Leigh Stuart Sutherland

Technical University of Lisbon | UTL · Centre for Marine Technology and Ocean Engineering (CENTEC)

Sandwich structures comprising glass-fibre reinforced polymer faces and low-density core constitute an efficient and versatile constructive system for civil and ocean engineering structures. However, being multilayered with relatively soft core materials, they are particularly susceptible to damage under concentrated loads. Whilst numerous studies...

Although composite materials are now used throughout the marine industry their susceptibility to impact events is still an unresolved problem. The complex nature of the problem in terms of the distinct material and impact event parameters specific to marine applications, damage tolerance and durability has been discussed in parts I, II and III of t...

A fully iterative ‘two-way’ fluid-structure interaction (FSI) tool of a commercially available composite windsurfer fin was developed, which was then used to investigate the normally hidden fin behaviour for a range of typical sailing conditions. The ‘two-way’ FSI analysis gave significantly better insights into the fin behaviour than the simpler ‘...

The introduction of a thin cork layer was investigated as a means to improve the impact resistance of composite foam sandwich laminates whilst maintaining structural performance. Six configurations of this ‘cork-skinned’ sandwich architecture were evaluated via extensive experimental comparisons with a ’baseline’ GRP/ PVC foam sandwich laminate as...

The paper presents low-velocity impact tests and finite element simulations of carbon/glass fibre- reinforced hybrid composite laminates struck by a pyramidal frustum impactor in order to examine crushing deformations and failure mechanisms. Three mass ratios between the carbon and glass fibre (1:2, 1:1 and 2:1) are considered to compare the influe...

Weight reduction and materials sustainability are becoming of primary importance for marine structures. A solution to both issues could lie in the application of all-metal sandwich structures. The study suggests the substitution of common marine structures with aluminium honeycomb sandwich structures (AHS), as a green and lightweight alternative, t...

This work studies the low-velocity impact response of 3D-printed layered structures made of thermoplastic materials (PLA and PETg), which form sacrificial claddings for impact protection. The analyzed structures are composed of crushable cellular cores placed in between terminal stiffening plates. The cores tessellate either honeycomb hexagonal uni...

One of the most important design strategies for increasing the speed and/or efficiency of marine vehicles is that of weight reduction. This can be achieved by optimising structural design via judicious distribution of the most apt materials and via the application of innovative lightweight structures. Sandwich structures are ideal candidates for st...

This work studies the low-velocity impact response of 3D-printed layered structures made of thermoplastic materials (PLA and PETg), which form sacrificial claddings for impact protection. The analyzed structures are composed of crushable cellular cores placed in between terminal stiffening plates. The cores tessellate either honeycomb hexagonal uni...

A large statistical design of experiments (DOE) based investigation has been completed into the effects of surface preparation, cleaning method and adhesive choice on the strength of marine composite T-joints. Using a new extended experimental data set guidelines for the best adhesive, surface-preparation and cleaning combinations were verified. St...

Structural analyses, both numerical and experimental, have been made of a composite windsurf fin. Structural analyses, both numerical and experimental, have been made of a composite windsurf fin. An FE model was developed employing commercial software ANSYS using both linear and nonlinear analyses of the structural response due to external loads (s...

Composite materials are now used throughout the marine industry but their susceptibility to impact events is still an unresolved problem. There is a huge body of work in the area, succinctly summarised here, but the great majority concerns impact events and composite materials more relevant to the aeronautical industry. A discussion of the complexi...

Composite materials are now used throughout the marine industry but their susceptibility to impact events is still an unresolved problem. The complex nature of the problem in terms of the distinct material and impact event parameters specific to marine applications has been discussed in parts I & II. Tolerance to impact damage is usually of greater...

Composite materials are now used throughout the marine industry but their susceptibility to impact events is still an unresolved problem. The complex dependence of the impact behaviour and damage on the many material and impact event parameters discussed in part I means that impact testing must simulate the particular in-service case well. Hence, t...

The use of marine composite materials, especially Glass Reinforced Polymers (GRP), offer many advantages such as low weight (for transport, installation, and operation), durability (fatigue and corrosion), low maintenance and ease of producing complex seamless forms. This paper presents an overview of the applications of composite materials to wave...

Statistical experimental design techniques were used to study the strength of ‘T’-Joints representative of various connections used to fabricate marine composite structures via a large test program. The effects of different surface preparations and cleaning methods, and adhesives were investigated. An analysis of variance was conducted, giving an e...

This paper presents an experimental study of the quasi-static indentation behaviour of a pultruded glass fibre reinforced polymer (GFRP) multicellular deck panel used in footbridges. To simulate the applied loads to be experienced by such a deck during its service life, various sets of specimens extracted from the panel cross-section were perforate...

This work is motivated by the ever increasing range of applications of sandwich composite materials in the marine industry. A brief literature review is presented, followed by the manufacture and flexure, quasi-static and impact tests of a series of marine sandwich composites. Different core materials (PVC, Balsa Corecork NL10 and NL20) are used to...

