Pianc Article Irm
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ELASTOMERIC CHARACTERISTIC AND PIANC-2002 FENDER TESTING GUIDELINES engineering fenders Indian company, IRM Offshore and Marine Engineers Pvt Ltd is a well known fender manufacturing company and puts in continuous effort for improving the products, processes and testing methods for fenders. In this article Dr Sujit Datta,Senior Technical Manager at IRM offers a commentary on the PIANC-2002 Testing Protocols. esting Protocols for evaluation of Fender Performance and reporting in PIANC- 2002 guideline can be briefly classified in two main categories,(A) Type approval testing where influence of berthing conditions and environmental factors like temperature are discussed and (B) Verification and quality assurance testing where the discussion is based on different compliance testing.Type approval testing mainly deals with “in the lab” simulation testing of a scaled down model of a fender of specific size under different conditions.These variables are: a) Variable Velocity - Velocity Factor b) Variable Ambient Temperature - Temperature Factor c) Variable contact / berthing angle - Effect of contact angle Solid rubber elements of different profiles are one of the integral components of fendering systems, used in berth side application for commercial and naval vessels. Rubber fenders are available with several variations of its material besides shape and sizes.The “visco-elastic” behavior of rubber is exploited in the selection of rubber fender, being an energy absorbing element. Completely elastic materials require the same stress, which was applied during the last moment of deformation, to maintain the deformation indefinitely and do not show any dependence on the rate of deformation. In the case of liquids, deformation in the static sense does not exist; progressive deformations are not recovered and energy cannot be stored in the liquid or regained. Instead, the process of deformation requires force, and the work done in this irreversible process is quantitatively dissipated as heat.The term “visco-elastic” has come to refer to the dealing of those materials which show a behavior intermediate between those of liquids and solids. In rubbers, the elastic element forms the continuous phase but encompasses frictional viscous elements. Such materials are termed visco elastic.When they are deformed, the viscous element consumes energy and retard the elastic deformation; similarly energy is dissipated when the elastic phase returns in the process of strain recovery and releases its stored energy.The viscose element or internal frictions are thus responsible for the energy difference or hysteresis between work recovered and expended.The superimposed elastic and viscous behavior of rubbers is clearly demonstrated during cyclic deformation. Consider a rubber fender subjected to a sinusoidally varying deformation. During a deformation half cycle - from zero deformation, through a maximum, to zero deformation - the rate of deformation and hence the viscous force is a maximum at zero deformation and zero at maximum deformation.The force due to such cycling may be elastic owing to the deformation or viscous owing to the rate of deformation. Each of these force components will be in phase with its contributing process and therefore 900 out of phase with each other in the cycle; their vector sum is the resultant force which is parallel to the rate and extent of the deformation. In an ideally elastic material, all stress is due to strain and is in phase with the deformation; in an ideally viscose material, the stress is in phase with the rate of straining or deformation. In visco-elastic materials, the resultant stress magnitude lags behind the deformation by a phase angle; the more viscose the material, the greater the lag and hence phase angle.The response of rubber to imposed stresses is governed by a characteristic parameter with the dimension of time, which is called relaxation or retardation time, and defined as the ratio of viscous modulus to elastic modulus of a rubber vulcanizate. Raw rubber consists of a large number of flexible long chain molecules possessing a structure which permits free rotation about certain chemical bonds along the chain.The balanced vulcanization introduce cross links distributed randomly throughout the material and build up a three dimensional network structure. Controlled spatial distribution of network structure throughout the rubber vulcanizate helps to resist flow and thus balance the viscous component as well as partly overcomes the irreversible deformation.The elastic component (responsible for recovery from a given deformation) of rubber vulcanizate (visco elastic material) responds instantaneously and does not dissipate energy, but viscose flow or relaxation requires time in dissipating energy proportional to the deformation rate. At low deformation frequency the viscose element will operate but contribute little and the stress will be almost in phase with the deformation.As the deformation frequency is raised the dissipative effort will rise sharply and the stress will become increasingly out of phase with the deformation and largely dependent on the rate of straining or deformation. PIANC-2002 guideline for establishing the performance data corroborate the principles of