scholarly journals Interdigital Piezopolymer Transducers for Time of Flight Measurements with Ultrasonic Lamb Waves on Carbon-Epoxy Composites under Pure Bending Stress

2015 ◽  
Vol 2015 ◽  
pp. 1-11 ◽  
Author(s):  
Andrea Bulletti ◽  
Lorenzo Capineri
Keyword(s):  
Lamb Waves ◽  
Fiber Composite ◽  
Time Of Flight ◽  
Bending Moment ◽  
Wave Mode ◽  
Guided Wave ◽  
Pure Bending ◽  
Carbon Fiber Composite ◽  
Central Wavelength ◽  
Bending Stresses

Interdigital transducers fabricated with piezopolymer film have been realized to excite ultrasonic Lamb waves in a composite laminate subjected to pure bending stresses. Lamb waves were generated and detected in a cross-ply [0°/90°] 4 mm thick carbon-fiber composite, by using two interdigital transducers in pitch-catch configuration. We demonstrate that the choice of the piezopolymer transducer technology is suitable for this type of investigation and the advantages of the proposed transducer assembly and bonding are described. A full set-up is described to determine the relationship between the time of flight of the recorded signals and the applied bending moment. Interdigital transducers were designed according to simulations of the dispersion curves, in order to operate at a central frequency of 450 kHz. This frequency corresponds to a central wavelength of 16 mm and to a group velocity of about 6000 m/s for the first symmetric guided wave mode. The variations in the time of flight of ultrasonic recorded signals were measured as a function of the variations in the bending moment. The static and dynamic load tests were in good agreement with strain gage measurements performed in the micro deformation range (0–1400 µm/m).

scholarly journals The behaviour of three single crystals of aluminium in fatigue under complex stresses

1935 ◽  
Vol 149 (867) ◽  
pp. 312-326 ◽  
Keyword(s):  
Single Crystals ◽  
Test Piece ◽  
Testing Machine ◽  
Bending Moment ◽  
Stress System ◽  
Pure Bending ◽  
Bending Strain ◽  
Bending Stresses ◽  
Ordinary Type ◽  
New Type

In the ordinary type of Wöhler machine used for testing materials in fatigue under reversed bending stresses, the load system is stationary in space, and variation of the stress system with respect to the test piece is obtained by rotating the test piece. It is, of course, essential to the success of the test that the system of displacements caused by the application of the load system to the test piece should remain stationary in space; but, since the test piece rotates, this requirement can only be fulfilled if the material of the test piece is isotropic. Thus, if an attempt were made to test a single crystal in a Wöhler machine it might be anticipated that either actual elastic antisotropy or the virtual anisotropy due to restricted slip movement would cause the deformation to vary with the orientation of the stress system relative to the axes of the crystal and that "whipping" of the specimen would occur. Three such attempts have indeed been made: but in spite of great care exercised in setting up the specimens and in applying the loads, only in one case, in which the orientation of the crystal was such as to provide effective symmetry about the axis of the specimen, was the test successful. A new type of testing machine recently developed at the N. P. L. for testing specimens in fatigue under systems of combined bending and torsional stresses, differs in principle from the Wöhler machine in that the variation of stress is produced by actual variation of load. In this machine both me test piece and the orientation of the stress system remain stationary, only the magnitude of the stresses being varied. The deformation of the test piece is therefore only that due to one type of stress system fixed in relation to the orientation of the test piece and varying only in magnitude. Moreover, the construction of the machine is such that the strain of the test piece is not required to be of the same type as the stress system applied, e. g ., the application of pure bending moment does not restrict the test piece to pure bending strain and the test piece remains free to twist also if necessary. These conditions render this type of machine perfectly suitable for test on single crystals. Accordingly, tests have been carried out in this machine on three single crystals of aluminium; the first was tested under reversed flexural stresses, the second under reversed torsional stresses and the third under a combination of reversed flexural and reversed torsional stresses.

scholarly journals Guided Waves for Damage Detection in Complex Composite Structures: The Influence of Omega Stringer and Different Reference Damage Size

2020 ◽  
Vol 10 (9) ◽  
pp. 3068
Author(s):  
Jochen Moll ◽  
Christian Kexel ◽  
Jens Kathol ◽  
Claus-Peter Fritzen ◽  
Maria Moix-Bonet ◽  
...  
Keyword(s):  
Composite Structures ◽  
Guided Waves ◽  
Fiber Composite ◽  
Composite Plates ◽  
Guided Wave ◽  
Probability Of Detection ◽  
Carbon Fiber Composite ◽  
Technical Validation ◽  
Pod Analysis ◽  
The Impact

The third dataset dedicated to the Open Guided Waves platform aims at carbon fiber composite plates with an additional omega stringer at constant temperature conditions. The two structures used in this work are representative for real aircraft components. Comprehensive measurements were recorded in order to study (I) the impact of the omega stringer on guided wave propagation, and (II) elliptical reference damages of different sizes located at three separate positions on the structure. Measurements were recorded for narrowband excitation (5-cycle toneburst with varying carrier frequencies) and broadband excitation (using chirp waveforms). The paper presents the results of a technical validation including numerical modelling, and enables further research, for example related to probability of detection (POD) analysis.

