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