A. Rahman et al., USE OF LEAST-SQUARES METHOD TO OBTAIN RELAXATION FUNCTION OF AS4 CARBON-PEEK 3D BRAIDED COMPOSITES FROM DMA DATA, Journal of advanced materials, 27(3), 1996, pp. 51-54
Viscoelastic behavior is inherent to polymer matrix composites such as
an AS4 Carbon - PEEK 3D composite system. Two common quantities of ch
aracterizing viscoelastic behavior are the relaxation ''function'' G(t
), and the complex ''modulus'' G(omega). These two measures are relat
ed: for linear viscoelastic materials, the complex modulus is the Four
ier transform of the relaxation function. Thus, theoretically one only
needs to perform either of the two experiments and mathematically rec
over the other Practical considerations in converting G(omega) to G(t
) are discussed in this paper A method based upon the feast square tec
hnique is used. The method is applied to a AS4-PEEK 3D braided composi
te system. Complex shear modulii of the composite system are used to o
btain the corresponding time domain shear relaxation modulii. The conv
ersion is useful to generate time domain data from frequency domain da
ta when such data is unavailable from a conventional creep or stress r
elaxation test.