Use Of Nanoindentation Testing Research Articles

An Innovative Procedure for the In-situ Characterization of Elastomeric Bearings by Using Nanoindentation Test

ABSTRACT Control and inspection of the conditions of elastomeric bearings used for seismic isolation purpose is a fundamental activity in ensuring and preserving the performance of a structure. The methods currently used, such as visual inspections, Operational Modal Analysis (OMA), release tests, very often present strong limitations due to their qualitative nature or else to the costs associated with their implementation and functioning. An innovative procedure based on the use of nanoindentation tests is proposed and validated through an experimental campaign. Its main benefits consist in the possibility of quantitatively estimating the current characteristics of elastomeric bearings, in conjunction with low implementation costs and influence on the isolating devices. The innovative procedure consists of coring a very small sample of rubber from a bearing and testing it with a nano-indenter in order to estimate the actual characteristics in terms of shear stress-strain relationships. The experimental tests showed good agreement between the properties calculated with the proposed method and the ones obtained directly through a traditional shear test, making such procedure a promising tool.

Elastic properties of multilayer oxide coatings on float glass

The damage resistance of multilayer oxide coatings on glass used for optical applications often depends on contact damage and the stress generation and relaxation mechanisms during coating deposition and subsequent application. Whereas it is relatively easy to design the optical properties of a multilayer coating to meet a particular specification it is more difficult to design its mechanical response. In part this is due to a lack of reliable mechanical property data for design, chief of which is the elastic modulus of each coating layer in the multilayer stack. Indentation tests can be used to determine the elastic and plastic properties of relatively thick (>1 μm) coatings but, whereas it is possible to measure the plastic response of submicron coatings provided the indenter penetration is less than 10% of the coating thickness this is not the case for elastic properties where a much lower penetration is required. In this study the use of nanoindentation testing in conjunction with a simple modelling approach to determine suitable elastic properties of individual oxide layers in a multilayer coating stack is assessed. It is demonstrated that the ISO14577 extrapolation approach underestimates the contact moduli for 200 nm thick coatings but a multilayer model can be used to determine more realistic properties. Variations in elastic properties of the glass substrate in the near-surface region need to be taken into consideration to get good data from the model.

A preliminary study of hardness and modulus of elasticity in sheep mandibles submitted to distraction osteogenesis and low-level laser therapy

Objectives: The objective this study is validate the use of nanoindentation tests in research and to assess the quality of newly formed bone in sheep mandibles submitted to Distraction osteogenesis (DO) and low-level laser therapy (LLLT) based on hardness and modulus of elasticity values. We also aim to determine the best moment for the application of laser therapy.

Stress states and nonlinear mechanical behavior associated with nanoindentation testing of polymers

Interest in determining material properties on the nanoscale has promoted use of nanoindentation testing as a measurement technique. Classical elasticity solution of indentation geometry has provided values of the mechanical properties for linear elastic materials. Recent attempts to apply this test technique to polymers have given indications of time dependent response in the early relaxation period. There is corresponding interest in the possibility of obtaining their nonlinear viscoelastic behavior. As a preliminary to analytical study providing a basis for such testing, the first part of this paper examines the initial stress and strain condition in the vicinity of the indenter. Data from recent tests on poly(vinyl acetate) material at load levels typical of current testing indicate that stress magnitudes in the nonlinear and possibly plastic-like range are present near the specimen surface. The second part of this study pursues the examination of how the heavily nonlinear region may be characterized for polymers in analogy with the treatment utilized for metals and other elastic-plastic materials. As an example, analysis of data on PVAc indicates that its behavior in nanoindentation should in several respects correspond to materials exhibiting a relatively low value of the ratio of elastic modulus to yield stress.

Mechanical modelling of indentation-induced densification in amorphous silica

Despite their brittleness, silicate glasses undergo plastic deformation at the microscopic scale. Mechanical contact and indentation are the most common situations of interest. The plasticity of glasses is characterized not only by shear flow but also by a permanent densification process. After indentation, densification can locally reach 20% in a pure silica glass. In this paper, a new constitutive model, derived from experimental observations, is presented to account for the plasticity of fused silica. The use of nanoindentation tests to identify the plastic behaviour of amorphous silica is discussed. A set of material properties is determined by comparing experimental load–displacement indentation curves to the results of finite element simulations. The numerical results show good agreement with recent experimental indentation-induced densification maps obtained by Perriot et al. [Perriot A, Vandembroucq D, Barthel E, Martinez V, Grosvalet L, Martinet Ch, et al. J Am Ceram Soc 2006;89:596].