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Lamb Wave Propagation and Low Velocity Impact Damage Identification in Carbon Fiber Reinforced Plastic (CFRP) Laminates
No full textIn the present work, A0 Lamb wave mode is used to identify the impact damages in the composite plate structures. Different bi-directional carbon fiber reinforced plastic (CFRP) laminated plates are considered with surface mounted PZT sensors. The Lamb waves are generated using the PZT patches, mounted at the center of the plate and the propagating Lamb waves are subsequently captured by the PZT sensors, arranged in a circular array configuration. The damages are introduced in the plates using a low velocity impact test facility with different intensity and the impact damages are then identified through Lamb wave technique. Different CFRP plates are scanned using Laser vibrometer in order to examine the Lamb wave propagation. A 3.5 cycle windowed signal of 35 KHz frequency is used to generate Lamb wave in the plate structure. It is noticed that, the wave dynamics and moving patterns are distinctly different in various CFRP plates. The wave propagation pattern is elliptical in case of cross ply and angle ply laminated plates, whereas in multi directional composite plate the wave propagates in nearly circular form. Further, Lamb waves propagate faster in fiber direction compared to non-fiber direction in all the three plates. This is evident because CFRP plates are made of bi-directional pre-preg where fibers are oriented in 0 and 90 degrees (cross ply) and ± 45 degrees (angle ply). In case of multi directional plate, the fibers are oriented in 0, 90 and ± 45 degrees which lead the waves to propagate in circular form. The travelling speed of the waves along the fiber direction and matrix is different which is clearly seen from the experimental evidence captured through Laser Doppler Vibrometer (LDV). With these identified, distinguishable patterns, one can reasonably assess fiber dominated failures or matrix-based failures. Further, in the CFRP laminated plate, BVID's are identified with damage identifying parameters using Lamb wave technique but C-Scan, a non-destructive evaluation technique could not able to detect the BVID. The damaged CFRP plates are subsequently scanned using LDV, in order to examine the Lamb wave propagation in damaged area. It is evident that, on-line data capturing is the right approach to monitor the impact event; however, the presence of damage, if any due to impact event may be diagnosed by the sensors, placed close to that particular event. The proposed Lamb wave-based methodology using PZT sensor network can be applied for impact related damage detection in real time applications
Synthesis, structure and ionic conductivity of nanocrystalline Ce1−xLaxO2−δ as an electrolyte for intermediate temperature solid oxide fuel cells
No full textLa-doped CeO2 nanoparticles of composition Ce1−xLaxO2−δ (0 ≤ x ≤ 0.1) have been studied here as prospective electrolytes for intermediate temperature solid oxide fuel cells (IT-SOFCs). They were synthesized by auto-combustion method and the powder samples were calcined at 700 °C to get ultrafine nanocrystalline particles. They were characterized by XRD, Raman, FTIR, XPS, DRS, FESEM/EDX, particle size analyzer and ac-impedance techniques. Ionic conductivity was measured from 350 − 750 °C. The Ce0.90La0.1O2−δ (0.1 LDC) and Ce0.95La0.05O2−δ (0.05 LDC) showed a maximum conductivity of 8.89 × 10−3 and 8.32 × 10−3 S cm−1 at 700 °C, respectively. The σt of 0.1 LDC = 1.01 × 10−2 S cm−1 at 750 °C. The activation energy of 0.1 LDC and 0.05 LDC was found to be 0.70 eV and 0.87 eV, respectively. These values are higher than those reported for La-doped CeO2 in literature. The SOFC performance with 0.05 LDC as electrolyte showed open circuit voltage of 0.81 V and maximum power density of 41 mW cm−2 at 650 °C using hydrogen as fuel
A Brief Review on the Fatigue Behavior of Continuous Fiber Reinforced Thermosetting Epoxy Polymer Based Nano
No full textThermosetting epoxy polymer reinforced with continuous fibers, well known as fiber-reinforced polymer (FRP) composites are extensively used in structural applications because of their high specific strength and stiffness. Structural components made from FRP composites experience fatigue loads in service and hence, possessing high fatigue life is one of the important requirements in these materials. Recent efforts made to enhance the fatigue properties of FRP composites by incorporating micro and nano-sized fillers in the epoxy matrix have led to some promising results. Composites containing nano-sized fillers in the epoxy, known as polymer nanocomposites are gaining importance from the viewpoint of enhanced mechanical properties. The presence of nano fillers improve the fatigue life of pure epoxies and also FRPs with nano-modified epoxy matrix. Parameters such as nanofiller type, size, shape, volume fraction and uniformity of dispersion in the epoxy, influence the fatigue properties of nanocomposites significantly. In this paper, the effect of various types of nano fillers on the fatigue life of bulk epoxies and FRPs is briefly reviewed. The mechanisms for observed enhancements in fatigue properties and fatigue behavior under spectrum fatigue loads are also discussed. Effect of environment on the fatigue behavior of nanocomposites is briefly highlighted. The current limitations and the future course of research required are also highlighted
