Development of a Multibody Model to Predict the Settling Point and Interfacial Pressure Distribution in a Seat–Occupant System

2015 ◽  
Vol 10 (3) ◽  
Author(s):  
Yousof Azizi ◽  
Tarun Puri ◽  
Anil K. Bajaj ◽  
Patricia Davies
Keyword(s):  
Viscoelastic Model ◽  
Viscoelastic Behavior ◽  
Elastic Behavior ◽  
Type Model ◽  
Model Parameters ◽  
Force Distribution ◽  
Compression Tests ◽  
Static Compression ◽  
Multibody Model ◽  
Nonlinear Elastic

The location of the hip-joint (H-Point) of a seat occupant is an important design specification which directly affects the seat static comfort. Most car seats are made of polyurethane foam and so the location of the H-Point is dependent on the quasi-static behavior of foam. In this research, a previously developed model of the seat–occupant system is refined by incorporating an improved foam model which is used to study seat and occupant interactions and the location of occupant’s H-Point. The seat is represented by a series of discrete nonlinear viscoelastic elements that characterize the seating foam behavior. The nonlinear elastic behavior of these elements is expressed by a higher order polynomial while their viscoelastic behavior is described by a hereditary type model with parameters that are functions of the compression rate. The nonlinear elastic and viscoelastic model parameters were estimated previously using data obtained from a series of quasi-static compression tests on a car seat foam sample. The occupant behavior is described by a constrained two-dimensional multibody model with five degrees of freedom. A Lagrangian formulation is used to derive the governing equations for the seat–occupant model. These differential equations are solved numerically to obtain the H-Point location. These results are then used to calculate the force distribution at the seat and occupant interfaces. The force distribution at the seat–occupant interface is also investigated experimentally and is found to match qualitatively with the results obtained using the seat–occupant model.

Development of a Multi-Body Model to Predict the Settling Point of a Seat-Occupant System

2014 ◽  
Author(s):  
Yousof Azizi ◽  
Anil K. Bajaj ◽  
Patricia Davies
Keyword(s):  
Polyurethane Foam ◽  
Viscoelastic Model ◽  
Elastic Behavior ◽  
System Response ◽  
Type Model ◽  
Model Parameters ◽  
Static Compression ◽  
Body Model ◽  
Multi Body ◽  
Nonlinear Elastic

The location of the hip-joint (H-Point) of a seat occupant is an important design specification which directly affects the seat comfort. Most car seats are made of polyurethane foam so the location of the H-Point is dependent on the quasi-static behavior of foam. In this study a multi-body seat-occupant model is developed which incorporates a realistic polyurethane foam model. The seat-occupant model consists of two main components: the seat model and the occupant model. In this study the seat is represented by a series of discrete nonlinear viscoelastic elements. The nonlinear elastic behavior of these elements is expressed by a higher order polynomial while their viscoelastic behavior is described by a global hereditary type model with the parameters which are functions of the compression rate. The nonlinear elastic and viscoelastic model parameters were estimated previously using the data obtained from conducting a series of quasi-static compression tests on a car seat foam sample. The occupant behavior is described by a two-dimensional multi-body model with 5 degrees of freedom. A Lagrangian formulation is used to derive the governing equations for the seat occupant model. These differential equations are solved numerically to obtain the H-Point location. These results are then used to calculate the force distribution at the seat and the occupant interfaces. The effects of different system parameters on the system response and the interfacial pressure distribution are also studied.

Identification of Nonlinear Viscoelastic Models of Flexible Polyurethane Foam From Uniaxial Compression Data

2016 ◽  
Vol 138 (2) ◽  
Author(s):  
Yousof Azizi ◽  
Patricia Davies ◽  
Anil K. Bajaj
Keyword(s):  
Uniaxial Compression ◽  
Viscoelastic Model ◽  
Viscoelastic Behavior ◽  
Model Parameters ◽  
Viscoelastic Models ◽  
Nonlinear Viscoelastic ◽  
Compression Data ◽  
Computationally Intensive ◽  
Nonlinear Viscoelastic Model ◽  
Flexible Polyurethane

