Arvin Ebrahimkhanlou

Damage localization in metallic plate structures using edge-reflected lamb waves

This paper presents a model-based guided ultrasonic waves imaging algorithm, in which multiple ultrasonic echoes caused by reflections from the plates boundaries are leveraged to enhance imaging performance. An analytical model is proposed to estimate the envelope of scattered waves. Correlation between the estimated and experimental data is used to generate images. The proposed method is validated through experimental tests on an aluminum plate instrumented with three low profile piezoelectric transducers. Different damage conditions are simulated including through-thickness holes. Results are compared with two other imaging localization methods, that is, delay and sum and minimum variance.

Acoustic emission source localization in thin metallic plates: A single-sensor approach based on multimodal edge reflections

HIGHLIGHTSDevelopment of a one‐sensor AE source localization algorithm for metallic plates.Development of an analytical model to reconstruct edge‐reflected late arrivals.Fusing the reflection‐based and modal acoustic emission techniques.Experimental performance evaluation of the proposed algorithm.Discussion on the accuracy and computation cost of the proposed algorithm. ABSTRACT This paper presents a new acoustic emission (AE) source localization for isotropic plates with reflecting boundaries. This approach that has no blind spot leverages multimodal edge reflections to identify AE sources with only a single sensor. The implementation of the proposed approach involves three main steps. First, the continuous wavelet transform (CWT) and the dispersion curves of the fundamental Lamb wave modes are utilized to estimate the distance between an AE source and a sensor. This step uses a modal acoustic emission approach. Then, an analytical model is proposed that uses the estimated distances to simulate the edge‐reflected waves. Finally, the correlation between the experimental and the simulated waveforms is used to estimate the location of AE sources. Hsu‐Nielsen pencil lead break (PLB) tests were performed on an aluminum plate to validate this algorithm and promising results were achieved. Based on these results, the paper reports the statistics of the localization errors.

Multifractal analysis of crack patterns in reinforced concrete shear walls

Conventionally, the assessment of reinforced concrete shear walls relies on manual visual assessment which is time-consuming and depends heavily on the skills of the inspectors. The development of automated assessment employing flying and crawling robots equipped with high-resolution cameras and wireless communications to acquire digital images and advance image processing to extract crack patterns has paved the path toward implementing an automated system which determines structural damage based on visual signals acquired from structures. Since there are few, if any, studies to correlate crack patterns to structural integrity, this article proposes to analyze crack patterns using a multifractal analysis. The approach is initially tested on synthetic crack patterns, and then it is applied to a set of experimental data collected during the testing of two large-scale reinforced concrete shear wall subjected to controlled reversed cyclic loading. The structural response data available for each specimen are used to link the multifractal parameters with the structural performance of the two specimens. A relationship between the multifractal parameters and the crack patterns’ evolution and mechanism is noted. The results show that as the crack patterns extend and grow, multifractal parameters move toward higher values. The parameters jump as the mechanical response shows severe stiffness loss. In this study, no attempt is made to automate the process of mapping cracks from images.

Effect of pressurization on helical guided wave energy velocity in fluid-filled pipes

HighlightsTheory of acoustoelastic leak Lamb waves presented.Energy velocity of acoustoelastic leaky Lamb waves derived.Energy velocity direction‐dependent and varies linearly with respect to pressurization (stress).Theory compared to experimental helical guided wave measurements in pressurized pipe. ABSTRACT The effect of pressurization stresses on helical guided waves in a thin‐walled fluid‐filled pipe is studied by modeling leaky Lamb waves in a stressed plate bordered by fluid. Fluid pressurization produces hoop and longitudinal stresses in a thin‐walled pipe, which corresponds to biaxial in‐plane stress in a plate waveguide model. The effect of stress on guided wave propagation is accounted for through nonlinear elasticity and finite deformation theory. Emphasis is placed on the stress dependence of the energy velocity of the guided wave modes. For this purpose, an expression for the energy velocity of leaky Lamb waves in a stressed plate is derived. Theoretical results are presented for the mode, frequency, and directional dependent variations in energy velocity with respect to stress. An experimental setup is designed for measuring variations in helical wave energy velocity in a thin‐walled water‐filled steel pipe at different levels of pressure. Good agreement is achieved between the experimental variations in energy velocity for the helical guided waves and the theoretical leaky Lamb wave solutions.

A guided ultrasonic imaging approach in isotropic plate structures using edge reflections

This paper presents an imaging technique to locate damage in plate-like structures by permanently attached piezoelectric transducers (PZT) capable to generate and receive guided ultrasonic waves. The technique is based on a model capable of predicting envelope of scattered waves. Correlations between the estimated scattered waves and experimental data are used for image reconstruction. The approach is validated on an aluminum plate and results are compared with two common imaging algorithms, that is, Delay and Sum (DS) and Minimum Variance (MV). Damage is simulated by placing two magnets on sides of the plate. It is shown that the inclusion of Lamb wave reflections improves the localization accuracy while making use of fewer number of sensors possible.

