Tham khảo tài liệu 'composite materials handbook part 5', 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 cern therefore is to get good quality specimens from these plates with no mistakes and minimal material waste. Due to the inhomogeneity that is hard ceramic fibers and soft matrix and the extreme anisotropy of these materials they are not easily machined. This is exacerbated by the fact that the plates are often slightly warped due to the high residual stresses due to the CTE mismatch between the fibers and the matrix as well as from irregular lay-ups that is fiber misalignment non-uniform matrix layers from manufacturing of the plates. For these reasons conventional machining practices do not work. Non-conventional machining methods have been successfully used for these materials. There are three ways in which these materials have typically been machined wire electro-discharge machining abrasive water-jet machining or diamond cutting grinding of the entire specimen. All of these methods have been used successfully for thinner materials 8-ply or less . For thicker materials abrasive water-jet cutting does not have a sufficient force to cut through the material and maintain accurate geometries therefore one of the other machining methods must be used. The machining method chosen should be maintained throughout the entire test program if possible to eliminate machining as a possible lurking variable in the data. When preparing 0 specimens care must be taken to ensure that the fibers are aligned parallel to the coupon axis. Likewise when preparing specimens with off-axis or cross-ply fiber orientations good alignment should also be maintained between the coupon axis and the desired orientation. Large deviations could result in errors in the mechanical properties. Typically an alignment of 1 is desired. Larger deviations in alignment should be reported. If damage on the edge of the gage section this is a machined surface is of concern either because it is too rough to support an extensometer too irregular to get an accurate measurement of the .
