In an article recently published in the open access journal Scientific ReportsIn this article, the researchers discussed a non-destructive method for assessing the quality of metallic polymer laminates using digital 3D oscillometrics and convection waves.
Stady: A non-destructive technology that uses 3D digital vibration measurement and load waves to determine the quality of metallic polymer laminates. Image Credit: Joshua Sanderson Media / Shutterstock.com
Metallic polymer chips have become more and more popular in recent years. Auto manufacturers are increasingly trying to dilute their products to increase operational efficiency and lower production costs. The materials for the plate partners must be selected based on certain characteristics.
These days, the two components are assembled directly during processing without the need for any further stages, using standard techniques such as injection molding with metal inserts. However, accelerated production cycles of metallic and polymeric junctions can lead to defects in conduction.
Although metallic polymer foil production processes are becoming more and more common, a major concern still remains that there are hidden or barely noticeable defects. While internal defects in such materials are difficult to detect, the presence of which can have a significant impact on the strength of the final product, surface defects in such materials can be identified quite simply. A non-destructive test (NDT) is a useful technique for checking individual parts for possible hidden defects. For large objects and high stimulation frequencies, conventional and known non-destructive testing techniques that use convective waves are applied.
Lateral inspection of a specimen with a specific defect; Sizes in mm. Image credit: Nowak-Grzebyta, J et al., Scientific Reports
About the study
In this study, the authors used a non-destructive technique called holographic digital tremors (DHV) to find separation spots in strips made of aluminum and polymer. The amplitude and phase patterns of sample vibration were simultaneously recorded for the metallic and polymer side of the sheets at frequencies as low as 30 kHz using A0 Lamb waves. These patterns were used to identify the dissolved spots in the chips. The frequency range in which uniform load waves were seen, the amplitude of the load waves, and frequency-dependent load wave propagation velocities were investigated with respect to transmission qualities at lower frequencies.
The team showed that when a defect in the plates manifests itself, these traits are also altered. It was possible to determine whether the sample was damaged based on the behavior of the load waves even when the problem was not identified. The methodology was expanded, and symmetric A0 counter-load waves with different vibration frequencies were observed in samples of laminated aluminum made of three different polymers, and their behavior was used to search for hidden defects. For high frequencies of 100 kHz and above, the load wave propagation in a well-defined isotropic medium. For chips and a relatively low frequency range of up to 30 kHz, this was not the case.
The researchers focused on the effect of the defect on chips in the low-frequency range of vibrations that occur in everyday life, for example, in frequently used tools such as ultrasonic animal repellents or washing machines, as well as in public places such as train stations or libraries. Three-dimensional digital vibration (DHV) was used to track synchronous load wave propagation on the sides of the metal and polymer sheets. Especially for chips, it was very helpful to keep an eye on both sides. In this way, the bonding efficacy of the flakes formed from polymer and aluminum alloy mixtures was evaluated.
Botton view of a sample with the placement of both types of piezo transducer used: 1: sample, 2: piezo transducer; Left: KingState KPE-827, Right: PI P-010.00P; Sizes in mm. Image credit: Nowak-Grzebyta, J et al., Scientific Reports
The range of Lamb Wave Frequency (LFOR) monitoring at which a laminate defect could be seen depended more on the size of the defect than on the type of polymer used. The polymer-in-metal convective wave propagation is followed for all aluminum and polymer flawless strips. This suggested a strong adhesion between the two layers and demonstrated the feasibility of using any of the examined polymers to create a strong laminate. The proposed setup necessitated access to both sides of the sample as its metallic and polymeric surfaces were simultaneously observed. There were different ways in which the same threading error could appear. In each case, the defect reduced LFOR.
The antisymmetric A0 Lamb wave velocity curves versus frequency curves were also significantly changed. At frequencies greater than 10 kHz, differences between the curves of the metal and semi-crystalline polymers were evident. The polymer fraction of the Al D polyvinylidene fluoride (PVDF) sheets with a defect had a Lamb wave velocity that was ~40% lower at a frequency of 15 kHz than that of the aluminum layer. In the case of semi-crystalline polymers, a lamellar defect widened the gap between the metal-polymer vibration amplitudes.
This discrepancy increased from 40-50% for PVDF Al to 60-70% for PVDF Al D, especially for PVDF, which showed the lowest vibration transmission among the investigated materials. However, even for the defective chips, there was little difference in the vibration amplitudes of the amorphous Al PC. Therefore, in the case of chips with polymers that have good vibration transmission in the low-frequency test range, the amplitude criterion was not useful.
Comparison of the load-wave phase velocities of polymer and pure aluminum samples. Image credit: Nowak-Grzebyta, J et al., Scientific Reports
In conclusion, this study used two semi-crystalline polymers and one amorphous polymer to develop the flakes.
The authors stated that the test samples tested with the proposed technology had appropriate dimensions for additional strength tests. This was useful for testing standard components in a laboratory environment as well as in an industrial production environment.
The team emphasized that the NDT approach described in this study needs a short period of time to assess the extent of contact of two laminated materials. They stressed that it is a useful extension of typical lamination tests that can also be performed on a manufacturing line to employ DHV to detect load waves.
Nowak-Grzebyta, J., Stachowska, E., Meijer, F., and others. (2022) A non-destructive technology that uses 3D digital vibration measurement and convection waves to determine the quality of metallic polymer laminates. Scientific ReportsAnd the 12, s. 18041. https://www.nature.com/articles/s41598-022-22853-2