Geopolímero é um material que possui boas propriedades físicas e químicas como resistência mecânica, resistência a ataque químico, material inerte depois de pronto, é de fácil obtenção, pois a sua base é uma argila, material abundante e de baixo custo. Muitos trabalhos são desenvolvidos com o geopolímero, como aplicações para pisos, cimentos, refratários, adesivos e isolamento acústico e térmico. O desenvolvimento do geopolímero é simples, são necessário um percussor que pode ser metacaulim ou argilas com quantidades aceitáveis de SiO2 e Al2O3, um ativador alcalino como NaOH, KOH ou silicato de sódio e aditivos se necessário para contribuir com algumas relações molares que devem ser atendidas para a formação do geoplímero. A formação do geopolímero ocorre através de reações de policondensação originando uma estrutura amorfa e até cristalina dependendo do processo. O uso de aditivos e agregados conferem características desejadas como melhor resistência mecânica, melhor capacidade de isolamento térmico ou acústico, melhor resistência química entre outros fatores. A execução foi a partir do metacaulim com o uso de NaOH e aditivos, a serragem e fibras de sisal ( algave sisalana ) para conferir maiores porosidades no geopolímero desenvolvido. O geopolímero desenvolvido gerou valores de resistência mecânica na ordem de 20 MPa em um tempo de cura de 11 dias, sua densidade variou de 1,0 a 2,5 g/ml, a porosidade volumétrica ficou na faixa de 25,0% a 47,0%, as concentrações utilizadas de NaOH foram entre 0,0 e 15,0 mol/Litro. Todos os dados foram compatíveis com dados verificados em literatura. / Geopolymer is a material that has good physical and chemical properties such as mechanical resistance, chemical etch resistance, inert material after ready, it is easy to obtain because its base is a clay, abundant material and low cost. Many jobs are developed with the geopolymer, such as floor applications, cements, refractories, adhesives and acoustic and thermal insulation. The development of the geopolymer is simple, a percussor is required which may be metakaolin or clays with acceptable amounts of SiO2 and Al2O3, an alkaline activator such as NaOH, KOH or sodium silicate and additives if necessary to contribute some molar ratios that must be met for the formation of the geoplímero. The formation of the geopolymer occurs through polycondensation reactions leading to an amorphous and even crystalline structure depending on the process. The use of additives and aggregates impart desired characteristics such as better mechanical strength, better thermal or acoustic insulation capacity, better chemical resistance among other factors. The execution was from metacaulim with the use of NaOH and additives, sawdust and sisal fibers (algae sisalana) to impart larger porosities in the developed geopolymer. The developed geopolymer generated values of mechanical strength in the order of 20 MPa in a cure time of 11 days, its density ranged from 1.0 to 2.5 gmL-1, the volumetric porosity was in the range of 25.0% to 47,0%, the concentrations of NaOH used were between 0.0 and 15.0 mol / Liter. All data were compatible with data verified in the literature.

