492 research outputs found
Experimental Study of Impact-Damage Detection in Composite Laminates using a Cross-Modulation Vibro-Acoustic Technique
No full textThe paper demonstrates the application of cross-modulation vibro-acoustic technique for impact-damage detection in composite laminates. A composite plate is monitored for damage resulting from a low-velocity impact. The plate is excited simultaneously with two harmonic signals: a slow amplitude-modulated vibration pumping wave and a constant amplitude-probing wave. The frequency of both the excitation signals coincides with the resonances of the plate. An electromagnetic shaker is used to introduce the pumping wave to the plate. Two surface-bonded, low-profile piezoceramic transducers are used for probing-wave excitation and measurement. The wave modulation is transferred from the pumping wave to the probing wave in the presence of impact damage. This effect is exhibited in a power spectrum of the probing wave by a pattern of sidebands around the carrier harmonic. The results show that the amplitude of the sidebands is related to the severity of damage. The study also investigates also the effect of boundary conditions on the result
Impact damage detection in light composite sandwich panels
No full textThe paper presents a comparative study on impact damage detection in light composite sandwich panels. Three different nondestructive testing methods were used to characterize damage in a test specimen that resulted from a controlled low velocity impact event. The analyzed test methods include the ultrasonic c-scan, vibrothermography and shearography. All considered techniques were positively verified for detecting damage in a sandwich panel. The paper gives details about the experimental procedures and equipment required to perform the tests
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A Theory of Skilled Memory
No full textA theory of mnemonic expertise is outlined along
with findings from initial tests. The expertise belongs
to a nonnal adult ( D D ) w h o developed a digit-span of
104 through extended practice. The theory describes
h o w mechanisms consistent with the principles of
skilled m e m o r y (Chase & Ericsson, 1982; Ericsson
& Staszewski, 1989) and identified by analyses of
DD's behavior, support his skill. Implemented as a
computational model, the theory assumes that distinct
knowledge structures mediate both DD's encoding of
short segments of trial lists as elaborate, well-
structured L T M representations and their retrieval in
several recall tasks. Current testing investigates the
model's ability to generate contextual codes, a class of
patterned m e m o r y elaborations experimentally shown
to improve DD's serial recall (Staszewski, 1990).
Given the same lists D D received, it successfully
generates over 8 0 % of the contextual codes in his
verbal reports. Because successful simulation of
contextual codes entails accurate simulation of
operations performed by first-order coding
mechanisms, results support theoretical assumptions
about the knowledge underlying DD's coding
operations. The model's overly powerful coding
suggests that more stringent architectural constraint
must be incorporated to rigorouslydemonstrate h o w
skilled m e m o r y can increase working m e m o r y
capacity in a normal cognitive architecture and
support expertise
Damage imaging in composites using nonlinear vibro‐acoustic wave modulations
No full textThe paper deals with the application of nonlinear vibro‐acoustic modulation technique for detection and localization of impact damage in a laminated composite plate. An imaging procedure—based on the nonlinear vibro‐acoustic modulation sidebands—is proposed. The procedure relies on simultaneous low‐frequency modal and high‐frequency ultrasonic excitations. Laser scanning vibrometry is used to analyze the amplitude of modulation sidebands in vibro‐acoustic responses. This analysis is performed for different positions on monitored structure to reveal the location and shape of damage. The method is illustrated using a simple example of impact damage detection in a composite plate. The experimental damage detection results are compared with the results obtained from the previously used approach on the basis of higher harmonic generation. The proposed method demonstrates better ability to locate damage in these comparative tests without the need to increase the measurement bandwidth to the higher harmonics regime. The work shows that the local defect resonance analysis can improve damage detection results of both compared approaches
Czasowo-częstotliwościowa analiza systemów zmiennych w czasie
