International Journal of Materials Research Volume 98 Issue 5

International Journal of Materials Research

Volume 98 Issue 5

Contents
Journal Overview

May 23, 2013 Page range: 351-351

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Editorial

Holger Pfaff, Mathias Göken May 23, 2013 Page range: 352-352

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Basic

Getting accurate nanoindentation data from time-dependent and microstructural effects of zinc

Reza R. Tohid, Steve J. Bull May 23, 2013 Page range: 353-359

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Abstract

The main objective of this study was obtaining accurate data from nanoindentation experiments on zinc. Nanoindentation experiments can be performed under displacement control, load control, or open loop conditions at different loading/unloading rates. All the above control schemes and range of loading rates were used to test pure zinc samples with different surface preparation using a Hysitron Triboindenter fitted with a blunt Berkovich indenter. The results showed that displacement control with a high loading/unloading rate gave the most reliable results. However, because of the anisotropy of zinc and its large grain size the material should be considered as a single crystal on the scale of the impression generated. It has been found that using the feedback control of nanoindentation experiments can give a significant improvement in the results compared to open loop control due to the time-dependent behaviour of zinc. A full factorial design of experiments approach was performed to investigate the optimum combination of the feedback parameters to obtain accurate and reliable data for the hardness and Young's modulus of zinc.

Indentation-induced densification of soda-lime silicate glass

Satoshi Yoshida, Jean-Christophe Sanglebœuf, Tanguy Rouxel May 23, 2013 Page range: 360-364

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Abstract

Glass is densified under a sharp diamond indenter. The densification is not a volume conservative process, and does not contribute to the volume strain around the indentation. This means that densification affects residual stresses around the indentation impression. In order to estimate the densification volume, three-dimensional images of Vickers indentations on soda-lime silicate glasses were obtained before and after annealing. Only the densified volume can be recovered by annealing. After annealing at around glass transition temperature, large volume recovery (55 – 80 %) of Vickers indentation was observed for soda-lime silicate glass. The volume recovery is much larger than the recoveries of indentation diagonal and depth. It is found that the densification of glass under the sharp indenter cannot be ignored for evaluating crack initiation and brittleness of glass. In addition, the residual stresses around the indentation impression were also estimated from the plastically deformed volume and the size of plastic zone around the indentation.

Nanomechanical characterization of relaxation processes in As–S chalcogenide glasses

Michael Trunov, Peter M. Nagy, Sergey Dub, Erika Kalman May 23, 2013 Page range: 365-369

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Abstract

Nanoscale mechanical properties of As – S binary chalcogenide glasses for bulk and thin-film samples have been studied, using the nanoindentation technique for a step loading procedure. All components of glass deformation (plastic, elastic. and visco-elastic, or retarded) have been evaluated during the nanoindentation process. An essential redistribution of these components was observed during unloading depending on the composition of the glasses. The same nanoindentation procedure was applied to bulk, as-deposited and annealed thin-film samples of the glasses. Plots of deformation components vs. As concentration (or average covalent coordination number <r>) show a minimum around the As 25 S 75 – As 30 S 70 composition (<r> ≈ 2.30), which corresponds to the rigidity percolation composition, i. e., the transition from the floppy phase to the intermediate one.

Nanoindentation behavior and mechanical properties measurement of polymeric materials

Robert F. Cook, Michelle L. Oyen May 23, 2013 Page range: 370-378

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Abstract

During sharp contacts, polymeric materials can exhibit elastic (reversible), plastic (instantaneous irreversible), and viscous (time-dependent irreversible) deformation. Due to viscous effects commonly observed in experiments conducted on polymeric materials, the analytical methods developed for instrumented indentation testing (“nanoindentation”) of elastic-plastic materials cannot be used to determine polymer mechanical properties. Here, a viscous-elastic-plastic sharp indentation model is reframed into normalized coordinates. The updated scheme allows the mechanical properties of polymeric materials to be determined simply from single- or multiple-cycle nanoindentation tests; output parameters are the relative resistance to plastic vs elastic deformation during indentation and the relative time scales for viscous flow during the contact event. The scheme allows the indentation behavior of all materials to be placed on a single map.

