ASSESSMENT OF THE INFLUENCE OF R-PHASE FORMATION ON THE MATERIAL BEHAVIOR OF NiTi USING A MICROMECHANICAL MODEL

2012 ◽  
Vol 05 (01) ◽  
pp. 1250015 ◽  
Author(s):  
RAINER HEINEN ◽  
SHORASH MIRO
Keyword(s):  
Phase Transformation ◽  
Energy Dissipation ◽  
Phase Formation ◽  
Energy Minimization ◽  
Micromechanical Model ◽  
Strain Curve ◽  
Material Behavior ◽  
Cell Geometry ◽  
Stress Strain Curve ◽  
Geometrical Change

Shape memory alloys (SMA) show several interesting features in their material behavior which are due to martensitic phase transformation. In NiTi , this transformation covers the three crystallographic phases of austenite, martensite, and R-phase. This publication analyzes the influence of the R-phase formation on the overall material behavior by means of a micromechanical model. The model is based on energy minimization with the assumption of a certain energy dissipation when martensite is formed. To simplify the formulation, the dissipation associated with the transformation between austenite and R-phase is neglected, since the geometrical change in unit cell geometry is relatively small in this case. Numerical simulations show that especially the slope reduction in the stress–strain curve, which is known from experiments, can be explained by R-phase formation.

scholarly journals Analysis of damage-plasticity model of concrete under uniaxial compression loading

2021 ◽  
Vol 10 (1) ◽  
pp. 29
Author(s):  
Mohammad Rafiqul Islam ◽  
Abbas Ali ◽  
Md. Jahir Bin Alam ◽  
Tanvir Ahmad ◽  
Salman Sakib
Keyword(s):  
Analytical Data ◽  
Strain Curve ◽  
Material Behavior ◽  
Elastic Behavior ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Compression Loading ◽  
Model Code ◽  
Concrete Damage ◽  
Two Phases

Concrete is a quasi-brittle material and shows different behavior in compression and tension. It shows elastic behavior at initial stage and damage-plasticity behavior beyond elastic limit. Therefore, development of material behavior model of concrete is a complex phenomenon. In this study, concrete damage plasticity theory has been described under experiment on concrete cylinder considering uni-axial compression loading and interpreted with analytical data calculated using CEB-FIP model code equation. The code has divided the stress-strain curve for concrete compression into three sections according to concrete’s elastic and non-elastic behaviors. Those three sections have been considered to calculate analytical data. In experiment, concrete behavior has been observed in two phases. The damage value for different stresses at the various points on the stress strain curve has been calculated. According to analytical data, the concrete shows elastic behavior up to 8.3MPa stress point and no damage occur in the concrete within the limit. However, in experimental data, concrete shows elastic behavior up to only 2.28MPa and damage occurred beyond the stress. Finally, the percentage of damage of concrete due to compression obtained from analysis and experiment has been assessed and compared. Above 32 percent of concrete damage is found for 22.5 MPa in both cases.  

A new loading history for identification of viscoplastic properties by spherical indentation

2004 ◽  
Vol 19 (1) ◽  
pp. 101-113 ◽  
Author(s):  
N. Huber ◽  
E. Tyulyukovskiy
Keyword(s):  
Strain Curve ◽  
Material Behavior ◽  
Creep Process ◽  
Spherical Indentation ◽  
Loading History ◽  
Viscoplastic Material ◽  
Stress Strain Curve ◽  
Material Parameters ◽  
Depth Data ◽  
Variable Combination

In this paper a new loading history for extracting the stress–strain curve as well as the viscosity and creep behavior from indentation experiments is developed. It is based on a simple model describing the viscoplastic spherical indentation with a power-law hardening rule and a velocity-dependent overstress. Using this model, patterns were generated consisting of load-depth data and corresponding material parameters. The loading history for the simulation of the patterns was considered as a variable combination of loading and creep processes. To compare the identification potential of different loading histories, the inverse problem of determining the viscoplastic material parameters was solved by using neural networks. The emerging loading history uses a multiple-creep process with equidistant load steps and allows an identification of material parameters with much higher accuracy than with single creep. It will be used for further work, where the identification method is generalized using more realistic finite element simulations for a finite deformation elastic–viscoplastic material behavior.

