New Non-destructive Evaluation Research Articles

Detection of defects in cellular solids using highly nonlinear solitary waves: a numerical study of the proximal femur.

This study investigates the suitability of a relatively new non-destructive evaluation (NDE) technique for the detection of non-visible defects in cellular solids using highly nonlinear solitary waves (HNSWs) in a one-dimensional granular chain. Specifically, the HNSW-based NDE approach is employed to identify the existence of micro-fractures in trabecular bone within the femoral neck (FN) and the intertrochanteric (IT) region of the proximal femur which are fracture-prone sites due to their relatively low bone density, particularly in osteoporosis patients. The availability of a HNSW-based bone quality assessment tool could not only help in early diagnosis of osteoporosis but also affect surgical decisions and improve clinical outcomes in joint replacement surgeries which motivated this study. To obtain a realistic representation of the trabecular microstructure, high-resolution finite-element (FE) models of the FN and the IT region are first constructed using a topology optimization-based bone reconstruction scheme. Then, artificial defects in the form of fractured ligaments are generated in the FN and IT models by selectively disconnecting various struts within the trabecular network. Using the FE models as the inspection medium, hybrid discrete-element/finite-element (DE/FE) simulations are performed to examine the interaction of the HNSWs with the cellular bone samples through two different inspection modes, i.e., inspection via direct contact with the sample and indirect contact through an adequately chosen face sheet inserted between the cellular sample and the granular chain. The delays and amplitudes of the HNSWs are used to estimate the effective elastic moduli of the cellular samples and these estimates were found to be reasonably accurate only in case the face sheet was applied. For the latter case, it was shown that the HNSW-based modulus estimates can be used as indicators for defect detection, allowing to discern between pristine and damaged cellular solids. These results suggest that HNSW-based NDE is a reliable and cost-effective technique for the identification of defects in cellular solids, and is expected to find applications in various fields, such as non-invasive screening of bone diseases and fractures, or damage detection in additively manufactured cellular structures.

Corrosion Depth Inversion Method Based on the Lift-Off Effect of the Capacitive Imaging (CI) Technique

As a new Non-destructive Evaluation (NDE) technique, capacitive imaging (CI) has been used to detect defects in oil pipelines, composite sucker rods and storage tanks in recent years. When a CI sensor is used to detect corrosion defect on a conducting surface with or without an insulation layer, the depth information of corrosion defect is difficult to acquire due to the non-linearity of the probing field. This paper proposed a corrosion depth inversion method based on the lift-off effect of the CI technique. The proposed depth inversion method, which includes three steps, namely establishing the lift-off curve, obtaining the scan curve and fitting inversion, are introduced and evaluated. In the FE simulations, the error rates of the inversion depths are less than 1.20%. CI experiments were carried out to acquire the depth information of a step shape specimen using the CI experimental system and the proposed corrosion depth inversion method. The results show that the depth inversion method can meet the need of obtaining the actual depth information with the error rates of the inversion depths being less than 10.00%. A CI experiment on a machined and corroded specimen was carried out to further demonstrate the feasibility of the proposed inversion method for corrosion defects with different depths. Both results from FE models and experiments indicate that the proposed method is promising to achieve the quantitative NDE of the Corrosion Under Insulation (CUI).

Novel non-destructive evaluation technique for the detection of poor dispersion of carbon nanotubes in nanocomposites

A wide use of advanced carbon nanotube polymer composites can be boosted by new non-destructive evaluation (NDE) techniques that can test the quality of the products to ensure that their specifications are met. It is well known in literature that the parameter that far more than others can affect the enhancing capabilities of the carbon nanotubes is their dispersion. Here we have presented a novel NDE technique based on infrared thermography able to evaluate the dispersion of the added nanoparticles in polymer nanocomposites. The NDE technique was used to compare pairs of samples whose difference is represented only by the level of dispersion. It was found a significant difference in the thermal response to heat transfer transients. Thus, the thermal response of a nanocomposite allows one to identify consistently good levels of dispersion with respect to lower levels of dispersion. A reference product, which has the expected dispersion level and achieves the desired design performance, can be used to test the thermal behaviour of other products coming out of the production process and those with poor dispersion can be identified. The physical phenomena that can explain the effects of multi-walled carbon nanotubes (MWCNTs) dispersion on the thermal response of the nanocomposites to the heat transfer transients were also identified.

