4D Printing Prospects for the Aerospace Industry: a critical review

ScienceDirect

Available online at www.sciencedirect.com Procedia Manufacturing 00 (2018) 000–000

ScienceDirect

Available Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com

www.elsevier.com/locate/procedia

ScienceDirect ScienceDirect 

www.elsevier.com/locate/procedia

Procedia Manufacturing 00 (2018) 000–000 Procedia Manufacturing 18 (2018) 120–129

Procedia Manufacturing 00 (2017) for 000–000 18th Machining Innovations Conference Aerospace Industry, MIC 2018

www.elsevier.com/locate/procedia

4D Printing Prospects for the Aerospace Industry: a critical 18th Machining Innovations Conference for Aerospace Industry, MIC 2018review ,c

b a KyriakosProspects Ntouanogloufor , Panos Stavropoulosa Industry: * and Dimitris Mourtzisreview 4D Printing the Aerospace a critical

Manufacturing Engineering Conference 2017, MESICUniversity 2017, 28-30 Laboratory for Manufacturing Systems and Society Automation,International Department of Mechanical Engineering and Aeronautics, of Patras,June Patras ,c b aSpain a 26500, Greece 2017, Vigo (Pontevedra), b Hellenic Air Force, 120 Air Training Wing, 24100, Kalamata, Greece c a Department of Aeronautical Studies, HellenicDepartment Air Force Academy, Dekelia Air-Forceand Base, TGA 1010 University Athens, Greece Laboratory for Manufacturing Systems and Automation, of Mechanical Engineering Aeronautics, of Patras, Patras 26500, Greece b Hellenic Air Force, 120 Air Training Wing, 24100, Kalamata, Greece Abstract c Department of Aeronautical Studies, Hellenic Air Force Academy, Dekelia Air-Force Base, TGA 1010 Athens, Greece a

Kyriakos Ntouanoglou , Panos Stavropoulos * and Dimitris Mourtzis

Costing models for capacity optimization in Industry 4.0: Trade-off between used capacity and operational efficiency

a a 220% increase b Considering that from 1981 up 2016 there was production, due to thebincreased by 4.7% Compound A.to Santana , P. Afonsoa,*, inA.aircraft Zanin , R. Wernke Abstract Annual Growth Rate (CAGR) of travel demand, we can see through about the airlines industry prospects. Market’s free competition a and technology itself offer great opportunities to the of global aerospace where the demands for lower costs in manufacturing University Minho, 4800-058industry, Guimarães, Portugal b was a 220% increase in aircraft production, due to the increased by 4.7% Compound Considering thatassembly from 1981 up to - simplicity in - and per2016 hourthere flying costs - better aerodynamic - constantly increasing. Innovated 4D Unochapecó, 89809-000 Chapecó, characteristics SC, Brazil Annual Growth Ratecan (CAGR) of travel we can seeby through about the airlines industry prospects. Market’stime free competition printing techniques step further thedemand, above mentioned, minimizing component’s number and assembly in one hand and technology itself in offer great opportunities to the global aerospace industry, the demands lower manufacturing a radical change Computational Fluid Dynamics (CFDs) philosophy on where the other; prospectsfor that this costs papersinaims to review. - simplicity in assembly - and per hour flying costs - better aerodynamic characteristics - constantly increasing. Innovated 4D Abstract printing techniques can step further the above mentioned, by minimizing the component’s number and assembly time in one hand and a radical change inPublished Computational FluidB.V. Dynamics (CFDs) philosophy on the other; prospects that this papers aims to review. © 2018 The Authors. by Elsevier Under the concept of "Industry 4.0", production processes pushed Innovations to be increasingly interconnected, Peer review under responsibility of the scientific committee of the will 18th be Machining Conference for Aerospace © 2018 The Authors. Published by Elsevier B.V. information based on a real time basis and, necessarily, much more efficient. In this context, capacity optimization Industry. Peer-review under responsibility of the scientific committee of the 18th Machining Innovations Conference for Aerospace Industry. © 2018 The Authors. Published by of Elsevier B.V.maximization, contributing also for organization’s profitability and value. goes beyond the traditional aim capacity Peer review under responsibility ofcontinuous the scientific committee the 18th Machining Innovations Conference forinstead Aerospace Keywords: smart materials; additiveand manufacturing; self-assembly; shapeofoptimization; aircraft design Indeed, lean management improvement approaches suggest capacity optimization of Industry. maximization. The study of capacity optimization and costing models is an important research topic that deserves

contributions from both the practical and theoretical perspectives. This paper presents and discusses a mathematical Keywords: smart materials; additive manufacturing; self-assembly; shape optimization; aircraft design 1. Introduction model for capacity management based on different costing models (ABC and TDABC). A generic model has been developed and it was used to analyze idle capacity and to design strategies towards the maximization of organization’s Aviation development has two main Key Performance Indicators (KPIs), and the fuel and the value. Thesustainable trade-off capacity maximization vs operational efficiency is highlighted it is consumption shown that capacity 1. Introduction aircraft’s emissions (fuel and noise). Improved operational performance, mainly including greater range, better optimization might hide operational inefficiency. altitude capability, better low-speed performance, lower noise, wide-body comfort, better cargo handling, improved © 2017 Thesustainable Authors. Published by Elsevier B.V.main Key Performance Indicators (KPIs), the fuel consumption and the Aviation development has longer two systems response and redundancy, and structural took place dueEngineering to improved aircraft weight, by the use of Peer-review under responsibility of the scientific committee oflife; the Manufacturing Society International Conference aircraft’s emissions noise). performance, mainly including greater (fig.1). range, better light-weight materials(fuel [1], and trending the Improved aerospace operational industry to reduce fuel consumption and emissions Smart 2017. altitude better low-speed performance, noise, wide-body comfort, better cargo handling, materialscapability, and additive manufacturing technologieslower trends are said to assist aerospace industry to furtherimproved suppress systems response and redundancy, and longer structural life; took place due to improved aircraft weight, by the use of Keywords: Cost Models; ABC; TDABC; Capacity Management; Idle Capacity; Operational Efficiency light-weight materials [1], trending the aerospace industry to reduce fuel consumption and emissions (fig.1). Smart materials and additive manufacturing technologies trends are said to assist aerospace industry to further suppress * Corresponding author. Tel.: 30-2610-910160; fax: +30-2610-997744. 1. Introduction E-mail address: [email protected]

