research on structures at uos lret utc - nus … s3 structures and... · research on structures at...

Research on Structures at UoS LRET UTC

R Aji Sh iR. Ajit ShenoiProfessor

The University of SouthamptonThe University of Southampton

The Lloyd’s Register Educational Trust (LRET) y g ( )Marine & Offshore Research Workshop

16-18 February, 2010 at Engineering Auditorium, NUS

Research on Structuresat UoS LRET UTC

2nd International LRET Marine Research Workshop

National University of Singapore, 17-18 February 2010

Professor R A Shenoi February 2010 Lloyd’s Register Educational Trust

University Technology Centre

Structures

Lloyd’s Register Educational Trust

University Technology Centre

Professor Janice BartonDr. James BlakeDr. Stephen BoydDr. Simon QuinnProfessor Ajit ShenoiDr. Yeping Xiong

Contents of talk

• Background

• Smart structures

– Passive– Active

• Behaviour modelling

– High strain rate– Reliability– Power flow

• Sandwich

– Hybrid steel-composite– Repair– Steel-concrete-steel

• Issues

– Life cycle assessment– Sustainable composites

• Societal/industrial impact

Lloyd’s Register Educational TrustUniversity Technology Centre

Background

• Focus of the UTC at Southampton has been Hydrodynamics, Hydroelasticity an the Mechanics of Composites.

• Three themes in the latter are:

– Quasi static limit state analysis

– Durability and long term performance

– Concurrent engineering


The subject coverage


Limit state Durability Conc Engg




Material failure studiesStructural failure studiesFailure modelling criteriaProgressive failurePerfect vs imperfectRepair





Fatigue of laminatesFatigue of sandwichHygrothermal ageingDamage tolerance Intervention strategiesFracture behaviour






ProducibilityOperabilityLCCLCASustainability







Numerical modelling Experimental modelling







Plate elements Grillages and structural assemblies Joints

Numerical modelling Experimental modelling

Facilities

• Eight advanced computer controlled servo-controlled testing machines (1kN -1MN), with static and dynamic loading (frequencies up to 100Hz)

• High strain rate servo-hydraulic test machine with 100kN load capacity at 20m/s

• State-of-the art Electro-Puls electrodynamic test machine with 1kN load capacity at more than 100Hz

• Multi-axis loading capabilities (bi-and tri-axial configurations), including linear and rotational actuators

• Environmental control, including temperature, humidity level andfluid/aqueous environments

• Load spectrum control, including multi-axial spectrum operation, programmed loading and real spectrum playback

• Lightning strike testing in Tony Davies High Voltage Laboratory

• Capabilities for acoustic fatigue testing in reverberation chamber

• Fire testing

Material Characterisation

Extensive facilities for experimental stress analysis and crack/damage monitoring

– acoustic emission (AE)

– full-field stress imaging (Thermoelastic Stress Analysis (TSA))

– strain measurement by laser shearography and Digital Image Correlation (DIC)

– ultrasonic scanning, reflection photoelasticity

– potential drop measurements

– strain sensing optical fibres

– crack compliance measurement

– X-ray computed tomography (CT)

– direct surface replication

– SEM and TEM

Manufacturing

Composite fabrication and processing

– autoclave (1m in diameter by 1.5m in length)

– vacuum assisted liquid resin infusion

– Plastech resin transfer moulding

– flow modelling facilities through channel and radial flow techniques

– flow and cure monitoring in FRP fabrication processes using thermistor and dielectric sensors, chemical analysis and cutting facilities

– experience with nano-clay and carbon nanotube composites

14

Passively adaptive tidal turbine blades


Motivation

• Increased interest in capturing energy from naturally occurring resources

• UK has a high tidal range with very favourable tidal velocities

• Actively adaptive turbine blades (e.g. variable pitch) are complex and relatively inaccessible

• Composites provide a tailored material, whose properties can be exploited in the turbine industry in order to reduce loads and enhance stall control


Methods

• 1.25m bend-twist coupled double box beam modelled in ANSYS 11.0 in high strength carbon pre-preg.


