Influences of Temperature and Strain-Rate on Yield Mode Transition and Slip Line Growth Behavior of Amorphous Polymers

The effects of mechanical factors on crack growth behavior during the second stage of high pH stress corrosion cracking in pipeline steel were investigated by applying several loading scenarios on compact tension (CT) specimens. The main mechanism for stage 2 of intergranular crack propagation is anodic dissolution ahead of the crack tip which is highly dependent on crack-tip strain rate. The maximum and minimum crack growth rates were 3 × 10−7 mm/s and 1 × 10−7 mm/s, respectively. It was observed that several factors such as mean stress intensity factor, amplitude, and frequency of loading cycles determine the crack-tip strain rate. Low R-ratio cycles, particularly high-frequency ones, enhance secondary crack initiation, and crack coalescence on the free surface. This mechanism accelerates crack advance on the free surface which is accompanied with an increase in mechanical driving force for crack propagation in the thickness direction. These findings have implications for pipeline operators and could be used to increase the lifespan of the cracked pipelines at stage 2. For those pipelines, any loading condition that increases the strain rate ahead of the crack tip enhances anodic dissolution and is detrimental. Additionally, secondary crack initiation and coalescence could be minimized by avoiding internal pressure fluctuation, particularly rapid large pressure fluctuations.

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Rubber-Modified Glassy Amorphous Polymers Prepared via Chemically Induced Phase Separation. 3. Influence of the Strain Rate on the Microscopic Deformation Mechanism

Macromolecules ◽

10.1021/ma981406n ◽

1999 ◽

Vol 32 (19) ◽

pp. 6283-6289 ◽

Cited By ~ 13

Author(s):

B. J. P. Jansen ◽

S. Rastogi ◽

H. E. H. Meijer ◽

P. J. Lemstra

Keyword(s):

Phase Separation ◽

Strain Rate ◽

Deformation Mechanism ◽

Amorphous Polymers ◽

Chemically Induced ◽

Microscopic Deformation

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Direct mapping of deformation in punch indentation and correlation with slip line fields

Journal of Materials Research ◽

10.1557/jmr.2009.0094 ◽

2009 ◽

Vol 24 (3) ◽

pp. 760-767 ◽

Cited By ~ 5

Author(s):

T.G. Murthy ◽

J. Madariaga ◽

S. Chandrasekar

Keyword(s):

Strain Rate ◽

Slip Line ◽

Large Strain ◽

Shear Bands ◽

Indentation Hardness ◽

Large Area ◽

Line Field ◽

Slip Line Field ◽

Perfectly Plastic ◽

Analysis Technique

Deformation field parameters in plane-strain indentation of a perfectly plastic solid with a punch have been mapped using particle image velocimetry, a correlation-based image analysis technique. Measurements of velocity and strain rate over a large area have shown that the deformation resembles that of the slip line field of Prandtl. A zone of dead metal is found to exist underneath the indenter adjoining which is a transition region of material flow similar to the centered-fan region in the slip line field. Shear bands demarcate the boundaries of these deformation regions. The observations suggest that a representative strain rate may be assigned to the indentation. By integrating the strain rate field along particle trajectories, the strains in the indentation region have been estimated. The strain values are seen to be large, 0.5 to 4, over a region extending to about twice the indenter half-width. A pocket of large strain, ∼4, is found to exist close to the edge of the indenter–specimen contact. Prandtl’s slip line field is modified based on the observations and used to estimate the strain field. The measurements of the deformation parameters are found to compare mostly favorably with the predictions of the slip line field and prior observations of indentation. The implications of these findings for analysis and interpretation of indentation hardness are briefly discussed.

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Nonequilibrium tensile deformation of amorphous polymers in the rubbery state: Temperature, strain rate, and strain effects. I

Journal of Macromolecular Science Part B ◽

10.1080/00222347908212301 ◽

1979 ◽

Vol 16 (3) ◽

pp. 355-375 ◽

Cited By ~ 7

Author(s):

J. P. Ibar

Keyword(s):

Strain Rate ◽

Tensile Deformation ◽

Amorphous Polymers ◽

Strain Effects ◽

Rubbery State ◽

Temperature Strain

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The Effect of Small Amounts of Yttrium Addition on Static and under Superplastic Deformation Grain Growth in Newly Developed α+β Type, Ti-4.5Al-6Nb-2Mo-2Fe Alloy

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.15-17.970 ◽

2006 ◽

Vol 15-17 ◽

pp. 970-975 ◽

Cited By ~ 1

Author(s):

Behrang Poorganji ◽

S. Hotta ◽

Taichi Murakami ◽

Takayuki Narushima ◽

Yasutaka Iguchi ◽

...

Keyword(s):

Grain Size ◽

Strain Rate ◽

Grain Growth ◽

Hot Deformation ◽

Superplastic Deformation ◽

Superplastic Forming ◽

Growth Behavior ◽

Two Phase ◽

Yttrium Addition ◽

Grain Growth Behavior

New α+β type titanium alloy with Ti-4.5Al-6Nb-2Mo-2Fe was developed on the basis of using biocompatible elements and eliminating the cytotoxic ones such as Vanadium, while achieving the desirable mechanical properties such as appropriate strength, cold workability and low superplastic forming (SPF) temperature. The present study was conducted to investigate the effect of yttrium addition of less than 0.05% into this alloy on static and under superplastic deformation grain growth behavior. The new alloy bar manufactured by α+β processing and annealed at 1073K yielded extremely fine two-phase microstructure with α grain size around 2μm. Specimens were heated at temperatures of 1048, 1073 and 1098K and kept for times between 3.6 to 172.8KS. Yttrium forms in-situ Y2O3 particles, and the presence of these particles yield finer two phase microstructure due to their retardation effect on β phase grain growth. Grain growth behavior during hot deformation was investigated by hot compression test in use of a hot working simulator of THERMEC-Master Z. Strain rate was varied from 2×10-2 to 2×10-4S-1 and strain was 0.69. Grain size of both α and β phases increased with a reduction of strain rate, and Y2O3 particle was also effective to retard grain growth under hot deformation. It was confirmed from comparison of grain growth during isothermal heating with and without hot deformation that grain growth was much accelerated by deformation. All of these results were discussed based on grain growth mechanism or model for two-phase microstructures as well as superplastic deformation mechanism.

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