WHY MONITOR ACOUSTIC EMISSIONS DURING NANOMECHANICAL TESTS?

Acoustic Emissions (AE) monitoring has been proved as an effective non-destructive technique at the macro scale. Nevertheless, it may also be employed at nano/micro scale during nanomechanical and nanotribological testing. Local mechanical properties of surfaces or micro object are routinely explored using nanoindentation, scratch test or dynamic impact tests that are evaluated based on analysis of depth-load-time records or microscopic observation of residual indents, scratch grooves or impact craters, respectively. Although these approaches have been proven to be sufficient in most cases for a variety of materials, there are many situations where they do not provide sufficient information for a complex understanding of the deformation response. On the other hand, analysis of AE signals generated during these tests may provide valuable complementary information and provide some insight into the dynamics of phenomena like cracking, phase transitions, plastic instabilities, etc. That means that the analysis of acoustic emissions provides a better understanding and more complex interpretation of the results obtained by the above-mentioned tests. The strength of the AE based method is demonstrated for optical thin films deposited on glass tested via scratch test. Combination of AE and nanoindentation will be presented for various types of glasses. The complementary analysis of the time and frequency domain will draw the potential of the AE extended approach. Especially dynamics of the failure and fracture processes will be distinguished and elucidated. In both cases the analysis of AE events will be correlated with standard approaches

LASER-INDUCED SURFACE ACOUSTIC WAVES FOR THIN FILM CHARACTERIZATION

Knowledge of mechanical properties of thin films is essential for most of their applications. However, their determination can be problematic for very thin films. LAW (Laser-induced acoustic waves) is a combined acousto-optic method capable of measuring films with thickness from few nanometers. It utilizes ultrasound surface waves which are excited via short laser pulses and detected by a PVDF foil. Properties such as Young’s modulus, Poisson’s ratio and density of both the film and the substrate as well as film thickness can be explored.Results from the LAW method are successfully compared with nanoindentation for Young’s modulus evaluation and with optical method for film thickness evaluation and also with literature data. Application of LAW for anisotropy mapping of materials with cubic crystallographic lattice is also demonstrated

BENEFITS OF USE OF ACOUSTIC EMISSION IN SCRATCH TESTING

Scratch test is regularly used for assessment of cohesive and adhesive strength of thin films and coatings. By default, its evaluation is based on analysis of depth-load-time record and microscopic observation of residual scratch groove. The visual analysis of the residual groove provides the most detailed description of the final damage of the surface (crack patterns, extent of plastic deformation, delamination, etc.), but it may be a time demanding approach. Although the continuous recording of indenter penetration depth and applied load offers instantaneous information about the performance of the tested material, it may not provide sufficient description of the sample’s deformation behaviour. Therefore, other complementary techniques for description of the deformation response to scratch loading are desirable. Continuous recording of acoustic emissions (AE) generated during the test could be a possible solution. It is especially the ability of AE method to detect the very first and even subsurface failures of the material that is of the most importance and otherwise inaccessible by standardly used techniques. What is more, it is a non-destructive and real-time method. In principle, AE method can be beneficially employed for a wide range of materials explored via scratch test. The strength of the AE analysis of the nano/micro scratch test will be demonstrated on various types of materials including optical thin films, durable metal and hard ceramic films as well as bulk laser cladding. Selected phenomena and features of the use of AE during scratch testing will be presented, including effect of scratch load on character of AE records (burst vs. continuous) for TiO2 on glass, subsurface damage of SiC films on silicon and selective failure of hard carbide phase embedded in a metal matrix in case of laser re-melted layers

Nanoindentation induced reversible plasticity detected by acoustic emission

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CHARACTERIZATION OF TITANIUM LASER WELDS

Butt welding of commercially pure titanium Grade 1 and Ti6Al4V alloy sheets using a pulsed Nd:YAG laser KLS 246 - 102 LASAG were carried out to determine optimal values of pulse energy and pulse length to create completely penetrated weld. Surface peak power density of about 3.105 W.cm−2 was found as an optimal value. Weld dimensions, both face width and penetration depth, are found to be proportional to increasing energy and decreasing pulse length. Gentle sagging and root penetration were revealed by means of contact surface profilometry. The nanohardness tests on transverse cross-sections detected approximately 50% higher hardness in the fusion zone than in the base material