Monitoring the water absorption in GFRE pipes via an electrical capacitance sensors

One of the major problems in glass fiber reinforced epoxy (GFRE) composite pipes is the durability under water absorption. This condition is generally recognized to cause degradations in strength and mechanical properties. Therefore, there is a need for an intelligent system for detecting the absorption rate and computing the mass of water absorption (M%) as a function of absorption time (t). The present work represents a new non-destructive evaluation (NDE) technique for detecting the water absorption rate by evaluating the dielectric properties of glass fiber and epoxy resin composite pipes subjected to internal hydrostatic pressure at room temperature. The variation in the dielectric signatures is employed to design an electrical capacitance sensor (ECS) with high sensitivity to detect such defects. ECS consists of twelve electrodes mounted on the outer surface of the pipe. Radius-electrode ratio is defined as the ratio of inner and outer radius of pipe. A finite element (FE) simulation model is developed to measure the capacitance values and node potential distribution of ECS electrodes on the basis of water absorption rate in the pipe material as a function of absorption time. The arrangements for positioning12-electrode sensor parameters such as capacitance, capacitance change and change rate of capacitance are analyzed by ANSYS and MATLAB to plot the mass of water absorption curve against absorption time (t). An analytical model based on a Fickian diffusion model is conducted to predict the saturation level of water absorption (MS) from the obtained mass of water absorption curve. The FE results are in excellent agreement with the analytical results and experimental results available in the literature, thus, validating the accuracy and reliability of the proposed expert system.

FE and ANN model of ECS to simulate the pipelines suffer from internal corrosion

As the study of internal corrosion of pipeline need a large number of experiments as well as long time, so there is a need for new computational technique to expand the spectrum of the results and to save time. The present work represents a new non-destructive evaluation (NDE) technique for detecting the internal corrosion inside pipeline by evaluating the dielectric properties of steel pipe at room temperature by using electrical capacitance sensor (ECS), then predict the effect of pipeline environment temperature (o) on the corrosion rates by designing an efficient artificial neural network (ANN) architecture. ECS consists of number of electrodes mounted on the outer surface of pipeline, the sensor shape, electrode configuration, and the number of electrodes that comprise three key elements of two dimensional capacitance sensors are illustrated. The variation in the dielectric signatures was employed to design electrical capacitance sensor (ECS) with high sensitivity to detect such defects. The rules of 24-electrode sensor parameters such as capacitance, capacitance change, and change rate of capacitance are discussed by ANSYS and MATLAB, which are combined to simulate sensor characteristic. A feed-forward neural network (FFNN) structure are applied, trained and tested to predict the finite element (FE) results of corrosion rates under room temperature, and then used the trained FFNN to predict corrosion rates at different temperature using MATLAB neural network toolbox. The FE results are in excellent agreement with an FFNN results, thus validating the accuracy and reliability of the proposed technique and leads to better understanding of the corrosion mechanism under different pipeline environmental temperature.

Planar array 3D electrical capacitance tomography

Electrical capacitance tomography (ECT) is a promising non-invasive imaging technique that is capable of mapping the dielectric permittivity of an object. ECT has great potential to be used as a new non-destructive evaluation (NDE) method. In the majority of NDE applications for ECT there is only limited access to the targeted objects, making conventional circular array ECT impractical. In this paper, a planar array ECT system is developed and proposed for 3D subsurface imaging as a form of limited access tomography. The sensor development, practical implications, capabilities and limitations of the proposed planar array ECT system are discussed. The experimental results are used to evaluate the system performance. A depth of up to 53% of the length of the sensor array can be achieved using experimental data using an array of 4 × 3 electrodes.

