| Abstrakt: |
The use of composite structures has seen increasing use in the aerospace industry to meet ever more aggressive weight and performance targets. These structures must meet stringent damage tolerance requirements, which can be demonstrated by sizing the structure to withstand the compressive loads with a 0.25 in open hole. This testing is performed to the requirements of ASTM D6484 (ref 1). The test method is also used to generate open-hole data that is part of the input to bearing bypass analysis tools. To address the effect of short edge distance of bolt holes, the width of the specimen is reduced. Paragraph 6.2 of ASTM D6484 describes the specimen geometry. The following statement is made in para 6.2, "Results may also be affected by the ratio of ungripped specimen length to specimen width; this ratio should be maintained at 2.7, unless the experiment is investigating the influence of this ratio." This approach requires a different length of specimen for each value of w/D. The intention is to maintain a constant hole diameter and vary the width of the specimen, requiring the ungripped length to change to maintain the 2.7 ratio. A study was made of this requirement. It suggested that this 2.7 value is a minimum, rather than an absolute requirement, for number of laminates. For laminates with a high Poisson's ratio (a +/-45 laminate), the 2.7 value is shown to be inadequate to produce an accurate measure of the open hole strength. [ABSTRACT FROM AUTHOR] |