Application: turbine performance

• Turbine performance illustrated by means of a Cpow-λ curve

• Smaller λ equates to higher flow velocities and vice versa

• While there is less power density at lower flow velocities they are more common hence the increase in area under the graph of the adaptive device means it is more efficient

• Adaptive bladed turbine achieves a 2% increase in annual energy capture and a 10% decrease in detrimental thrust force when compared to a fixed bladed device


18

Active smart materials and structures for vibration damping


Motivation

• Smart materials have ability to change one or more material properties or shape under the influence of external stimuli, such as stress, electric or magnetic fields, temperature, etc.

• Magnetorheological Elastomer (MRE) material consisting of a natural or synthetic rubber filled with micron sized iron particles is a promising smart material.

• Viscoelastic, rheological properties and stiffness of MRE can be controlled by applying magnetic field.

• To understand dynamic performance of MRE and MRE cored sandwich structures

• Develop smart and effective vibration control device.


20

• Scanning Electron Microscope (SEM) images of MRE

Particles aligned under the applied magnetic field.

Randomly dispersed Particles

Magnetorheological elastomer


21

Dynamic Shear Property of MRE

0 1 2 3 4 5 6 7 8 9 100

2

4

6

8

Strain (%)

Shear

Modulu

s (

MP

a)

30Hz Frequency (30 vol% 24hr curing MRE)

No Magnet Field

0.3 Tesla

Modulus Changes

0 1 2 3 4 5 6 7 8 9 100

0.1

0.2

0.3

0.4

Strain (%)

Tan δ

No Magnet Field

0.3 Tesla

Tan δ ChangesElectromagnet

Specimen

Shear property change depending onstrain ranges and magnetic field strength

Experiment set up


22

MRE Cored Sandwich Beam

Sandwichbeam

Shaker

Sensor

Permanent magnets

•Vibration test of MRE sandwich beam in magnetic field

To understand shear property, effect of magnetic field strength, boundary conditions, shear strain effect, localised magnetic effect on the dynamic performance of MRE cored sandwich structures.

•Curing process under magnetic field with a permanent magnet


23

Magnetic Field Effect on Vibration Response

Comparison of vibration responses of MRE cored sandwich beam with and without magnetic field


100 200 300 400 500 600 700 800 900 1000-30

-25

-20

-15

-10

-5

0

5

10

Frequency (Hz)

Accele

rance (

dB

, re

1m

s-2

/N)

No magnetic field

0.3 Tesla

100 200 300 400 500 600 700 800 900 1000-50

-40

-30

-20

-10

0

10

Frequency (Hz)

Accele

rance (

dB

, re

1m

s-2

/N)

No magnetic field

0.3 Tesla

(a) Theoretical predictions (b) Experimental results

Shaft Vibration Control using MRE


Excitation force and response measurement points interested

(a) Cross section of MRE-shaft assembly (B) Experiment set up

25

300 400 500 600 700 800 900 1000-35

-30

-25

-20

-15

-10

-5

0

5

Frequency (Hz)

Accele

rance (

20lo

g(g

/N))

no Magnet

Magnet

Accelerance at point 1

Experimental Results


300 400 500 600 700 800 900 1000-60

-50

-40

-30

-20

-10

0

Frequency (Hz)

Accele

rance (

20lo

g(g

/N))

no Magnet

Magnet

Accelerance at point 4

26

Conclusions

• MRE materials can change their dynamic stiffness and damping rapidly, continuously and reversibly under the controllable external magnetic field.

• MRE is a promising smart material due to its real-time controllable mechanical property responding instantly to the applied magnetic field.

• MRE core embedded sandwich structures can achieve adjustable stiffness with improved damping to dissipate vibration energy.

• Theoretical and experimental studied agree well and have demonstrated the effective real time control capabilities of MRE.

• MRE control devices are fail-free, if a power system failure, the device retains a minimum passive performances and have wide applications in automobile , maritime and civil industries.


