Static hardness tests

During static hardness tests with plastic materials by observation of the changes in depth of penetration by a ball or pyramid taking place in time at a constant load, two stages of deformation of material are distinguishable ... 

Correction of measuring errors in static hardness tests by microscopic methods... 

All indentation equipment contains some mechanism for applying the load to the surface. For the commonest technique, the static hardness test, it is inherent in the apparatus that the load be applied incrementally and not instantaneously. These two methods of load application produce fundamentally different values for the hardness of any sample. When the load is applied incrementally, then the indentation is in equilibrium with the load throughout the test. 

The radiation and temperature dependent mechanical properties of viscoelastic materials (modulus and loss) are of great interest throughout the plastics, polymer, and rubber from initial design to routine production. There are a number of laboratory research instruments are available to determine these properties. All these hardness tests conducted on polymeric materials involve the penetration of the sample under consideration by loaded spheres or other geometric shapes [1]. Most of these tests are to some extent arbitrary because the penetration of an indenter into viscoelastic material increases with time. For example, standard durometer test (the "Shore A") is widely used to measure the static "hardness" or resistance to indentation. However, it does not measure basic material properties, and its results depend on the specimen geometry (it is difficult to make available the identity of the initial position of the devices on cylinder or spherical surfaces while measuring) and test conditions, and some arbitrary time must be selected to compare different materials. 

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. 

Microindentation hardness normally is measured by static penetration of the specimen with a standard indenter at a known force. After loading with a sharp indenter a residual surface impression is left on the flat test specimen. An adequate measure of the material hardness may be computed by dividing the peak contact load, P, by the projected area of impression1. The hardness, so defined, may be considered as an indicator of the irreversible deformation processes which characterize the material. The strain boundaries for plastic deformation, below the indenter are sensibly dependent, as we shall show below, on microstructural factors (crystal size and perfection, degree of crystallinity, etc). Indentation during a hardness test deforms only a small volumen element of the specimen (V 1011 nm3) (non destructive test). The rest acts as a constraint. Thus the contact stress between the indenter and the specimen is much greater than the compressive yield stress of the specimen (a factor of 3 higher). 

A further development of static methods of hardness testing was a method devised by Brinell (1900), which consisted of driving a steel ball into the mineral to be tested for hardness under a pressure of 29.4 kN for about 30 seconds. Brinell hardness is defined as the ratio of load to surface of round indentation. The method has found wide use in engineering—for metals it is excellent, but in mineralogy it has proved unsatisfactory because of the high brittleness of most minerals and their non-deformability under the action of the steel ball. The ever wider application of Brinell s method and of a similar method developed by Janko in hardness determination of wood (Krzysik, 1974) should be noted. They are most useful in testing hard wood-base materials, such as compressed wood. 

Khrushchev (1957) considers that the need to measure the force T has not been sufficiently well substantiated, nor has a sufficiently precise and easy in service hardness tester been developed yet for determinations of this type. However, he appreciates the usefulness of scratch hardness tests, especially at low loads, as a non-destructive technique. He recommends these methods as very useful for hardness determination of metallic layers or of materials exposed to abrasive wear under operating conditions (plastics, organic coatings, such as varnishes and paints, etc.). Scratch methods are especially important in tests of anisotropic materials where a change in scratch width is the measure of anisotropy. In static indentation methods, the indentations obtained in anisotropic materials are misformed, varying... 

CLASSIFICATION OF HARDNESS TEST METHODS 1 STATIC MEASUREMENT METHODS... 

This opens up the possibility of linking the Mohs scale and related hardness test methods additionally to another group called abrasiveness tests. These include Bohme s, Scott s, Mackensen s and other methods which are dynamic hardness test methods unlike the previously mentioned static methods. In many cases they are more useful than static tests, since they resemble better the conditions under which wear of a material takes place during commercial use. 

Effects on Aquatic Organisms (Refs 31 44). An LD50 of 3.6mg/J2 was found in 96-hr static bioassay tests of RDX on bluegill sunfish (Lepomis macrochirus) at pH 6 and 35mg/G water hardness, and represents the lowest LC50 found for any aquatic species. The chronic and acute levels are very close in aquatic organisms. Thus, the lowest observable chronic effect, decreased length of fathead minnow (Pimphales promelas) fry,occurred at 3.0mg/6 of RDX this effect was not seen at 1.2mg/fi. RDX shows extremely little bioconcn... 

There are two types of hardness test static tests that involve the formation of a permanent indentation on the surface of the test material and dynamic tests in which a pendulum is allowed to strike the test material from a known distance. Vickers and Brinell tests, two examples of static methods, are the most commonly used methods for determining the hardness of pharmaceutical materials. In the Brinell test, a steel ball of diameter D is pressed on to the surface of the material, and a load F is applied for 30 sec and then removed. The diameter dj of the indentation produced is measured, and the Brinell Hardness Number (BHN) calculated by... 

The indenters and their indentation shapes vary widely, leaving different impressions. The appropriate dimensions of these impressions on the surfaces are measured to obtain interesting research data. Conversion charts, from hardness to other properties of interest, appear in the literature. Basically, glass and ceramic hardness tests are carried out using static methods, usually by means of a diamond indenter and low test loads, because brittle materials tend to propagate cracks. 

The static loading method is divided into Brinell, Rockwell, and Shaw hardness tests because of different shapes of the head and different calculation methods. 

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... 

Static Indentation Tests, by far the most widely used, the most widely analyzed, and the most generous in the breadth of data they supply. A ball, cone, or pyramid is forced into a surface and the load per unit area of impression is considered the material s hardness. Several types of such tests are well known Brinnel, Vickers, Rockwell, and Knoop. 

Results of subcritical crack growth analysis show that for hard metals it is not easy to find out the parameters n and A. The different strain rate method is probably not applicable for these materials because of a large scatter of strength values, Fig. 12. An approximate calculation based on these results gives a value of n cca 200. From results achieved in static bending tests on specimens with artificial cracks (Fig. 13) using equations (8) and (9) we have achieved for n a value of 180 and 60, resp. According to our opinion for determination of n and A the most suitable method is the lifetime measurement and the determination of the v vs. K relation... 

Cleanliness Hardness Hydrostatic Tests Blade Shaker (Static) Rotor balance O Standard O High Speed Final Surface Inspection Crating inspection Spare Rotor Fit ... 

The Rockwell method is based on measurement of two-stage penetration of a diamond cone or steel ball into a flat, well polished surface of the material under test (Fig. 4.3.9a). The cone has an included angle of 120° and a radius of curvature of 0.2 mm. The initial static load P0 penetrates the cone to a depth which depends on the hardness of the material—thus the zero position is fixed. Next, the main load is applied and the cone moves further down by a value ht. On removal of the main load, the ma-... 

---