No full textSystem identification is an important and often complex process in many areas of engineering. This process is not easy when parameters of the analysed system vary with time. In such cases classical methods fail to identify parameters properly. The work demonstrated in this paper deals with time-frequency representations for identification of natural frequencies of time-variant systems. The method involves the estimation of time-variant transfer functions. A "Crazy Climbers" algorithm - based on Monte Carlo simulations and Markov chains - is used to overcome difficulties associated with the method.Identyfikacja parametrów systemów mechanicznych jest bardzo ważnym i skomplikowanym procesem. Proces ten jest o wiele bardziej skomplikowany kiedy dotyczy systemów mechanicznych, których parametry zmieniają się w czasie. W takim przypadku klasyczne metody identyfikacji nie są w stanie poprawnie zidentyfikować tych parametrów. Artykuł zajmuje się wykorzystaniem reprezentacji czasowo-częstotliwościowych w celu identyfikacji częstotliwości drgań rezonansowych systemów o zmiennych w czasie parametrach. Jednym z kroków podczas estymacji funkcji przejścia jest dzielenie spektrum odpowiedzi przez spektrum wymuszenia, co często prowadzi do dzielenia przez wartości bliskie zera, a to prowadzi do nieskończonych (lub niezdefiniowanych) wartości. W celu ominięcia tego problemu zastosowano probabilistyczną metodę „CrazyClimbers”, opartą na symulacjach Monte Carlo oraz łańcuchach Markova
Dzieło z zakresu malarstwa pt. Lustro 3 / The 26th International Eastern Salon of Art in Lublin 2022 w Centrum Spotkania Kultur w Lublinie oraz Ogólnopolski Konkurs Malarski Moje Zakopane 2022 w Miejskiej Galerii Sztuki im. Wł. Hr. Zamoyskiego w Zakopanem
No full textNowatorski obraz M. Drozd - Witek (technika mieszana na płótnie, 100 x 120 cm, 2021 r.) został zakwalifikowany na jedną z największych i najważniejszych cyklicznych (tradycja sięga 1936 r.), interdyscyplinarnych prezentacji sztuki współczesnej, której celem jest ukazanie najistotniejszych tendencji i poszukiwań w obrębie formy i treści. Patronat nad Wschodnim Salonem Sztuki sprawuje Ministerstwo Kultury i Dziedzictwa Narodowego. Jury reprezentujące różne środowiska twórcze (prof. Błażej Ostoja Linski, ASP Warszawa - przewodniczący) wybrało spośród 325 zgłoszonych prac, 91. Uczestnicy wystawy pokonkursowej to m.in.: A. Romaniuk, J. Staszewski, P. Słota, A. Cwalina, P. Desperak, S. Cholewa. Obraz pokazano również (decyzja jury pod przewodnictwem prof. Wydziału Malarstwa ASP w Warszawie Arkadiusza Karapudy) na ogólnopolskiej wystawie pokonkursowej 3. Ogólnopolskiego Konkursu Malarstwa w Miejskiej Galerii Sztuki w Zakopanem. Początki Galerii sięgają 1911 roku. Prace prezentowali tam na przestrzeni lat m.in.: M. Jarema, T. Pągowska, M. Abakanowicz, J. Cybis, T. Kantor, T. Brzozowski, J. Duda Gracz, W. Hasior, Z. Beksiński, J. Nowosielski, J. Waltoś, S. Rodziński
Analysis of elastic nonlinearity for impact damage detection in composite laminates
No full textThis paper concerns the experimental analysis of nonlinear response features of a
composite laminate plate for impact damage detection. The measurement procedure is based on
the Scaling Subtraction Method (SSM) and consists in exciting the damaged specimen with two
sinusoidal signals at different amplitude. The linearly rescaled response signal at low amplitude
excitation is subtracted from the response at large amplitude excitation to extract the nonlinear
signatures. The latter are analysed in the time domain to infer the presence of damage. Results
are compared with frequency domain analyses using the nonlinear vibro-acoustic modulation
technique (NWMS). Changes in amplitude and phase as well as modulation effects of the
acquired responses are also monitored. Surface-bonded, low profile piezoceramic transducers
are used for excitation and sensing. Both measurements techniques are applied to detect barely
visible impact damage in laminate composite plate. Non-destructive penetrant-enhanced X-ray
inspections are carried out to characterize the extent of internal damage. The behavior of the
nonlinear features and the sensitivity of each technique are also investigated in the paper
Triple correlation for detection of damage-related nonlinearities in composite structures
No full textNonlinear effects in vibration responses are investigated for the undamaged composite plate and the composite plate with a delamination. The analysis is focused on higher harmonic generation in vibration responses for various excitation amplitude levels. This effect is investigated using the triple correlation technique. The dynamics of composite plate was modelled using two-dimensional finite elements and the classical lamination theory. The doubled-node approach was used to model delamination area. Mode shapes and natural frequencies were estimated based on numerical models. Next, the delamination divergence analysis was used to obtain relative displacements for delaminated plies. Experimental modal analysis test carried out to verify the numerical models. The two strongest vibration modes as well as two vibration modes with the smallest and largest motion level of delaminated plies were selected for nonlinear vibration test. The Fisher criterion was employed to verify the effectiveness and confidence level of the proposed technique. The results show that the method can be used not only to reveal nonlinearities, but also to reliably detect impact damage in composites. These resultsare confirmed using the statistical analysis
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