Student progress assessment with the help of an intelligent pupil analysis system

Students and lecturers would like to know how well students have learned the study materials being taught. A formal test or exam would cause needless stress for students. To resolve this problem, the authors of this article have developed an Intelligent Pupil Analysis (IPA) System. A sufficient amount of studies worldwide prove an interrelation between pupil size and a person's cognitive load. The obtained research results are comparable with the results from other similar studies. The original contribution of this article, compared to the research results published earlier, is as follows: the IPA System developed by the authors is superior to the traditional pupil analysis research due to the integration of pupil analysis with subsystems of decision support, recommender and intelligent tutoring systems and innovative Models of the Model-base, which permit a more detailed analysis of the knowledge attained by a student. This article ends with a case study to demonstrate the practical operation of the IPA System.     

Ultrasonic air-coupled testing of square-shape CFRP composite rods by means of guided waves

In aerospace industry, one of the most important parts of gliders and motor-gliders is a lightweight longeron reinforcement made of carbon fibre reinforced plastics (CFRP) rods, known as Graphlite SM315 composite. During manufacturing, the rods as constructional elements are glued together in epoxy-filled matrix in order to build the arbitrary spar profile. The defects present in single rods such as breakage of fibres, multiple delaminations due to the lack of bonding between fibres and reduction in density affect essentially the strength and the fail-safety of the overall construction.The aim of the present work is to investigate the effects (transmission, reflection, scattering and mode conversion) of guided waves propagation along a square-shape CFRP rod in the case of contactless excitation/reception and interaction with region of multiple delaminations applying the numerical model and performing experiments.The square-shape CFRP composite rods possessing internal artificial delamination type defects have been investigated by numerical modelling and experiments employing the developed air-coupled technique (pitch-catch set-up) for cases of conventional transmission and advanced back-scattering configurations. Numerical predictions of guided wave interaction with a multiple delamination type defect in a CFRP composite rod have been made and the interaction mechanism explained. It is possible to conclude, that the actual sizes of the internal defects have been clearly detected using reception of the back-scattered waves over the edges of the defective regions only.     

The Capability Assessment of the Spectrum Decomposition Technique for Measurements of the Group Velocity of Lamb Waves

The ultrasonic guided waves are dispersive waves characterized by the phase and group velocities dispersion curves. In order to use guided waves in various industrial applications, their parameters must be known. Since these guided wave velocities depend on the frequency and thickness of the material, they propagate differently comparing to bulk ultrasonic waves. Therefore, to analyze the parameters of such waves, new measurement techniques should be proposed and possibilities of their application have to be investigated. In this paper possibilities to measure the group velocity based on the spectrum decomposition approach are presented. The investigations are carried out using the simulated and experimental signals of Lamb wave propagating in a 2 mm thickness aluminium plate. The two fundamental modes \(\hbox {A}_{0}\) and \(\hbox {S}_{0}\) are selected. Using the proposed technique, segments of the group velocity dispersion curves have been reconstructed and compared with the dispersion curves calculated by the SAFE method to estimate errors. Accordingly to the obtained lower absolute and relative errors, an optimal set of narrowband filters with bandwidth from 20 kHz up to 100 kHz for the \(\hbox {A}_{0}\) mode and from 80 kHz up to 160 kHz for the \(\hbox {S}_{0}\) mode are proposed. Applying the proposed optimal frequency sets of narrowband filters for the experimental signals, segments of the group velocity dispersion curves for both modes are reconstructed. The average relative error for the \(\hbox {A}_{0}\) mode is 1.7–2.2% (expanded relative uncertainty ± (2.2–2.8)%) and 0.78–1.2% (expanded relative uncertainty ± (0.5–0.8)%) for the \(\hbox {S}_{0}\) mode.     

Application of the ultrasonic pulse-echo technique for quality control of the multi-layered plastic materials

The main aim of the ultrasonic pulse-echo technique application for quality control is to characterize the internal structure of the object under investigation. The advantage of such technique is a possibility to perform non-contact and one-side access measurements, and to investigate the internal structure of multi-layered materials as well. The presented novel application of the ultrasonic pulse-echo technique for characterization of the multi-layered plastic materials covers the complete attenuation measurement in the frequency domain and is based on ill-posed Tikhonov regularization task for each layer separately. The law of the frequency-dependent attenuation has been estimated from the inverse transfer function approximation in the frequency domain. Phase velocity dispersion curves have been estimated in two ways: from the experimental signal phase spectra and from the causal Kramers–Kronig relations. The developed method enables to predict waveforms of the reflected signals from the interfaces of the individual layers in on-line mode.According to this approach, the step-by-step iterative analysis has been performed for each layer using the information about the previous layers. During each step, the acoustic properties of an individual layer, such as density, absorption, ultrasound velocity and phase velocity dispersion, have been recovered using numerical optimization. Optimization has been performed comparing the real ultrasonic signal, reflected by multi-layered object, with the simulated response of the model. The comparison of the predicted waveforms with the experimental ones has shown a good correspondence.     

Application of the ultrasonic characterization methods for highly attenuating plastic materials

In this paper, prediction of the back surface reflection, which is based on attenuation and phase velocity dispersion estimation method, in highly attenuating plastic (polyvinylidene fluoride—PVDF) has been described. Estimation of the attenuation law is based on the inverse transfer function of the object approximation in the frequency domain. The oscillating character of the inverse transfer function of the highly attenuating plastic material gives rise to an ill-posed problem for approximation. It has been solved in two ways: application of the Tikhonov regularization process and iterative adjustment of the approximation parameters. The estimated attenuation coefficient α₀ and power n have been used for calculation of phase velocity dispersion using the Kramers–Kronig relations and having attenuation coefficient measured at single-frequency value.The reconstructed waveforms of the ultrasonic back surface reflections using the estimated attenuation and phase velocity dispersion curves have been presented and compared with the experimental one.     

Application of ultrasonic guided waves for non-destructive testing of defective CFRP rods with multiple delaminations

One of the most important parts of gliders is a lightweight longeron reinforcement made of carbon fibre reinforced plastic (CFRP) rods. During manufacturing, in order to build the arbitrary spar profile, these small diameter (few millimetres) rods are glued together into epoxy filled matrix. Still, defects present in the rods, such as break of fibres, multiple delaminations due to lack of bonding and reduction in density affect construction strength markedly and are extremely complicated to eliminate. Therefore, appropriate non-destructive testing techniques intended for carbon fibre rods should be applied prior to gluing them together.The aim of the present paper is to analyse development possibilities of NDT technique based on application of ultrasonic guided waves and intended for CFRP rods that are used for aerospace applications and are defective with multiple delaminations.The regularities of ultrasonic guided wave propagation in a defective CFRP circular-shape rod with multiple delaminations have been investigated using 3D numerical simulations, finite difference and finite element models. The corresponding experiments have been conducted as well. Based on leaky wave suppression over a defective region due to the weak vertical component of particle displacements, the mechanism of guided wave interaction with the region of multiple delaminations is explained from the ultrasonic NDT viewpoint.