model ◽  
Material Behavior ◽  
Fiber Reinforced Composites ◽  
Material Modeling ◽  
Reinforced Composites ◽  
The Matrix ◽  
Nonlinear Elastic ◽  
Loaded Fiber

Micromechanical analyses of transversely loaded fiber-reinforced composites are conducted to gain a better understanding of the damage behavior and to predict the composite behavior from known parameters of the fibers and the matrix. Currently, purely elastic material models for the epoxy-based polymeric matrix do not capture the nonlinearity and the tension/compression-asymmetry of the resin’s material behavior. In the present contribution, a purely elastic material model is presented that captures these effects. To this end, a nonlinear-elastic orthotropic material modeling is proposed. Using this matrix material model, finite element-based simulations are performed to predict the composite behavior under transverse tension, transverse compression and shear. Therefore, the composite’s cross-section is modeled by a representative volume element. To evaluate the matrix modeling approach, the simulation results are compared to experimental data and the prediction error is computed. Furthermore, the accuracy of the prediction is compared to that of selected literature models. Compared to both experimental and literature data, the proposed modeling approach gives a good prediction of the composite behavior under matrix-dominated load cases.

Delamination in the scoring and folding of paperboard

TAPPI Journal ◽  
2012 ◽  
Vol 11 (1) ◽  
pp. 61-66 ◽  
Author(s):  
DOEUNG D. CHOI ◽  
SERGIY A. LAVRYKOV ◽  
BANDARU V. RAMARAO
Keyword(s):  
Finite Element ◽  
Plane Deformation ◽  
Strain Analysis ◽  
Local Strain ◽  
Uniaxial Stress ◽  
Material Model ◽  
Element Model ◽  
Plastic Behavior ◽  
Stress Strain ◽  
Strain Fields

Delamination between layers occurs during the creasing and subsequent folding of paperboard. Delamination is necessary to provide some stiffness properties, but excessive or uncontrolled delamination can weaken the fold, and therefore needs to be controlled. An understanding of the mechanics of delamination is predicated upon the availability of reliable and properly calibrated simulation tools to predict experimental observations. This paper describes a finite element simulation of paper mechanics applied to the scoring and folding of multi-ply carton board. Our goal was to provide an understanding of the mechanics of these operations and the proper models of elastic and plastic behavior of the material that enable us to simulate the deformation and delamination behavior. Our material model accounted for plasticity and sheet anisotropy in the in-plane and z-direction (ZD) dimensions. We used different ZD stress-strain curves during loading and unloading. Material parameters for in-plane deformation were obtained by fitting uniaxial stress-strain data to Ramberg-Osgood plasticity models and the ZD deformation was modeled using a modified power law. Two-dimensional strain fields resulting from loading board typical of a scoring operation were calculated. The strain field was symmetric in the initial stages, but increasing deformation led to asymmetry and heterogeneity. These regions were precursors to delamination and failure. Delamination of the layers occurred in regions of significant shear strain and resulted primarily from the development of large plastic strains. The model predictions were confirmed by experimental observation of the local strain fields using visual microscopy and linear image strain analysis. The finite element model predicted sheet delamination matching the patterns and effects that were observed in experiments.

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