Plastic Dissipation Mechanisms in Periodic Microframe‐Structured Polymers

Abstract

Novel lightweight micro‐ and nanostructured materials are being used as constituents in hierarchically structured composites for providing high stiffness, high strength, and energy absorbing capability at low weight. Three dimensional SU‐8 periodic microframe materials with submicrometer elements exhibit unusual large plastic deformations. Here, the plastic dissipation and mechanical response of polymeric microframe structures is investigated using micromechanical modeling of large deformations. Finite element analysis shows that multiple deformation domains initiate, stabilize, and then spread plasticity through the structure; simulated deformation mechanisms and deformation progression are found to be in excellent agreement with experimental observation. Furthermore, the geometry can be used to tailor aspects of 3D behavior such as effective lateral contraction ratios (elastic and plastic) during tensile loading as well as negative normal stress during simple shear deformation. The effects of structural geometry on mechanical response are also studied to tailor and optimize mechanical performance at a given density. These quantitative investigations enable simulation‐based design of optimal lightweight material microstructures for dissipating energy.

Small-scale mechanical behavior of a eutectic high entropy alloy

“…Following this, there was plastic deformation of both B2 and L1 2 as the load increased. This double yielding behavior has been reported for several composite materials including bulk metallic glass composites 44 and polymer micro-frames 45 . However, the multiple yield points were not detected in bulk tensile or compression tests likely due to the small difference between the modulus of B2 and L1 2 phases (Table 1) which could not be captured by the lower resolution of the bulk experiments.…”

Enhanced Energy Dissipation in Periodic Epoxy Nanoframes

“…We also calculated energy dissipation ( W A ), the area enclosed by loading and unloading curves, as an indicator of plastic deformation during loading. As expected, the plasticity of the uniform SU-8 films is more sensitive to cross-linking than the modulus since the material is in its glassy state at room temperature for all cross-link densities ( T g > 100 °C) . The loss of plasticity at higher doses causes the energy dissipation to drop rapidly and saturates to a rather small value (∼25% of the value of the lowest dose).…”

Co‐Continuous Composite Materials for Stiffness, Strength, and Energy Dissipation

“…While the feature lengthscale of the current study is at the millimeter scale, these results extend down to micron or sub‐micron lengthscales where fabrication challenges can be met with innovative lithography15 and other processing techniques such as block copolymer for periodic structures 3, 36. At these smaller scales, further property enhancement may result due to lengthscale effect on, for example strength and ductility 16, 26. Ongoing and future research addresses the study of the shape memory effect, thermal and electrical conductivity, and opportunities at different lengthscales.…”