A Lamb wave-based damage identification method called damage imaging method for composite shells is presented. A
damage index (DI) is generated from the delay matrix of the Lamb wave response signals, and it is used to indicate the
location and approximate area of the damage. A piezoelectric actuator is employed to generate the Lamb waves that are
subsequently captured by a fiber Bragg grating (FBG) sensor element array multiplexed in a single fiber connected to a
high-speed fiber-optic sensor system. The high-speed sensing is enabled by an innovative parallel-architecture optical
interrogation system. The viability of this method is demonstrated by analyzing the numerical and experimental Lamb
wave response signals from laminated composite shells. The technique only requires the response signals from the plate
after damage, and it is capable of performing near real-time damage identification. This study sheds some light on the
application of a Lamb wave-based damage detection algorithm for curved plate/shell-type structures by using the
relatively low frequency (around 100 kHz) Lamb wave response and the high-speed FBG sensor system.
In this paper, the material property assessment and crack identification of concrete using embedded smart cement
modules are presented. Both the concrete samples with recycled aggregates (RA) and natural aggregates (NA) were
prepared. The smart cement modules were fabricated and embedded in concrete beams to serve as either the actuators or
sensors, and the elastic wave propagation-based technique was developed to detect the damage (crack) in the recycled
aggregate concrete (RAC) beams and monitor the material degradation of RAC beams due to the freeze/thaw (F/T)
conditioning cycles. The damage detection results and elastic modulus reduction monitoring data demonstrate that the
proposed smart cement modules and associated damage detection and monitoring techniques are capable of identifying
crack-type damage and monitoring material degradation of the RAC beams. Both the RAC and natural aggregate
concrete (NAC) beams degrade with the increased F/T conditioning cycles. Though the RAC shows a lower reduction
percentage of the modulus of elasticity from both the dynamic modulus and wave propagation tests at the given maximum F/T conditioning cycle (i.e., 300 in this study), the RAC tends to degrade faster after the 180 F/T cycles. As observed in this study, the material properties and degradation rate of RAC are comparable to those of NAC, thus making the RAC suitable for transportation construction. The findings in development of damage detection and health monitoring techniques using embedded smart cement modules resulted from this study promote the widespread application of recycled concrete in transportation construction and provide viable and effective health monitoring techniques for concrete structures in general.
In this paper, a novel vibration-based methodology for fast inverse identification of delamination in E-glass/epoxy
composite panels has been proposed with experimental demonstration using a scanning laser vibrometer (SLV). The
methodology consists of 1) a parameter subset selection for delamination damage localization and 2) iterative inverse
eigenvalue analysis for damage quantification. It can potentially lead to a functional formulation relating spatial and
global damage indices such as curvature damage factor to local damage parameters. The functional relationship will be
suitable to fast or real-time in-situ delamination damage identification. To accomplish the objectives, a shear-locking
free higher-order finite element model has been combined with a micromechanics theory-based continuum damage
model as an identification model for locating delamination. Applications of the proposed methodology to an Eglass/
epoxy panel [CSM/UM1208/3 layers of C1800]s = [CSM/0/(90/0)3]s with delamination have been demonstrated
both numerically and experimentally using a piezoelectric actuator, a PVDF sensor and non-contact measuring SLV.
Experimental modal analysis has been successfully conducted using the sample specimen to demonstrate the proposed
Fractal as a novel mathematical tool has a great potential to deal with transit events in a complex waveform. In this
paper, fractal is introduced to detect irregularity of vibration mode shapes without using a baseline requirement.
Different from the popular Katz's waveform fractal dimension (KWD), a novel approximate waveform capacity
dimension (AWCD) specialized in irregularity detection in vibration mode shapes is introduced, from which an AWCD-based
modal abnormality algorithm (AWCD-MAA) is established. The fundamental characteristics of AWCD-MAA,
such as crack location identification and size quantification, are investigated using an analytical crack model of
cantilever beams. An experimental modal shape evaluation of a cracked composite cantilever beam using smart
piezoelectric sensors/actuators (i.e., Piezoelectric
lead-zirconate-titanate (PZT) and polyvinylidene fluoride (PVDF)) is
conducted to confirm the feasibility of the proposed algorithm. The proposed AWCD-MAA is capable of locating and
quantifying the crack in a beam-type structure without prior requirement of baseline reference data.
In this study, a newly-developed technique, so-called "integrated wavelet transform (IWT)", is applied to damage
detection of laminated composite beams. The novel IWT technique combines advantages of stationary wavelet
transform (SWT) and continuous wavelet transform (CWT) to improve the robustness of wavelet-based modal analysis
in damage detection. Two progressive wavelet analysis steps are considered, in which the SWT-based multi-resolution
analysis (MRA) is first employed to refine the retrieved mode shapes, followed by the CWT-based multiscale analysis
(MSA) to magnify the effect of slight abnormality. The SWT-MRA is utilized to eliminate random noise and regular
interferences, separate multiple component signal, and thus extract purer damage information; while the CWT-MSA is
employed to smoothen, differentiate or suppress polynomial of mode shapes to magnify the effect of abnormality. The
effectiveness of IWT in damage detection is illustrated using the vibration mode shape data acquired from the
experimental testing of a cantilever laminated composite beam with a through-width crack. As demonstrated in the
successful detection of a crack in composite beams, the progressive wavelet transform analysis using IWT provides a
robust and viable technique to identify minor damage in a relatively lower signal-to-noise ratio environment.
