scholarly journals In-situ study of strain and texture evolution during continuous strain path change

2021 ◽  
Author(s):  
Sisir Dhara ◽  
Scott Taylor ◽  
Łukasz Figiel ◽  
Darren Hughes ◽  
Barbara Shollock ◽  
...  
Keyword(s):  
Strain Path ◽  
Texture Evolution ◽  
Test Method ◽  
Image Correlation ◽  
Field Strain ◽  
Correlation Technique ◽  
Full Field ◽  
Multi Stage ◽  
Experimental Apparatus ◽  
Strain Path Change

Automotive stamping is a multi-stage process where a sheet material is drawn in first stage and then redrawn, flanged and pierced in subsequent stages. In the first draw stage, continuous strain path change is induced in the material while a discontinuous strain path change occurs when the material is processed in the subsequent stages of a multi-stage stamping operation. The strain path transition can potentially alter the forming limit of the material. Previous research has investigated the effect of the discontinuous mode of strain path change by loading the sample in one strain path, unloading it, then reloading it in a second path. Thus, discontinuous strain path change was obtained. In this work, the effect of continuous strain path change was investigated with a novel experimental design that allowed cruciform samples to change strain path continuously without unloading. The work was carried out in two stages. In the first stage, the design of the cruciform sample was verified with finite element modelling to ensure the occurrence of continuous strain path change and this was validated experimentally using DX54 material by capturing full-field strain measurements data using digital image correlation technique. The size of the experimental apparatus permitted it to be placed inside a scanning electron microscope chamber. In the second stage, the validated test method was used to evaluate microstructural changes during the deformation including full-field strain and texture evolution. The micro-strain evolution showed rotation of strain bands while the texture evolution conveyed grain rotation during continuous strain path change.

scholarly journals Full-Field Strain Measurement and Numerical Analysis of a Microalloyed Steel Subjected to Deformation with Strain Path Change

Materials ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 5543
Author(s):  
Paulina Lisiecka-Graca ◽  
Janusz Majta ◽  
Krzysztof Muszka
Keyword(s):  
Strain Measurement ◽  
Strain Path ◽  
Surface Strain ◽  
Image Correlation ◽  
Bending Test ◽  
Model Parameters ◽  
Full Field ◽  
Advantages And Disadvantages ◽  
Chaboche Model ◽  
Strain Path Change

This study presents an effective technique for taking advantage of the full-field measurement method of Digital Image Correlation (DIC) for the assessment of the strain distribution during the metal forming process when the strain path change was performed. The applied methodology is based on the combination of a numerical simulation for the stress calculation and full-field surface strain measurement in a forward/reverse three-point bending test. In the numerical part, the Chaboche model and dislocation density-based model were selected and verified in terms of the prediction of a softening/hardening effect occurring during strain reversal. The Chaboche model parameters identification procedure, on the basis of a cyclic torsion test, combined with inverse analysis, was also described. The results of the study showed the advantages and disadvantages of both of the analyzed work hardening models. The obtained results were analyzed in the light of the deformation inhomogeneity and reorganization of the dislocation structure during the cyclic deformation test.

scholarly journals Material parameter identification using finite elements with time-adaptive higher-order time integration and experimental full-field strain information

2021 ◽  
Author(s):  
Stefan Hartmann ◽  
Rose Rogin Gilbert
Keyword(s):  
Experimental Data ◽  
Finite Elements ◽  
Parameter Identification ◽  
Material Parameter ◽  
Measurement Data ◽  
Least Square ◽  
Image Correlation ◽  
Field Strain ◽  
Material Parameter Identification ◽  
Full Field

AbstractIn this article, we follow a thorough matrix presentation of material parameter identification using a least-square approach, where the model is given by non-linear finite elements, and the experimental data is provided by both force data as well as full-field strain measurement data based on digital image correlation. First, the rigorous concept of semi-discretization for the direct problem is chosen, where—in the first step—the spatial discretization yields a large system of differential-algebraic equation (DAE-system). This is solved using a time-adaptive, high-order, singly diagonally-implicit Runge–Kutta method. Second, to study the fully analytical versus fully numerical determination of the sensitivities, required in a gradient-based optimization scheme, the force determination using the Lagrange-multiplier method and the strain computation must be provided explicitly. The consideration of the strains is necessary to circumvent the influence of rigid body motions occurring in the experimental data. This is done by applying an external strain determination tool which is based on the nodal displacements of the finite element program. Third, we apply the concept of local identifiability on the entire parameter identification procedure and show its influence on the choice of the parameters of the rate-type constitutive model. As a test example, a finite strain viscoelasticity model and biaxial tensile tests applied to a rubber-like material are chosen.

