The nonlinear acoustic approach is assessed for applications as a nondestructive tool for reconstructing stress-strain curves and quantifying the ultimate tensile strength for variety of materials. The direct algorithm uses the polynomial stress-strain expansion up to the third power of strain and the literature data on the second-order nonlinearity parameters to calculate relevant segments of the stress-strain curves. Since the third-order nonlinearity parameters are unknown for majority of materials the calculations used an iteration scheme to obtain closer approximations to the experimental data available from static tensile tests. The solution to the inverse problem identifies the range of the nonlinearity parameters for a given tensile strength and enables to categorize the contribution of the quadratic and cubic nonlinearities in mechanical response for different materials.
3D printing has established itself in the 21st century as the process for producing prototypes and very small series. In the plastics sector, the fused filament fabrication (FFF) process is used in particular. A plastic filament is melted in a nozzle and a component is built up layer by layer. As with all manufacturing processes, there is an interest in continuously optimizing and improving the FFF process. One possibility is based on process simulations, which enable a better understanding of the entire process. Afterwards a validation of the simulation with the real process is always necessary. In the case of FFF, this validation was so far only possible to a limited extent. In this work, a method is presented that enables a non-destructive investigation of the melting behavior during the printing process. For this purpose, a 3D printer nozzle with an extruder was integrated into an X-ray computed tomography system. Thus, a computed tomography scan (CT scan) can be performed during the extrusion process. By using filaments with high absorbent tungsten, a sufficient contrast can be created between the metal nozzle and the plastic filament, which allows an analysis of the melting behavior. This setup allows to distinguish between the solid filament area and the melt area, as well as to determine contact between the filament and the nozzle wall. In this way, the simulations can be validated and nozzle geometries to be improved in the future by means of improved simulation tools.
Kissing bonds are critical defects in adhesively bonded parts. These defects result in a weak bonding in the interface region between the adherent and the adhesive. Unlike delaminations, kissing bonds induce a delicate change in contact properties. Thus, conventional non-destructive testing methods are not able to detect kissing bonds reliably. In this work various non-destructive testing techniques on kissing bonds were investigated. The manufactured kissing bond containing specimens were investigated with different non-destructive testing methods such as conventional ultrasound, aircoupled ultrasound, x-ray and shearography. Unfortunately, those non-destructive testing methods weren’t able to detect the kissing bonds dependably. On the contrary, the application of nonlinear ultrasound demonstrated the most reliable results in detecting kissing bonds. With this testing setup, the specimens were excited with a piezo shaker in a continuous wave mode and the vibration on the surface of the specimen was detected by laser Doppler vibrometry. After fast Fourier transform (FFT), a dramatic increase in the higher harmonic amplitudes were detected in an area with lower bonding force. The low adhesive forces lead to a higher nonlinearity of the kissing bond area, what results in substantial rise of the higher harmonic amplitudes. The measurements on the kissing bonds with their reduced adhesive force show a substantial rise of higher harmonic amplitudes, which makes it a suitable method for the detection of kissing bonds.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.