visco elastic material such as rubber. It demonstrates the process of evaluation of performance parameters like reaction force and energy absorption at different strain rates or berthing velocities. Different initial velocities have been taken into consideration to evaluate the velocity factor on scaled down model fenders of specific size.Velocity factor thus evaluated in a laboratory simulation test on model fender can be applied on actual size fender to calculate corrected performance parameters in practical use. In most practical situations the frequency of deformation of actual fender is low and thus a pre-assumption is made in guideline that the deflection (berthing) frequency of not less than one hour i.e., maximum deformation cycle is one per hour. This assumption greatly reduces the effect of viscous component on overall performance of the fender and thus the resultant property tends to be more elastic at different deflection rates.As a result the magnitude of deviation of performance parameters at different deformation rates from that at RPD deformation T ELASTOMERIC CHARACTERISTIC AND PIANC-2002 FENDER TESTING GUIDELINES Rubber - the visco-elastic material Necessity of velocity correction
description
Elastomeric Characteristics and PIANC 2002 Fender Testing Guideline.It is testing protocol for evaluation of Fender Performance
Transcript of Pianc Article Irm
ELASTOMERIC CHARACTERISTIC AND PIANC-2002
FENDER TESTING GUIDELINES
e n g i n e e r i n g f e n d e r s
Indian company, IRM Offshore and MarineEngineers Pvt Ltd is a well known fendermanufacturing company and puts in continuous effort for improving the products,processes and testing methods for fenders.In this article Dr Sujit Datta, Senior TechnicalManager at IRM offers a commentary onthe PIANC-2002 Testing Protocols.
esting Protocols for evaluation of FenderPerformance and reporting in PIANC-2002 guideline can be briefly classified in
two main categories, (A) Type approval testingwhere influence of berthing conditions andenvironmental factors like temperature arediscussed and (B) Verification and qualityassurance testing where the discussion is basedon different compliance testing.Type approvaltesting mainly deals with “in the lab” simulationtesting of a scaled down model of a fender ofspecific size under different conditions.Thesevariables are:a) Variable Velocity - Velocity Factorb) Variable Ambient Temperature - Temperature
Factorc) Variable contact / berthing angle - Effect of
contact angle
Solid rubber elements of different profiles areone of the integral components of fenderingsystems, used in berth side application forcommercial and naval vessels. Rubber fendersare available with several variations of its materialbesides shape and sizes.The “visco-elastic”behavior of rubber is exploited in the selectionof rubber fender, being an energy absorbingelement. Completely elastic materials requirethe same stress, which was applied during thelast moment of deformation, to maintain thedeformation indefinitely and do not show anydependence on the rate of deformation. In thecase of liquids, deformation in the static sensedoes not exist; progressive deformations arenot recovered and energy cannot be storedin the liquid or regained. Instead, the processof deformation requires force, and the workdone in this irreversible process is quantitativelydissipated as heat.The term “visco-elastic” has
come to refer to the dealing of those materialswhich show a behavior intermediate betweenthose of liquids and solids. In rubbers, the elasticelement forms the continuous phase butencompasses frictional viscous elements. Suchmaterials are termed visco elastic.When theyare deformed, the viscous element consumesenergy and retard the elastic deformation;similarly energy is dissipated when the elasticphase returns in the process of strain recoveryand releases its stored energy.The viscoseelement or internal frictions are thus responsiblefor the energy difference or hysteresis betweenwork recovered and expended.The superimposedelastic and viscous behavior of rubbers is clearlydemonstrated during cyclic deformation.Considera rubber fender subjected to a sinusoidallyvarying deformation. During a deformationhalf cycle - from zero deformation, through amaximum, to zero deformation - the rate ofdeformation and hence the viscous force is amaximum at zero deformation and zero atmaximum deformation.The force due to suchcycling may be elastic owing to the deformationor viscous owing to the rate of deformation.Each of these force components will be in phasewith its contributing process and therefore900 out of phase with each other in the cycle;their vector sum is the resultant force whichis parallel to the rate and extent of thedeformation. In an ideally elastic material, allstress is due to strain and is in phase with thedeformation; in an ideally viscose material,the stress is in phase with the rate of strainingor deformation. In visco-elastic materials, theresultant stress magnitude lags behind thedeformation by a phase angle; the more viscosethe material, the greater the lag and hencephase angle.The response of rubber to imposedstresses is governed by a characteristic parameterwith the dimension of time, which is calledrelaxation or retardation time, and defined asthe ratio of viscous modulus to elastic modulusof a rubber vulcanizate.