The cost of idle capacity is a fundamental information for companies and their management of extreme importance *2351-9789 Corresponding author. Tel.: 30-2610-910160; fax: +30-2610-997744. 2018 The Authors. Published by Elsevier in modern©production systems. In general, it isB.V. defined as unused capacity or production potential and can be measured E-mail address: Peer-review [email protected] responsibility of the scientific committee of the 18th Machining Innovations Conference for Aerospace Industry. in several ways: tons of production, available hours of manufacturing, etc. The management of the idle capacity * Paulo Afonso. Tel.: +351 253 510 761; fax: +351 253 604 741 2351-9789 © 2018 The Authors. Published by Elsevier B.V. E-mail address: [email protected] Peer-review under responsibility of the scientific committee of the 18th Machining Innovations Conference for Aerospace Industry. 2351-9789 © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the Manufacturing Engineering Society International Conference 2017. 2351-9789 © 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the 18th Machining Innovations Conference for Aerospace Industry. 10.1016/j.promfg.2018.11.016

2

Kyriakos Ntouanoglou et al. / Procedia Manufacturing 18 (2018) 120–129 K. Ntouanoglou et al / Procedia Manufacturing 00 (2018) 000–000

121

Airline Cost Structure (ACS), after the polymer’s revolution occurred. For instance, use of carbon fibre epoxy resin composite resulted in weight reduction, by up to 40% compared to aluminium. Airbus manufactures A380 by using approximately 25% composites parts [2] while the Boeing 787 utilises about twice this amount [3]. An optimized airfoil, by utilizing smart materials, can produce the optimum Lift to Drag (L/D) ratio and drastically contribute in the optimization of the aforementioned KPIs. After 1980, the L/D ratio has significantly improved, by about 15% compared to the past [4]. Numerous costs contribute in an ACS for an airline company (fig. 2). By optimizing the airfoils for several kinds of speed, we can intervene to some of them, such as Aircraft Fuels [5] or Maintenance, Repair, and Overhaul (MRO) (containing Airframe Materials, Direct Maintenance and Labour for Airframes), constituting almost 42.8% of the total ACS [6], a very significant percentage. The design phase up to now is a very strict process for engineers, depending on aircraft specifications and performance requirements. Optimization of aircraft wing design for just one flight status is required. Smart materials are providing the chance to optimize wing shape for all the flight status by reshaping them. Depending on the smart materials specifications and by using appropriate Computational Aided Design (CAD) software for modelling, simulation and multi-objective design optimization it is far freer for the engineers to ignore the design restrictions and extend the limits of the “trade-offs” [7]. Optimum goal for aircraft design engineers is biomimetic. Changing the geometry of wings and tails, jackdaws [8] and other birds [9], manoeuvres during flight. There are several ways in order to transform wings to minimize drag and gain lift, such as: a) wing folding or expanding, b) wing twisting supinating or pronating, c) wrist flexing or extending [10], d) “groovy” skin etc., and there are several examples that inspired aircraft engineers to introduce them in aerospace industry such as movable wing surfaces to counteract gusts loads (sea birds), winglets providing a barrier against the vortex (eagles) and innovated ideas such as retractable brush fringe and a velvet-like coating on aircraft landing gear (owls) and “groovy” skin like dolphins and sharks to reduce their drag [11]. By 2025, 4D-printing technology in aerospace is anticipated to hold a market share of over 25%, following the military and defence sector [12]. The 4D printing, space memory technique, could help in forming a self-deploying structure, which is applicable in the aerospace segment such as recent developments in Airbus S.A.S. [13].

Figure 1: Average fuel burn for new commercial jet aircraft 1960 to 2014 (1968=100) [5]

Figure 2: 2014 Cost Management Group (CMG) [6]

2. Motivation With a based on a 3.6% average CAGR travel demand, International Air Transport Association (IATA) expects 7.8 billion passengers to travel in 2036, a near doubling of the 4 billion air travellers expected to fly this year [14]. Airline companies’ strong demand and the aircraft manufacturer’s competition are pointing to a great robust aerospace market for the next years. Backlog orders across the industry are being increased, and for both Boeing and Airbus exceed the 12,000 aircrafts. This backlog is split evenly between the two rivals. The value of all these planes is likely in excess of $2 trillion, as Airbus stated in mid-2017 that its backlog value alone exceeds $1 trillion. It needs more than 8 years, to clear the total backlog using recent annual delivery data from both firms. The value of aircraft sub-components including pumps, motors and actuators have increased thanks in small part to new aircraft production, but largely as a result of increasing demand for air services [15]. Introducing 4D-printing, AM could minimize the value concerning spare parts, by minimizing their use and their needs for service. Currently,

122

Kyriakos Ntouanoglou et al. / Procedia Manufacturing 18 (2018) 120–129 K. Ntouanoglou et al / Procedia Manufacturing 00 (2018) 000–000

3

despite growing revenue, the average profit margin for the airlines hovers at about 2.5% on a global basis. To cope with expansion demands, most airlines by focusing on a lean strategy are increasingly outsourcing, because of their needs for specialized MRO and for reducing inventory risk, complexity and cost. This strategy could be significantly be changed by introducing 4D printing [16]. With rapidly aging fleets in the mature markets, many airline companies are now focused on replacing their older fleets for more fuel-efficient, technologically advanced aircrafts. In fact, it is estimated that around 40% of all new aircraft deliveries over the next 20 years, will be for replacement purposes [17]. One of the most exciting trends in the aviation sector is moving towards smart materials, in a long term, Graphene considered one of the most popular among these, but in a short term, Boeing’s “Microlattice”, which is a light, flexible yet extremely strong material, used in non-structural parts of the plane such as seats and the interior, stands out [18]. Aerospace systems are complex internally and externally, containing functional relationships and interactions that exhibit a challenging array of design features, technical specialties, materials, manufacturing processes, and assembly methods. The challenge here is not just the many elements, but also the fact that they interact in ways that are not always straightforward, comprising larger systems [19]. Innovation, as proposed by Utterback, is a key point in conjunction with the evolution strategy [20]. The Fluid Phase, is characterized by extremely rapid product innovation, many variety of products and the firms building those proliferate. The Transition Phase comes next, where innovation shifts to processes – that means, design, development, and manufacturing innovation, now, the number of firms participating drops quickly. In the final Specific Phase, even major process changes are unlikely, and competition reduces to cost and customer satisfaction, achieved through incremental improvements. In this innovated project, where AM for different aerospace parts is now changing by adding “time” (fig.3), the largest companies are being followed by Small and Medium Enterprises (SME’s) in this Fluid Phase, adding each one her different “trigger” striving their new processes into this path.