Elastoplastic behavior of the metal matrix nanocomposites containing carbon nanotubes: A micromechanics-based analysis

2017 ◽  
Vol 233 (4) ◽  
pp. 676-686 ◽  
Author(s):  
M Haghgoo ◽  
R Ansari ◽  
MK Hassanzadeh-Aghdam ◽  
A Darvizeh
Keyword(s):  
Carbon Nanotubes ◽  
Volume Fraction ◽  
Micromechanical Model ◽  
Strain Curve ◽  
Successive Approximation Method ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Elastoplastic Behavior ◽  
Metal Matrix Nanocomposites ◽  
Elastoplastic Stress

The elastoplastic behavior of aluminum (Al) nanocomposites reinforced with aligned carbon nanotubes (CNTs) is characterized using a unit cell micromechanical model. The interphase zone caused by the chemical reaction between CNT and Al matrix is included in the analysis. To attain the elastoplastic stress–strain curve of the nanocomposites, the successive approximation method together with the von Mises yield criterion is employed. The effects of several important factors including the volume fraction and diameter of CNT, material properties, and size of interphase on the elastoplastic stress–strain curve of the nanocomposites during uniaxial tension are studied. The results indicate that the interphase characteristics significantly affect the elastoplastic behavior of the CNT-reinforced Al nanocomposites. It is also found that the yield stress of the nanocomposites rises with increasing CNT volume fraction or decreasing CNT diameter. Besides, the elastoplastic stress–strain curve of the CNT-reinforced Al nanocomposites is presented for multiaxial tension. The initial yield envelopes of the nanocomposites under longitudinal–transverse biaxial tension are provided too. Comparison between the elastic results of the present model with those of other available micromechanical analyses shows a very good agreement.

The Dynamic Stress-Strain Behavior in Torsion of 1100-0 Aluminum Subjected to a Sharp Increase in Strain Rate

1972 ◽  
Vol 39 (4) ◽  
pp. 939-945 ◽  
Author(s):  
R. A. Frantz ◽  
J. Duffy
Keyword(s):  
Strain Rate ◽  
Strain Curve ◽  
Initial Response ◽  
Material Behavior ◽  
High Rate ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Strain Behavior ◽  
Split Hopkinson ◽  
Explosive Charges

A modification of the torsional split Hopkinson bar is described which superimposes a high rate of shear strain on a slower “static” rate. The static rate of 5 × 10−5 sec−1 is increased to 850 sec−1 at a predetermined value of plastic strain by the detonation of small explosive charges; the rise time of the strain-rate increment is about 10 microsec. During deformation at the dynamic rate, direct measurement is made of the excess stress above the maximum static stress attained. Results for 1100-O aluminum show that the initial response to the strain rate increment is elastic, followed by yielding behavior reminiscent in appearance to an upper yield point. The incremental stress-strain curve always lies beneath the stress-strain curve obtained entirely at the higher strain rate but approaches it asymptotically with increasing strain. It is concluded that the material behavior is a function of strain, strain rate, and strain rate history.

Study of True Stress-Strain Curve after Necking for Application in Ductile Fracture Criteria in Tube Hydroforming of Aerospace Material

2012 ◽  
Vol 504-506 ◽  
pp. 95-100 ◽  
Author(s):  
Mehdi Saboori ◽  
Henri Champliaud ◽  
Javad Ghoulipor ◽  
Augustin Gakwaya ◽  
Jean Savoie ◽  
...  
Keyword(s):  
Tube Hydroforming ◽  
Strain Curve ◽  
True Stress ◽  
Material Behavior ◽  
Loading Path ◽  
Burst Pressure ◽  
Uniaxial Tensile ◽  
Aerospace Materials ◽  
Stress Strain Curve ◽  
Stress Strain

