基于自动铺放技术的热塑性复合材料原位固化成型研究进展：热传导行为及层间性能

A Review of Robotic Prepreg Placement and In-situ Consolidation for Manufacturing Fiber-reinforced Thermoplastic Composites:Heat Transfer Behavior and Interlaminar Properties

纤维增强复合材料具有轻质、高强、性能可设计等特性,在减重、抗疲劳、耐腐蚀、维修性等方面明显优于传统金属材料,在航空航天、交通运输、国防等领域的应用越来越广泛,其中热塑性复合材料具有高韧性、高冲击性、无限储存周期、可回收利用等众多优点。复合材料自动铺放技术成型效率高、自动化程度高,特别适用于大尺寸和复杂构件的制造。同时,热塑性复合材料原位固化技术不断发展和进步,生产效率显著提高,生产成本降低,构件质量得以提升。因此,基于自动铺放技术的热塑性复合材料原位固化成型将会是未来大飞机主承力部件的重要成型方法。然而,热塑性复合材料铺放成型过程经历高温制造,伴随着热力学耦合等相关问题。对于原位固化方法,热源的选择颇为关键,将直接影响铺放成型的效果和效率。在铺放成型过程中,热塑性聚合物分子链受热发生流动,宏观上则是热塑性树脂发生从固态到熔融态再到固态的物理变化。整个成型过程持续时间较短,但又涉及一系列的物理变化,是一个非常复杂的过程,目前已成为国际上高性能热塑性复合材料的研究热点之一。热塑性复合材料纤维铺放成型常用的热源主要包括热空气、激光、超声波、电子束等。其中针对热空气的研究较早,建立了铺层内的热传导理论模型,就铺层基层中温度场展开了许多工作并取得了相应的成果。对激光加热成型获得的铺放构件的诸多研究表明,激光作为热源相比于热空气可以大幅提升层间性能。此外,学者们还提出了不同的理论模型来预测最终的熔合强度,但测试结果显示铺放构件的力学性能不及热压罐固化的构件,进一步的理论和实践探索仍然很有必要。本文主要聚焦基于预浸料自动铺放技术的热塑性复合材料原位固化成型工艺,从工艺过程中的热传导行为、铺层的性能指标两方面介绍或探讨了铺放工艺过程、热传递模型、原位固化热源、铺层间紧密接触度、熔合度及熔合强度等的研究现状。

Light weight,high strength and designable performance make fiber-reinforced composites far superior to metallic materials in weight reduction,fatigue resistance,corrosion resistance,maintainability,and increasingly prevalent in aerospace,transportation,national defense and other fields.Thermoplastic composites have a great deal of advantages such as high toughness,high impact,unlimited storage cycle and recyclability.The robotic placement technology is especially suitable for forming large-size and complicated composite components by virtue of high forming efficiency and high automation.On the other hand,the rapid development of in-situ consolidation technology for thermoplastic composites has led to increased production efficiency,reduced production cost,and significantly improved product quality.Hence the robotic prepreg placement and in-situ consolidation has the potential to become an advanced and promising technique for manufacturing main load-bearing parts of large aircraft in the future.However,as a high-temperature manufacturing process,the placement-consolidation of thermoplastic composite involves some related problems such as thermodynamic coupling.The adoption of heat source is a crucial point for in-situ consolidation,which directly affects the quality and placement efficiency.The heat input to the system can cause molecular chain flow,and the attendant macroscopic change,during the placement-consolidation process,manifests as the transformation of thermoplastic polymer from solid state to molten state and then again to solid state.The whole process is short-duration but quite complicated and associated with a series of physical changes,and has become one of the global hotspots in the field of high-performance thermoplastic composites.The commonly used heating sources in the placement-consolidation of thermoplastic composites mainly include hot air,laser,ultrasonic wave,electron beam,etc.Among them,hot air heating has long been studied with a well-established theoretical interlaminar heat transfer model,and considerable and fruitful efforts have been made focusing on the temperature field of the mat layer.At present,the majority of foreign researchers are dedicated to laser heating,and sufficient results have proved that laser has a significant superiority in product’s interlaminar properties against hot air as auxiliary heat source.In addition,researchers have proposed various theoretical models for the prediction of the final fusion strength,but actually the placement-consolidation derived components have inferior mechanical properties to the autoclave cured ones according to the measurements,demonstrating the necessity for further theoretical and practical exploration.The present review is mainly concerned with the technology of robotic prepreg placement and in-situ consolidation with respect of thermoplastic composites manufacturing.It renders a detailed introduction and discussion,from the perspectives of heat transfer behavior and product’s interlaminar properties,over the research progress in various aspects of this emerging technology,such as the placement process,the heat transfer model,the heat source for in-situ consolidation,the degree of intimate contact,the degree of healing and the interlaminar bonding,etc.