Approach for characterizing propagation of metallic short cracks and long cracks

A method for characterizing propagation of metallic short cracks and long cracks, comprising the following steps:

• acquiring crack tip opening displacement in a metallic notched sample under cyclic loading, wherein the metallic notched sample comprises one of 316H austenitic stainless steel, 6063-T6 aluminum alloy and TC4 titanium alloy;
• acquiring crack tip opening displacement amount caused by a single monotonic tensile in the metallic notched sample, and crack tip opening displacement caused by monotonic tensile in the metallic notched sample under a maximum far-field stress;
• based on an original Shyam model, constructing, according to the crack tip opening displacement amount and the crack tip opening displacement caused by the monotonic tensile and by obtaining yield strength of the metallic notched sample, a Tmφc model for characterizing the propagation of the metallic short cracks and long cracks, wherein the Tmφc model is representing a growth rate of the metallic short cracks and long cracks;
• wherein an expression of the Tmφc model is:
• da/dN=k(Tmφc)m2
• wherein da/dN represents the growth rate of the metallic short cracks and long cracks, φc represents the crack tip opening displacement under cyclic loading, Tm is the crack tip opening displacement caused by the monotonic tensile under static toughness dissipation and crack tip strain energy of materials, and k and m2 represent fitting parameters;
• and
• wherein an expression of the crack tip opening displacement is:
• φ
• c
• =
• 8
• ⁢
• σ
• ys
• (
• 1
• -
• v
• 2
• )
• ⁢
• a
• π
• ⁢
• E
• ⁢
• ln
• ⁡
• (
• sec
• ⁡
• (
• (
• 1
• -
• R
• )
• ⁢
• π
• ⁢
• σ
• max
• 4
• ⁢
• σ
• ys
• )
• )
• wherein R represents a stress ratio, V represents a Poisson's ratio, α represents a crack length, σys represents a material yield strength, σmax represents the maximum far-field stress, and E represents a Young's modulus;
• wherein the method for characterizing the propagation of the metallic short cracks and long cracks further comprises:
• applying the Tmφc model to characterize propagation behavior of metallic short cracks and long cracks of different metal materials to obtain growth rates and life prediction of the short cracks and long cracks on the different metal materials, thereby performing fatigue crack propagation experiment under different working conditions on notched samples of different metal materials as engineering material performance evaluation for equipment.