| CPC G01N 29/07 (2013.01) [G01N 29/34 (2013.01); G01N 29/36 (2013.01); G01N 29/46 (2013.01); G01N 2291/0427 (2013.01)] | 6 Claims |
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1. A method of non-baseline on-line stress monitoring based on multi-mode Lamb wave data fusion, wherein the method comprises the following steps:
step 1: establishing a Lamb wave dispersion curve according to geometric dimensions and material parameters of a measured object, obtaining a cut-off frequency of a first-order Lamb wave mode, determining an excitation frequency of a Lamb wave signal, and then obtaining pure Lamb waves in S0 and A0 modes obtained inside the measured object;
step 2: after determining the excitation frequency of the Lamb wave signal, solving an elastodynamic equation of the measured object under a prestress condition;
the elastodynamic equation of the measured object under the prestress condition being:
 wherein,
 in the equation, Cαβγδ represents a second-order elastic modulus of the measured object, Cαβγδεη represents a third-order elastic modulus of the measured object, eiαβ represents an initial strain caused by a prestress, uiα represents an initial displacement caused by the prestress, and ρ0 represents a density of the measured object;
a relationship between a group velocity and a frequency and a wave number of the Lamb wave satisfying:
 wherein cg is the group velocity of the Lamb wave, ω is the frequency of the Lamb wave, and k is the wave number of the Lamb wave;
step 3: obtaining a first relationship between a group velocity change of the Lamb wave in S0 mode and a stress of the measured object, and a second relationship between the group velocity change of the Lamb wave in A0 mode and a stress of the measured object;
Step 4: according to the group velocity of the Lamb waves in the S0 mode without a stress, the group velocity of the Lamb waves in the A0 mode without a stress, the first relationship and the second relationship, obtaining a first linear relationship between the group velocity of the Lamb waves in the S0 mode and a uniaxial prestress in a propagation direction under the excitation frequency, and a second linear relationship between the group velocity of the Lamb waves in the A0 mode and a uniaxial prestress in a propagation direction under the excitation frequency:
cg(S0)=5.5625×10−7σ+5296.38 (8)
cg(A0)=1.675×10−7σ+2891.56 (9)
wherein cg(S0) is the group velocity of the Lamb wave in the S0 mode, and cg(A0) is the group velocity of the Lamb wave in the A0 mode, σ is the uniaxial prestress in a propagation direction;
step 5: according to the first linear relationship and the second linear relationship, obtaining an approximately linear relationship between a propagating sound-time ratio of the Lamb waves in the S0 and A0 modes at a fixed propagation distance L and a stress:
 wherein, the propagating sound-time ratio of the Lamb waves in the S0 and A0 modes is a ratio of a propagating sound-time of the Lamb waves in the A0 mode at a fixed propagation distance L to a propagating sound-time of the Lamb waves in the S0 mode at a fixed propagation distance L;
step 6: processing data by an on-line monitoring system; and
step 7: calculating a stress gradient in a depth direction, performing Hilbert transformation on a signal received by a piezoelectric wafer sensor (4) to extract an amplitude envelope of the received signal, calculating the propagating sound-time ratio of the Lamb waves in the S0 and A0 modes, substituting the propagating sound-time ratio into the approximately linear relationship established in step 5 to determine a magnitude and a direction of a uniaxial stress inside the measured object, and finally representing a stress state of the measured object;
wherein the on-line monitoring system comprises a waveform generator (1), a power amplifier (2), a piezoelectric wafer exciter (3), a piezoelectric wafer sensor (4), a high-bandwidth receiving and amplifying device (5), a high-speed data acquisition system (6) and a PC (7);
the waveform generator (1) generates a low-voltage modulation signal, and generates a Lamb wave for the piezoelectric wafer exciter (3) after amplification by the power amplifier (2), and Lamb waves in S0 and A0 modes propagate inside a measured object and are received by the piezoelectric wafer sensor (4);
the piezoelectric wafer sensor (4) inputs an obtained signal into the high-bandwidth receiving and amplifying device (5), and ensures that the signal is amplified into an input range of a digital-to-analog conversion chip through coarse gain tuning and fine gain tuning, and then a lower cut-off frequency and an upper cut-off frequency of a filter are set according to a bandwidth of an excitation signal, the amplified and filtered signal is input into the high-speed data acquisition system (6), the signal is encoded and processed by an FPGA chip, and a sampled signal is transmitted to the PC (7) by using a PXIE bus for storage.
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