Tube hydroforming (THF) is an advanced metal forming process that is used widely in automotive industry, but the application of the THF process in aerospace field is comparatively new with many challenges due to high strength and limited formability of aerospace materials. The success of THF process largely depends on many factors, such as mechanical properties of the material, loading path during the process, tool geometry and friction condition. Due to complexity of this process, finite element modeling (FEM) can largely reduce the production cost. One of the important input in FEM is the material behavior during hydroforming process. The true stress-strain curve before necking can be easily determined, using either tensile testing or bulge testing, but for an accurate failure prediction in a large deformation, such as hydroforming, the study of true stress-strain curve after necking is important because it improves the quality of the analysis due to utilizing a real extended stress-strain curve. Hence, the objective of this research was to establish a methodology to determine the true stress-strain curve after necking in order to predict burst pressure in the THF of aerospace materials. Uniaxial tensile tests were performed on standard tensile samples (ASME E8M-04) to determine the true stress-strain before and after necking, using an analytical method presented in this study. To validate the approach, burst pressure in the THF process was predicted using the extended stress-strain curve in conjunction with Brozzo's decoupled fracture model. The approach was evaluated using data obtained from the free expansion (tube bulging) tests performed on stainless steel 321 tubes with 2 inches diameter and two different thicknesses, 0.9 mm and 1.2 mm. The comparison of the predicted and measured burst pressures was promising, indicating that the approach has the potential to be extended to predict formability limits in THF of complex shapes.

scholarly journals A Numerical Study on the Progressive Failure of 3D Four-Directional Braided Composites

2013 ◽  
Vol 2013 ◽  
pp. 1-14 ◽  
Author(s):  
Kun Xu
Keyword(s):  
Finite Element ◽  
Tensile Stress ◽  
Damage Accumulation ◽  
Numerical Study ◽  
Micromechanical Model ◽  
Strain Curve ◽  
Braided Composites ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
3D Braided Composites

The complexity of the microstructure makes the strength prediction and failure analysis of 3D braided composites difficult. A new unit cell geometrical model, taken as the representative volume element (RVE), is proposed to describe the yarn configuration of 3D braided composites produced by the four-step 1 × 1 method. Then, based on the periodical boundary conditions, a RVE-based micromechanical model by using the nonlinear finite element method has been presented to predict the progressive damage and the strength of 3D braided composites subjected to tensile loading. The numerical model can simulate the effect of damage accumulation on the tensile stress-strain curve by combining the proposed failure criteria and the stiffness degradation model. The longitudinal shear nonlinearity of braiding yarn is considered in the model. To verify the model, two specimens with typical braiding angles were selected to conduct the simulations. The predicted stress-strain curves by the model compared favorably with the experimental data, demonstrating the applicability of the micromechanical finite element model. The effect of the nonlinear shear parameter on the tensile stress-strain curve was discussed in detail. The results indicate that the tensile mechanical behaviors of 3D braided composites are affected by both the yarn shear nonlinearity and the damage accumulation.

scholarly journals Influence of Carbonization Process on the Mechanical Properties of Nano-MgO Modified Cement Soil

2021 ◽  
Vol 13 (6) ◽  
pp. 3558
Author(s):  
Wei Wang ◽  
Hang Zhou ◽  
Jian Li ◽  
Feifei Tao ◽  
Cuihong Li ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Energy Dissipation ◽  
Dissipation Rate ◽  
Strain Curve ◽  
Energy Dissipation Rate ◽  
Peak Strain ◽  
Test Results ◽  
Stress Strain Curve ◽  
Strength Tests ◽  
Cement Soil