Vibration analysis of gearbox fault diagnosis using DWT and statistical features
No full texthe gearbox is one of the critical subsystems in any rotating machinery, which plays a major role in mechanical power transmission in terms of speed and torque. It plays a vital role in patching different industrial functionalities. The advent of developing different gear technologies and the requirement to fulfil the desired mechanical benefits lead to add more importance to the gearbox health condition monitoring from various types of fault occurrences at an earlier stage. This paper presents the vibration analysis of gearbox fault diagnosis using discrete wavelet transform (DWT) and statistical features. The fault diagnosis has presented with an emphasis in time domain followed by two different approaches. The approach-1 is illustrated as windowing of raw signal, feature extraction and feature classification using support vector machine (SVM). The approach-2 is illustrated as after windowing the raw signal - each window of original vibration signal has converted into wavelet coefficients reconstructed signals (without leaving the time domain) using discrete wavelet transform (DWT) at different levels of decomposition followed by approach-1. The fault classification accuracy of SVM are presented with 100 Monte Carlo runs to validate the consistency in the accomplished result. By observing the success rates in two approaches, it is clear that approach-2 with wavelet coefficient’s reconstructed signal is providing better classification accuracy, which can be practically deployed to diagnose the gearbox fault
Wideband, polarization independent electromagnetic wave absorber using cross arrow resonator and lumped SMD resistors for C and X band applications
No full textIn this work, a polarization independent and wideband electromagnetic (EM) waves absorbing frequency selective surface (FSS) structure is presented. The unit cell of the proposed FSS consists of an assembly of cross arrow resonators with four SMD resistors mounted on it, to enhance the absorbance bandwidth. This unit cell also possesses a four-fold symmetry which makes it polarization insensitive. The designed unit cell is compact with the length and width dimensions as 0.19λL × 0.19λL, and thickness of 0.13λL, where λL is the guided wavelength corresponding to the lowest operating frequency. The proposed absorber is theoretically and experimentally tested for its absorbance, cross-polarization level, and radar cross section (RCS) characteristics. The computer-aided simulation and practical measurements indicate that the proposed absorber offers more than 90% (with a fractional bandwidth of 93%) absorbance for normal incidence at 4.5–12.4 GHz frequency band. The cross-polarization reflection coefficient analysis indicates that the proposed FSS configuration behaves as an absorber and not a polarization convertor. The input impedance plot, surface current distribution, and E-field distribution of the unit cell were also analyzed and presented to understand the absorbance mechanism. The RCS of the proposed FSS is compared with the RCS of a reflective (metallic) sheet to analyze its suitability for practical applications (RCS reduction) within the working band. The 3D simulated and 2D calculated RCS results indicate that the proposed FSS is suitable for wideband EM wave absorber applications
Study on galling behaviour of HiPIMS deposited Mo/DLC multilayer coatings at ambient and elevated temperature
No full textGalling has been a severe concern in oil – gas, automotive, and nuclear sectors. SS 304 steel is used in these industries despite its low galling resistance because it possesses good corrosion resistance properties. The threads of bolt, nut or a tapped hole and fasteners made of SS 304 experience severe damage due to galling or cold working. Therefore, the galling characteristics of the coated SS 304 samples were studied against the uncoated counterpart. A multilayer coating of molybdenum (Mo) and diamond like carbon (DLC) was deposited through dual sputtering using a high power impulse magnetron sputtering (HiPIMS) power source for graphite target and pulsed DC power source for Mo target. The Mo/DLC multilayer coating was optimized for antiwear and low friction properties. The evaluation of friction properties was done through a nanotribometer. The galling samples of SS 304 steel were prepared following the ASTM G196 standard, and the optimized coating was deposited on the galling samples. The adhesion strength of the coating was analyzed with the help of a nanoscratch tester. The galling behavior of coated and uncoated samples was investigated at room temperature (RT) and 300 °C. Galling damage was quantified by calculating the galling area on the galled sample. Image processing and computer vision tools were used to calculate the galled area. The tribopair having coated (Mo/DLC multilayer coating on SS 304) and the uncoated sample (SS 304) showed lower galled area than the tribopair containing both uncoated samples in every test conditions. At RT the coated sample failed at 15 MPa, whereas the uncoated samples failed at 5 MPa. Similar type of results were obtained when the samples were tested at 300 °C. The characterization of the coating and the mechanism of galling were studied in detail with the help of Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nanoindentation, stereo-zoom optical microscopy, and scanning electron microscopy (SEM)
