Nonlinear Analysis Techniques for Shear Band Formation at High Strain-Rates

1992 ◽  
Vol 45 (3S) ◽  
pp. S82-S94 ◽  
Author(s):  
Athanasios E. Tzavaras
Keyword(s):  
Strain Rate ◽  
Shear Strain ◽  
Nonlinear Analysis ◽  
Strain Rate Sensitivity ◽  
Strain Softening ◽  
High Strain ◽  
Rate Sensitivity ◽  
Strain Rates ◽  
High Strain Rates ◽  
Analysis Techniques

One of the most striking manifestations of instability in solid mechanics is the localization of shear strain into narrow bands during high speed, plastic deformations of metals. According to one theory, the formation of shear bands is attributed to effective strain-softening response, which results at high strain rates as the net outcome of the influence of thermal softening on the, normally, strain-hardening response of metals. Our objective is to review some of the insight obtained by applying nonlinear analysis techniques on simple models of nonlinear partial differential equations simulating this scenario for instability. First, we take up a simple system, intended as a paradigm, that describes isothermal shear deformations of a material exhibiting strain softening and strain-rate sensitivity. As it turns out, for moderate amounts of strain softening strain-rate sensitivity exerts a dissipative effect and stabilizes the motion. However, once a threshold is exceeded, the response becomes unstable and shear strain localization occurs. Next, we present extensions of these results to situations where explicit thermal effects are taken into account.

Strain-Rate Sensitivity Enhanced by Grain-Boundary Sliding in Creep Condition for AZ31 Magnesium Alloy at Room Temperature

2016 ◽  
Vol 838-839 ◽  
pp. 106-109 ◽  
Author(s):  
Tetsuya Matsunaga ◽  
Hidetoshi Somekawa ◽  
Hiromichi Hongo ◽  
Masaaki Tabuchi
Keyword(s):  
Grain Boundary ◽  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Room Temperature ◽  
High Strain ◽  
Rate Sensitivity ◽  
Grain Boundary Sliding ◽  
Strain Rates ◽  
High Strain Rates ◽  
Boundary Sliding

This study investigated strain-rate sensitivity (SRS) in an as-extruded AZ31 magnesium (Mg) alloy with grain size of about 10 mm. Although the alloy shows negligible SRS at strain rates of >10-5 s-1 at room temperature, the exponent increased by one order from 0.008 to 0.06 with decrease of the strain rate down to 10-8 s-1. The activation volume (V) was evaluated as approximately 100b3 at high strain rates and as about 15b3 at low strain rates (where b is the Burgers vector). In addition, deformation twin was observed only at high strain rates. Because the twin nucleates at the grain boundary, stress concentration is necessary to be accommodated by dislocation absorption into the grain boundary at low strain rates. Extrinsic grain boundary dislocations move and engender grain boundary sliding (GBS) with low thermal assistance. Therefore, GBS enhances and engenders SRS in AZ31 Mg alloy at room temperature.

Investigation on Strain Rate Sensitivity of 3D Printed sPEEK-HAP/rGO Composites

2021 ◽  
Author(s):  
Sagar Mahalingappa Baligidad ◽  
Chethan Kumar Gangadhara ◽  
Maharudresh Aralikatte Chandrashekhar
Keyword(s):  
Strain Rate ◽  
Polymer Composites ◽  
Strain Rate Sensitivity ◽  
High Strain ◽  
Rate Sensitivity ◽  
Sensitivity Factor ◽  
Strain Rates ◽  
High Strain Rates ◽  
Compression Behaviour ◽  
Yield Behaviour

Abstract Nanofillers can be added to polymers to improve their mechanical behavior. However, the yield behaviour of most polymer composites is influenced by strain rate. The majority of the research focused on the behaviour of polymer composites at high strain rates. This work aims to investigate how hydroxyapatite (HAP) and reduced Graphene Oxide (rGO) nanofillers affect the mechanical properties of sulphonated polyetheretherketone (sPEEK) at low (tensile and compression behaviour) and high strain rates (compression behaviour). The thermal, mechanical, and energy absorption responses of sPEEK filled with HAP and varying mass fraction (Mf) of rGO (0.5%, 1%, and 1.5%) at different strain are studied in detail. The strong strain rate effect was seen in HAp and rGO loaded sPEEK composites. The strain rate sensitivity factor of sPEEK-HAP/rGO improved as the strain rate increased, but decreased when the Mf of rGO increased. Under low strain rate compression, HAp and rGO loaded sPEEK absorbed more energy at Mf about 4%. SEM micrography was used to study the microstructures of the fractured interfaces of the components, revealing that the HAp and sPEEK materials formed a good compatibility in presence of rGO.

scholarly journals Dynamic Shear Characteristic and Fracture Feature of Inconel 690 Alloy under Different High Strain Rates and Temperatures

