Identification of Stress-Strain Relation of Aluminium Foam Cell Wall by Spherical Nanoindentation

2014 ◽  
Vol 606 ◽  
pp. 11-14 ◽  
Author(s):  
Vlastimil Králík ◽  
Jiří Němeček ◽  
Petr Koudelka
Keyword(s):  
Cell Walls ◽  
Foam Cell ◽  
Plastic Material ◽  
Aluminium Foam ◽  
Analytical Models ◽  
Spherical Indentation ◽  
Isotropic Hardening ◽  
Stress Strain Relation ◽  
Indentation Tests ◽  
Constitutive Parameters

The aim of this paper is to identify, in addition to elastic properties, inelastic properties of tiny aluminium foam cell walls that can be directly deduced from the loaddepth curves of spherical indentation tests using formulations of the representative strain and stress. Constitutive parameters related to plastic material with linear isotropic hardening, the yield point (122 ± 17 MPa) and tangent modulus (950 ± 377 MPa), were obtained in this work. Spherical indentation and uniaxial tension experiments have also been performed on a standard aluminium alloy EN AW 6060 to explore the accuracy of the analytical models used to predict the uniaxial stressstrain in wide strain ranges. Some deviations received from different tests arose and, therefore, their effect on the evaluation of inelastic properties was discussed.

Local Mechanical Characterization of Metal Foams by Nanoindentation

2015 ◽  
Vol 662 ◽  
pp. 59-62 ◽  
Author(s):  
Jiří Němeček ◽  
Vlastimil Kralik
Keyword(s):  
Cell Walls ◽  
Plastic Material ◽  
Spherical Indentation ◽  
Isotropic Hardening ◽  
Plastic Properties ◽  
Macro Scale ◽  
Static Indentation ◽  
Indentation Tests ◽  
Constitutive Parameters

This paper deals with microstructure and micromechanical properties of two commercially available aluminium foams (Alporas and Aluhab). Since none of the materials is available in a bulk and standard mechanical testing at macro-scale is not possible the materials need to be tested at micro-scale. To obtain both elastic and plastic properties quasi-static indentation was performed with two different indenter geometries (Berkovich and spherical tips). The material phase properties were analyzed with statistical grid indentation method and micromechanical homogenization was applied to obtain effective elastic wall properties. In addition, effective inelastic properties of cell walls were identified with spherical indentation. Constitutive parameters related to elasto-plastic material with linear isotropic hardening (the yield point and tangent modulus) were directly deduced from the load–depth curves of spherical indentation tests using formulations of the representative strain and stress introduced by Tabor.

A study on determination of tensile properties of metals at elevated temperatures from spherical indentation tests

2019 ◽  
Vol 54 (5-6) ◽  
pp. 331-347
Author(s):  
Tairui Zhang ◽  
Shang Wang ◽  
Weiqiang Wang
Keyword(s):  
Tensile Properties ◽  
Analytical Model ◽  
Elevated Temperatures ◽  
Regression Function ◽  
Maximum Error ◽  
Analytical Models ◽  
Uniaxial Tensile ◽  
Spherical Indentation ◽  
Material Parameters ◽  
Indentation Tests

In this study, spherical indentation tests were used to determine the uniaxial tensile properties of metals at elevated temperatures (200 °C, 400 °C, and 600 °C). Taking the difference between spherical indentation tests at room and elevated temperatures into consideration, the incremental and analytical models were used to determine material parameters ( σ0, Ep, and n) and thermal softening parameters ( Eeff and m) in the Johnson–Cook constitutive equation, respectively. A discussion on the stability of the analytical model proved that despite in relative complicated forms and with three intercoupling material parameters, the analytical model is still effective for tensile property calculation. From the investigation on the relationship between pm and pi, it was found that correlating coefficient ξ is actually a function of both indentation depth and material parameters, and thus, a regression function was proposed for a more accurate description of ξ. Effectiveness of the spherical indentation tests was verified through experiments on three steels, SA508, 15CrMoR, S30408, and one titanium alloy, TC21, which proved that the spherical indentation tests can provide both proof and tensile strength calculations with a maximum error around 15% at room temperature and within 20% at elevated temperatures, and thus satisfy the demands for engineering applications.

Spherical indentation of ductile power law materials

2004 ◽  
Vol 19 (9) ◽  
pp. 2641-2649 ◽  
Author(s):  
Roberta Mulford ◽  
Robert J. Asaro ◽  
Robert J. Sebring
Keyword(s):  
Power Law ◽  
Contact Surface ◽  
Indentation Test ◽  
Strain Curve ◽  
Spherical Indentation ◽  
Actual Contact ◽  
Indentation Tests ◽  
Surface Profiles ◽  
Constitutive Parameters ◽  
Versus Strain

A procedure for extracting simple constitutive parameters from microindentationtests is described. The analysis used to interpret the indentation tests is based onthe analysis of the spherical indentation test developed by Hill et al. for power law materials. Indentation tests are supplemented by scanning interference microscopyof the residual indented surface profiles and a method is suggested for using the residual surface profiles to estimate the actual contact surface. This, in turn, allowsfor the construction of the entire stress versus strain curve.