The material properties of four laminates with different skin/core/production method are compared in order to identify their mechanical properties. In this study, 3-point flexural beam tests following the ASTM standard C393 are carried out on each of the four laminates and the results are compared. The main experimental conclusions were that lamina...

This paper presents experimental and numerical results of a series of drop weight impact tests examining the dynamic response of fully clamped aluminium 5083/H111 circular plates struck laterally at the centre by a mass with a spherical indenter. The impact velocity varied from 1.0 to 6.0 m/s. The plates showed no visible damage at the very low inc...

The paper discusses the design requirements for development of sailing yachts adapted to disabled people. A large percentage of the population has some kind of limitation, either in terms of mobility, sensorial, or intellectual. In general these limitations prevent the practice of sailing sport because the vessels are not adapted to deal with the l...

The paper presents numerical simulations of previously reported drop weight impact tests examining the dynamic response of fully clamped steel circular plates struck transversely at the centre by a mass with a spherical indenter. The impact velocity varied from 0.5 to 6.0 m/s. The plates showed no visible damage at the very low incident energies, b...

'This patent concerns yards of traditional and replica craft, fabricated in two halves, from an epoxy-unidirectional glass and carbon fibre composite, and reinforced with marine plywood and an exterior woven roving glass fibre layer. The fabrication process is suitable for small shipyards.' O PRESENTE INVENTO DIZ RESPEITO A VERGAS PARA EMBARCAÇÕES...

Mandate Concern for the structural design of sailing yachts and other craft. Consideration shall be given to the materials selection, fabrication techniques and design procedures for yacht hull, rig and appendage structures. The role of standards, safety and reliability in the design and production processes should be addressed. Attention should be...

Comparative experimental data has been obtained for GRP laminates, and Aluminium 5083 and steel circular fully-clamped plates subjected to lateral impact. The metal plates were much more resistant to perforation than the laminated plates, but the behaviour up to perforation was more complex. A decrease in maximum force and an increase in maximum an...

Worldwide the production of composite vessels is moving rapidly towards ‘closed-mould’ production techniques, especially Resin Infusion. This change is driven by reduced costs, stricter environmental regulation and higher laminate quality. The process essentially uses vacuum pressure to drive resin into a dry reinforcement stack (placed on a mould...

The impact behaviour of single-skin laminates was investigated experimentally and described in terms of 'un-delaminated', 'delaminated' and 'fibre damage' responses. The behaviour depended on the thickness to diameter ratio. Damage occurred at extremely low incident energies and damage modes were multiple, complex and interacting. Impact response w...

A dimensional analysis approach has been used to develop scaling laws for impact on marine composite materials. An experimental study has been carried out to verify these relationships for the transverse impact of a hemispherical ended impactor on fully clamped circular hand laid-up glass–polyester plates at three different scales. Although the mod...

A necessidade de ensaios para investigação do comportamento de componentes estruturais em materiais compósitos reforçados por fibra, utilizados na construção naval, conduziu ao projecto de um pórtico de ensaios com actuador servo-hidráulico adaptável, a custo reduzido. Neste trabalho, descreve-se a abordagem adoptada no seu projecto, identificando...

Quasi-static indentation tests on low fibre-volume, hand-produced, E-glass/polyester ‘marine’ laminates have been performed. A Hertzian contact law fitted well the initial response. Considerable material variability was seen in the Hertzian behaviour of the woven roving tests. The presence of an irregular resin-rich surface was influential at initi...

Impact tests on composite plates were performed using an instrumented drop-weight machine. Orthophthalic and isophthalic resin, and different woven-roving reinforcements were considered. Degree of fibre-crimp was more influential than the type of polyester resin. Multiple, complex and interacting damage mechanisms occurred even at very low incident...

The impact response of five marine laminates has been investigated experimentally and described in terms of undelaminated, delaminated and fibre damage responses. The exact behaviour depended on the thickness to diameter ratio, but at incident energies up to fibre damage the impact responses were very similar for all lay-ups. Fibre damage was most...

Drop-weight impact tests have been carried out for low fibre-volume glass-polyester laminates for a range of diameter to thickness ratios. Three damage stages were defined, ‘un-delaminated’, ‘delaminated’ and ‘fibre damage’. Analysis of the impact response using a mainly graphical methodology allowed further characterisation of the behaviour. Impac...

O estudo do fenómeno de indentação é necessário à modelação da resposta ao impacto de peças laminadas de compósitos utilizados na indústria naval. Para isso, realizam-se testes de indentação em laminados de poliéster reforçado a fibra de vidro tipo E com uma baixa relação fibra/volume. Uma lei de contacto Hertziana descreveu satisfatoriamente a res...

