Static indentation tests

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. 

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,... 

Fig. 2. Schematic illustration of the contact geometry of a p3rramid indenter during a static indentation test at zero load, under load, and after load release.

The first of these considers elastic interactions only between the target and the streams of particles which produce ring cracks on the surface of the target. The ring cracks eventually intersect, and material is removed. This model does most closely suit the impingement of low velocity spherical particles. Clearly the Brinell static indentation test is most closely similar because overloaded Brinell spheres produce this type of damage (see 5.2.2). 

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. 

Figure 2. An overall view of quasi static indentation testing system.

Before the impact test, quasi-static indentation tests were performed on the same machine (MTS 810), as shown in Figure 19.2, to investigate the strain-rate effect and perforation energy of the proposed composite laminates. 

Fignre 19 J Comparison of reaction force—displacement curves under a quasi-static indentation test. 

Similar to quasi-static indentation tests, the effect of 1 wt% NC and 1 wt% GB fillers on the impact response of GFRP was initially investigated. Figure 19.13 shows representative force—time curves for each material configuration. As seen in Figure 19.13,... 

Rectangular plates of about 8-10 mm in width, about 45-50 mm in length, and about 2.2 mm (for SiC/SiC) or 3.0 mm (for oxide/oxide) in as-fumished thickness were cut from the composite panels for FOD as well as static indentation testing. Table 1 summarizes basic physical and mechanical properties of the two composites. 

The simplicity of this plastic model is that all the parameter that is required isp , which can be determined through routine static indentation testing, as also demonstrated for various ductile projectiles (steels and brass) impacted on silicon nitride targets [10]. However, pertinent experimental techniques should be sought to determine more accurately the related dynamic patameters such as impact force, stresses, deformation, duration of impact, coefficient of restitution, and stress wave propagations, etc. Frictional constraint by property mismatch between projectiles and targets of dissimilar materials needs to be taken into account in some cases. 

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