scholarly journals Lamb wave–based detection of a controlled disbond in a lap joint

2017 ◽  
Vol 17 (3) ◽  
pp. 668-683 ◽  
Author(s):  
Wern Hann Ong ◽  
Nik Rajic ◽  
Wing Kong Chiu ◽  
Cedric Rosalie
Keyword(s):  
Lamb Wave ◽  
Lamb Waves ◽  
Mode Conversion ◽  
Numerical Study ◽  
Lap Joints ◽  
Single Frequency ◽  
Lap Joint ◽  
Frequency Selection ◽  
Almost All ◽  
Shed Light

Lap joints are widely used across many critical structures such as aircraft and bridges. Lamb waves have long been proposed to monitor lap joints against defects such as disbonds. However, there are many challenges which must be answered to make use of Lamb wave technology. Frequency selection is often overlooked, and many authors will select a single frequency without knowing if other frequencies will result in better sensitivity. Another challenge is the features (mode conversion, attenuation, reflection) associated with damage are also inherent in a lap joint. This sharing of features can lead to confusion (false positive/negative) depending on the chosen damage detection strategy. Furthermore, almost all proposed methods require a baseline reading of the structure in its flawless state. Relying on a baseline reading can result in false positives due to shifts in sensor outputs caused by ageing and inconsistent environmental conditions. Instead of a baseline, this article proposes a technique which uses strategically positioned sensors to detect Lamb wave modes generated only in the presence of a disbond. The technique is first developed using a numerical study and then verified with an experimental study. Several frequencies are trialled and detailed in this article which shed light on the ideal frequency selection when using this method.

scholarly journals Lamb Waves Topological Imaging of Multiple Blind Defects in an Isotropic Plate

2019 ◽  
Vol 24 (2) ◽  
pp. 320-326 ◽  
Author(s):  
Wen-Fa Zhu ◽  
Hai-Yan Zhang Zhang ◽  
Meng-Yun Xu ◽  
Guo-Peng Fan
Keyword(s):  
Lamb Wave ◽  
Isotropic Plate ◽  
Lamb Waves ◽  
Mode Conversion ◽  
Image Resolution ◽  
Imaging Method ◽  
Wave Fields ◽  
Face To Face ◽  
Element Simulation ◽  
Reference Medium

The study investigates the feasibility of the Lamb wave topological imaging method for detecting multiple blindholes in an isotropic plate. The topological imaging method is performed based on the computations of two wave fields, a forward and an adjoint, in the defect-free reference medium using different emitting sources. The image is computed by multiplying the forward and adjoint wave fields together and integrating them over time or frequency. The interferences of multimode aliasing and the scattering effect can thus be eliminated at the defectfree positions with an improved image resolution. To investigate the physical mechanism, the refocusing process of the multimode Lamb waves at the defect positions is presented by a face-to-face comparison between the snapshots of the forward and adjoint wave fields using the finite element simulation. The Lamb wave topological imaging method is numerically and experimentally verified to identify multiple blind-holes in an isotropic aluminium plate. The results demonstrate that the topological imaging method enables the suppression of the sartefacts resulting from the mode conversion and achieve high-resolution imaging of the blind defects

Numerical Study of the Prestressed Connectors and Their Distribution on the Strength of a Single Lap, a Double Lap and Hybrid Joints Subjected to Uniaxial Tensile Test

2013 ◽  
Vol 58 (2) ◽  
pp. 579-585 ◽  
Author(s):  
T. Sadowski ◽  
P. Golewski
Keyword(s):  
Mechanical Response ◽  
Numerical Study ◽  
Lap Joints ◽  
Uniaxial Tensile ◽  
Uniaxial Tensile Test ◽  
Shear Stresses ◽  
Lap Joint ◽  
Positive Effects ◽  
Single Lap Joint ◽  
Hybrid Joints