<p>Generally, heavier noise control treatments are favored over lighter ones since heavier acoustical materials tend to insulate (block) noise sources more effectively than do lighter materials. In automotive applications, however, heavier materials cannot always be adopted because of concerns over the total weight of the vehicle. Thus, it would be useful to identify lightweight acoustical treatments that can mitigate vehicle interior noise. Automotive sound packages have both absorption and barrier characteristics, and there is inevitably a trade-off between these two. Therefore, it is important to study the exchange between the absorption and transmission of acoustical materials particularly as it pertains to weight. Here, a procedure based on plane wave analysis is described that can be used to identify weight reduction opportunities by adjusting the acoustical properties of a generic sound package, consisting of a fibrous layer and a flexible microperforated panel surface treatment, so that it meets a target sound pressure level in a downstream interior space. It has been found, for the configuration studied here, that there are lightweight sound package configurations that can maintain acoustical performance equivalent to that of heavier noise treatments, and further, it has been found that the lightest treatments tend to favor barrier performance rather than absorption. Further, the impact of acoustical leaks has been considered, and it has been found that even very small leaks can result in a very substantial weight penalty if a specified level of acoustical performance is to be ensured. Further, the impact of changing the underlying panel mass and altering the frequency weighting used in the optimization process has also been considered.</p> <p>The optimizer used in the proposed procedure requires considerable calculation time; hence, the acoustic pressure calculation time needs to be minimized to enhance the efficiency of the solution process. Thus, the transfer matrix method (TMM) for a two-dimensional case was used to calculate the interior acoustic pressure for a simple geometry as a starting point in the process of identifying the minimum-weight sound packages. The TMM is a widely used analytical approach to predicting the sound pressure (and particle velocity) for a system that can be represented as a series of subsystems. Although the TMM can offer fast and simple calculations for the acoustic system, its application is limited to a plane-wave-based model. Thus, the TMM is not the best option for the acoustic pressure prediction in a complex geometry such as a vehicle interior, that involves non-planar wave propagation. Therefore, a hybrid TMM-FEA method is proposed in this research to evaluate the acoustical performance of the sound package in more complex geometries (here, a vehicle-like cavity). So, in this research, the TMM was introduced to obtain the initial solutions that can be used in conjunction with the FEA tool to calculate the sound pressure field in the complex geometry case. The correlation between the results of these two approaches was then analyzed to develop a space-averaged pressure prediction model for various absorptive cases in the interior space. Finally, this SAP prediction model was used to generate an acoustic map that can be used to graphically estimate the SAPs in the complex geometry case.</p> <p>In order to validate the usage of the developed equation for different sets of boundary conditions, several case studies were performed to study the effects of the surface impedance arrangements, geometrical shapes, and, lastly, the presence of extra features in the interior space. Finally, the SAP difference between the area near the driver’s right ear and the total interior cavity was studied to show that the SAP of the total cavity can be adjusted to evaluate the acoustic performance of the sound packages along the lines of conventional industry practice. </p>

Testing equipment based on the propagation of elastic waves are commonly used for measuring specific material properties. As a prerequisite for accurate measurements a reliable acoustic coupling of probe and specimen is highly important. Therefore, high-resolution testing equipment is using fluids as couplant. In certain conditions, only non-contacting methods can be considered. This is the case for example, if particular high or low temperatures are present, if topographic features impede the use of ultrasonic probes, diffusion or solubility processes exist, measurements at vacuum are addressed and if high purity requirements need to be fulfilled. Hence, subject of this work is a method which offers to handle these constraints. With the emergence of modern laser systems the scientific basics for a non-contacting, laser-acoustic excitation of ultrasound were discovered. The tremendous development of commercially available laser systems during the last