Investigation of Effect of Non-Uniformities in Unidirectional Carbon Fiber Composite on the Lcr Waves Speed Using Phased Arrays

2015 ◽  
Author(s):  
Vanessa Vieira Gonçalves ◽  
Auteliano Antunes dos Santos ◽  
Paulo Pereira
Keyword(s):  
Carbon Fiber ◽  
Stress Measurement ◽  
Signal To Noise Ratio ◽  
Fiber Composite ◽  
Time Of Flight ◽  
Fiber Direction ◽  
Carbon Fiber Composites ◽  
Carbon Fiber Composite ◽  
Uniform Region ◽  
Significant Difference

Structural parts benefit on a reliable, nondestructive inspection technique to measure stresses, both applied and residual. Among the candidates, ultrasonic techniques have proven to have enough sensitivity to strain to be employed in service. The way to obtain the stresses is through the measurement of the time-of-flight inside the material and relates it to the strain by acoustoelastic theory or previous measurements. However, stress measurement using ultrasound strongly depends on the uniformity of the material under inspection. In composite materials, the time-of-flight is influenced by microdefects and misalignments in the fibers as well as by the applied strain and temperature. This last factor can be known and controlled, but non uniformities are a characteristic of one particular region or part. Thus, unless employed to a very particular case of a completely uniform region been inspected in a special developed part, UT could not be used to measure stresses in this kind of material without some previous information about it. This work presents an investigation about the effect of non-uniformities in carbon fiber-epoxy pre-preg composites and how to relate them with the time-of-flight of critically refracted longitudinal waves (Lcr) propagating in the fiber direction (main structural direction). A Phased Array System (PAS) with probe of 5 MHz and 64 transducers are employed to generate an image of each part in the region where the Lcr wave travels. The image is created employing the Total Focusing Method (TFM). Two bars of carbon fiber composites with epoxy matrix (HexTow® AS4 / Hexply® 8552) were tested. Five measurement positions are selected, uniformly distributed on the part surface. Statistically significant differences between the parts were found in the time-of-flight for Lcr waves when no stress is applied; even knowing they were manufactured using the same process and materials. The parts were evaluated using the PAS. No difference was found between measurements in the same bar. The parameter chosen to evaluate the non-uniformity was the peak value of the back-wall signal divided by the RMS value of the noise intensity, which was called signal-to-noise ratio (SNR). The results show also significant difference between the SNR of both parts, although with higher dispersion than with Lcr. It can be noticed that there is a correlation between the time-of-flight of Lcr waves and the SNR, indicating that the research could be extended to the development of a new joint technique to be used to measure stresses in composite parts.

scholarly journals Modeling Magnetostrictive Transducers for Structural Health Monitoring: Ultrasonic Guided Wave Generation and Reception

Sensors ◽  
2021 ◽  
Vol 21 (23) ◽  
pp. 7971
Author(s):  
Gaofeng Sha ◽  
Cliff J. Lissenden
Keyword(s):  
Structural Health Monitoring ◽  
Health Monitoring ◽  
Guided Waves ◽  
Lamb Waves ◽  
Wave Mode ◽  
Wave Generation ◽  
Guided Wave ◽  
Diverse Range ◽  
Structural Health ◽  
Phase Velocity Dispersion

Ultrasonic guided waves provide unique capabilities for the structural health monitoring of plate-like structures. They can detect and locate various types of material degradation through the interaction of shear-horizontal (SH) waves and Lamb waves with the material. Magnetostrictive transducers (MSTs) can be used to generate and receive both SH and Lamb waves and yet their characteristics have not been thoroughly studied, certainly not on par with piezoelectric transducers. A series of multiphysics simulations of the MST/plate system is conducted to investigate the characteristics of MSTs that affect guided wave generation and reception. The results are presented in the vein of showing the flexibility that MSTs provide for guided waves in a diverse range of applications. In addition to studying characteristics of the MST components (i.e., the magnetostrictive layer, meander electric coil, and biased magnetic field), single-sided and double-sided MSTs are compared for preferential wave mode generation. The wave mode control principle is based on the activation line for phase velocity dispersion curves, whose slope is the wavelength, which is dictated by the meander coil spacing. A double-sided MST with in-phase signals preferentially excites symmetric SH and Lamb modes, while a double-sided MST with out-of-phase signals preferentially excites antisymmetric SH and Lamb modes. All attempted single-mode actuations with double-sided MSTs were successful, with the SH3 mode actuated at 922 kHz in a 6-mm-thick plate being the highest frequency. Additionally, the results show that increasing the number of turns in the meander coil enhances the sensitivity of the MST as a receiver and substantially reduces the frequency bandwidth.

