Composites

Experimental Facilities

Specifically developed for general purpose research and development work on FRP composites and light structural components is a new multiple configuration test facility, FORTRESS (Flexible Orthogonal Rig for Testing REal Ship Structures). This is capable of undertaking static and fatigue testing of flat and three dimensional panels up to 2.5 metres by 2.5 metres by 1.5 metres. It can generate multi axis loads in three dimensions of up to 100 tonnes. Loads are generated by a hydraulic power unit and controlled through a micro computer based, signal conditioning unit capable of sampling several input and output channels. The rig can be used to test single skin and sandwich panels, flat and curved, as well as complex joint designs, such as bulkhead to skin connections, at full scale.

More conventional test machines are also available for testing structural and material samples in tensile, compressive, flexural, shear, torsional or multimode configurations under static and/or dynamic load regimes. Additionally, there are extensive materials laboratories for examining microstructural characteristics using, for example, the scanning electron microscope.

Examples of Recent Projects

The following examples will give an idea of the work that can be carried out on composite materials. It is not intended to be all inclusive and we would be pleased to discuss any problem or project that you may have.

Behaviour of Structural Composite Tee Joints

Failure mechanisms and their dependence on joint design were studied to determine joint response under static (tensile and compressive) loading for both single skin and sandwich panels. In the single skin case, design variables investigated included corner radius, length of overlap on the arms of the Tee and type of layup. In the sandwich case, three types of joint designs were looked at, namely filler fillet (with appropriate radii), triangular foam insert and foam pad based joints. The study included the development of an analytical procedure, experimental work and F.E. analysis.

Fatigue Characteristics of Bonded Tee Connections

Designed to assess the through life characteristics of bonded connections of single skin panels, this programme tested adequate numbers of structural samples in order to generate S-N curves; developed algorithms for the assessment of material/stiffness/strength degradations; and applied the techniques to evaluate cumulative damage in structural connections under different load spectra.

Large Deflection of FRP Panels with Attachments

This project studied attachments to FRP panels such as top hat stiffeners or boundary angles, simulating, for example, shell to bulkhead connections. It stemmed from the lack of analytical procedures for predicting the shock response of such structures. The first phase of the work examined the non linear behaviour of the panels under large amplitude static loading. The study included the development of the analytical procedure, validation through experimentation and prediction of detailed stress fields through F.E. analysis.

Fatigue Behaviour of Sandwich Beams

The aim of this project was to derive S-N curves for the bottom shell laminate of high performance rescue craft. The shell was represented by a "long beam" (about 1400 mm x 200 mm x 75 mm) subject to a one sided flexural load. The maximum value of this was determined from craft operating conditions. The frequency of load application was about I Hz. The project included a study of the failure mechanisms within the sandwich at different load and life cycle limits.

Ultimate Strength Characteristics of FRP Panels

An investigation was conducted into the behaviour of modern marine composite panels, both single skin and sandwich, under extreme pressure loads. The work determined which material features exercised most influence over composite panel capability. It tested various designs of single skin and sandwich panels under very large pressure loads, the variations including aspect ratio, material types used and layup procedure. The test data was analyzed to provide design guidance.

A Unified Approach to the Design of Marine FRP Panels

This research developed an approach to design which incorporates within it both material and structural failure norms. It included the development of micromechanics algorithms incorporating localised laminate mechanics and materials failure phenomena, the creation of routines for the assessment of structural adequacy of layered shells or panels, the combination of these two models in an integrated manner and the application of the combined model to the design of practical FRP panels in an industrial context.

Strength Scaling Problems in FRP: A Taguchi Approach

This work was carried out because of the reported evidence of differences in results pertaining to strength and stiffness of various sealed FRP test models. Its purpose was to explain these variations through a statistical experimentation programme which involved the examination of the fundamentals of the mechanics of multiphase materials together with dimensional analysis to generate similitude relationships. These relationships and the strength/stiffness formulae were then subjected to systematic Taguchi style experiments to assess the relative importance of different variables on performance.

Ships Propeller Brackets from Composite Materials

This study covered design, materials, production and experimental validation of a full scale ship's propeller shaft support bracket. An algorithm for the analysis of forces acting on the shaft bracket was developed. This was incorporated into a design synthesis procedure covering both hydrodynamic and structural aspects. A new production process was developed which was used to construct a full scale bracket. The design and production methods were validated by a series of structural tests on the bracket. F.E. analysis, used in conjunction with the tests, further confirmed the adequacy of design and material layup. Finally, a new and simple arrangement for mounting the propeller bracket on a ship was developed.

FRP Structures for SWATHs

The principal components of the structural design process for Small Waterplane Area Twin Hull Ships (SWATHS) were addressed, particular attention being devoted to the materials engineering aspect. Hybrid construction involving FRP hulls fastened to aluminium decks was found to be a very desirable option from an economic viewpoint. The problems involved in such a design were analyzed in depth. The work included estimation of loads acting on the structure, choice of materials, structural geometry and production procedure, testing of a FRP structural model and detailed F.E. studies.

Composite Materials Engineering for High Performance Craft

High performance craft are very weight sensitive and this is the principal factor governing the use of advanced composites for their structure. This project sought to develop a design procedure involving specification of loadings, choice of materials, failure modes predictions, structural synthesis method and, finally, production techniques. Included in the study was an evaluation of alternative structural configurations including monocoque sandwich versus stiffened single skin design, new materials (including stitched rather than woven cloth) and novel core shear connections.