27

Adhesively bonded joints subjected to high strain rate loads


Motivation

• Increasing use of composite materials in primary structure

• Methods of attachment have been on going research for years

• Performance evaluation of joints at increased operational velocities is key to the safe application of composite structures


UoS Capabilities

• A Very High Speed (VHS) servo-hydraulic test machine: capable of testing ISO standard specimens at loads of up to 20kN and speeds of up to 20m/s producing strain rates in excess of 100 strain-s

• Ability to test adhesively bonded structures and capture non-contact full field stress and strain data simultaneously

• Use of high speed digital image correlation to assess the load transfer across the adhesively bonded joint subject to high speed impact


Example Results

6kN 5kN 20Hz

20 40 60 80 100

50

100

150

200

250

300

-8000

-7000

-6000

-5000

-4000

-3000

-2000

-1000

0

0.5

1

1.5

2

2.5

3

3.5

Sum of the principal stresses

Thermoelastic stress analysis

Digital Image Correlation

εxx

εyy

Feature identification is similar for both non-contact full field techniques


31

Reliability engineering of composite structures


Motivation

• Insertion of novel materials and topologies restricted by rule-based design

• Uncertainty and variability in design, manufacture and operationcan be accounted for statistically

• Statistical approach satisfies a goal-based design, allowing greater flexibility for structural engineering

• What is the likelihood of failure of typical and novel compositetopologies?

• How sensitive is the survivability of a composite structure to variations in design, manufacture and operation?


Resistance variables & uncertainties

Effect of fibre misalignment on laminate stiffness Simplistic representation of wave slap pressure load on composite casing panel

Required level of numerical modelling complexity


• Phase 1

� Analysis of simple steel or FRP plates under in plane and out of plane loading

� FORM/SORM & Monte Carlo simulations to determine probability of failure

• Phase 2

� Use of grillage analysis to simulate 4x4 and 4x5 stiffened steel panels subject to out of plane loading

� Incorporation of equivalent elastic properties for stiffened FRP panels subject to out of plane loading

• Phase 3

� Extension of analytical grillage model to encompass buckling response

� Incorporation of failure criteria models

– Finite element simulations with response surface method for morecomplex topologies

Progress


0

5

10

15

20

25

30

1 2 3 4 5 6

β

Factor of Safety

Buckling:• Phase 1

• Phase 2

• Phase 3

Progress

Probability of Failure,

Pf ( x10-6)

MethodReliability

Index, β

Deflection Limit State

Stress Limit State

FORM 4.6927 1.348 0

SORM 4.7446 1.045 0

Sensitivity factors 4x4 box stiffened composite grillage

Deflection Limit State Stress Limit State

Volume fraction & applied load most important

Sensitivity factors

Diminishing reliability as applied load approaches maximum compressive strength:


36

Power flow analysis


Motivation

• Power flow analysis provides a technique to characterise dynamic behaviours in medium to high frequency ranges where FEA encountered significant numerical difficulties.

• It provides a common approach for various mechanical, structural, acoustic, fluid, thermal, electrical systems.

• Most research on dynamics, vibration control and power flow focuses on traditional approach that requires all system information.

• To reveal the inherent power flow behaviours and effectively control vibration energy transmission, power flow mode theory and control approaches are developed based on system’s damping distributions.



Application: ride comfort of high speed craft

39

• Total power and mode power

Evaluation of energy dissipations in a passive control system: total power and each mode power


40

• Effect of active feedback control

10-1 100 101 102 103102

103

104

105

Power flow Pm

Frequency (Hz)

gs = 5000

gb = 0

passive

gb = 5000

gs = 0

Active damping increases the power dissipation.


• Power flow mode theory straightforwardly reveals vibration energy dissipation and transmission mechanisms.

• The eigenvalues and eigenvectors of the characteristic damping matrix of a dynamic system identify system’s natural power flow behaviour.

• Total power comprises of power dissipated by all independent mode power.

• A larger value of damping factor (eigenvalues) implies a larger energy dissipation.

• The theory provides new control approach by design systems’ damping distributions using passive and/or active control means to satisfy engineering requirements.

• It provide a simple tool to estimate power flow bounds relating to the damping of the system only without requiring vibration sources.