Model of a superlattice indentation

A. Kravchuk, Z. Rymuza May 23, 2013 Page range: 379-383

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Abstract

This paper deals with the problem of penetration of a conical indenter into a multilayer rigid – perfectly-plastic body. The penetration of the indenter is studied on the basis of the Haar and von Karman hypothesis. The analytical distribution of the contact stress is obtained. A relationship between Meyer hardness and yield stresses of the layers is established.

Nanomechanical studies of MEMS structures

Marius Pustan, Grzegorz Ekwinski, Zygmunt Rymuza May 23, 2013 Page range: 384-388

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Abstract

The stiffness is a fundamental qualifier of elastically deformable mechanical microcomponents and micromechanisms whose static, modal or dynamic responses need to be evaluated. This paper presents the results of theoretical studies of microcantilevers and microbridges and also a method for experimental stiffness testing using atomic force microscopy. Castigliano's displacement theorem is used herein to derive the stiffness equations. The results of the theoretical and experimental studies are compared and discussed.

Mechanical properties of nanostructured polymer particles for anisotropic conductive adhesives

J. Y. He, Z. L. Zhang, H. Kristiansen May 23, 2013 Page range: 389-392

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Abstract

Metal-coated polymer particles are used as a critical component in anisotropic conductive adhesives. The mechanical properties of polymer particles are of crucial importance to both application and design. In this study, a nanoindentation-based flat punch test approach has been developed to determine the mechanical properties of two polymer particles. Particle A failed at an average deformation of 67.2 %, while no failure was observed for particle C when a maximum 10 mN normal load was applied. The contact stress – strain behavior and contact modulus were obtained from the flat punch test.

Nanomechanical studies of ultrathin polymeric resist films

Adam Koszewski, Tomasz Gorski, Freimut Reuther, Zygmunt Rymuza May 23, 2013 Page range: 393-396

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Abstract

An atomic force microscope with a specially constructed stiff cantilever was used to study the mechanical properties of ultrathin polymeric resist films devoted to use in nanoimprint lithography. The methodology, the equipment used in these studies and the results of the estimation of the Young's modulus versus temperature are presented and discussed.

Testing the viscoelastic properties of SU8 photo resist thin films at different stages of processing by nanoindentation creep and stress relaxation

Kirsten Ingolf Schiffmann, Carsten Brill May 23, 2013 Page range: 397-403

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Abstract

The viscoelastic properties of SU8-25 photo resist coatings have been investigated by means of nanoindentation creep and stress relaxation tests. Different stages of processing of SU8 have been tested: (a) Spin coating and pre-bake only, (b) exposure to ultraviolet light for different durations, (c) different cross-linking times of the resist and finally (d) the completely processed sample (post-bake, develop and hard-bake). At each stage creep and stress relaxation tests have been performed with loads of 2 mN or indentation depth of 500 nm covering creep/relaxation times from 0.1 s to 1000 s. From the raw data the following viscoelastic functions have been computed: the creep compliance J(t) and relaxation modulus G(t), the relaxation and retardation time spectra H() and L(), and the dynamic viscosity (t). It has been found that different pre-bake times influence the viscosity of the film. The cross-linking of the SU8 starts immediately after exposure even without applying a post-bake. A strong increase in viscosity can be observed within the first 4 h after exposure due to the progress of cross-linking at room temperature. After the finish of cross-linking the dynamic viscosity has increased by 50 times. Observation of impression recovery after unloading over 3 days indicated up to 75 % immediate and retarded elastic recovery for the fully processed film, while the simply pre-baked sample only exhibied 25 % recovery and 75 % irreversible viscous flow.

Microscale characterization of bitumen – back-analysis of viscoelastic properties by means of nanoindentation

Andreas Jäger, Roman Lackner, Klaus Stangl May 23, 2013 Page range: 404-413

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Abstract

In order to understand the complex thermo-rheological behavior of asphalt, stemming from the viscoelastic nature of bitumen, the nanoindentation (NI) technique is employed. Hereby, the load history applied onto the indenter tip is characterized by a loading, holding, and unloading phase. As regards the identification of viscoelastic properties, a recently published back-analysis scheme, employing the holding phase of the NI test, is extended towards fractional-creep models. In fact, this type of model is found to perfectly describe the viscoelastic behavior of bitumen. Based on the identified viscoelastic model parameters, the influence of loading rate, maximum load, and temperature on these parameters is investigated. Hereby, the temperature dependence of creep parameters follows an Arrhenius-type law. In addition to the model parameters, application of the so-called grid-indentation technique within NI testing provides insight into the bitumen microstructure and the mechanical behavior of the different bitumen phases. The results obtained indicate the existence of a string-like microstructure embedded into a less viscous matrix material.

