scholarly journals Independent Validation of Generic Specimen Design for Inverse Identification of Plastic Anisotropy

2021 ◽  
Author(s):  
Yi Zhang ◽  
Sam Coppieters ◽  
Sanjay Gothivarekar ◽  
Arne Van de Velde ◽  
Dimitri Debruyne
Keyword(s):  
Model Updating ◽  
Yield Criterion ◽  
Plastic Anisotropy ◽  
Design Procedure ◽  
Ground Truth ◽  
Element Model ◽  
Material Behavior ◽  
Identification Accuracy ◽  
Image Correlation ◽  
Automated Method

Advanced inverse material identification procedures rely on the richness of strain fields generated in a complex specimen. Currently, the design of a complex specimen is mainly based on engineering judgement and experience that are often user-specific. This intuitive approach forms the crux of the problem, addressed in the current research. To this end, the paper embarks on devising a generic and automated method to design mechanical heterogeneous experiments. A notched tensile specimen is optimized to maximize a previously proposed heterogeneity indicator-IT. The effectiveness of this procedure for identifying the anisotropic parameters of the Hill48 yield criterion is validated using two independent methodologies, namely the identifiability method and the Finite Element Model Updating (FEMU) approach to assess the parameter identification quality. The latter approach is based on carefully generated synthetic experiments including the metrological aspects of Digital Image Correlation (DIC) while having access to the ground truth material behavior. For the plane stress Hill48 anisotropic yield criterion, it is shown that the IT-based design procedure correlates with both the identifiability method and the identification accuracy obtained through FEMU.

The influence of sliding velocity and effective stress on the distribution of strain in subglacial till

2020 ◽  
Author(s):  
Dougal Hansen ◽  
Anders Daamsgard ◽  
Lucas Zoet
Keyword(s):  
Effective Stress ◽  
Dynamic Models ◽  
Ground Truth ◽  
Element Model ◽  
Image Correlation ◽  
Sliding Velocity ◽  
Fine Grained ◽  
Ring Shear ◽  
Sample Chamber ◽  
Convex Upward

<p>The distribution of strain in actively deforming subglacial till is an important control on the sliding velocity and sediment transport of soft-bedded glaciers. In situ field observations, laboratory experiments, and numerical simulations have demonstrated that strain accumulation within subglacial till is often greatest at the ice-bed interface and decreases monotonically with depth, forming a convex-upward profile. However, the mechanisms that set the form of the profile and depth of deformation remain unconstrained. Here we systematically test the influence of two independent variables, effective stress and sliding velocity, on the distribution of strain in a fine-grained, sandy till emplaced beneath a layer of moving ice. Laboratory sliding experiments, conducted with a brand-new ring-shear device with a transparent sample chamber, are coupled with two suites of state-of-the-art numerical experiments using 1) a discrete element model and 2) a non-local granular fluidity continuum model designed to emulate till deformation. Five effective stresses and five sliding velocities are tested with the other parameter held constant (velocity and effective stress, respectively). For the ring shear experiments, images of the till bed are acquired at regular intervals, and we quantify the displacement of sediment grains that occurs between image captures using digital image correlation. These experiments represent the first instance where the deformation of till during glacier slip can be observed in real-time and linked directly to its controlling processes. Furthermore, they provide an opportunity to juxtapose the predictions of two new granular dynamic models against empirical observations in a controlled setting, providing an invaluable ground truth for future, larger-scale implementations simulating bedform genesis and soft-bedded glacier dynamics.</p>

Finite element model updating from full-field vibration measurement using digital image correlation

2011 ◽  
Vol 330 (8) ◽  
pp. 1599-1620 ◽  
Author(s):  
Weizhuo Wang ◽  
John E. Mottershead ◽  
Alexander Ihle ◽  
Thorsten Siebert ◽  
Hans Reinhard Schubach
Keyword(s):  
Finite Element ◽  
Digital Image Correlation ◽  
Finite Element Model ◽  
Digital Image ◽  
Model Updating ◽  
Element Model ◽  
Image Correlation ◽  
Vibration Measurement ◽  
Finite Element Model Updating ◽  
Full Field

Identification of a 3D Anisotropic Yield Surface of X70 Pipeline Steel Using a Multi-DIC Setup

