Analysis of metallic nanomaterials with NDT ultrasound
The increasing requirements and diversity of nanotechnology applications have motivated scientists and researchers to work on the development of nanomaterials. The evolution of science and technology in recent years has produced manufacturing industries capable of synthesizing high-end nanomaterials.
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These nanomaterials have different mechanical and physical characteristics, which require identification of test techniques. The evaluation of the mechanical properties of materials is very important because it improves their quality and ensures their reliability. Therefore, testing techniques have great importance and are applied in manufacturing industries.
Non-destructive testing technique and its application
Non-destructive testing (NDT) techniques are the most widely used testing technique in which the existence and absence of defects in nanomaterials are identified. These defects are characterized by their shape, location, orientation and nature. As their name suggests, NDT techniques study the properties of materials without altering their function or disfiguring them.
Non-destructive testing has many applications in the field of nanomaterials because it allows to visualize and analyze their microstructure and nanostructure, to accurately measure their nano-displacements and, above all, to inspect the macro and micro-defects that ‘they contain. These test methods have led to the development and improvement of highly sophisticated microelectronic products.
There are several methods of non-destructive testing, and each has its advantages and disadvantages. These methods use different procedures to perform the intended task, such as laser testing (LM), leak testing (LT), ultrasonic testing (UT), and radiographic testing (RT).
Besides defect identification, one of the key parameters to assess the structural integrity of metallic nanomaterials is to identify their material properties. The most widely used NDT technique for determining material properties is ultrasonic non-destructive testing.
Ultrasonic non-destructive test method
The ultrasonic testing technique is ideal for inspecting different nanomaterials without damaging the tested nanomaterial. It can inspect defects, measure their depth, identify their orientation and nature with greater precision compared to other non-destructive testing techniques.
Ultrasonic testing techniques involve various test parameters for the characterization of nanomaterials such as velocity, attenuation, spectral analysis, backscatter amplitude, critical angles, and acoustic measurements. Some of these techniques are inherently complicated and expensive.
The most important feature of a test technique is its accurate results and ultrasonic methods are well known for their accuracy.
Analyze metallic nanomaterials
Research published in IOPScience presents a new non-destructive ultrasonic technique to assess the mechanical properties of metallic nanomaterials without degrading the surface of the sample under test.
Here, the researchers propose an efficient method that uses the defocus measurement and the time discrimination method to measure the surface wave velocity at different points of metallic nanomaterials to evaluate the mechanical characteristics.
Construction of a non-destructive ultrasonic testing platform
The test platform for carrying out this ultrasonic non-destructive testing comprises a surface wave velocity measurement module and a defocus measurement time discrimination module.
The surface wave velocity measurement module transmits and receives ultrasonic waves. The density and modulus of elasticity of metallic nanomaterials depict the speed of ultrasonic waves within their structure.
The received ultrasonic waves are processed and the mechanical properties of the tested sample are analyzed using a defocus measurement time discrimination module. This module consists of an ultrasound probe (concave shape) and operates on the principle of the law of refraction.
Operating principle of the proposed technique
When focused, this probe can receive reflected waves directly from the surface of the surface of the metallic nanomaterial under test. The probe descends and a defocus measurement is taken. The time-resolved method can help measure surface velocity by detecting the echo signal from an ultrasonic probe at multiple points.
The time difference between the arrival of the reflected waves at different points of the probe is calculated. The least squares regression method is used to calculate the velocity of longitudinal and surface waves.
In this experiment, an online focused ultrasound probe is used. The piezoelectric material used for this probe is a PVDF film. Its concept is to change the direction of propagation of surface acoustic waves of the tested elements to detect the different mechanical characteristics of materials in different directions.
The shape and size of the PVDF film represents the strength of the waves reflected from the surface of a test metallic nanomaterial. The accuracy of the results measured using this technique depends on the wider measuring range of the probe and the strength of the reflected signal. The researchers propose a reduction in the width of the PVDF file, which significantly improves the resolution of the test probe.
Comparison between the traditional technique and the proposed technique
The researchers conducted an experiment considering ten groups of metallic nanomaterials, each group containing nanomaterials with the same mechanical characteristics.
The mechanical properties of these metallic nanomaterials were tested using the proposed non-destructive technique of ultrasound and the traditional measurement method.
Experimental measurements were compared to actual measurements and the accuracy of both tests was recorded. The proposed method was found to be nearly 18-20% more accurate than the traditional test method.
It is also able to keep the surface wave velocity direction unchanged which does not cause any kind of deformation in the tested metallic nanomaterials, thus allowing the tested nanomaterials to maintain their original mechanical properties.
Challenges associated with the non-destructive ultrasound technique
There is no doubt that ultrasonic testing has become a state-of-the-art non-destructive technique; however, there are some challenges associated with it. Unlike radiography, there is no lasting record of the inspection in ultrasonic testing. The complexity of the geometry of nanomaterials poses more challenges during their testing and inspection.
False indications and misinterpretation of signals can lead to inaccurate results. However, recent modern equipment and techniques have proven to be more effective and can overcome the associated challenges.
Prospects of the non-destructive ultrasonic technique
Scientists and researchers are currently trying to find inexpensive, more flexible, and more accurate ultrasonic testing methods that may ultimately lead to the development of more sophisticated nanomaterials.
Continue Reading: Magnetic Nanoparticles in Solid Phase Extraction Approaches
References and further reading
Gupta, R. et al. (2021) Review of sensing technologies for non-destructive evaluation of structural composite materials. Journal of Composite Sciences. Available at: https://www.mdpi.com/2504-477X/5/12/319.
Podymova, N.B. et al. (2019) Laser Ultrasonic Nondestructive Evaluation of Porosity in Particle Reinforced Metal Matrix Composites, ultrasound, 99(July), p. 105959. Available at: https://doi.org10.1016/j.ultras.2019.105959.
Rinkevich, AB, Korkh, Y. V and Smorodinskii, YG (2010) Prospects for the application of non-destructive testing to the diagnosis of nano and microstructural materials, (March 2014). Available at: https://doi.org/10.1134/S1061830910010031.
Science, E. (2021) Ultrasonic non-destructive testing method for mechanical properties of metallic nanomaterials Ultrasonic non-destructive testing method for mechanical properties of metallic nanomaterials. Available at: https://doi.org/10.1088/1755-1315/632/5/052094.