The performance of machine learning algorithms is conditioned by the availability of training datasets, which is especially true for the field of nondestructive evaluation. Here we propose one ...reconfigurable specimen instead of numerous reference specimens with known, unchangeable defect properties, which are usually complicated to fabricate. It consist of a shape memory polymer foil with temperature-dependent Young’s modulus and ultrasound attenuation. This open a possibility to generate a reconfigurable defect by projecting a heating laser in the form of a short line on the specimen surface. Ultrasound is generated by a laser pulse at one fixed position and detected by a laser vibrometer at another fixed position for 64 different defect positions and 3 different configurations of the specimen. The obtained diversified datasets are used to optimize the neural network architecture for the interpretation of ultrasound signals. We study the performance of the model in cases of reduced and dissimilar training datasets. In our first study, we classify the specimen configurations with the defect position being the disturbing parameter. The model shows high performance on a dataset of signals obtained at all the defect positions, even if trained on a completely different dataset containing signals obtained at only few defect positions. In our second study, we perform precise defect localization. The model becomes robust to the changes in the specimen configuration when a reduced dataset, containing signals obtained at two different specimen configurations, is used for the training process. This work highlights the potential of the demonstrated machine learning algorithm for industrial quality control. High-volume products (simulated by a reconfigurable specimen in our work) can be rapidly tested on the production line using this single-point and contact-free laser ultrasonic method.
Air-coupled ultrasound sensors have advantages over contact ultrasound sensors when a sample should not become contaminated or influenced by the couplant or the measurement has to be a fast and ...automated inline process. Thereby, air-coupled transducers must emit high-energy pulses due to the low air-to-solid power transmission ratios (10
to 10
). Currently used resonant transducers trade bandwidth-a prerequisite for material parameter analysis-against pulse energy. Here we show that a combination of a non-resonant ultrasound emitter and a non-resonant detector enables the generation and detection of pulses that are both high in amplitude (130 dB) and bandwidth (2 µs pulse width). We further show an initial application: the detection of reflections inside of a carbon fiber reinforced plastic plate with thicknesses between 1.7 mm and 10 mm. As the sensors work contact-free, the time of flight and the period of the in-plate reflections are independent parameters. Hence, a variation of ultrasound velocity is distinguishable from a variation of plate thickness and both properties are determined simultaneously. The sensor combination is likely to find numerous industrial applications necessitating high automation capacity and opens possibilities for air-coupled, single-side ultrasonic inspection.
Abstract We introduce a reconfigurable medium for the manipulation of elastic propagation properties of Lamb waves. It is based on a shape memory polymer (SMP) with temperature-dependent Young’s ...modulus. Waves are excited by a laser pulse and detected by a laser vibrometer. A two-dimensional temperature field is controlled by a scanning heating laser. We use genetic algorithms to determine optimal distributions of mechanical properties for the following criteria: the wave amplitude has to be maximized at a given location and at the same time minimized at one or two other locations. Due to the reconfigurability of the medium, the optimization process is performed directly on the object of optimization, and not on a numerical or analytical representative, based on a direct measurement of the fitness. The optimized configuration makes the waves propagate away from (or around) the point of minimization towards the point of maximization. We improve the genetic algorithm by adapting the mutation probability of individual genes according to specific criteria, which depend on the surrounding genes (distributed in two dimensions). This provides the advantages: concentrating the mutations in the areas of genetic inconsistencies and counterbalancing the error of the fitness measurement. The method is applicable for the intelligent design of wave energy harvesters, ultrasonic transducers, and analogue wave computing devices.
V naši raziskavi smo pri konjih haflinške pasme v Sloveniji za lastnosti zunanjosti ocenjevali komponente (ko)varianc. V podatkovni zbirki je bilo skupaj 3371 živali, od tega smo jih v raziskavo ...vključili 600 (15 žrebcev in 585 kobil). Živali, ki smo jih vključili v analizo, so imele zapise desetih ocen in/ali devetih meritev ter znanega vsaj enega od staršev. Model je za vse ocenjene in izmerjene lastnosti vseboval leto ocenjevanja in/ali merjenja kot sistematski vpliv in naključni vpliv živali. Uporabili smo metodo omejene največje zanesljivosti (REML) v programu VCE. Pozitivno definitne matrike smo dobili s pomočjo postopka, ki se imenuje ukrivljanje matrik (ang. bending). Za ocenjene lastnosti so znašale heritabilitete od 0,40 za prednji del trupa do 0,78 za pasemsko značilnost. Heritabilitete za izmerjene lastnosti so se gibale med 0,20 za globino prsi in 0,62 za višino vihra, merjeno s palico. Genetske korelacije so bile v večini pozitivne. Najvišja genetska korelacija pri ocenjenih lastnostih je 0,92 med skupno oceno in zadnjim delom trupa. Med oceno pasemske značilnosti in oceno prednjih nog korelacije ni bilo. Pri izmerjenih lastnostih so bile genetske korelacije ocenjene od 0,38 med dolžino trupa in obsegom prsi do 0,95 med višino vihra, merjeno s palico in višino vihra, merjeno s trakom.
•Mechanical responses of a plate excited by laser pulses were effectively detected.•Thickness resonance frequency and time of arrival are independent parameters.•Reliefs of both plate surfaces were ...visualized together with the plate thickness.•One of the measured reliefs is unaffected by changes in the plate material.
