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In order to evaluate the thermal ageing of silicone rubber for cable intermediate joint insulation layer, this paper proposed an evaluation method based on nonlinear ultrasonic signal characterization. Firstly, a ultrasonic detection simulation model of silicone rubber ageing was established, and tests were conducted on the real cable joint specimens with different thermal ageing time at 200℃. Then the nonlinear ultrasonic detection was carried out at typical positions by using wedge coupling method. Lastly, the correlation between the ageing time and ultrasonic nonlinear coefficient was verified and the mechanism was explored. The results show that the experimental and simulation results are highly consistent in the change trends of the characteristic parameters of transmitted wave signal in time-domain and frequency-domain. Specifically, as the ageing time increases, the fundamental wave amplitude and the second harmonic amplitude both gradually decrease, and the ultrasonic nonlinear coefficients gradually increase. Under actual ageing time of 480, 720, and 960 h, the relative errors between the ageing time of silicone rubber obtained by substituting the nonlinear ultrasound coefficients obtained from the experiment into the fitting relationship equation and the actual ageing time are 1.58%-5.66%, 2.57%-6.66%, and 0.85%-4.75%, respectively, and the consistency between the fitted results and the actual ageing time is better, which verifies the validity of nonlinear ultrasonic testing method in the assessment of thermal ageing damage of silicone rubber.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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