High Performance Discontinuous Fibre Composites - a sustainable route to the next generation of composites

在结构性能方面，连续碳纤维复合材料能够与先进金属直接竞争。复合材料的优势来自于制造复杂形状的能力，通常在相对较小的批量生产中，减轻重量和耐腐蚀性。然而，连续纤维复合材料制造困难，导致成本高，并有可能产生一系列严重影响性能的缺陷。此外，连续纤维复合材料不能直接回收，因为没有办法重复使用可以提取的长纤维，但不是连续的和拓扑有序的形式。通过对复合材料行业现状的考察，可以发现两大挑战。第一个目标是将无缺陷的产量至少提高一个数量级——直接导致简化和自动化制造过程的需求。第二是通过开发能够保留材料的机械性能和经济价值的回收工艺，向基于循环经济的模型[13]迈进，从而产生更可持续的复合材料解决方案。原则上，对这些挑战的分析并没有什么新东西，然而，在过去的二十年里，在这些领域进行了大量的研究活动，但却没有在能力上取得阶段性的变化。本提案的中心论点是，实现低成本、可靠、大批量生产和易于回收的先进复合材料的主要困难来自一个单一的来源：纤维是连续的，这两个问题领域都可以通过采用高度排列的不连续纤维增强复合材料（ADFRCs）直接解决。我们的愿景是通过进一步开发和应用HiPerDiF（高性能不连续纤维）技术来生产高性能ADFRCs，从而在复合材料行业产生根本性的变化。这种新型的大批量制造方法是由英国布里斯托尔大学在EPSRC资助的高性能韧性复合材料技术项目（EP/I02946X/1）中发明的。其基本概念是，如果不连续纤维精确排列，其长度明显长于临界纤维长度，则得到的复合材料的拉伸模量、强度和破坏应变与连续纤维复合材料相当。该技术是在HiPerDuCT项目中开发的，它还显示了定制复合材料力学行为的潜力，通过杂交和纤维拔出机制提供了伪延展性。HiPerDiF技术为实现排列不连续纤维复合材料的潜力提供了机会，并产生了重大的工业和社会影响。在不影响机械性能的情况下，将纤维增强几何形状从连续变为不连续，将对复合材料工业产生广泛的影响。纤维的不连续性将提高自动化制造过程的生产率和复杂几何形状的可成形性，减少制造过程中产生的缺陷。ADFRC的使用将提高复合材料的可定制性，从而实现真正的多功能复合材料，能够响应多种设计要求。ADFRC将为复合材料行业采用循环经济模式开辟道路，允许以高性能和高价值的原料重新制造再生碳纤维，并生产更容易回收的材料。

Continuous carbon fibre composites are capable of competing directly with advanced metals in terms of structural performance. The advantages of composites come from the ability to manufacture complex shapes, generally in relatively low volume production, in weight saving and corrosion resistance. However, continuous fibre composites are difficulties to manufacture, leading to both high costs and to the potential for generation of a range of defects impacting strongly on performance. In addition, continuous fibre composites cannot be directly recycled as there is no way of reusing the fibres that can be extracted in long, but not continuous and topologically ordered form. From an examination of the current status of the composites industry two big challenges can be identified. The first is to increase defect-free production volumes by at least an order of magnitude - leading directly to the need to simplify and automate the manufacturing processes [12]. The second is the requirement to generate more sustainable composites solutions by moving towards a circular economy based model [13] via the development of recycling processes able to retain the material's mechanical properties and economic value. In principle, there is nothing new in this analysis of the challenges, however, a great deal of research activity has been expended in these areas in the last two decades without achieving a step-change in capability. The central thesis of this proposal is that the principal difficulties in both achieving low cost, reliable, high volume production and readily recyclable advanced composites arise from a single source: the fact that the fibres are continuous and that both problem areas can be directly tackled by adopting highly Aligned Discontinuous Fibre Reinforced Composites (ADFRCs). Our vision is to generate a fundamental step-change in the composite industry by further developing and applying the HiPerDiF (High Performance Discontinuous Fibre) technology to produce high performance ADFRCs. This new, high volume manufacturing method was invented at the University of Bristol in the EPSRC funded HiPerDuCT (High Performance Ductile Composite Technology) programme (EP/I02946X/1). The basic concept is that if discontinuous fibres are accurately aligned and their length is significantly longer than the critical fibre length, the tensile modulus, strength and failure strain of the obtained composites are comparable to those of continuous fibre composites. This technique, developed in the HiPerDuCT programme has also shown the potential to tailor mechanical behaviour of composite materials, delivering pseudo-ductility via hybridisation and fibre pull-out mechanisms. The HiPerDiF technology offers the opportunity to realise the potential of aligned discontinuous fibre composites and produce a significant industrial and societal impact. Changing the fibre reinforcement geometry from continuous to discontinuous, without compromising the mechanical properties, will have a wide impact on the composite industry. The fibre discontinuity will allow an increase in the productivity of automated manufacturing processes and the formability of complex geometries, reducing the manufacturing generated defects. The use of ADFRC will increase the tailorability of composite materials by leading to truly multifunctional composite materials, able to respond to multiple design requirements. ADFRC will open the way for the adoption of a circular economy model in the composite sector by allowing the remanufacturing of reclaimed carbon fibres in high performance and high value feedstock and by producing more readily recyclable materials.