A composite finite element to predict failure progress in composite laminates accounting for nonlinear material properties

2011 ◽  
Vol 18 (7) ◽  
pp. 752-768
Author(s):  
Ghazi A. Abu-Farsakh ◽  
Amin H. Almasri
Keyword(s):  
Finite Element ◽  
Material Properties ◽  
Composite Laminates ◽  
Nonlinear Material

Fracture Prediction for the Proximal Femur Using Finite Element Models: Part I—Linear Analysis

1991 ◽  
Vol 113 (4) ◽  
pp. 353-360 ◽  
Author(s):  
J. C. Lotz ◽  
E. J. Cheal ◽  
W. C. Hayes
Keyword(s):  
Finite Element ◽  
Fracture Risk ◽  
Strain Gage ◽  
Proximal Femur ◽  
Material Properties ◽  
The United States ◽  
Nonlinear Material ◽  
Finite Element Models ◽  
Model Predictions

Over 90 percent of the more than 250,000 hip fractures that occur annually in the United States are the result of falls from standing height. Despite this, the stresses associated with femoral fracture from a fall have not been investigated previously. Our objectives were to use three-dimensional finite element models of the proximal femur (with geometries and material properties based directly on quantitative computed tomography) to compare predicted stress distributions for one-legged stance and for a fall to the lateral greater trochanter. We also wished to test the correspondence between model predictions and in vitro strain gage data and failure loads for cadaveric femora subjected to these loading conditions. An additional goal was to use the model predictions to compare the sensitivity of several imaging sites in the proximal femur which are used for the in vivo prediction of hip fracture risk. In this first of two parts, linear finite element models of two unpaired human cadaveric femora were generated. In Part II, the models were extended to include nonlinear material properties for the cortical and trabecular bone. While there was poor correspondence between strain gage data and model predictions, there was excellent agreement between the in vitro failure data and the linear model, especially using a von Mises effective strain failure criterion. Both the onset of structural yielding (within 22 and 4 percent) and the load at fracture (within 8 and 5 percent) were predicted accurately for the two femora tested. For the simulation of one-legged stance, the peak stresses occurred in the primary compressive trabeculae of the subcapital region. However, for a simulated fall, the peak stresses were in the intertrochanteric region. The Ward’s triangle (basicervical) site commonly used for the clinical assessment of osteoporosis was not heavily loaded in either situation. These findings suggest that the intertrochanteric region may be the most sensitive site for the assessment of fracture risk due to a fall and the subcapital region for fracture risk due to repetitive activities such as walking.

Probabilistic Models to Approximate Highly Repetitive Linear and Nonlinear Finite Element Analyses of Nuclear Components

2009 ◽  
Author(s):  
Dan Vlaicu ◽  
Mike Stojakovic
Keyword(s):  
Finite Element ◽  
Material Properties ◽  
Probabilistic Models ◽  
Nonlinear Material ◽  
Superposition Method ◽  
Loading Conditions ◽  
Finite Element Analyses ◽  
Axisymmetric Nozzle ◽  
Nonlinear Superposition ◽  
Pipe Bend

In the development and technical support of nuclear plants, Engineers have to deal with highly repetitive finite element analyses that involve modeling of local variations of the initial design, local flaws due to corrosion-erosion effects, material properties degradation, and modifications of the loading conditions. This paper presents the development of generic models that emulate the behavior of a complex finite element model in a simplified form, with the statistical representation based on a sampling of base-model data for a variety of test cases. An improved Latin Hypercube algorithm is employed to generate the sampling points based on the number and the range of the variables that are considered in the design space. Four filling methods of the approximation models are discussed in this study: response surface, nonlinear, neural networks, and piecewise polynomial model. Furthermore, a bootstrapping procedure is employed to improve the confidence intervals of the original coefficients, and the single-factor or double-factor analysis of variance is applied to determine whether a significant influence exists between the investigated factors. Two numerical examples highlight the accuracy and efficiency of the methods. The first example is the linear elastic analysis of a pipe bend under pressure loading. The objective of the probabilistic assessment is to determine the relation between the loading conditions as well as the geometrical aspects of this elbow (pipe wall thickness, outside diameter, elbow radius, and maximum ovality tolerance) and the maximum stress in the elbow. The second example is an axisymmetric nozzle under primary and secondary cycling loads. Variations of the geometrical dimensions, nonlinear material properties, and cycling loading are taken as the input parameters, whereas the response variable is defined in terms of Melan’s theorem translated into the Nonlinear Superposition Method.

A Finite Element Based Procedure for Simulating the Transient Response and Failure of a Two-Dimensional Continuum With Nonlinear Material Characteristics

1973 ◽  
Vol 95 (1) ◽  
pp. 345-352 ◽  
Author(s):  
D. B. Wallace ◽  
A. Seireg
Keyword(s):  
Finite Element ◽  
Material Properties ◽  
Impulsive Loading ◽  
Nonlinear Material ◽  
Two Dimensional ◽  
Arbitrary Geometry ◽  
Failure Patterns ◽  
Nonlinear Properties ◽  
Hollow Cylinders ◽  
Failure Theories

This paper presents a finite element based procedure for the analysis and graphic display of the response and failure patterns of a two-dimensional continuum subjected to impulsive loading. Elastic, anelastic, plastic and other nonlinear material properties and failure theories can be incorporated in the analysis. The procedure is illustrated by examples of elastic and anelastic impact of solid and hollow cylinders. The developed technique gives a powerful tool for the evaluation of transient stresses, deformations, yield and fracture modes in two-dimensional continuum with arbitrary geometry and nonlinear properties.