Prestressed joints are widely used in construction using connectors in the form of screws, whose task is to strong clamping of joined parts, thereby the internal forces in joint are transferred by surface friction contact of the elements. In the automotive and aerospace industries hybrid joints are more widely applied. Mechanical connectors are added to the adhesive joint in form of rivets, screws or clinch increasing its strength properties. The aim of this study was to determine how the prestressed connectors influence the mechanical response of hybrid, single and double lap joints. The influence of different distribution of the connectors was also investigated. Numerical study was conducted in ABAQUS program. Mechanical connectors were modeled by using fasteners, that allowed for a considerable simplification of the numerical model. In their application, there is no need for an additional submodels for connectors in the form of the rivet or the bolt. Prestressing is activated by direct application of the force to the connector. In the numerical examples the authors assumed that the diameter of the mechanical connectors was equal to 6mm and shear strength was equal 1kN. Adhesive layers were modeled by using cohesive elements for which maximum shear stresses and fracture energy were specified. The layer thickness was assumed to be equal 0.1mm and it was initially removed from the areas where mechanical connectors were placed. Two types of joints were analysed in the study: the single lap joint with lap dimensions 40x40mm as well as the double lap joint with lap dimensions 40x20mm, from which it results that theoretical strength of both connections should be the same. The prestressing of connectors was introduced by the force 1.5kN. For all pure - mechanical joints and for single lap joints positive effects were obtained. For double lap joints additional prestressing did not significantly affect for their strength. The influence of distribution of mechanical connectors was additionally analyzed by consideration of three configurations, where the rows of rivets were located at distances of 5, 10 and 15mm from the lap edge. The maximum increase of the load capacity by 24% was achieved for single lap joint as well as 35.7% for double lap joint. The obtained numerical results indicate the positive effects of additional pressure and allows for practical suggestions how to correct and optimize spacing distance of mechanical connectors in hybrid joints to get better mechanical response.

scholarly journals Detection of coatings within liquid-filled tubes and containers by mode conversion of leaky Lamb waves

2013 ◽  
Vol 2 (1) ◽  
pp. 73-84 ◽  
Author(s):  
M. Schmitt ◽  
K. Schmidt ◽  
S. Olfert ◽  
J. Rautenberg ◽  
G. Lindner ◽  
...  
Keyword(s):  
Lamb Wave ◽  
Single Phase ◽  
Lamb Waves ◽  
Mode Conversion ◽  
Conversion Process ◽  
Outer Side ◽  
Acoustic Sensor ◽  
Wave Excitation ◽  
Excitation Mode ◽  
Leaky Lamb Waves

Abstract. In this paper, a new acoustic sensor principle for coating detection within liquid-filled tubes and containers based on mode conversion of leaky Lamb waves is introduced. Leaky Lamb waves are excited and detected by single-phase transducers, which are attached on the outer side of a tube or container. By transmission time and amplitude measurements, coating formation within the liquid-filled tube and container is detected non-invasively. This new sensor principle is subdivided into the separate considerations of Lamb wave excitation, mode conversion and inverse mode conversion. The Lamb wave excitation by a single-phase transducer is visualized by scanning laser Doppler vibrometer imaging. The mode conversion process of leaky Lamb waves is measured by membrane hydrophone measurements and Schlieren visualization; afterwards, the measured emission angles are compared with the theoretical one. The inverse mode conversion process of pressure waves back to leaky Lamb waves is visualized by Schlieren images. By merging the results of Lamb wave excitation, mode conversion and inverse mode conversion, the new sensor concept is explained. Theoretical considerations and measurement results of adhesive tape coating inside a liquid-filled plastic tube and a liquid-filled stainless steel container verify the new acoustic sensor principle. Finally the measuring sensitivity and the technical realization are discussed.

scholarly journals Numerical Study of Concrete Mesostructure Effect on Lamb Wave Propagation

Materials ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2570 ◽  
Author(s):  
Beata Zima ◽  
Rafał Kędra
Keyword(s):  
Particle Size ◽  
Wave Propagation ◽  
Lamb Wave ◽  
Lamb Waves ◽  
Numerical Study ◽  
Diagnostic Methods ◽  
Material Parameters ◽  
The Difference ◽  
Dispersion Solution ◽  
Lamb Wave Propagation

