Inverse analysis and DIC as tools to determine material parameters in isotropic metal plasticity models with isotropic strain hardening

2016 ◽  
Vol 58 (10) ◽  
pp. 818-825 ◽  
Author(s):  
Marcin Gajewski ◽  
Łukasz Kowalewski
Keyword(s):  
Strain Hardening ◽  
Inverse Analysis ◽  
Metal Plasticity ◽  
Material Parameters ◽  
Isotropic Metal

scholarly journals Cure Kinetics and Inverse Analysis of Epoxy-Amine Based Adhesive Used for Fastening Systems

Materials ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 3853
Author(s):  
Bilen Emek Abali ◽  
Michele Zecchini ◽  
Gilda Daissè ◽  
Ivana Czabany ◽  
Wolfgang Gindl-Altmutter ◽  
...  
Keyword(s):  
Inverse Analysis ◽  
Building Materials ◽  
Cure Kinetics ◽  
Accurate Estimation ◽  
Curing Process ◽  
Degree Of Cure ◽  
Material Parameters ◽  
Epoxy Amine ◽  
Thermosetting Polymers ◽  
Material Equation

Thermosetting polymers are used in building materials, for example adhesives in fastening systems. They harden in environmental conditions with a daily temperature depending on the season and location. This curing process takes hours or even days effected by the relatively low ambient temperature necessary for a fast and complete curing. As material properties depend on the degree of cure, its accurate estimation is of paramount interest and the main objective in this work. Thus, we develop an approach for modeling the curing process for epoxy based thermosetting polymers. Specifically, we perform experiments and demonstrate an inverse analysis for determining parameters in the curing model. By using calorimetry measurements and implementing an inverse analysis algorithm by using open-source packages, we obtain 10 material parameters describing the curing process. We present the methodology for two commercial, epoxy based products, where a statistical analysis provides independence of material parameters leading to the conclusion that the material equation is adequately describing the material response.

scholarly journals On the recovery of the stress-free configuration of the human cornea

2020 ◽  
Vol 2 (4) ◽  
pp. 11-33
Author(s):  
Anna Pandolfi ◽  
Andrea Montanino
Keyword(s):  
Numerical Simulations ◽  
Inverse Analysis ◽  
Material Model ◽  
Free State ◽  
Human Cornea ◽  
Material Models ◽  
Material Parameters ◽  
Optimal Values ◽  
Stress Free State ◽  
Actual Stress

Purpose: The geometries used to conduct numerical simulations of the biomechanics of the human cornea are reconstructed from images of the physiological configuration of the system, which is not in a stress-free state because of the interaction with the surrounding tissues. If the goal of the simulation is a realistic estimation of the mechanical engagement of the system, it is mandatory to obtain a stress-free configuration to which the external actions can be applied. Methods: Starting from a unique physiological image, the search of the stress-free configuration must be based on methods of inverse analysis. Inverse analysis assumes the knowledge of one or more geometrical configurations and, chosen a material model, obtains the optimal values of the material parameters that provide the numerical configurations closest to the physiological images. Given the multiplicity of available material models, the solution is not unique. Results: Three exemplary material models are used in this study to demonstrate that the obtained, non-unique, stress-free configuration is indeed strongly dependent on both material model and on material parameters. Conclusion: The likeliness of recovering the actual stress-free configuration of the human cornea can be improved by using and comparing two or more imaged configurations of the same cornea.

A New Global Optimization Algorithm and its Application

2008 ◽  
Vol 33-37 ◽  
pp. 1407-1412
Author(s):  
Ying Hui Lu ◽  
Shui Lin Wang ◽  
Hao Jiang ◽  
Xiu Run Ge
Keyword(s):  
Global Optimization ◽  
Objective Function ◽  
Optimization Algorithm ◽  
Inverse Analysis ◽  
Optimization Problem ◽  
Practical Application ◽  
Global Optimization Algorithm ◽  
Material Parameters ◽  
Non Linear ◽  
Variable Space

In geotechnical engineering, based on the theory of inverse analysis of displacement, the problem for identification of material parameters can be transformed into an optimization problem. Commonly, because of the non-linear relationship between the identified parameters and the displacement, the objective function bears the multimodal characteristic in the variable space. So to solve better the multimodal characteristic in the non-linear inverse analysis, a new global optimization algorithm, which integrates the dynamic descent algorithm and the modified BFGS (Brogden-Fletcher-Goldfrab-Shanno) algorithm, is proposed. Five typical multimodal functions in the variable space are tested to prove that the new proposed algorithm can quickly converge to the best point with few function evaluations. In the practical application, the new algorithm is employed to identify the Young’s modulus of four different materials. The results of the identification further show that the new proposed algorithm is a very highly efficient and robust one.

scholarly journals Characterizing Heterogeneous Properties of Cerebral Aneurysms With Unknown Stress-Free Geometry: A Precursor to In Vivo Identification

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
Xuefeng Zhao ◽  
Madhavan L. Raghavan ◽  
Jia Lu
Keyword(s):  
Inverse Analysis ◽  
Cerebral Aneurysms ◽  
Strain Energy Function ◽  
Metric Tensor ◽  
Tissue Properties ◽  
Material Parameters ◽  
Biomechanical Behavior ◽  
Aneurysm Wall ◽  
Nodal Displacements

