Rate Data and Material Model Parameter Estimation

1998 ◽  
Vol 120 (1) ◽  
pp. 7-12 ◽  
Author(s):  
A. F. Fossum
Keyword(s):  
Parameter Estimation ◽  
Correlation Coefficients ◽  
Material Model ◽  
Parameter Estimates ◽  
Viscoplastic Material ◽  
Stress Strain ◽  
Material Models ◽  
Response Models ◽  
Strain Data ◽  
Rate Form

Traditionally stress-strain data are used to estimate material parameters in viscoplastic material models. Since the models exist in rate form, they must be integrated in time for the duration of the laboratory tests to give response models for parameter estimation. In this paper the alternative is considered in which the rate form of the material models is fitted to time differentiated stress strain data. Material parameteres, their 95 percent confidence intervals, and their correlation coefficients are compared with their counterparts determined from the more traditional stress versus strain form of the data. It was found that the use of the stress rate form of the data gave well determined parameter estimates with equivalent or superior fitting statistics to the same data can be used to extract significant and distinct sensitivity coefficients to enchance the overall robustness of an optimization algorithm for a parameter estimation.

scholarly journals On a Class of Thermo-Visco-Plastic Constitutive Equations for Semi-Solid Alloys

2008 ◽  
Vol 141-143 ◽  
pp. 653-658 ◽  
Author(s):  
Stefan Benke ◽  
G. Laschet
Keyword(s):  
A356 Alloy ◽  
Material Model ◽  
Viscoplastic Material ◽  
Micro Structure ◽  
Material Models ◽  
Equiaxed Solidification ◽  
Coherency Temperature ◽  
Yield Functions ◽  
Semi Solid ◽  
Solid Alloys

The behavior of semi-solid alloys is quite different in tension, compression and shear and depends strongly on the morphology of the micro-structure. This article outlines a generalized viscoplastic material model for semi-solid alloys which reflects this complex viscoplastic behavior. From the generalized model a number of well known yield functions and viscoplastic material models for semi-solid and solid materials can be reproduces. The general model is applied to describe the behavior of the semi-solid A356 alloy below the coherency temperature during equiaxed solidification.

Critical Buckling Strain in High Strength Steel Pipes Using Isotropic-Kinematic Hardening

2010 ◽  
Author(s):  
A. Fathi ◽  
J. J. Roger Cheng ◽  
Samer Adeeb ◽  
Joe Zhou
Keyword(s):  
Kinematic Hardening ◽  
High Strength ◽  
Material Model ◽  
Test Results ◽  
Stress Strain ◽  
Hardening Material ◽  
Anisotropic Models ◽  
Steel Pipes ◽  
Strain Data ◽  
Critical Buckling Strain

High strength steel pipes (HSSP) have become more popular recently for highly pressurized pipelines built to transport natural gas from remote fields to energy markets. Material tests on HSSP showed significant material anisotropy caused by the pipe making process, UOE. A combined isotropic-kinematic hardening material model is developed based on observations made on longitudinal and transverse stress strain data of HSSP. This material model combines linear isotropic hardening with Armstrong-Fredrick kinematic hardening and can be easily calibrated by longitudinal and transverse tension coupon test results. The proposed material model is used to show how considering material anisotropy affects the critical buckling strain of HSSP in the longitudinal direction. Finite element (FE) models are developed to simulate one pressurized and one unpressurised HSSP tested under monotonic displacement-controlled bending. Isotropic and anisotropic material modeling methods are used for each HSSP models. In the isotropic material model, longitudinal stress-strain data of HSSP material is used to define the stress-strain relationship. In the anisotropic model combined hardening material model, calibrated by longitudinal and transverse HSSP stress-strain data, is used. Critical buckling strain predictions by isotropic and anisotropic models of these pipes are compared with test results and also with some available criteria in standards and literatures. These comparisons show that anisotropic models give predictions closer to test results.

Application Concepts and Experimental Validation of Constitutive Material Models for Creep-Fatigue Assessment of Components

2019 ◽  
Author(s):  
Christian Kontermann ◽  
Stefan Linn ◽  
Matthias Oechsner
Keyword(s):  
Model Development ◽  
Fatigue Loading ◽  
Material Model ◽  
Equation System ◽  
Current Status ◽  
Viscoplastic Material ◽  
Material Models ◽  
Constitutive Material Model ◽  
Creep Fatigue ◽  
Constitutive Material

Abstract The possibility to use real operational data as an input for lifetime assessment methods is a key requirement in terms of both service applications as well as within the design of components by underlying specific service relevant scenarios. To address this, so called “Constitutive Viscoplastic Material Models” have been developed which represent a more generalized alternative for assessing turbo machinery components which undergo an irregular creep-fatigue loading. Based on several experimental and theory related national research programs, performed within the German working group W10 in the last years, the current status of the model development and the performance potentials are summarized in this paper. Within the first part, the general and developed model structure of one candidate material model is introduced by discussing different aspects of the equation system together with the specific practical related aspects. Secondly, the validation of this constitutive material model is shown by comparing the model results with a set of conducted complex experiments, like ansiothermal service like experiments performed on smooth, notched and biaxially loaded cruciform test samples. As the third focus, the applicability and the potential of using such a model for assessing real components will be discussed e.g. by introducing extrapolation or cycle jump concepts which allows to majorly reduce the calculation time without decreasing the result accuracy significantly. Finally, future potentials will be introduced with the goal to use such sophisticated models to train meta-models and finally allow for a machine-learning based on-site and service related on-line component assessment.