Distinguishing process - Impact of down milling and up milling in machining aluminium thin wall
No full textThe study aims to understand the deformation mechanics that occurs during down and up milling of aluminium thin wall fabrication. With cutting forces as inputs, material properties were defined by the Coffin-Manson relation and the Smith-Watson-Topper model. Hysteresis was found in the process of machining aluminium thin walls. Furthermore, the pattern of cutter loads differentiated the up and down milling through hysteresis. The finite element method was followed using ANSYS v14.5 software in the fatigue workbench to analyse the aspect. Down milling introduced both deflection and deformation. Conversely, up milling did not exhibit deflection. However, the Bauschinger effect and distinct fracture surfaces were diagnosed during up milling. By exploring the nature of hysteresis and fracture surfaces, the selection of down and up milling was made
Solvent casting-assisted synthesis of thermally responsive shape memory polymer and its composites
No full textThe present study illustrates a simple and universally applicable method of synthesizing a new thermal stimuli-responsive thermoplastic shape memory polymer (SMP) and its composites through solvent casting method followed by the hot-pressing technique using polymers like polyvinyl acetate, polysulfone and polystyrene. The process parameters have been optimized to get a uniform film without any phase separation. Polyaniline (PANI), Al2O3, TiO2 and their combinations with PANI such as Al2O3–TiO2, Al2O3–PANI, and TiO2–PANI have been used as fillers to obtain the shape memory polymer composites (SMPCs). Under the thermal stimulus, the shape recovery rate of the SMPC containing Al2O3–PANI hybrid filler was faster, having a quick response time (150 s) compared to the response time of the neat SMP (210 s). Moreover, the SMP containing Al2O3 + TiO2 filler exhibited a higher Young’s modulus (˃ 62%) compared to the neat SMP. The maximum stress of 37 MPa and 4.5% recoverable strain was observed in the SMP containing Al2O3 + TiO2 hybrid filler. Interestingly, no stored strain evolved upon cooling below Tg. The effect of physical aging on the mechanical and thermomechanical properties of SMP and its composites was studied. The synthesized SMP polymer is environmentally friendly and showed an excellent shape memory effect exhibiting a high Tg (~ 80 °C), self-healing property and good mechanical properties. Due to the multifunctional properties of the newly designed SMP and its composite, it may be a promising material for load-bearing applications
Machine learning augmented multi-sensor data fusion to detect aero engine fan rotor blade flutter
No full textFlutter-induced fatigue failure investigation of the fan blades of aero-engines necessitates extensive testing. During engine ground testing, strain gauges on rotor fan blades and casing vibration sensors were employed to investigate structural dynamic aspects. The correlation between strain sensor signals and fan casing vibration signals allowed the diagnosis of fluttering fan blades. For automated flutter detection during engine development testing, a machine learning-augmented information fusion methodology was developed. The method analyses casing vibration signals by extracting time-domain statistical features, intrinsic mode function characteristics through empirical mode decomposition, and recurrence quantification features. Feature vectors obtained from a relatively large set of engine tests were subjected to dimension reduction by applying machine learning techniques to rank them. Reduced feature vector space was labelled as "flutter"or "normal"based on the correlation of rotor strain gauge signals. In addition, the labelled feature vectors were employed to train classifier models using supervised learning-based algorithms such as Support Vector Machines, Linear Discriminant Analysis, K-means Clustering, and Artificial Neural Networks. Using only vibration signals from the casing, the trained and validated classifiers were able to detect flutter in fan baldes with a 99% probability during subsequent testing
A modified piecewise linear constant life diagram for fatigue life prediction of carbon fiber/polymer multidirectional laminates
No full textPrediction accuracy of constant life diagrams (CLDs) for fiber-reinforced plastics varies with the stacking, tensile/compression dominated failure, input S–N curves, the complexity of the plot, and so forth. The article's authors propose a modified piecewise linear CLD and compare its prediction accuracy with traditional piecewise and 2-segment anisomorphic CLD. The constant amplitude fatigue life data for three different carbon fiber reinforced polymer composites multidirectional laminates that is (+45, −45, +45, and −45)2S, (+45, −45, 0, and 90)2S, and (0, 90, 0, and 90)2S were generated at five different stress ratios (R = σmin/σmax) that is, R = 0.1 and 0.5 (T–T), −1 and critical stress ratio (T–C), and 5 (C–C). The proposed modified Piecewise linear CLD considers the critical stress ratio (UCS/UTS) as a definite input node. The prediction accuracy of the proposed CLD and others was evaluated using additional fatigue testing at random stress ratios and stress levels. The proposed CLD showed the highest prediction accuracy compared to Piecewise or Anisomorphic CLD. The non-linear CLD plotted using single S-N curve data may save time and effort but achieving absolute accuracy will ultimately depend on the stacking sequence