دانلود رایگان مقاله لاتین شکلی برگشت پذیر در نانولوله کربن از سایت الزویر
عنوان فارسی مقاله:
اثر شکل پذیری حافظه شکلی برگشت پذیر در نانولوله های کربنی تقویت شده نانوکامپوزیت اپوکسی
عنوان انگلیسی مقاله:
Reversible plasticity shape memory effect in carbon nanotubes reinforced epoxy nanocomposites
سال انتشار : 2016
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مقدمه انگلیسی مقاله:
1. Introduction
Shape Memory Polymers (SMPs) are smart materials which can be programmed to hold a temporary shape under certain environmental conditions and revert back to its original shape on application of suitable external stimulus [1]. SMPs have been designed to respond to various stimuli like temperature change, light, electricity, solvent, change in pH, etc [2,3]. Conventionally a thermo-mechanical cycle of a thermally activated SMP involves a programming step and a recovery step. In the programming step, the SMP is deformed at a temperature above the glass transition (Tg) and subsequently cooled below Tg while holding the deformation to fix a temporary shape. The recovery step involves reheating the SMP above Tg to recover the original shape. Contrary to the conventional method, in order to realize Reversible plasticity shape memory (RPSM) effect, a modified programming step is employed wherein the temporary shape can be fixed by plasticallydeforming the material at a temperature lower than Tg. This modified approach offers several advantages over the conventional approach like simplified programming step, improved recovery stress, faster recovery rate and higher recovery ratios [4,5]. It is to be noted that RPSM effect can be realized only when the material is deformed within a limit where no permanent defects like cracks occur and above the elastic limit (yield point) where there is plastic deformation. Another major drawback is low shape fixity due to the instantaneous recovery of elastic deformation. The effect of deformation temperature (Td) on the mechanical and shape memory properties have been studied by several researchers. Gall and coworkers [6,7] showed that the failure strain is maximum when Td is at the onset of the glass transition rather than above Tg. They also showed an improved recovery stress and recovery time when Td is less than Tg. Feldkamp and Rousseau [8] studied the effect of Td on epoxy based SMP and showed that the failure strain increased by five times at the onset of Tg. Lakhera et al. [9] studied an acrylate based SMP and observed a peak near the vicinity of Tg during constrained stress recovery for samples programmed at a temper- * Corresponding author. ature below Tg which was not observed for samples programmed attemperatures above Tg. Thereby showing that the recovery stress in cold programmed SMP is higher than that of SMP programmed at temperatures above Tg. Hence from the above studies it can be concluded that the glass transition region must be ideally in the vicinity of room temperature in order to realize RPSM at large plastic strains. The effect of stress relaxation on the shape fixity by programming under cold-compression was studied by Li and Xu [10]. They used a polystyrene based SMP to show that the shape fixity increased (>90%) with the increase in relaxation time. The term “RPSM” first appeared in the work of Rodriguez et al. [11] where they used a combination of a cross-linked network polymer with a linear polymer network to achieve shape memory assisted self-healing. The importance and distinction of RPSM effect were further emphasized in a review by Xie [4]. The ability to recover large plastic deformations by materials with RPSM properties has been applied in designing thermally activated self healing systems. Wornya et al. [12] performed nanoindentation tests on an acrylate based SMP and showed that the samples were able to completely heal the surface deformation when heated above Tg. Xiao et al. [13] developed graphene reinforced epoxy nanocomposites and studied the ability to heal surface scratches and observed that even with a very low volume percentage (0.0025%) of graphene the self-healing ability increased significantly. Li et al. [14] reinforced SMP fibers stretched at a temperature below Tg in a thermosetting polymer matrix and showed that the system was able to close wide cracks via localized heating. They also showed that increase in pre-strain increased the recovery stress which in turn improved the crack closing efficiency. A two-step bio-mimetic method was proposed by Li and coworkers [15,16] to seal and then heal the polymeric systems. The RPSM property assists in bringing