Plastic indentation

Fig. 10. Typical load-displacement graph for elasto-plastic indentation.

Lankford, J., and Davidson, D. L., The Crack-Initiation Threshold in Ceramic Materials Subject to Elastic/Plastic Indentation, /. Mater. Sen, Vol. 14,1979,pp. 1662-1668. 

If slip-line fields do not control plastic indentation, what does The answer is not the beginning of the plastic deformation, but the end of it. The end means after deformation hardening has occurred. That is, it is not the initial yield stress, Y0, that controls indentation, but the limiting yield stress, Y. This is... 

Lankford J., Davidson D. L., 1979a, The crack-initiation threshold in ceramic materials subject to elastic-plastic indentation, J. Mater. Sci., 14, 1662-1668. 

Lawn B. R., Evans A. G., 1977, A model for crack initiation in elastic-plastic indentation field, J. Mater. Sci., 12, 2195-2199. 

Many polymers, which are brittle in tension or bending, may readily yield in other types of deformation, and show a high ductility. In indentation hardness experiments, plastic indentation can often be made in relatively brittle materials. Hardness values thus obtained are a measure of the plastic properties of the brittle solid ... 

Modern indentometers for the measurement of the hardness of thin films use a computer controlled step-wise increase of the load up to a chosen maximum Zvmax followed by a step-wise unloading. Instead of measuring the diagonal of the plastic deformation, the indentation depth, h, is measured electronically and the indentation curve evaluated (see Fig. 2a). The plastic hardness is calculated from the maximum load, Lmax> d the depth of the plastic indentation. Aplastic,... 

C. M. Perrott, Elastic-plastic indentation Hardness and fracture, Wear, 1977,45, 293-309. 

Lawn, B.R., and Evans, A.G., Elastic/plastic indentation damage in ceramics the median radial crack system, /. Ant. Ceram. Soc., 1980, 63. 

When the particles touch, the force of attraction rises to such a large value that deformation of the particles occurs. This may be elastic deformation as demonstrated by Johnson et al. or it may be plastic indentation as noted by Krupp." In the elastic case, spherical particles form a small circle of intimate contact diameter d, which depends on the elastic modulus E, the Poisson ratio v of the material and the particle diameter D according to... 

B. R. Lawn. A. G. Evans and D. B. Marshall, Elastic/Plastic Indentation Damage in Ceramics The Median/Radial Crack system, Am. Ceram. Soc., 63,574-81 (1980). 

Burnett, P.J., Rickerby, D.S., 1988. The scratch adhesion test an elastic-plastic indentation analysis. Thin Solid Films 157, 233—254. 

According to the classical theory of plasticity, indentation hardness for a Vickers indenter is approximately equal to three times the 5deld stress measured in frictionless compression, Yc (1). However, recent data evidence that the theory fails when dealing with polymers (24). Indeed, hardness-to-compressive yield stress ratios of H Yc 2 have been found for various chain-folded and chain-extended PE samples due to the nonnegligible elastic strains of the indented material (24). On the other hand, hardness-to-tensile yield stress ratios of HfYt >= 3 have been obtained on a wide variety of PE samples, provided the strain rate of the tensile test is comparable to that employed in the hardness test (24,25). 

The repeated impact of liquid against a solid surface using an intermittent jet at sufficiently high speeds leads to a form of erosion. At impact, a liquid drop produces a very high compressive stress in the vicinity of the area of contact, and this is followed by outward, radial flow of liquid at very high speed which shears and erodes the surface. Erosion-corrosion in alpha-brass comprises two parts. The initial progressive plastic indentation is followed by the formation of an annulus where pits gradually form. 

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