Length-scale dependency of biomimetic hard-soft composites

Area of Science:

• Materials Science
• Mechanical Engineering
• Composite Materials

Background:

• Biomimetic composites combine hard and soft materials, often using multi-material additive manufacturing (AM).
• AM techniques have inherent resolution limits, establishing a minimum feature length scale.
• The impact of this minimum length scale on hard-soft composite performance remains poorly understood.

Purpose of the Study:

• To investigate the effect of minimum feature length scale on the fracture toughness of biomimetic composites.
• To analyze how phase arrangement (random, semi-random, ordered) and volumetric ratios influence this effect.
• To elucidate the underlying mechanisms responsible for changes in fracture toughness.

Main Methods:

• Fabrication of single-edge notched specimens using multi-material additive manufacturing.
• Systematic variation of the minimum feature length scale from 40 to 960 μm.
• Testing of specimens with five different hard-to-soft phase volumetric ratios and varying arrangements.

Main Results:

• Fracture toughness decreased by approximately four-fold as the length scale increased.
• The observed effect of length scale was modulated by the arrangement and volumetric ratio of the hard and soft phases.
• Key mechanisms included a reduced crack tip plastic zone, crack propagation through the soft phase, and strain localization away from the crack tip.

Conclusions:

• The minimum feature length scale is a critical parameter influencing the fracture toughness of additively manufactured biomimetic composites.
• Material design, including phase arrangement and ratio, must consider the length scale limitations of AM for optimal performance.
• Understanding these scale-dependent mechanisms is crucial for designing advanced composite materials.