Abstract
Terahertz (THz) spectroscopy is an important method in noninvasive detection and diagnosis for historic relics. A new nondestructive testing (NDT) method based on terahertz time-domain spectroscopy (THz-TDS) technology was developed to measure the hollowing deterioration of the Yungang Grottoes in this paper. Hollowing deterioration samples were strictly prepared, and a series of experiments were conducted to ensure the representativeness of the experimental results. A hollowing thickness model was established by the relationship between the thickness of the hollowing deterioration sample and the time difference of the front flaked stone surface and the stone wall surface of the hollowing deterioration samples. The results show that the R-squared value of the model equation reached 0.99795, which implies that this model is reliable. Therefore, the actual hollowing thickness of the Yungang Grottoes can be obtained by substituting the time difference in the proposed thickness hollowing model, where the time difference is obtained from measured THz spectra. The detection method of stone relic hollowing deterioration is easy to apply, which can not only realize qualitative NDT but also quantitative hollowing deterioration thickness determination. This method has crucial practical significance for the repair and strengthening of stone relics similar to the Yungang Grottoes.
Highlights
Stone relics are monuments consisting of natural stones, including buildings, grottoes, stone tablets, etc., which have very high historical and artistic values, as well as represent a specific kind of geological engineering requiring long-term preservation
The hollowing deterioration samples are tested with a THz‐TDS1008 test system, In is this paper, the hollowing deterioration samples are tested with aantenna
Our analysis suggests that THz technology can be can be calculated by substituting measured THz spectra in the proposed model, which can applied to efficiently detect hollowing deterioration, as it reflects the thickness of hollowing provide effective references for repairing and reinforcing ancient relics
Summary
Stone relics are monuments consisting of natural stones, including buildings, grottoes, stone tablets, etc., which have very high historical and artistic values, as well as represent a specific kind of geological engineering requiring long-term preservation. With the intensification of environmental pollution and under the influence of natural and human factors, stone relics (especially open stone relics) are being damaged at an alarming rate [1–3]. This damage has endangered the safety of cultural relic preservation and has affected the historical and cultural values of stone relics. With the Yungang Grottoes as an example, as shown, the surface of stone relics is corroded, and the internal layered or sheet-like clay mineral and gypsum components produce a high expansion pressure under the action of natural precipitation, such as rain. When a rock formation has low rock strength, a hollowing structure will be produced, which comprises three parts, namely, the front rock wall (flaked stone), the air layer, Electronics 2020, 9, 625; doi:10.3390/electronics9040625 www.mdpi.com/journal/electronics
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