Study of Structural Criteria for Composite Airframes. Volume II. Current/Criteria/Selected Rationale Review and Evaluation.

摘要

Criteria and design practices currently used for aircraft structures are examined and evaluated for applicability to composite structures. Selected probabilistic or statistical rationales are also reviewed and evaluated for possible applications. From these studies a plan was developed for acquiring understanding and data from which structural criteria and design practices applicable to composite airframes may be written. The basic characteristics of filamentary composites that are unique in comparison to those of metals are defined and explored. Special areas investigated include laminates,joints,and cutouts. The structural criteria derived from metallic structure experiences are not applicable to composite structure because the critical interaction of a low strain to failure material with structural complexity is not recognized;universal requirements and rigid design practices irrespective of material,design concept or manufacturing methods,or size effects are imposed,and an assumption of translation of residual strength and lifetime allowables from the material level to the component level,which is incompatible with observed composite behavior is imposed. Accelerated test procedures have not been developed successfully;therefore,near-term composite designs should be developed using a realistic random load and environment simulation. In order to achieve the necessary confidence in structural integrity,the composite design should acknowledge fleet size,reliability goals,structural complexity,scaling from test specimen-to-component level. (Modified author abstract)