Abstract
Silkworm cocoons are multi-layered composite structures comprised of high strength silk fiber and sericin, and their mechanical properties have been naturally selected to protect pupas during metamorphosis from various types of external attacks. The present study attempts to gain a comprehensive understanding of the mechanical properties of cocoon shell materials from wild silkworm species Antheraea pernyi under dynamic loading rates. Five dynamic strain rates from 0.00625 s-1 to 12.5 s-1 are tested to show the strain rate sensitivity of the cocoon shell material. In the meantime, the anisotropy of the cocoon shell is considered and the cocoon shell specimens are cut along 0°, 45° and 90° orientation to the short axis of cocoons. Typical mechanical properties including Young’s modulus, yield strength, ultimate strength and ultimate strain are extracted and analyzed from the stress-strain curves. Furthermore, the fracture morphologies of the cocoon shell specimens are observed under scanning electron microscopy to help understand the relationship between the mechanical properties and the microstructures of the cocoon material. A discussion on the dynamic strain rate effect on the mechanical properties of cocoon shell material is followed by fitting our experimental results to two previous models, and the effect could be well explained. We also compare natural and dried cocoon materials for the dynamic strain rate effect and interestingly the dried cocoon shells show better overall mechanical properties. This study provides a different perspective on the mechanical properties of cocoon material as a composite material, and provides some insight for bio-inspired engineering materials.
Highlights
Silkworms and a range of arthropods and insects including spiders and bees have evolved to spin protein fibers that nicely combine high strength and toughness for multiple functions.PLOS ONE | DOI:10.1371/journal.pone.0149931 March 3, 2016Mechanical Behaviors of Silkworm Cocoon Shells data collection and analysis, decision to publish, or preparation of the manuscript
It appears that the trend of the stress-strain curve of cocoon materials is quite similar to that of steels [20,21,22], it is a type of fiber reinforced polymer material, where four stages can be clearly observed, including elastic region, yielding, plastic stage and fracture
When stress reaches its maximum value with an ultimate strain higher than 20%, the curve starts to fall rapidly when the cocoon material fails
Summary
Silkworms and a range of arthropods and insects including spiders and bees have evolved to spin protein fibers that nicely combine high strength and toughness for multiple functions. The widely studied silk fibers from the Bombyx mori silkworm cocoons are used as textile materials, and as multifunctional materials [11, 12]. Much research focus have been put on the mechanical behaviors of the silk fibers unravelled from cocoons, their structure-property relations and the biodegradability. The typical mechanical properties, such as Young’s modulus, ultimate strength and thermo-mechanical parameters, were experimentally measured to be different from innermost pelade to the outermost floss in the thickness direction of Bombyx mori cocoon. A direct measurement of cocoon shells under dynamic loading conditions between quasi-static and impact rates is still lacking. In the present study, a focused experiment investigation on the mechanical properties of cocoon shells from wild silkworm species Antheraea pernyi of three different orientations under various dynamic strain rates is conducted. Each dog-bone shaped specimen was marked and placed in plastic bags before and after the experiment
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