Figure 3: Flow chart of 3D design process (bottom) and proposed 4D design process (upper).

3. Morphing structures for aerospace The aircraft design and modern morphing structures are connected to a unique way, for example, according to thrust and airspeed, there will be an ideal wing configuration for every mission [21]. The primary category of wing configuration is comprised of collapsing wings, variable-clear wings, variable-traverse wings, and deployable wings. The secondary category is comprised of curving wing, adaptable winglets, variable-harmony wings, and variablecamber wings. Finally, the third and smaller category is comprised of variable-airfoil and bulging wings [22]. The three major categories of wing morphing are shown in the following table: planform alteration, out-of- plane transformation, and airfoil adjustment. Next figure includes the sum, of the available literature for every parameter of wing morphing, along with additional information that provide the researcher a wide range of the accomplished work

4

Kyriakos Ntouanoglou et al. / Procedia Manufacturing 18 (2018) 120–129 K. Ntouanoglou et al / Procedia Manufacturing 00 (2018) 000–000

123

in this sector [23]. According to Jian Su et al. there are four morphing structures fulfilling the needs for aerospace surfaces: auxetic honeycomb structures, variable-stiffness tube structures, multi-stable structures, corrugated structures.

Figure 4: Three major types of shape morphing wings [24]

Results demonstrate that the achievement of noise gradation can vary from -3 db to +2 db, in the case of small angles of attack, by adapting the morphing profiles. Nevertheless, the tailoring process does not affect or improve in any way the lift coefficient and lift-to-drag ratio for certain cases [24]. The following special properties are attributed to the Materials with Negative Poisson’s Ratio (NPR), for example the auxetic honeycomb structures: a) High in-plane indentation resistance; b) Good fracture toughness;季c) High transverse shear modulus; and, d) High dynamic properties [25]. With the use of Finite Elements Module (FEM), Quantian Luo and Liyong Tong [26][27] have demonstrated that the outcomes of the extensional disfiguration and constraint moments for symmetric planes are, as expected, significant and thus they should be taken into consideration. The two major pros of morphing structures are strength and deformability. The existing types of variable-stiffness tube structures are the following three: a) pneumatic muscle fiber, b) SMP composite tube and c) fluidic flexible matrix composite (F 2MC) tube, offering a flexible matrix in order to create a structure [27]. The ability that multi-stable stages structures have to reform into different phases depends heavily on stimuli’s range [28]. A large variety of morphing structures have been developed: from morphing-airfoil wings with bi-stable structures switching from stiff to compliant modes [29] up to morphing wing trailing edges controlling four states by changing the upper surface and the lower surface, both of which are made of bi-stable structures [30] and with different shape states such as from straight to fully swept [31]. Let us assume a morphing wing that is heavier than a regular wing of a similar size due to the inclusion of pivots, hinges, actuators, and so on. Moreover, the power required to impel the morphing wing is computed as a percentage increase in mission fuel required. Both of these 'penalties' are considered over a considerable amount of values, keeping in mind that the end goal is to exhibit the sensitivity to these effects. The energy efficiency is represented by the optimization metric of minimum weight of fuel burned, rather than the traditional methodology of minimizing the vehicle weight, similarly optimized non-morphing (fixed-wing) configuration. From the results, we can understand that there are some boundaries. Giving an example, of adding ‘good weight’ to a baseline, the weight factor were about two and the actuation penalty 10%, then, in this case, the mission benefit would be approximately 22% less fuel burned. Any actual values, including reduced vehicle weight, or increased range, etc. (and also the cost effects) would obviously be specific to the mission [32]. Another key problem concerns the various design patterns of the morphing structures, depending on the purpose that was manufactured for. For example, there have been up to this point various compliant structures-approaches, which aim was to seal the gaps between high lift devices and the wing [33]. Kunz was the first to present a kind of sliding interface, with an additional flap attached to the main flap [34], where dislocations between flap and wing have been detected. Diller and Miller [35], later developed and patented a by some manner cumbersome due to elastomer skins, mechanical/compliant transition to cover the span-wise and end-chord partial dislocations between the flap and wing. Caton et al. [36] followed with the development of a similar design, which consisted of two short rods sliding into the elastomer skin, in addition to the mechanical one rod mechanism of prementioned. Lastly, Boeing [37] presented the concept of multiple ribs that slide in and out of a spanwise rod embedded within the wing and NASA [38] of a wedge elastomer skin to bridge the span-wise gap between the flap and wing. Furthermore, the main problem of corrugated structures is that an appropriate configuration of a flexible skin must be performed with a valid method, in order to optimize a smooth configuration, when there is the need for bending or folding [22]. These kinds of morphing structures are covered with corrugated skins [39] and with the use of flexible rubber to fill the structure and become smooth [40][41] or with the use of a segmented skin similar to fish scales as a cover [42], can be morphed within a

124

Kyriakos Ntouanoglou et al. / Procedia Manufacturing 18 (2018) 120–129 K. Ntouanoglou et al / Procedia Manufacturing 00 (2018) 000–000

