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.

Comparative Study of the Dynamic Behavior of AA2519 Aluminum Alloy in T6 and T8 Temper Conditions

2019 ◽  
Author(s):  
Adewale Olasumboye ◽  
Gbadebo Owolabi ◽  
Olufemi Koya ◽  
Horace Whitworth ◽  
Nadir Yilmaz
Keyword(s):  
Plastic Deformation ◽  
Aluminum Alloy ◽  
Stress Response ◽  
Flow Stress ◽  
Yield Strength ◽  
Strain Rate ◽  
High Strain ◽  
Second Phase ◽  
Strain Rates ◽  
High Strain Rates

Abstract This study investigates the dynamic response of AA2519 aluminum alloy in T6 temper condition during plastic deformation at high strain rates. The aim was to determine how the T6 temper condition affects the flow stress response, strength properties and microstructural morphologies of the alloy when impacted under compression at high strain rates. The specimens (with aspect ratio, L/D = 0.8) of the as-cast alloy used were received in the T8 temper condition and further heat-treated to the T6 temper condition based on the standard ASTM temper designation procedures. Split-Hopkinson pressure bar experiment was used to generate true stress-strain data for the alloy in the range of 1000–3500 /s strain rates while high-speed cameras were used to monitor the test compliance with strain-rate constancy measures. The microstructures of the as received and deformed specimens were assessed and compared for possible disparities in their initial microstructures and post-deformation changes, respectively, using optical microscopy. Results showed no clear evidence of strain-rate dependency in the dynamic yield strength behavior of T6-temper designated alloy while exhibiting a negative trend in its flow stress response. On the contrary, AA2519-T8 showed marginal but positive response in both yield strength and flow behavior for the range of strain rates tested. Post-deformation photomicrographs show clear disparities in the alloys’ initial microstructures in terms of the second-phase particle size differences, population density and, distribution; and in the morphological changes which occurred in the microstructures of the different materials during large plastic deformation. AA2519-T6 showed a higher susceptibility to adiabatic shear localization than AA2519-T8, with deformed and bifurcating transformed band occurring at 3000 /s followed by failure at 3500 /s.

Strain Rate Effects and Rate-Dependent Constitutive Models of Lead-Based and Lead-Free Solders

2009 ◽  
Vol 77 (1) ◽  
Author(s):  
Fei Qin ◽  
Tong An ◽  
Na Chen
Keyword(s):  
Strain Rate ◽  
Impact Analysis ◽  
Solder Joints ◽  
High Strain ◽  
Drop Impact ◽  
Lead Free ◽  
Strain Rates ◽  
High Strain Rates ◽  
Rate Dependent ◽  
Lead Free Solders

As traditional lead-based solders are banned and replaced by lead-free solders, the drop impact reliability is becoming increasingly crucial because there is little understanding of mechanical behaviors of these lead-free solders at high strain rates. In this paper, mechanical properties of one lead-based solder, Sn37Pb, and two lead-free solders, Sn3.5Ag and Sn3.0Ag0.5Cu, were investigated at strain rates that ranged from 600 s−1 to 2200 s−1 by the split Hopkinson pressure and tensile bar technique. At high strain rates, tensile strengths of lead-free solders are about 1.5 times greater than that of the Sn37Pb solder, and also their ductility are significantly greater than that of the Sn37Pb. Based on the experimental data, strain rate dependent Johnson–Cook models for the three solders were derived and employed to predict behaviors of solder joints in a board level electronic package subjected to standard drop impact load. Results indicate that for the drop impact analysis of lead-free solder joints, the strain rate effect must be considered and rate-dependent material models of lead-free solders are indispensable.

Effect of Temperature and Strain Rate on the Mechanical Properties of 99.5 Aluminium Rods Extruded by KOBO

2016 ◽  
Vol 879 ◽  
pp. 230-235
Author(s):  
Sonia Boczkal ◽  
Marzena Lech-Grega ◽  
Wojciech Szymanski ◽  
Paweł Ostachowski ◽  
Marek Lagoda
Keyword(s):  
Strain Rate ◽  
Room Temperature ◽  
High Strain ◽  
Effect Of Temperature ◽  
Recrystallization Process ◽  
Extrusion Force ◽  
Strain Rates ◽  
High Strain Rates ◽  
Constant Frequency ◽  
Increasing Temperature

In this study, aluminium rods were cold extruded in a direct process by KOBO method in two variants: variant I with varying (decreasing) frequency of die oscillations necessary to maintain a constant extrusion force, and variant II with constant frequency of die oscillations, leading to a decrease in the extrusion force. The tensile test of rods was carried out in a temperature range of 20 - 200°C and at a strain rate from 8xE10-5 to 8xE10-1 s-1. Significant differences in the elongation of the tested rods were observed. It was found that rods extruded at variable die oscillations and stretched at room temperature had similar elongation, independent of the strain rate. With the increase of temperature, the elongation of samples stretched at a low speed was growing from a value of about 8% at room temperature up to 40% at 200°C. At high strain rates, despite the increasing temperature, the elongation remained at the same level, i.e. 5-6%. In rods extruded at constant die oscillations, the elongation at a low strain rate was growing with the temperature from 10% at room temperature up to 29% at 200°C. At high strain rates, the elongation decreased from 28% at room temperature to 11% at 200°C. The results were interrelated with examinations of the structure of rods and fractures of tensile specimens. In the material extruded by KOBO method with constant die oscillations, the beginnings of the recrystallization process were observed, absent in the material extruded at variable die oscillations.

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.

