Davide Tumino

Mechanical behavior of a sandwich with corrugated GRP core: numerical modeling and experimental validation

In this work the mechanical behaviour of a core reinforced composite sandwich structure is studied. The sandwich employs a Glass Reinforced Polymer (GRP) orthotropic material for both the two external skins and the inner core web. In particular, the core is designed in order to cooperate with the GRP skins in membrane and flexural properties by means of the addition of a corrugated laminate into the foam core. An analytical model has been developed to replace a unit cell of this structure with an orthotropic equivalent thick plate that reproduces the in plane and out of plane behaviour of the original geometry. Different validation procedures have been implemented to verify the quality of the proposed method. At first a comparison has been performed between the analytical model and the original unit cell modelled with a Finite Element mesh. Elementary loading conditions are reproduced and results are compared. Once the reliability of the analytical model was assessed, this homogenised model was implemented within the formulation of a shell finite element. The goal of this step is to simplify the FE analysis of complex structures made of corrugated core sandwiches; in fact, by using the homogenised element, the global response of a real structure can be investigated only with the discretization of its mid-surface. Advantages are mainly in terms of time to solution saving and CAD modelling simplification. Last step is then the comparison between this FE model and experiments made on sandwich beams and panels whose skins and corrugated cores are made of orthotropic cross-ply GRP laminates. Good agreement between experimental and numerical results confirms the validity of the proposed model.

Redesign of a reverse shoulder prosthesis: Kinematic and mechanical study

In this work a commercial reverse shoulder prosthesis has been redesigned to improve performances in terms of range of movements of the implant and stability to dislocation. A kinematic and mechanic study has been performed using a realistic solid model of the prothesised shoulder: in particular, all the components of the prosthesis have been acquired via a 3D laser scanner and inserted in a virtual humerus-glenoid system by reproducing the common surgical procedure. The final model has been used to measure the maximum angles of abduction and rotation of the arm and the shear forces that cause dislocation. Modifications proposed to the commercial prosthesis are: a different orientation of the cutting plane of the glenoid component and the interposition of a spacer to move the center of rotation of the arm.

Modal and Structural FEM Analysis of a 50 ft Pleasure Yacht

In this paper a structural Finite Element analysis of a 50 ft pleasure vessel is presented. The study is performed under different loads conditions: modal analyses have been done in order to find the natural frequencies of the vessel, structural analyses to verify the strength of the vessel to design loads. The design loads for the vessel considered are computed according to RINA rules for the construction and classification of pleasure vessels [1]. Two different composites are used for the lamination: one is a monolithic sequence of short fibre and balanced glass lamina, used for the bottom of the vessel and for structural reinforcements, the other is a sandwich made of glass fibre composite skins and a PVC core, used for the main deck and sides of the vessel. All the analyses are performed by using Patran/Nastran™ finite element commercial software in order to identify critical areas where possible reinforcement or redesign needs to be considered.

A method based on point cloud sectioning to evaluate different sources of error on the shape of a manufactured object

ABSTRACT This paper presents a method to evaluate the accuracy of a manufactured object with respect to its original CAD model. Different errors caused by the manufacturing process are assumed to come from global axis deformation and transverse sections rotation of the object with respect to its ideal CAD. Object and CAD shapes are given in form of point clouds, the former derived from a laser-scanning measurement, the latter from sampling the ideal surface by a dense and uniform point grid. Point clouds are sectioned in a finite number of thin blocks. This method has been applied to the analysis of a helical Darrieus blade prototype, parametrically designed and modelled with McNeel Rhinoceros and Grasshopper software, manufactured with a three-axes Computer Numerical Control machine. This procedure is able to check the conformity of the manufactured airfoil to the theoretical one and to establish the efficiency of the final prototype of the blade turbine.

A New ESO-Based Method to Find the Optimal Topology of Structures Subject to Multiple Load Conditions

In the field of topology optimization problems, the Evolutionary Structural Optimization (ESO) method is one of the most popular and easy to use. When dealing with problems of reasonable difficulty, the ESO method is able to give very good results in reduced times and with a limited request of computational resources. Generally, main applications of this method are addressed to the definition of the optimal topology of a component subjected to a single load condition. In this work, a new methodology, based on the ESO approach, is introduced for the study of the optimal topology of a component subjected to multiple load conditions. The new procedure, entirely developed in the APDL programming language, has been tested with a holed plate subject to two different load conditions; the obtained results are promising in terms of mass reduction and structural performances.