5

specified Reynolds Number, the eddies of their surfaces can be formed similar to streamline airfoils [43]. With detailed examination of the above, we draw to a close that there is no standard procedure for designing a morphing structure and depends heavily on the aerodynamic characteristics that the user wishes to embed to the morphing airfoil. 4. Smart/adaptive materials According to Bogue, the recent developments in smart material technology can be divided into three main categories: self-healing (SH) materials, smart sensing materials and sensing skins and shape-changing materials [44]. The self healing materials of the first category can react to failures or damages, a very important ability, when we have to assure the quality of the final product. The research covers a broad field of various materials, ranging from epoxy system that uses microcapsules which contain a healing agent and a catalyst [45], to metallosupramolecular polymers that must be exposed to UV light in order to be repaired [46] or the development of a self-healing coating for metals, that starts healing instantly after being damaged, in order to prevent corrosion of the underlying metal [47]. The detection of a possible deterioration or potential damage of a material in the initial stage is a very important asset for aerospace engineers. The detection of the stresses and therefore the overall fatigue is basic for prevention. A class of fiber Bragg grating (FBG) sensors have been developed and attracted much interest, due to their ability to incorporate into various materials such as polymeric [48] or composite materials [49], in order to detect key variables such as stress and strain, pressure, vibration, impact and temperature, for constant monitoring. Despite the abandonment of these kinds of projects in the 1990s, because it was suggested that they were not capable to be routinely deployed due to fabrication obstacles, European Union funded SmartFiber project that started in 2010 and was completed in 2014. The next stage was the development of a new type of sensor interrogation method by Dellicolli. This sensor was based on a numerical analysis of an FBG sensor subjected to non-uniform strain [50] as part of a project funded from the US Defense Department [51] for similar research in the Michigan State University. Finally, a variety of projects started developing in mid-1990 from NASA’s Langley Research Center in the field of the shape-change materials. The main goal of these projects was to explore related key enabling technologies. The most famous of these technologies was a wing known as DARPA (Defense Advanced Research Projects Agency)/AFRL (Air Force Research Laboratories)/NASA Smart Wing program [52], which was morphable, high rate and hingeless. The prementioned projects have spanned many research programs from many universities worldwide. Their main goal was the research in the possible combinations of different materials, such as the magnet-filler polymer matrix composite (MAGPOL), which contains magnetic nanoparticles attached to a soft polymer (silicone) matrix which has the ability to deform in a large scale. As an example, we will make a reference to the Nanyang Technological University [53] or at Beijing Jiao-Tong where two types of SMP-based structures were examined: aluminum/SM-polyurethane/aluminum and steel/SM-polyurethane/steel. The results demonstrated that the development of sandwich-like structures had a significant improvement in shape recovery stress [54]. Finally, MIT Self-assembly Lab has developed a conceptual project for a system of programmable materials called Logic Matter that demonstrates embedded computation and programmability (the digital logic gate, into a physical module, as a mechanical NAND gate) within a physical building block [55]. Addington and Schodek [56] suggest that the majority of these smart materials have five characteristics in common: immediacy, transiency, self-actuation, directness and selectivity. In order to quantify the benefits of smart materials, an accurate categorization needs to be done, depending on the stimuli and their responsiveness to the user. This can be achieved by defining a system with inputs and outputs (fig.5) [57]. The categorization process of the stimuli and their response can be charted in different ways; one of the key objectives of materials science is to incorporate as many lines as possible inside this circle, in order to have as a result greater flexibility in the fields of design and manufacturing. Depending the needs, we can proceed to the choice of the preferred material, for example, if the user’s material needs includes the ability to withstand high strains (8–10%), this makes SMAs useful for enduring large deformations [58], such as morphing wings [59] or Boeings’ high stiffness aerostructures [60]. Another aspect of the smart materials is their interaction with the inputs and outputs, for example it can be a bi-directional equation or in balance (fig.6). An accurate example of a bi-directional equation is the development of piezoelectric smart materials, which they show response to an electrical stimulus by producing deformation, and further respond to a deformation by producing electricity [61][62]. The general conclusion is that the core difference of the smart materials is their flexibility concerning the designer, the product and the user [63]. The Arnall’s concept “material immateriality” is better understood if we examine carefully that he combined characteristics of versatility, the concept of smart materials occupying the space and the

6

Kyriakos Ntouanoglou et al. / Procedia Manufacturing 18 (2018) 120–129 K. Ntouanoglou et al / Procedia Manufacturing 00 (2018) 000–000

125

concept of “immediate response” [64]. These kinds of materials are highly complex in nature, thus creating obstacles concerning the processing and producing, where unfortunately there has not been developed an efficient way to use them. Furthermore, the philosophy behind the design process is very different in comparison to the conventional materials. In order to fully incorporate the smart materials in various aerospace applications, and be products of the mass industry, we need to develop new methodologies and studies, so we can understand their functionality and efficiency of these materials, and not just their separate properties. This process is up to now uncharted, without specific methodologies or addressing problems concerning quality assurance, and for this reason, studies for different applications are taking part, estimating the whole transformation spectrum and not only two or more statuses. Thorough examination must be done, in order to investigate the nature of their properties, the material’s life cycle (fatigue etc.), and their efficiency in terms of functionality throughout their lifespan [65].

Figure 6: Smart materials having a bi-directional effect [66]

Figure 5: Graph of the transition phenomena connecting stimulus and response [66]

5. 3D - Additive Manufacturing (AM) for aerospace Airbus holds the record with more than one thousand 3D printed parts. Fusion Deposition Modeling (FDM) materials of high performance, the most well known of them being the excellent strength-to-weight ratio compliant material ULTEM 9085, are used in the new A350 XWB [67]. The 3D printing technology market for the aerospace industry is expected to grow from USD 714.5 Million in 2017 to USD 3,057.9 Million by 2022, with a CAGR of 27.42% [68]. Thanks to these incredibly high grow rates, which are the result of the increasing interest for air travel, AM attracts the interest of investors and technology specialists. AM’s immeasurable contribution in the field of industry designs, constructs and repairs aircraft is in the aviation supply chain [69], where evaluation tests are taking part for estimating future prospects concerning spare parts [70], the impact of reducing inventory levels as well as the costs of logistics [71]. Currently, more and more parts for aircraft and tooling are being produced by AM technology. Great companies examples are GE Aviation’s 3D-printed fuel nozzles for jet engines, which consists of 20 separately parts assembled to one piece, thus reducing the cost of manufacturing by 75% [72] and the Airbus replacements of the traditional interior components, such as brackets or cable routing plates [73]. In addition, Boeing decided to incorporate 3D thermoplastic printing for prototypes and components for 737, 747, 777 and 787 aircrafts [74]. According to Butler, the producers and parts suppliers insist for Just In Time (JIT) management, in order to reduce the cost of expensive tooling, minimize the time of production process, reduce and eliminate waste disposal and weight, customize parts and incorporate new designs to minimize the quantity of parts required for assembly [75]. Furthermore, the outcome from the reduction of part counts and connection points has a major improvement in reliability [76] while waste production is minimized, a highly important attribute when expensive aerospace materials are being used, such as titanium [77]. Finally, technology’s versatility is enhanced, leading to the manufacturing of different products with reduced changeover time and effort [78]. In the other hand, experts are quite thoughtful and suggest that integrated and thorough research has to be developed first before they start production of 3D printed parts, and the main reason is the assurance of the flight safety [75]. Furthermore, Birtchnell et al. have stated that traditional methods used in

