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A modified shear-compression specimen (SCS), for large strain testing over a wide range of strain rates is presented. The original SCS design includes two rectangular slots that are machined at 45°with respect to the longitudinal axis. The modification consists of creating two diametrically opposed semi-circular slots. The new "circular" specimen is first thoroughly investigated numerically under quasi-static and dynamic loading using an elastoplastic material model. The results of the comparison between the two-slot designs confirm the feasibility of the new specimen for larger strain testing and indicates its advantages over the rectangular slot design: larger strain range characterization, failure and fracture within the gauge, and constant Lode parameter during plastic deformation. Both types of SCS as well as cylindrical specimens are used to characterize the flow behavior of steel 1020, in the quasi-static and dynamic regimes using a split Hopkinson pressure bar. Dog-bone specimens are also tested quasi-statically in tension. A very good agreement is achieved for the results of all specimens in both the quasi-static and dynamic regimes. The numerical validation procedure shows that the flow stress of 1020 steel obtained with the new SCS is~3 % lower in the quasistatic regime, and 8 % lower in the dynamic regime with respect to the flow stress of the rectangular SCS. This difference is attributed to effect of the third invariant of the stress deviator (i.e., Lode parameter), which is considerably lower in the new SCS design.

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In this study, a newly developed nanoscale modulus mapping is applied in order to visualize the 2D‐distribution of mechanical characteristics in the aragonitic nacre layer of Perna canaliculus (green mussel) shells. Modulus maps provide lateral resolution of about 10 nm. They allow the aragonitic mineral (CaCO3) tablets and the interfaces between them to be clearly resolved, which are filled by an organic substance (mainly beta‐chitin). The experimental data are compared with finite element simulations that also take into account the tip radius of curvature and the thickness of organic layers, as measured by means of scanning electron microscopy with back‐scattered electrons. Based on this comparison, the Young modulus of beta‐chitin is extracted. The obtained number, Eβ = 40 GPa, is higher than previously evaluated. The collected maps reveal that the elastic modules in the nacre layer change gradually across the ceramic/organic interfaces within a spatial range four times wider than the thickness of the organic layers. This is possibly due to inhomogeneous distribution of organic macromolecules within ceramic tablets. According to the data, the concentration of macromolecules gradually increases when approaching the organic/ceramic interfaces. A behavior of this type is unique to biogenic materials and distinguishes them from synthetic composite materials. Finally, three possible mechanisms that attempt to explain why gradual changes of elastic modules significantly enhance the overall resistance to fracture of the nacre layer are briefly discussed. The experimental findings support the idea that individual ceramic tablets, comprising the nacre, are built of the compositionally and functionally graded ceramic material. This sheds additional light on the origin of the superior mechanical properties of biogenic composites.