Earthquake-induced rock shear through a deposition hole: Laboratory tests on bentonite-material models and modelling of three scale tests

Clay Minerals ◽  
2018 ◽  
Vol 53 (2) ◽  
pp. 213-235
Author(s):  
Lennart Börgesson ◽  
Ann Dueck ◽  
Jan Hernelind
Keyword(s):  
Finite Element ◽  
Laboratory Tests ◽  
Spent Nuclear Fuel ◽  
Material Model ◽  
Spent Fuel ◽  
Stress Strain ◽  
Element Mesh ◽  
Material Models ◽  
Bentonite Buffer ◽  
Nonlinear Stress

ABSTRACTEarthquake-induced rock shear through a bentonite-filled deposition hole in a repository for spent nuclear fuel is an important scenario for the safety analysis because it may cause substantial damage to the canister hosting the spent fuel. Appropriate tools to investigate the effects on the buffer and the canister are required.The study described here explored the laboratory tests conducted to develop a material model of the bentonite buffer to be used in the simulations, the material models that these tests have provided and finite element (FE) simulations of three scale tests of a rock shear for comparison between modelled and measured results. The results were used for validation of the material models and the calculation technique that was used for modelling different rock-shear cases.The laboratory study consisted of swelling-pressure tests and tests to determine shear strength and stress-strain properties. The material model is elastic-plastic with a nonlinear stress-strain relation which depends on the density of the bentonite buffer and is a function of the strain rate. The three scale tests were modelled using theAbaqusfinite element code. Good agreement between modelled and measured results was observed, in spite of the complexity of the models and the difficulties associated with measuring stresses and strains under the very fast shear.The modelling results thus validate the modelling of the SR-Site. The modelling technique, the element mesh and the material models used in these analyses are well fitted and useful for this type of modelling.

Determination of Suitable Hyper Elastic Material Model through Non-Linear Regression Analysis

2018 ◽  
Vol 9 (5) ◽  
Author(s):  
D. Kamalakannan ◽  
V. Arun Baskar ◽  
B. Prabu
Keyword(s):  
Plastic Material ◽  
Biaxial Tension ◽  
Pure Shear ◽  
Linear Regression Analysis ◽  
Material Model ◽  
Good Prediction ◽  
Stress Strain ◽  
Material Models ◽  
Axial Tension ◽  
Hyper Elastic

The material behaviour of elastomers can be simulated through Strain Energy Density (SED) function which can be defined by the following hyper plastic material models: (i) Neo-Hookean, (ii) Mooney-Rivlin, (iii) Yeoh and (iv) Ogden. The stress-strain relations of the above-mentioned SED functions for uni-axial tension, planar (pure shear) tension and equi-biaxial tension are validated with Treloar’s data. Different combinations of Treloar’s data are used to determine the co-efficient of SED functions of the above said models. These co-efficient values are determined using the software like ANSYS, MATLAB and POLYMATH and the validation of the results is carried out based on sum of squared error (SSE) which is calculated between the experimental values and predicted values. From the result, it is found that SSE less than 5 and closer to 0 can be taken as good prediction for selection of material model and co-efficient of material models. The engineering stress-strain behaviour of synthetic rubber (NBR) is obtained experimentally from uni-axial tension test and the co-efficient of SED functions are determined.

Sequential accuracy in parameter estimation for population correlation coefficients.

2019 ◽  
Vol 24 (4) ◽  
pp. 492-515 ◽  
Author(s):  
Ken Kelley ◽  
Francis Bilson Darku ◽  
Bhargab Chattopadhyay
Keyword(s):  
Parameter Estimation ◽  
Correlation Coefficients ◽  
Population Correlation

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.

Experimental Characterization of Mechanical Behavior of Cord-Rubber Composites

1982 ◽  
Vol 10 (1) ◽  
pp. 37-54 ◽  
Author(s):  
M. Kumar ◽  
C. W. Bert
Keyword(s):  
Response Characteristic ◽  
Cord Compression ◽  
Complete Characterization ◽  
Strain Response ◽  
Strain Gages ◽  
Experimental Characterization ◽  
Rubber Composites ◽  
Stress Strain ◽  
Strain Data

Abstract Unidirectional cord-rubber specimens in the form of tensile coupons and sandwich beams were used. Using specimens with the cords oriented at 0°, 45°, and 90° to the loading direction and appropriate data reduction, we were able to obtain complete characterization for the in-plane stress-strain response of single-ply, unidirectional cord-rubber composites. All strains were measured by means of liquid mercury strain gages, for which the nonlinear strain response characteristic was obtained by calibration. Stress-strain data were obtained for the cases of both cord tension and cord compression. Materials investigated were aramid-rubber, polyester-rubber, and steel-rubber.

Sign in / Sign up

Export Citation Format

Share Document