Raw rubber consists of a large number offlexible long chain molecules possessing astructure which permits free rotation about
certain chemical bonds along the chain.Thebalanced vulcanization introduce cross linksdistributed randomly throughout the materialand build up a three dimensional networkstructure. Controlled spatial distribution ofnetwork structure throughout the rubbervulcanizate helps to resist flow and thus balancethe viscous component as well as partlyovercomes the irreversible deformation.Theelastic component (responsible for recoveryfrom a given deformation) of rubber vulcanizate(visco elastic material) responds instantaneouslyand does not dissipate energy, but viscoseflow or relaxation requires time in dissipatingenergy proportional to the deformation rate.At low deformation frequency the viscoseelement will operate but contribute little andthe stress will be almost in phase with thedeformation.As the deformation frequency israised the dissipative effort will rise sharplyand the stress will become increasingly outof phase with the deformation and largelydependent on the rate of straining or deformation.PIANC-2002 guideline for establishing theperformance data corroborate the principlesof visco elastic material such as rubber. Itdemonstrates the process of evaluation ofperformance parameters like reaction forceand energy absorption at different strain ratesor berthing velocities. Different initial velocitieshave been taken into consideration to evaluatethe velocity factor on scaled down modelfenders of specific size.Velocity factor thusevaluated in a laboratory simulation test onmodel fender can be applied on actual sizefender to calculate corrected performanceparameters in practical use. In most practicalsituations the frequency of deformation ofactual fender is low and thus a pre-assumptionis made in guideline that the deflection (berthing)frequency of not less than one hour i.e.,maximum deformation cycle is one per hour.This assumption greatly reduces the effect ofviscous component on overall performanceof the fender and thus the resultant propertytends to be more elastic at different deflectionrates.As a result the magnitude of deviationof performance parameters at different deformation rates from that at RPD deformation
T
ELASTOMERIC CHARACTERISTIC AND PIANC-2002
FENDER TESTING GUIDELINES
Rubber - the visco-elastic material
Necessity of velocity correction
e n g i n e e r i n gf e n d e r s
rate is low. Further the balanced compoundingand state of vulcanization can produce therubber article with optimized elastic-viscouscomponent, which perform within a closetolerance (e.g., ± 10% of the performancevalue at RPD velocity).
A laboratory evaluation has been tried toestablish the variation of key property of wellbalanced rubber compound (e.g., modulus)with variable strain rates followed by the effectof strain rate on the properties of scaleddown model fenders of specific size. In thisexperiment the modulus of elasticity of rubbercompound at different strains has been measuredat variable deformation rate e.g., 100, 200,300, 400, 500 mm/min. Modulus factor andstrain ratio have been calculated as follows:Strain ratio = Strain Rate
Standard strain rate(A moderate strain rate - 300 mm/min is takenas standard strain rate)Modulus Factor = Modulus of Elasticity at
a particular strain rate
Modulus at 300 mm/minFigure 1 shows the variation of modulus factorof modulus at different strain (50, 100, 200 &300%) with strain ratio.Very marginal variationof modulus factor with the strain ratio isobserved for all four modulus. Scale downmodel fenders (Cell & Cone fender of 100mmheight are manufactured from the same rubbercompound and deformed up to 55% for cellfender and 72% for cone fender at differentstrain rate as stated above. In both the cases(Figures-2 & 3), the variation of both reactionfactor as well as energy factor is marginal withthe strain ratio. Reaction factor and energyfactor are determined as follows:Reaction factor = Reaction at a particular
strain rate
Reaction at standard strain rate (300 mm/min)
Energy factor = Energy absorption at a particular strain rate
Energy absorption at standardstrain rate (300 mm/min)
The above laboratory evaluation demonstratesthat the performance of rubber compound canpredict the different performance parametersof actual fender if made up of same rubbercompound at variable conditions.