Knowledge of elastic properties of cerebral aneurysms is crucial for understanding the biomechanical behavior of the lesion. However, characterizing tissue properties using in vivo motion data presents a tremendous challenge. Aside from the limitation of data accuracy, a pressing issue is that the in vivo motion does not expose the stress-free geometry. This is compounded by the nonlinearity, anisotropy, and heterogeneity of the tissue behavior. This article introduces a method for identifying the heterogeneous properties of aneurysm wall tissue under unknown stress-free configuration. In the proposed approach, an accessible configuration is taken as the reference; the unknown stress-free configuration is represented locally by a metric tensor describing the prestrain from the stress-free configuration to the reference configuration. Material parameters are identified together with the metric tensor pointwisely. The paradigm is tested numerically using a forward-inverse analysis loop. An image-derived sac is considered. The aneurysm tissue is modeled as an eight-ply laminate whose constitutive behavior is described by an anisotropic hyperelastic strain-energy function containing four material parameters. The parameters are assumed to vary continuously in two assigned patterns to represent two types of material heterogeneity. Nine configurations between the diastolic and systolic pressures are generated by forward quasi-static finite element analyses. These configurations are fed to the inverse analysis to delineate the material parameters and the metric tensor. The recovered and the assigned distributions are in good agreement. A forward verification is conducted by comparing the displacement solutions obtained from the recovered and the assigned material parameters at a different pressure. The nodal displacements are found in excellent agreement.

The Effects of Material Properties on Crack Tip Constraint and CTOD Fracture Toughness for Commonly Used Pipelines Steels

2020 ◽  
Author(s):  
Yinhui Zhang ◽  
Jian Shuai
Keyword(s):  
Fracture Toughness ◽  
Yield Strength ◽  
Strain Hardening ◽  
Oil And Gas ◽  
Volume Fraction ◽  
Petroleum Industry ◽  
Void Volume Fraction ◽  
Void Volume ◽  
Strain Hardening Exponent ◽  
Material Parameters

Abstract As the main transportation carrier of oil and gas, pipelines play a very important role in the petroleum industry. When the crack-containing pipelines subjected to external loads, the cracks may propagate gradually, and result in serious failure eventually. Therefore, accurately obtaining the fracture toughness is very essential for the safety assessment of the crack-containing pipelines. However, the fracture toughness is not a material intrinsic parameter, but heavily depends on the constraint. To obtain the accurate relationship between the constraint and the fracture toughness for different materials, it is necessary to determine the effects of different material parameters on the change characteristics of the constraint and the fracture toughness. In this work, the commonly used pipelines steels are selected as the research materials. The SENB specimens and the complete Gurson model are used to conduct the simulation with ABAQUS. The material parameters analyzed include strain hardening exponent, yield strength and initial void volume fraction. The results show that for the thinner specimen, the higher strain hardening capacity will result in lower constraint. The higher strain hardening capacity will result in higher constraint for the thicker specimen. For the thinner specimen, the constraint is approximately the same for the materials with different yield strength. The constraint will decrease with the increase of yield strength for the thicker specimen. In the middle range of the thickness of specimen, higher initial void volume fraction will result in higher constraint. For the thicker and thinner specimen, the effect of initial void volume is very weak. As the increase of strain hardening capacity and yield strength, the decreasing degree of the fracture toughness becomes higher in the increasing process of the constraint. A higher initial void volume will result in a lower decreasing degree of the fracture toughness. All of the results indicate that the strain hardening capacity is the main factor affecting the constraint and the fracture toughness. The initial void volume also has a significant effect on the fracture toughness. For the relationship between the constraint and the fracture toughness, the main affecting factor is the strain hardening capacity.

A full-range stress-strain model for metallic materials depicting non-linear strain-hardening behavior

2020 ◽  
pp. 030932472095779
Author(s):  
Digendranath Swain ◽  
S Karthigai Selvan ◽  
Binu P Thomas ◽  
Ahmedul K Asraff ◽  
Jeby Philip
Keyword(s):  
Constitutive Model ◽  
Strain Hardening ◽  
Image Correlation ◽  
Linear Strain ◽  
Stress Strain ◽  
Material Parameters ◽  
Hardening Behavior ◽  
Non Linear ◽  
Strain Hardening Behavior ◽  
Strain Model

Ramberg-Osgood (R-O) type stress-strain models are commonly employed during elasto-plastic analysis of metals. Recently, 2-stage and 3-stage R-O variant models have been proposed to replicate stress-strain behavior under large plastic deformation. The complexity of these models increases with the addition of each stage. Moreover, these models have considered deformation till necking only. In this paper, a simplistic multi-stage constitutive model is proposed to capture the strain-hardening non-linearity shown by metals including its post necking behavior. The constitutive parameters of the proposed stress-strain model can be determined using only elastic modulus and yield strength. 3-D digital image correlation was used as an experimental tool for measuring full-field strains on the specimens, which were subsequently utilized to obtain the material parameters. Our constitutive model is demonstrated with an aerospace-grade stainless steel AISI 321 wherein deformation response averaged over the gauge length (GL) and at a local necking zone are compared. The resulting averaged and local material parameters obtained from the proposed model provide interesting insights into the pre and post necking deformation behavior. Our constitutive model would be useful for characterizing highly ductile metals which may or may not depict non-linear strain hardening behavior including their post necking deformations.

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