Study of dynamic characteristics of impact of two solid deformable bodies at impact speed of up to 100 m/s

The paper analyzes the dynamic dependencies between the impact force and the depth of the indenter penetration into the obstacle. The indenter is a hardened steel ball. The target is made in the form of a rod from various types of steel, duralumin, aluminum and lead. As a result of digitizing the graphs of dependencies, interpolation formulas are obtained for different phases of the impact (the first phase of the impact is compression; the second phase of the impact is unloading). In the course of the analysis of interpolation formulas, absolute and relative data on the transformation of the initial kinetic energy of the indenter into the distribution of energies after impact are obtained: the value of the kinetic energy of the indenter after the impact, the values of the energy of elastic and plastic deformations, and the energy of shock waves. The results obtained can be used to design impact machines with an indenter impact speed against an obstacle up to 100 m/s.

Temperature dependence of indentation behavior of Ti-6Al-4V alloy for bio medical applications

Numerical analysis of spherical indentation was carried out to study temperature dependence (300-673K) of elasto-plastic deformation behavior of Ti-6Al-4V alloy. Flow stress and strain hardening exponent ‘n’ were determined from load versus indenter penetration depth profiles generated through FE model using Dao’s reverse analysis approach. The upward flow around the residual impression as a function of average strain, which describes the strain hardening behaviour of the alloys was also investigated. The simulated values of CF have been used to predict high strain-rate plastic flow behavior considering indentation data. It was observed that there is a good correlation between data from simulation and experimental results in the literature. The FE model developed in the current investigation can be used for simulating the flow behavior of Ti-6Al-4V alloy. The temperature dependent CF value in the fully plastic regime from the current study is approximately 2.69 against experimentally evaluated value of 2.95. Meyer’s hardness is generally high due to the presence of cold layer resulting from grinding and polishing of the test specimen. Absence of such effects in simulation of spherical indentation resulted in reduced value of CF.

Composite Material Mechanical Properties Evaluation Using a Dynamic Indentation Method

Introduction. Dynamic indentation method is considered promising in testing mechanical properties of composite materials. Today, composite materials are widely used in the aviation and aerospace industries. That’s why, testing of mechanical properties of composite materials is so vital. Method. To register the current velocity of the indenter penetration into the tested composite material, use is made of a device that enables a contactless measurement of the indenter penetration velocity after the indenter strikes the tested product. The data obtained is digitized and sent to a PC for further processing. Results. The experiment produced "contact force – penetration depth" diagrams for three test zones in the prepared samples. The analysis showed that the non-uniformity of mechanical properties in the rod’s butt end and side surface is stipulated by pores and microcracks, and this is confirmed by computer tomography. It is shown that dilaminations, microcracks and local non-uniformity zones in the structure tell on the elasticity modulus measurements. Conclusions. The dynamic indentation method allows one to test composites at the micro- and macrostructural level, as well as compute their integral mechanical properties.

Investigation on Mechanical Properties of 6H-SiC Crystal

In this work, the mechanical properties, such as Vickers microhardnessHv, fracture toughnessKc, yield strengthσvand brittleness indexBi, of <0001> oriented 6H-SiC crystal are systematically evaluated using a microindentation technique under 0.1-2 kg applied load. It is found theHvis decreased as the applied load is increased which is mainly attributed to the effect of indenter penetration. TheHvvalue can be effectively presumed by Kicks law and the Meyers indexnis determined to be 1.73. However, theKcvalue is measured nearly a constant (~0.148 MPa.m1/2) which reveals the toughness of 6H-SiC(0001)crystal is much weaker than those of Si(100)and GaAs(100)crystals. The variation ofσvto the load is similar to that ofHv. The brittleness indexBialso exhibits deceasing tendency as the applied load is added.

Nanoindentation: Application to dental hard tissue investigations

In the last decade, most publications on the mechanical properties of dental calcified tissues were based on nanoindentation investigation. This technique has allowed a better understanding of the mechanical behavior of enamel, dentin, and cementum at a nanoscale. The indentations are normally carried out using pointed or spherical indenters. Hardness and elastic modulus are measured as a function of indenter penetration depth and from the elastic recovery upon unloading. The unique microstructure of each calcified tissue significantly contributes to the variations in the mechanical properties measured. As complex hydrated biological composites, the relative proportions of the composite components, namely, inorganic material (hydroxyapatite), organic material, and water, determines the mechanical properties of the dental hard tissues. Many pathological conditions affecting dental hard tissues cause changes in mineral levels, crystalline structures, and mechanical properties that may be probed by nanoindentation. This review focuses on relevant nanoindentation techniques and their applications to enamel, dentin, and cementum investigations.

On the Characterization of Thin Film-only Mechanical Property Based on the Indentation Image Analysis

Conventional nanoindentation testing generally uses a peak penetration depth of less than 10 % of thin-film thickness in order to measure film-only mechanical properties, without considering the critical depth for a given thin film-substrate system. The uncertainties in this testing condition make hardness measurement more difficult. We propose a new way to determine the critical relative depth for general thin-film/substrate systems; an impression volume analyzed from the remnant indent image is used here as a new parameter. Nanoindents made on soft Cu and Au thin films with various indentation loads were observed by atomic force microscope. The impression volume calculated from 3D remnant image was normalized by the indenter penetration volume. This indent volume ratio varied only slightly in the shallow regime but decreased significantly when the indenter penetration depth exceeded the targeted critical relative depth. Thus, we determined the critical relative depth by empirically fitting the trend of the indent volume ratio and determining the inflection point. The critical relative depths for Cu and Au films were determined as 0.170 and 0.173, respectively, values smaller than 0.249 and 0.183 determined from the hardness variation of the two thin films. Hence the proposed indent volume ratio is highly sensitive to the substrate constraint, and stricter control of the penetration depth is needed to measure film-only mechanical properties.

Evaluation of elastic modulus and hardness of thin films by nanoindentation

Simple equations are proposed for determining elastic modulus and hardness properties of thin films on substrates from nanoindentation experiments. An empirical formulation relates the modulus E and hardness H of the film/substrate bilayer to corresponding material properties of the constituent materials via a power-law relation. Geometrical dependence of E and H is wholly contained in the power-law exponents, expressed here as sigmoidal functions of indenter penetration relative to film thickness. The formulation may be inverted to enable deconvolution of film properties from data on the film/substrate bilayers. Berkovich nanoindentation data for dense oxide and nitride films on silicon substrates are used to validate the equations and to demonstrate the film property deconvolution. Additional data for less dense nitride films are used to illustrate the extent to which film properties may depend on the method of fabrication.