Key Findings

42

Hybrid steel-composite sandwich structures


Motivation

• Requirement for lighter more stable ships

• Total use of FRP not feasible on vessels > 150m

• Limits use to weight critical areas

• Requires joints between dissimilar materials

• Performance characterisation of joints statically, dynamically and in the marine environment in required

• Joints must be efficiently designed for purpose


Progressive Damage


Optimisation

Property Baseline

Parametric

hybrid

Optimum

(weight)

Adhesive Thickness (mm) 0.5 2 2.15

Steel/GRP overlap length (mm) 240 240 240

Taper length (mm) 120 150 196

Steel Thickness (mm) 6 5 2.4

Skin Thickness (mm) 4 6 4

Glue Young's Mod (MPa) 3600 3600 3600

Steel stub length (mm) 110 110 110

Core thickness (mm) 38 30 21

Baseline

Properties:

Weight: 2.97 kg

Stress: 12.79 MPa

Stiffness: 49500 N/mm


Contribution

• This research provided three unique firsts in the understanding of steel-composite hybrid connections with respect to load transfer:

– Combined hygrothermal/strength/fatigue characterisation of hybrid connections

– Use of progressive damage modelling for hybrid connections

– Use of genetic algorithms for the design and sizing of hybrid connections


47

Repair of sandwich structures


Motivation

• Extensive studies on repair of composite laminate but less so on sandwich structure repair.

• Most research concentrations on honeycomb or foam based sandwich structures .

• GRP/Balsa Sandwich structure is the core material of choice fornaval marine applications

• Various repair configurations e.g. overlap patch, scarf repair, step repair have been adopted from single skin repairs for the repair of sandwich structures – scarf repairs providing good efficiencies


Design charts

• Theoretical Prediction of undamaged sandwich

bCL

dtP

ff

f

σ=

Face yielding

Face wrinkling

bL

GEEdtP

ccff

f

3

1

)(8=

Core shear

dbP cf τ2=

10

110

210

310

410

510

610

710

20 220 420 620 820 1020 1220 1420 1620 1820

L/t

Core density (Kg/m3)

indentation Core shear A

Face

wrinkling

Face yield

Core shear B

common panel


Lessons learnt

• The efficiency of the repair is only an issue if the sandwich topology is such that face sheet failure is the mode of failure

• If the sandwich failure mechanism is driven by core shear failure then efficiencies of repair remain high

• Prediction of failure mechanism can aid the repair technique used and ensure sufficient sandwich efficiency

Core shearRepaired core and face sheet


51

An alternative design of SCS sandwich beam with bi-directional CSC system

Alternative sandwich construction of

1. Unfilled steel sandwich beam

2. Concrete-filled SCS sandwich beam


Background

• A SCS sandwich beam is a special formof sandwich structure.

• Being originated in civil/structural application,it is now being developed forshipbuilding/offshore application.

• The research trend is to introduceeither a new shear connector systemor a lightweight concrete.(example researches: NUS - Prof. Richard Liew )

52Lloyd’s Register Educational TrustUniversity Technology Centre

Aims and Objectives

• To present an alternative construction of SCS sandwich beam in which the new concept design of aligning the shear connector in the inclined direction is proposed.

• To present the possibility to implement this SCS system.

• To present the advantages of this novel beam in both unfilled and concrete-filled sandwich beam type.(emphasizing on effect of inclined angle)

53Lloyd’s Register Educational TrustUniversity Technology Centre

Unfilled beam: shear stiffness

• Methodology: a combination of

– 2D Plane Frame Model

– Force & Distortion of Unit Cell

– Modified Stiffness Matrix

54

80% more shear stiffness compared with

sx/d = 0.25 (idealized vertical web)

max. shear stiffness

θ ~ 40°


Concrete-filled Beam

• Conceptual model

– As RC Beam (no contributionof steel face plates)

• Research is on going…using 3D FE model with SOLID elementto study the effect of sx/d to the transverse shear strengthof SCS sandwich beam.

55

Idealised optimisation point

Bi-Steel?

