Natural frequencies and damping ratios of multi-layered laminated glass beams using a dynamic effective thickness

Multi-layered laminated glass panels are those with at least three monolithic glass layers and two viscoelastic interlayers. Multi-layered laminated glass panels are commonly used in floors, roofs and other horizontal glazing accessible to the public where a high level of security is required. Although the glass can be consider a linear-elastic material, the viscoelastic interlayers determine a non-linear behaviour of the laminated structure that must be taken into consideration. In this paper, an analytical model based on the effective thickness concept and the Ross, Kerwin and Ungar model is proposed to predict the dynamic behaviour of multi-layered laminated glass beam-like structures with different boundary conditions and at different temperatures. This analytical model allows the simplification of the calculus on this multi-layered laminated components opposite to use time-consuming numeric models. In this work, a study was carried out on a multi-layered laminated glass beam composed of three annealed glass layers and two polymeric interlayers. The analytical predictions are validated by numerical simulations and experimentally using operational modal analysis tests. The proposed model predicts the natural frequencies with errors less than 5% whereas the discrepancies in damping ratios are less than 50%

An effective thickness to estimate stresses in laminated glass beams under dynamic loadings

Finite element models for estimating stresses and displacements in laminated glass elements under dynamic loadings are very time-consuming because (1) many small 3D elements are needed to model accurately all the layers of the sandwich element and (2) the core usually shows a time and temperature dependent behaviour. In the last years, the concept of effective thickness using a quasi-elastic solution has got the attention of the research community because of its simplicity and reasonable level of accuracy achieved in the calculation of laminated glass elements under static loadings. In this paper, a dynamic effective thickness to estimate stresses in laminated glass beams under dynamic loadings in the frequency domain is derived using the correspondence principle. The analytical equations are validated by experimental tests carried out on simply supported and free–free laminated glass beams at different temperatures in the range 20–40 °

Dynamic effective thickness in laminated-glass beams and plates

In recent years, several equations have been proposed to calculate deflections and stresses in laminated-glass beams and plates under static loading using the concept of effective thickness, which consists of calculating the thickness of a monolithic element with equivalent bending properties to a laminated element. Recently, an effective thickness for the dynamic behavior of laminated-glass beams has been proposed to enable the modal parameters (natural frequencies, loss factors and mode shapes) to be determined using an equivalent monolithic model. In the present paper, the technique has been extended to the two-dimensional case of rectangular laminated-glass plates and the steps needed to estimate the modal parameters of laminated-glass elements using this methodology are presented. The dynamic effective thickness concept has been validated by experimental tests made on a laminated-glass beam and a laminated-glass plate. The results show that good accuracy is achieved in the natural frequencies and mode shapes but high scatter is encountered in the loss factor

Scaling Factor Estimation Using an Optimized Mass Change Strategy, Part 1: Theory

In natural input modal analysis, only un-scaled mode shapes can be obtained. The mass change method is, in many cases, the simplest way to estimate the scaling factors, which involves repeated modal testing after changing the mass in different points of the structure where the mode shapes are known. The scaling factors are determined using the natural frequencies and mode shapes of both the modified and the unmodified structure. However, the uncertainty on the scaling factor estimation depends on the modal analysis and the mass change strategy (number, magnitude and location of the masses) used to modify the dynamic behavior of the structure. In this paper, a procedure to optimize the mass change strategy is proposed, which uses the modal parameters (natural frequencies and mode shapes) of the original structure as the basic informatio