In order to explore the modification effect of carbonization time on nano-MgO-modified cement soil, unconfined compressive strength tests of nano-MgO-modified cement soil with carbonization times of 0 h, 6 h, 1 d, 2 d and 4 d were carried out. A method for normalizing the stress–strain curve was proposed, and the influence of nano-MgO content and carbonization time was investigated from the three aspects of compressive strength, peak strain and energy dissipation. The test results show the following: (1) The compressive strength of the modified cement soil can be significantly improved by adding 1.0% nano-MgO and after 1 d carbonization. (2) Under the same nano-MgO content, the peak strain of the modified cement soil after 2 d carbonization reaches the maximum, which can significantly increase its ductility. However, the nano-MgO content has little influence on the peak strain of the modified cement soil. (3) Under the same nano-MgO content, the energy dissipation rate of the modified cement soil after 1 d carbonization reaches the maximum, which can better resist the damage of external load.

A modified version of MATLAB application window for predicting the weld bead profile and stress–strain plot of AA5052 CMT weldment using ER4043

SIMULATION ◽  
2021 ◽  
pp. 003754972110315
Author(s):  
B Girinath ◽  
N Siva Shanmugam
Keyword(s):  
Strain Curve ◽  
Weld Bead ◽  
Welding Parameters ◽  
Bead Geometry ◽  
Hybrid Technique ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Weld Bead Geometry ◽  
Inference System ◽  
Engineering Stress

The present study deals with the extended version of our previous research work. In this article, for predicting the entire weld bead geometry and engineering stress–strain curve of the cold metal transfer (CMT) weldment, a MATLAB based application window (second version) is developed with certain modifications. In the first version, for predicting the entire weld bead geometry, apart from weld bead characteristics, x and y coordinates (24 from each) of the extracted points are considered. Finally, in the first version, 53 output values (five for weld bead characteristics and 48 for x and y coordinates) are predicted using both multiple regression analysis (MRA) and adaptive neuro fuzzy inference system (ANFIS) technique to get an idea related to the complete weld bead geometry without performing the actual welding process. The obtained weld bead shapes using both the techniques are compared with the experimentally obtained bead shapes. Based on the results obtained from the first version and the knowledge acquired from literature, the complete shape of weld bead obtained using ANFIS is in good agreement with the experimentally obtained weld bead shape. This motivated us to adopt a hybrid technique known as ANFIS (combined artificial neural network and fuzzy features) alone in this paper for predicting the weld bead shape and engineering stress–strain curve of the welded joint. In the present study, an attempt is made to evaluate the accuracy of the prediction when the number of trials is reduced to half and increasing the number of data points from the macrograph to twice. Complete weld bead geometry and the engineering stress–strain curves were predicted against the input welding parameters (welding current and welding speed), fed by the user in the MATLAB application window. Finally, the entire weld bead geometries were predicted by both the first and the second version are compared and validated with the experimentally obtained weld bead shapes. The similar procedure was followed for predicting the engineering stress–strain curve to compare with experimental outcomes.

scholarly journals Material parametrization of natural rubber based compound and characterization of crack propagation under consideration of dissipative effects

2021 ◽  
Author(s):  
Dan Pornhagen ◽  
Konrad Schneider ◽  
Markus Stommel
Keyword(s):  
Energy Dissipation ◽  
Crack Propagation ◽  
Natural Rubber ◽  
Experimental Tests ◽  
Material Behavior ◽  
Prony Series ◽  
Material Forces ◽  
Cracking Behavior ◽  
Dissipative Effects

AbstractMost concepts to characterize crack propagation were developed for elastic materials. When applying these methods to elastomers, the question is how the inherent energy dissipation of the material affects the cracking behavior. This contribution presents a numerical analysis of crack growth in natural rubber taking energy dissipation due to the visco-elastic material behavior into account. For this purpose, experimental tests were first carried out under different load conditions to parameterize a Prony series as well as a Bergström–Boyce model with the results. The parameterized Prony series was then used to perform numerical investigations with respect to the cracking behavior. Using the FE-software system ANSYS and the concept of material forces, the influence and proportion of the dissipative components were discussed.

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