Crack propagation rate measurement method

Abstract

The invention discloses a crack propagation rate measurement method. The method comprises the steps of applying alternating load to a test piece with a single-side penetrated crack by a testing machine; measuring load-displacement curves at an interval of certain loading cycles and fitting a linear segment to obtain the non-dimensional flexibility value of the test piece; acquiring the length of the crack according to the relation of the non-dimensional flexibility value of the single-side penetrated crack and the length of the crack under a clamped boundary condition; recording the number of the current loading cycles to obtain a crack length-load cycle number curve, and determining the crack propagation rate; and calculating the corresponding stress intensity factor, acquiring discrete data and fitting to obtain the parameters of the crack propagation rate. The method has the advantages that the method is suitable for measuring the crack propagation rate under positive and negative stress ratios and can be used for measuring the crack length automatically; and the measurement system has wide application range and is particularly suitable for measuring the crack propagation rate of novel materials such as a metal laminated board, a metal / composite material laminated board, a ceramic matrix composite material, a welding material.

Description

technical field [0001] The invention relates to the field of crack growth rate testing, specifically, a method for automatically testing the crack growth rate by using a unilateral penetration crack test piece, and is especially suitable for new-type metal laminates, metal / composite material laminates, and ceramic substrates. Crack growth rate testing of new materials / processes such as composite materials and welding materials. Background technique [0002] Fatigue failure under alternating loads is the most typical failure form of aircraft structures. In order to ensure the safety of the structure, the design and analysis of the damage tolerance of the structure must be carried out. The fatigue crack growth performance of the material is the design and analysis of the structural damage tolerance For this reason, the crack growth rate parameter test of the material under various stress ratios must be carried out. [0003] According to the requirements of ASTM E647-2013 "Sta...

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Problems solved by technology

[0004] (1) Central penetration crack specimen (M(T) specimen), although this specimen is suitable for the crack growth rate test under the full range (positive and negative stress ratio), but the specimen will appear during the test Asymmetric crack growth phenomenon, resulting in invalid test data;

[0005] (2) The compact tensile test piece (C(T) test piece) requires a relatively large thickness of the test piece, which can only be tested under a positive stress ratio, and cannot be tested for the crack growth rate under a negative stress ratio;

[0006] (3) The three-point bending specimen (SEB(T) specimen) requires a large thickness of the specimen, and can only be tested under a positive stress ratio, and cannot test the crack growth rate under a negative stress ratio.

However, when the central penetration crack test piece is used to test the crack growth rate, it is particularly easy to produce asymmetric crack growth.

Especially in order to meet the low weight, long life and high reliability design requirements of advanced aircraft structures, new materials / processes are more and more widely used, such as metal laminates, metal / composite laminates, ceramic matrix composites, various welding Materials, etc. If the above-mentioned new materials / processes use M(T) specimens to test the crack growth rate, asymmetric crack growth is more likely to occur, and once the crack growth is asymmetrical, not only the measurement results are invalid, but also because the material / process is expensive. , Human consumption is large, resulting in serious economic losses

[0008] At present, there is a lack of testing methods and systems for the crack growth rate under the action of positive and negative stress ratio loads that can avoid asymmetric crack growth in the test at home and abroad.

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