A Comparison of EFGM and FEM for Nonlinear Solid Mechanics Problems

2013 ◽  
Vol 535-536 ◽  
pp. 434-437
Author(s):  
Rajesh Kumar ◽  
Indra Vir Singh ◽  
B.K. Mishra ◽  
R. Cardoso ◽  
J.W. Yoon
Keyword(s):  
Solid Mechanics ◽  
Plastic Material ◽  
Isotropic Hardening ◽  
Test Problems ◽  
Flow Rule ◽  
Stress Strain Relation ◽  
Nonlinear Solid Mechanics ◽  
Updated Lagrangian Approach ◽  
Updated Lagrangian ◽  
Element Free

In this paper, element free Galerkin method (EFGM) has been applied to solve nonlinear solid mechanics problems using updated Lagrangian approach. The nonlinear equations have been solved using Newton Raphson method. An associative J2 flow rule and isotropic hardening has been used for the modelling of elasto-plastic material behaviour. Elastic predictor and plastic corrector algorithm has been used for the integration of incremental stress-strain relation. Few test problems involving large deformations have been simulated and the results obtained by EFGM have been compared with those obtained by FEM.

Identification of Hardening Parameters of Metals From Spherical Indentation Tests

2001 ◽  
Vol 123 (3) ◽  
pp. 245-250 ◽  
Author(s):  
S. Kucharski ◽  
Z. Mro´z
Keyword(s):  
Indentation Test ◽  
Strain Curve ◽  
Load Level ◽  
Spherical Indentation ◽  
Indentation Tests ◽  
Geometric Sequence ◽  
Loading And Unloading ◽  
Plastic Hardening ◽  
Hardening Curve ◽  
Two Parameters

The identification method of hardening parameters specifying stress-strain curve is proposed by applying spherical indentation test and measuring the penetration depth during loading and unloading. The loading program is composed of a geometric sequence of loading and partial unloading steps from which the variation of permanent penetration with load level is determined. This data is used for specification of two parameters k and m occurring in the plastic hardening curve εp=σ/k1/m, where εp denotes the plastic strain.

scholarly journals Stress-Softening in Particle-Filled Polyurethanes under Cyclic Compressive Loading

Polymers ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 1588
Author(s):  
Wenshuai Xu ◽  
Mangong Zhang ◽  
Yu Liu ◽  
Hao Zhang ◽  
Meng Chen ◽  
...  
Keyword(s):  
Compressive Loading ◽  
Compressive Load ◽  
Soft Materials ◽  
Constitutive Parameter ◽  
Spherical Indentation ◽  
Mullins Effect ◽  
Stress Softening ◽  
Loading And Unloading ◽  
Load Displacement ◽  
Constitutive Parameters

Elastomer compositions containing various particulate fillers can be formulated according to the specific functions required of them. Stress softening—which is also known as the Mullins effect—occurs during high loading and unloading paths in certain supramolecular elastomer materials. Previous experiments have revealed that the load–displacement response differs according to the filler used, demonstrating an unusual model of correspondence between the constitutive materials. Using a spherical indentation method and numerical simulation, we investigated the Mullins effect on polyurethane (PU) compositions subjected to cyclic uniaxial compressive load. The PU compositions comprised rigid particulate fillers (i.e., nano-silica and carbon black). The neo-Hooke model and the Ogden–Roxburgh Mullins model were used to describe the nonlinear deformation behavior of the soft materials. Based on finite element methods and parameter optimization, the load–displacement curves of various filled PUs were analyzed and fitted, enabling constitutive parameter prediction and inverse modeling. Hence, correspondence relationships between material components and constitutive parameters were established. Such relationships are instructive for the preparation of materials with specific properties. The method described herein is a more quantitative approach to the formulation of elastomer compositions comprising particulate fillers.

