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Experimental investigation of Euler’s elastica: in-situ SEM nanowire post-buckling

Manecka-Padaż Aleksandra, Jenczyk Piotr, Pęcherski Ryszard B., Nykiel Anna

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2022

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Vol. 70, nr 6

art. no. e143648

EN

An in-situ nanoindenter with a flat tip was employed to conduct buckling tests of a single nanowire with simultaneous SEM imaging. A series of SEM images allowed us to calculate deflection. The deflection was confronted with the mathematical model of elastica. The post-buckling behaviour of nanowires is conducted in the framework of the nonlinear elasticity theory. Results show the significant effect of geometrical parameters on the stability of buckled nanowires.

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Silne efekty entropowe orientacji molekularnej w kinetyce krystalizacji polimerów

Ciupak Marcelina, Misztal-Faraj Beata, Pęcherski Ryszard B.

Przemysł Chemiczny

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2019

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T. 98, nr 11

1760--1764

PL

Obliczono i przedyskutowano wpływ orientacji molekularnej oraz temperatury na szybkość nukleacji i wzrostu kryształów ze wskazaniem na rolę entropii w kinetyce krystalizacji polimerów. W celu określenia efektów entropowych w całym zakresie orientacji molekularnej wywołanej naprężeniami rozciągającymi zastosowano dwa przybliżenia statystyki molekularnej. Badania doświadczalne kinetyki krystalizacji orientowanej przeprowadzono dla orientowanej włókniny z polilaktydu (PLLA) oraz nieorientowanego granulatu PLLA jako przykładowego polimeru, z wykorzystaniem różnicowego kalorymetru skaningowego DSC. Przedstawiono znaczny wpływ orientacji molekularnej na szybkość nukleacji, wzrostu kryształów i szybkość krystalizacji, wynikający ze spadku entropii fazy amorficznej w warunkach orientacji. Ujęte jest to w rozszerzonych modelach Hoffmana i Lauritzena oraz Avramiego i Evansa dla orientowanej krystalizacji i w eksperymentalnych wynikach badań kalorymetrycznych DSC.

EN

Effect of mol. orientation and temp. on the nucleation and crystal growth rates of polymers were calcd. and discussed to indicate the role of entropy in the kinetics of its crystn. Two approximations of mol. statistics were used to det. the entropic effects in the entire range of mol. orientation produced by tensile stresses. The exp. investigations on the oriented crystn. kinetics of polylactide nonwoven fibres and unoriented pellets were carried out by differential scanning calorimetry. High effects of the mol. orientation in the entropy strongly affecting the nucleation and crystal growth rates, as well as the crystn. rate were shown based on the Hoffman-Lauritzen and Avrami-Evans models.

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Virtual additive manufacturing based on semicrystalline polymer polyetheretherketone (PEEK)

Bajerski Paweł, Pęcherski Ryszard B., Chudy Damian

Engineering Transactions

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2019

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Vol. 67, iss. 2

157--165

EN

Virtual additive manufacturing (AM) is one of the new directions of research that is necessary to improve AM technology. Abaqus/SIMULIA software allows to simulate the whole process using user subroutines to expand solver capabilities. Two of the most important subroutines are UepActivationVol and UMATHT. The UepActivationVol is related to an activation of elements in accordance with the defined path of the process. The second one the UMATHT is used to implement and combine thermal and crystallization process [2]. The presented investigations describe the dual crystallization kinetics model for considered high temperature thermoplastic material Polyetheretherketone (PEEK). Furthermore, it is shown how to analyse the overall process with use of Abaqus/SIMULIA software. The innovation of the presented approach lies in the proper interpreting of the G-Code from Computeraided manufacturing software (CAM), which is an input for the real machines dedicated to AM. The path (coordinates of discrete points) and time of particular steps of the manufacturing process are extracted from the G-Code and are included as input parameters in the simulation code. The discretized part is simplification of the Computer-aided design (CAD) geometry. The final results show the effect implemented in user subroutines. Additionally, Differential Scanning Calorimetry (DSC) test results are presented in order to calculate crystallization and melting parameters. The presented work is the basis of the following investigations covering prediction of residual stresses, volumetric shrinkage and deformations.