Kyriakos Ntouanoglou et al. / Procedia Manufacturing 18 (2018) 120–129 K. Ntouanoglou et al / Procedia Manufacturing 00 (2018) 000–000

126

7

manufacturing industry are up to this point more efficient, even to an increased AM printing speed [79], and the main reason is the underperformance of AM, when producing large Aerospace and Defense (A&D) components [80]. Another concern is the ability of AM technology to perform on the sectors of accuracy and the replication. The A&D needs are less than 10 microns with almost 2-micron replication; while in most metal 3D printers is 30-40 microns [77]. Lastly, other reasons that AM can’t make its breakthrough in the aerospace industry yet, are the materials’ costs (high) and diversity (high) (AM stainless steel costs 100 times more than this used for commercial-grade) [81] and the lack of design philosophy and versatility (systems’ availability that can print on different materials is considerably low) [82] and thorough examination of issues concerning the quality assurance and the safety are holding up the AM’s technology “bing-bang”. Nevertheless, several sectors of AM technology are being developed in the field of quality issues, as well as different methods, from infra-red and high speed visual up to simple temperature or a combination [83]. 6. 4D – Additive Manufacturing for aerospace The term 4D Printing refers to the use of the traditional 3D printing for the creation of objects with the incorporation of different materials, which are defined as smart materials and have the unique property of changing shape over time or other properties, when triggered by an external source of energy [84]. Due to the new challenges, arises simultaneously the necessity for deeper knowledge from engineers, of AM, advanced smart materials and design (aerospace’s morphing structures) key cores insights [85]. These new requirements sometimes push these key cores separately to their limits; AM for example needs to pass from the phase of producing monofunctional parts to the use of nanotechnologies [86]. While the analysis of the future aspects of 4D printing technology market is already in progress, specifically in the topics of programmable matter, end user industry and future scope, it is expected that 4D printing technology market will be broadly commercialized by 2019. Although the printing technology is still in its infancy, the global market is expected to grow with compound annual growth of 42.5% between 2019 and 2025, reaching USD 537.8 million. The 4D printing industry is expected to have a major future impact into sectors such as aerospace, military and defense, healthcare, automotive, clothing and construction [87], in the same manner as the impact that 3D technology had in the past. The commercial smart materials are classified in two main categories: 1) Shape Memory Alloys (SMAs) and 2) Shape Memory Polymers (SMPs) [88]. The transformation of the SMA’s, takes Table 1: SMA and SMP comparison

Material Property

Ti/Ni Shape Memory Alloy

Recovery Stress Recovery strain
 At low temperature At high temperature Density
 Phase transformations Shaping
 Cost
 Heat conductivity

200-400 MPa 6% Soft Hard 6-7 g/cm3 Martensitic, R-phase Difficult Expensive High

Shape Memory Polymer 1-3 MPa 50-600% Hard Soft 1 g/cm3 Glass Transition Easy Cheap Fig. 7: The 3 main technologies constituting 4D printing, Low with their pros and cons

place when balancing between two phases, martensite (low temperature) and austenite phase (high temperature) [89][90]; the transformation of the SMP’s occurs in a bi-directional manner to a temporary shape when exposed to a number of external stimuli such as temperature [91][92]. Hiltz’s compared Nitinol, an extremely popular in aerospace industry Titanium/Nickel SMA, that was developed at the Naval Ordinance Lab [93] with an SMP, that both have been already 4D printed [94] [95] [96], and the results are shown in previous table [97].

8

Kyriakos Ntouanoglou et al. / Procedia Manufacturing 18 (2018) 120–129 K. Ntouanoglou et al / Procedia Manufacturing 00 (2018) 000–000

127

7. Prospects As it is represented in previous figure, the merger of the 3 main innovated technologies results in the 4D printing technology, along with some pros and cons we have already mentioned (fig.7). In order to gain a better understanding of the future prospects, first we have to proceed to a thorough examination of what are the actual pros and cons that 4D printing technology has to offer to the aerospace industry. To summarize, smart materials can be used to replace actuators and hinges, thus minimizing the heavier morphing in comparison to the conventional one. Furthermore, the existence of various structures (concerning the gaps between high lift devices and the wing), renders the need for different design obsolete. Thus, the focus is on the establishment of the design philosophy behind the material transformation, which depends on the volume of the planned transformation and the customization of properties that are set to meet user demands. Regarding the smart materials, there is an imperative need for the development of methodologies and their incorporation in aerospace applications, in order to provide assurance for various quality issues, for example the accuracy of the product and its replication. Lastly, it will be required the incorporation of the latest technology innovation from AM companies, in order to cover the increasing demands of the aerospace industry for the production of larger and more complex parts, which are constructed from multiple materials. 8. Conclusions For fulfilling the objective purpose of this paper, an effort was made, for collectively referred of summarized pros and cons, for what 4D printing in aerospace industry composed of (Morphing Structures, Smart Materials, 3D AM) recognizing this way the prospects. It is a fact that the efforts of the researchers and the AM companies needs to be concentrated in documentation of the methodologies for each material and procedure, for the first ones, and innovation for the 4D printers and their software for the others. Most often used forms of 4D printing, constitutes, up to now, Polyjet and syringe printing. However, there are so many other 3D printing techniques that can be developed into 4D, each of them, with their pros and cons [88]. 9. References

