Indentation Sensitivity Research Articles

Finite element modelling to predict hardness of Mg alloy reinforced with Ti/Hydroxyapatite hybrid composites – An axisymmetric approach

Magnesium based MMCs are widely investigated for orthopaedic applications because of its degradable property. In order to reduce the experimental trials on designing these composites that mimic the natural human bone, Finite element method has been widely employed. This work analyses finite element model of Mg-3Zn alloy matrix reinforced with micron sized 1% Ti particles/ 1.5 % hydroxyapatite particles (hybrid reinforcements) to predict hardness indentation load displacement curves as these composites can be used as load bearing support for fractured bone. Local mechanical responses measured by indentation technique by local measurements are correlated. Stiffness response of the composite to indentation sensitivity is analysed with constitutive parameters. Relations between influence of reinforcements and the material property to aid experimentation are addressed. Critical differences and similarities in strain fields shape, magnitude and size are established. It was observed that the experimental hardness results of the composites are in good agreement with the simulated results.

Effects of grain size and indentation sensitivity on deformation mechanism of nanocrystalline tantalum

Nanoindentation process is performed by molecular dynamics simulations to investigate the plastic deformation phenomena and mechanical properties of the polycrystalline tantalum (Ta) substrate. The comparison of mechanical behaviors between the single crystal and polycrystalline Ta is analyzed. The effects of grain size, indenter radius, indentation velocity, and temperature are deeply investigated. Further, the important factors of mechanical property such as the plastic deformation, dislocation, amorphization process, indentation force, yield pressure, and von Mises stress are evaluated. The results show that the phase transformations and dislocations almost absent in the grains. Instead, the dislocations densely occur in the grain boundaries, the amorphization regions are formed around the indentation areas and develop along the grain boundaries. The high von Mises stresses are mainly distributed around the indentation areas and in the grain boundaries. The single crystal tantalum shows better mechanical characteristics than the polycrystalline tantalum such as harder to deform, higher yield pressure, and lower dislocation.

A damage index of indentation sensitivity in low velocity impact conditions

The empirical model recently found by the authors for the prediction of the indentation depth was verified for composite laminates different in matrix and fiber subjected to low velocity impact loads. The data obtained in a previous research on common glass and carbon fiber laminates made by commonly used epoxy matrix, were here compared to the results obtained on laminates made by glass fibers immersed in phenolic matrix and novel basalt fibers immersed in epoxy resin. The model takes into explicitly account the tup diameter and presents the advantage that only a single material constant to be experimentally determined is necessary for the prediction. The comparison showed that the value of the constant is different for the different material systems analyzed so that it can be assumed as an index for the indentation sensitivity. POLYM. COMPOS., 36:987–991, 2015. © 2015 Society of Plastics Engineers

Indentation-sensitive parsing for Parsec

Several popular languages including Haskell and Python use the indentation and layout of code as an essential part of their syntax. In the past, implementations of these languages used ad hoc techniques to implement layout. Recent work has shown that a simple extension to context-free grammars can replace these ad hoc techniques and provide both formal foundations and efficient parsing algorithms for indentation sensitivity. However, that previous work is limited to bottom-up, LR($k$) parsing, and many combinator-based parsing frameworks including Parsec use top-down algorithms that are outside its scope. This paper remedies this by showing how to add indentation sensitivity to parsing frameworks like Parsec. It explores both the formal semantics of and efficient algorithms for indentation sensitivity. It derives a Parsec-based library for indentation-sensitive parsing and presents benchmarks on a real-world language that show its efficiency and practicality.

A new damage index for the indentation depth evaluation of composites under low velocity impact loads

The effectiveness of a new empirical model, aiming to predict the indentation depth resulting in a composite laminate from a hemispherical tup impacting it at low velocity, is here proposed. With this simple model including only the diameter of the impactor and the ratio between the impact energy and the perforation one, a material-independent parameter characterising the indentation depth is identified. Several samples with different thicknesses, impacted by various impactor tips, are tested for estimating this parameter. To reach the above mentioned scopes, low velocity impact tests were carried out on two different composite systems with different stacking sequences, thicknesses and fiber volume fractions: (a) glass/epoxy prepreg; (b) graphite/epoxy prepreg. The samples were simply supported on steel plates or clamped and they were struck at the center by hemispherical steel noses having 16 and 19.8 mm diameters. After impact, indentation was measured according to EN 6038 standard. The CFRP indentation data were drawn from a database: about 200 test records, generated by various researchers were individuated. The advantages of the new model are that the effect of the tup diameter is explicitly accounted for. Furthermore, a single material constant has to be experimentally determined and it can be assumed as an index for the indentation sensitivity, on the basis of which different materials can be ranked. The constant was found similar for GFRP and CFRP laminates denoting independence of constraint conditions, laminate type or laminae orientation and stacking sequence. POLYM. COMPOS., 34:2061–2066, 2013. © 2013 Society of Plastics Engineers

MEMS-based force-clamp analysis of the role of body stiffness inC. eleganstouch sensation