Flexible polyethylene foam is used in many engineering applications. It exhibits nonlinear and viscoelastic behavior which makes it difficult to model. To date, several models have been developed to characterize the complex behavior of foams. These attempts include the computationally intensive microstructural models to continuum models that capture the macroscale behavior of the foam materials. In this research, a nonlinear viscoelastic model, which is an extension to previously developed models, is proposed and its ability to capture foam response in uniaxial compression is investigated. It is hypothesized that total stress can be decomposed into the sum of a nonlinear elastic component, modeled by a higher-order polynomial, and a nonlinear hereditary type viscoelastic component. System identification procedures were developed to estimate the model parameters using uniaxial cyclic compression data from experiments conducted at six different rates. The estimated model parameters for individual tests were used to develop a model with parameters that are a function of strain rates. The parameter estimation technique was modified to also develop a comprehensive model which captures the uniaxial behavior of all six tests. The performance of this model was compared to that of other nonlinear viscoelastic models.

Application of Fractional Derivatives to Modeling the Quasi-Static Response of Polyurethane Foam

2003 ◽  
Author(s):  
Rong Deng ◽  
Patricia Davies ◽  
Anil K. Bajaj
Keyword(s):  
System Identification ◽  
Polyurethane Foam ◽  
Elastic Model ◽  
Compression Tests ◽  
Static Compression ◽  
Identification Method ◽  
Dissipative Effects ◽  
Identification Technique ◽  
Nonlinear Elastic ◽  
Quasi Static Compression

A fractional derivative model of dissipative effects is combined with a nonlinear elastic model to model the response of polyurethane foam in quasi-static compression tests. A system identification method is developed based on a separation of the elastic and viscoelastic parts of the response, which is possible because of symmetries in the imposed deformation timehistory. Simulations are used to evaluate the proposed identification method when noise is present in the response. The system identification technique is also applied with some success to experimental data taken from several compression experiments on two types of polyurethane foam blocks.

Identification of Nonlinear Viscoelastic Models of Flexible Polyurethane Foam From Uniaxial Compression Data

2012 ◽  
Author(s):  
Yousof Azizi ◽  
Patricia Davies ◽  
Anil K. Bajaj
Keyword(s):  
Uniaxial Compression ◽  
Viscoelastic Model ◽  
Viscoelastic Behavior ◽  
Model Parameters ◽  
Viscoelastic Models ◽  
Nonlinear Viscoelastic ◽  
Compression Data ◽  
Computationally Intensive ◽  
Nonlinear Viscoelastic Model ◽  
Flexible Polyurethane

Flexible polyethylene foam, which is used in many engineering applications, exhibits nonlinear and viscoelastic behavior. To date, several models have been proposed to characterize the complex behavior of foams from the computationally intensive microstructural models to continuum models that capture the macroscale behavior of the foam materials. A nonlinear viscoelastic model, which is an extension of previously developed models, is proposed and its ability to capture foam response in uniaxial compression is investigated. It is assumed in the model that total stress is decomposed into the sum of a nonlinear elastic component, which is modeled by a higher order polynomial, and a nonlinear hereditary type viscoelastic component. System identification procedures are developed to estimate the model parameters using uniaxial compression data from experiments conducted at different rates. The performance of this model is compared to that of other nonlinear viscoelastic models.

A New Constitutive Model for the Compressibility of Elastomers at Finite Deformations

2001 ◽  
Vol 74 (4) ◽  
pp. 541-559 ◽  
Author(s):  
Jeffrey E. Bischoff ◽  
Ellen M. Arruda ◽  
Karl Grosh
Keyword(s):  
Uniaxial Tension ◽  
Volume Change ◽  
Constitutive Models ◽  
Hydrostatic Compression ◽  
Constitutive Law ◽  
Elastic Behavior ◽  
Compression Tests ◽  
Volume Response ◽  
Using Data ◽  
Nonlinear Elastic