Probabilistic location estimation of acoustic emission sources in isotropic plates with one sensor

This paper presents a probabilistic acoustic emission (AE) source localization algorithm for isotropic plate structures. The proposed algorithm requires only one sensor and uniformly monitors the entire area of such plates without any blind zones. In addition, it takes a probabilistic approach and quantifies localization uncertainties. The algorithm combines a modal acoustic emission (MAE) and a reflection-based technique to obtain information pertaining to the location of AE sources. To estimate confidence contours for the location of sources, uncertainties are quantified and propagated through the two techniques. The approach was validated using standard pencil lead break (PLB) tests on an Aluminum plate. The results demonstrate that the proposed source localization algorithm successfully estimates confidence contours for the location of AE sources.

Helical guided waves in liquid-filled cylindrical shells subjected to static pressurization stress

Helical guided waves in pipelines are studied under the effects of pressurization stresses from a contained liquid. The pipeline is approximated by an “unwrapped” plate waveguide, and a transfer matrix method is used to solve for guided wave velocity and attenuation dispersion curves in a multilayered plate waveguide subject to an arbitrary triaxial state of initial stress. The matrix-based model is able to incorporate both elastic and viscoelastic solid materials, as well as approximate non-uniform distributions in initial stress through the thickness of a waveguide. Experiments on a steel pipe filled with pressurized water are carried out to validate the modeling approach.

Multifractal analysis of two-dimensional images for damage assessment of reinforced concrete structures

The most common assessment technique for reinforced concrete shear walls (RCSW) is Visual Inspection (VI). The current practice suffers from subjective and labor intensive nature as it highly relies on judgment and expertise of the inspectors. In post-earthquake events where urgent and objective decisions are crucial, failure of the conventional VI could be catastrophic. Conventional VI is mainly based on width of residual cracks. Given that cracks could close partially (e.g., due to weight of the structure, behavior of adjacent elastic members, earthquake displacement spectrum, etc.), methods based on crack width may lead to underestimating the state of damage and eventually an erroneous decision. This paper proposes a novel method to circumvent the aforementioned limitations by utilizing the information hidden in crack patterns. Crack patterns from images of the surface cracks on RCSW are extracted automatically, and Multifractal Analysis (MFA) are applied on them. Images were taken from two large scale low aspect ratio RCSW under quasi-static cyclic loading, and MFA showed clear correlation with tri-linear shear controlled behavior of walls which was observed in their backbone curves.

Damage Localization in Plate-like Structures Using Guided Ultrasonic Waves Edge Reflections

This paper proposes a novel idea for ultrasonic imaging of plate structures with a small number of permanently attached ultrasonic sensors. Guided ultrasonic waves excited and captured by a single actuator-sensor pair suffice as input for the proposed imaging technique. Taking advantage of several reflections from boundaries and geometric features of plates, the number of inspection lines is artificially increased. Only the first antisymmetric mode (A0) is used for imaging, because it has higher excitability than the first symmetric mode (S0) and simpler reflection behavior. Mode conversion from reflections is avoided by exciting below the first cut-off frequency of higher order propagating antisymmetric modes. The path and distance traveled by each echo is calculated using a ray tracking model, and a drop in energy of each echo compared to its baseline is associated with the presence of damage. Dispersion curves are used to calculate wave velocity and expected arrival times of the reflected echoes. Based on the expected time of arrival, a gate is defined for each echo, and an energy comparison is conducted for the high energy gated portion of the echo. A probabilistic method for image reconstruction is also proposed to locate damage. The proposed imaging method combines information from several inspection paths using a Bayesian probabilistic framework. To validate the approach, experiments have been carried out on an aluminum plate, instrumented with only two permanently attached low profile circular piezoelectric sensors. A tone burst packet is used an input excitation, and multiple echoed packets have been recorded at a receiving sensor. A large C-clamp is used to locally scatter the waves and simulate damage. Damage is simulated in nine locations, and the proposed method achieves notable success in localizing the applied damage with only two sensors. doi: 10.12783/SHM2015/313

Corrosion damage estimation in multi-wire steel strands using guided ultrasonic waves

This study presents a nondestructive evaluation method based on guided ultrasonic waves (GUW) to estimate corrosion in steel strands. Steel strands are one of the main components in constructing prestressed structures. Hidden corrosion in these structures has become a concern for designers, owners and regulators as it can eventuate in disastrous failure. In this study, a reference-free algorithm is proposed to quantify the extent of corrosion through estimating the cross section loss using dispersion curves and the velocity of certain frequency components in the waveform. Experimental test setups were designed to accelerate corrosion on two similarly loaded steel strands. One strand was embedded in concrete (to simulate a prestressed concrete beam) and the other was free (to resemble a prestressed cable). Visual inspection, halfcell potential, and mass loss measurements were employed as supporting evidences for the state of corrosion. An uncertainty analysis was also carried out to investigate how close this method can estimate the diameter of wires in a strand. The method could reasonably estimate the diameter of the wires without a reference baseline.