Specimen-test machine coupling and its implications for plastic-deformation models

Conference · Thu Jan 01 04:00:00 UTC 1981

OSTI ID:6501705

Holbrook, J. H.; Swearengen, J. C.; Rohde, R. W.

The equation relating uniaxial strain rates to the crosshead speed of a test machine of arbitrary stiffness is carefully examined. It is demonstrated that an accurate formulation of the specimen/machine coupling relation requires exact additivity of elastic and plastic strain contributions and that this is only possible with a specific set of definitions for these strains. When these definitions are implemented to insure additivity, two strain-dependent terms in the coupling relation are identified that have been treated as constants in previous studies. One term is shown to account for the decreasing true total strain rate with increasing plastic strain at a fixed crosshead speed. The second term accounts for strain dependence of the combined specimen/machine modulus due to change in length and area of the specimen. Several applications of the coupling relation are given that illustrate the importance of treating the specimen and test machine as a well-defined system when inferring infomation about plastic-deformation models from raw data. Topics covered include (1) effect of machine stiffness on workhardening behavior, (2) variation of total and plastic strain rate during tensile deformation, (3) effect of machine stiffness on stress relaxation behavior, (4) relationship between stress rates before and after a change in crosshead speed, and (5) deductions about mobile dislocation density from observed stress-time behavior.

• Research Organization: Battelle Columbus Labs., OH (USA); Sandia National Labs., Livermore, CA (USA); Sandia National Labs., Albuquerque, NM (USA)
• DOE Contract Number: AC04-76DP00789
• OSTI ID: 6501705
• Report Number(s): SAND-80-1840C; CONF-801148-5
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
420500* -- Engineering-- Materials Testing
DEFORMATION
DESTRUCTIVE TESTING
MATERIALS
MATERIALS TESTING
MATHEMATICAL MODELS
MECHANICAL PROPERTIES
MECHANICAL TESTS
OPERATION
PERFORMANCE
PLASTICITY
RELAXATION
STRAIN RATE
STRESS RELAXATION
TENSILE PROPERTIES
TEST FACILITIES
TESTING