Development of wall thinning screening system and its application to a commercial nuclear power plant

A new non-destructive evaluation (NDE) method has been developed for metal pipes for the detection wall thinning. The method has been showed to be suitable for applications to electric power generation plants where flow accelerated corrosion (FAC) of carbon steel piping is a significant cause of increased maintenance and plant personnel casualty. The wall thinning screening system (WalSS) was developed in two major phases. In the first phase, the equipotential switching direct current potential drop (ES-DCPD) method was developed for piping wall (Ryu et al., 2008a, 2010). In the second phase, in this paper, a quantitative detection criteria was developed. The relative ES-DCPD change of 3.8% has been defined as the screening criteria for wall thinning schematization. This criteria means that the component with measured ES-DCPD change greater than 3.8% is called for a more comprehensive examination. In the criteria development, all variables were taken into consideration based on commercial plant piping inspection data such as initial thickness distributions, wall thinning shape and nominal thickness. The developed WalSS based on ES-DCPD was applied to a moisture separator reheater (MSR) drain line of a commercial nuclear power plant (NPP) during a scheduled overhaul. The measured ES-DCPD change was 2.16%, which is lower than the ES-DCPD criteria, identifying the pipe having adequate wall thickness. This is confirmed by site thickness inspection using ultrasonic technique (UT).

Development Of NRU Reflector Wall Inspection System

In 2009 May, the National Research Universal (NRU) calandria leaked. During the next year, the calandria was inspected with six new Non-Destructive Evaluation (NDE) techniques to determine the extent of the corrosion, repaired, and finally the repair was inspected with four additional new NDE techniques before the reactor was returned to service.The calandria is surrounded by a light-water reflector vessel fabricated from the same material as the calandria vessel. Concerns that the same corrosion mechanism had damaged the reflector vessel led to the development of a system to inspect the full circumference of the reflector wall for corrosion damage. The inspection region could only be accessed through 64 mm diameter ports, was 10 m below the port, and had to be inspected from the corroded surface. The ultrasonic technique was designed to produce a closely spaced wall thickness (WT) grid over an area of approximately 5 m2on the corroded surface using a very small probe holder.This paper describes the Reflector Wall Inspection (RWI) development project and the system that resulted.

Monitoring the strength development in concrete by EMI sensing technique

For any new nondestructive evaluation (NDE) technique, prior to full commercialization and real field application, rigorous studies are needed to address its practicality and reproducibility of the results under nominally the same conditions. Recently, the applicability of electro-mechanical impedance (EMI) sensing technique has been extended to monitoring of concrete curing and strength gain. Experimental investigations of this relatively new NDE technique for damage detection in structures have been successfully demonstrated by many researchers. The objective of the present study is to further develop the application of the EMI sensing technique for in situ monitoring of concrete using the low cost piezoceramic (PZT) patches. In this investigation, resonant frequencies of the surface bonded PZT patches were tracked using an impedance analyzer by sweeping the frequency within the range of 100–400 kHz. The experimental results verify the practicality of the EMI sensing technique for monitoring the strength development in concrete. Using an established empirical relationship, the relative strength gain of concrete can be predicted by monitoring the resonant frequency shift. The quantitative approach based on the statistics metrics such as RMSD, MAPD and CCD to compare the EMI spectra is also presented.

Coplanar capacitance sensors for detecting water intrusion in composite structures

Composite materials are becoming more affordable and widely used for retrofitting, rehabilitating and repairing reinforced concrete structures designed and constructed under older specifications. However, the mechanical properties and long-term durability of composite materials may degrade severely in the presence of water intrusion. This study presents a new non-destructive evaluation (NDE) technique for detecting the water intrusion in composite structures by evaluating the dielectric properties of different composite system constituent materials. The variation in the dielectric signatures was employed to design a coplanar capacitance sensor with high sensitivity to detect such defects. An analytical model was used to study the effect of the sensor geometry on the output signal and to optimize sensor design. A finite element model was developed to validate analytical results and to evaluate other sensor design-related parameters. Experimental testing of a concrete specimen wrapped with composite laminate and containing a series of pre-induced water intrusion defects was conducted in order to validate the concept of the new technique. Experimental data showed excellent agreement with the finite element model predictions and confirmed sensor performance.

Non-destructive thermal barrier coating (TBC) damage assessment using laser-induced luminescence and infrared radiometry

A new non-destructive evaluation (NDE) approach for assessing damage in thermal barrier coating (TBC) systems is described. It is based on a combined measurement of the optical and thermal response due to photo-excitation, through the TBC, of Cr 3+ ions within the thermally grown oxide (TGO). This method has subsurface selectivity to the TBC/TGO interface, as it is based on using a laser wavelength to which the TBC is transparent but the TGO absorbs strongly, so that the energy of the laser is converted into both luminescence and heat within the TGO. Using mid-infrared detection, the subsequent change in temperature of the TGO is measured as heat is conducted away from the TGO into the adjacent alloy and TBC coating. Damage decreases the rate at which the heat decays away and can be quantified from measurements of the transient temperature changes. The luminescence signal may be used to quantify the compressive stress and the thickness of the TGO, using photoluminescence piezospectroscopy and luminescence lifetime measurements, respectively. Both the optical arrangement used for implementing this new approach and the results obtained from a series of thermally cycled TBCs are described.

