The precursor decay and stress relaxation behavior of 20 steel under shock compression were studied using planar impact experiments with different sample thickness. Time resolved free surface velocity profile measurements are performed by means of a velocity interferometer system for any reflector (VISAR) with the time resolution of 1 ns. The results show an apparent decay in the Hugoniot elastic limit with increasing propagation distance, as well as a stress relaxation behind the elastic wave front, and nearly 44% loss of Hugoniot elastic limit was observed in the present sample thickness range. The rise time of elastic wave fronts as a function of the sample thickness has also been determined accurately. Experiments with different impact velocities are carried out, and indicate apparently the independence of the dynamic yield behavior on the loading stress amplitude.
| 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 |