Polymer & Composite Engineering (PaCE) Group, Department of Chemical Engineering, Imperial College London , South Kensington Campus, London, SW7 2AZ, UK.
ACS Appl Mater Interfaces. 2013 Sep 25;5(18):9111-9. doi: 10.1021/am402495n. Epub 2013 Sep 13.
High performance carbon fiber reinforced composites with controllable stiffness could revolutionize the use of composite materials in structural applications. Here we describe a structural material, which has a stiffness that can be actively controlled on demand. Such a material could have applications in morphing wings or deployable structures. A carbon fiber reinforced-epoxy composite is described that can undergo an 88% reduction in flexural stiffness at elevated temperatures and fully recover when cooled, with no discernible damage or loss in properties. Once the stiffness has been reduced, the required deformations can be achieved at much lower actuation forces. For this proof-of-concept study a thin polyacrylamide (PAAm) layer was electrocoated onto carbon fibers that were then embedded into an epoxy matrix via resin infusion. Heating the PAAm coating above its glass transition temperature caused it to soften and allowed the fibers to slide within the matrix. To produce the stiffness change the carbon fibers were used as resistance heating elements by passing a current through them. When the PAAm coating had softened, the ability of the interphase to transfer load to the fibers was significantly reduced, greatly lowering the flexural stiffness of the composite. By changing the moisture content in PAAm fiber coating, the temperature at which the PAAm softens and the composites undergo a reduction in stiffness can be tuned.
具有可控刚度的高性能碳纤维增强复合材料可以彻底改变复合材料在结构应用中的使用方式。在这里，我们描述了一种结构材料，其刚度可以根据需要进行主动控制。这种材料可能在变形机翼或可展开结构中有应用。描述了一种碳纤维增强环氧树脂复合材料，该复合材料在升高的温度下可以经历 88%的弯曲刚度降低，并在冷却时完全恢复，而没有明显的损坏或性能损失。一旦刚度降低，所需的变形就可以在更低的致动力下实现。在这项概念验证研究中，将一层薄薄的聚丙烯酰胺 (PAAm) 通过电泳涂层涂覆到碳纤维上，然后通过树脂注入将其嵌入环氧树脂基体中。将 PAAm 涂层加热到玻璃化转变温度以上会使其软化，并允许纤维在基体中滑动。为了产生刚度变化，将碳纤维用作电阻加热元件，通过它们传递电流。当 PAAm 涂层变软时，界面传递负载到纤维的能力大大降低，从而大大降低了复合材料的弯曲刚度。通过改变 PAAm 纤维涂层中的水分含量，可以调整 PAAm 变软和复合材料刚度降低的温度。