Abstract Although traditional constitutive models for rubbery elastic materials are incompressible, many materials that demonstrate nonlinear elastic behavior are somewhat compressible. Clearly important in hydrostatic deformations, compressibility can also significantly affect the response of elastomers in applications for which several boundaries are rigidly fixed, such as bushings, or triaxial states of stress are realized. Compressibility is also important for convergence of finite element simulations in which a rubbery elastic constitutive law is in use. Volume changes that reflect compressibility have been observed historically in both uniaxial tension and hydrostatic compression tests; however, there appear to be no data obtained from both types of tests on the same material by which to validate a compressible hyperelastic law. In this paper, we propose a new compressible hyperelastic constitutive law for elastomers and other rubbery materials in which entropy and internal energy changes contribute to the volume change. Using data from the literature, we show that this law is capable of reproducing both the pressure—volume response of elastomers in hydrostatic compression, as well as the stress—stretch and volume change—stretch data of elastomers in uniaxial tension.

scholarly journals Comparison of Pavement Layers Responses with Considering Different Models for Asphalt Concrete Viscoelastic Properties

2013 ◽  
Vol 21 (2) ◽  
pp. 15-20 ◽  
Author(s):  
Mehdi Koohmishi
Keyword(s):  
Asphalt Concrete ◽  
Structural Model ◽  
Viscoelastic Model ◽  
Viscoelastic Behavior ◽  
Maxwell Model ◽  
Elastic Behavior ◽  
Linear Elastic ◽  
Concrete Layer ◽  
Linear Viscoelastic Behavior ◽  
Linear Viscoelastic

Abstract In this paper, a comparison between pavement responses is performed by considering two different models for the linear viscoelastic behavior of an asphalt concrete layer. Two models, the Maxwell model and the Kelvin-Voigt model, are generalized. The former is used in ABAQUS and the latter in KENLAYER. As a preliminary step, an appropriate structural model for a flexible pavement structure is developed in ABAQUS by considering linear elastic behavior for all the layers. According to this model, when the depth of a structural model is equal to 6 meters, there is a good agreement between the ABAQUS and KENLAYER results. In this model, the thickness of the pavement is equal to 30 centimeters, and the thickness of the subgrade is equal to 5.7 meters. Then, the viscoelastic behavior is considered for the asphalt concrete layer, and the results from KENLAYER and ABAQUS are compared with each other. The results indicate that the type of viscoelastic model applied to an asphalt concrete layer has a significant effect on the prediction of pavement responses and, logically, the predicted performance of a pavement.

Modeling Deformation Behavior of the Baseball

2005 ◽  
Vol 21 (1) ◽  
pp. 18-30 ◽  
Author(s):  
Rochelle Llewelyn Nicholls ◽  
Karol Miller ◽  
Bruce C. Elliott
Keyword(s):  
Shear Modulus ◽  
Transient Behavior ◽  
Future Research ◽  
Type Model ◽  
Compression Tests ◽  
Element Analysis ◽  
Static Compression ◽  
Linear Viscoelastic Material ◽  
Model C ◽  
Force Displacement

Regulating ball response to impact is one way to control ball exit velocity in baseball. This is necessary to reduce injuries to defensive players and maintain the balance between offense and defense in the game. This paper presents a model for baseball velocity-dependent behavior. Force-displacement data were obtained using quasi-static compression tests to 50% of ball diameter (n = 70 baseballs). The force-displacement curves for a very stiff baseball (Model B) and a softer type (Model C) were characterized by a Mooney-Rivlin model using implicit finite element analysis (ANSYS software, version 6.1). Agreement between experimental and numerical results was excellent for both Model B (C10 = 0, C01 = 3.7e6 Pa) and Model C (C10 = 0, C01 = 2.6e6 Pa). However, this material model was not available in the ANSYS/LSDYNA explicit dynamic software (version 6.1) used to quantify the transient behavior of the ball. Therefore the modeling process was begun again using a linear viscoelastic material. G∞, the long-term shear modulus of the material, was determined by the same implicit FEA procedure. Explicit FEA was used to quantify the time-dependent response of each ball in terms of instantaneous shear modulus (G0) and a decay term (β). The results were evaluated with respect to published experimental data for the ball coefficient of restitution at five velocities (13.4–40.2 ms–1) and were in agreement with the experimental values. The model forms the basis for future research on baseball response to impact with the bat.

