Indentation Hardness Tests

Quantitative hardness tests slowly apply a fixed load to an indentor that is forced into the smooth surface of the specimen. After the load is removed, either the diameter across the impression or the depth of the impression is measured. The size of the penetration is proportional to the material s hardness. Rockwell, Brinnell, Vickers, and Knoop are well-known indentation hardness testing instruments. 

Because the penetrator is applied to the surface of the material, the surface must be prepared such that it is representative of the structure of the material. The surface should be free from surface imperfections, such as scales and pits, and the surface should be flat. Some tests may require the surface to be highly polished. 

Rockwell hardness tests apply a minor load and a major load. The minor load essentially sets the indentor on the surface of the material and through any slight imperfections. The major load pushes the indentor into the material to be tested. The minor and major loads vary depending on the test. 

---

A hardness indentation causes both elastic and plastic deformations which activate certain strengthening mechanisms in metals. Dislocations created by the deformation result in strain hardening of metals. Thus the indentation hardness test, which is a measure of resistance to deformation, is affected by the rate of strain hardening. 

Anisotropy in metals and composite materials is common as a result of manufacturing history. Anisotropic materials often display significantly different results when tested along different planes. This appHes to indentation hardness tests as well as any other test. 

Although indentation hardness tests are usually classified as nondestmctive they do in fact leave a permanent indentation on the surface of the... 

Brinell. The first rehable indentation hardness test was developed by BrineU in 1900 and used ball bearings to make indentations in steel (1). The technique has remained rehable and essentially unchanged for nearly 100 years. The test, described by ASTM Standard ElO (2), is stiU in use. 

Apphcations of microhardness testing greatly extend the conventional indentation hardness test to glass and ceramics, metaHographic constituents, and to thin coatings or other surface treatments not otherwise testable. 

Scleroscope hardness It is a dynamic indentation hardness test using a calibrated instrument that drops a diamond-tipped hammer from a fixed height onto the surface of the material being tested. 

B. W. Mott, Micro-indentation Hardness Testing, p. 247, Butterworths Scientific Publications, London, UK (1956). 

X. Cai, Effect of Friction in Indentation Hardness Testing A Finite Element Study , Jour. Mater. Sci. Lett., 12, 301 (1993). 

Although indentation hardness tests are usually classified... 

Many special applications of indentation hardness testing techniques to unusual materials or conditions have been developed, some of which are listed in Table 4. 

Mott B. W., 1960, Micro-Indentation Hardness Testing, Butterwords, London. 

There are two main techniques used to measure the fracture toughness of ceramics fracture stress and hardness indentation. The former measures the load to fracture of a pre-cracked specimen using a single edge notched beam (SENB) or a chevron notched beam (CNB) sample. The main drawback of this technique is ensuring that the crack tip is atomically sharp. The second method uses the crack formed at the corners of the indentation produced during a Vickers indentation hardness test. This technique is rapid and relatively inexpensive. However, the toughness values measured are those of the surface, unlike the values obtained by fracture of the pre-cracked beams which are a measure of the bulk material properties. 

The measurement of local mechanical properties is an important step in understanding of the macroscopic behavior of multiphase materials. The indentation hardness test is probably the simplest method of measuring the mechanical properties of materials. Figure 12.2b shows the evolution of the microhardness as a function of the thermal treatment temperature of a Nasicon sample. The use of load-controlled depth-sensing hardness testers which operate in the (sub)micron range enables the study of each component of the composite more precisely. 

Method 7 - Indentation hardness tests Part 3 1989. Methods 8 and 9, 12 pp Method 8 - Creep... 

Hardness Tests measure resistance of samples or the part surface to indentation or scratching. Indentation hardness tests... 

An alternative method of determining the plasticity and elasticity of a material is indentation hardness testing. The principle of indentation hardness testing is that a hard indenter of specified geometry, either a sphere or square-based pyramid, is pressed onto the surface of the test... 

