Page 175 - Mechanical Behavior of Materials

176 Chapter 4 Mechanical Testing: Tension Test and Other Basic Tests

Impact energies often exhibit a temperature transition, below which the behavior is brittle. Thus,
impact energy versus temperature curves are useful in comparing the behavior of different materials.
However, too much significance should not be attached to the exact position of the temperature
transition, as this is sensitive to the details of the test and will not in general correspond to the
engineering situation of interest.
Bending tests on unnotched bars are useful for evaluating the elastic modulus and strength
of brittle materials. Since linear-elastic behavior is assumed in data analysis, strengths will differ
from those in tension tests, if significant nonlinear stress–strain behavior occurs prior to fracture.
A special bending test called the heat-deflection test is used to identify the limits of usefulness of
polymers with respect to temperature. Torsion tests permit direct evaluation of the shear modulus, G,
and also can be used to determine strength and ductility in shear. Thin-walled tubes tested in torsion
have nearly constant stress and strain through the wall thickness, so such tests may be employed to
obtain stress–strain curves in shear.

NEW TERMS AND SYMBOLS

bending (flexure) test percent reduction in area, %RA
bend strength, σ fb proportional limit, σ p
Brinell hardness, HB Rockwell hardness, HRC,etc.
Charpy V -notch test strain hardening exponent, n
compression test strength coefficient, H
corrected true stress, ˜σ B tangent modulus, E t
elastic limit tensile toughness, u f
engineering strain, ε torsion test
engineering stress, σ true fracture strain, ˜ε f
heat-deflection temperature true fracture strength, ˜σ f , ˜σ fB
indentation hardness true strain, ˜ε
Izod test true stress, ˜σ
necking true toughness, ˜u f
notch-impact test ultimate tensile strength, σ u
offset yield strength, σ o Vickers hardness, HV
percent elongation, 100ε f yielding

REFERENCES

(a) General References
ASTM. 2010. Annual Book of ASTM Standards, ASTM International, West Conshohocken, PA. (Multiple
volume set published annually.)
BARSOM,J.M., andS.T. ROLFE. 1999. Fracture and Fatigue Control in Structures,3ded., ASTM
International, West Conshohocken, PA.
BRIDGMAN, P. W. 1952. Studies in Large Plastic Flow and Fracture, McGraw-Hill, New York.
DAVIS, J. R., ed. 1998. Metals Handbook: Desk Edition, 2d ed., ASM International, Materials Park, OH.