抄録
Since brittle lacquer coating of air-drying type displays viscoelastic behaviour, brittleness of the lacquer coating is markedly dominated by loading time and test temperature. When the technique of brittle coating is applied in the strain measurement, it is necessary to compare the coating cracks on the calibration bars with those on the engineering structures to be inspected, although these two type of specimens have been subjected to different load application time. Besides, the relaxation method is often utilized to analyze the compressed regions on the structure.
Few studies have been made on the mechanical properties of the coating by taking viscoelasticity into account, because it is too difficult to make mechanical tests on a coating film of high brittleness separately. In this study, therefore, the influence of both loading time and test temperature on the strain sensitivity of some brittle lacquer coatings were investigated on the calibration bars by using a new loading device controlling the load application time.
The results obtained are as follows.
The influence of loading and relaxation time on the strain sensitivity was clarified at various test temperatures. It was confirmed that the strain sensitivity scarcely changed with time up to about 10 seconds. The sensitivity master curves presenting the combination of the loading time, the test temperature and the acid value of basic ingredients were composed successfully by applying the reduction principle.
