The growing requirements and diversity of nanotechnology applications have motivated scientists and researchers to work on the development of nanomaterials. The evolution of science and technology over the past 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 testing techniques to be identified. Evaluating the mechanical properties of materials is very important as it helps improve their quality and ensure their reliability. Therefore, testing techniques have great importance and application in manufacturing industries.
Nondestructive Testing Technique and its Application
Nondestructive testing (NDT) techniques are the most widely used testing technique in which the existence and absence of flaws in nanomaterials are identified. These flaws are characterized by their shape, location, orientation, and nature. As depicted by the name, NDT techniques investigate material properties without impairing their function and defacing them.
Nondestructive testing has wide applications in the sphere of nanomaterials as it helps to visualize and analyze their microstructure and nanostructure, accurate measurement of their nano displacements, and most importantly, to inspect macro and micro defects present in them. These testing methods have led to the development and improvement of highly sophisticated microelectronics products.
There are several nondestructive testing methods, and each has its pros and cons. These methods employ different procedures to carry out the intended task, such as laser testing (LM), leak testing (LT), ultrasonic testing (UT), and radiographic testing (RT)
Apart from identifying the defect, one of the key parameters to evaluate the structural integrity of metallic nanomaterials is to identify their material properties. The most widely used NDT technique to determine the material properties is ultrasonic nondestructive testing.
Ultrasonic Nondestructive Testing Method
The ultrasonic testing technique is ideally suitable for inspecting different nanomaterials without damaging the nanomaterial being tested. It can inspect the flaws, measure their depth, identify its orientation and nature with greater accuracy as compared to the other nondestructive testing techniques.
The ultrasonic testing techniques involve various testing parameters for nanomaterial characterization such as velocity, attenuation, spectral analysis, backscatter amplitude, critical angles, and acoustic measurements. Some of these techniques are complicated in nature and costly.
The most important characteristic of a testing technique is its accurate results and ultrasonic methods are well-known for their accuracy.
Analyzing Metallic Nanomaterials
The research published in IOPScience presents a novel ultrasonic nondestructive technique to assess the mechanical properties of metallic nanomaterials without defacing the tested specimen’s surface.
The researchers here propose an efficient method that uses defocusing measurement and time discrimination method to measure the surface wave velocity at different points of metallic nanomaterials to assess the mechanical characteristics.
Construction of Ultrasonic Nondestructive Testing Platform
The testing platform to carry out this ultrasonic nondestructive test comprises a surface wave velocity measurement module and a defocusing measurement time discrimination module.
The surface wave velocity measurement module transmits and receives ultrasonic waves. The density and elastic modulus 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 specimen are analyzed using defocusing measurement time discrimination module. This module consists of an ultrasonic probe (concave-shaped) and works on the principle of refraction law.
Working Principle of the Proposed Technique
When focused, this probe can receive the reflected waves directly from the surface of the tested metallic nanomaterial surface. The probe moves downward and a defocusing measurement is carried out. The time resolution method can aid in measuring the surface velocity by detecting the echo signal of an ultrasonic probe at several points.
The time difference between the arrival of reflected waves at different points of the probe is calculated. The least-square regression method is used to calculate the longitudinal and surface wave velocity.
In this experiment, a line-focused ultrasonic probe is used. The piezoelectric material used for this probe is PVDF film. Its concept is to change the propagation direction of the surface acoustic waves of the tested items to detect differing mechanical characteristics of materials in different directions.
The shape and size of PVDF film depict the strength of the reflected waves from the surface of a test metallic nanomaterial. The accuracy of the results measured using this technique depends upon the wider measurement 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 testing probe.
Comparison between Traditional and Proposed Technique
The researchers conducted an experiment by considering ten groups of metallic nanomaterials, each group containing nanomaterials having the same mechanical characteristics.
The mechanical properties of these metallic nanomaterials were tested using the proposed ultrasonic nondestructive technique and the traditional measurement method.
The experimental measurements were compared with the actual measurements and the accuracy of both tests was recorded. The proposed method was found to be almost 18-20% more accurate than the traditional testing method.
It is also capable of keeping the direction of surface wave velocity unchanged which does not cause any type of deformation in tested metallic nanomaterials, thus allowing the tested nanomaterials to hold their original mechanical properties.
Challenges Associated with Ultrasonic Nondestructive Technique
There is no doubt that ultrasonic testing has emerged as a leading nondestructive 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 causes more challenges in their testing and inspection.
False indications and signal misinterpretation can lead to inaccurate results. However, the recent modern equipment and techniques are proved to be more efficient and can overcome the associated challenges.
Prospects of Ultrasonic Nondestructive Technique
Scientists and researchers are currently trying to find inexpensive, more flexible, and more accurate ultrasonic testing methods which can ultimately lead towards the development of more sophisticated nanomaterials.
Continue reading: Magnetic Nanoparticles in Solid-Phase Extraction Approaches
References and Further Reading
Gupta, R. et al. (2021) A Review of Sensing Technologies for Nondestructive 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 particulate reinforced metal-matrix composites, Ultrasonics, 99(July), p. 105959. Available at: https://doi.org/10.1016/j.ultras.2019.105959.
Rinkevich, A. B., Korkh, Y. V and Smorodinskii, Y. G. (2010) Prospects of the Application of Nondestructive Testing to the Diagnostics of Nano and Microstructural Materials, (March 2014). Available at: https://doi.org/10.1134/S1061830910010031.
Science, E. (2021) Ultrasonic Nondestructive Testing Method for Mechanical Properties of Metallic Nanomaterials Ultrasonic Nondestructive Testing Method for Mechanical Properties of Metallic Nanomaterials. Available at: https://doi.org/10.1088/1755-1315/632/5/052094.
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