Tham khảo tài liệu 'mil-hdbk-17-4 - composite materials handbook vol4 [us dod 1999] 4ah episode 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | MIL-HDBK-17-4 ployed that reveals the influence of neighboring tests. The testing sequence will be dependent on the test specimen and fiber arrangement. A simple example of a testing sequence is shown in Figure . This testing order will help determine if there is an effect of neighboring fibers. For example if the average of tests 7 8 and 9 are statistically different from the average of 1 2 3 4 5 and 6 then previously tested fibers probably influence adjacent fiber results. Likewise if the average of tests 1 2 3 4 is statistically different from the average of tests 5 6 10 and 11 an edge effect may be present. It is obvious that several baseline tests are required to obtain a good understanding of the pushout behavior and the factors which affect the results. 0000 D@ 0000 OOOI IỘOOO OỔỎÒÓOỎŨỎỎ oooooojoooo OOOỊOe OOOO 0000 0 0000 OOOOOOIOOOO ooooootoooo OOOOOOjOOOO 000@ @i0000 WRONG CORRECT a b FIGURE Sample testing sequences. Effects of environment Most fiber push-out tests are performed in room laboratory air without considering the effects that moisture or other constituents of air may have on the test results. Recent studies References n and have suggested that the presence of moisture and or oxygen in the testing environment can substantially alter fiber sliding behavior in some composite materials. As an example Figure e shows a set of seven push-out curves obtained in laboratory air and seven tests performed in dry nitrogen on the same SCS-6 Ti-24-11 specimen. These curves show that frictional sliding loads were consistently lower and the decrease in load after debonding much more abrupt in the tests performed in room air compared to tests performed in nitrogen. Such large differences appear to be associated with interfacial failure in a carbon-rich zone where fiber sliding would be expected to show similar environmental sensitivity to sliding graphite surfaces which need adsorbed moisture to
