Análisis de pos pandeo en paneles laminados de materiales compuestos

En este trabajo se propone la investigación experimental del comportamiento estructural de paneles reforzados laminados en materiales compuestos sujetos a cargas de cizallamiento en el plano. El objetivo es desarrollar un ensayo capaz de caracterizar el comportamiento en el régimen de pos pandeo de paneles reforzados sujetos a cargas de cizallamiento en el plano, proyectar el dispositivo de ensayo y cuantificar los desplazamientos fuera del plano del panel en pos pandeo utilizando instrumentos ópticos sin contacto (topogrametria). Una metodología de ensayo será propuesta con la finalidad de obtener resultados confiables y reproducibles. Serán establecidos: cuerpo de prueba, mecanismo de ensayo, instrumentación, metodología de adquisición y análisis de los resultados adquiridos. Resultados preliminares con la configuración estudiada indican que paneles reforzados laminados en materiales compuestos sujetos a cargas de cizallamiento en el plano tienen una considerable capacidad de carga pos pandeo.Facultad de Ingenierí

A numerical model for bird strike simulations in composite aerostructures

The present paper describes the implementation of an improved damage mechanics based material model combined with an equation of state to simúlate the progressive failure in composite aerostructures subjected to bird strike loading. A series of bird strike impacts on flat panels fabricated from low cosí woven glass composite materials are used to valídate the material model for practical composite component applications. The panels are modelled with shell elements only. The proposed material model can capture the strain rate enhancement to strength and strain in shear observed in composite materials. A hydrodynamic model for the bird, based on 90% water and 10% air, is derived to represent the behaviour of the bird for all impact scenarios considered. The bird is heterogeneous in nature. However, a uniform material behaviour is assumed with a geometry based on a 2:1 length to diameter ratio with a cylindrical body and spherical end caps using Lagragian mesh. Appropriate contact definitions are used between the bird and the composite panel. The simulations results are compared to experimental results and conclusions drawn.Facultad de Ingenierí

Experimental validation of the vibration correlation technique robustness to predict buckling of unstiffened composite cylindrical shells

Considering the design of aerospace structures, an experimental campaign is essential for validating the sizing methodology and margins of safety. Particularly for buckling-critical cylindrical shells, the traditional buckling test could lead the specimen to permanent damage. Therefore, the validation of nondestructive experimental procedures for estimating the buckling load of imperfection-sensitive structures from the prebuckling stage is receiving more attention from the industry. In this context, this paper proposes an experimental verification of the robustness of a vibration correlation technique developed for imperfection-sensitive structures. The study comprises three nominally identical unstiffened composite laminated cylindrical shells. Each specimen is tested 10 times for buckling at DLR and, the reproducible results — within a small range of deviation between them — corroborate the equivalence of the cylinders. For the robustness assessment of the vibration correlation technique, two different buckling test facilities are considered. Furthermore, the material properties are recalculated through composite composition rules and the influence of enhanced theoretical buckling loads on the VCT predictions is verified. The experimental campaigns corroborate that the vibration correlation technique provides appropriate estimations representing the influence of the different test facilities; moreover, enhanced theoretical buckling loads can improve the predictions for some of the test cases

Mode I Interlaminar Fracture Toughness Analysis of Co-Bonded and Secondary Bonded Carbon Fiber Reinforced Composites Joints

<div><p>Aiming to reduce aircraft weight, aeronautic industry seeks alternative materials and processes used to join its different structural parts. An option to traditional methods are high performance adhesive joints, which reduce weight, number of parts and component final cost, also resulting in higher strength structures. Although, the lack of experimental data to provide a detailed structural characterization of these joining techniques had limited their commercial application. The proposal of this work is to investigate the Mode I interlaminar fracture toughness under quasi-static loading using DCB specimens of carbon composite joints made by co-bonding and secondary bonding techniques, the latter giving more reliable results. For a better understanding on the failure in the systems, DSC and microscopy techniques were applied, from which three stages of delamination process during testing were observed: 1st Stage) Cohesive failure represented by an unstable crack propagation from a high energy level; 2nd Stage) transition from cohesive to adhesive and final intralaminar failure mode with lower energy levels than Stage 1; and 3rd Stage) completely stable propagation at low energy levels (delamination migrates from intralaminar to interlaminar, entirely in the substrate).</p></div