Electrical Resistance Change Method Research Articles

Structural health monitoring of scarf bonded repaired glass/epoxy laminates interleaved with carbon non-woven veil

Bonded repair patches/joints often introduce vulnerabilities in composite laminates, making them prime candidates for structural health monitoring (SHM). In this study, stepped-scarf bonded joints were manufactured using glass fibre-reinforced epoxy laminates as representative repair patches, and a novel SHM approach through the electrical resistance change method was applied. To establish an electrically conductive path within the stepped-scarf joint, non-woven carbon fibre veils with areal weights of 10 g/m² and 20 g/m² were interlaid along the stepped bondline. Two types of tensile tests were performed. In the first set of tests, the stepped-scarf joints underwent monotonic quasi-static tensile loading until the bondline was completely fractured (catastrophic failure) and the change in electrical resistance was continuously monitored. The failure stress of the joint with a 10 g/ m² carbon veil was only marginally decreased (∼2 %) in comparison with that of the joints without a carbon veil, while the failure stress of the joint with a 20 g/m² carbon non-woven veil was considerably decreased (by ∼9 %). However, the joints with 10 g/m² and 20 g/m² carbon veils exhibited a significant change in electrical resistance (∼200 % and ∼1000 %, up to full failure, respectively). Simultaneously, the change in electrical resistance was used for the detection of damage initiation and progression, supported by digital images taken during the tests. In the second set of tests, the joints were subjected to a cyclic tensile loading/unloading regime and the change in electrical resistance was monitored. A significant amount of permanent change in resistance during the unloading phases (up to 120 % in the bondline with a 20 g/m² veil) was observed, providing insights into the laminate and bondline damage evolution. In addition, thermal images obtained with the joule heating method in the cyclic tensile tests were used to confirm the damage detected with the electrical resistance change method. Moreover, the micrographs from the fracture surfaces indicated that the variations in electrical resistance change are largely caused by damage occurring within or near the carbon veils. In conclusion, the results demonstrate that the presented SHM approach, which incorporates carbon non-woven fibre veils within non-conductive laminate composites, holds promise for monitoring damage initiation and propagation in repaired composite laminates as well as adhesively bonded composite laminate joints, without adversely influencing the structural integrity of the bondline.

Non-destructive health monitoring of glass fibre epoxy composites under fatigue loading using electrical resistance change method

ABSTRACT This study investigates the effect of stress amplitude on the damage sensing characteristic of glass fibre reinforced (GFRP) composites under fatigue loading using the electrical resistance change (ERC) method. The electrical conductivity of GFRP composites was achieved by incorporating 0.3 wt.% multi-walled carbon nanotubes (MWCNTs) into epoxy resin by ultrasonication method. In-situ electrical resistance measurements during fatigue tests of MWCNT-filled GFRP (MWNCT/GFRP) composites were conducted at two different stress amplitudes, S = 0.6 and S = 0.5. The average stiffness losses at failure were observed as 28% and 25% for S = 0.6 and S = 0.5 respectively. The corresponding ERC ratios at failure were found as 153% and 59% for S = 0.6 and S = 0.5, respectively. A two-parameter Weibull analysis, based on the ERC ratios corresponding to 40%, 60%, 80%, and 100% (failure) fatigue life, was implemented to establish reliability curves at the two stress amplitudes. The ERC ratios at failure with a 95% reliability for S = 0.6 and S = 0.5 were determined as 64% and 23%, respectively. Finally, the remaining fatigue life and the stiffness loss of composite specimens at the ERC ratios corresponding to various Weibull reliability were found for both stress amplitudes.

