The Migration of Stress Concentrations in Integrated Composite Structures.

为了实现这些目标，航空航天工业对减轻重量、提高组件性能和复合结构部件的制造速度的不断需求，导致了对使用离散刚度定制（DST）的兴趣。传统上，单层纤维层内的纤维角度始终朝向单一方向，并且根据所需的刚度和强度优化了层的堆叠顺序。然而，离散刚度裁剪旨在以不连续的方式改变零件几何形状的纤维角度和厚度。ESPRC之前赞助的一个项目发现，如果同时优化复合材料结构的层角和厚度，则可以最大程度地减轻40%的重量。这种优化可以通过横跨平板宽度的至少三个离散条带或区域来实现，其中纤维的方向是恒定的，但在每个条带内不同。理论上，DST层压板结构可以使用自动铺带（ATL）机器制造，与其他制造方法相比，它能够以高速率沉积材料。该技术与离散双轴复合带（即无卷曲织物）的使用相结合，理论上具有双重优势，可以将沉积速率提高到目前的8倍，并使结构的性能提高40%。然而，使用DST技术创建的结构在强度方面可能受到严重影响，因为相邻条带之间的关节容易受到影响。由于带钢之间的刚度变化、接头本身以及由于优化而引入的任何可能的锥度而产生的应力集中尚未得到充分的研究。该项目的目的是初步表征纤维条之间的应力集中，然后研究锥度在应力传递中的作用，并能够分析地定义这一点。最终目标是开发带状沉积的设计策略，考虑到最小化制造时间，材料浪费等并优化组件强度。这些目标将通过实验和分析工作相结合来实现。该博士学位是ADAPT ESPRC赞助项目的一部分，该项目的总体目标是将刚度定制材料的沉积增加四倍，以满足未来20年新型短程飞机的需求，并提高部件性能。ESPRC已将未来制造业确定为当前研究的关键主题；这个项目的重点是高度相关的，以发展当前的生产流程为目标。该项目由工业合作伙伴GKN提供支持；同时也会有来自Chomarat（薄板制造商）和空中客车的参与。

Constant demand from the aerospace industry to reduce weight, and to increase both component performance and the manufacturing rates of composite structural parts has led to interest in the use of discrete stiffness tailoring (DST), in order to realise these targets. Traditionally, the fibre angle within a single ply layer is constantly orientated in a single direction, and it is the stacking sequence of plies that is optimised for the required stiffness and strength. Discrete stiffness tailoring however, seeks to alter the fibre angle and thickness across the geometry of a part in a discontinuous fashion. A previous ESPRC sponsored project found that a maximum weight saving of 40% was achievable if both the ply angle and thickness were simultaneously optimised for composite structures. This optimisation could be achieved with a minimum of three discrete strips or zones across the width of a flat panel, where the orientation of the fibre is constant but different within each strip. DST laminate structures can theoretically be manufactured using Automated Tape Laying (ATL) machines, which are able to deposit material at a high-rate when compared to other manufacturing methods. This technology, combined with the use of discrete bi-axial composite tapes (i.e. Non Crimp Fabrics) has in theory the twofold advantage of increasing the deposition rate by as much as eight times currently achieved, and creating structures with a 40% improvement in performance.However, structures created using the DST technique may be critically affected in terms of strength due to the vulnerability of the joints between the adjacent strips. The stress concentrations developed as a result of the stiffness changes between strips, the joint itself, and any possible taper introduced as a result of the optimisation have not yet been investigated fully. The aim of this project is to initially characterise the stress concentrations between the fibre strips, and then to investigate the role of taper on stress transfer, and to be able to define this analytically. The final objective is to develop design strategies for strip deposition taking into account minimising the manufacturing time, material wastage etc. and optimising the component strength. These aims will be met through a combination of experimentation and analytical work.This PhD is part of the ADAPT ESPRC sponsored project, the overall aim of which is to produce a fourfold increase in the deposition of stiffness tailored material, in order to meet demand for new short-range aircraft in the next 20 years, as well as improving component performance. The ESPRC have identified Manufacturing the Future as a key theme for current research; a focus for which this project is highly relevant, in terms of aiming to develop current production processes. The project is supported by an industrial partner, GKN; and also will incorporate some involvement from Chomarat (thin-ply manufacturer) and Airbus.