Local ultrasonic resonance spectroscopy (LURS) is a new approach to material inspection, where the specimen is locally excited by a short mechanical impulse while its local mechanical response is recorded at a position nearby. The local material and geometrical properties can be extracted from the frequency spectrum of the response and visualized by performing a scan over the inspected area. In our experiment, the plate thickness and the reliefs of both plate surfaces (plate curvature) were obtained from thickness resonance and time of arrival analysis without physical contact to the specimen. Ultrasound was generated on the specimen surface by a laser pulse. Local mechanical response of a carbon fiber-reinforced polymer plate with a thickness ranging from 0.6 mm to 4.3 mm was recorded with a broadband optical microphone in through-transmission setup. The precision of this arrangement greatly exceeded the precision of conventional methods limited by the ultrasound wavelength. For thicknesses in the range around 1 mm, standard deviations of up to several µm were achieved. An influence of the through-plate ultrasound velocity on the measured relief of the plate surface nearest to the optical microphone was eliminated by a joint evaluation of thickness resonance and time of arrival. Furthermore, we demonstrated that internal delaminations have an influence on the spectrum of the local mechanical response and can therefore be detected by LURS.
In the nineteenth and early twentieth century the Medžimurje horse played an important role as a draft and working horse in the river Mura region. Nowadays, this area is split between Hungary, ...Austria, Slovenia and Croatia. In the frame of the project "Management of traditional transboundary breeds on example of a nearly forgotten breed the Murinsulaner", we collected data for cold blooded horses similar to the Medžimurje horse. Horses of this type do not exist in Austria anymore, in Croatia they were registered as an authothonous breed »Medjimurje horse«, and in Slovenia and Hungary this horse has a special section in the stud book for cold blooded horses as a Medžimurje type of horse. The Slovenian part of the population of the Medžimurje horse is quite heterogeneous regarding body measures. With respect to the scoring system used in the above mentioned project, the majority of scored animals were classified as »desired« or »satisfactory«. In order to further develop or to preserve this type of horse or to form a consolidated breed we would have to make a breeding program which would prevent mating among related animals and to cooperate with neighbouring countries in the field of breeding and selection. The only hope to preserve this type of horse on the long term in the region is by using it as a tourist attraction for carriage riding and/or as a draft horse in agriculture in marginal regions.
The pedigree information of 3613 animals registered in the Slovenian Haflinger stud book from birth year 1905 to 2008 were analysed using PROC INBREED in SAS/ STAT with the purpose of analysis of ...inbreeding level in Slovenian Haflinger population. Relationship (R) analysis was restricted to possible mating partners that had offspring born between 2004 and 2008 (i.e., 323 mares and 58 stallions). An increasing trend of inbreeding coefficients (F) was observed in recent years, although a generally low F was detected. Mean values of R between possible mating partners were mostly around zero, while maximum values ranged up to 0.63. The development of application that would ease the calculations of F and R could help breeders to prevent related mating in the future.
In the rapidly expanding composite industry, novel inspection methods have been developed in recent years. Particularly promising for air-coupled testing are cellular polypropylene transducers which ...offer better impedance matching to air than piezoelectric transducers. Furthermore, broadband transmitters (laser-induced ultrasound and thermoacoustic emitters) and receivers (optical microphones) have opened a completely new chapter for advanced contact-free ultrasound inspection. X-ray dark-field radiography offers a different approach to detect porosity and microcracks, employing small angle X-ray scattering. These innovative ultrasonic and radiographic alternatives were evaluated in comparison with well-established inspection techniques. We applied thirteen different non-destructive methods to inspect the same specimen (a carbon fiber-reinforced polymer laminate with induced impact damage): air-coupled ultrasound testing (using piezoelectric transducers, broadband optical microphones, cellular polypropylene transducers, and a thermoacoustic emitter), laser-induced ultrasound testing, ultrasonic immersion testing, phased array ultrasonic testing, optically excited lock-in thermography, and X-ray radiography (projectional absorption and dark-field, tomosynthesis, and micro-computed tomography). The inspection methods were qualitatively characterized by comparing the scan results. The conclusions are advantageous for a decision on the optimal method for certain testing constraints.
We introduce a Lamb-wave medium with tunable propagation velocities, which are controlled by a two-dimensional heating pattern produced by a laser beam. We utilized it to demonstrate that waves in an ...appropriately designed medium can propagate in the form of concentric squares, in contrast to the circular patterns typically emitted by a point source in a homogeneous two-dimensional medium. In order to avoid the concentration of wave energy in the middle of the sides of the squares, we propose two alternatives: a square wave that either rotates or exponentially decelerates as it expands. Additionally, we present how circular waves can be transformed into spiral waves utilizing the same tunable medium. The described experimental platform offers a new tool to generate shaped pulses for ultrasonic applications, which has the potential to improve the efficiency of energy and information transport.
Wakes are medium perturbations created by a moving object, such as wave patterns behind boats, or wingtip vortices following an aircraft. Here, we report about an experimental study of an uncharted ...form of parabolic wakes occurring in media with the group velocity twice larger than the phase velocity, as opposed to the conventional case of Kelvin wakes. They are formed by moving a laser spot on a thin plate, which excites a unique wake pattern made of confocal parabolas, due to the quadratic dispersion of the zero-order flexural Lamb mode. If the spatial dimensions are rescaled by the perturbation velocity and material constant, we obtain a single universal wake with constant parabolic focal lengths. We demonstrate an evanescent regime above the critical frequency where the wave components oscillate exclusively in the direction parallel to the perturbation path, with an opening angle of 90{\deg}. We define a dimensionless number analogous to Froude and Mach numbers, which determines whether the complete parabolic wake pattern will be excited by the moving source or not.
PDF
