Weibull statistics of the lap-shear strength of a symmetric interface of amorphous poly(ethylene terephthalate)
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Weibull statistics of the lap‑shear strength of a symmetric interface of amorphous poly(ethylene terephthalate) Yuri M. Boiko1 Received: 10 June 2019 / Revised: 13 November 2019 / Accepted: 17 December 2019 © Springer-Verlag GmbH Germany, part of Springer Nature 2019
Abstract For the first time, the distribution of the lap-shear strength (σ) developed upon the contact of two amorphous bulk samples of poly(ethylene terephthalate) (PET) in the surroundings of the PET bulk glass transition temperature has been analysed as a function of healing temperature and healing time by using a Weibull statistical model. The Weibull parameters, Weibull modulus (m) and scale factor (σ0) of partially self-healed symmetric amorphous PET–PET interface have been estimated by analysing some tens of the lap-shear strength experimental data sets. It has been found that the σ0 values are very close to the corresponding mean σ values averaged for each test series, meaning that the Weibull analysis gives physically meaningful results. It has been shown that the majority of the σ experimental data sets can be described properly with the standard Weibull distribution function proposed for brittle solids. The m values for the PET–PET interface have been compared with those reported recently for the polymer–polymer interfaces of non-crystallizable amorphous polymers. The impact of the potential ability of an amorphous polymer to crystallize on the scatter in the measured interface lap-shear strength has been discussed. Keywords Interfaces · Self-healing · Adhesion · Glass transition · Mechanical properties · Statistics
Introduction The kinetics of the development of the “macroscopic” adhesion/cohesion interface mechanical properties such as lap-shear strength and fracture energy in the course of contact of two polymer pieces has been used successfully to analyse the “microscopic” molecular mechanisms of the self-healing process of polymer–polymer * Yuri M. Boiko [email protected] 1
Laboratory of Physics of Strength, Ioffe Physical-Technical Institute, 26 Politekhnicheskaya, St. Petersburg, Russia 194021
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interfaces [1–12] consisting in gradual disappearance of the interface gap via the chain segments interdiffusion, in the absence of low-molecular-weight species such as adhesives, additives, solvents, etc. For this purpose, the mean value of the interface strength (σav) or fracture energy averaged from a set of fracture tests of adhesive joints (or self-healed interfaces) formed at identical time–temperature and pressure conditions has commonly been used. By contrast, rather less attention has been paid to studying the distribution statistics of the interface strength itself. However, this factor can give an additional useful information aimed at a better understanding of the self-healing mechanisms of polymer–polymer interfaces and of the fracture mechanisms thereof [13–17]. More specifically, a Weibull statistical model [18–25], that had initially been proposed for brittle high-strengt
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