[1] Christopher ST, Joshua DZ, James IN. Managing New Product Development and Supply Chain Risks: The Boeing 787 Case. Supply Chain Forum: An International Journal 2015;10(2):74-86. [2] NRC. Aeronautical Technologies for the Twenty-First Century. The National Academies Press; 1992. [3] Mocenco D. Supply Chain Management Risks: The A350 Development Program. In: Ana JS, Vladimir K, Jadranka B, editors. Economic and Social Development (Book of Proceedings), 5th Eastern European Economic and Social Development Conference on Social Responsibility, 21-22 May, Belgrade, Serbia; 2015, p. 38-49. [4] Joosung JL. Historical and Future Trends in Aircraft Performance, Cost, and Emissions. Massachusetts Institute of Technology; 2000. Journal 2015;10(2):74-86. [5] Anastasia K, Daniel R. Fuel efficiency trends for new commercial jet aircraft: 1960 to 2014. International Council on Clean Transportation; 2015. [6] EUROCONTROL. Standard Inputs for EUROCONTROL Cost-Benefit Analyses. 7th ed. Brussels: EUROCONTROL Headquarters; 2015. [7] Tibbits SJE. 4D Printing – Multi-Material Shape Change. Architectural Design 2014; 84(1): 116–121. [8] Rosen M, Hedenstrom A. Gliding flight in a jackdaw: a wind tunnel study. Journal of Experimental Biology 2001; 204:1153-1166. [9] Thomas ALR. The flight of birds that have wings and a tail: variable geometry expands the envelope of flight performance. Journal of Theoretical Biology 1996;183:23745. [10] Douglas LA, Joseph WB, Roslyn D, Andrea HG, Benjamin G, David L, Paolo SS, Dimitri AS. The biophysics of bird flight: functional relationships integrate aerodynamics, morphology, kinematics, muscles, and sensors. Canadian Journal of Zoology 2015; 93(12): 961-75. [11] Biomimeticsummit.com. Airbus aircraft design inspired by Nature; 2018. [12] Ramesh S, Sai KR, Usha C, N KN, Adithyakumar CR, Lohith KR. Advancements in the Research of 4D Printing-A Review. IOP Conference Series: Materials Science and Engineering, International Conference on Advances in Manufacturing, Materials and Energy Engineering, 2-3 March, Karnataka, India; 2018, 376:012123. [13] Grand View Research Inc. 4D Printing Market Analysis By Material (Programmable Carbon Fiber, Programmable Wood, Programmable Textiles), By End-use (Defense, Aerospace, Automotive, Textile, Healthcare), By Region, And Segment Forecasts, 2018-2025; 2017. [14] International Air Transport Association (IATA). 2036 Forecast Reveals Air Passengers Will Nearly Double to 7.8 Billion; 2017. [15] Guckes M. High Demand Creates Growth in Aerospace Industry. In: Chris Koepfer, editor-in-chief. Production Machining, Cincinnati: Gardner Business Media, Inc.; 2017. [16] Borgogna A, Majdalani F, Monti L, Tahan C. How rapid growth and change are reshaping aviation. In: strategy& report. Global Aerospace Summit 2014 [17] Gates D. 5 Key Trends Impacting the Aerospace Sector and What They Mean for Growth. Industry Week 2016. [18] Stannard J. Top 5 aviation innovations for the future. The New Economy 2017. [19] Murman E, Allen T, Bozdogan K, Cutcher-Gershenfeld J, McManus H, Nightingale D, Rebentisch E, Shields T, 
Stahl F, 
Walton M, Warmkessel J, Weiss S, Widnall S. Lean EnterpriseValue, Insights from MIT’s Lean Aerospace Initiative. 1st ed. New York: Palgrave; 2002. [20] Utterback JM. Mastering the dynamics of innovation, How companies can seize opportunities in the face of technological change. 1st ed. Boston, Mass.: Harvard Business School Press; 1994. [21] Joshi SP, Tidwell Z, Crossley WA, Sekaripuram Ramakrishnan. Comparison of morphing wing strategies based upon aircraft performance impacts. In: Proceedings of the 45th AIAA/ASME/ ASCE/AHS/ASC structures, structural dynamics, and materials conference, 19-22 April, Palm Springs: California; 2004, Paper 2004-1722.

128

Kyriakos Ntouanoglou et al. / Procedia Manufacturing 18 (2018) 120–129 K. Ntouanoglou et al / Procedia Manufacturing 00 (2018) 000–000