In Vitro Mechanical Properties of Mineral Trioxide Aggregate in Moist and Dry Intracanal Environments

Introduction: The purpose of this study was to examine the microhardness and modulus of elasticity (MOE) of White ProRoot MTA (Dentsply Tulsa Dental, Tulsa, OK) after setting in moist or dry intracanal conditions. Methods and Materials: To simulate root canal system, 14 polyethylen molds with internal diameter of 1 mm and height of 12 mm were used. These molds were filled with 9-mm thick layers of White ProRoot Mineral Trioxide Aggregate (MTA; Dentsply Tulsa Dental, Tulsa, OK). The experimental group (n=7) had a damp cotton pellet with 1.5 mm height and a 1.5 mm layer of resin composite placed on it. In control group (n=7) the whole 3 mm above MTA were filled with resin composite. The specimens were kept in 37°C and relative humidity of 80% for 4 days in order to simulate physiological conditions. Specimens were longitudinally sectioned and nanoindentation tests were carried out using Berkovich indenter at loading rate of 2 mN/s at 4×5 matrices of indents which were located in the coronal, middle and apical thirds of the specimen’s cross section, to evaluate the microhardness and modulus of elasticity of the specimen to appraise the progression of the setting process. Differences were assessed using nonparametric generalized Friedman rank sum and Wilcoxon Rank-Sum tests. Results: Statistical analysis showed that there was a significant difference in microhardness and MOE between control and experimental groups at coronal (P<0.001), middle (P<0.001) and apical (P<0.001) thirds of the simulated rod from simulated apical foramen. Kruskal-Wallis test showed no significant effect of depth on microhardness of material in experimental or control groups. Conclusion: Within limitations of this in vitro study, it seems that moist intracanal environment improves setting of MTA in various depths.Keywords: Microhardness; Mineral Trioxide Aggregate; Modulus of Elasticity; Nanoindentatio

Měření tvrdosti nehomogenních plazmových nástřiků

Paper deals with testing of mechanical properties of plasma sprayed coatings TiO2 by Depth Sensing Indentation performed on measuring system NanoTest 600™. The NT600™ is a modular measuring instrument with unique design, which applies the loading force in horizontal direction. The platform can measure and evaluate hardness, elastic modulus, adhesion, wear, fracture and also dynamic properties. In the last years the new plasma spraying technology of ceramic and ceramic-metal materials has became as very convenient technique in many industrial and reconstruction processes. The investigated samples of plasma sprayed coatings were prepared in Institute of Plasma Physics of the Academy of Sciences of the Czech Republic. The goal of this paper is to contribute to deepening the knowledge in local distribution of mechanical properties in plasma sprayed coatings, especially of hardness and elastic modulus

Hardness measurement of inhomogeneous plasma sprayed coatings

This article deals with an examination of mechanical properties of TiO.sub.2./sub. plasma sprayed coatings using nanoindentation method DSI and measuring instrument NanoTest 600 TM

Evaluation of mechanical properties of thin films and coatings by the system NanoTest™ NT600

This article deals with evaluation of mechanical properties of thin films and coatings by the system NanoTest™ NT600

Why monitor acoustic emissions during nanomechanical tests?

Acoustic Emissions (AE) monitoring has been proved as an effective non-destructive technique at the macro scale. Nevertheless, it may also be employed at nano/micro scale during nanomechanical and nanotribological testing. Local mechanical properties of surfaces or micro object are routinely explored using nanoindentation, scratch test or dynamic impact tests that are evaluated based on analysis of depth-load-time records or microscopic observation of residual indents, scratch grooves or impact craters, respectively. Although these approaches have been proven to be sufficient in most cases for a variety of materials, there are many situations where they do not provide sufficient information for a complex understanding of the deformation response. On the other hand, analysis of AE signals generated during these tests may provide valuable complementary information and provide some insight into the dynamics of phenomena like cracking, phase transitions, plastic instabilities, etc.\