The article presents the results of the numerical investigation of Lamb wave propagation in concrete plates while taking into account the complex concrete mesostructure. Several concrete models with randomly distributed aggregates were generated with the use of the Monte Carlo method. The influence of aggregate ratio and particle size on dispersion curves representing Lamb wave modes was analyzed. The results obtained for heterogeneous concrete models were compared with theoretical results for homogeneous concrete characterized by the averaged macroscopic material parameters. The analysis indicated that not only do the averaged material parameters influence the dispersion solution, but also the amount and size of aggregate particles. The study shows that Lamb waves propagate with different velocities in homogeneous and heterogeneous models and the difference increases with aggregate ratio and particle size, which is a particularly important observation for wave-based diagnostic methods devoted to concrete structures.

A Numerical Study of MSD in Aircraft Lap Joints

2006 ◽  
Vol 324-325 ◽  
pp. 927-930
Author(s):  
Yue Liang Chen ◽  
Da Zhao Yu ◽  
Cheng Mei Duan
Keyword(s):  
Crack Growth ◽  
Load Distribution ◽  
Structural Integrity ◽  
Numerical Study ◽  
Crack Tip ◽  
Point Load ◽  
Lap Joints ◽  
Lap Joint ◽  
Military Aircraft ◽  
Original Design

Many military aircraft have reached or exceeded their original design life, and have been subject to significant increase in maintenance and repair cost due to multiple site damage (MSD). In order to assessing the effects of MSD on the structural integrity of aircraft lap joints, the wing lap joint of certain model military aircraft with MSD was analyzed using special code FRANC2D/L. The rivet holes along the top row of the outer skin of lap joint were considered as the independent structural unit for the simulated MSD cracks. The stress intensity factors (SIFs) at each crack tip with different distribution loads at the rivet holes were computed and show that the analysis results have good coherence with the available literature data. It also shows that the SIF at each crack tip s a function of crack length can be calculated by the crack growth simulation capability of FRANC2D/L. The SIF values are not sensitive to the rivet load distribution manner, which has seriously influence on MSD crack growth direction. Rivet loading can be best molded quadratic load distribution over one half of rivet hole relative to uniform load distribution and point load. As a result of this analysis, it is postulated that for MSD in aircraft lap joints, compliance measurements may provide a useful tool for assessing the structural integrity of the lap joints.

Scattering analysis of nonlinear Lamb waves at delaminations in composite laminates

2021 ◽  
pp. 107754632199014
Author(s):  
Reza Soleimanpour ◽  
Ching-Tai Ng
Keyword(s):  
Harmonic Generation ◽  
Lamb Wave ◽  
Composite Laminates ◽  
Lamb Waves ◽  
Mode Conversion ◽  
Experimental Studies ◽  
Acoustic Nonlinearity ◽  
Higher Harmonic Generation ◽  
Higher Harmonic ◽  
Contact Acoustic Nonlinearity

This study investigates the higher harmonic generation of the Lamb wave at a delamination due to contact acoustic nonlinearity, which is a clapping phenomenon between sublaminate surfaces due to the Lamb wave interaction with the delamination. In this study, higher harmonics of the Lamb wave induced at the delamination in composite laminates are studied in detail. This study performs both numerical and experimental studies. A three-dimensional finite element model is proposed for predicting the propagation of nonlinear Lamb waves in composite laminates and is verified using experimentally measured data. The results show the proposed numerical model can reasonably predict higher harmonic generated by contact acoustic nonlinearity. It is found that the delamination is the major source of contact acoustic nonlinearity in the composite laminates. A mode conversion study is also carried out to gain further physical insight into the higher harmonic generation of the Lamb wave at the delamination.

scholarly journals The numerical analysis of the interaction between the low-order Lamb wave modes and surface breaking cracks

2019 ◽  
Vol 254 ◽  
pp. 08001 ◽  
Author(s):  
Michal Šofer ◽  
Petr Ferfecki ◽  
Martin Fusek ◽  
Pavel Šofer ◽  
Renata Gnatowska
Keyword(s):  
Lamb Wave ◽  
Guided Waves ◽  
Lamb Waves ◽  
Numerical Study ◽  
Large Structures ◽  
Piping Systems ◽  
Geometric Discontinuities ◽  
Surface Breaking Crack ◽  
Wave Modes ◽  
Low Order

