Effect of strain rate on plastic flow and failure in polycrystalline tungsten

Journal Article · Mon Nov 02 04:00:00 EST 1998 · Acta Materialia

DOI:https://doi.org/10.1016/S1359-6454(98)00255-9· OSTI ID:302357

Duemmer, T ^[1]; LaSalvia, J C ^[2]; Ravichandran, G ^[3]; Meyers, M A ^[4]

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1. Univ. Karlsruhe (Germany). Dept. of Mechanical Engineering
2. Army Research Lab., Aberdeen, MD (United States). Materials Div.
3. California Inst. of Tech., Pasadena, CA (United States). Graduate Aeronautical Labs.
4. Univ. of California, San Diego, La Jolla, CA (United States). Dept. of Applied Mechanics and Engineering Sciences

Polycrystalline tungsten (less than 100 p.p.m. impurities) was subjected to different heat treatments to yield different grain morphologies and tested at quasi-static (3 {times} 10{sup {minus}3}) and dynamic (10{sup 3}--4 {times} 10{sup 3}/s) strain rates. Three mechanisms of deformation were identified and evaluated: slip, twinning, and intergranular cracking. Whereas plastic flow by slip has considerable strain-rate sensitivity in tungsten (which is found to be well represented by the Mechanical Threshold Stress constitutive equation) the cohesive strength of the grain boundaries was found to decrease with heat treatment temperature, but was insensitive to strain-rate changes. Low-strain-rate deformation yielded limited damage at strains as high as 0.25, whereas high-strain-rate deformation led to catastrophic failure at strains between 0.05 and 0.10. Slip and grain-boundary decohesion being competing deformation mechanisms, the material undergoes a ductile-to-brittle transition as the strain rate is increased from 10{sup {minus}3} to 10{sup 3}/s. Two failure modes are identified: debonding initiated by shear along a grain-boundary facet (similar to the wing-crack mechanism) and debonding initiated at voids. The interactions between microcracks and twins are characterized, and there is both evidence of fracture initiation at twins (intergranular cracks),a nd twin initiation at cracks (transgranular cracks). Calculations based on existing wing-crack models enable the estimation of the grain-boundary cohesive energies.

• OSTI ID: 302357
• Journal Information: Acta Materialia, Journal Name: Acta Materialia Journal Issue: 17 Vol. 46; ISSN 1359-6454; ISSN ACMAFD
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CRACK PROPAGATION
DEFORMATION
DUCTILE-BRITTLE TRANSITIONS
FAILURES
PLASTICITY
SHEAR PROPERTIES
SLIP
STRAIN RATE
TUNGSTEN
TWINNING