Structural Health Monitoring (SHM) is becoming an increasingly important tool for the maintenance, safety and integrity of aerospace structural systems. Immune to electromagnetic interference, Fiber Bragg Grating (FBG) optical sensor matrices are light-weight and multiplexable, allowing many sensors on a single fiber to be integrated into smart structures. Highly sensitive to minute strains, they can facilitate maximum SHM functionality, with minimum weight and size. Consequently, these optical systems, in conjunction with advanced damage characterization algorithms, are expected to play an increasing role in extending the life and reducing costs of new generations of structures and airframes. In this paper, we discuss the development of both hardware and algorithms to detect, locate and quantify delamination in composite laminated beam structures. We present an integrated SHM system including (a) the capability of interrogating over 50 FBG sensors simultaneously with sub-picometer resolution at over 50 kHz, (b) an FBG-sensor/piezo-actuator matrix smart skin design and methodology, and (c) damage detection location and quantification algorithms based on mode shape or other relevant advanced algorithmic-based damage diagnosis and prognosis techniques. Comparison with other SHM systems (e.g., based on piezo-electric (PVDF) and Scanning Laser Vibrometer sensors) demonstrates better signal-to-noise and damage detection for our FBG system.
Accurate interpretation of data measurement is a major challenge for development of reliable and effective diagnostic system. This paper presents experimental results of a proposed damage identification candidate based on Lamb wave propagation analysis. Carbon/epoxy laminated composite plate specimens with various damage, i.e., delamination and impact damage, are evaluated. Damage location is extracted from the measured time history data of the propagated wave and the wave traveling time. Assuming the wave propagates with a constant speed, the summation of the distance from the transmitter to the damage and the distance from the damage to the receiver is constant. The possible damage location combining with the locations of the transmitter and receiver forms an elliptical path, where the locations of the transmitter and receiver serve as the foci of the ellipse. Piezoelectric transducers (PZTs) are used as the wave transmitters and receivers. Post-processing of the recorded signals using wavelet transform allows better isolation of the interested propagation mode and the extraction of the traveling time, which enhance the accuracy of damage localization. Results of the damage location estimation are presented.
In this study, the guided wave technique is applied to nondestructively assess the damage in various engineering materials, like alumina, laminated composites, and composite sandwiches. A combined theoretical, numerical and experimental investigation of the pulse-echo method using piezoelectric sensors and actuators is conducted. The dispersion effect of wave guides on these materials is first analyzed, and the transient propagation process of wave guides and its interaction with inside damages are then numerically simulated. The implementations of the pulse echo method are illustrated in experimental testing and damage detection of aluminum beams, carbon/epoxy laminated composite plates, and composite sandwich beams. In particular, the experimental results on damage detection of the composite sandwich beams are reported and discussed. As illustrated in this study, the pulse-echo method combined with piezoelectric material can be used effectively to locate damage in various engineering materials and structures.
Composite materials are widely applied in aerospace, mechanical and civil structures. Delamination of composite material happens due to aging, chemical corruption and mechanical vibration, among other factors. It is important to detect the delamination in the incipient stage before the delamination reaches a notable level. Piezoelectric material can act as both actuators and sensors. In this research, two composite plates are fabricated as test specimen, of which one has a small delamination and the other is healthy. Four PZT patches are bonded at four corners of each composite plate, and one PZT patch is bonded in the middle of the composite plate. Wavelet packet analysis is applied as the signal-processing tool to analyze the sensor data. A damage index is formed based on the wavelet packet analysis to show the existence and the severity of damage. The experiment results show the proposed method can detect the delamination. This sensitive method is suited for delamination detection of inaccessible composite structures without using additional excitation facility.
Fiber reinforced polymer (FRP) composites have been increasingly used for civil infrastructure in recent years, and the applications have promoted interest in health monitoring of structural composites. Although primary layouts of these composite structures are similar, the FRP composites used in civil engineering structures are usually relatively thicker and larger in size. Hence, more power authority is needed in the experimental procedure for health monitoring purposes. In this study, health monitoring of thick composite structures using smart piezoelectric materials is presented. Monitoring technique based on wave propagation is evaluated for possible damage detection in civil composite structures. For comparison purposes, the composite laminated beams with two different thickness are made of E-glass fiber and epoxy resins by vacuum bagging process, and the damage in the form of delamination is created by inserting Teflon sheet between the lamina at certain location. Smart piezoelectric materials are used as both the emitter and receiver of the wave. The exploratory experimental program developed in this study can be used for better understanding of the possibility of wave propagation based technique in health monitoring and damage detection of large civil FRP composite structures.
Advanced and innovative materials and structures are increasingly used in civil infrastructure applications. By combining the advantages of composites and smart sensors and actuators, active or smart composite structures can be created and be efficiently adopted in practical structural applications. This paper presents results of active vibration control of a pultruded fiber-reinforced polymer (FRP) composites thin-walled I-beams using smart sensors and actuators. The FRP I-beams are made of E-glass fibers and polyester resins. The FRP I-beam is in a cantilevered configuration. PZT (Lead zirconate titanate) type of piezoelectric ceramic patches are used as smart sensors and actuators. These patches are surface-bonded near the cantilevered end of the I-beam. Utilizing results from modal analyses and experimental modal testing, several active vibration control methods, such as position feedback control, strain rate feedback control and lead compensator, are investigated. Experimental results demonstrate that the proposed methods achieve effective vibration control of FRP I-beams. For instance, the modal damping ratio of the strong direction first bending mode increases by more than 1000 percent with a positive position feedback control.