Sarnas sarcóptica, psoróptica e corióptica dos animais domésticos. Demodicose

Titulación: Grao en Veterinaria -- Materia: Enfermidades Parasitarias IIOs contidos desta unidade didáctica van dirixidos a estudantes de 4º curso do Grao en Veterinaria con coñecementos previos de enfermidades parasitarias I, parasitoloxía, epidemioloxía, bioloxía Animal, microbioloxía, inmunoloxía, citoloxía e histoloxía veterinaria, fisioloxía animal, patoloxía xeral, propedéutica clínica, anatomía patolóxica veterinaria e farmacoloxía, farmacia e terapéutica, e serán impartidos en tres sesións de docencia teórica, unha de prácticas clínicolaboratoriais e dúas de seminarios. A formación que os alumnos adquiren sobre a disciplina de enfermidades parasitarias achega ao profesional veterinario un amplo coñecemento sobre as causas, natureza, mecanismos de transmisión, acción patóxena, diagnose, tratamento e medidas de prevención e control dos principais procesos parasitarios que afectan aos animais, tanto de forma individual como colectiva, e especialmente, neste último caso, posto que as enfermidades parasitarias están entre os procesos patolóxicos máis comúns das colectividades animais. Así mesmo, os coñecementos adquiridos no estudo de Enfermidades parasitarias son básicos para controlar as afeccións que se transmiten dos animais ao home (zoonoses) e de certas enfermidades de declaración obrigatoria. Do mesmo xeito, o estudo desta disciplina é básico para establecer os correspondentes Programas de Sanidade Animal e Saúde Pública Veterinaria que a administración debe elaborar e implantar para manter e mellorar no posible o estado da gandería española e da saúde humana.Universidade de Santiago de Compostela. Servizo de Normalización Lingüístic

The effective-thickness concept in laminated-glass elements under static loading

Laminated glass is a sandwich element consisting of two or more glass sheets, with one or more interlayers of a polymer such as polyvinyl butyral (PVB). The static response of sandwich elements such as laminated-glass beams and plates can be modeled using analytical or numerical models in which the glass is usually modeled as linear-elastic and the PVB as linear-viscoelastic material, respectively. As a way to simplify the laminated-glass calculations, the concept of effective thickness has been recently proposed, which allows the calculation of laminated-glass beams as monolithic beams using an apparent or effective thickness. In this work, equations for the effective thickness of laminated-glass beams are derived from the analytical model proposed by Koutsawa and Daya and the results provided by this model are compared with the models of Bennison et al. and Galuppi and Royer-Carfagni. Finally, some static experimental tests were performed on several laminated-glass beams under distributed loading in order to validate the predictions of the model

Scaling Factor Estimation Using Optimized Mass Change Strategy, Part 2: Experimental Results

The mass change method is used to estimate the scaling factors, the uncertainty is reduced when, for each mode, the frequency shift is maximized and the changes in the mode shapes are minimized, which in turn, depends on the mass change strategy chosen to modify the dynamic behavior of the structure. On the other hand, the aforementioned objectives are difficult to achieve for all modes simultaneously. Thus, a study of the number, magnitude and location of the masses must be performed previously to the modal tests. In this paper, the mass change method was applied to estimate the scaling factors of a steel cantilever beam. The effect of the mass change strategy was experimentally studied by performing several modal tests in which the magnitude, the location and the number of the attached masses were change

Porovnání metod pro analýzu dat z termografických měření meze únavy materiálu Al 2024 pro R=0,1

The traditional methods for fatigue characterization of metallic materials are expensive and extremely time consuming. In order to overcome these shortcomings, the Thermographic Method (TM), based on thermographic analysis, is applied to estimate the fatigue limit of Al 2024. The temperature increase due to localized microplasticity is considered as the fatigue damage indicator. An experimental program is carried out to assess the fatigue limit both as resulting from the S–N field and, directly, from thermographic measurement. For the latter, three different methods are applied for the estimation of the AL 2024 fatigue limit and the out-coming results discussed. The values of fatigue limit predicted from the thermographic method according to the three methods are in good agreement to that derived from the traditional S-N procedure.Stanovení meze únavy kovových materiálů tradičními metodami je ekonomicky a časově velmi náročné. Za účelem snížení časové a finanční zátěže je provedeno srovnání termografické metody (TM) při stanovení cyklické meze únavy hliníkové slitiny AL 2024. V důsledku lokalizace mikroplasticity se zvýší teplota, kterou lze považovat za indikátor vzniku trvalého únavového poškození. Experimenty jsou provedeny ve dvou rovinách. Tradiční cestou jsou změřeny S-N křivky a souběžně jsou provedena termografická měření na materiálu AL 2024. Pro zpracování naměřených dat z TM jsou využity tři dostupné vyhodnocovací metody, známé z literatury. Je hodnocena/diskutována přesnost odhadu/určení meze únavy AL 2024 z jednotlivých metod. Odhad/určení meze únavy z tradičních metod a za použití termografické metody vykazují shodné výsledky