Mechanical performance of an optimized cork agglomerate core-glass fibre sandwich panel

Effect of Post-Cure on the Static and Viscoelastic Properties of a Polyester Resin

“…In both cases, the data were analyzed according to the respective ASTM standards. On the other hand, and as reported in the open literature [ 26 , 27 , 28 ], these short-term tests reveal to be an easy, fast, and reliable method to predict long-term behavior. In fact, due to the main costs incurred with long-term test programs, in addition to the fact that long periods between the development of new or improved materials and their applications are not allowed, it is highly desirable that the design data could be obtained by extrapolating the results obtained by short-term tests.…”

“…In general, the stress decreased over time to one value expected to be constant, but in the present work, this constant bending stress was not achieved because it focuses on short-term tests. These tests represent an easy, fast, and reliable method to predict long-term behavior [ 26 , 27 , 28 ]. Another similarity with the open literature is the existence of an initial stage, in which the stress decreases considerably with the remaining time [ 38 , 39 , 40 ].…”

“…In terms of stress relaxation, for example, literature reports complex models to the detriment of those based on spring-dashpot systems, because the data are not fitted by a linear function. Therefore, the Kohlrausch–Williams–Watts (KWW) function, an empirical “stretched exponential” function, is suggested by the open literature as an appropriate methodology to model the stress relaxation [ 27 , 28 , 39 , 40 , 48 , 49 ]. According with this model, the relaxation function ∅ as a function of time is given by Equation (4): where σ ( t ) and σ 0 are the stress at time t and at t = 0, respectively, β a fractional power exponent (known as non-exponential factor), and τ the KWW relaxation time.…”

“…The Findley’s power law is given by Equation (5): where ε ( t ) is the creep displacement at time t , ε 0 is the instantaneous elastic displacement or time-independent, A is the amplitude of transient creep (time-dependent), and n is a constant independent of the stress and generally less than one [ 51 ]. Several studies can be found in the open literature, where the Findley’s power law was also applied to short-term creep data [ 27 , 28 , 51 , 52 , 53 ].…”

Mechanical characterization of different epoxy resins enhanced with carbon nanofibers

“…For Ebalta neat resin this decrease is around 14.8%, and for Ebalta resin with 0.5 wt.% CNFs is about 13.2%. For the neat resins, in the literature essentially two mechanisms are referenced that can induce stress relaxation: a) chemical stress relaxation due to chain scission and crosslinking formation or scission, and b) physical stress relaxation due to molecular rearrangements that involve little primary bonding formation or breakage [42]. However, the CNFs presence demonstrated an effective enhancement of the mechanical properties with increasing filler content, up to 0.75% for Sicomin and 0.5% for Ebalta [43].…”