Viscoelastic properties, reinforced plastics

Chazeau, L., Cavaille, J. Y, Canova, G., Dendievel, R., and Boutherin, B. (1999). Viscoelastic properties of plasticized PVC reinforced with cellulose whiskers,71,1797-1808. 

Chazeau L, Cavaille JY, Canova G et al (1999a) Viscoelastic properties of plasticized PVC reinforced with cellulose whiskers. J Appl Polym Sci 71 1797-1808 Chazeau L, Cavaille JY, Terech P (1999b) Mechanical behaviour above Tg of a plasticised PVC reinforced with cellulose whiskers a SANS structural study. Polymer 40 5333-5344 Chazeau L, Paillet M, Cavaille JY (1999c) Plasticized PVC reinforced with cellulose whiskers. I. Linear viscoelastic behavior analyzed through the quasi-point defect theory. J Polym Sci Part B Polym Phys 37 2151-2164... 

The viscoelastic nature of the matrix in many fibre reinforced plastics causes their properties to be time and temperature dependent. Under a constant stress they exhibit creep which will be more pronounced as the temperature increases. However, since fibres exhibit negligible creep, the time dependence of the properties of fibre reinforced plastics is very much less than that for the unreinforced matrix. 

Fejes-Kozma, Zs. Karger-Kocsis, J. (1994). Fracture Mechanical Characterization of a Glass Fiber Mat-reinforced Polypropylene by Instrumented Impact Bending. Journal of Reinforced Plastics and Composites, Vol.l3, No.9, pp. 822-834 ISSN 0731-6844 Ferry, J. D. (1980). Viscoelastic Properties of Polymers, 3rd Edition, Wiley Press, ISBN 978-0471048947, New York... 

All polymer materials used in reinforced plastics display some viscoelastic or time-dependent properties. The origins of creep in composites stem from the behaviour of polymers under load together with local stress redistributions between fibre and matrix as a function of time. There is little creep at normal temperatures in the reinforcing fibres. The origin of the creep mechanisms is related to the nature and levels of internal bonding forces between the chains of the polymer, which are influenced by temperature and moisture. 

Information on the study of viscoelastic and rheometric properties of reinforced plastics is summarized in Table 2.8. 

Stiffness properties of RPs are used (as with other materials) for the usual purposes of estimating stresses and strains in a structural design, and to predict buckling capacity under compressive loads. Also, stiffness properties of individual plies of a layered flat plate approach may be used for the calculation of overall stiffness and strength properties. The relationship between stress and strain of unreinforced or reinforced plastics varies from viscous to elastic. Most RPs, particularly RTSs are intermediate between viscous and elastic. The type of plastic, stress, strain, time, temperature, and environment all influence the degree of their viscoelasticity. 

H. Yoshida, Viscoelastic Properties of Fiber Reinforced Plastics, Am. Chem. Soc. Div. Org. Coat. Plast. Prepr. 40, 707 (1979). 

This section reviews the static property aspects that relate to short-term loads (Figure 7.15 and Table 7.8). As reviewed with RTFs the TPs being viscoelastic respond to induced stress by two mechanisms viscous flow and elastic deformation occurs. Viscous flow ultimately dissipates the applied mechanical energy as frictional heat and results in permanent material deformation. Elastic deformation stores the applied mechanical energy as completely recoverable material deformation. The extent to which one or the other of these mechanisms dominates the overall response of the material is determined by the temperature and by the duration and magnitude of the stress or strain. The higher the temperature, the most freedom of movement of the individual plastic molecules that comprise the TP and the more easily viscous flow can occur with lower mechanical performances. Reinforcements in TPs significantly reduce this situation compared to UTPs. 

The stiffness response of RPs can be identified as viscoelasticity. RPs are nearly elastic in behavior and tend to reduce the importance of the time-dependent component of viscoelastic behavior. Also, the stiffness of fiber reinforcements and the usual TS resin matrices are less sensitive to temperature change than most unreinforced plastics. The stiffness of both the fibers and the matrices are frequently more stable on exposure to solvents, oils, and greases than TPs although for certain composites water, acids, bases, and some strong solvents still may alter stiffness properties significantly. 

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