Impact localization of composite laminates based on weight function compensation localization algorithm of thin film sensors

ABSTRACT Composite structures are sensitive to impact damage in practical engineering. Electric resistance change method (ERCM) is an ideal technique for damage monitoring of composite structures. Due to the anisotropy of fiber-resin matrix composites, impact location monitoring is difficult, and research on impact location of fiber composite laminates (FRPs) is limited. A preparation method of MXene/CNT/CuNps thin film sensor is proposed. According to the modeling simulation and theoretical calculation, the resistance change characteristics of the thin film sensor are obtained, the relationship between the impact distance and the resistance change is established, and the sensor array is designed. A three-point localization algorithm and a weight function compensation localization algorithm are proposed, which can improve the imaging accuracy of the impact position. The impact point location was observed and analyzed using ultrasonic C-scan technology. The results show that the weight function compensation positioning algorithm can accurately locate the impact of the composite structure, and the error in the X direction is 7.1%, the error in the Y direction is 0.03%, which verifies the effectiveness of the method.

A statistical approach to predict fatigue failure of leaf springs manufactured with nanotube incorporated epoxy‐woven glass fiber composites

AbstractIn this study, a statistical approach was developed to predict fatigue failure of laminated composite leaf springs prepared with carbon nanotube (CNT) filled epoxy/woven glass fibers. Electrical resistance change method and the Weibull analysis were adopted to develop a statistical approach. The electrical conductivity for successful application of health monitoring of leaf springs was achieved by dispersing 0.4 wt% of CNTs into epoxy resin. In‐situ monitoring of damage in composite leaf springs during fatigue tests applied as cyclic flexural deflection was carried out at nine different displacement ratios. The critical fatigue cycle and the corresponding change in electrical resistance were determined at each displacement ratio. Then, the critical electrical resistance change to cyclic fatigue was found 0.15% with 95% reliability by the Weibull analysis. The average fatigue life and the average strength loss corresponding to the 0.15% resistance change ratio were found to be 48.33% and 9.88%, respectively. The reported statistical concept based on the monitoring of change in electrical resistance during deflection can be successfully employed as a useful tool to predict safety limits of composite structures subjected to fatigue loading, especially in aerospace industry.

Electrical-mechanical behaviors of three-dimensional braided composites under three-point bending

Electrical responses of three-dimensional braided composites under mechanical loads are important for the design of structural health monitoring in real time. Here we reported electrical properties and electrical-mechanical behaviors of three-dimensional braided composites with different braiding angles under three-point bending load, and investigated the correlation between electrical resistance and damage of the three-dimensional braided composites. We found that change of resistance reflected damage modes of the composite. In addition, we proposed an electrical-mechanical model to explain the resistance changes of three-dimensional braided composites based on the Weibull distribution function. The results of the model verify the effectiveness and rationality of the experimental results under bending load, which provides a theoretical basis for the structural health monitoring of three-dimensional braided composites through a electrical resistance change method.

Self-Monitoring of Damage Evolution in Asphalt Concrete Based on Electrical Resistance Change Method

Abstract Asphalt pavements expose early damage during their service life. The early damage grows internally until it accumulates and transforms into macro-damage that leads to structural failure. To promote real-time monitoring of internal damage evolution in asphalt pavements, this study proposes an electrical resistance change (ERC) method that exploits the piezoresistive properties of conductive asphalt concrete as a nondestructive testing technique capable of detecting microstructural defects. For this purpose, the traditional asphalt mixtures were first made electrically conductive by adding carbon fibers and iron tailing aggregates as conductive aggregates to satisfy the piezoresistivity requirements. Secondly, piezoresistivity experiments were performed by applying cyclic tensile force in fatigue and progressively increasing mode. The self-monitoring ability of damage evolution was assessed based on the correlation between the fractional change in electrical resistance (FCR), displacement, and damage degree for each mode of the force application. It was observed that under fatigue mode, the FCR and displacement increase upon loading and decrease reversibly upon unloading in each cycle. Compared with the displacement, the FCR exhibits partial reversibility upon unloading, indicating damage initiation in each cycle. The damage grows with the number of loading cycles until it accumulates in the elastic regime and gradually affects the load-carrying capacity of the mixture. Under a progressively increasing mode, the mixture exhibits a good correlation between the FCR and force in the elastic regime, ensuring real-time monitoring of internal micro-damage. However, the FCR develops a nonlinear correlation with the force in the inelastic regime that reflects damage to the conductive network and eventually structural failure. In summary, the ERC method provides real-time monitoring of microstructural defects that manifest as early damage and gradually transform into macro-damage under repeated traffic loads.