9

[22] Sun J, Guan Q, Liu Y, Leng J and the references therein. Morphing aircraft based on smart materials and structures: A state-of-the-art review. Journal of Intelligent Material Systems and Structures
2016; 27(17): 2289-312. [23] Barbarino S, Bilgen O, Ajaj RM, Friswell MI, Inman DJ. A Review of Morphing Aircraft. Journal of Intelligent Material Systems and Structures 2011; 22(9):823-77. [24] Ai Q, Azarpeyvand M, Lachenal, X, Weaver PM. Aerodynamic and aeroacoustic performance of airfoils with morphing structures. Wind Energy 2015, 19:1325–39. [25] Q. Liu. Literature Review: Materials with Negative Poisson's Ratios and Potential Applications to Aerospace and Defence. DSTO Defence Science and Technology Organisation; 2006. [26] Quantian L, Liyong T. Adaptive pressure-controlled cellular structures for shape morphing, I: design and analysis. Smart Materials and Structures 2013; 22(5):16pp. [27] Quantian L, Liyong T. Adaptive pressure-controlled cellular structures for shape morphing, II: design and analysis. Smart Materials and Structures 2013; 22(5):12pp. [28] Kumar P, Kumar S. Shape Memory Alloy (SMA) A Multi Purpose Smart Material. International Journal of Engineering and Technical Research 2014; April’s Special Issue: p. 282-85. [29] Andres AF, Izabela KK, Mathias R, Waeber T, Ermanni P. Passive load alleviation aerofoil concept with variable stiffness multi-stable composites. Composite Structures 2014; 116:235-42. [30] Mattioni F, Weaver PM, Friswell MI, Potter KD. Modelling and applications of thermally induced multistable composites with piecewise variation of lay-up in the planform. In: Proceedings of the 48th AIAA/ASME/ASCE/AHS/ASC structures, structural dynamics, and materials conference, Honolulu: Hawaii; 2007, Paper 2007-2262. [31] Mattioni F, Gatto A, Weaver PM, Friswell MI, Potter KD. The application of residual stress tailoring of snap-through composites for variable sweep wings. In: Proceedings of the 47th AIAA/ASME/ASCE/AHS/ASC structures, structural dynamics, and materials conference, Newport: Rhode Island ; 2006, Paper 2006-1972. [32] Moorhouse D, Sanders B, M. von Spakovsky, Butt J. Benefits and design challenges of adaptive structures for morphing aircraft. Aeronautical Journal 2006;110(1105):157-62. [33] Ninian D, Dakka SM. Design, Development and Testing of Shape Shifting Wing Model. Journal Aerospace 2017;4(4):52. [34] Kunz R. Apparatus for Closing an Air Gap between a Flap and an Aircraft. U.S. Patent No. US4471925A, 18 September 1984. [35] Diller JB, Miller NF. Elastomeric Transition for Aircraft Control Surface. U.S. Patent No. US6145791A, 14 November 2000. [36] Caton JH, Hobey MJ, Groeneveld JD, Jacobs JH, Wille RH, Brase LO Jr. Control Surface for an Aircraft. U.S. Patent No. US6349903B2, 26 February 2002. [37] Etling KA. Morphing Control Surface Transition. U.S. Patent No. US8342447B2, 1 January 2013. [38] Khorrami MR, Lockard DP, Moore JB, Su J, Turner TL, Lin JC, Taminger KM, Kahng SK, Verden SA. Elastically Deformable Side-Edge Link for Trailing-Edge Flap Aeroacoustic Noise Reduction. U.S. Patent No. US8695925B2, 15 April 2014. [39] Shaw AD, Dayyani I, Friswell MI. Optimisation of composite corrugated skins for buckling in morphing aircraft. Composite Structures 2015;119:227-37. [40] Yokozeki T, Sugiura A, Hirano Y. Development of variable camber morphing airfoil using corrugated structure. Journal of Aircraft 2014;51(3):1023-29. [41] Yokozeki T, Takeda SI, Ogasawara T, Takashi I. Mechanical properties of corrugated composites for candidate materials of flexible wing structures. Composites Part A: Applied Science and Manufacturing 2006;37:1578-86. [42] Thill C, Etches J, Bond I, Potter KD, Weaver PM. Composite corrugated structures for morphing wing skin applications. Smart Materials and Structures 2010;19(12):124009. [43] Xia Y, Bilgen O, Friswell MI. The effect of corrugated skins on aerodynamic performance. Journal of Intelligent Material Systems and Structures 2014;25(7):786-94. [44] Bogue R. Smart materials: a review of recent developments. Assembly Automation 2012;32(1):13-7. [45] Wool RP. A material fix. Nature 2001;409(6822):773-4. [46] Burnworth M, Tang L, Kumpfer JR, Duncan AJ, Beyer FL, Fiore GL, Rowan SJ, Weder C. Optically healable supramolecular polymers. Nature 2011;472(7343):3347. [47] Huang M, Yang J. Facile microencapsulation of HDI for self-healing anticorrosion coatings. Journal of Materials Chemistry 2011;21(30):11013-440. [48] Botsis J, Humbert L, Colpo F, Giaccari P. Embedded fiber Bragg grating sensor for internal strain measurements in polymeric materials. Optics and Lasers in Engineering 2005;42(3-5):491-510. [49] Kuang KSC, Kenny R, Whelan MP, Cantwell WJ, Chalker PR. Embedded fibre Bragg grating sensors in advanced composite materials. Composites Science and Technology 2001;61(10):1379-87. [50] Dellicolli A. Development of self-diagnostic composite structures using embedded fiber-Bragg grating sensors. MSc Thesis, USA: Michigan State University; 2012,. [51] Gianaris N. Advanced Composites for Air and Ground Vehicles: final report (ARL-CR-0775). US Army Research Laboratory, USA: Michigan State University (under contract W911NF-11-2-0017); 2012. [52] McGowan AMR, Washburn AE, Horta LG, Bryant RG, Cox DE, Siochi EJ, Padula SL, Holloway NM. Recent results from Nasa’s morphing project. Proceedings of the 9th SPIE’s Annual International Symposium on Smart Structures and Materials. Proceeding V.4698, Smart Structures and Materials 2002: Industrial and Commercial Applications of Smart Structures Technologies, 9 July 2002, San Diego, California; 2002. 
 [53] Nguyen VQ, Ahmed AS, Ramanujan RV. Morphing soft magnetic composites. Advanced Materials 2012;24(30):4041-54. [54] Li ZF, Wang ZD. Studies on the Shape Frozen/Recovery Behaviors of SMP-based Sandwich Structure. Journal of Intelligent Material Systems and Structures 2011;22(14):1605-12. [55] Tibbits SJE. Logic Matter, Digital logic as heuristics for physical self-guided-assembly. MSc Thesis, USA: Massachusetts Institute of Technology; 2010. [56] Addington M, Schodek D. Smart Materials and Technologies for the Architecture and Design Professions. UK, London: Taylor & Francis Group; 2016. [57] Ashby M, Bréchet Y, Cebon D, Salvo L. Selection Strategies for Materials and Processes. Advanced Engineering Materials 2004;4(6):327-34. [58] Mavroidis C, Pfeiffer C, Mosley M. Conventional actuators, shape memory alloys, and electrorheological fluids. Automation, Miniature Robotics and Sensors for NonDestructive Testing and Evaluation 1999;p.10-21. [59] Stroud HR, Leal PBC, Hartl DJ, Darren J. Hartl. Experimental multiphysical characterization of an SMA driven, camber morphing owl wing section. Proceedings SPIE 10599, Nondestructive Characterization and Monitoring of Advanced Materials, Aerospace, Civil Infrastructure, and Transportation XII, 105990Z (29 March 2018). [60] Widdle RD JR, Grimshaw MT, Crosson-Elturan KS, Mabe JH, Calkins FT, Gravatt LM, Shome M. High Stiffness Shape Memory Alloy Actuated Aerostructure. U.S. Patent No. US9856012B2, 2 January 2018. [61] David EH II, Wang KW, Smith EC. Dual-stack Piezoelectric Device with Bidirectional Actuation and Improved Performance. Journal of Intelligent Material Systems and Structures 2004;15(7):p.565-74. [62] Wang G. Research on the Dynamic Model of the Bi-directional Smart Active Structure with two Piezoelectric Stacks. International Conference on Control and Automation 2007, 17-20 October 2006, Seoul, South Korea; 2007, p. 2984-89. [63] Konarzewska B. Smart Materials in Architecture: Useful Tools with Practical Applications or Fascinating Inventions for Experimental Design?. IOP Conference Series: Materials Science and Engineering 245 2017;052098. [64] Arnall T. Exploring ‘Immaterials’: Mediating Design’s Invisible Materials. International Journal of Design 2014;8(2):101-17.

