PSI - Issue 70

Arpit Singh et al. / Procedia Structural Integrity 70 (2025) 580–587

585

Table 2: Combination from Hixon table corresponding to frequency vs real and imaginary part obtain in calculation of electrical signature = 2 2 2 + ( − ) 2 = ⌊ 2 + ( − )⌋ 2 + ( − ) 2 Mass, stiffness and damping combination Real part (x) Imaginary part (y) 3.7. Monitoring and visualization Information obtained from PZT sensors is treated and presented through a digital interface for real-time structural health monitoring. Time-varying changes in impedance signatures reflect incipient defects or structural degradation, which are measured by diagnostic algorithms. This diagnosis guides specific maintenance actions, such as localized repair or retrofitting, depending on the extent and location of detected anomalies. 4. Results and discussion The EMI signals of samples were first measured in their unaltered state, and an initial baseline was established. Afterward, gradual controlled artificial damage was introduced progressively, and measurements of EMI signals were continued uninterruptedly. Three samples were individually tested to determine the reproducibility. The impedance data, being taken from the analyzer, consisted of real and imaginary parts. Of these, the real part-translated as conductance-was primarily investigated because it exhibited the most distinct changes with changing sample conditions such as age, humidity, and composition. These distinct changes reflect the utility of the conductance parameter as a reliable measure of damage evolution and structural condition. Fig. 4 illustrates the conductance frequency curve, where a leftward and upward shift of the conductance peak is correlated with a measurable decrease in structural stiffness.

3.90E-03

3.40E-03

2.90E-03

• Healthy: undamaged conductance signature; • D1 – D12: progressive damage states signature.

2.40E-03

Conductance (G)

1.90E-03

200

210

220

230

240

250

260

270

280

290

300

Frequency (in Thousands)

Healthy

D1 D8

D2 D9

D3

D4

D5

D6

D7

D10

D11

D12

Fig. 4: Frequency vs Conductance graph

The frequency vs. conductance data collected from the sensor are processed through the impedance equation (Eq. 2) to separate the real and imaginary parts and plot the graph of frequency vs. real part (x). The plots in Fig. 5(a) and Fig. 5(b) are the respective plots for the mathematical formula for stiffness, damping, and mass as formulated by Hixon (1988). For the model that was identified with damping (c) and stiffness (k) in parallel and mass (m) in series, the average stiffness values were calculated. In order to establish the impact of damage seriousness on structural stiffness, artificial cracks were induced in a concrete beam 5 cm away from the sensor with 2 cm spacing and depths