3R Composites: Knockdown Effect Assessment and Repair Efficiency via Mechanical and NDE Testing

In this study, the mechanical properties of purposefully synthesized vitrimer repairable epoxy composites were investigated and compared to conventional, commercial systems. The purpose was to assess the knockdown effect, or the relative property deterioration, from the use of the vitrimer in several testing configurations. Mechanical tests were performed using ILSS, low-velocity impact, and compression after impact configurations. At modeled structure level, the lap strap geometry that can simulate the stiffening of a composite panel was tested. Several non-destructive evaluation techniques were utilized simultaneously with the mechanical testing in order to evaluate (i) the production quality, (ii) the damage during or after mechanical testing, and (iii) the repair efficiency. Results indicated that the new repairable composites had the same mechanical properties as the conventional aerospace-grade RTM6 composites. The electrical resistance change method proved to be a valuable technique for monitoring deformations before the initiation of the debonding and the progress of the damage with consistency and high sensitivity in real time. In terms of repair efficiency, the values ranged from 70% to 100%.

Nonlinear behavior mechanism of change in electrical resistance on 3D printed carbon fiber / PA6 composites during cyclic tests

The aim of this paper is to investigate the cause of nonlinear behavior mechanism of change in electrical resistance of 3D printed carbon fiber reinforced plastics (CFRP) due to tensile loading. The electrical resistance change method is a nondestructive testing method that helps detect strain and damage. In previous research for electrical resistance change method applied to 3D printed CFRP, the change in electrical resistance is different compared with the one of conventional CFRP. The behavior makes health monitoring difficult, and the phenomenon needs to be clarified. In this research, we focused on the electrode fabrication method and viscoelasticity effect during cyclic tests. Polishing and laser processing are used as surface treatments for electrode fabrication. Consequently, the treatments are found to affect the reverse piezo-resistivity. In addition, the decrease in electrical resistance depends on the test speeds of cyclic test. The viscoelasticity is found to affect the nonlinear behavior.

Impact damage localization and mode identification of CFRPs panels using an electric resistance change method

Electric resistance change method (ERCM) has shown potential as a good candidate for performing in-situ damage sensing in carbon fiber reinforced plastic composites (CFRPs), however, studies that investigated the impact damage localization and mode identification of CFRPs were limited. This paper investigates a novel ERCM technique for damage localization and mode identification in CFRPs under normal impact load with energies of 50 and 80 J. The impact damage characteristics of the CFRPs were firstly analyzed, and the corresponding electrical resistance was measured. A damage localization algorithm was designed according to the resistance characteristics obtained by the theoretical calculation and simulation. A relationship between CFRPs thickness and the electrical resistance was built, and damage modes were analyzed with assistance of computed tomography observations. Results show that the electric resistance changes between electrode networks could be used to help imaging the damage positions with a very high accuracy (6% error). The linear relationship between the electrical resistance, incident energy, and the panel thickness could be adopted to predict the damage modes in CFRPs after impact.

Real-time monitoring of fatigue damage by electrical resistance change method

In this work, Electrical Resistance Change (ERC) was measured during fatigue tests of notched metal specimens at different stress levels. The comparison of the resistance data measured at initial and different phases of fatigue tests showed the existence of measurable variations related to fatigue damage progression: in particular the resistance first decreases, in the initial stages of loading, and subsequently, starting approximately from 30 to 40% of fatigue life, presents a quick increase, which could be associated to the irreversible phenomena induced by fatigue load cycles. The applied experimental method proved to be valid for studying the evolution of fatigue damage.

