Mechanical tests hardness

The compounds were mixed on a two-roll mill at 320°F. for 8 minutes, then molded into test plaques at 340°F. and 1500 p.s.i. Samples for mechanical testing, hardness, compatibility, and Clash-Berg temperature were 0.075 inch thick while carbon black volatility and extractions were performed on 0.010 inch films. All testing was in accordance with ASTM specifications, and results are summarized in Tables II through V. 

Mechanical Tests. Hardness measurements taken with a Shore A durometer are reported every time a pad specimen has been removed from its water bath for compression-deflection tests. Separate flat slabs, 0.12 and 0.50 in. thick, of polyurethane elastomer, which were cast from the same batch of material and given identical exposure to water as the pads, were employed for the hardness tests. 

Mechanical properties. Hardness is the most common mechanical test. See Chapter 5, Mechanical Testing. Hardness testing, for instance, may be used to indicate whether fasteners in specific critical services are greater or less than the value required to avoid a premature failure. Mechanical tests other than hardness are destructive. If a destructive test is required to ensure compliance it is performed on a sample piece from the lot. Mechanical tests are time consuming and only used when required by the specification. 

Jinl] Mechanical tests Hardness, tensile properties, fracture mode... 

K10] Mechanical tests Hardness, formability, tensile and torsion properties... 

Jun] Mechanical tests Hardness compression and creep (900-1250°C)... 

Mun] Mechanical tests Hardness, yield stress, fracture stress and strain at fracture... 

Bal] Mechanical tests Hardness yield stress, ultimate tensile stress and elongation (RT-600°C)... 

Cho] Mechanical tests Hardness, strength, and elongation up to 520°C... 

Mur] Mechanical tests Hardness and indentation fiacture toughness... 

Pal] Mechanical tests Hardness, compressive yield stress, ductile-to-brittle transition temperature, steady state creep rate, and oxidation kinetics... 

Figure 7-10 shows durometer scale relationships and hardness ranges. The letter designations refer to the Shore hardness test (Chapter 5, MECHANICAL PROPERTY, Hardness). 

Tests for indention under load are performed basically like the ASTM measure the hardness of other materials, such as metals and ceramics. There are at least four popular hardness scales in use. Shore A and Shore D is for soft to relatively hard plastics and elastomers. Barcol is used from the mid-range of Shore D to above it as well as RPs. Rockwell M is used for very hard plastics (Chapter 5, MECHANICAL PROPERTY, Hardness),... 

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. 

FIGURE 17.8 Mechanical testing results for cured compounds showing tensile, hardness, and tear properties. 

The mechanical properties of a material describe how it responds to the application of either a force or a load. When this is compared to an area, it is called stress, another term for pressure. Three types of mechanical stress can affect a material tension (pulling), compression (pushing), and shear (tearing). Figure 15.27 shows the direction of the forces for these stresses. The mechanical tests consider each of these forces individually or in some combination. For example, tensile, compression, and shear tests only measure those individual forces. Flexural, impact, and hardness tests involve two or more forces simultaneously. 

Chemical, Physical, and Mechanical Tests. Manufactured friction materials are characterized by various chemical, physical, and mechanical tests in addition to friction and wear testing. The chemical tests include thermogravimetric analysis (tga), differential thermal analysis (dta), pyrolysis gas chromatography (pgc), acetone extraction, liquid chromatography (lc), infrared analysis (ir), and x-ray or scanning electron microscope (sem) analysis. Physical and mechanical tests determine properties such as thermal conductivity, specific heat, tensile or flexural strength, and hardness. Much attention has been placed on noise /vibration characterization. The use of modal analysis and damping measurements has increased (see Noise POLLUTION AND ABATEMENT). 

It is interesting to consider hardness as an example of how mechanical tests for rubber have, or have not developed. Firstly, despite the very imprecise relationship with modulus and the lack of any fundamental significance, hardness measurements have continued to be used and even now new ones are being introduced. The far more sensible method of measuring force to produce a given deformation, which would also allow stress relaxation to be conveniently measured, has not been adopted. However, the instrumentation has been updated so that the old measure can be made with electrical transducers and fed directly to a computer. On the other hand, perhaps the fact that hardness is a non-destructive method that can be applied to virtually any product is justification that it should thrive. 

The values of the various softening temperatures can now be related to the shape and the position of the E(T) curves, discussed in Chapters 3 and 4. A satisfactory comparison is hardly possible, because the time scales of the tests differ too much E(T) curves have, in most cases, been measured by dynamical-mechanical tests at a time scale round one second, whereas the determination of softening temperatures extends over several minutes. In principle, however, the picture presented in Figure 8.1 is valid (see also Qu. 8.3). 

Some tubes were split open and subsequent examination showed the presence of very hard deposits on the surface (Figure 7.32). Isolated, but deep pits were present under the hard deposits (Figure 7.33). The measured thickness of the tube, mechanical tests, chemical analysis and etching showed the tubes to conform to the properties specified for SA 179 tubes. 

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