Ultrasonic Measurement of the Crack Depth and the Crack Opening Stress Intensity Factor Under a No Load Condition

This paper describes a new methodology for evaluating the crack depth and the crack opening stress intensity factor of small closed cracks using an ultrasonic technique. Surface connected back-wall cracks of depth ranging from 0.4 to 4.0 mm in steel specimens are considered. The crack corner echo amplitude of an ultrasonic shear wave, SW, beam of 50° incidence in material is used. First, the ultrasonic echo response of an open crack is determined as a function of crack depth. Next, based on changing the crack closure stress, an empirical relation between the crack closure stress and the crack-echo response is formulated. The crack depth and the crack closure stress of an unknown closed crack based on these relations are determined by inverse analysis of the ultrasonic response of the crack. From the evaluated crack depth and crack closure stress, the crack opening stress intensity factor is determined. The accuracy and reliability of this new nondestructive evaluation (NDE) method is verified by comparing the evaluated crack depth with the actual one. The latter is measured on the fractured surface obtained after carrying out ultrasonic testing. The ultrasonic method developed is proved to be a powerful tool for quantitative and nondestructive evaluation of the crack depth as well as the crack closure stress.

Overview of Piezoelectric Impedance-Based Health Monitoring and Path Forward

In this paper we summarize the hardware and software issues of impedance-based structural health moni- toring based on piezoelectric materials. The basic concept of the method is to use high-frequency structural excitations to monitor the local area of a structure for changes in structural impedance that would indicate imminent damage. A brief overview of research work on experimental and theoretical stud- ies on various structures is considered and several research papers on these topics are cited. This paper concludes with a discussion of future research areas and path forward. Piezoelectric materials acting in the manner pro- duce an electrical charge when stressed mechanically. Con- versely, a mechanical strain is produced when an electrical field is applied. The direct piezoelectric effect has often been used in sensors such as piezoelectric accelerometers. With the converse effect, piezoelectric materials apply local- ized strains and directly influence the dynamic response of the structural elements when either embedded or surface bonded into a structure. Piezoelectric materials have been widely used in structural dynamics applications because they are lightweight, robust, inexpensive, and come in a variety of forms ranging from thin rectangular patches to complex shapes being used in microelectromechanical systems (MEMS) fabrications. The applications of piezoelectric mate- rials in structural dynamics are too numerous to mention and are detailed in the literature (Niezrecki et al., 2001; Chopra, 2002). The purpose of this paper is to explore the importance and effectiveness of impedance-based structural health mon- itoring from both hardware and software standpoints. Imped- ance-based structural health monitoring techniques have been developed as a promising tool for real-time structural dam- age assessment, and are considered as a new non-destructive evaluation (NDE) method. A key aspect of impedance-based structural health monitoring is the use of piezoceramic (PZT) materials as collocated sensors and actuators. The basis of this active sensing technology is the energy transfer between the actuator and its host mechanical system. It has been shown that the electrical impedance of the PZT material can be directly related to the mechanical impedance of a host structural component where the PZT patch is attached. Uti- lizing the same material for both actuation and sensing not only reduces the number of sensors and actuators, but also reduces the electrical wiring and associated hardware. Fur- thermore, the size and weight of the PZT patch are negligible compared to those of the host structures so that its attach- ment to the structure introduces no impact on dynamic char- acteristics of the structure. A typical deployment of a PZT on a structure being monitored is shown in Figure 1. The first part of this paper (Sections 2 and 3) deals with the theoretical background and design considerations of the impedance-based structural health monitoring. The signal processing of the impedance method is outlined in Section 4. In Section 5, experimental studies using the impedance approaches are summarized and related previous works are listed. Section 6 presents a brief comparison of the imped- ance method with other NDE approaches and, finally, sev- eral future issues are outlined in Section 7. 2. Theoretical Background