Stress Softening in Carbon Black Reinforced Vulcanizates. Strain Rate and Temperature Effects

1966 ◽  
Vol 39 (5) ◽  
pp. 1530-1543 ◽  
Author(s):  
G. Kraus ◽  
C. W. Childers ◽  
K. W. Rollmann
Keyword(s):  
Carbon Black ◽  
Strain Rate ◽  
Low Temperatures ◽  
High Strain ◽  
Failure Behavior ◽  
Strain Rates ◽  
High Strain Rates ◽  
Temperature Function ◽  
Network Chain ◽  
Stress Softening

Abstract Stress softening of carbon black reinforced butadiene styrene rubber was studied as a function of the rate and temperature of the original tensile deformation. To a good approximation, stress softening depends on the product of the extension rate and a temperature function which is analytically well represented by the familiar Williams-Landel-Ferry relationship. When the elongation of the original deformation is also varied, a good correlation is obtained between stress softening and the maximum stress attained in the original extension, irrespective of the particular combination of strain, strain rate, and temperature used to achieve this stress. Variables which tend to increase the stiffness of the vulcanizate, such as increased degree of crosslinking or carbon black chain structure, also increase stress softening; dilution by plasticizers decreases it. Prestressing at high strain rates and low temperatures affects the stress—strain curve of the softened vulcanizates beyond the elongation of the original extension. Connections are established between stress softening and viscoelastic and failure behavior. The evidence presented favors the contribution of several mechanisms to the general phenomenon of stress softening. These are thixotropy of transient filler structures, network chain rupture, and breakage of “permanent” filler structure. The latter appears to be most important at high strain rates, low temperatures, and with highly reticulated “structure” blacks.

A Dynamic Mechanical Analysis of T2 Copper at High Strain Rates

2019 ◽  
Vol 812 ◽  
pp. 38-44
Author(s):  
Shuai Chen ◽  
Wen Bin Li ◽  
Xiao Ming Wang ◽  
Wen Jin Yao
Keyword(s):  
Yield Strength ◽  
Strain Rate ◽  
High Strain ◽  
Split Hopkinson Pressure Bar ◽  
Pure Copper ◽  
Dislocation Slip ◽  
Strain Rates ◽  
High Strain Rates ◽  
Stress Strain ◽  
Shpb Test

This work compares the pure copper (T2 copper)’s stress-strain relationship at different strain rates in the uni-axial tension test and Split Hopkinson Pressure Bar (SHPB) test. Small samples were utilized in the high strain rate SHPB test in which the accuracy was modified by numerical simulation. The experimental results showed that the T2 copper’s yield strength at high strain rates largely outweighed the quasi static yield strength. The flow stress in the stress-strain curves at different strain rates appeared to be divergent and increased with the increase in strain rates, showing great strain strengthening and strain rate hardening effects. Metallographic observation showed that the microstructure of T2 copper changed from equiaxed grains to twins and the interaction between the dislocation slip zone grain boundary and twins promoted the super plasticity distortion in T2 copper.

Tensile behaviors of co-woven-knitted fabric reinforced composites under various strain rates

2011 ◽  
Vol 45 (24) ◽  
pp. 2495-2506 ◽  
Author(s):  
Pibo Ma ◽  
Hong Hu ◽  
Lvtao Zhu ◽  
Baozhong Sun ◽  
Bohong Gu
Keyword(s):  
Strain Rate ◽  
Failure Modes ◽  
Shear Failure ◽  
High Strain ◽  
Tensile Failure ◽  
Knitted Fabric ◽  
Strain Rates ◽  
High Strain Rates ◽  
Textile Composite ◽  
Interface Failure

This article reports the tensile behaviors of a novel kind of 3D textile composite, named as co-woven-knitted fabric (CWKF) reinforced composite, under quasi-static and high strain rates. The tensile tests were conducted along the warp direction (0°), bias direction (45°), and weft direction (90°) at quasi-static strain rate of 0.001/s and high strain rates ranging from 1589/s to 2586/s. The results indicate that the tensile strength, failure strain, tensile stiffness, energy absorption, and resilient energy are strain rate sensitive along all the three directions. The relationships between the mechanical parameters and the strain rate were also analyzed. The fractograph of the CWKF composite demonstrate that the tensile failure modes are matrix shear failure and fibers breakage under the quasi-static testing condition while interface failure and fibers pullout are at high strain rates.

