A plane stress measurement method for CFRP material based on array LCR waves

Accurate non-destructive characterization of the stress state of CFRP is crucial for evaluating material performance and guaranteeing structural safety. A method for characterizing plane stress in CFRP using arrayed LCR waves is proposed in this study. Considering the impact of CFRP anisotropy on ultrasonic wave propagation, a linear relationship between stress variations and acoustic time changes in anisotropic materials is determined based on the acoustic elastic effect. A measurement model for plane stress of CFRP is developed, and the magnitude and orientation of the principal stresses in the plane were calculated using the acoustic time characteristics of echo signals in three detection directions. Accurate extraction of the acoustic time of the echo signal is the key to stress measurement. A novel acoustic time extraction algorithm that integrates the Gaussian empirical model with the Gabor transform domain is proposed to address the challenges posed by noise and aliasing distortion in echo signals. The problem of parameter estimation and noise reduction in echo signals is transformed into a function optimization problem. The acoustic time and center frequency of the echo signal are then estimated using the best similarity model. Gaussian white noise with a signal-to-noise ratio of 1 dB is introduced to the echo signal, followed by processing using the proposed algorithm. The relative error in acoustic time extraction is found to be less than 0.32 %. Then, the CFRP sample undergo the stress coefficient calibration experiment. Following the pre-calibrated stress coefficient, uniaxial tensile tests were performed on the identical batch of CFRP samples. The experimental results show that in the range of 0-160 MPa, the measurement errors for stress and angle are less than 8.96 MPa and 6.87 degrees, respectively. And the standard deviations for stress and angle repeatability measurements are less than 4.95 MPa and 2.99 degrees, respectively. The experiments demonstrate that the proposed method in this study offers a viable technology for measuring plane stress in large components with orthotropic anisotropy.