Modelling the effect of voids in Composite Components

减少航空航天和可再生能源部门对环境影响的关键战略之一是用先进的纤维增强复合材料取代金属合金。这种材料不仅通过更轻的重量和改进的气动弹性行为提供直接的性能益处，而且还通过更高的耐久性（例如更好的耐腐蚀性和抗疲劳性）和更低的制造总能量要求提供相当大的寿命周期益处。然而，使用复合材料的缺点之一是它们对制造缺陷的特殊敏感性，最常见的是由最终固结期间气体的截留或沉淀引起的孔隙度。为了达到可接受的生产成本或废品率，必须容忍一定程度的材料孔隙率，这通常通过引入保守的设计容许值和安全系数来实现，这些设计容许值和安全系数主要基于经验方法。保守的设计规则往往会否定首先采用复合材料的好处，随着传统的高压釜制造被更节能的“高压釜外”制造技术所取代，这个问题可能变得至关重要。该项目将侧重于开发新的多尺度分析方法，以预测复合材料结构的制造宏观尺度机械性能，同时考虑详细的（介观和微观尺度）孔隙率特性，如局部空隙含量（相对于零件几何形状），空隙尺寸和形态的局部分布，以及相对于介观和微观尺度材料结构的空隙位置。该项目建立在该研究小组以前的工作基础上，研究了复合材料中的孔隙率表征、过程建模和损伤与断裂的多尺度分析。最先进的技术将得到结合和进一步发展，包括（但不限于）：-复合材料的工艺建模，以预测微观尺度下的制造材料结构（单个纤维），中尺度下（单纱或纤维束），中尺度上部（单独的层或层）和宏观尺度（组件级）;- 高性能计算技术和软件，用于分析微观和中尺度的损伤和断裂，能够分析数千种不同的材料和装载配置，考虑材料的可变性和其他不确定性，与统计推断方法相结合，可用于实验设计分析;- 基于响应面方法和/或机器学习的多尺度建模策略，以适用于详细设计和设计的宏观尺度预测模型的形式实现上述学习/推断的材料行为，复合材料部件的制造。这种建模能力有可能取代目前在考虑复合材料制造缺陷方面所涉及的大部分理论，从而缩短设计周期，减少物理测试，提高设计安全系数，降低报废率，并在生命周期碳足迹方面提高复合材料结构的效率。该项目福尔斯主要属于EPSRC研究领域“材料工程-复合材料”。这项工作是在布里斯托大学与BAE系统公司合作进行的，获得了CerTest计划资助（EPSRC编号18939/05 2018-4088）。

One of the key strategies in reducing the environmental impact of the aerospace and renewable energy sectors is to replace metal alloys with advanced fibre-reinforced composites. Such materials offer not only immediate performance benefits through lighter weight and improved aero-elastic behaviour, but also provide considerable life-cycle benefits through greater durability (e.g. better corrosion and fatigue resistance) and lower overall energy requirements for manufacture. One of the downsides of using composites, however, is their particular susceptibility to manufacturing defects, most commonly porosity caused by the entrapment or precipitation of gasses during final consolidation. In order to achieve acceptable production costs or scrap rates, some level of material porosity must be tolerated, which is often done by the introduction of conservative design allowables and safety factors mostly based on empirical methods. Conservative design rules tend to negate the benefits of adopting composite materials in the first place, a problem which may become critical as traditional autoclave manufacture is replaced by more energy-efficient 'out-of-autoclave' manufacturing techniques. This project will focus on the development of novel multi-scale analysis methods to predict the asmanufactured macro-scale mechanical performance of composite structures taking into account detailed (meso- and micro-scale) porosity characteristics such as local void content (relative to part geometry), local distributions of void sizes and morphologies, and the location of voids relative to the meso- and micro-scale material architecture. This project builds on previous work by this research group on porosity characterisation, process modelling, and multi-scale analyses of damage and fracture in composites. State-of-the-art techniques will be combined and further developed, including (but not limited to): - Process modelling of composites to predict the as-manufactured material architecture at the micro-scale (individual fibres), lower meso-scale (individual yarns or fibre bundles), upper mesoscale (individual layers or plies), and macro-scale (component-level); - High Performance Computing techniques and software for the analysis of damage and fracture at the micro- and meso-scales, enabling the analysis of thousands of different material and loading configurations, accounting for material variability and other uncertainties, which in combination with statistical inference methods can be used in design-of-experiment analyses; - Multi-scale modelling strategies based on response surface methods and/or machine learning, to implement the learned/inferred material behaviour above in the form of macro-scale predictive models suitable for the detailed design and design-for-manufacture of composite parts. Such a modelling capability has the potential to replace much of the empiricism currently involved in accounting for manufacturing defects in composites, leading to faster design cycles, fewer physical tests, more accurate design safety factors, lower scrap rates, and more efficient composite structures in terms of their life-cycle carbon footprints. This project falls mostly within the EPSRC research area 'Materials Engineering - Composites'. The work is conducted at the University of Bristol in collaboration with BAE Systems plc under the CerTest Programme Grant (EPSRC no. 18939/05 2018-4088).