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.

scholarly journals An Image-Based Impact Test for the High Strain Rate Tensile Properties of Brittle Materials

2018 ◽  
Vol 183 ◽  
pp. 02042
Author(s):  
Lloyd Fletcher ◽  
Fabrice Pierron
Keyword(s):  
Tensile Strength ◽  
Elastic Modulus ◽  
High Strain Rate ◽  
Strain Rate ◽  
Stress Wave ◽  
High Strain ◽  
Brittle Materials ◽  
Test Method ◽  
Strain Rates ◽  
High Strain Rates

Testing ceramics at high strain rates presents many experimental diffsiculties due to the brittle nature of the material being tested. When using a split Hopkinson pressure bar (SHPB) for high strain rate testing, adequate time is required for stress wave effects to dampen out. For brittle materials, with small strains to failure, it is difficult to satisfy this constraint. Because of this limitation, there are minimal data (if any) available on the stiffness and tensile strength of ceramics at high strain rates. Recently, a new image-based inertial impact (IBII) test method has shown promise for analysing the high strain rate behaviour of brittle materials. This test method uses a reflected compressive stress wave to generate tensile stress and failure in an impacted specimen. Throughout the propagation of the stress wave, full-field displacement measurements are taken, from which strain and acceleration fields are derived. The acceleration fields are then used to reconstruct stress information and identify the material properties. The aim of this study is to apply the IBII test methodology to analyse the stiffness and strength of ceramics at high strain rates. The results show that it is possible to identify the elastic modulus and tensile strength of tungsten carbide at strain rates on the order of 1000 s-1. For a tungsten carbide with 13% cobalt binder the elastic modulus was identified as 516 GPa and the strength was 1400 MPa. Future applications concern boron carbide and sapphire, for which limited data exist in high rate tension.

Tensile Behavior of Ti-5Al-2.5Sn Alloy at Low Temperatures and High Strain Rates

2019 ◽  
Vol 794 ◽  
pp. 135-141
Author(s):  
Bin Zhang ◽  
Yang Wang
Keyword(s):  
Strain Rate ◽  
Strain Hardening ◽  
Low Temperatures ◽  
High Strain ◽  
Testing Temperature ◽  
Tensile Behavior ◽  
Experimental Results ◽  
Strain Rates ◽  
Increasing Temperature ◽  
Strain Hardening Rate

The mechanical responses of Ti-5Al-2.5Sn alloy at low temperatures were investigated under quasi-static and dynamic tensile loads using MTS system and SHTB system, respectively. Tensile stress-strain curves were obtained over the temperature range of 153 to 298K and the rate range of 0.001 to 1050 s-1. Experimental results indicate that the tensile behavior of Ti-5Al-2.5Sn alloy is dependent on strain rate and temperature. Yield stress and flow stress increase with increasing strain rate and decrease with increasing temperature. Results also indicate that strain hardening rate of Ti-5Al-2.5Sn alloy is lower at high strain rate, while strain hardening rate varies little with testing temperature. The Khan-Huang-Liang constitutive model was chosen to characterize the tensile responses of Ti-5Al-2.5Sn alloy at low temperatures and different strain rates. The model results coincide well with the experimental results within the tested temperature and rate ranges.