2013 ◽  
Vol 2013 ◽  
pp. 1-5
Author(s):  
Tao-Hsing Chen ◽  
Chih-Kai Tsai ◽  
Te-Hua Fang
Keyword(s):  
Strain Rate ◽  
Shear Strain ◽  
High Strain ◽  
Rate Sensitivity ◽  
Shear Behaviour ◽  
Strain Rates ◽  
Dynamic Shear ◽  
Fracture Feature ◽  
Strain And Strain Rate ◽  
Inconel 690

The high strain shear rate behaviour of Inconel 690 alloy was investigated by using the split Hopkinson torsional bar. The shear strain rates were tested at 900 s−1, 1900 s−1, and 2600 s−1and at temperatures of −100°C, 25°C, and 300°C, respectively. It was found that the dynamic shear behaviour of Inconel 690 alloy was sensitive to strain rate and temperature. The fracture shear strain increased with increasing strain rate and temperature. In addition, the strain rate sensitivity was increased with increasing strain and strain rate but decreased with increasing temperature. Finally, the fracture surfaces were found to contain dimple-like features, and the dimple density increased with increasing strain rate and temperature.

Rate Dependent Deformation of Semi-Crystalline Polypropylene Near Room Temperature

1997 ◽  
Vol 119 (3) ◽  
pp. 216-222 ◽  
Author(s):  
E. M. Arruda ◽  
S. Ahzi ◽  
Y. Li ◽  
A. Ganesan
Keyword(s):  
Plastic Deformation ◽  
Strain Rate ◽  
Room Temperature ◽  
Strain Softening ◽  
High Strain ◽  
Constant Strain Rate ◽  
Strain Rates ◽  
High Strain Rates ◽  
Rate Dependent ◽  
Static Conditions

We examine the strain rate dependent, large plastic deformation in isotropic semi-crystalline polypropylene at room temperature. Constant strain rate uniaxial compression tests on cylindrical polypropylene specimens show very little true strain softening under quasi-static conditions. At high strain rates very large amounts (38 percent) of apparent strain softening accompanied by temperature rises are recorded. We examine the capability of a recently proposed constitutive model of plastic deformation in semi-crystalline polymers to predict this behavior. We neglect the contribution of the amorphous phase to the plastic deformation response and include the effects of adiabatic heating at high strain rates. Attention is focused on the ability to predict rate dependent yielding, strain softening, strain hardening, and adiabatic temperature rises with this approach. Comparison of simulations and experimental results show good agreement and provide insight into the merits of using a polycrystalline modeling assumption versus incorporating the amorphous contribution. Discrepancies between experiments and model predictions are explained in terms of expectations associated with neglecting the amorphous deformation.

High Strain Rate Behaviour of Iron and Nickel

1972 ◽  
Vol 14 (3) ◽  
pp. 161-167 ◽  
Author(s):  
T. Muller
Keyword(s):  
Strain Rate ◽  
High Strain ◽  
True Strain ◽  
Rate Sensitivity ◽  
Correction Method ◽  
Strain Rates ◽  
High Strain Rates ◽  
Controlling Mechanism ◽  
Split Hopkinson ◽  
Rate Behaviour

An investigation into the mechanical behaviour of iron and nickel at high strain rates is carried out, using a split Hopkinson bar method. Some special adaptations, a correction method for the effects arising from the adiabatic conditions of dynamic deformation and a simplified data processing procedure are described in detail. The test conditions covered a range of strain rates between 500 and about 10 000/s and temperatures from 20 to 500°C. For both metals, the results are presented by means of a family of true stress-true strain curves. The strong strain rate sensitivity at high strain rates indicates that the rate controlling mechanism differs from that operative at ‘static’ strain rates.

Low Temperature Superplasticity in Ultrafine-Grained AZ31 Alloy

2018 ◽  
Vol 385 ◽  
pp. 59-64 ◽  
Author(s):  
Roberto B. Figueiredo ◽  
Pedro Henrique R. Pereira ◽  
Terence G. Langdon
Keyword(s):  
Plastic Deformation ◽  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Room Temperature ◽  
High Strain ◽  
High Pressure Torsion ◽  
Rate Sensitivity ◽  
Az31 Alloy ◽  
Strain Rates ◽  
Ultrafine Grained

The mechanical behavior of an AZ31 magnesium alloy processed by high-pressure torsion (HPT) was evaluated by tensile testing from room temperature up to 473 K at strain rates between 10-5 – 10-2 s-1. Samples tested at room temperature and at high strain rates at 373 K failed without any plastic deformation. However, significant ductility, with elongations larger than 200%, was observed at 423 K and 473 K and at low strain rates at 373 K. The high elongations are attributed to a pronounced strain hardening and a high strain rate sensitivity. The results agree with reports for a similar alloy processed by severe plastic deformation. However, the level of flow stress is lower and the strain rate sensitivity and the elongations are larger than observed in this alloy processed by conventional thermo-mechanical processing.

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