Applied

Visco-elastic properties of thin nylon films using multi-cycling nanoindentation

Asta Richter, Hubert Gojżewski, Joseph J. Belbruno May 23, 2013 Page range: 414-423

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Abstract

Time dependent behavior of thin nylon films is investigated by depth sensing nanoindentation. Different loading rates and holding times are applied in single indentation procedures to study the relaxation behavior of nylon resulting in a characteristic nonlinear displacement – time dependence. Several load – time functions of multi-cycling indentation are developed, such as constant load repetition and incremental load increase mode sometimes containing holding segments. Hysteresis loops in multi-cycling nanoindentation quantify the visco-elastic energy of nylon films. The loading rate does not change the loop size if the maximum and minimum load of the cycle are the same. The unloading process has to be sufficiently large to allow the performance of the visco-elastic relaxation of the material.

Area function calibration in nanoindentation using the hardness instead of Young's modulus of fused silica as a reference value

Kirsten Ingolf Schiffmann May 23, 2013 Page range: 424-429

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Abstract

For nanoindentation hardness and Young's modulus measurements the area function of the indenter has to be calibrated carefully since direct measurement of the contact area is not possible. Most often this is done by making a series of indentations into a material with known Young's modulus, e. g. fused silica. In this paper it will be shown that this method may lead to significant deviations in hardness values found over the lifetime of the indenter due to successive rounding of the tip. Additionally, depth-dependent hardness values may apparently be found which would falsify all hardness determinations. Using instead the hardness of fused silica as a reference value these problems will be avoided. Additionally, the calibration becomes independent of material constants such as the Young's modulus of the diamond tip and the Poisson ratios of both indenter and sample, which enter into the conventional calibration method. Finally, this paper discusses whether the indentation modulus determined by nanoindentation and the Young's modulus determined by, for example, tensile testing, are quantitatively equal. This is a precondition for the traceability of the Young's modulus method often mentioned as its main advantage.

Multiscale modelling of nanoindentation

Edward McGee, Roger Smith, S. D. Kenny May 23, 2013 Page range: 430-437

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Abstract

The process of nanoindentation causes physical phenomena not only at the nano-scale, but at multiple length scales up to the macroscopic. We present a model that links atomistic scale molecular dynamics to a finite element model in order to extend the length scales that can be modelled. We illustrate how this has been used in some studies of nanoindentation, to test the coupled model, and secondly to compare the results to atomistic only models. These studies show that by extending the length scales, the results from the model are in closer agreement with the experiment.

Unusual architecture of the exceedingly tough Macadamia “nut”-shell as revealed by atomic force microscopy and nanomechanics

M. R. Naimi-Jamal, G. Kaupp May 23, 2013 Page range: 438-445

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Abstract

Unlike previous assumptions, the 3D microscopic construction of the macadamia wooden shell (a model for bionics' design) is far from being “isotropic”. The consequences for the exceedingly high toughness towards cracking are investigated by atomic force microscopy to evaluate the vertical stiffeners in a fullerene-type surface architecture of the only 160 μm thick hardshell that is known to withstand up to 2000 N compressive load. Nanoindentations provide hardness and elasticity modulus at stiffeners and more compliant polygon material, as well as differences of indentation coefficients and work of indentation. Nanoscratching provides scratch coefficients and specific full scratch work values that can be compared with varied other materials using interpolations with linear relations between nanomechanical parameters. A particular lotus-type effect is found for the macadamia hardshell surface.

Notifications

DGM News

May 23, 2013 Page range: 446-448

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About this journal

The International Journal of Materials Research (IJMR) publishes original high quality experimental and theoretical papers and reviews on basic and applied research in the field of materials science and engineering, with focus on synthesis, processing, constitution, and properties of all classes of materials. Particular emphasis is placed on microstructural design, phase relations, computational thermodynamics, and kinetics at the nano to macro scale. Contributions may also focus on progress in advanced characterization techniques.
All articles are subject to thorough, independent peer review.