2016 ◽  
Author(s):  
Kristof Denys ◽  
Sam Coppieters ◽  
Renaat Van Hecke ◽  
Steven Cooreman ◽  
Dimitri Debruyne
Keyword(s):  
Mechanical Properties ◽  
Digital Image Correlation ◽  
Digital Image ◽  
Model Updating ◽  
Element Model ◽  
Image Correlation ◽  
Finite Element Model Updating ◽  
Line Pipe ◽  
Strain Fields ◽  
Stereo Digital Image Correlation

A new method is proposed combining multiple synchronized digital image correlation setups (multi-DIC) and finite element model updating to identify the hardening behaviour and anisotropy of 23.5 mm thick X70 line pipe steel. Curved tensile samples have been cut from a coil. While performing a tensile test on those samples, the force was obtained from the load cell and the back and front surface strain fields were measured by means of two synchronized stereo digital image correlation setups. The tests on the curved samples are reproduced with FE simulations, applying the same boundary conditions as the experimental setup to obtain the numerical force and strain fields. While simultaneously minimising the discrepancy between the experimentally and numerically obtained force and strain fields, the strain hardening behaviour is identified beyond the point of maximum uniform elongation. A profound understanding of the anisotropy is also mandatory because the hot rolling operation develops substantial anisotropy which has an important influence on the line pipe performance. Due to the 23.5 mm thick steel that is used in this work, it is possible to measure the front and side surfaces with two synchronized stereo digital image correlation setups. Because full field information is available in all 3 material directions (lateral, longitudinal and through thickness direction), a 3D anisotropic yield criterion can be identified. A prerequisite for stable and accurate identification of the yield locus parameters is that the governing parameters are sufficiently sensitive to the experimentally measured response. For this purpose, a double perforated specimen has been designed which includes a side perforation. The latter guarantees the necessary through-thickness information to inversely identify the 3D anisotropic yield function through multi-DIC and finite element model updating. The presented procedure could potentially be used by line pipe manufactures to verify whether the mechanical properties meet the specified requirements. The proposed approach has some advantages compared to conventional methods to determine mechanical properties of large diameter pipe. The curved specimen geometry is modelled in the FE simulation, hence the detrimental effects of flatting the tensile specimen can be avoided. Further, the new approach enables to consider the complete wall thickness as opposed to conventional testing with round bar samples of which a part of the wall thickness is removed during manufacturing.

scholarly journals Experimental and numerical analysis of cord–elastomer composites

2021 ◽  
Author(s):  
Stephan Weiser ◽  
Thomas Lehmann ◽  
Ralf Landgraf ◽  
Niels Goldberg ◽  
Hendrik Donner ◽  
...  
Keyword(s):  
Correlation Method ◽  
Element Model ◽  
Simulation Method ◽  
Material Behavior ◽  
Image Correlation ◽  
Industrial Project ◽  
Inelastic Material ◽  
Deformation Processes ◽  
Elastomer Composites ◽  
Comparison Of The Results

AbstractIn this paper, experimental and numerical investigations on cord–elastomer composites are presented. A finite-element model is introduced, which was developed within the framework of an industrial project. The model is able to simulate an elastomer matrix with inserted cords as load bearing elements and to predict the strains and stresses in cord and elastomer sections. The inelastic material behavior of the elastomer matrix and the yarns is described by corresponding material models suitable for large deformation processes. With the help of a specially developed demonstrator bellows, which is similar to an air spring, the simulation results are compared with experiments. For this purpose, the digital image correlation method is used to determine the deformations on the outer surface of the demonstrator bellows and to calculate the strains on and between the cords. The comparison of the results shows that the employed simulation method is very well suited to predict the strains in these cord–elastomer composites.

scholarly journals Plasticity and Formability of Annealed, Commercially-Pure Aluminum: Experiments and Modeling

Materials ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 4285
Author(s):  
Jinjin Ha ◽  
Johnathon Fones ◽  
Brad L. Kinsey ◽  
Yannis P. Korkolis
Keyword(s):  
Yield Criterion ◽  
Pure Aluminum ◽  
Plastic Anisotropy ◽  
Rate Sensitivity ◽  
Hydraulic Press ◽  
Image Correlation ◽  
Forming Limit ◽  
Isotropic Hardening ◽  
Commercially Pure ◽  
Strain Paths