Optimization of constitutive model parameters for simulation of polystyrene concrete subjected to impact

2017 ◽  
Vol 9 (2) ◽  
pp. 121-140 ◽  
Author(s):  
Tae Kwang Yoo ◽  
Tong Qiu
Keyword(s):  
Constitutive Model ◽  
Strain Rate ◽  
Rate Sensitivity ◽  
Material Model ◽  
Drop Impact ◽  
Model Parameters ◽  
Compression Tests ◽  
Static Compression ◽  
Impact Tests ◽  
Quasi Static Compression

This article presents the results of a series of experimental testing and numerical modeling studies to optimize the parameters of a constitutive material model to accurately simulate the behavior of polystyrene crushable concrete during impact loading using LS-DYNA. Quasi-static compression tests and confined drop impact tests were conducted. To model the quasi-static compression tests, the response surface methodology was used to optimize Poisson’s ratio and friction angle in the pseudo-tensor model in LS-DYNA. Using the optimized model parameters, the simulated compression stress versus strain relationship showed an excellent agreement with those from the compression tests. To model the confined drop impact tests, the strain rate sensitivity parameter in LS-DYNA was optimized by comparing the drop impact simulations at different strain rate sensitivity values with the drop impact tests. This study suggests that the pseudo-tensor material model is potentially suitable for modeling crushable concrete. Although the optimized constitutive model parameters are specific for the polystyrene concrete mix used in this study, similar approach can be used to optimize model parameters for other polystyrene concrete mixes.

A Single Integral Finite Strain Viscoelastic Model of Ligaments and Tendons

1996 ◽  
Vol 118 (2) ◽  
pp. 221-226 ◽  
Author(s):  
G. A. Johnson ◽  
G. A. Livesay ◽  
S. L-Y. Woo ◽  
K. R. Rajagopal
Keyword(s):  
Finite Strain ◽  
Viscoelastic Model ◽  
Three Dimensional ◽  
Uniaxial Extension ◽  
Viscoelastic Behavior ◽  
Nonlinear Behavior ◽  
Biological Tissues ◽  
Model Parameters ◽  
Three Dimensional Model ◽  
Single Integral

A general continuum model for the nonlinear viscoelastic behavior of soft biological tissues was formulated. This single integral finite strain (SIFS) model describes finite deformation of a nonlinearly viscoelastic material within the context of a three-dimensional model. The specific form describing uniaxial extension was obtained, and the idea of conversion from one material to another (at a microscopic level) was then introduced to model the nonlinear behavior of ligaments and tendons. Conversion allowed different constitutive equations to be used for describing a single ligament or tendon at different strain levels. The model was applied to data from uniaxial extension of younger and older human patellar tendons and canine medial collateral ligaments. Model parameters were determined from curve-fitting stress-strain and stress-relaxation data and used to predict the time-dependent stress generated by cyclic extensions.

Nonlinear Elastic Behavior of Unidirectional Composites With Fiber Waviness Under Compressive Loading

1996 ◽  
Vol 118 (4) ◽  
pp. 561-570 ◽  
Author(s):  
H. M. Hsiao ◽  
I. M. Daniel
Keyword(s):  
Constitutive Relations ◽  
Compressive Loading ◽  
Nonlinear Material ◽  
Elastic Behavior ◽  
Compression Tests ◽  
Fiber Waviness ◽  
Unidirectional Composites ◽  
Nonlinear Stress ◽  
Material Nonlinear ◽  
Nonlinear Elastic

Nonlinear elastic behavior of unidirectional composites with fiber waviness under compressive loading was investigated theoretically and experimentally. Unidirectional carbon/epoxy composites with uniform, graded, and localized fiber waviness were studied. Complementary strain energy was used to derive the material nonlinear stress-strain relations. Nonlinear material properties obtained from shear and longitudinal and transverse compression tests were incorporated into the analysis. Compression tests of specimens with known fiber waviness were conducted to verify the constitutive relations. Experimental results were in good agreement with predictions based on the constitutive model.

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