Free volumes introduced by fractures of CFRP probed using positron annihilation

Uedono, Akira; Sako, K.; Ueno, Wataru; Kimura, Masao

doi:10.1016/j.compositesa.2019.04.020

Cited by 11 publications

(4 citation statements)

References 20 publications

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“…A carbon fiber reinforced polymer consisting of a bisphenol-A epoxy resin and PAN-based carbon fibers were investigated by PALS and X-ray computed tomography, in order to elucidate the microstructural changes occurring during fracture [ 84 ]. In situ measurements of X-CT during a tensile test allowed to observe the crack initiation and propagation in the sample.…”

Section: Discussion Of Some Pals Results In Polymeric Systemsmentioning

confidence: 99%

Probing the Free Volume in Polymers by Means of Positron Annihilation Lifetime Spectroscopy

Consolati

Nichetti²,

Quasso

2023

Polymers

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Positron annihilation lifetime spectroscopy (PALS) is a valuable technique to investigate defects in solids, such as vacancy clusters and grain boundaries in metals and alloys, as well as lattice imperfections in semiconductors. Positron spectroscopy is able to reveal the size, structure and concentration of vacancies with a sensitivity of 10−7. In the field of porous and amorphous systems, PALS can probe cavities in the range from a few tenths up to several tens of nm. In the case of polymers, PALS is one of the few techniques able to give information on the holes forming the free volume. This quantity, which cannot be measured with macroscopic techniques, is correlated to important mechanical, thermal, and transport properties of polymers. It can be deduced theoretically by applying suitable equations of state derived by cell models, and PALS supplies a quantitative measure of the free volume by probing the corresponding sub-nanometric holes. The system used is positronium (Ps), an unstable atom formed by a positron and an electron, whose lifetime can be related to the typical size of the holes. When analyzed in terms of continuous lifetimes, the positron annihilation spectrum allows one to gain insight into the distribution of the free volume holes, an almost unique feature of this technique. The present paper is an overview of PALS, addressed in particular to readers not familiar with this technique, with emphasis on the experimental aspects. After a general introduction on free volume, positronium, and the experimental apparatus needed to acquire the corresponding lifetime, some of the recent results obtained by various groups will be shown, highlighting the connections between the free volume as probed by PALS and structural properties of the investigated materials.

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Section: Discussion Of Some Pals Results In Polymeric Systemsmentioning

confidence: 99%

Probing the Free Volume in Polymers by Means of Positron Annihilation Lifetime Spectroscopy

Consolati

Nichetti²,

Quasso

2023

Polymers

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“…However, when considering the fatigue phenomenon of materials, if the microscopic behavior of the material is irreversible with respect to cyclic loading, it will eventually fatigue, and if it is reversible, there may be a fatigue limit. In a recent study, Uedono et al (2019) and Uematsu et al (2022) reported that the free volume of the matrix resin of CFRP increases when the material is deformed by static tensile loading or fatigue loading. In this study, the S-N diagram showed that a fatigue Fig.…”

Section: Results Of Positron Annihilation Methodsmentioning

confidence: 99%

“…The results revealed that the free volume increased with the number of cycles, but craze was not confirmed. Uedono et al (2019) conducted tensile tests using CFRPs and measured the free volume using positron annihilation. Their results confirmed that the free volume increased near the fracture.…”

Section: Introductionmentioning

confidence: 99%

Very high-cycle fatigue properties of 90° unidirectional CFRP laminates and evaluation of fatigue limits by free volume measurement using positron microscopy