Instrumented falling weight tests led to the definition of three behaviour `regimes'; `undamaged', `internal delamination' and `severe' (at low, medium and high incident energies, respectively). The reduction in stiffness due to the internal delamination gave a bi-linear force–deflection relationship. A shear-dominated theory and an energy balance...

A Servo-hydraulic rig for quasi-static and fatigue material and structural testing has been designed, constructed and commissioned. The test rig consists of three distinct parts: a rigid steel test frame, a hydraulic system and a data acquisition and control system. During the commissioning tests very high performance was seen despite the fact that...

Falling weight impact tests on circular low fibre-volume E-glass / polyester composite plates have been performed. Three behaviour ‘regimes’ have been defined; ‘Undelaminated’, ‘Delaminated’ and ‘Severe damage’. Bending and shear deflections, and indentation and membrane effects have been modelled. Delamination initiation was accurately predicted b...

Dada a complexa micro – estrutura e variabilidade dos materiais compósitos, que em aplicações navais são frequentemente produzidos manualmente, é imperativo a obtenção de propriedades mecânicas precisas para qualquer modelação numérica ou analítica dos mesmos. Qualquer pequena alteração nos materiais constituintes e/ou no processo de fabrico de com...

Falling-weight impact tests on circular low fibre-volume E-glass / polyester composite plates have been performed. Three behaviour ‘regimes’ have been defined; ‘Undelaminated’, ‘Delaminated’ and ‘Fibre damage’. A fracture mechanics model describes extremely well the sudden onset of delamination, and gives good scaling between specimen sizes. Bendin...

A necessidade de ensaios para investigação sobre o comportamento de componentes estruturais em materiais compósitos utilizados na construção naval conduziu ao projecto de uma plataforma de testes servo-hidráulica, de baixo custo. Projectou-se a plataforma de forma a ter a máxima adaptabilidade possível, permitindo a realização de uma ampla gama de...

An instrumented falling weight machine was used to investigate the effects of test parameters on the impact response of low fibre-volume E-glass woven-roving reinforced polyester coupons. Statistical experimental design techniques were used to plan the experiment and to analyse the data. All the parameters considered were found to affect the respon...

Instrumented falling weight impact tests have been used to study the impact behaviour of hand laid-up, low fibre-fraction, glass-fibre reinforced polyester laminates. The effects of laminate reinforcement and thickness, and of impact energy and velocity were studied. Failure modes were found to be complex, but a simple analysis assuming shear-domin...

A large number of impact tests have been carried out on woven-roving and chopped-strand-mat glass reinforced, hand laid-up polyester laminates of different thicknesses and weights. Deflection, force, absorbed energy and damaged area results for these tests have been presented and compared, and the failure modes described. A simple analysis assuming...

Experimental results of low-energy drop-weight impact tests on woven-roving E-glass/polyester composites are presented. The effects of specimen thickness, impactor kinetic energy, velocity of impact and laminator are investigated. Damage was observed for all impact energies. The assumption that shear deformation dominates the response gives good ag...

This paper is concerned with the scale and size effects in the strength characterisation of composite materials with particular reference to hand laid-up unidirectional laminates. Attention has been focused on the tensile and flexural strengths of glass/epoxy and carbon/epoxy laminates. The experiments have been designed through the use of statisti...

This paper is concerned with a review of the size and scale effects involved in the prediction of strength of fibre-reinforced-plastic (FRP) composite materials and structures. The review covers the basic principles in the establishment of scaling laws and the application of the Buckingham-Pi theorem. An analysis of various theories used in categor...

This paper is concerned with scale and size effects in the strength characterisation of composite materials with particular reference to woven-roving laminates. Attention has been focused on the tensile and flexural strengths of glass/polyester laminates fabricated by hand lay-up techniques. Factorial experiments have been designed to allow investi...

The available literature concerning probabilistic models describing the strength of composite materials has been reviewed to highlight the important aspects of this behaviour which will be of interest to the modelling and analysis of a complex system. The success with which these theories have been used to predict experimental results has been disc...

In this study, the problem of scaling design data from test to ship scales has been outlined. The meaning of the term ‘size effect’ has been clarified through the consideration of dimensional analysis and engineering modelling techniques. The mathematical models used to quantify the strength ‘size’ effect for fibrous composites have been described,...

The methods of statistical design and analysis of experiments have been introduced and a description given of their application to composite strength testing in order to explore possible effects of size and fabrication related variables. Experience in the use of experimental design techniques in destructive composite testing has been gained through...

The methods of statistically based experimental design have been applied to the flexural and tensile testing of unidirectional E glass and carbon epoxy composites. Experience has been gained in the application of these methods with respect to the destructive testing of FRP composites. Statistical analysis of the results has indicated some strength...

The windsurfer fin provides most of the 'lift' force opposing the side force produced by the sail, the performance of the windsurfer being extremely sensitive to that of its fin. This thesis compares both theoretical and empirical data with the existing theories of windsurfer fin design and operation. There are three main areas considered by the re...