Laurent Mezeix

Fabrication and Mechanical Testing of a New Sandwich Structure with Carbon Fiber Network Core

The aim is the fabrication and mechanical testing of sandwich structures including a new core material known as fiber network sandwich materials. As fabrication norms for such a material do not exist as such, the primary goal is to reproduce successfully fiber network sandwich specimens. Enhanced vibration testing diagnoses the quality of the fabrication process. These sandwich materials possess low structural strength as proved by the static tests (compression, bending), but the vibration test results give high damping values, making the material suitable for vibro-acoustic applications where structural strength is of secondary importance e.g., internal paneling of a helicopter.

Entangled Cross-Linked Fibres for an Application as Core Material for Sandwich Structures - Part I: Experimental Investigation

Entangled cross-linked fibres were studied for an application as core material for sandwich structures. Specimens were produced from carbon, aramid and glass fibres, and cross-links were achieved using epoxy spraying. It was observed that this type of entangled cross-linked fibres could be fabricated without any major technical difficulties. The scope of this paper is to study the effect of some different parameters on the mechanical properties of these materials. Different effects were investigated: effect of fibres length, of fibres nature, of mixing fibres, of carbon skins and of the resin. The first part of this paper deals with the production of these entangled cross-linked fibres. The compression, tension and three point bending tests are detailed in the second part and the results are compared with usual core material currently used in industries.

Evaluation of the impact resistance of various composite sandwich beams by vibration tests

Impact resistance of different types of composite sandwich beams is evaluated by studying vibration response changes (natural frequency and damping ratio). This experimental works will help aerospace structural engineer in assess structural integrity using classification of impact resistance of various composite sandwich beams (entangled carbon and glass fibers, honeycomb and foam cores). Low velocity impacts are done below the barely visible impact damage (BVID) limit in order to detect damage by vibration testing that is hardly visible on the surface. Experimental tests are done using both burst random and sine dwell testing in order to have a better confidence level on the extracted modal parameters. Results show that the entangled sandwich beams have a better resistance against impact as compared to classical core materials.

Entangled Cross-Linked Fibres for an Application as Core Material for Sandwich Structures - Part II: Analytical Model

Entangled cross-linked carbon, aramid and glass fibres were recently produced by epoxy spraying for an application as core material for sandwich panel. The Young’s moduli in compression and tension have been previously measured and briefly summarized in this paper. To optimize the core structure, modelling of these properties has been achieved in the present paper. The cross-link fibres have a random orientation and the stiffness of the epoxy joint is modelled by a torsion spring. A parallel model is chosen for homogenisation. It was found that the experimentally estimated stiffness of these materials fits fairly well with the modelled ones.

Experimental analysis of impact and post-impact behaviour of inserts in Carbon sandwich structures

In aeronautics, honeycomb sandwich structures are widely used for secondary structures such as landing gear doors, flaps or floors, and for primary structures in helicopters or business jets. These structures are generally joined by using local reinforcements of the insert type. In the present study, 50 J low velocity impact tests were performed on inserts using a drop-weight device and the impact response and failure patterns were analysed. Impacted specimens were then pull-through tested to failure. Some of the tests were stopped before final failure in order to obtain precise details on the failure scenario. It was shown that, in the cases studied, the residual strength after impact was very high (about 90%) in comparison to the large reductions habitually observed in compression after impact tests.

Fibers Networks as a New Type of Core Material. Processing and Mechanical Properties

Fibers networks materials have been elaborated from different fibers: metallic fibers, glass fibers and carbon fibers. Cross-links have been achieved using epoxy spraying. The scope of this paper is to analyze the mechanical behavior of these materials and to compare it with available models. The first part of this paper deals with elaboration of fibers network materials. In the second part, compression tests are performed. The specific mechanical behavior obtained is discussed.