Finite Element Simulation of PZT-Aided Interrogation of Composite Laminates Exhibiting Damage

2016 ◽  
Author(s):  
Amany G. B. Micheal ◽  
Yehia A. Bahei-El-Din
Keyword(s):  
Finite Element ◽  
Material Properties ◽  
Composite Laminates ◽  
Fibrous Composite ◽  
Electric Pulse ◽  
Load Level ◽  
Element Solution ◽  
Damage Mechanisms ◽  
Laminated Beam ◽  
Element Simulation

Piezoelectricity has proved effective in capturing changes in structures caused by various damage mechanisms. In one approach, piezoelectric wafer active sensors (PWAS) are mounted on the surface of the host structure and utilized as both actuators and sensors to interrogate the structure and monitor its health. This is achieved by subjecting the PWAS to a transient electric pulse and reading the resulting voltage. Changes in the stiffness of the substrate due to structural damage affect the response of the PWAS, which could be correlated to integrity of the structure. Applying this technique to fibrous composite laminates encounters particular challenges due to the presence of multiple damage mechanisms in one or more plies. Simulation of the procedure using advanced computational techniques and material models helps in understanding the reliability of PWAS in sensing damage in fibrous laminates. This paper combines the finite element method and micromechanical modeling of composites to simulate damage detection using surface mounted PWAS. The finite element solution is obtained by the ABAQUS code with user defined material properties, which reflect the underlying damage modes. The latter are obtained in a preprocessing exercise in which the composite laminate is first subjected to a given mechanical load level and the damage mechanisms in the plies are identified using transformation field analysis, TFA (Bahei-El-Din el al., 2010). In the present work, the Mori-Tanaka averaging model is utilized within the TFA and local failure modes, which are a function of the matrix average stresses were specified. Material properties of the individual plies, which correspond to the damage mechanisms introduced at the given load level are then determined numerically in terms of the overall moduli and utilized in the finite element solution of the laminate using ABAQUS. The methodology is applied to a quasi-isotropic, symmetric laminated beam subjected to bending. In the finite element simulation, each fibrous composite ply of the laminated beam is modelled using shell elements while the surface mounted PWAS are modeled with 3D solid elements. The bending moment is applied to the beam intermittently to allow interrogation of the laminate by applying a transient electric pulse to the PWAS and allowing the beam to vibrate for a very short period of time, which is followed by reading the voltage response. The voltage readings are correlated to the damage mechanisms in the plies.

Shakedown Analysis of Axisymmetric Nozzles Under Primary and Secondary Cyclic Loads

2009 ◽  
Author(s):  
Dan Vlaicu
Keyword(s):  
Finite Element ◽  
Lower Bound ◽  
Stress Field ◽  
Material Properties ◽  
Cyclic Load ◽  
Elastic Stress ◽  
Nonlinear Material ◽  
Cyclic Loads ◽  
Shakedown Analysis ◽  
Elastic Plastic

In this paper, the finite element method is used to develop the lower bound limit for the elastic shakedown analysis of axisymmetric nozzles under periodic loading conditions. The Nonlinear Superposition Method is employed to calculate the lower bound shakedown loads by quoting Melan’s theorem in a nonlinear finite element analysis. The calculation is divided into two separate iterations which are blended with a technique that matches the elastic-plastic part of the analysis with the linear part. In the first part of the calculation, the cyclic load is applied as a static load to generate an elastic stress field in the structure. The same cyclic load is subsequently combined with the constant fraction of the load in the second part of the calculation, and the total load is applied in an elastic-plastic analysis that exceeds the yield limit. For each solution increment, the residual stress is generated from the superposition of the elastic stress field scaled through the applied cyclic load and the shakedown stress field calculated from the nonlinear analysis. The results obtained from the lower bound method are compared with the full cyclic loading analyses based on nonlinear material properties, and this paper discusses the choice of the global shakedown in terms of the radial strain, and the local through thickness shakedown defined by the hoop strain. Furthermore, this paper presents the development of a generic model that emulates the behavior of the finite element model under cyclic loads in a simplified form, with the statistical representation based on a sampling of base-model data for a variety of test cases. The probabilistic method takes variations of the geometrical dimensions, nonlinear material properties, and pressure load as the input parameters, whereas the response variable is defined in terms of the lower bound of the shakedown loads.

