scholarly journals A Robust Image Processing Algorithm for Optical-Based Stress–Strain Curve Corrections after Necking

2021 ◽  
Author(s):  
Feng Lu ◽  
Tomáš Mánik ◽  
Ida Lægreid Andersen ◽  
Bjørn Holmedal
Keyword(s):  
Surface Roughness ◽  
Finite Element ◽  
Pure Aluminum ◽  
Strain Curve ◽  
Tracking Algorithm ◽  
Ductile Material ◽  
Radius Of Curvature ◽  
Contour Tracking ◽  
Stress Strain Curve ◽  
Stress Strain

AbstractTo determine the stress–strain curve of a ductile material up to the fracture from a tensile test, the necking contour is measured by an optical measurement technique. The radius of the minimal cross-sectional area and the radius of curvature are used as input for analytical necking corrections of the stress–strain curve, as well as for finite element inverse simulations. Due to the increasing surface roughness that develops during testing, a precise determination of the specimen contour is very challenging. This is crucial, since the second derivative is required for estimating the radius of curvature. A dedicated contour-tracking algorithm was developed to deal with the surface roughness and a specimen painted white with black background was found to provide enough contrast. The new algorithm was implemented in a software, which is made available as open source. Tests were made for an isotropic, commercially pure aluminum alloy and for an axisymmetric, peak aged AA6082 alloy, based on image recording by a digital camera and synchronized force measurements. Modeling by finite element simulations was performed to assess the accuracy of analytical corrections of the stress–strain curves by inverse modeling and for designing a robust contour-tracking algorithm.

scholarly journals Transformation of Surface Roughness of Mg Alloy Tubes During Laser Dieless Drawing

2020 ◽  
Vol 29 (11) ◽  
pp. 7736-7743
Author(s):  
Andrij Milenin ◽  
Tsuyoshi Furushima ◽  
Jiří Němeček
Keyword(s):  
Surface Roughness ◽  
Longitudinal Strain ◽  
Maximum Stress ◽  
Experimental Studies ◽  
Strain Curve ◽  
Surface Roughening ◽  
Drawing Process ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Dieless Drawing

AbstractThe paper investigates the transformation of surface roughness of tubes made from magnesium and magnesium alloys as a function of their longitudinal strain during laser dieless drawing. Experimental studies on three materials (AZ31, MgCa08, and pure Mg) have shown that the dependence of roughness on the longitudinal strain is nonlinear and exhibits a minimum. The proposed explanation for this is that the transformation of surface roughness occurs following two mechanisms. The first mechanism involves stretching of the tube and the decreasing of existing roughness with the increasing elongation. The second mechanism is based on the strain-induced surface roughening phenomenon. This mechanism leads to an increase in roughness with the increasing elongation. To analyze these mechanisms, a numerical model of roughness formation is used. It is experimentally shown that the position of the minimum roughness concerning the tube longitudinal strain is correlated with the stress-strain curve of the material under laser dieless drawing conditions. The obtained results provide a practical way to reduce surface roughness of tubes produced by the laser dieless drawing process. According to the proposed method, to achieve minimum roughness, it is necessary to keep the longitudinal strain under a specific value. This value is close to the strain, which corresponds to the maximum stress on the stress-strain curve of the material for temperature and strain rate, corresponding laser dieless drawing conditions.

Significance of Lu¨der’s Plateau on Pipeline Fault Crossing Assessment

2010 ◽  
Author(s):  
Lanre Odina ◽  
Robert J. Conder
Keyword(s):  
Finite Element ◽  
Compressive Strain ◽  
Strain Curve ◽  
Isotropic Hardening ◽  
Flow Rule ◽  
Pipe Material ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Integrity Assessment ◽  
Analytical Approaches

When subjected to permanent ground deformations, buried pipelines may fail by local buckling (wrinkling under compression) or by tensile rupture. The initial assessment of the effects of predicted seismic fault movements on the buried pipeline is performed using analytical approaches by Newmark-Hall and Kennedy et al, which is restricted to cases when the pipeline is put into tension. Further analysis is then undertaken using finite element methods to assess the elasto-plastic response of the pipeline response to the fault movements, particularly the compressive strain limits. The finite element model is set up to account for the geometric and material non-linear parameters. The pipe material behaviour is generally assumed to have a smooth strain hardening (roundhouse) post-yield behaviour and defined using the Ramberg-Osgood stressstrain curve definition with the plasticity modelled using incremental theory with a von Mises yield surface, associated flow rule and isotropic hardening. However, material tests on seamless pipes (X-grade) show that the stress-strain curve typically displays a Lu¨der’s plateau behaviour (yield point elongation) in the post-yield state. The Lu¨der’s plateau curve is considered conservative for pipeline design and could have a significant impact on strain-based integrity assessment. This paper compares the pipeline response from a roundhouse stress-strain curve with that obtained from a pipe material exhibiting Lu¨der’s plateau behaviour and also examines the implications of a Lu¨der’s plateau for pipeline structural integrity assessments.

