Indentation techniques, mechanical

Another largely unexplored area is the change of dynamics due to the influence of the surface. The dynamic behavior of a latex suspension as a model system for Brownian particles is determined by photon correlation spectroscopy in evanescent wave geometry [130] and reported to differ strongly from the bulk. Little information is available on surface motion and relaxation phenomena of polymers [10, 131]. The softening at the surface of polymer thin films is measured by a mechanical nano-indentation technique [132], where the applied force and the path during the penetration of a thin needle into the surface is carefully determined. Thus the structure, conformation and dynamics of polymer molecules at the free surface is still very much unexplored and only few specific examples have been reported in the literature. 

The two mechanical properties measured most frequently using indentation techniques are the hardness, H, and the elastic modulus, E. A t5pical load-displacement curve of an elastic-plastic sample during and after indentation is presented in Fig. 30, which also serves to define some of the experimental quantities involved in the measurement. 

A.G. Evans, "Fracture Toughness The Role of Indentation Techniques" pp. 112-35 in Fracture Mechanics Applied to Brittle Materials. (Edited by S.W. Freiman. Am. Soc. Test. Mater, Spec. Tech, Publ. 678, 1978. 

Evans, A.G., 1979. Fracture toughness The role of indentation techniques. In Fracture Mechanics Applied to Brittle Materials. ASTM STP No. 678, p. 112. 

G.R. Anstis, P. Chantikul, B.R. Lawn, and D.B. Marshall, A Critical Evaluation of Indentation Techniques for Measuring Fracture Toughness I. Direct Crack Mechanisms, J. Am. Ceram. Soc., 64, 553-58 (1981). 

Indentation techniques were widely used for a long time to investigate the plasticity of silicon at low temperature. However, a difficulty arises because silicon shows a phase transition from diamond-cubic structure to p-Sn metallic Si at a pressure of about 12GPa [49]. As the shear stress increases during an indentation test, the hydrostatic component simultaneously increases and the critical pressure for the phase transition can be reached. In such conditions, the hardness values and dislocation microstructures cannot be representative of dislocation-induced plasticity mechanisms. Indeed, the occurrence of the phase transition under indentation was found to explain the observed saturation of hardness values below 400 °C ([50,51] see also Fig. 8). Dislocations were nevertheless observed after indentation at temperatures lower than 400 °C, but their possible connection with the phase transition was not investigated. 

Over recent years, sharp-contact indentation techniques (i.e. Vickers, Knoop, Berkovich, etc.) have been a convenient and universally accepted method to ascertain the mechanical property of hardness for a ceramic. Such a process involves penetrating the polished surface of a material with a loaded diamond indenter of a predetermined configuration. The hardness (H) can then be substantiated as a ratio of the applied load (P) to resultant contact area of the residual impression ... 

The present paper is specially focused on the surface mechanieal properties of polypropylene films heterogeneous modified by using acrylic acid as grafting agent in solution. Surface mechanical properties have been measured by nano-indentation techniques and the chemical treatment induced variation of the mean image roughness, reduced modulus and surface hardness have been assessed. Whetha- beneficial bulk mechanical properties remained actually unaffected by surface chemical modification was checked by determining the tensile deformation behavior, static fracture behavior and dart impact response. 

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. 

Since the early 1980s, the study of mechanical properties of materials on the nanometre scale has received much attention, as these properties are size dependent. The nanoindentation and nanoscratch are the important techniques for probing mechanical properties of materials in small volumes. Indentation load-displacement data contain a wealth of information. From the load-displacement data, many mechanical properties such as hardness and elastic modulus can be determined. The nanoindenter has also been used to measure the fracture toughness and fatigue properties of ul-... 

Nanoindentation techniques were used to determine the hardness of Cu, Ta W metal discs and thin films on silicon substrates as a function of load or indentation depth. Cu films exposed to oxidizing solutions containing H2O2 exhibited a higher hardness at the surface while no such change was observed for W exposed to ferric nitrate. The implication of these measurements and their relationship to chemical-mechanical polishing rates are discussed. 

Pellicle and tea-immersed pellicle were analyzed using nanoDMA (dynamic mechanical analysis) to see if the tannins had an effect on the viscoelasticity of the pellicle. NanoDMA is a technique used to study and characterize mechanical properties in viscoelastic materials. The method is an extension of nanoindentation testing [58, 59], An analysis of the nanoindentation load-depth curve gives the hardness (H) and reduced elastic modulus (E ), provided the area of contact, A, between the indenter tip and the sample is known [ 13]. By... 

To measure the hardness and elastic modulus of thin films while avoiding the influence of the substrate, peak indentation depth cannot exceed about 30% of the film thickness.Because commercial nanoindenters can make a minimum penetration depth of 10-15 nm, hardness and elastic modulus of films thinner than 30 nm cannot be measured. Clearly, new techniques for fabricating sharper indenters and new nanoindentation theories are needed to extend this technique. For film thicknesses less than 30 nm, nanoscratch tests are widely accepted to evaluate the mechanical properties (discussed later). Alternatively, assuming the hardness and elastic modulus of a film do not change with thickness, thicker films can be used. 

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