Dynamic‐mechancial response of graphita/epoxy composite laminates and neat resin

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Abstract
The dynamic mechanical properties of carbon‐fiber‐reinforced, epoxy‐matric‐composite laminates subjected to loading perpendicular to the plane of lamination and of neat epoxy resin are reported. The dynamic mechanical measurements were performed in the frequency range from 0.1 to 40 Hz and at temperatures between 20° and 200°C at deformation levels within the linear viscoelastic region by the use of a Dynastat apparatus. It is found that thein‐phase and out‐of phase stiffnesses superpose to form master curves covering a frequency range of 12 decades. By a suitable scaling procedure of the master curves, it is found that thein‐phase stiffiness has tbe same shape and the out‐of‐phase stiffness has the same dispersion for all laminates irrespective of the stacking sequence and are nearly identical to those for neat epoxy resin, An empirical function for the relaxation modulus is developed that, when converted to dynamic modulus, gives a good overall agreement for both components of the dynamic stiffness as a function of frequency. Absorbed moisture is found to cause a reduction in thhe elevated temperature mechanical properties of a laminate due to a reduction in the glass‐transition temperature of the resin. It is also found thatthemositure absorption is a reversible process, in the sense that the initially dry properties of the laminate are recovered afterredrying the wet sample.

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