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.

Numerical Simulation of Double Specimens in Split Hopkinson Pressure Bar Testing

2010 ◽  
Vol 654-656 ◽  
pp. 2483-2486
Author(s):  
Muhammad Agus Kariem ◽  
John H. Beynon ◽  
Dong Ruan
Keyword(s):  
Dynamic Behaviour ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Performance ◽  
Strain Curve ◽  
Hopkinson Pressure Bar ◽  
Stress Strain ◽  
Element Analysis ◽  
Specimen Test ◽  
Split Hopkinson ◽  
Pressure Bar

The split Hopkinson pressure bar (SHPB) is the most commonly used technique to characterize the dynamic behaviour of materials at very high strain rates. However, a classic single specimen test only generates a single stress-strain curve at the average strain rate of the test. This paper proposes three arrangements on the use of double specimens in SHPB compression testing. All waves propagating along the bars have been used to analyse the dynamic behaviour of the specimens. To simulate the test and predict its dynamic performance, an axisymmetric finite element analysis using LS-DYNA was conducted for the experiment using 13 mm bar diameter. The validity of the simulations was checked with experimental data from normal SHPB testing. Based on the simulations, the modified techniques are achievable and at least two stress-strain curves of materials can be extracted without violating the requirement of a valid SHPB test.

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 Study on Characteristic and Energy of Argillaceous Weakly Cemented Rock under Dynamic Loading by Hopkinson Bar Experiment

Energies ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 3215
Author(s):  
Lingdong Meng ◽  
Lijun Han ◽  
Qingbin Meng ◽  
Kexiang Liu ◽  
Maolin Tian ◽  
...  
Keyword(s):  
Elastic Modulus ◽  
Dynamic Loading ◽  
Impact Velocity ◽  
Wave Amplitude ◽  
Impact Resistance ◽  
Strain Curve ◽  
Hopkinson Pressure Bar ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Pressure Bar

To study the mechanical properties of argillaceous weakly cemented rock under dynamic loading, a sample reconstituted and graded loading scheme is firstly designed, and then the reorganization rock sample is used as the research object. Using a Hopkinson pressure bar test, the responses of an argillaceous weakly cemented rock mass under different reorganization loads and different impact velocities is studied, and changes in specimen shape after impact are also analyzed. The study found that with increased of the recombination load, the amplitude of the transmitted wave increases. With increasing impact velocity, the rate of the increase in the incident wave amplitude is much larger than that of the transmission wave amplitude. The dynamic stress–strain curve can be divided into a compaction stage, an approximate linear elastic stage, a microcrack growth stage and a strain softening stage. The larger the reorganization load is, the less obvious the compression stage of the stress–strain curve is, and the greater the elastic modulus is. The peak strength and elastic modulus increase with increasing strain rate before 500 s−1. When the reorganization load is increased, the deformation decreases, and its impact resistance increases. With increasing impact velocity, the deformation of the specimen increases.

A Study on Reduction of Friction in Impact Compressive Test Based on the Split Hopkinson Pressure Bar Method by Using a Hollow Specimen

2014 ◽  
Vol 566 ◽  
pp. 548-553 ◽  
Author(s):  
Nobuhiko Kii ◽  
Takeshi Iwamoto ◽  
Alexis Rusinek ◽  
Tomasz Jankowiak
Keyword(s):  
Impact Test ◽  
Split Hopkinson Pressure Bar ◽  
Strain Curve ◽  
Hopkinson Pressure Bar ◽  
Compressive Test ◽  
Friction Effect ◽  
Wide Range ◽  
Split Hopkinson ◽  
Pressure Bar ◽  
The Impact

The split Hopkinson pressure bar (SHPB) technique is widely-used to describe the impact compressive behavior of different materials including metals. During the impact test, the specimen deforms in a wide range of impact strain rate from 102 to 104 s-1. It is a reason why the method is studied for many years even though the structure of the apparatus based on the SHPB is simple. Actually, the cylindrical specimens are widely used for a compressive test and it is clearly seen that stress measured by the test includes the increment of stress (an error) derived by friction effect between a specimen and pressure bars. Therefore, it is important that the measured stress should indicate similar value as the proper stress of the material by reducing friction effect during not only quasi-static but also the impact test. Various attempts to reduce a friction effect in past have been conducted. A method to reduce friction effect is in general a use of lubricants. However, it is ineffective because it can be considered that this method contributes to an attenuation of the stress wave for obtaining the stress-strain curve under impact loading. Thus, rise time of waves obtained by the experiment becomes longer compared with a case not to use lubricants. Recently, a study can be found using a ring specimen, however, the determined thickness of the specimen is quite thin and it can be considered that a buckling effect cannot be vanished. In this study, a use of hollow specimen is suggested to solve the problem related to reduce the friction effect by decreasing a contact area between a specimen and pressure bars instead of a cylindrical specimen. The compressive experiments at various strain rates are conducted by using a hollow specimen.

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