A property of visco-elastic materials like rubber
Figure 1: Modulus Factor vs. Strain Ratio
Figure 2: Reaction and Energy Factor vs Strain Ratio (scale down cell fender)
Figure 3: Reaction and Energy Factor vs Strain Ratio (scale down cone fender)
Velocity correction - an experiment
Temperature effect
e n g i n e e r i n g f e n d e r s
is that they progressively stiffen as the temperature decreases. PIANC-2002 guidelinefor type approval test also considers this fact.It suggests the method of evaluation of temperature factor over a wide temperaturerange i.e. -300C to 500C. Figure 4 shows theservice temperature range of different elastomer.Variation of berthing angle also has influenceon performance parameter i.e. reaction forceand energy absorption.Variation of contactangle has been taken into consideration overa wide range from 30 to 200. Studies prevailthat both the reaction force and energyabsorption value decrease with increase incontact angle.
The second part of the guideline deals withverification / quality assurance testing of actualfenders as well as the importance of evaluationof physical properties of rubber compound.Evaluation of physical properties of rubbercompound and the performance of production /actual fender is extremely important in viewof real functioning. On site performance trialof actual fender under all possible real environmental conditions is probably moreeffective than test on scale down model fenderunder ideal laboratory simulated working aswell as environmental condition. However at
shop level the testing can be carried out atspecified velocity, temperature and angle andthe performance can be adjusted as per thecorrections factors arrived at during the prototype testing.
Figure 4: Service temperature range of different rubbers
Compression testing of scale down model cone fender in high capacity computer controlled compression test equipment
Dr Sujit Datta (M.Tech, PhD in PolymerScience and Technology) is a Sr. Manager(Technical) of IRM offshore and MarineEngineers Pvt. Ltd - India, having substantialexperience in research & development aswell as manufacturing field. He has publishedmany papers in International Journals andConference. If you have any query relatedto content of this article, feel free to contact on [email protected]
☛ Established in 1964, having extensive experience of manufacturing entire rangeof Marine Fenders and Offshore Rubber Engineering Products.
☛ Becoming the first Fenders and OffshoreRubber Product manufacturing company in this part of the World having completeIMS (ISO 9001 : 2000, ISO 14001 : 2004,OHSAS 18001 :1999) certified byGermanischer Lloyd GmbH - Germany.
☛ Having valid Manufacturers Capability Certificate (MCC) certified by Germanischer Lloyds - Germany to manufacture any type and size of Solid and Pneumatic Fenders available in today’sMaritime World.
☛ A corporate Member of PIANC.☛ Offers the widest range of Marine Fenders
and Rubber Engineering Products for offshore platform installation and protection.
☛ Products and process conform to various international standards like ASTM/BS/ ASME/ PIANC/ AWS/ ISO/ and DIN.
☛ Fully Integrated quality management system to ensure best quality of productsand services.
☛ Offers the full range of services- from designing to manufacturing, testing,installation and maintenance.
☛ Well equipped Research, Development and Testing Laboratory approved by GL - Germany.
☛ Globally networked for sales and services.☛ Worldwide acceptance.☛ Impressive clientele and supply record.
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