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Fatigue life enhancement of aircraft structures through bonded crack retarders (BCR)

机译:通过粘结减缓剂(BCR)延长飞机结构的疲劳寿命

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摘要

The trend in aircraft design is to produce greener airplanes through lighter structures and/or structures with extended life and reduced maintenance. Bonded crack retarders (BCR) are one of the solutions towards that objective. BCR are reinforcing straps bonded to the structure in order to improve the fatigue and damage tolerance properties of the assembly. The aim of this study was to demonstrate that the BCR hybrid technology – beneficial for upper wing cover – could also be applied to lower wing covers. The project also focused on evaluating BCR most important parameters.The fatigue life improvement obtained from BCR was evaluated through a series of coupons and skin-stringer assemblies tested under constant and variable amplitude loading. While the coupon tests demonstrated a life improvement of only 17% under constant amplitude loading, the variable amplitude load tests performed on the skin-stringer assembly demonstrated increased fatigue lives with a factor of 5 and reduced crack growth rates with a factor of 5 to 6.A finite element calculation tool was developed in order to conduct a parametric analysis of BCR geometry through the evaluation of the substrate stress intensity factor in the case of fatigue loading. The main difficulty was to include the interacting mechanism of the substrate lead crack and the disbond of the adhesive layer. The novelty of the approach was to incorporate the fatigue delamination calculation in order to evaluate the fatigue disbond propagation with crack growth. This was embedded in a 3D finite element design tool ReSLIC (Reinforced Structures Life Improvement Calculation). A necessary step to the development of ReSLIC was the analysis of fatigue properties of the adhesive system in order to provide input data for fatigue delamination calculations. To that end, a series of fatigue tests were performed in pure Mode I, pure Mode II and mixed mode with ratios of 25%, 50% and 75% of mode II ... [cont.].
机译:飞机设计的趋势是通过更轻的结构和/或具有更长寿命和减少维护的结构来生产更环保的飞机。粘结抗裂剂(BCR)是实现该目标的解决方案之一。 BCR是粘合到结构上的加强带,目的是改善组件的疲劳和损伤承受能力。这项研究的目的是证明BCR混合技术(有益于上机翼罩)也可以应用于下机翼罩。该项目还专注于评估BCR最重要的参数。通过在恒定和可变振幅载荷下测试的一系列试样和纵梁组件评估了从BCR获得的疲劳寿命改善。试样测试表明,在恒定振幅载荷下,寿命只有17%的改善,而在纵梁总成上进行的可变振幅载荷测试表明,疲劳寿命增加了5倍,裂纹扩展率降低了5到6倍开发了一种有限元计算工具,以便在疲劳载荷情况下通过评估基底应力强度因子来进行BCR几何参数分析。主要困难在于包括基体铅裂纹与胶粘剂层脱粘的相互作用机理。该方法的新颖之处在于结合了疲劳分层计算,以评估随着裂纹扩展的疲劳剥离扩展。它被嵌入到3D有限元设计工具ReSLIC(增强结构寿命改进计算)中。开发ReSLIC的必要步骤是分析胶粘剂系统的疲劳特性,以便为疲劳分层计算提供输入数据。为此,在纯模式I,纯模式II和混合模式下分别进行了一系列疲劳测试,比例分别为模式II的25%,50%和75%。

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    Doucet Jeremy;

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