Conical Nanoindentation Allows Azimuthally Independent Hardness Determination in Geological and Biogenic Minerals

The remarkable mechanical performance of biominerals often relies on distinct crystallographic textures, which complicate the determination of the nanohardness from indentations with the standard non-rotational-symmetrical Berkovich punch. Due to the anisotropy of the biomineral to be probed, an azimuthal dependence of the hardness arises. This typically increases the standard deviation of the reported hardness values of biominerals and impedes comparison of hardness values across the literature and, as a result, across species. In this paper, we demonstrate that an azimuthally independent nanohardness determination can be achieved by using a conical indenter. It is also found that conical and Berkovich indentations yield slightly different hardness values because they result in different pile-up behaviors and because of technical limitations on the fabrication of perfectly equivalent geometries. For biogenic crystals, this deviation of hardness values between indenters is much lower than the azimuthal variation in non-rotational-symmetrical Berkovich indentations.

The non-stationary dynamic of a beam under the elastic-plastic impact of a conical indenter

The problem of impact interaction of a conical indenter with the surface of a steel beam under elastic-plastic deformation is considered. The analysis of the dynamic reaction of the beam to the impact is considered analytically and numerically. The analytical solution is based on the phenomenological model of conical indentation and the solution of wave equations of beam dynamics at impact. The numerical study of the indentation process was carried out using the ANSYS software. The dynamic response of the beam is analyzed for different geometric parameters and different values of strength characteristics. Such tasks are widely used in construction practice in the implementation of non-destructive methods of assessing the mechanical characteristics of structures.

Experimental and numerical investigation on the effect of projectile nose shape in low-velocity impact loading on fiber metal laminate panels

In this paper, low-velocity impact responses of 2/1 GLARE 3 (a commercial type of fiber metal laminate) specimens were studied experimentally and numerically. The effects of indenter's nose shape (flat, conical, and hemispherical) on energy absorption and failure mechanisms were thoroughly investigated. Drop weight testing machine with different impact energies was used for experimental tests and numerical simulation was also carried out. Failure mechanisms, such as delamination, debonding, aluminum sheet rupture, and composite laminate fracture, were discussed by sectioning the tested specimens. The results indicate that maximum and minimum contact force occurred with flat and conical indenters, respectively. Also, the target absorbs the utmost energy under the penetration of flat indenter and least energy during conical indenter perforation. It is depicted that the deflection at the peak load represents the main failure of the panel. Consequently, front aluminum sheet failure is determinant in fiber metal laminate panels impacted by flat and hemispherical indenters where back aluminum sheet is more significant for fiber metal laminate panels impacted by the conical indenter. Numerical simulation verified by experimental results is extended to lower impact weights and more velocities, which are discussed.

The Impact of the Conical Indenter on a Plate Laying on a Winkler Foundation

In the practice of civil engineering, the methods of impact diagnostics of materials find their application, allowing quickly and accurately measure the required strength characteristics at any point in the structure. Impact methods offer many advantages, for example, at smaller dimensions can be developed big the contact force, it can be recorded more information about the response of the material to dynamic impact and others. This approach is widely used in determining the hardness of materials and makes it possible to determine the complex mechanical characteristics: yield strength, ultimate strength, and elongation. In the paper we consider the axisymmetric problem of the impact of the conical indenter on the plate, laying on Winkler Foundation under elastic-plastic deformation. The solution is based on the phenomenological model of elastic-plastic indentation in a quasistatic formulation. The general deformations of the plate are considered elastic, and the local, in the contact zone, are elastoplastic. The main characteristics of the impact are determined: the force of the contact interaction, the local indentation, the contact time. The device and methods of determining the strength characteristics of plates under specified conditions of impact were developed on the basis of obtained solutions. The proposed method has been tested on many building structures: bridges, trusses, structural structures of artificial structures, reinforcement bars, welded joints.

Dynamic response of a plate laying on elastic base during the impact of a conical indenter

The article presents an analytical and numerical study of a dynamic conical indentation during impact process. The circular plate laying on the elastic base is subjected to impact load by the conical indenter. Local deformations in imprint zone are considered as elastic-plastic and general plate deformations are only elastic. According to Timoshenko method, the general plate displacement is considered as the sum of the elastic-plastic displacement of the indenter and the elastic displacement of the plate at the impact point. The solution is constructed with Fourier transforms and the Green function of the dynamic process is obtained. The numerical study of impact indentation is received by FEM method. The dependences of displacements, velocities, and accelerations of the plate on time is obtained during impact. The experimental data obtained with the special device is compared with the results of the numerical analysis. The method of an assessment of the mechanical characteristics of steel is proposed on the basis of the research. Analysis of the dynamic response and non-stationary effects on structural elements is carried out on the base of the calculated impact process.