Response of Dolos Concrete Armor Units to Impact Loads

1991 ◽  
Vol 113 (4) ◽  
pp. 286-291 ◽  
Author(s):  
J. W. Tedesco ◽  
P. B. McGill ◽  
W. G. McDougal
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Material Properties ◽  
Concrete Strength ◽  
Impact Resistance ◽  
Nonlinear Material ◽  
Impact Loads ◽  
Model Formulation ◽  
Element Analysis ◽  
The Impact

A finite element analysis is conducted to determine the critical impact velocities for concrete dolos. The model formulation includes deformations at the contact surface and nonlinear material properties. Two dolos orientations are considered: vertical fluke seaward and horizontal fluke seaward. In both cases, the larger units fail at lower angular impact velocities. It is also shown that doubling the concrete strength increases the impact resistance by approximately 40 percent.

Nonlinear Piezoelectric Material Properties and Non-Uniform Poling in a Flexible Electro-Active Composite Finite Element Model

2016 ◽  
Author(s):  
Joseph Calogero ◽  
Hassene Ben Atitallah ◽  
Nicholas Wyckoff ◽  
Zoubeida Ounaies ◽  
Mary Frecker
Keyword(s):  
Finite Element ◽  
Electric Field ◽  
Finite Element Model ◽  
Electric Fields ◽  
Lead Zirconate Titanate ◽  
Material Properties ◽  
Electromechanical Coupling ◽  
Element Model ◽  
Nonlinear Material ◽  
Interdigitated Electrodes

Active Fiber Composites (AFCs) are piezoelectric devices comprised of long cylindrical fibers, typically made of ceramic lead zirconate titanate (PZT), embedded in an epoxy polymer. AFCs use interdigitated electrodes to produce electric field lines parallel to the fibers (33-mode) rather than across the diameter, exploiting the stronger out-of-plane electromechanical coupling. Nonlinear piezoelectric and dielectric terms and non-uniform poling are often neglected in modeling AFCs due to the added complexity, however including the terms improves accuracy for strong electric fields and where the electrode geometry causes non-uniform electric fields. For that reason, a new finite element model of the AFC is developed which includes the effect of nonlinearities in piezoelectric strain constants and electric permittivity due to a non-uniform applied electric field resulting from two sets of interdigitated electrodes. The methods used to apply the nonlinear constitutive equations and poling are described. A comparison of the AFC response with linear and nonlinear material properties, with non-uniform poling, is shown for increasing applied electric fields. The difference in AFC response illustrates the necessity to include Rayleigh Law terms and non-uniform poling in the model.

MICRO-FINITE ELEMENT ANALYSIS OF TRABECULAR BONE YIELD BEHAVIOR — EFFECTS OF TISSUE NONLINEAR MATERIAL PROPERTIES

2011 ◽  
Vol 11 (03) ◽  
pp. 563-580 ◽  
Author(s):  
HE GONG ◽  
MING ZHANG ◽  
YUBO FAN
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Trabecular Bone ◽  
Bone Tissue ◽  
Material Properties ◽  
Material Nonlinearity ◽  
Nonlinear Material ◽  
Yield Strain ◽  
Element Analysis ◽  
Tissue Material

Bone tissue material nonlinearity and large deformations within the trabecular network are important for the characterization of failure behavior of trabecular bone at both the apparent and tissue levels. Micro-finite element analysis (μFEA) is a useful tool for determining the mechanical properties of trabecular bone due to certain experimental difficulties. The aim of this study was to determine the effects of bone tissue nonlinear material properties on the apparent- and tissue-level mechanical parameters of trabecular bone using μFEA. A bilinear tissue constitutive model was proposed to describe the bone tissue material nonlinearity. Two trabecular specimens with different micro-architectures were taken as examples. The effects of four parameters, i.e., tissue Young's modulus, tissue yield strain in tension, tissue yield strain in compression, and post-yield modulus on the apparent yield stress/strain, tissue von Mises stress distribution, the amount of tissue elements yielded in compression and tension under compressive and tensile loading conditions were obtained using nine cases for different values of those parameters by totally 36 nonlinear μFEA. These data may provide a reference for more sophisticated evaluations of bone strength and the related fracture risk.

Nonlinear Finite Element Analysis of the Temperature Field of Special-Shaped Concrete-Filled Steel Tubular Column under Standard Fire Condition

2012 ◽  
Vol 226-228 ◽  
pp. 980-985
Author(s):  
Ya Wen Wang ◽  
Yan Bo Li ◽  
Zhi Hua Chen ◽  
Xiao Dun Wang ◽  
Bo Song ◽  
...  
Keyword(s):  
Finite Element ◽  
Temperature Field ◽  
Material Properties ◽  
Element Model ◽  
Nonlinear Finite Element ◽  
Nonlinear Material ◽  
Element Analysis ◽  
Thermal Boundary Conditions ◽  
Standard Fire ◽  
Fire Condition

The special-shaped concrete-filled steel tubular column (SCFST column) is recognized to have high bearing capacity and good fire resistance. This paper introduced a nonlinear FEA approach to analysis the temperature field of SCFST under standard ISO-834 fire condition. Finite element model was built with nonlinear material properties elements in ANSYS; thermal boundary conditions were applied to the model with convection and radiation combined to simulate the fire condition, and several conclusion were obtained from the nonlinear FEA results.

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