62 J. Liu et al. 7.2 Specimen First, the water absorption ratio was measured to clarify saturated water absorption capacity of CFRP material. Epoxy resin was used for the matrix of CFRP in this test. As shown in the Fig. 7.1, CFRP had width of 12 mm, length of 20 mm, and thickness of 2 mm. The fiber directions were 0 and 90 degrees, and the laminate structure has a total of 15 layers. The content of resin and density of CFRP were 40 ±2Wt% and 1.5 g/cm3, respectively. Percentage of volatile components is less than 2.0Wt%. The specimen used in the impact compression test is shown in Fig. 7.2. The CFRP was 12 mm in inner diameter, 14 mm in outer diameter, and 7 mm in thickness. The fiber direction was 90 degrees’ perpendicular to the compression direction. 7.3 Experiment First, drying treatment was conducted for the specimen in a drying furnace at a constant temperature of 343 K. The processing time is set to 24 h so as to dry specimen completely. Nine specimen were put in distilled water at 323 K and 298 K (normal temperature), respectively, and specimen mass was measured from 2 h to 2 weeks after the water absorption experiment. The calculation formula of water absorption is expressed as follows: C=(Mt −M0)/M0 ×100% Where C, M0, and Mt are mass change rate, mass before water absorption, and mass after water absorption. In terms of impact compression test, the split Hopkinson pressure bar test method (SHPB method) is used to provide high strain rate. In order to satisfy the experimental equipment needs of SHPB method, cylindrical CFRP material was used for impact compression test. The input bar, output bar, and striker of the SHPB testing machine were all solid bars with a diameter of 16 mm made of SUJ2 high-carbon chromium bearing steel. The input bar was 2500 mm in length, the output bar was 1300 mm in length, and striker was 1000 mm in length, respectively. As shown in Fig. 7.3, according to the one-dimensional stress wave theory, the dynamic stress-strain curve and the dependence relationship between compression Fig. 7.1 Water absorption test specimen Fig. 7.2 Impact test specimen
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