Reusable piezo-sandwiched PTFE film for in-process monitoring of advanced composites

2021 ◽  
pp. 1045389X2110026
Author(s):  
Elie Mahfoud ◽  
Mohammad Harb
Keyword(s):  
Electromechanical Coupling ◽  
Lamb Waves ◽  
Fiber Composite ◽  
Composite Plates ◽  
Assessment System ◽  
Film Material ◽  
Carbon Fiber Composite ◽  
Low Frequencies ◽  
Ptfe Film ◽  
Manufacturing Defects

Environmental and cost-saving advantages derived from the use of composites attract aerospace and automotive industries as these materials offer significant structural and aerodynamic advantages over traditional metal structures. The composites industry, however, is concerned with the manufacturing processes as they cannot provide fast enough cycle time to match metal alloy processes. Our research aims to develop a sensing technology in the form of a reusable in situ cure monitoring and assessment system that can predict the formation of manufacturing defects and monitor the degree of cure. Thin-film material is chosen from various PTFE-based material by prioritizing the debonding effect and signal transmission through the composite part. Then, the film is used to sandwich piezoelectric actuators and sensors to monitor out-of-autoclave carbon fiber composite plates using ultrasonic Lamb waves by temporarily adhering to the manufactured part creating an effective electromechanical coupling between the sensing film and the laminate. Initial results, through the analysis of the fundamental antisymmetric A0 mode at low frequencies, indicate that analyzing the velocity and amplitude of these waves over cure time determines gelation and vitrification points. Experimental results have also proved the feasibility of using such a reusable film for different curing cycles, always determining certain cure parameters.

scholarly journals Fully Noncontact Wave Propagation Imaging in an Immersed Metallic Plate with a Crack

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Jung-Ryul Lee ◽  
Jae-Kyeong Jang ◽  
Cheol-Won Kong
Keyword(s):  
Wave Propagation ◽  
Lamb Wave ◽  
Continuous Wave ◽  
Imaging System ◽  
Lamb Waves ◽  
Laser Doppler Vibrometer ◽  
Wave Dispersion ◽  
Wave Mode ◽  
Dispersion Curves ◽  
Guided Wave

This study presents a noncontact sensing technique with ultrasonic wave propagation imaging algorithm, for damage visualization of liquid-immersed structures. An aluminum plate specimen (400 mm × 400 mm × 3 mm) with a 12 mm slit was immersed in water and in glycerin. A 532 nm Q-switched continuous wave laser is used at an energy level of 1.2 mJ to scan an area of 100 mm × 100 mm. A laser Doppler vibrometer is used as a noncontact ultrasonic sensor, which measures guided wave displacement at a fixed point. The tests are performed with two different cases of specimen: without water and filled with water and with glycerin. Lamb wave dispersion curves for the respective cases are calculated, to investigate the velocity-frequency relationship of each wave mode. Experimental propagation velocities of Lamb waves for different cases are compared with the theoretical dispersion curves. This study shows that the dispersion and attenuation of the Lamb wave is affected by the surrounding liquid, and the comparative experimental results are presented to verify it. In addition, it is demonstrated that the developed fully noncontact ultrasonic propagation imaging system is capable of damage sizing in submerged structures.

Scattering of Lamb Waves by a Cylindrical Mass Attached to the Surface of a Plate

2016 ◽  
Author(s):  
Andrew Golato ◽  
Sridhar Santhanam ◽  
Fauzia Ahmad ◽  
Moeness G. Amin
Keyword(s):  
Lamb Wave ◽  
Lamb Waves ◽  
Plate Theory ◽  
Wave Mode ◽  
Guided Wave ◽  
Potential Functions ◽  
Mindlin Plate ◽  
Detection Scheme ◽  
Linear System Of Equations ◽  
Scattering Response

Defect classification is the logical next step after localization in a Lamb wave based Guided Wave Structural Health Monitoring (GWSHM) defect detection scheme. Lamb waves are a preferred wave mode in GWSHM; therefore, classification can be facilitated via understanding of the Lamb wave scattering characteristics of defects. Many defects can be modeled either as (part-) through holes or accumulated masses on the surface. We consider and analytically solve the scenario of an attached mass on the surface of a plate. The mass is treated as an elastic isotropic homogeneous cylinder and the scattering response is obtained for incident fundamental symmetric and antisymmetric waves. Propagation is modeled via Mindlin plate theory, utilizing infinite series of Bessel functions as potential functions. Boundary and continuity conditions provide a linear system of equations for the expansion coefficients of the potential functions, which, solved numerically, produce the scattering response of the defect.

Sign in / Sign up

Export Citation Format

Share Document