scholarly journals Determination of Plastic Properties of Polycrystalline Metallic Materials by Nanoindentation – Experiments and Finite Element Simulations

2004 ◽  
Vol 841 ◽  
Author(s):  
Karsten Durst ◽  
Björn Backes ◽  
Mathias Göken
Keyword(s):  
Finite Element ◽  
Strain Curve ◽  
Finite Element Simulations ◽  
Metallic Materials ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Plastic Properties ◽  
Ultrafine Grained ◽  
Indentation Tests

ABSTRACTThe determination of plastic properties of metallic materials by nanoindentation requires the analysis of the indentation process and the evaluation methods. Particular effects on the nanoscale, like the indentation size effect or piling up of the material around the indentation, need to be considered. Nanoindentation experiments were performed on conventional grain sized (CG) as well as on ultrafine-grained (UFG) copper and brass. The indentation experiments were complemented with finite element simulations using the monotonic stress-strain curve as input data. All indentation tests were carried out using cube-corner and Berkovich geometry and thus different amount of plastic strain was applied to the material, according to Tabors theory. We find an excellent agreement between simulations and experiments for the UFG materials from which a representative strain of εB ≈ 0.1 and εcc ≈ 0.2 is determined. With these data, the slope of the stress-strain curve is predicted for all materials down to an indentation depth of 800 nm.

scholarly journals Preservation Methods Influence the Biomechanical Properties of Human Lateral Menisci: An Ex Vivo Comparative Study of 3 Methods

2019 ◽  
Vol 7 (4) ◽  
pp. 232596711984162
Author(s):  
Christophe Jacquet ◽  
Roger Erivan ◽  
Akash Sharma ◽  
Martine Pithioux ◽  
Sebastien Parratte ◽  
...  
Keyword(s):  
Elasticity Modulus ◽  
Tensile Force ◽  
Strain Curve ◽  
Biomechanical Properties ◽  
Ductile Material ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Preservation Methods ◽  
Significant Difference ◽  
The Mean

Background: Three main meniscal preservation methods have been used over the past decade: cryopreservation, freezing, and freezing with gamma irradiation. Hypothesis: All 3 preservation methods will result in similar biomechanical properties as defined by tensile and compression testing. Study Design: Controlled laboratory study. Methods: A total of 24 human lateral menisci were collected from patients who underwent total knee arthroplasty. Inclusion criteria were patients younger than 70 years with primary unilateral (medial) femorotibial knee osteoarthritis. Each meniscus was divided into 2 specimens cross-sectionally. One specimen was systematically cryopreserved and constituted the control (Cy; –140°C), and the other specimen was used for either the simple frozen group (Fr; –80°C) or the frozen+irradiated group (FrI; –80°C + 25-kGy irradiation). Compression and tensile tests were performed to analyze the elasticity modulus (Young modulus) in compression, the elasticity modulus in tension, the tensile force at failure, and the rupture profile of the tensile stress-strain curve. Results: A significant difference in the mean compression elasticity modulus was observed between the Cy and Fr groups (28.86 ± 0.77 vs 37.26 ± 1.08 MPa, respectively; P < .001) and between the Cy and FrI groups (28.86 ± 0.77 vs 45.92 ± 1.09 MPa, respectively; P < .001). A significant difference in the mean tensile elasticity modulus was also observed between the Cy and Fr groups (11.66 ± 0.97 vs 19.97 ± 1.37 MPa, respectively; P = .008) and between the Cy and FrI groups (11.66 ± 0.97 vs 45.25 ± 1.39 MPa, respectively; P < .001). There were no significant differences between the control and study groups in tensile force at failure. The analysis of the stress-strain curve revealed a slow-slope curve with a nonabrupt rupture (ductile material) for the Cy samples versus a clear rupture of the curve for the Fr and FrI samples (more fragile material). Conclusion: Cryopreservation allows for more elastic and less fragile tissue compared with simple freezing or freezing plus irradiation. Clinical Relevance: The study results exhibit the detrimental effect of simple freezing and freezing plus irradiation on human meniscal mechanical properties. If these effects occur in menisci prepared for allograft procedures, important differences could appear in the graft’s mechanical behavior and thus patient outcomes.

scholarly journals Stress-strain curve of pure aluminum in a super large strain range with strain rate and temperature dependency