Lamb waves, as one of the types of guided waves, are extensively used for inspecting large structures as well as for structure health monitoring applications. One of the biggest benefits of guided waves is their ability to travel over long distances without much attenuation. Lamb waves are often used for inspection of piping systems and similar geometries where the dimension in the third direction is significantly smaller than the other two. No wonder that the study of the interaction of Lamb waves with particular types of geometric discontinuities is a frequent topic of research. The main aim of the proposed paper is to present the findings related to the numerical study of the interaction between low-order Lamb wave modes and surface breaking crack oriented at different angles relative to the free surface.

scholarly journals Effect of Pressure Distribution on the Energy Dissipation of Lap Joints under Equal Pre-tension Force

Open Physics ◽  
2019 ◽  
Vol 17 (1) ◽  
pp. 320-328
Author(s):  
Delin Sun ◽  
Minggao Zhu
Keyword(s):  
Energy Dissipation ◽  
Pressure Distribution ◽  
Theoretical Basis ◽  
Lap Joints ◽  
Power Exponent ◽  
Lap Joint ◽  
Stick Slip ◽  
Pressure Distributions ◽  
Hysteretic Characteristics ◽  
Effective Use

Abstract In this paper, the energy dissipation in a bolted lap joint is studied using a continuum microslip model. Five contact pressure distributions compliant with the power law are considered, and all of them have equal pretension forces. The effects of different pressure distributions on the interface stick-slip transitions and hysteretic characteristics are presented. The calculation formulation of the energy dissipation is introduced. The energy dissipation results are plotted on linear and log-log coordinates to investigate the effect of the pressure distribution on the energy distribution. It is shown that the energy dissipations of the lap joints are related to the minimum pressure in the overlapped area, the size of the contact area and the value of the power exponent. The work provides a theoretical basis for further effective use of the joint energy dissipation.

scholarly journals Coronavirus and Soft Law in Germany: Business as Usual?

2021 ◽  
pp. 1-17
Author(s):  
Matthias Knauff
Keyword(s):  
Legal Order ◽  
Soft Law ◽  
Constitutional Order ◽  
Binding Forms ◽  
Almost All ◽  
Business As Usual ◽  
Shed Light ◽  
Made In

In combating the coronavirus pandemic in Germany, soft law has played an important, albeit not a central, role. Its use basically corresponds to that of under “normal circumstances”. In accordance with the German constitutional order, almost all substantial decisions are made in a legally binding form. However, these are often prepared through or supplemented by soft law. This article shows that soft law has played an important role in fighting the pandemic and its effects in Germany, although there cannot be any doubt that legally binding forms of regulation have prevailed. At the same time, the current pandemic has shed light on the advantages and effects of soft law in the context of the German legal order.

Inspection of Concrete-Metal Rod Interface Using Guided Waves

2000 ◽  
Author(s):  
Won-Bae Na ◽  
Tribikram Kundu ◽  
Mohammad R. Ehsani
Keyword(s):  
Lamb Wave ◽  
Guided Waves ◽  
Lamb Waves ◽  
Guided Wave ◽  
Ultrasonic Transducers ◽  
Interface Debonding ◽  
Long Distance ◽  
Steel Rebar ◽  
Steel Bars ◽  
Steel Rebars

Abstract The feasibility of detecting interface degradation and separation of steel rebars in concrete beams using Lamb waves is investigated in this paper. It is shown that Lamb waves can easily detect these defects. A special coupler between the steel rebar and ultrasonic transducers has been used to launch non-axisymmetric guided waves in the steel rebar. This investigation shows that the Lamb wave inspection technique is an efficient and effective tool for health monitoring of reinforced concrete structures because the Lamb wave can propagate a long distance along the reinforcing steel bars embedded in concrete as the guided wave and is sensitive to the interface debonding between the steel rebar and concrete.

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