Knoop Microindentation Research Articles

Evaluation of Young's modulus of polymers from Knoop microindentation tests

The Young's modulus to hardness ratio of small-scale polymer specimens is measured by means of a Knoop indentation procedure. The technicue assumes that the extent of elastic recovery of a Knoop indent is linearly related to the modulus to hardness ratio. A semiempirical linear relationship is proposed for the elastic recovery of the small diagonal of a Knoop incenter as a function of the modulus to hardness ratio for polymer materials, provided that indenting loads of at least 4 N are used. The major benefit of the procedure is that measurements of Knoop microhardness and indentation recovery enable the evaluation of Young's modulus of small-scale polymer specimens.

Fractographic analysis of vitreous calcia-alumina eutectic fibres produced by inviscid melt spinning (IMS)

The mechanical properties of inviscid melt spun (IMS) CaO-Al2O3 (46.5 wt % CaO-53.5 wt % Al2O3) eutectic fibres were examined by fractographic analysis as well as four-point bending and micro-indentation. The averaged fracture strength and elastic modulus values of the IMS Calcia-Alumina (CA) fibre were determined to be 460 MPa and 99.8 GPa, respectively by using four-point bending tests. The inner mirror constant (M) was determined to be 2.39 MPa·m1/2 by using the plot of the fracture strength (σf) obtained from the bending tests as a function of r−1/2, where r is the inner mirror radius measured from scanning electron microscopy (SEM) on the fractured CA fibres. The flaw-to-mirror ratio (c/r) for the CA fibre was calculated to be 1∶11.24. Also, the critical flaw size (c) of the CA fibre was estimated to be 2.35 μm. The averaged elastic modulus value from Knoop micro-indentation was determined to be 102.5 GPa which is in good agreement with that from the four-point bending tests.

Tribological characteristics of graded pencil cores on paper

Despite the long, rich history and widespread use of pencils and paper, the literature of tribology is remarkably devoid of published research on the subject. The present investigation was conducted to investigate the effects of writing core (i.e. “lead”) grade on the wear response and static and kinetic friction coefficients associated with writing on three types of paper: standard 20 lb copier paper, heavier manila cover stock, and Tyvek™, a spunbonded olefin paper product commonly used for mailing envelopes and surgical clothing. Three mechanical pencil core grades (2B, HB, and 2H) were used. These materials varied in Knoop microindentation hardness by a factor of approximately two. Static friction coefficients were determined from simple, inclined-plane tests of the various core-paper combinations, and kinetic friction coefficients were determined by pin-on-disk tests. Against all but the Tyvek™, static friction coefficients were not dependent on core grade or paper type. Kinetic friction coefficients were not clearly correlated with paper type or core grade; however, significant differences in the core wear and paper in-filling characteristics were observed. Scanning electron microscopy and quantitative image analysis were used to study the manner and extent to which the core wear particles were embedded and agglomerated within the tangled fibers of the papers. A clear correlation was observed between the degree of transfer of wear particles to the paper and the hardness of the core in two of the three paper types.

Raman mapping of the microdeformed zone produced by Vickers and Knoop microindentation techniques in poly(vinylidene fluoride)

Raman microspectroscopy was used to follow the crystalline phase transformation produced when Knoop and Vickers microindentations are made in poly(vinylidene fluoride). An evolution of the degree of crystalline phase transformation was observed along the microindentations which can be schematized into three regions. A high gradient in the degree of crystalline transformation was detected near the centre of the indentation, whereas Raman microanalysis of the region near the edges of the impression did not indicate a significant variation in the crystalline phase modification. An explanation for these observations is proposed.

Surface Hardening of Ceramic Oxide and Metal Alloy Single Crystals by Ultrasonic Cavitation

ABSTRACTCavitation effects have long been considered to be undesirable phenomena that resulted in the damage and failure of metallic components. In the present work, we establish that, in fact, controlled applications of ultrasonic cavitation phenomena can be used to enhance the surface properties of both ceramics and metals. Polished (100) surfaces of single-crystal MgO and single crystals of 70%Fe-15%Ni-15%Cr (stainless-steel) were subjected to ultrasonically induced cavitation by exposure to 20 kHz excitations (at ∼ 100 W/cm2) in isopropanol. Knoop micro-indentation hardness measurements on untreated and ultrasonically treated areas of the surfaces revealed a hardening that increased with the duration of the ultrasonic treatment up to a saturation level. Relative increases in the surface hardness of up to 30% in the case of MgO and ∼250% in the case of Fe-Ni-Cr were obtained. It was found that the rate of hardening was not uniform over the surface but was more rapid on those portions of the surface that were directly under the edge of the ultrasonically vibrating horn tip.

Mechanical properties of coated copper mirrors

Copper mirrors are generally used in optical systems for handling CO 2 laser beams. The presence of a protective coating on the mirror surface is necessary to increase the lifetime of mirrors working in a hostile environment. The mechanical properties (adhesion, hardness and abrasion) of Y 2O 3 and a-C:H protective thin films on copper mirrors have been investigated. Y 2O 3 and a-C:H coatings have been deposited by rf sputtering and dual ion beam sputtering, respectively. The coating adhesion has been measured by the ‘scratch test’ and the ‘topple test’, while the hardness has been measured with the knoop microindentation technique. In order to estimate the abrasion resistance of the samples, the ‘eraser test’ has been performed with a custom-made instrument.

Industrial Diamond Substitutes: I, Physical and X‐Ray Study of Hafnium Carbide

A study of hard materials in an effort to find possible substitutes for industrial diamonds led to research on hafnium carbide. This compound was prepared from a mixture of hafnium dioxide and lampblack in a carbon resistance furnace by solid‐state reaction or from a melt. Some factors affecting the combined carbon content of the re‐ action products were qualitatively evaluated. A hafnium carbide prepared from a melt at a temperature slightly above 2800°C. with no holding time had a combined carbon content within 98% of the theoretical value. A curve was obtained by plotting combined carbon against cubic unit‐ cell dimension (a0) for the hafnium carbide‐ “hafnium monoxide” solid solution series. Extrapolation gave 4.641 ± 0.001 a.u. for the cell edge of hafnium carbide of theoretical composition; a0 was observed as high as 4.640 a.u. Density values within 99% of theoretical were obtained. Knoop microindentation hardness measurements with both dry and oil‐immersion objectives indicated a hardness in the silicon carbide range. Owing to its high cost and relatively low hard‐ ness, hafnium carbide is presently not considered to be a promising substitute for industrial diamonds.