Shape Memory Polymers and Composites in Aerospace Applications

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Shape Memory Polymers and Composites in Aerospace Applications

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Prajakta Dipak Dhakate, Samyak Nilesh Chordia

Department of Polymer Engineering, Maharashtra Institute of Technology (MIT), Pune University, Pune-411038, Maharashtra, India

Abstract:- Shape memory polymers (SMP) and SMP based composites are typical smart materials, which can transform from their temporarily fixed configuration to their original configuration under external stimuli. Shape memory effect is an intrinsic property of polymers and changes according to different molecular weight and components of different polymers. They have inherent advantages like lightweight, large recoverable deformation capability, biocompatibility, etc. This paper reviews status of SMP nanocomposites, SMP filler composites in aerospace applications. We will discuss about the materials and structures which could be used and also about the general mechanism of SMPs and their composites, which have great potential for novel aerospace applications development.

Keywords: Shape memory polymers, SMP, polymers, composites, aerospace, applications

INTRODUCTION

SMPs are type of macro molecules which respond to external stimulus by changing its macroscopic properties (such as shape and color) and then recover its original shape from its temporary shape. SMPs have advantages of being lightweight and inexpensive and of having low density, high shape deformability, good biodegradability and an easily tailorable glass transition temperature compared with shape memory alloys (SMAs) and shape memory ceramics. Main drawbacks of SMPs are low recovery stress, low deformation stiffness, smaller energy output and longer recovery time.

To overcome these deficiencies, shape memory polymer composites (SMPCs) have come into existence. The results of studies on SMPCs indicate that they have superior strength, higher stiffness and certain special characteristics determined by what fillers are added, which can offer further advantages over SMPs.

SMP based composites are generally divided into particles- reinforced and fiber-reinforced composites. Particles- reinforced SMPCs, whose fillers are carbon black, carbon nanotubes, Fe3O4 nanoparticles, etc are used more as functional materials. Fiber-reinforced SMPCs, whose fillers include carbon, glass and Kevlar fibers, etc are usually used as structural materials because of their good mechanical properties.

There are some excellent reviews about the development and application of SMPs and SMPCs, such as a review written by Liu et al on SMPs and SMPCs and their applications in Aerospace applications. In addition to this, an article by Fengfeng Li et al, explains us about the progress of shape memory polymers and their composites in aerospace applications. This review focuses on the SMP/SMPC materials and their applications in aerospace field, which includes reflecting antennas, SMPC hinges, etc. Our goal is to track the applications, who have already completed the space

experiments, and to list new applications, who are potential for the aerospace-based industry.

MECHANISM OF SMP AND SMPCS

SMPs and SMPCs most valuable characteristics are their variable material properties above and below the transition temperature (glass transition temperature (Tg) or melting transition temperature (Tm)). Polymers are covalent or physically cross-linked, exhibiting viscoelastic to large strain above either Tm (crystalline polymers) or Tg (amorphous polymers), and elastic to small strain at low temperature. At the temperature above Tm/Tg, the polymer chain segments deform freely, and twist randomly around the skeleton bond, thereby leading to maximum entropy. The shape memory mechanism for polymers with significant shape memory property involves, accomplishment of shape programming by locking the polymeric segments without creep; a sharp transition of the modulus corresponding to temperature, which would promptly lead to a temporarily fixed shape at low temperature and stimulate shape recovery at high temperature; viscoelasticity above Tm/Tg which ensures a relatively complete shape recovery without residual strain.

The low mechanical properties of SMPs are limiting factors for their commercial applicability. Therefore, to overcome these drawbacks, SMPCs are developed. Reinforcing capability of continuous fibers is highest, followed by short fibers and finally particles. SMPCs for aerospace application is primarily continuous fiber reinforced SMPCs, normally carbon fiber. These continuous fiber reinforced SMPCs are able to undergo large macro bending deformations. Micro buckling will take place under large bending ratio when SMPC is heated to a temperature above Tg/Tm. Here, SMPC does not have enough stiffness to support those fibers in compression and thereby leading to microbuckling. It should be noted that the thickness of the SMPC is usually less than 2 mm, since a thicker laminate or a laminate with large modulus would have a large shear force to prevent the bending of fibers or damage the matrix.

EFFECT OF VARIOUS SPACE ENVIRONMENTS AND FACTORS ON SMP/SMPC

The selection of new raw materials for aerospace applications needs to withstand various ground simulated space conditions such as UV radiations, atomic oxygen, plasma environment(ions and electrons), space debris, etc which can lead to degradation of material in space environment , lead to damage in the structure and reduce the systems reliability. In this section, we will have a look through some of the important factors, which will affect the structures service life in the space environment

1. Vacuum2. Thermal cycling3. UV radiation1. Thermally responsive SMPs & SMPCs2. Electro-responsive SMPs and SMPCs3. Other responsive SMPs and SMPCsSMPC HingeSMPC boomsSMPC reflector antennasSolar arrays and deployable panelsMorphing structuresSMP and SMPC mandrels

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