The plasticity and formability of a commercially-pure aluminum sheet (AA1100-O) is assessed by experiments and analyses. Plastic anisotropy of this material is characterized by uniaxial and plane-strain tension along with disk compression experiments, and is found to be non-negligible (e.g., the r-values vary between 0.445 and 1.18). On the other hand, the strain-rate sensitivity of the material is negligible at quasistatic rates. These results are used to calibrate constitutive models, i.e., the Yld2000-2d anisotropic yield criterion as the plastic potential and the Voce isotropic hardening law. Marciniak-type experiments on a fully-instrumented hydraulic press are performed to determine the Forming Limit Curve of this material. Stereo-type Digital Image Correlation is used, which confirms the proportional strain paths induced during stretching. From these experiments, limit strains, i.e., the onset of necking, are determined by the method proposed by ISO, as well as two methods based on the second derivative. To identify the exact instant of necking, a criterion based on a statistical analysis of the noise that the strain signals have during uniform deformation versus the systematic deviations that necking induces is proposed. Finite element simulation for the Marciniak-type experiment is conducted and the results show good agreement with the experiment.

A Method for Identifying Transverse and Thickness Compressive Modulus of Glass Fiber Reinforced Composites Based on DIC

2021 ◽  
Vol 1027 ◽  
pp. 86-90
Author(s):  
Zhao Yan Liu ◽  
Chuang Liu ◽  
Dong Li ◽  
Ti Ren He
Keyword(s):  
Composite Laminates ◽  
Failure Modes ◽  
Model Updating ◽  
Element Model ◽  
Unidirectional Composite ◽  
Image Correlation ◽  
Glass Fiber Reinforced ◽  
Short Beam ◽  
Beam Shear ◽  
Constitutive Parameters

In this paper, the short beam shear (SBS) test combined with digital image correlation (DIC) and finite element model updating (FEMU) method is conducted for identification the constitutive parameters of unidirectional composite laminates by minimizing the objective function which is established based on the variance of measured strain and numerical calculated strain. This method has the advantages of insensitive to initial value and high identification efficiency. By changing the test parameters, specimens with different principal planes were used in the SBS test and different failure modes achieved. The standard deviation of E22C and E33C was 8.47% and 3.58% respectively. The comparison of the identification results of the same batch of specimens, different principal planes, different failure modes and different ROI shows that the results of constitutive identification using the area directly under the indenter is reliable.

scholarly journals Stiffness Estimation and Equivalence of Boundary Conditions in FEM Models

2021 ◽  
Vol 11 (4) ◽  
pp. 1482
Author(s):  
Róbert Huňady ◽  
Pavol Lengvarský ◽  
Peter Pavelka ◽  
Adam Kaľavský ◽  
Jakub Mlotek
Keyword(s):  
Boundary Condition ◽  
Finite Element ◽  
Boundary Conditions ◽  
Model Updating ◽  
Element Model ◽  
Computational Time ◽  
Stiffness Coefficients ◽  
First Case ◽  
Numerical Approaches

The paper deals with methods of equivalence of boundary conditions in finite element models that are based on finite element model updating technique. The proposed methods are based on the determination of the stiffness parameters in the section plate or region, where the boundary condition or the removed part of the model is replaced by the bushing connector. Two methods for determining its elastic properties are described. In the first case, the stiffness coefficients are determined by a series of static finite element analyses that are used to obtain the response of the removed part to the six basic types of loads. The second method is a combination of experimental and numerical approaches. The natural frequencies obtained by the measurement are used in finite element (FE) optimization, in which the response of the model is tuned by changing the stiffness coefficients of the bushing. Both methods provide a good estimate of the stiffness at the region where the model is replaced by an equivalent boundary condition. This increases the accuracy of the numerical model and also saves computational time and capacity due to element reduction.

A new method for finite element model updating in structural dynamics

2010 ◽  
Vol 24 (7) ◽  
pp. 2137-2159 ◽  
Author(s):  
J.L. Zapico-Valle ◽  
R. Alonso-Camblor ◽  
M.P. González-Martínez ◽  
M. García-Diéguez
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Structural Dynamics ◽  
Model Updating ◽  
Element Model ◽  
New Method ◽  
Finite Element Model Updating
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