Nondestructive measurement method for M-integral of multi-defective material

Abstract

The invention discloses a nondestructive measurement method for the M-integral of a multi-defective material. The method comprises: by means of digit speckle correlated technologies, utilizing optical measurement equipment ARAMIS 4M(GOM mbh) to measure the displacement field on the surface of a test piece; conducting smoothing treatment on the displacement field by a mean filter, and using cubic spline fitting to obtain gradients of the displacement field along two coordinate axes; through a constitutive equation of the material, calculating the stress field on the material surface as well as the strain energy density distribution; and carrying out substitution on a definition expression of the M-integral, choosing any defect-containing closed path, as well as calculating the M-integral through numerical integration. Applicable to various defects and defect clusters, the method of the invention can be used for assessing various forms of material damage and structural integrity in the fields of aerospace, aviation, and machinery, etc.

Description

technical field [0001] The invention relates to a non-destructive measurement method of a mechanical parameter-M integral. technical background [0002] In the study of damage mechanics of multi-defect materials, the M-integral around the defect characterizes the energy release rate of the self-similar expansion of the defect. As a material fracture toughness parameter, it can be widely used in the design of aerospace vehicles and a large number of engineering structures. Its definition expression is as follows: [0003] [0004] where w = σ ij ε ij / 2, σ kj , ε ij , u k and n i are the material strain energy density, stress, strain, displacement, and the external normal vector of the closed integral path C around the defect, respectively; where u k，i is the displacement relative to the coordinate x i partial differential. Similar to the J integral, the M integral is also a path-independent integral whose value does not depend on the path selection. After decad...

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Problems solved by technology

[0010] (1) In order to increase the gray contrast value of the digital speckle in order to increase the gray contrast value of the micro-defect group in the complex situation of the two-dimensional component, firstly, the surface of the specimen is sprayed into a randomly distributed speckle state, and the angle between the two lenses of ARAMIS is set to 25°, load the specimen with MTS equipment

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