Researchers examine the Australian orb spider to toughen composite laminates using additive manufacturing.
By Christopher Howe, Associate Technical Fellow, Boeing Research & Technology and Justin Hicks, Materials & Processes Technology Engineer, 787 Production Support Engineering
Spider silk is known to be one of the toughest materials in nature because of the molecular arrangement of proteins. Spiders are able to readily fabricate lightweight webs that are durable, resilient and easily repaired.
Interestingly, these requirements are also common to aircraft materials and structures.
Developing advanced composite materials that enable higher-performance and lighter-weight aircraft structures is an enduring challenge for materials engineers. Current interlayer technology, used in resin-infused composite structures, is described as a continuous filament mat in random orientation, like fairy floss, with limitations on the minimum thread diameter and areal weight.
A spider does not fabricate a random pattern for its web, but rather a controlled structure at many scales, from the molecules to web architecture. The key features from spider web structural hierarchy can be translated into improved toughening interlayers for composite laminates.
We can now replicate the efficient controlled structure of webs made by Australian orb spiders and rapidly deposit web-like interlayers onto carbon fabrics. To enable this level of control for applying toughening interlayers in composites, Boeing and Australia’s RMIT University researchers looked to additive manufacturing of thermoplastics to fabricate spider weblike interlayers. This level of control was based on different scales, including controlling the level of crystallinity, filament diameter and web patterns of 3D-printed polyamides.
The process flow for controlled fabrication of weblike interlayers on carbon reinforcement using 3D printing of polyamide includes design, coding and deposition. A reduced content of thermoplastic can be achieved when depositing the weblike interlayers, compared to current random mat interlayers. Each strand of the web interlayer, located between carbon fabric plies, contributes to stopping or catching cracks caused from impact damage to composite laminates.
Learnings from nature indicate that highly ordered thermoplastic interlaminar architectures provide greater toughening efficiency than less-ordered architectures. Results of this work showed weblike interlayers could be manufactured using fused filament fabrication of thermoplastics with excellent control of the areal weight, surface morphology, thread diameters, thread properties, mesh width and nodal intersections. These types of patterns are captured by a Boeing U.S. patent.
A further pending Boeing patent is based on the method of creating the fine silklike threads from the 3D-printing nozzle, based on a drop, draw and extrude method. This method enables controlled fabrication of continuous fine filament threads, akin to the spider.
The effective toughening of the web-inspired interlayers achieved a 40% reduction in damage area, for web areal weights less than 1.5 grams per square meter (gsm). Current random mat interlayers are 6 gsm, to achieve the same effective toughening. The crack path and direction were also controlled based on the location and geometry of the web filaments.
This bio-inspired study showed that new materials can be designed that are more effective at toughening composite laminates by controlling the content and arrangement of thermoplastic through use of 3D-printing technology.
We can think and act like spiders to engineer controlled structures for aircraft materials.
Out in the wild
To understand why spider webs are effective structures, researchers from Boeing and RMIT University, along with Mary Whitehouse from Australia’s Commonwealth Scientific and Industrial Research Organisation, visited the outback of New South Wales to study two spider species: Eriophora transmarina, commonly known as the garden orb spider, and Nephila edulis, the golden orb spider.
The nocturnal garden orb spider rapidly creates a new lightweight web every night to catch airborne insects. The silk is extremely fine and easily repaired when damaged. When dawn arrives, the spider digests the web and finds a secure hiding spot. This web is designed around speed with minimum effort required to catch prey.
The larger golden orb spider, however, spends more time creating a more robust web that lasts many days. The web contains stiff dragline threads that can span many meters, with finer silk acting as the radial threads for catching prey. The golden orb also creates a space-framelike shield, around the main web to protect against enemies.
The orb spider can tailor the silk to be either flexible in order to serve as the catching net for prey or stiff for use as the supporting draglines.