Indentation testing

Many types of hardness tests have been devised. The most common in use are the static indentation tests, eg, Brinell, Rockwell, and Vickers. Dynamic hardness tests involve the elastic response or rebound of a dropped indenter, eg, Scleroscope (Table 1). The approximate relationships among the various hardness tests are given in Table 2. 

Rockwell. The invention of the Rockwed hardness tester in 1919 was an advance over previous indentation tests requiring accurate indentation measurement and tabular reduction to derive a hardness number. In the Rockwed test the hardness number is read direcdy from the instmment dial (1,3). 

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). 

Hay, J.L. and Pharr, G.M., Instrumented indentation testing. In ASM Handbook Mechanical Testing and Evaluation. ASM International, Materials Park, OH, 2000. 

The present review shows how the microhardness technique can be used to elucidate the dependence of a variety of local deformational processes upon polymer texture and morphology. Microhardness is a rather elusive quantity, that is really a combination of other mechanical properties. It is most suitably defined in terms of the pyramid indentation test. Hardness is primarily taken as a measure of the irreversible deformation mechanisms which characterize a polymeric material, though it also involves elastic and time dependent effects which depend on microstructural details. In isotropic lamellar polymers a hardness depression from ideal values, due to the finite crystal thickness, occurs. The interlamellar non-crystalline layer introduces an additional weak component which contributes further to a lowering of the hardness value. Annealing effects and chemical etching are shown to produce, on the contrary, a significant hardening of the material. The prevalent mechanisms for plastic deformation are proposed. Anisotropy behaviour for several oriented materials is critically discussed. 

The plastic properties of a material are often determined by an indentation test [28]. Both static and dynamic test methods are available, but all generally determine the pressure necessary to cause permanent and nonrecoverable deformation. 

Kharrat, M., Chateauminois, A., Carpentier, L. and Kapsa, P., On the interfacial behavior of a glass/epoxy composite during a micro-indentation test assessment of interfacial shear strength using reduced indentation curves, Composites, A, 28, 39 (1997). 

Meda, G., Hoysan, S.F. and Sleif, P.S. (1993). The effect of fiber Poisson expansion in micro-indentation tests. Trans. ASME J. Appl. Mech. 60, 986-991. 

Shetty, D.K. (1988). Shear-lag analysis of fiber push-out (indentation) tests for estimating interfacial friction stress in ceramic-matrix composites. J. Am. Ceram. Soc. 71, C.107-109,... 

Indentation hardness determinations were performed in dynamic mode ( 1500 mm/sec impact speed) using a pendulum impact device and in quasistatic mode ( 0.008 mm/sec impact speed) with a custom-built indentation tester. The spherical indenters were of 2.54 cm diameter and 65.6 g mass, and the pendulum length was 92.3 cm with a release angle of 30°. Quasistatic indentation forces were selected to produce indentations of a similar size to the dynamic indentation test (1.5 to 2.0 mm radius). The compact indentations were measured using a white light interferometer (Zygo Corporation, Middlefield, Connecticut, U.S.A.) and the dent depth, dent diameter, apparent radius of curvature, and pendulum initial and rebound heights were used to calculate the indentation hardness of the compacts. 

Hardness is measured by the Rockwell A-scale diamond cone indentation test (HRA) or by the Vickers diamond pyramid indentation test (HV). Although the Rockwell scale has been used for decades in the carbide industry as a measure of hardness, a true indication of the resistance of the tool to deformation in metal-cutting operations can be obtained only by measuring hardness at elevated temperatures. The hardness of cemented carbides decreases monotonically with increasing temperatures. 

Surface destructive alterations around the action site of the indenter are used to determine the degree of brittleness of a material (Section 6.3). They are the outcome of a destructive deformation of the crystal induced by multidirectional shear forces released in the crystal structure. The shear stresses liberated in static indenter tests are significantly in excess of those registered under other methods, being of the order of 50 MPa (Yushkin,... 

Tate D. R., 1945, A comparison of micro-hardness indentation tests, Trans. Am. Soc. Metals, 35, 374-389. 

Slope of load (P) vs. total crack length (211,) in a P vs. 21, plot obtained from indentation tests. 

Tensile strength can also be measured indirectly by means of a number of compression, bending and indentation tests in which, for brittle isotropic... 

A simple, but not very quantitative, hardness test has been used for hundreds of years— the fingernail indentation test. The indentation that a fingernail makes in the edge of an adhesive bond or in the body of a sealant can often be used as an approximate indication of hardness of the material. 

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