Numerical Investigation of Heat Partition in the Primary Shear Zone in Metal Cutting

2005 ◽  
Author(s):  
Vasant Pednekar ◽  
Vis Madhavan ◽  
Amir H. Adibi-Sedeh
Keyword(s):  
Partition Coefficient ◽  
Strain Rate ◽  
Shear Zone ◽  
Metal Cutting ◽  
Plastic Material ◽  
Shear Plane ◽  
Analytical Models ◽  
Machined Surface ◽  
Element Analysis ◽  
Heat Partition

The fraction of heat generated in the primary shear zone that is conducted into the workpiece is a key factor in the calculation of the shear plane temperature and in calculating the cutting forces based on material flow stress. Accurate analytical, numerical, or experimental determination of this heat partition coefficient is not available to date. This study utilizes a new approach to obtain the heat partition coefficient for the primary shear zone using results for strain, strain rate, and temperature distribution obtained from a coupled thermo-mechanical finite element analysis of machining. Different approaches, using strain rate and equivalent strain, are used for calculating the total plastic power in the primary shear zone and the heat generated by plastic deformation below the plane of the machined surface. The heat carried away by the workpiece is obtained by calculating the heat flow by convection in regions where the conduction is expected to be small. We have used an elastic perfectly plastic material model and constant thermal properties to mimic the assumptions used in analytical models. The fraction of the total heat generated in the primary shear zone that is conducted into the machined workpiece is found and compared to the prediction of different analytical models. It is found that for most of the cutting conditions, the values of heat partition coefficient are closest to those provided by Weiner’s model.

Application of Advanced Constitutive Models to the Simulation of Machining

2009 ◽  
Author(s):  
David A. Miller ◽  
Cameron K. Chen
Keyword(s):  
Elevated Temperatures ◽  
High Strain ◽  
Plastic Material ◽  
Constitutive Models ◽  
Surface Damage ◽  
Machining Process ◽  
Material Response ◽  
Tension And Compression ◽  
Split Hopkinson ◽  
Constitutive Parameters

Advanced constitutive models have long been used to describe plastic material response at high strains and high strain rates. These models include the Johnson-Cook, Zerrelli-Armstrong and Material Threshold Stress (MTS) formulations, each with a separate fidelity. The constitutive parameters for these complex models are commonly identified using laboratory techniques such as quasi-static load frames at room and elevated temperatures, Split Hopkinson Pressure Bars (SHPB) in tension and compression, gas guns, and Taylor impact cylinders. However, while the models are able to adequately describe material response under high strain and high strain rate, the loadings are all uniaxial in nature. The ability of these constitutive models and parameters to describe a different dynamic loading event, namely shear dominated machining, has not been thoroughly investigated. This work will develop numerical simulations applying multiple constitutive models with material parameters experimentally determined for fully annealed copper samples. Ultimately, the machining simulation will be compared with high fidelity experimental machining data. The utility of this research extends to the fundamental questions that surround the machining process, such as tool forces, surface damage, precision and quality.

Stress Analysis of SS316L Tube Die Expansion for High Pressure Gas Coolers

2020 ◽  
Author(s):  
Zijian Zhao ◽  
Abdel-Hakim Bouzid
Keyword(s):  
Residual Stress ◽  
High Pressure ◽  
Plastic Material ◽  
Research Work ◽  
Material Behavior ◽  
Isotropic Hardening ◽  
Plastic Behavior ◽  
Expansion Process ◽  
Elastic Plastic ◽  
Stress States

Abstract SS316L finned tubes are becoming very popular in high-pressure gas exchangers and particularly in CO2 cooler applications. Due to the high-pressure requirement during operation, these tubes require an accurate residual stress evaluation during the expansion process. Indeed, die expansion of SS tubes creates not only high stresses when combined with operation stresses but also micro-cracks during expansion when the expansion process is not very well controlled. This research work aims at studying the elastic-plastic behavior and estimating the residual stress states by modeling the die expansion process. The stresses and deformations of the joint are analyzed numerically using the finite element method. The expansion and contraction process is modeled considering elastic-plastic material behavior for different die sizes. The maximum longitudinal, tangential and contact stresses are evaluated to verify the critical stress state of the joint during the expansion process. The importance of the material behavior in evaluating the residual stresses using kinematic and isotropic hardening is addressed.

scholarly journals Numerical verification for instrumented spherical indentation techniques in determining the plastic properties of materials

2009 ◽  
Vol 24 (12) ◽  
pp. 3653-3663 ◽  
Author(s):  
Taihua Zhang ◽  
Peng Jiang ◽  
Yihui Feng ◽  
Rong Yang
Keyword(s):  
Numerical Experiments ◽  
Spherical Indentation ◽  
Numerical Verification ◽  
Instrumented Indentation ◽  
Plastic Properties ◽  
Wide Range ◽  
Validity Range ◽  
Indentation Tests ◽  
Properties Of Materials ◽  
Indentation Methods

Instrumented indentation tests have been widely adopted for elastic modulus determination. Recently, a number of indentation-based methods for plastic properties characterization have been proposed, and rigorous verification is absolutely necessary for their wide application. In view of the advantages of spherical indentation compared with conical indentation in determining plastic properties, this study mainly concerns verification of spherical indentation methods. Five convenient and simple models were selected for this purpose, and numerical experiments for a wide range of materials are carried out to identify their accuracy and sensitivity characteristics. The verification results show that four of these five methods can give relatively accurate and stable results within a certain material domain, which is defined as their validity range and has been summarized for each method.

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