Tazuke

Miyakoshi

Hosoi

et al. 2023

Mechanical Engineering Journal

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The objective of this study was to experimentally evaluate the fatigue limit of 90° unidirectional carbon fiber reinforced plastic (CFRP) laminates. The very high-cycle fatigue properties of the specimens were evaluated using ultrasonic and electromagnetic fatigue testing machines. Ultrasonic fatigue tests were conducted to obtain the fatigue properties under the giga-cycle regime. The specimen geometry was designed to resonate at 20 kHz, the specimen consisted of CFRP laminate and a metal tab to connect to the horn end of the testing machine. Additionally, the free volume of the matrix material, namely, epoxy resin, of the CFRP laminates was evaluated using the positron annihilation method. A slit was introduced in the specimen surface to identify the location of damage development, which facilitated the free volume measurement by positron microscopy. The obtained S-N curves reveal that failure did not occur at strain levels lower than εmax = 0.75% at the slit tip for all specimens up to N = 1.0  10 9 cycles. The free volume measurement for a specimen set above the threshold strain level revealed that the free volume increased in size and decreased in amount as the number of cycles increased. The test results revealed that the opposite trend existed below the threshold, which suggests that a fatigue limit may exist.

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“…Next, hybrid film-5, composite film-5, and the MSQ film were subjected to positron annihilation spectroscopy to investigate the formation of intramolecular void spaces and their size. Positron annihilation spectroscopy is quite useful for analyzing nanometer-sized pores; details regarding positron annihilation spectroscopy and its application for amorphous polymers are described elsewhere. − In the present experiments, the lifetime spectra of the samples were decomposed into three components. The longest lifetime (τ 3 ) corresponds to the pick-off annihilation of ortho -positronium ( o -Ps).…”

Section: Results and Discussionmentioning

confidence: 99%

Thermal Insulating Property of Silsesquioxane Hybrid Film Induced by Intramolecular Void Spaces

Hamada

Nakanishi

Okada

et al. 2021

ACS Appl. Polym. Mater.

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In the field of organic/inorganic hybrid polymers with the application as thermal insulating materials, ethylene-bridged polysilsesquioxane films are promising materials with enhanced thermal insulating properties due to the presence of intramolecular void spaces in their frameworks. With the aim of increasing the content in intramolecular void spaces to further enhance the thermal property of the resulting material, this paper describes the hydrosilylation reaction of hydrodimethyl-silylated oligomethylsilsesquioxane (MSQ-SiH) and octavinyl polyhedral oligomeric silsesquioxane (Vinyl-POSS) to produce a hybrid film with intramolecular void spaces, which was colorless and transparent due to the formation of covalent SiCCSi bonds. As a control experiment, a polymethylsilsesquixane (MSQ) film and an MSQ film containing 5 wt % of Vinyl-POSS (composite film-5) were prepared. Hybrid film-5 (prepared from MSQ-SiH and 5 wt % of Vinyl-POSS) exhibited lower density and thermal diffusivity (1.19 g/cm 3 and 1.21 × 10 −7 m 2 /s) than the MSQ film (1.34 g/cm 3 and 1.36 × 10 −7 m 2 /s) and composite film-5 (1.37 g/cm 3 and 1.58 × 10 −7 m 2 / s). Hybrid film-5 showed a 5% weight loss temperature (T d 5) and a 10% weight loss temperature (T d 10 ) of 382 and 453 °C, respectively, which were lower than those of the MSQ film (T d 5 of 436 °C and T d 10 of 481 °C) and higher than those of composite film-5 (T d 5 of 325 °C and T d 10 of 453 °C). Positron annihilation lifetime technique revealed that the hole volumes estimated from the value of the positronium lifetime component decreased in the order hybrid film-5 > MSQ film > composite film-5. Taken together, the results demonstrate that the thermal insulating property of the polysilsesquioxane film was improved by the formation of intramolecular void spaces around the POSS molecules.

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Free volumes introduced by fractures of CFRP probed using positron annihilation

Cited by 11 publications

References 20 publications

Probing the Free Volume in Polymers by Means of Positron Annihilation Lifetime Spectroscopy

Probing the Free Volume in Polymers by Means of Positron Annihilation Lifetime Spectroscopy

Very high-cycle fatigue properties of 90° unidirectional CFRP laminates and evaluation of fatigue limits by free volume measurement using positron microscopy

Thermal Insulating Property of Silsesquioxane Hybrid Film Induced by Intramolecular Void Spaces

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