10

Kyriakos Ntouanoglou et al. / Procedia Manufacturing 18 (2018) 120–129 K. Ntouanoglou et al / Procedia Manufacturing 00 (2018) 000–000

129

[65] Lefebvre E, Piselli A, Faucheu J, Delafosse D, Curto B. Smart materials: development of new sensory experiences through stimuli responsive materials. 5th STS Italia Conference A Matter of Design: Making Society through Science and Technology, 12-14 June 2014, Milan, Italia; 2014, p. 367-82. [66] Lee AY, An J, Chua CK. Two-Way 4D Printing: A Review on the Reversibility of 3D-Printed Shape Memory Materials. Engineering 2017;3(5):663-674. [67] Ku C. 3-D Printed Parts on Airplanes Are Just the Beginning of a Movement. Apex 2015, available at: https://apex.aero/airbus-boeing-3D-print-stratasys. [68] ResearchandMarkets. Aerospace 3D Printing Market to Grow at a CAGR of 27.4% by 2022: Increased Demand for Technologies Capable of Manufacturing Complex Aerospace Parts With Ease From the Aerospace Industry - Research and Markets. Aerospace 3D Printing Market - Global Forecast to 2022, Ireland, Dublin; 2017. [69] Wagner MS, Walton RO. Additive manufacturing’s impact and future in the aviation industry. Production Planning & Control, The Management of Operations 2016;27(13):1124-30. [70] Liu P, Huang SH, Mokasdar A, Zhou H, Hou L. Additive manufacturing’s impact and future in the aviation industry. Production Planning & Control, The Management of Operations 2013;25(13-14):1169-81. [71] Pannett L. 3D: The future of 3D printing. Supply Management 2014;19(1):34-37. [72] D’Aveni R. The 3-D Printing Revolution. Harvard Business Review 2015, available at: https://hbr.org/2015/05/the-3-d-printing-revolution. [73] Warwick G. 3-D-Printed Parts Prove Beneficial For Airbus And ULA. Aviation Week & Space Technology 2015, available at: http://aviationweek.com/technology/3d-printed-parts-prove-beneficial-airbus-and-ula. [74] Weller C, Kleer R, Piller TF. Economic implications of 3D printing: Market structure models in light of additive manufacturing revisited. International Journal of Production Economics 2015;164:43-56. [75] Butler, A. Speed and Precision. Aviation Week & Space Technology 2015;177(7):55-56. [76] Schiller, GJ. Additive Manufacturing for Aerospace. Proceedings of the IEEE Aerospace Conference, 7-14 March 2015, Big Sky, MT, USA; 2015, pp. 1-8. [77] Cotteleer M, Holdowsky J, Mahto M, Coykendall J. 3D opportunity in aerospace and defense, Additive manufacturing takes flight. A Deloitte series on additive manufacturing: Deloitte University Press; 2014. [78] Cotteleer M, Joyce J. Deloitte Review, 3D opportunity: Additive manufacturing paths to performance, innovation, and growth. Deloitte Review Issue 14: Deloitte University Press; 2014. [79] Birtchnell T, Urry J, Cook C, Curry A. Freight miles: The impacts of 3D printing on transport and society. ESRC Project ES/J007455/1, Lancaster University; 2012. [80] Hague R. Q&A: Additive manufacturing - Add up the benefits. Getting the inside track on additive manufacturing and 3D printing, Stephen Harris report. the Engineer 2014; p.35-38. [81] Morgan Stanley Research. Cost-benefit analysis: 3D printing versus traditional manufacturing; 2013. [82] Excell J. The rise of multi-material 3D printing. the Engineer; 2013. [83] Shesh S. Additive Manufacturing (AM)
Design and Simulation Tools Study, Final Report. Under contract to Air Force Research Laboratory and Manufacturing Directorate (Case Number: 88ABW-2014-3753); 2014. [84] Zhou Y, Huang WM, Kang SF, Wu XL, Lu HB, Fu J, Cui H. From 3D to 4D printing: approaches and typical applications. Journal of Mechanical Science and Technology 2015;29(10):4281-88. [85] Lin D, Nian Q, Deng B, Jin S, Hu Y, Wang W, Cheng GJ. Three-Dimensional Printing of Complex Structures: Man Made or toward Nature? ACS Nano 2014;8:97105. [86] Jean-Claude André. From Additive Manufacturing to 3D/4D Printing 2, Current Techniques, Improvements and their Limitations. 1st ed., ISTE Ltd and John Wiley & Sons, Inc., UK: London & USA: Hoboken; 2017. [87] Marketsandmarkets. 3D Printing Market by Offering (Printer, Material, Software, Service), Process (Binder Jetting, Direct Energy Deposition, Material Extrusion, Material Jetting, Powder Bed Fusion), Application, Vertical, and Geography - Global Forecast to 2023; 2017. [88] Leist SK, Zhou J. Current status of 4D printing technology and the potential of light-reactive smart materials as 4D printable materials. Virtual and Physical Prototyping 2016;11(4):249-62. [89] Brinson LC, Bekker A, Hwang S. Deformation of shape memory alloys due to thermo-induced transformation. Journal of Intelligent Material Systems and Structures 1996;7(1):97-107. [90] Auricchio F, Scalet G, Urbano M. A numerical/ experimental study of nitinol actuator springs. Journal of Materials Engineering and Performance 2014;23(7):2420-28. [91] Pretsch T. Review on the functional determinants and durability of shape memory polymers. Polymers 2010;2:120-58. [92] Zarek M, Layani M, Cooperstein I, Sachyani E, Cohn D, Magdassi S. 3D printing of shape memory polymers for flexible electronic devices. Advanced Materials 2015;28(22):4449-54. [93] Humbeeck J. Non-medical applications of shape memory alloys. Materials Science and Engineering 1999;A(273-275):134-48. [94] Shishkovsky I, Scherbakov V. 4D manufacturing of intermetallic SMA fabricated by SLM process. Proceedings of SPIE 10523, Laser 3D Manufacturing, V.1052311; 26 February 2018. [95] Ly ST, Kim JY. 4D Printing – Fused Deposition Modeling Printing with Thermal-Responsive Shape Memory Polymers. International Journal of Precision engineering and Manufacturing-Green Technology 2017;4(3):267-72. [96] Lee AY, An J, Chua CK
. Two-Way 4D Printing: A Review on the Reversibility of 3D-Printed Shape Memory Materials. Engineering 2017;3:663-74. [97] Hiltz JA. Shape Memory Polymers, Literature Review. Defence R&D Canada, Atlantic: 2002;TM 2002-127.