0.707


56

Life cycle assessment for alternative material selection


Motivation

• Desire to design marine structures to include entire life ratherthan immediate structural and operational performance

• Develop a credible methodology utilising Life Cycle Assessment (LCA) to make informed material selection choices

• Assess the feasibility of a Design for Life Cycle approach


LCA description

• Standardised methodology (ISO 14040)

• Open to interpretation in its application and results

ISO 14040 standard LCA

LCA approach adopted


Example Result

• It has been demonstrated that fuel consumption is the overarching contributor to the energy life cycle assessment approach

• Therefore a fixed installed power approach was adopted thereforenormalising for fuel consumption in a simplified boat synthesis exercise

Modified Faltinsen Approach

Lloyds Special Service Craft Rules


Conclusions

• A LCA framework was adapted for material selection for life cycle environmental impact.

• It has highlighted the environmental properties of four candidate materials by adapting the design to an LCA impact target and a life cycle scenario.

• Thermoplastic Matrix Composites (TMC) show some of the lowest energy results especially in the full boat synthesis

• Research demonstrates that one can optimise design for structural and operational performance as well as indicating thepotential environmental impact


61

Sustainable composites


• Extraction rate of crude oil to meet demand is unsustainable

• Plastics and resin industry:

– one of the largest consumers of petrochemicals

– responsible for a tenth of all released toxicity in the US

– fourth largest contributor to greenhouse gases

Motivation

Campbell & Laherrère, “The End of Cheap Oil”, Scientific American, 1998

Hubbert & Roper prediction models


Motivation

Princess 65 Charter Mallorca (source: Princess Yachts) Mercedes-Benz E Class (source: Daimler Chrysler)

• Resin in a typical glass reinforced composite accounts for 65% of the environmental cost

• Fibre accounts for around 7% of environmental cost

• Marine sector is the second largest user (automotive 1st)

• End of Life:

– EU legislation bans landfill disposal of composites

– EU legislation requires automotives to be 95% recyclable by 2015


Derobert, S. “Performance Analysis of Naturally Derived Resin for Marine Sandwich Structures”, MSc thesis, Uni. of Southampton, 2008

• Use of non-agricultural crops for resin and bast fibre production

– increase in fallow land use

– boost local rural economies

– offset carbon footprint

– sustainable

Alternatives

• Competitive with conventional composites

Fowler et al. “Biocomposites: technology, environmental credentials & market forces”, J. Sci Food & Agric, 86, 2006

• Structural designers confident?


65

Industrial/societal impact


Impact - practical outcome I

Standards

Extensive fundamental research from late 1980s on FRP materials for RN/MoD/industry

• Focus on understanding design, production and operational issues for GRP ships

• FSI tasked by MoD to examine all NESs pertinent to marine composites in DEFSTAN format with new, updated and validated advice

Impact - practical outcome II

Transfer from marine to civil construction – Design practice

Extensive fundamental research from late 1980s on FRP materials for RN/MoD/industry

• Focus on understanding design, production and operational issues for GRP ships

• Technology transfer from marine to civil construction

• FSI tasked by European industrial consortium to assist in writing Design Code with focus on jointing

Impact - practical outcome III

Design guides

• Manual for fatigue design of sandwich configuration boats

• Repair manual for RNLI fleet

• Fire safety case in design of rescue boats

Closure

• Background

• Smart structures

– Passive– Active

• Behaviour modelling

– High strain rate– Reliability– Power flow

• Sandwich

– Hybrid steel-composite– Repair– Steel-concrete-steel

• Issues

– Life cycle assessment– Sustainable composites

• Societal/industrial impact


70

Contacts

Professor Janice Barton http://www.soton.ac.uk/ses/people/staff/BartonJM.html

Dr. James Blake http://www.soton.ac.uk/ses/people/staff/BlakeJIR.html

Dr. Stephen Boyd http://www.soton.ac.uk/ses/people/staff/BoydSW.html

Dr. Simon Quinn http://www.soton.ac.uk/ses/people/staff/QuinnS.html

Professor Ajit Shenoi http://www.soton.ac.uk/ses/people/staff/ShenoiRA.html

Dr. Yeping Xiong http://www.soton.ac.uk/ses/people/staff/XiongYP.html


research on structures at uos lret utc - nus … s3 structures and... · research on structures at...

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