2017 ◽  
Vol 207 ◽  
pp. 161-166 ◽  
Author(s):  
Yasuhiro Yogo ◽  
Masatoshi Sawamura ◽  
Risa Harada ◽  
Kosei Miyata ◽  
Noritoshi Iwata ◽  
...  
Keyword(s):  
Strain Rate ◽  
Large Strain ◽  
Pure Aluminum ◽  
Strain Curve ◽  
Strain Range ◽  
Temperature Dependency ◽  
Stress Strain Curve ◽  
Stress Strain

scholarly journals Finite Element Analysis of Square RC Columns Confined by Different Configurations of Transverse Reinforcement

2017 ◽  
Vol 11 (1) ◽  
pp. 292-302 ◽  
Author(s):  
Xiang Zeng
Keyword(s):  
Finite Element ◽  
Strain Curve ◽  
Transverse Reinforcement ◽  
Plasticity Model ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Rc Columns ◽  
Rc Structures ◽  
Concrete Damaged Plasticity ◽  
Uniaxial Compressive Stress

Introduction:Square reinforced concrete (RC) columns with the confinement effect of transverse reinforcement perform well in ductility and have been used widely in RC structures. Its behavior is the classic topic of anti-seismic and anti-collapse analysis of RC structures. With the advancement of the finite element (FE) analysis technology, the general-purpose simulation tools such as ABAQUS and ANSYS have been universally used to analyze the behavior of structures and members, where the material constitutive model is a key problem in the analysis.Methods:In this study, a new uniaxial compressive stress-strain curve of the confined concrete considering confinement effect of transverse reinforcement in square RC columns was proposed for the concrete damaged plasticity model in ABAQUS to solve the problem that there is no proper uniaxial compressive stress-strain curve for the concrete damaged plasticity model to describe the behavior of concrete confined by transverse reinforcement. Based on the proposed stress-strain relationship, a FE model was developed to analyze the behaviour of laterally confined RC columns under concentric loading.Results:The finite element model is able to predict the response of the confined RC columns from different experiments with reasonable accuracy. Finally, a parametric study was conducted in order to evaluate the effect of confinement reinforcement configuration on the behavior of core concrete in square section.

scholarly journals Finite Element Analysis on a Newly-Modified Method for the Taylor Impact Test to Measure the Stress-Strain Curve by the Only Single Test Using Pure Aluminum

Metals ◽  
2018 ◽  
Vol 8 (8) ◽  
pp. 642 ◽  
Author(s):  
Chong Gao ◽  
Takeshi Iwamoto
Keyword(s):  
Finite Element ◽  
Impact Test ◽  
Pure Aluminum ◽  
Strain Curve ◽  
Hopkinson Pressure Bar ◽  
Stress Strain ◽  
Hardening Law ◽  
Taylor Impact ◽  
Taylor Impact Test ◽  
Pressure Bar

In this study, finite element analyses are performed to obtain a stress-strain curve for ductile materials by a combination between the distributions of axial stress and strain at a certain time as a result of one single Taylor impact test. In the modified Taylor impact test proposed here, a measurement of the external impact force by the Hopkinson pressure bar placed instead of the rigid wall, and an assumption of bi-linear distribution of an axial internal force, are introduced as well as a measurement of deformed profiles at certain time. In order to obtain the realistic results by computations, at first, the parameters in a nonlinear rate sensitive hardening law are identified from the quasi-static and impact tests of pure aluminum at various strain rates and temperature conducted. In the impact test, a miniaturized testing apparatus based on the split Hopkinson pressure bar (SHPB) technique is introduced to achieve a similar level of strain rate as 104 s−1, to the Taylor test. Then, a finite element simulation of the modified test is performed using a commercial software by using the user-subroutine for the hardening law with the identified parameters. By comparing the stress-strain curves obtained by the proposed method and direct calculation of the hardening law, the validity is discussed. Finally, the feasibility of the proposed method is studied.

scholarly journals Non-linear finite element analysis of a Ti6Al4V/Inconel 625 joint obtained by explosion welding for sub-sea applications

2021 ◽  
Vol 38 (1) ◽  
pp. 13-16
Author(s):  
Pasqualino Corigliano
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Strain Curve ◽  
Explosion Welding ◽  
Inconel 625 ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Element Analysis ◽  
Linear Finite Element ◽  
Non Linear

Industries have shown interest in the use of dissimilar metals to make corrosion-resistant materials combined with good mechanical properties in marine environments. Explosive welding can be considered a good method for joining dissimilar materials to prevent galvanic corrosion. The aim of the present study was to simulate the non-linear behaviour of a Ti6Al4V/Inconel 625 welded joint obtained by explosion welding from the values of the tensile ultimate strength and yielding strength of the parent materials. The present study compared the stress-strain curve from tensile loading obtained by the non-linear finite element analysis with the experimental stress-strain curve of a bimetallic joint. The applied method provides useful information for the development of models and the prediction of the structural behaviour of Ti6Al4V/Inconel 625 explosive welded joints.

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