Compressive Behavior of Plain and Fiber-Reinforced High-Strength Concrete Subjected to High Strain Rate Loading

2011 ◽  
Vol 82 ◽  
pp. 57-62 ◽  
Author(s):  
Sha Sha Wang ◽  
Min Hong Zhang ◽  
Ser Tong Quek
Keyword(s):  
High Strain Rate ◽  
Strain Rate ◽  
High Strength Concrete ◽  
High Strain ◽  
Split Hopkinson Pressure Bar ◽  
High Strength ◽  
Strain Rates ◽  
Compressive Behavior ◽  
High Strain Rates ◽  
Strength Concrete

This paper presents a laboratory experimental study on the effect of high strain rate on compressive behavior of plain and fiber-reinforce high-strength concrete (FRHSC) with similar strength of 80-90 MPa. Steel fibers, polyethylene fibers, and a combination of these were used in the FRHSC. A split Hopkinson pressure bar equipment was used to determine the concrete behavior at strain rates from about 30 to 300 s-1. The ratio of the strength at high strain rates to that at static loading condition, namely dynamic increase factor (DIF), of the concretes was determined and compared with that recommended by CEB-FIP code. Fracture patterns of the specimens at high strain rates are described and discussed as well. Results indicate that the CEB-FIP equation is applicable to the plain high strength concrete, but overestimates the DIF of the FRHSC at strain rates beyond a transition strain rate of 30 s-1. Based on the experimental results, a modified equation on DIF is proposed for the FRHSC.

Fracture of Laminated and In Situ Niobium Silicide-Niobium Composites

1996 ◽  
Vol 434 ◽  
Author(s):  
J. D. Rigney
Keyword(s):  
Low Temperatures ◽  
Fracture Resistance ◽  
Fracture Behavior ◽  
High Strain ◽  
Theoretical Models ◽  
High Yield ◽  
Strain Rates ◽  
High Strain Rates ◽  
Ductile Phase

AbstractThe mechanisms contributing to the fracture resistance of refractory metal intermetallic composites containing a BCC metallic phase (niobium) were investigated using model Nb-Si laminates and in situ composites. The controlling influence of ductile phase yield strength and fracture behavior were investigated by varying laminate processing parameters, and/or altering temperatures and applied strain rates during fracture experiments on all materials. The fracture behavior of “ductile” constituents were found to be influenced by phase grain size, solid solution content, constraint (as influenced by interfacial bond strengths), and the testing condition (high strain rates and low temperatures). The measured fracture resistance, when compared to theoretical models, was shown to be controlled by the “toughness” of the “ductile” phase and independent of the fracture behavior promoted (cleavage and ductile). The loss in ductility due to cleavage by high constraint, high strain rates and/or low temperatures was compensated by high yield and cleavage fracture stresses in order to provide a level of toughening similar to that contributed by ligaments which failed with lower yield stresses and greater strains.

Experimental Studies of the Behaviour at High Strain Rates of Unfilled and Filled Polypropylenes

2006 ◽  
Vol 3-4 ◽  
pp. 363-368 ◽  
Author(s):  
N. Temimi ◽  
Noelle Billon
Keyword(s):  
Strain Rate ◽  
High Speed ◽  
High Strain ◽  
Experimental Studies ◽  
Young Modulus ◽  
Video Camera ◽  
Image Correlation ◽  
Strain Rates ◽  
High Strain Rates ◽  
Low Velocity

Thermo mechanical behaviour of unfilled and filled polypropylenes are studied in tension from 10-4 to 102 s-1. Complementary low velocity compression and shear tests are also performed. A high-speed video camera (up to 2500 frames/s) combined with image analysis, image correlation and an infra red pyrometer allow measuring 3D-strain fields and temperature during tests. Thus, data can be processed without restrictive assumptions. Beside usual (for polymers) temperature and strain rate sensitivities it is found that plastic deformation in these materials does not obey incompressibility assumption. Voiding damage is evidenced in the polymer matrix by SEM observations that result in volume change and significant decrease in Young modulus for both materials. Moreover, an increase in the temperature of more than 10 °C is observed and is likely to modify the behaviour of each material at high strain rates. Shear and compression measurements demonstrate that yield criteria and constitutive equation depend on loading. It is concluded that apparent yield stress in semi-crystalline polypropylene can be a result of a combination of “non strain rate sensitive” “non-cohesive mechanisms” and “strain rate sensitive” “cohesive mechanisms”. Experimental characterisation on polymers should then be revisited as most of the usual assumptions are invalid and non monotonic tests should be generalized.

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