decade was taken as reason to investigate, to which extent former scientifically designed laboratory setups can now be merged into one single application oriented measuring system. All considerations are based on the thermoelastic excitation of ultrasound in combination with a likewise laser-based detection. By this, a self-contained measuring chain is built which combines the attributes non-destructive, non-contacting and application oriented within one ultrasonic measurement system for the first time. Thermal calculations lead to more precise equations which predict a laser-induced, local temperature rise of about 100 K. The examination of sound field simulations, as a prerequisite for the design of ultrasonic systems, identified an additional complex of problems. Although existing calculation approaches presuppose laser intensity profiles what can be described in analytical terms, real-world laser sources exhibit a complex shaped spatial distribution of laser energy. Based on a preceding CEFIT simulation, the developed CPSS method enables the calculation of the time resolved, 3D wave propagation of arbitrary shaped sources. A comparison to measured data successfully validated the results of simulation. By presenting selected scenario of measurements, the practical suitability of this non-contacting method is demonstrated. Using a transmission setup enables the characterization of open-pore ceramic coatings as well as the deduction of longitudinal and transversal speeds of sound. Equally, the imaging and estimation of the depth position of artificial defects with 0.7 mm in diameter is shown. Measurements based on a reflection setup provided evidence of a resolution limit of at least FBH = 1 mm in 4.5 mm depth. Additional examples demonstrate the ability to detect close-surface defects, the analysis of the challenging lamb waves zero-group-velocity S1 mode as well as the utilization of buried laser-acoustic sources. / Prüfsysteme, welche die Ausbreitungseigenschaften elastischer Wellen zur Ableitung spezifischer Messgrößen nutzen, sind etablierte Messverfahren. Voraussetzung für zuverlässige Ergebnisse ist stets die sichere akustische Kopplung zwischen Sensor und Material. Daher arbeiten hochauflösende Prüfsysteme mit Fluiden als Koppelmedium. Unter bestimmten Bedingungen scheiden kontaktierende Ultraschallsysteme allerdings ersatzlos aus. Dies ist beispielsweise der Fall, wenn die Probe eine besonders niedrige oder hohe Temperatur besitzt, topografische Eigenschaften ein sicheres Ankoppeln der Kontaktprüfköpfe erschweren, Diffusionsvorgänge oder Löslichkeiten zu beachten sind, in Vakuum zu arbeiten ist oder erhöhte Reinheitsanforderungen vorliegen. Gegenstand der vorliegenden Arbeit ist eine Technik welche hilft, diese Einschränkungen zu umgehen. Mit dem Aufkommen der ersten Laserquellen entstanden die wissenschaftlichen Grundlagen zur kontaktlosen Anregung und Detektion von Ultraschall. Die rasante Entwicklung kommerziell verfügbarer Lasersysteme der vergangenen Dekade wurde zum Anlass genommen zu untersuchen, in wie weit sich die einst wissenschaftlich orientierte Laboraufbauten zu einem anwendungsnahen Messsystem zusammenführen lassen. Basis der Arbeiten ist die thermoelastische Anregung von Ultraschall in Kombination mit einer ebenfalls kontaktlosen Detektion. Damit entsteht eine geschlossene Messkette welche erstmals die Eigenschaften zerstörungsfrei, kontaktlos und anwendungsorientiert in einem Ultraschallmesssystem vereint. Ausgangspunkt stellt die thermische Simulation der Anregung dar. Mit Hilfe präzisierter Gleichungen wird eine lokale Erwärmung von lediglich 100 K vorausgesagt. Für die zur Auslegung eines akustischen Messsystems notwendige Schallfeldsimulation wurde eine weitere Problematik identifiziert. Während bekannte Rechenansätze stets analytisch beschreibbare Strahlprofile des Lasers voraussetzen, zeigen reale Laserquellen kompliziert gestaltete räumliche Intensitätsverteilungen. Auf Basis einer vorangestellten CEFIT-Simulation ist mit der entwickelten CPSS-Methode eine zeitdiskrete Berechnung der 3D-Wellenausbreitung beliebiger Quellgeometrien möglich. Vergleiche mit realen Messdaten bestätigen die Simulationsrechnungen. Anhand ausgewählter Messszenarien wird die Praxistauglichkeit der kontaktlosen Arbeitsweise demonstriert. Neben der Charakterisierung einer offenporigen keramischen Beschichtung erlauben Transmissionsmessungen die Berechnung der longitudinalen und transversalen Schallgeschwindigkeiten. Ebenso ist die Abbildung wie auch die Beurteilung der Tiefenlage von Referenzfehlern mit lediglich 0,7 mm Durchmesser möglich. In Reflexionsmessungen wurde eine Auflösungsgrenze von mindestens KSR = 1 mm in 4,5 mm Tiefe nachgewiesen. Weitere Beispiele zeigen die Sensitivität hinsichtlich oberflächennaher Fehler, die Auswertung der anspruchsvollen „Zero Group Velocity“ S1-Mode der Lambwelle wie auch die Nutzung eingebetteter Quellen.