Katia Genovese

An experimental investigation of static and fatigue behaviour of sandwich composite panels joined by fasteners

Abstract An experimental investigation has been carried out to estimate the static and fatigue behaviour of specimens made up of steel plates and sandwich composite panels joined together by either blind or mechanical lock fasteners. A preliminary study was carried out in order to analyse the drilling operation of sandwich panels to determine the best values of parameters to use for fastener installation. A first set of pull-out and shear static tests was performed in 1992, using sandwich panels composed of a nomex honeycomb core between two laminates of glass/graphite/kevlar fibres in epoxy matrix. The investigation was completed in 1998. It consisted of performing a set of pull-out and shear fatigue tests on joints with blind fasteners, and of performing a new set of static tests on identical specimens with the same loading conditions as in 1992 so as to evaluate the possible ageing effect on mechanical proprieties of sandwich panels tested.

A New Hybrid Technique for In-plane Characterization of Orthotropic Materials

In this paper we present a novel hybrid procedure for the in-plane mechanical characterization of orthotropic materials. The material identification reverse engineering problem is solved by combining speckle interferometry and numerical optimization. The rationale behind the entire process is the following: for any specimen to be characterized and which has been subjected to some loading condition, it is possible to express the difference between experimental data and analytical/numerical predictions by means of an error function ψ, which depends on the elastic constants of the material. The ψ error will decrease as the elastic constants come close to their target values. Here, we build the ψ function as the difference between the displacement field measured with speckle interferometry and its counterpart computed by means of finite element analysis. Since the ψ function is highly non-linear, it has to be optimized with a global optimization algorithm, which perform a random search in the elastic constants design space. The hybrid material identification process finally allows us to determine values of the elastic constants. In order to prove the feasibility of the present approach, we have determined the in-plane elastic properties of an eight-ply composite laminate (woven fiberglass-epoxy) used as a substrate for printed circuit boards. The results indicate that the procedure proposed in this paper was able to accurately characterize the material under investigation. Remarkably, the elastic constants found by the identification procedure were less than 0.7% different from their target values, while the residual error between the displacements measured by speckle interferometry and those computed at the end of the optimization process was less than 3%.

Structural behaviour of endodontically treated teeth under thermomechanical loading

Abstract Choosing the optimal combination of post construction and restorative materials to minimize thermomechanical stresses in endodontically post-restored teeth is a very challenging task. In fact, while thermal properties of metallic alloys used for endodontic posts are rather similar to those of natural dental tissues, composite restorative materials used for constructing post and postcore usually possess better mechanical properties than metallic alloys. This may make it very difficult to evaluate directly thermomechanical stresses in the restored tooth. Therefore, this paper presents a detailed analysis of the structural behaviour of several postendodontic restorations submitted to different combinations of thermomechanical load. The aim of the study is to compare the relative merits of different restoration concepts. Three-dimensional finite element method (FE) analysis is carried out for an upper incisor restored with composite as well as metallic post systems. Furthermore, customized and standard post constructions are compared. Two loading cases are considered: (a) exposure to cold irritants in absence of mastication; (b) mastication of cold or hot foods. Effects of thermal field inhomogeneity and occlusal force magnitude are also included in the analysis. Because of the transient nature of thermal loads, relative performance of different restorations is investigated as the thermal perturbation spreads through the restored tooth. Results indicate that composite post systems are globally more efficient than restorations including a metallic alloy post when thermal cycles and mastication act together. However, relative performance of different restoration concepts in the absence of mastication may depend strongly on the time of exposure to thermal irritants.

Identification of mechanical properties of bovine bones by combining PS-ESPI and global optimization

Identification of mechanical properties of materials is a complicated reverse engineering problem which can be solved by minimizing the difference between displacements measured experimentally and their counterpart predicted by FEM analysis. Non-linearity entailed by identification problem leads to combine global optimization techniques with full-field experimental techniques. This paper presents an example of application of a hybrid identification procedure to cortical bone specimens cut from bovine long bones. Specimens can be modeled in fashion of a transversely orthotropic material. In-plane displacements are measured by means of Phase Shifting Electronic Speckle Pattern Interferometry while stiffness parameters are determined by means of Simulated Annealing. Results show that material properties are in good agreement with data recently published in literature.

Topometry and color association by RGB fringe projection technique

Three-dimensional object topography is obtained by using the fringe projection technique. In fringe projection technique, digitalization is done when black and white lines are projected over the sample object and the image is captured by the CCD. It is applied the phase shifting method to evaluate the phase of the projected fringes. In this paper it is proposed a method in which red, green and blue fringes are projected sequentially. It is obtained the topography to each color (RGB) and finally the three obtained shapes are averaged. By using this method, we obtain information about color, texture and topography details of the object.

Panoramic fringe projection by using a conical mirror

In this work, we present a novel Panoramic Fringe Projection system (PFP) to retrieve the three-dimensional topography of quasi-cylindrical objects along their full length and around the entire circumference. The proposed procedure uses a 45° concave conical mirror to project a circular sinusoidal fringe pattern onto a specimen placed coaxially to the mirror and at the same time to image the modulated fringe pattern diffused from the object surface. In order to obtain the required sensitivity, an axicon is used to create a divergent fringe pattern with constant pitch. By processing the phase map, information on the radius over the full 360° surface of the sample can be obtained by using a single-view series of images captured from a single camera. To verify the feasibility of the PFP technique, a tubular sample with shape discontinuities has been tested. The proposed method demonstrated to be able to retrieve the accurate topography of quasi-axial-symmetric samples with complex geometries for a large variety of applications.

Spatial location of reference points for the study in 360° of an object using Stereo Vision

Stereo Vision is a powerful tool used to make a 360° scan of an object in order to obtain topography details or getting the spatial position of interest points, but the process could be slow due to the computing time. In this work we present the alternative of using high reflective markers, which are used as reference points to track an object movement. The advantage of these markers is that their detection is faster than a full scene correlation and it is done by comparing the position of the centroids of each marker without using pixel-pixel analysis.