PSI - Issue 64

Rui-Xin Jia et al. / Procedia Structural Integrity 64 (2024) 799–806 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

801

3

The theoretical values of group velocity for longitudinal modes can be found by solving the MATLAB joint (1) to (4). Figure 1 shows the theoretical group velocity dispersion curves for a 20 mm diameter cylinder.

Fig. 1 Group Speed dispersion curve of 20mm cylinder

From the Fig.1, it can be seen that the number of modes of the 20mm cylinder increases with the gradual increase in frequency. Selecting a single frequency for its excitation makes it easy to identify the first wave, so a frequency within 150kHZ is selected as the excitation source. 2.2. Acoustoelastic effect The theory of acoustoelasticity suggests that the velocity of an elastic wave in a solid material is related not only to the second- and higher-order elastic constants of the material, but also to the material density and stress level. When the rebar is subjected to axial stress, the relationship equations of ultrasonic guided wave longitudinal wave speed and transverse wave speed with stress and density are as follows (5) to (6).

2 (4 10 4 )( l m + + + + 

) /       +

 

(3)

2 L

c   

2 = + + 



 

3 2 +

 

4 4 / 4      + + + m n

 

2   c

= + 



(4)

 

T

3 2 +

 

Where, λ and µ are Lamey's constants, l , m and n are Murnaghan's third order elastic constants. Rebar material density λ = 115.9GPa, µ = 79.9GPa, l = -248GPa, m = -623GPa, n = -714GPa, and yield limit is 500MPa.

3. Experimental research 3.1. Experimental equipment

The experimental system consists of a tensioning system as well as a guided wave detection system as shown in Fig.2. The tensioning system mainly includes large hydraulic jacks, pressure sensors, and reaction frames. The ultrasonic guided wave detection system uses the PCI-2 Acoustic Emission Acquisition System. It mainly consists of preamplifier, acoustic emission acquisition card, receiving and excitation probes. The receiving probes are all selected as WSa models with a bandwidth range of 100kHZ-1MHz. Rebar with radius 10mm was selected for the experiment and the material parameters are shown in Table.1. The rebar for the experment was 2 m long, the tension section was 1.5 m long, and the spacing between the two sensors was 1.97 m. The sensor arrangement strategy is shown in Fig.2. The loading range of the rebar is 0~140 kN, and the loading is carried out in steps of 20 kN.