scholarly journals Identification of the Mechanical Properties of Superconducting Windings Using the Virtual Fields Method

2010 ◽  
Vol 24-25 ◽  
pp. 379-384
Author(s):  
J.H. Kim ◽  
F. Nunio ◽  
Fabrice Pierron ◽  
P. Vedrine
Keyword(s):  
Least Square Method ◽  
Numerical Differentiation ◽  
Tensile Tests ◽  
Least Square ◽  
Image Correlation ◽  
Stereo Image ◽  
Correlation Technique ◽  
Virtual Fields Method ◽  
Displacement Fields ◽  
Full Field

Tensile tests were performed in order to identify the stiffness components of superconducting windings in the shape of rings (also called ‘double pancakes’). The stereo image correlation technique was used for full-field displacement measurements. The strain components were then obtained from the measured displacement fields by numerical differentiation. Because differentiation is very sensitive to spatial noise, the displacement maps were fitted by polynomials before differentiation using a linear least-square method. Then, in the orthotropy basis, the four in-plane stiffnesses of the double pancake were determined using the Virtual Fields Method.

scholarly journals Towards a Planar Cruciform Specimen for Biaxial Characterisation of Polymer Matrix Composites

2010 ◽  
Vol 24-25 ◽  
pp. 115-120 ◽  
Author(s):  
Michael R.L. Gower ◽  
Richard M. Shaw
Keyword(s):  
Strain Distribution ◽  
Stress Raiser ◽  
Test Method ◽  
Image Correlation ◽  
Strain Gauges ◽  
Test Machine ◽  
Element Analysis ◽  
Full Field ◽  
Cruciform Specimen ◽  
Gauge Section

This paper details work undertaken towards the development of a standard test method for the biaxial response of planar cruciform specimens manufactured from carbon fibre-reinforced plastic (CFRP) laminates and subject to tension-tension loading. Achieving true biaxial failure in a cruciform specimen without the need for the inclusion of a stress raiser, such as a hole, in the gauge-section, is a subject attracting much research globally and is by no means a trivial exercise. Coupon designs were modelled using finite element analysis (FEA) in order to predict the stress and strain distributions in the central region of the specimen. An Instron biaxial strong-floor test machine was used to test the specimens. Strain gauges were used to measure the strain in the specimen arms and to assess the degree of bending. Digital image correlation (DIC) was used to measure the full-field strain distribution in the central gauge-section of the specimen and this was compared to values measured using strain gauges. The strain readings obtained from strain gauges, DIC and FEA predictions were in good agreement and showed that the strain distribution was uniform in the central gauge-section, but that strain concentrations existed around the tapered thickness zone. These regions of strain concentration resulted in interlaminar failure and delamination of the laminate propagating into the specimen arms.

Full-Field Displacement and Strain Measurement: Application of Digital Image Correlation to Reinforcement Corrosion Induced Concrete Fracture and Cover Cracking

2015 ◽  
Vol 738-739 ◽  
pp. 889-892
Author(s):  
Qiang Li ◽  
Hong Fa Yu ◽  
Jing Tong
Keyword(s):  
Reinforced Concrete ◽  
Steel Corrosion ◽  
Test Method ◽  
Image Correlation ◽  
Concrete Fracture ◽  
Reinforcement Corrosion ◽  
Full Field ◽  
Rc Structures ◽  
Whole Process ◽  
Cover Cracking

Cracking of the cover concrete due to steel corrosion is considered as one of the major issues of durability of reinforced concrete (RC) structures. This paper tentatively studies the feasibility of DIC to reinforcement corrosion induced concrete fracture and cover cracking measurement. Advantages and limitations of DIC-based non-contact full-field measurement for corrosion induced concrete fracture and cover cracking are discussed. Drawbacks in this test need improvement are pointed out and test method for further study of whole process of simulating the real reinforced concrete cracking is put forward.

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