Reverse piezo-resistivity of 3D printed continuous carbon fiber/PA6 composites in a low stress range

The 3D printing of carbon fiber reinforced thermoplastics (CFRTPs) is crucial in many fields such as aerospace engineering and electrical motorbikes. Structural health monitoring of 3D printed CFRTPs is important for its practical application. CFRTPs are monitored using the electrical resistance change method, but this method has not been applied to 3D printed CFRTPs. In this study, we used the electrical resistance change method to monitor CFRTPs. The electrical properties were measured in terms of fiber orientation and electrode distance. In addition, a cyclic test was performed to reveal the change in the electrical resistance. Our results reveal that the volume resistance along the 90° orientation has a larger standard deviation than those for the other specimens. The change in resistance exhibited reverse piezo-resistivity at the low stress range in the cyclic tests. The reverse piezo-resistivity occurred due to fiber waviness, which is generated during the 3D printing process.

Structural health monitoring of carbon fiber reinforced matrix by the resistance variation method

In this work, electrical resistance change method is used for carbon fiber reinforced thermoplastic polymers damage monitoring. The electrical resistance variation could be an interesting complementary to existing/classical damage monitoring methods. It is extremely attributed to electrical conductivity of composite material and it appears that enhancing the conductivity of materials, by the use of conductive nanofillers in our case, improves their sensitivity to mechanical loading. Carbon fiber reinforced thermoplastic polymers with different nanofillers types and concentrations were manufactured and tested in tensile loading. Concentration of 0 and 8 wt% of carbon black and 2.5 wt% of carbon nanotubes were used with Polyamide 6 sheets as matrix. Nanofillers weakening effect was discussed according to their concentrations and types. The acoustic emission, digital image correlation and in-situ microscopy were also recorded during testing. A correlation between all these signals and the evolution of the electrical resistance of the composites during the tensile loading was performed. It was found that CB enhances sensitivity of carbon fiber reinforced thermoplastic polymers to damage detection, especially delamination. For the carbon nanotubes, results are less promising. A discussion is held about the nanofillers concentration influence.

Numerical Analysis of Electrodes Position for Delamination Detection by Using Electric Resistance Change Method

The electric resistance method for detection of the internal delamination in laminated carbon-fiber-reinforced polymers composite material has been explored in the paper. The effect of spacing between electrodes on the crack detection efficiency has been investigated. The problem has been solved by the method of planning of the experiment and response surface method by using 2-D finite element model. The distance between the electrodes and the crack length have been selected as the parameters of the study. The results of the numerical solution have been obtained by using the four probe method of measurement of the surface and oblique electrical resistance. The optimal distance between the inner and outer probes for the effective detection of the crack and delamination has been determined. The influence of the distance between the internal and external probes has been identified to have greater effect on the detection of the crack than the distance between the internal probes.

In situ fabrication of copper electrodes on carbon-fiber-reinforced polymer (CFRP) for damage monitoring by printing and flash light sintering

The electrical resistance change method (ERCM) is a promising method for structural health monitoring (SHM) of composites. In this work, copper (Cu) nano-ink was printed and successfully sintered on carbon-fiber-reinforced polymer (CFRP) substrate for damage sensing via a flash light sintering method. Before printing, surface-polished CFRP substrate was flash light treated to remove remnant epoxy between carbon fibers. Then, Cu nano-ink was formulated and printed on the CFRP substrate, and the printed Cu nano-ink patterns were sintered within a few milliseconds using a range of flash light irradiation energies. A two-step flash light sintering method to reduce contact resistance between the Cu electrode and CFRP interface was further investigated. Fabricated Cu electrodes were characterized using scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). Using a two-step sintering approach, we fabricated Cu electrodes on CFRP with low contact resistance (0.93 Ω), high durability, and no mechanical degradation of CFRP substrate.

Experimental investigation of fatigue destruction of CFRP using the electrical resistance change method

CFRP (Carbon Fiber Reinforced Polymer) composites are one of the most popular composites used as the structural material in high-loaded structures. Important disadvantage of this material is the difficulty in predicting the time of fatigue destruction. These changes decrease the stiffness of the structure, but in practice it is usually not possible to measure it. Therefore, it is necessary to find another method to determine the moment when destruction of the composite begins. In this paper, one of possible methods – measuring of the electrical resistance change was investigated. Bending beam-shape specimens were tested under static and periodically varied load. Bending moment, deflection in the center of the probe and 8 voltages were measured. Performed experiment shows that measuring of the electrical resistance change provides better information about destruction of CFRP structure than a measure of the bending moment.