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.

scholarly journals Characterization of the strain-rate–dependent mechanical response of single cell–cell junctions

2021 ◽  
Vol 118 (7) ◽  
pp. e2019347118
Author(s):  
Amir Monemian Esfahani ◽  
Jordan Rosenbohm ◽  
Bahareh Tajvidi Safa ◽  
Nickolay V. Lavrik ◽  
Grayson Minnick ◽  
...  
Keyword(s):  
Cell Adhesion ◽  
Stress Relaxation ◽  
Strain Rate ◽  
Single Cell ◽  
High Strain ◽  
Cell Junction ◽  
Strain Rates ◽  
High Strain Rates ◽  
Rate Dependent ◽  
Cell Cell

Cell–cell adhesions are often subjected to mechanical strains of different rates and magnitudes in normal tissue function. However, the rate-dependent mechanical behavior of individual cell–cell adhesions has not been fully characterized due to the lack of proper experimental techniques and therefore remains elusive. This is particularly true under large strain conditions, which may potentially lead to cell–cell adhesion dissociation and ultimately tissue fracture. In this study, we designed and fabricated a single-cell adhesion micro tensile tester (SCAµTT) using two-photon polymerization and performed displacement-controlled tensile tests of individual pairs of adherent epithelial cells with a mature cell–cell adhesion. Straining the cytoskeleton–cell adhesion complex system reveals a passive shear-thinning viscoelastic behavior and a rate-dependent active stress-relaxation mechanism mediated by cytoskeleton growth. Under low strain rates, stress relaxation mediated by the cytoskeleton can effectively relax junctional stress buildup and prevent adhesion bond rupture. Cadherin bond dissociation also exhibits rate-dependent strengthening, in which increased strain rate results in elevated stress levels at which cadherin bonds fail. This bond dissociation becomes a synchronized catastrophic event that leads to junction fracture at high strain rates. Even at high strain rates, a single cell–cell junction displays a remarkable tensile strength to sustain a strain as much as 200% before complete junction rupture. Collectively, the platform and the biophysical understandings in this study are expected to build a foundation for the mechanistic investigation of the adaptive viscoelasticity of the cell–cell junction.

scholarly journals Microstructure and Mechanical Properties of Laser Welded 6061-T6 Aluminum Alloy under High Strain Rates

Metals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1145
Author(s):  
Jincheng Nie ◽  
Shengci Li ◽  
Huilong Zhong ◽  
Changjing Hu ◽  
Xiangsong Lin ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Plastic Deformation ◽  
Aluminum Alloy ◽  
High Strain Rate ◽  
Strain Rate ◽  
High Strain ◽  
Base Material ◽  
Strain Rates ◽  
High Strain Rates ◽  
Plastic Deformation Region

Laser welding is widely used for the joining of aluminum alloy in the automotive industry, and the vehicles produced are inevitably subjected to high strain rate loading during their service. Therefore, this paper studied the mechanical properties of 6061-T6 aluminum alloy and its laser welded joint at strain rates between 0.0003 and 1000 s−1. Results showed that the microstructure of welded material (WM) was much finer than base material (BM), typical columnar crystals grew perpendicularly to the fusion line, and the minimum hardness value (~56 HV) was obtained inside WM. The strength and dynamic factors of BM and WM increased with increasing strain rate, and the strength of WM was less sensitive to strain rate compared with BM. The strain rate effect was not homogenous in the plastic deformation region. The modified Johnson–Cook (J–C) model which introduced the term C = C1 + C2·ε could well describe the dynamic plastic deformation of BM. However, the fitted results of the simplified J–C model were overall better than the modified J–C model for WM, especially for high strain rate (1000 s−1). These findings will benefit the determination of the dynamic deformation behavior of laser welded aluminum alloy under high strain rates, and could provide a better understanding of lightweight and the safety of vehicles.

Low Temperature Effects on IM7/977-3 Cross-Ply Composite Material Properties at High Strain Rates

2002 ◽  
Author(s):  
Shunjun Song ◽  
Jack R. Vinson
Keyword(s):  
Composite Materials ◽  
Low Temperature ◽  
High Strain Rate ◽  
Strain Rate ◽  
Room Temperature ◽  
High Strain ◽  
Dynamic Properties ◽  
Strain Rates ◽  
High Strain Rates ◽  
Cold Regions

Composite materials are used in a wide variety of low temperature applications because of their unique and highly tailorable properties. These low temperature applications of composites include their use in Arctic environments and most of them involve dynamic loads, for example, spacecraft applications where they use cryogenic engines, hypervelocity impact situations at very high altitudes, civil engineering applications in extreme cold regions, and offshore structures in cold regions. The U.S. Navy stated that under certain conditions naval vessels might encounter strain rates up to 1200/sec. Because the dynamic properties of composite materials may vary widely with both strain rates and temperature, it is important to use the dynamic properties at the expected temperatures when the loading conditions involve high strain rates and extreme temperatures. Very few materials have been characterized at high strain rates even at room temperature. Still less effort has been spent in trying to model the high strain rate properties to develop a predictive capability at room temperature. It has been hoped that earlier modeling for metals, such as Johnson and Cook [1], and Zerilli and Armstrong [2] might be used for composite materials. The Johnson-Cook model was modified by Weeks and Sun [3] for composite materials. Other recent modeling research has been performed by Theruppukuzki and Sun [4], Hsiao, Daniel and Cordes [5] and Tsai and Sun [6]. Woldesenbet and Vinson [7] have characterized the high strain rate and fiber orientation effects on one typical graphite/epoxy composite. Most of these characterizations model ultimate strengths only.

Sign in / Sign up

Export Citation Format

Share Document