Service Life Simulation on Plastics under the Influence of Aggressive Fluids

[idw]

Components in the vehicle engine compartment must with¬stand high temperatures, mechanical vibration and the effect of aggressive substances such as fuel, brake fluid or engine oil. Until now, the durability of plastic com¬po¬nents has been extremely difficult to assess, consider¬ing the va¬riety of influencing factors. This is particularly im¬por¬¬tant for critical safety components, whose failure in¬volves a signi¬ficant danger potential and subsequent lia¬bility risks.At the "JEC" trade show held from 1 to 4 April in Paris, at its stand U74, hall 1.3, Fraunhofer LBF will present solutions for sim¬u¬¬lat¬ing the service life of components made from plastic and other composite materials.








The number and usage of components made from plas¬tic and composite materials has been growing steadi¬ly through¬¬out the last few years. Until now, reliable, mate¬rial-specific test¬ing methods and rating concepts for these plastic com¬ponents, enabling an assessment of their ex¬pected service life, have not been available. Within the frame¬work of a Wing Project of the German Federal Ministry for Education and Re¬search lead by Robert Bosch GmbH, engineers are cur¬rent¬ly working on new material tech¬no¬lo¬gies. Research scien¬tists at the Fraunhofer Institute for Dura¬bi¬lity and System Relia¬bility LBF in Darmstadt are developing a simulation method which will enable the reliable assess¬ment of fatigue and age¬ing of plastic components under various ambient in¬fluen¬ces. Using spe¬ci¬mens made from thermoplastic mate¬rials and re¬semb¬ling the actual com¬po¬nents, researchers have investi¬gated the behaviour of the materials in labora¬tory tests, as a func¬tion of mate¬rial, geo¬metry, manufactur¬ing process and vari¬ous environ¬mental factors (such as tem¬pe¬rature, fuel, or oil). These parameters are critical to strength, load-carrying ca¬pa¬bility and service life of the materials.


The effect of these combined parameters on material fa¬tigue can subsequently be shown in a numerical simulation of the com¬po¬nents. "First of all we analyse the vibratory strength of plastic spe¬ci¬mens immersed in an oil bath, by introducing cyclic loads", explains Andreas Büter, Head of Department at Fraunhofer LBF. "Depending on the load at which specimen fatigue or fracture occurs, the fatigue strength, i.e. the re¬lationship be¬tween the cyclic load applied and the maximum per¬mitted number of vibrations can be calcu¬lated." On the basis of the results obtained, a diagram called Wöhler curve is de¬termined by the engineers, which enables a statistical as¬sess¬ment of the fatigue life of a component.


How a fuel rail, for example, will withstand engine vibra¬tions under simultaneous contact with fuel, is simulated on the basis of the results obtained by means of a numerical model of the component. "We calculate the stress and strain oc¬cur¬ring in the material at various loads", explains Büter. "We know from experiments the stresses the mate¬rial can with¬stand without damage, and at which strains damage oc¬curs. Hence we can assess the service life of plastic com¬ponents with maximum reliability".


The purpose of the simulation models, which are adapted to the specific material in hand, is to enable designers to take into account ageing processes and the effects of various am¬bient factors on plastic components at an early stage in the develop¬ment phase - similar to metal compo¬nents. This will reduce the cost and time involved in design modifi¬ca¬tions and adap¬tation of shape.


Scientific contact at the show:
Dr. Andreas Büter, Julia Hartmann
mobile +49 172 6184202
julia.hartmann@lbf.fraunhofer.de


Quelle: idw