By R M Guedes
Creep is the tendency of fabrics to deform while subjected to long term pressure, rather while uncovered to warmth. Fatigue phenomena take place whilst a fabric is subjected to cyclic loading, inflicting harm that could development to failure. either are severe components within the long term functionality and reliability of fabrics comparable to polymer matrix composites, that are usually uncovered to those varieties of stresses in civil engineering and different purposes. this crucial publication stories the newest study in modeling and predicting creep and fatigue in polymer matrix composites. the 1st a part of the ebook stories the modeling of viscoelastic and viscoplastic habit as a fashion of predicting functionality and repair existence. half discusses suggestions for modeling creep rupture and failure. the ultimate a part of the booklet addresses methods of trying out and predicting long term creep and fatigue in polymer matrix composites.
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Additional info for Creep and Fatigue in Polymer Matrix Composites (Woodhead Publishing in Materials)
Example text
Whilst these methods are of considerable value for basic investigations, in some relatively long-term applications it is permissible to apply the strain over a longer period. However, there is always an effect of the different strain histories upon the subsequent initial stress relaxation behavior of a polymer. 12 shows schematically a typical stress–time trace. Several mathematical expressions exist for the description of stress relaxation phenomena in polymers at a given temperature. 49] where σ0 = the maximum stress developed at the end of the straining phase, σt = the stress at any time t after the elongation had ceased, t = time after the elongation phase was completed, ∆σ (t) = σ0 – σt, n = the slope of the plot of ∆σ (t) against log t; this is equivalent to a rate of stress relaxation, I = the intercept on the value of ∆σ (t)/σ0 when log t = 0.
Use of this model (Fig. 14) assumes linear viscoelastic behavior of the polymer under investigation. The experimental strain behavior of a polymer as a function of time has been represented by conditions in the model corresponding to certain times (Fig. 14). The specimens were subjected to a constant stress σ at time t0. During step 1 for a time interval (t1 – t0), we observe an immediate elastic deformation of the Maxwell spring (at time t0) corresponding to diagram (a) in Fig. 14, followed by a slower extension of the Voigt element, (b); finally the Maxwell dashpot begins to move, corresponding to inelastic deformation, also shown in diagram (b).
Transient compliance factor g1 has similar meaning, operating on the creep compliance component. The factor g2 accounts for the influence of load rate on creep and depends on stress and temperature. The factor aσ is a time scale shift factor. This factor is in general a stress and temperature dependent function and modifies the viscoelastic response as a function of temperature and stress. Mathematically, aσ shifts the creep data parallel to the time axis relative to a master curve for creep strain versus time.