Fracture toughness testing machine and fracture toughness test method

A testing machine for evaluating fracture toughness at a bonded interface of a specimen by applying a predetermined testing load to the specimen, the specimen being obtained by bonding a first member and a second member, which are made of dissimilar materials, in a state where a thermal residual stress is present therein, and having a crack formed at part of the interface between the members, the fracture toughness testing machine comprising:

• a base;
• specimen supporting portions fixed to the base;
• a testing-load applying device that is a tensile force applying portion configured to apply a tensile force as the predetermined testing load to the specimen so as to open the crack;
• and
• a cancelling-load applying device for applying a cancelling load to the specimen, including:
• a pressing-force applying portion that is configured to operate so as to apply a pressing force with a constant magnitude to the specimen as the cancelling load;
• and a pressing-force determining portion that is configured to determine the constant magnitude of the pressing force by calculating the constant magnitude of the pressing force with the use of pre-stored equations so that an energy release rate related to in-plane shear mode crack deformation becomes zero, corresponding to GII=0, whereby the cancelling-load applying device is configured to apply the cancelling load to the specimen so as to cancel the thermal residual stress,
• wherein the specimen supporting portions are configured to support two end portions of the specimen, one of the specimen supporting portions is disposed at one of the two end portions of the specimen where the testing-load applying device applies the predetermined testing load to the specimen, and the predetermined testing load to the specimen is changeable with respect to the constant magnitude of the pressing force, and
• the equations are following equations (1) to (5):
• G
• II
• =
• 1
• 2
• ⁢
• B
• ⁢
• (
• c
• 1
• +
• c
• 2
• +
• h
• 1
• 2
• 4
• ⁢
• d
• 1
• +
• h
• 2
• 2
• 4
• ⁢
• d
• 2
• )
• ⁢
• N
• c
• 2
• =
• 0
• (
• 1
• )
• N
• c
• =
• 2
• h
• 1
• ⁢
• ξ
• +
• 2
• ⁢
• η
• ⁢
• {
• -
• (
• ξ
• ⁢
• P
• D
• +
• h
• 2
• ⁢
• d
• 2
• 2
• ⁢
• P
• E
• 2
• )
• ⁢
• a
• +
• (
• α
• 2
• -
• α
• 1
• )
• ⁢
• Δ
• ⁢
• T
• }
• (
• 2
• )
• ξ
• =
• h
• 1
• 2
• ⁢
• d
• 1
• -
• h
• 2
• 2
• ⁢
• d
• 2
• η
• =
• c
• 1
• +
• c
• 2
• +
• h
• 2
• (
• h
• 1
• +
• h
• 2
• )
• 4
• ⁢
• d
• 2
• (
• 3
• )
• c
• i
• =
• U
• i
• R
• i
• ⁢
• U
• i
• -
• S
• i
• 2
• d
• i
• =
• R
• i
• R
• i
• ⁢
• U
• i
• -
• S
• i
• 2
• (
• 4
• )
• R
• i
• =
• B
• ⁢
• ∫
• E
• i
• ⁢
• d
• ⁢
• z
• i
• S
• i
• =
• B
• ⁢
• ∫
• E
• i
• ⁢
• z
• i
• ⁢
• d
• ⁢
• z
• i
• U
• i
• =
• B
• ⁢
• ∫
• E
• i
• ⁢
• z
• i
• 2
• ⁢
• d
• ⁢
• z
• i
• (
• 5
• )
• GII:
• energy release rate related to crack deformation of in-plane shear mode
• B:
• width of the specimen
• h1:
• thickness of the first member
• h2:
• thickness of the second member
• a:
• length of the crack
• α1:
• thermal expansion coefficient of material of the first member
• α2:
• thermal expansion coefficient of material of the second member
• ΔT:
• temperature difference between operation temperature and stress-free temperature
• PD:
• tensile force (the testing load)
• PE:
• pressing force (the cancelling load)
• z1:
• coordinate in thickness direction set for the first member
• z2:
• coordinate in thickness direction set for the second member
• E1:
• in-plane Young's modulus of the first member
• E2:
• in-plane Young's modulus of the second member
• i:
• subscript (1:
• the first member, 2:
• the second member).