Experiment indentation test

Penetration—Indentation. Penetration and indentation tests have long been used to characterize viscoelastic materials such as asphalt, mbber, plastics, and coatings. The basic test consists of pressing an indentor of prescribed geometry against the test surface. Most instmments have an indenting tip, eg, cone, needle, or hemisphere, attached to a short rod that is held vertically. The load is controlled at some constant value, and the time of indentation is specified the size or depth of the indentation is measured. Instmments have been built which allow loads as low as 10 N with penetration depths less than mm. The entire experiment is carried out in the vacuum chamber of a scanning electron microscope with which the penetration is monitored (248). 

In particular, phase transformations under contact loading need a more detailed investigation. Both static and dynamic interactions between hard surfaces may result in phase transformations. Hydrostatic and deviatoric stresses must be taken into account and phase transformations in contact loading can be described as deformation-induced transformations. At the same time, the transformation pressures for silicon obtained in indentation tests are in good agreement with the results from high-pressure cell experiments, which utilize hydrostatic loading. 

W. C. Ohver and G. M. Pharr, An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments, J. Mater. Res., 7, 1564 1583, (1992). ISO 14577 1, MetaUic materials Instrumented indentation test for hardness and materials parameters Part. 1 Test method, (2002). 

Perhaps the most significant complication in the interpretation of nanoscale adhesion and mechanical properties measurements is the fact that the contact sizes are below the optical limit ( 1 t,im). Macroscopic adhesion studies and mechanical property measurements often rely on optical observations of the contact, and many of the contact mechanics models are formulated around direct measurement of the contact area or radius as a function of experimentally controlled parameters, such as load or displacement. In studies of colloids, scanning electron microscopy (SEM) has been used to view particle/surface contact sizes from the side to measure contact radius [3]. However, such a configuration is not easily employed in AFM and nanoindentation studies, and undesirable surface interactions from charging or contamination may arise. For adhesion studies (e.g. Johnson-Kendall-Roberts (JKR) [4] and probe-tack tests [5,6]), the probe/sample contact area is monitored as a function of load or displacement. This allows evaluation of load/area or even stress/strain response [7] as well as comparison to and development of contact mechanics theories. Area measurements are also important in traditional indentation experiments, where hardness is determined by measuring the residual contact area of the deformation optically [8J. For micro- and nanoscale studies, the dimensions of both the contact and residual deformation (if any) are below the optical limit. 

Effect on Confined Systems Corrosion Problems Fracture Fatigue Nano Characterisation Test Methodology Computer Simulation Surface Modification Surface Treatments Surface Problems in Contact Mechanics Fracture Mechanics Coupled Analysis and Experiments Thin Coatings Thick Coatings Contact Mechanics Material Surfaces in Contact Applications and Case Studies Indentation and Hardness Adhesion Bonding. 

In the small punch tests (Figs. 11.18 and 11.19), the indentation force versus displacement responses of the punch head were recorded. These punch experiments were performed both at 20°C and at 200°C. Figure 11.20 illustrates representative results from these tests. 

Figure 10.36 (a) The indentation of a thin film. The indentation area and depth will depend on the properties of the indenter and the substrate as well as the film being tested, (b) Schematic unloading curve for a nano-indentation experiment. Adapted from G.M. Pharr and W.C. Oliver, 1992, Measurement of Thin Film Mechanical Properties Using Nano-indentation , Materials Research Society Bulletin XVII (July) 28... 

The accuracy of the test method relies critically on the accurate determination of the area function, which varies with tip geometry. At the scale of many nanoindentation experiments, minute differences in tip geometry—such as those caused by wear induced by repeated experiments—can have a large effect on the area function. For this reason, the area function is typically measured by indenting a known material to several depths and computing the function from Equation 39.37. This experimentally determined tip function is then used to interpret further tests on unknown materials. Fused silica (or quartz) is commonly used to calibrate the tip, that is, determine the area tip function, because its material response is nearly perfectly elastic and it does not exhibit adhesion with diamond indenter tips. 

It may be argued [3] that the goal hardly attainable in the experiments using high-pressure diamond anvil cells could be more easily achieved in as simple an experiment as a conventional hardness test. The well-documented indentation size effect (ISE) [189] reveals itself in the following relation between the Meyer hardness HM (equivalent to the mean contact pressure) and the applied load P [190] ... 

Mechanical properties of nanomaterials have been characterized using both tensile test and nanoindentation techniques. Nanoindentation experiments describe the deformation of the volume of material beneath the indenter (interaction volume). The nanoindentation of cellulose composites can be performed by using an AFM. 

High temperature crack growth behavior under creep conditions was studied in SiC whisker-reinforced mullite. Four-point flexumral specimens were prepared for crack growth experiments by introducing Vickers indentation-induced cracks on the tensile surface. Samples were tested in creep in air at a nominal smface tensile stress at 150 MPa and a temperature of 1400°C. Crack growth and nucleation, and extent of creep-strain were... 

The experiment demonstrated that the normal force applied to the indenter determined the brittle-ductile transition, and that the critical force was almost equivalent to the Knoop hardness of the test material. 

The nanoindentation experiments were conducted at room temperature with a Nano Indenter XP system (MTS Nanoinstruments, Knoxville, TN) using a Berkovich-type diamond tip. Before each test, the system was calibrated using a fused silica. The continuous stiffness mode (CSM) was used in the tests. Thirty randomly selected different fiber and CVI matrix locations were indented for each component of C/C composites. The method of Oliver and Pharr was employed for the elastic modulus calculations. ... 

At all the temperatures, the FG material is stronger than the CG material and the compressive strength is higher than the flexural strength. A large decrease in strength at 1200 °C is observed for both FG and CG microstructures, under compression and flexure. Experiments on microhardness by Vickers indenter were also performed on Ti3SiC2 ceramics specimens. The results of these tests are... 

The indentation load P and crack length C are obtained directly from testing. To determine the residual stress factor x, it is necessary to adopt certain models of plastic deformation as caused by the indentation. % can be determined by calibrating the fracture toughness in experiments with long cracks. According to Antis et al. (1981) the residual stress factor is determined by the following equation ... 

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