Flexural fatigue behavior of 2D cross-ply carbon/carbon composites at room temperature

The primary goal of this research was to study the flexural fatigue behavior and enhancement of residual strength in 2D cross-ply carbon-fiber-reinforced carbon (C/C) composites. Flexural fatigue behavior was simultaneously examined under two stress levels (70% and 65%) by electrical resistance change (ERC) method. Residual strength and fracture behavior of C/C composites were investigated as well. The results show that shapes of electrical resistance change rate–fatigue cycle curves could reflect applied stress levels and damage types during cyclic bending load. The enhancement of residual strength only occurs at a stress level lower than the fatigue limit, and the property of enhancement decreases with the increase of fatigue cycles. In addition, three-point bending fracture in both unfatigued and fatigued specimens is of delamination mode and cyclic loading cannot enhance both bending strength and plasticity at the same time.

Instant electrode fabrication on carbon-fiber-reinforced plastic structures using metal nano-ink via flash light sintering for smart sensing

The electrical-resistance-change method (ERCM) is a potential smart-sensing technique for carbon-fiber-reinforced plastic (CFRP) structures. However, a practical way to fabricate electrodes on CFRP structures, such as ink-jet printing with metal nano-inks, is necessary to reduce the time required for the process. As metal nano-inks can be sintered in a few milliseconds under ambient conditions using white-flash-light irradiation from a xenon lamp, the parameters of flash-light sintering such as light energy, duration, and number of pulses were investigated. The light intensity, which is the light energy divided by duration, was found to be an indicator of whether low electrical resistance was attained along with strong adhesion to the CFRP plate. The contact resistance between the electrode and CFRP plate was also examined in a tensile test to confirm the durability. The electrode sintered by flash light with the properly selected parameters exhibited high quality and strain monitoring capability.

Monitoring the damage evolution of flexural fatigue in unidirectional carbon/carbon composites by electrical resistance change method

This paper reported simultaneous monitoring damage evolution of flexural fatigue in unidirectional carbon-fiber-reinforced carbon composites (C/C composites) by electrical resistance change (ERC) methods. The degree of irregularity in electrical resistance changes increased with stress levels increasing. The shapes of electrical resistance change rate–fatigue cycle curves can reflect stress levels and damage types of tested samples: sawtooth shapes reflected delamination at a higher stress level; and “peak” shapes reflected inner damages in one fiber bundle at the fatigue limit stress level. In addition, the similarity of initial electrical resistance–fatigue life curve and S–N curve was observed clearly. In summary, ERC methods can monitor the damage evolution and qualitatively estimate the fatigue life of unidirectional C/C composites.

121 電気抵抗変化法によるC/C複合材料の損傷評価(材料力学II)

121 電気抵抗変化法によるC/C複合材料の損傷評価(材料力学II)

Delamination identification of CFRP structure using discriminant analysis via the support vector machine

This paper is about damage diagnosis using discriminant analysis via the support vector machine(SVM). For evaluation of reliability of the structure, condition of the structure is divided to several condition levels by the threshold in many cases. At these cases, identification of the damage as the discriminant levels is sufficient for the damage identification model. This paper is focused on the improvement of the identification accuracy of damage identification using discriminant analysis. SVM is one of linear learning machine which conduct 2 groups discrimination which used for discriminant analysis and pattern recognition. SVM is enable to use for the analysis which the boundary of the groups has nonlinear relation. About the damage identification, measurement data is affected by location and stage of the damage and simple linear discrimination is difficult to adopt as the method. In this paper, SVM is applied to identification of a delamination cracks in CFRP beams using the electric resistance change method. The effectiveness of this method is investigated from FEM model of electric resistance change due to the growth of the delamination crack. As a result, with weighted method for avoiding the risk side evaluation, the risk side evaluation which cause degradation of the reliability of structure was reduced.