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Unformatted text preview: 9.1 A Charpy machine with a hammer weighing 200N has a 1-m long arm. The initial
height ho is equal to 1.2m. The Charpy specimen, (See Figure 9.2), absorbs 80J of energy
in the fracturing process. Determine:
(a) The velocity of the hammer upon impact with the specimen. (b) The velocity of the hammer after breaking the specimen. (c) An average strain rate in the specimen (d) The final height attained by the specimen
From part (b) 9.6 A thermoplastic polymer has a plane-strain fracture toughness KIc=15MPa m1/2 and a
yield strength σy = 80MPa. Estimate the requirements for dimensions of a fracture
toughness specimen for this sample. Which means that 9.11 Norton NC-132 hot pressed Si3N4 has the following tensile strengths for the given
Three-point bending: 930 MPa
Four-point bending: 720 MPa
Uniaxial tension: 550 MPa
Larger measured failure stresses mean smaller flaw sizes were seen in the sample,
therefore the largest flaws were seen in the uniaxial tension test while smaller flaws led to
failure in the 3-point and 4-point bending tests. An alternative explanation is that flaws of
the same size could have led to failure in all of these tests, the difference being in that
uniaxial tension has the highest area where the max stress is applied therefore the stress
would “see” the flaws necessary to cause failure sooner than the other tests. Also the 4point bending test has a larger area of applied max stress than the 3-point bending test
therefore it would fail at lower stresses due to the fact that it is more likely to have a flaw
of the necessary size in the area where the max stress is applied.
9.14 In a sample of MoSi2, an indentation made by a Vickers indenter gave the
impression shown in Figure E9.14 under a load of 1kN. Compute the hardness H of
MoSi2. Taking E for MoSi2 to be 300 GPa, compute the fracture toughness of the sample.
Answers may vary due to differences in measurement from figure. ( ) ...
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- Spring '08