Hierarchical structure observation and nanoindentation size effect characterization for a limnetic shell

Abstract

In the present research, hierarchical structure observation and mechanical property characterization for a type of biomaterial are carried out. The investigated biomaterial is Hyriopsis cumingii, a typical limnetic shell, which consists of two different structural layers, a prismatic "pillar" structure and a nacreous "brick and mortar" structure. The prismatic layer looks like a "pillar forest" with variationsection pillars sized on the order of several tens of microns. The nacreous material looks like a "brick wall" with bricks sized on the order of several microns. Both pillars and bricks are composed of nanoparticles. The mechanical properties of the hierarchical biomaterial are measured by using the nanoindentation test. Hardness and modulus are measured for both the nacre layer and the prismatic layer, respectively. The nanoindentation size effects for the hierarchical structural materials are investigated experimentally. The results show that the prismatic nanostructured material has a higher stiffness and hardness than the nacre nanostructured material. In addition, the nanoindentation size effects for the hierarchical structural materials are described theoretically, by using the trans-scale mechanics theory considering both strain gradient effect and the surface/interface effect. The modeling results are consistent with experimental ones.

Microstructure Observation and Nanoindentation Size Effect Characterization for Micron-/Nano-Grain TBCs

“…where H 0 is the reference hardness value corresponding to deep indentation hardness, l is material length scale, h is indent depth, N is strain hardening exponent of material, β describes the angle of the circular conic indenter through area equivalency with true pyramid indenter. The trans-scale mechanics theory considering strain gradient and surface/interface effects was investigated by Song et al [30], the nanoindentation hardness H with respect to indent depth h for the case of circular conic indenter and TBCs can be expressed as…”

“…The above two types of mechanical properties obtained by the above two scale tests are extremely different. Many studies have shown that an apparent indentation size effect (ISE) of hardness for different kinds of materials was observed, such as brittle materials [26,27], metal materials [28,29], and biomaterials [30]. In order to describe the ISE, a series of different theoretical methods were presented.…”

“…Wei et al presented the strain gradient plasticity theory based on the thermodynamics frame to describe the ISE and cross-scale fracture [28,29], and they predicted the micrometer-sized parameter of strain gradient plasticity theory by the comparison of theoretical predictions with experimental measurements. Song et al [30] used the trans-scale mechanics theory presented by Wu et al [31] to model the nanoindentation size effect for limnetic shell, and they considered both the strain gradient effect and surface/interface effects.…”

Mechanical behavior and size effect of the staggered bio-structure materials

“…The characteristic length of the strain gradient organic matrix is an essential parameter in the proposed model. For metal, this characteristic length is in the order of micron, however for organic material (nacre), its value is also in the order of micron through comparing simulation results with experimental results for nanoindentation test (Song et al, 2015). So, in the following calculations, we will use the values of characteristic length for the organic matrix.…”

“…interlaminations, the rest 11.9% was in the mineral platelets, which divided the mineral platelet to many aragonite nanograins (Zhang et al, 2016 hardness showed a strong size effect. By a trans-scale mechanics theory (Song et al, 2014;Wu et al, 2012), which considered both strain gradient effect and the surface/interface effect, Song et al (2015) As mentioned above, the organic materials and the immersed mineral bridges, nanoasperities, etc. in the organic interlaminations can be regarded as an effective medium and its properties are size-dependence.…”