Touch is enabled by mechanoreceptor neurons in the skin and plays an essential role in our everyday lives, but is among the least understood of our five basic senses. Force applied to the skin deforms these neurons and activates ion channels within them. Despite the importance of the mechanics of the skin in determining mechanoreceptor neuron deformation and ultimately touch sensation, the role of mechanics in touch sensitivity is poorly understood. Here, we use the model organism Caenorhabditis elegans to directly test the hypothesis that body mechanics modulate touch sensitivity. We demonstrate a microelectromechanical system (MEMS)-based force clamp that can apply calibrated forces to freely crawling C. elegans worms and measure touch-evoked avoidance responses. This approach reveals that wild-type animals sense forces <1 μN and indentation depths <1 μm. We use both genetic manipulation of the skin and optogenetic modulation of body wall muscles to alter body mechanics. We find that small changes in body stiffness dramatically affect force sensitivity, while having only modest effects on indentation sensitivity. We investigate the theoretical body deformation predicted under applied force and conclude that local mechanical loads induce inward bending deformation of the skin to drive touch sensation in C. elegans.

The role of distributed viscoelastic coupling in sensory adaptation in an insect mechanoreceptor

1. Time-dependent mechanical coupling in proprioceptive campaniform sensilla of the cockroach leg was investigated by measuring the compliance of the sensillar cap with punctate, sinusoidal mechanical stimuli at forcing frequencies ranging 3 mHz (0.003 Hz) to 100 Hz. Coupling was described in terms of linear transfer functions for cap compliance and for sensory discharge sensitivity to both cap indentation and applied force. 2. Most sensilla stiffened viscoelastically as a power of frequency, with median power coefficient −0.058 for compliance, and with indentation lagging force by a constant phase angle, median −8.4°. This behavior indicates broadly distributed viscoelastic rate constants in individual sensilla. The extent of viscoelasticity also varied among sensilla; about a third were purely elastic, with constant compliance and zero phase angle. 3. Discharge sensitivity increased with forcing frequency, usually as a power function, and the sinusoidally modulated discharge peaked sooner than both indentation and force by essentially constant phase angles. Median power coefficients were 0.51 for indentation sensitivity and 0.38 for force sensitivity; corresponding phase angles were somewhat smaller than for a power law, respective medians 39° and 30°. Purely elastic caps gave identical values for indentation and force. 4. This means all sensilla adapted, and all were rate sensitive; but in viscoelastic ones these effects were greater for indentation than for force. 5. Discharge sensitivity for a few sensilla deviated systematically from a power law in that power coefficients and phase angles increased somewhat with forcing frequency. 6. Computed responses for viscoelastic caps showed creep under constant force, and stress relaxation under constant indentation, with faster and greater sensory adaptation for indentation than for force. 7. We conclude cap compliance exerts a mild filtering action throughout the entire time course of adaptation in viscoelastic sensilla, but has no role in the adaptation of purely elastic ones.

Compliance and sensitivity of a mechanoreceptor of the insect exoskeleton

1. The compliance (indentation per unit force) of the caps of proprioceptive campaniform sensilla of Group 6 of the cockroach leg has been measured in terms of the stimulating force generated per volt of input to a piezoelectric punctate stimulating device. The median compliance value at cap center in 19 preparations, using punctate forces which were modulated sinusoidally at 3 Hz, was 2.1 nm/ΜN (mm N−1), inner quartile range 1.5–3.7 nm/ΜN. 2. Sensitivity to punctate force (impulse frequency modulation per unit force) was meassured simultaneously with compliance. Median force sensitivity in 18 preparations was 3.2 Hz/ΜN (MHz N−1), inner quartile range 2.3–5.1 Hz/ΜN. 3. Sensitivity to indentation (impulse frequency modulation per unit indentation) was determined as force sensitivity divided by compliance. Median indentation sensitivity in 18 preparations was 1.7 Hz/nm (GHz m−1), inner quartile range 1.2–2.0 Hz/nm. Thus the magnitude of cap indentation associated with moderately brisk discharge frequencies of the order of 100 Hz, well within the range of linear encoding, is of the order of a few tens of nanometers. 4. The precision of the method in individual determinations, estimated as the propagated standard error, gave median values of 7.6% for cap compliance, of 5.8% for force sensitivity, and 9.8% for indentation sensitivity. The method was sufficiently precise to resolve variability of repeated measurements on the same sensillum. 5. The reproducibility of repeated measurements on individual sensilla, expressed as median coefficient of variation, gave values of 27% for cap compliance, 25% for force sensitivity, and 32% for indentation sensitivity. Analysis of variance indicated the method was sufficiently reproducible to resolve variability among the individual receptors comprising this study. 6. Cap compliance and indentation are discussed in terms of the structure of the sensillum. The measured compliance values agree quantitatively with simple models based on known mechanical properties of insect cuticle.

Plastic Indentation Resistance as a Function of Retained Austenite in Rolling Element Bearing Steel

Resistance to plastic indentation was measured on a series of 52100 bearing steel samples representing a wide range of heat treatments. The samples were subsequently analyzed for austenite content by an X-ray diffraction method. Within a limited hardness range definite positive correlation was found between austenite content and indentation sensitivity. This correlation was seen to improve further when austenitizing temperature was fixed, indicating that at a fixed hardness level, factors other than austenite content also influence the plastic indentation resistance of rolling element bearing steels.