Abstract
With the increasing demands for detailed design of composite aircraft structures, the method of covering all damages with low design allowables cannot meet the current requirements for aircraft structure design. Herein, this paper proposes a novel algorithm for design allowable determination of composite laminates by combining the damage distribution with damage factor model of design allowable, so as to provide different structures with more accurate design allowables based on their initial damages. For the composite laminates with initial delaminations, a model describing the effect of delamination size and depth position on the compression design allowable is developed and the compression design allowable of different aircraft structures are individually determined by employing abundant initial delamination statistics. Compared with the design allowable offered by the single-point method, the design allowable based on the initial damage can be increased by at least 5% to 20%, greatly improving the economic benefits of the aircraft structures and providing an important support for the damage tolerance design of the composite structures.
Highlights
ManolakosServing as the threshold of actual stress/strain, the design allowable plays a vital role in ensuring the safety and reliability of composite aircraft structures [1,2,3]
Fourthe strain gauges were atreduce the compression carrying capability ofstandard laminates, compression failure tached on both sides of the specimen to monitor the compression strain, so as to keep the strain decreases by more than 35% as the delamination size increases from 0 to 25 mm
Effects of Delamination Size and Depth Position rameters which can be estimated through linear regression, and ε is a random variable with compression failure strains of the laminates with delamination in h / 3(13), andit zeroThe expectation characterizing the stochastic nature of composites
Summary
Serving as the threshold of actual stress/strain, the design allowable plays a vital role in ensuring the safety and reliability of composite aircraft structures [1,2,3]. In terms of the strength distribution, the B-basis values of the open-hole strength is eventually estimated These studies mainly performed statistical analysis on the single-state data (the results of the same type of test) to generate the design allowable values, which implies that the worst environmental conditions and the most dangerous defects are taken into account, leading to a conservative design allowable. For the compressive load cases, the design allowable mainly generates based on the test data of specimens with impact damage [1,9], which can result in matrix cracking, delamination and fiber breakage of the laminates [13].
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