the cracked surfaces together while the reinforced thermoplastic particles ensure healing at a molecular level. Previous studies show that, RPSM materials can effectively recover/heal large plastic deformations and surface defects and also assist in healing wide cracks by enabling crack-closure through a thermal trigger. It should be noted that the RPSM materials cannot heal wide cracks independently and require a secondary system to re-bond the cracked surfaces [14,15]. SMPs have exceptional properties likes high recoverable strain, low cost, easy processing, etc. but, their low mechanical properties, low recovery stress, and inherent insulating properties limit their applications [17]. In order to improve these properties, various strategies have been adopted including reinforcing the polymer matrix with fillers ranging from macro to nano scale. Several studies [18e21] have shown that addition of various nano fillers can efficiently improve the properties of bulk polymer while maintaining the characteristic behavior of the matrix. Among them carbon nanotubes with their exceptional mechanical, thermal and electrical properties [22] have been found successful in improving the matrix properties while improving the shape memory property of the matrix [23e27]. Koerner et al. [28] used morthane, a polyurethane-based thermoplastic elastomer filled with CNT and studied the shape memory properties. When compared to neat elastomer, CNT filled elastomer showed a significant increase in mechanical properties and shape memory properties like recovery stress and shape fixity. They also showed that the CNT filled elastomer can be actuated electrically and by an infrared light source, whereas the pure polymer could be actuated only by heat. The addition of carbon nanotubes in the SMP matrix simultaneously improved mechanical, shape memory and conducting properties, thereby overcoming the drawbacks of SMPs. The improvement in conducting properties with the addition of MWCNT provides alternate actuating mechanism via electricity which offers several advantages over actuating through external heat [29e31]. In this paper a commercially available structural grade epoxy resin was tailored to realize RPSM effect. MWCNT was added to the epoxy matrix with an objective to improve the mechanical and shape memory properties. The prepared nanocomposites were characterized for their mechanical, thermal, morphological, crystallographic and RPSM properties. A comprehensive study was systematically conducted on the effect of filler content and programming conditions like deformation level, stress relaxation time and strain rate on the RPSM properties and the results are discussed.
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کلمات کلیدی:
Reversible plasticity shape memory polymers: Key factors and ... onlinelibrary.wiley.com/doi/10.1002/polb.23916/full Sep 28, 2015 - The concept “reversible plasticity shape memory (RPSM)” has been proposed. It is used to emphasize shape memory effect (SME) achieved ... New Design Strategy for Reversible Plasticity Shape Memory ... pubs.acs.org/doi/abs/10.1021/am505937p by T Lin - 2014 - Cited by 7 - Related articles Nov 12, 2014 - Reversible plasticity shape memory (RPSM) is a new concept in the study of shape memory performance behavior and describes a ... New Design Strategy for Reversible Plasticity Shape Memory ... pubs.acs.org/doi/pdf/10.1021/am505937p by T Lin - 2014 - Cited by 7 - Related articles Nov 12, 2014 - KEYWORDS: shape memory polymers, reversible plasticity, amorphous network, ... plastic fixing” of shape memory alloys (SMAs), which occurs. Mechanics for Materials and Technologies https://books.google.com/books?isbn=3319560506 Holm Altenbach, Robert V. Goldstein, Evgenii Murashkin - 2017 - Technology & Engineering Abishera R, Velmurugan R, Gopal KVN (2017) Reversible plasticity shape memory effect in epoxy/cnt nanocomposites – a theoretical study. Composites ... Reversible Crystal Plasticity - Page vii - Google Books Result https://books.google.com/books?isbn=0883188694 Vladimir Boyko, Ruvin Garber, Arnold Kossevich - 1997 - Science Double shape memory 163 5.5. Semimicroscopic description of superelasticity and shape memory effects 165 Chapter 6. Reversible Plasticity of Ferroelastics ... Self-Healing Composites: Shape Memory Polymer Based Structures https://books.google.com/books?isbn=1118452429 Guoqiang Li - 2014 - Technology & Engineering Shape Memory Polymer Based Structures Guoqiang Li ... This effect is also termed by Xie [13] as “reversible plasticity shape memory effect (RP-SME)” to ...
