Strain Rate and Anisotropic Microstructure Dependent Mechanical Behaviors of Silkworm Cocoon Shells

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.

Comparing the microstructure and mechanical properties of Bombyx mori and Antheraea pernyi cocoon composites

“…The wild, in the other hand, harbors a huge diversity of different species of silkworms, of which the best known is perhaps Anthearea pernyi (A. pernyi). As protective housing, wild cocoons have excellent mechanical properties such as high modulus, wear and impact resistance [8][9][10][11]. It appears that wild cocoons have evolved for protection against diverse threats as well as to regulate the internal environment by controlling the flow of water or gases such as oxygen and carbon dioxide [12,13].…”

Compression behavior and energy absorption capacity of woven flax-epoxy composite under various stain rates

“…(1)-(3) under the hypothesis of stress equilibrium within the specimen From the curves, one can find that the constitutive behavior of the tested material shows a bi-linear feature, i.e. the curve firstly experiences a linear increase within initial elastic response, then the slope gradually decreases up to an approximate yield point and entered the plastic reinforcement phase, highly similar to some typical materials such as dual phase steel [25], silkworm cocoon [26] and 3D braided composite [27]. The final failure modes are confirmed to be shear failure where a visible diagonal cracks through the flax weave layers in each specimen can be observed shown in Fig.…”

A Transparent, Skin‐Inspired Composite Film with Outstanding Tear Resistance Based on Flat Silk Cocoon

“…[19,20] Among them, the silk fiber is widely used as the reinforcing phase because of its low density, outstanding mechanical advantage, and sustainability. [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] Besides its high strength and toughness, another intriguing but less studied mechanical property of skin is its remarkable tear resistance, resulting from the rearrangement of skin collagen fibers in the tensile-loading direction. [39] In this work, we show that this stress redistribution mechanism can be utilized to construct fiber-reinforced supporting substrates with excellent tear resistance.…”