Fliestand and Smith (1984) proposed three indices referred to as Tabletting Indices. The three indices are a strain index, bonding index and the BFI, which was described in the section on Capping. The strain index is a measure of the strain present in a material following compaction and is a measure of elastic recovery calculated by a dynamic indentation hardness test. The bonding index is a measure of the material s ability to deform plastically and form bonds and is the ratio of a compact s tensile strength and indentation hardness. 

Compound Hardness (Shore D) Indentation Hardness Test ... 

There are four major indentation hardness tests, which differ from each other in the shape of the indenter (Figure 10.23). The first of these, described in 1900, was the Brinell test, using a 10 mm steel ball indenter (Figure 10.23a), giving the Brinell hardness number, BHN. This was suitable only for metals softer than steel. In 1920 Rockwell developed a number of tests, including the B, E, F and G scales, in which the indenter is steel, and the A, C and D scales, using a conical diamond indenter with a spherical tip (Figures 10.23b and 10.23c). In the Rockwell test the difference in size between the... 

In his 1950 review of the history of rubber testing, Buist (IJ observed that prototypes of many of the tests then in use had been tried with varying degrees of success before 1900. and there is no doubt that technologists of that period would still recognize many of the features of the present-day rubber laboratory. The value of tensile stress-strain properties as control measures was appreciated in the late nineteenth century the principles of the indentation hardness test were established before the First World War and the accelerated air-oven aging test dates back at least 80 years. 

A test more frequently found in Continental Europe than in the U.K. or the U.S.A. is the ball indentation hardness test, which is standardized in ISO 2039. Part 1 [5], also dual numbered as BS 2782. Method 365D [6]. In this a 5 mm diameter hardened steel ball is pressed into the test surface under a specified load so that the indentation is between 0.07 and 0.10 mm for method A. or between 0.15 and 0.35 mm for method B. The time of application of the load is 30 seconds, and a minimum test piece thickness of 4mm is recommended. Unlike the Shore or IRHD scales, vvherc hardness is directly related to the penetration of the indentor. the ball indentation hardness is given by ... 

FIGURE 3.42 Indentation hardness tests, (a) Brinell test, (b) Vickers test, (c) Knoop test. 

Indentation hardness tests are used to determine the hardness of a material to deformation. Hardness or stiffness of the gel is measured by placing a metal ball on top of the material and the hardness of the material depends on the amount of indentation caused by the ball. ... 

Knoop hardness test n. An indentation hardness test using calibrated machines to force a rhombic-based pyramidal diamond... 

Non-destructive test (1) A test that yields information about failure under mechanical stress without actually stressing to failure. (2) More broadly, any test to evaluate a property of a material, part, or structure that does not significantly damage the part. Techniques used include ultrasound, magnetic inspection of metals and welds. X-ray inspection, infrared, nuclear magnetic resonance, and sonic analysis. Although an indentation-hardness test leaves a permanent mark, in many tests of parts it is nondestructive. 

Hardness is the resistance that a body offers to penetration by a harder body. Polished sections of ceramic materials are primarily tested by the Vickers or Knoop methods, both of which can be described as indentation hardness testing methods (Fig. 143). The indenter used in Vickers hardness testing is a four-sided diamond pyramid with an included apical angle of 136°. The diamond indenter used in the Knoop method is also a four-sided pyramid, but this indenter has two different included apical angles, measuring 130° and 172°30. This causes an elongated indentation in the material being tested. 

Determining fracture toughness by indentation hardness testing... 

Berg Method. See diver method. Berkeley Clay. A plastic, refractory kaolin from S. Carolina P.C.E.34. Berkovich Indenter. A 3-faced diamond pyramid for indentation hardness tests. 

The second model improves on the first one in the way that static indentation hardness test theory has advanced by introducing plastic deformation into this dynamic system as a parameter. Plastic deformation of the contact area between the particles and the target surface causes radial cracks to propagate outwards from the contact zone and subsurface lateral cracks to move outwards on planes nearly parallel to the surface. Here the parallel with overloaded Vickers static indent tests, which are discussed in detail in... 

---