Interface ultrasonic reflectivity-pressure relation curve establishment method and loading testbed

1. A method for establishing an interface ultrasonic reflectivity-pressure relation curve, comprising:

S1, placing a loading surface in a loading system, determining a position of the loading system by using a laser probe, and determining a coordinate O 1 of a center of the loading surface, wherein the loading surface is a flat punch with rounded corner;

S2, scanning the loading surface under a scanning path by using a immersion ultrasonic transducer when no force is applied to the loading surface to obtain a zero point signal, applying a plurality of forces, one at a time, to the loading surface, scanning the loading surface along the same scanning path when each force is applied to the loading surface so as to obtain a plurality of characteristic signals, and calculating a plurality of ultrasonic reflectivity values, wherein each of the plurality of ultrasonic reflectivity values equals a ratio of one of the plurality of the characteristic signals to the zero point signal, then constructing a distribution curve of the ultrasonic reflectivity values, as shown in Equation (1):

R=f 1 ( r )   (1)

wherein r is a distance between a scanning area and O 1 , wherein a scanning area is a location on the loading surface that is scanned,

R is an average value of the ultrasonic reflectivity of the scanning area corresponding to r;

the scanning path comprises a plurality of sub-paths, wherein each sub-path starts from O 1 and extends to a boundary of the loading surface along a straight line, and then returns to O 1 along the same straight line;

S3, determining a coordinate O 2 that is a center of concentric circles formed by scanning areas having a same ultrasonic reflectivity, repeating S2 and S3 until when O 1 and O 2 coincide;

S4, determining a boundary characteristic value a, of a distribution boundary of the ultrasonic reflectivity, and calculating an average boundary characteristic value a, wherein a i , is a distance between the distribution boundary of the ultrasonic reflectivity and O 2 ;

S5, determining a pressure value at each scanning area, and then obtaining a corresponding relation between the distance r and the pressure P, as shown in Equation (2):

R=f 2 ( r )   (2)

S6, deducing a corresponding relation of R and P according to the Equation (1) and Equation (2) to obtain an initial ultrasonic reflectivity-pressure relation curve, as shown in Equation (3):

R=f 3 ( r )   (3)

S7, for each of the plurality of forces applied to the loading surface in step S2, calculating a pressure P′ i according to Equations (1) and (3), and calculating a total load W′ i by integrating P′ i over the loading surface according to Equation (4),

W′ i =∫P′ i dxdy   (4)

wherein dx and dy are variables in the integral, representing a finite area on the loading surface, W i is a load on the loading surface measured by a force sensor, and calculating a coefficient K i corresponding to each of the plurality of forces applied to the loading surface in step S2 according to Equation (5), and taking an average value of the plurality of coefficients K i to obtain an average correction coefficient K,

K

i

=

W

i

W

i

′

⁢

;

(

5

)

and

S8, correcting the initial reflectivity-pressure relation curve by using the average correction coefficient K to obtain a final reflectivity-pressure relation curve according to Equation (6):

P i =K i ×P′ i   (6).

2. The method according to claim 1 , wherein, in step S2 the plurality of forces are gradually increased at a same increment.

3. The interface ultrasonic reflectivity-pressure relation curve establishment method according to claim 1 , wherein, in step S2, calculating the ultrasonic reflectivity comprises:

performing fast Fourier transform on the zero point signal and the characteristic signals, and calculating the corresponding ultrasonic reflectivity according to Equation (7) to obtain the reflectivity distribution along the scanning path,

R

i

=

h

i

H

i

⁢

;

(

7

)

in which R i is an ultrasonic reflectivity, h i is an amplitude of the characteristic signal, and H i , is an amplitude of the zero point signal.