Pelayo Fernández

The region-dependent dynamic properties of porcine temporomandibular joint disc under unconfined compression.

In this study, the dynamic compressive properties in five different regions of the porcine temporomandibular joint (TMJ) disc are investigated over a wide range of loading frequencies. The aim was, thus far, to evaluate the regional difference and the frequency-related effect of the applied load on these properties. Eleven porcine TMJ discs were used; each disc was divided into 5 regions, anterior, central, posterior, lateral and medial. Sinusoidal compressive strain was applied with an amplitude of 1.0% and a frequency range between 0.01 and 10Hz. The dynamic storage and loss moduli increase with frequency, the highest values being attained at the posterior region, followed by the central and anterior regions. Loss tangent, tanδ, ranged from 0.20 to 0.35, which means that the disc is primarily elastic in nature and has a small but not negligible viscosity. The present results suggest that the dynamic viscoelastic compressive modulus is region-specific and depends on the loading frequency, thus having important implications for the transmission of load to the TMJ.

Experimental Evaluation of Mass Change Approaches for Scaling Factors Estimation

In operational modal analysis the input forces are unknown so the modes shapes are obtained with an arbitrary normalization. In some applications the mass normalized modes shapes are required and the scaling factors have to be estimated. A way of obtaining these factors is to modify the modal properties of the structure by introducing changes in the mass or stiffness; mass change is usually the most convenient way to modify the structural properties in a controlled manner. Different strategies and approaches to perform the mass change method have been proposed in recent years. In this work the scaling factors of a 15 tonnes concrete slab strip are obtained using several equations proposed by different authors and the results are compared. The results show that the scaling factors can be estimated with reasonable accuracy using the different equations if a good mass change strategy is applied.

Strain Estimation in a Glass Beam Using Operational Modal Analysis

A potential application of operational modal analysis is the prediction of strain or stress time histories which, on the other hand, are one of the most important sources of uncertainty in fatigue design and remaining fatigue life calculations. This is due to the difficulty of estimating the stiffness, mass and damping properties with accuracy, as well as the use of simplified loading models.

Dynamic Behavior of Laminated Glass Beams

Laminated glass beams can be considered sandwich elements consisting of two or more glass sheets and one or more interlayers such as polyvinyl butyral (PVB). The response of these elements present two borderline cases: (1) the monolithic limit, which appears at low temperatures and high frequencies and (2) the layered limit, which appears at high temperatures and low frequencies. In this work, the modal parameters of several laminated glass beams were estimated by operational modal analysis in the temperature range 10–45 °C. The results show that the natural frequencies decrease and the damping ratios increase with increasing temperature whereas there are not significant changes in the mode shapes. The experimental results are compared with those determined using the analytical models of Mead and Markus and Ross, Kerwin and Ungar.

Influence of the Support Conditions in the Modal Parameters of a Cantilever Beam

In modal analysis, previously to the modal testing, it is very common to assembly a finite element model, in order to know the frequency range of interest and the mode shapes of a structure. This information is very helpful for planning and developing the modal testing.