Characterisation of phases and deformation temperature for additively manufactured shape memory polymer components fabricated from rubberised acrylonitrile butadiene styrene

ABSTRACT

Integrating shape memory polymers into additive manufacturing processes enables a form of 4D printing where a printed part can be manipulated into varying geometries upon the application of external stimuli. The work here explores the raster pattern sensitivity of the shape memory properties of two iterations of a polymer blend system composed of thermoplastic rubber and acrylonitrile butadiene styrene. Tensile test specimens were fabricated in three different raster patterns through the use of material extrusion additive manufacturing and deformed at room (25°C), low (?40°C) and high temperatures (105 and 110°C). Shape memory parameters were assessed and the shape fixation ratio was found to exhibit a sensitivity to raster pattern when deformation occurred at room and low temperatures, while the shape recovery ratio was found to be sensitive to raster pattern when deformation occurred at elevated temperatures. The influence of phase content was also explored and a decrease in rubber content led to an improvement in shape memory properties. The alignment of polymer phases with print raster direction was also found to influence raster pattern sensitivity.     

Direct Fused Deposition Modeling 4D Printing and Programming of Thermoresponsive Shape Memory Polymers with Autonomous 2D-to-3D Shape Transformations

Herein, direct 4D printing of thermoresponsive shape memory polymers (SMPs) by the fused deposition modeling (FDM) method that enables programing of 2D objects during printing for autonomous 2D-to-3D shape transformations via simply heating is focused on. The programming process during printing is investigated through designs and experiments. The capability of programming SMPs during printing is illustrated by prestrain and bending capabilities, which are highly related to printing settings, such as nozzle temperature, print speed, layer height, infill patterns, and ratio of active parts in a bilayer structure. A nearly linear relationship for prestrain and bending parameters is experimentally revealed for different printing factors. Quantitative results are presented to be used as a guidance for designing complex 3D structures via 4D printing of 2D structures. Helix structure, twisting structure, DNA-like structures, and functional gripper are designed to demonstrate the potential of direct FDM 4D printing for creating complex 3D structures from simple 2D structures with advantages over traditional manufacturing methods. It is shown that, by removing the need for a layer-by-layer stacking process to achieve a complex 3D shape, FDM can promote sustainability via 4D printing of autonomous 2D-to-3D shape transformer structures with lower materials, time, energy, and longer service life.     

3D printing of smart materials: A review on recent progresses in 4D printing

ABSTRACT

Additive manufacturing (AM), commonly known as three-dimensional (3D) printing or rapid prototyping, has been introduced since the late 1980s. Although a considerable amount of progress has been made in this field, there is still a lot of research work to be done in order to overcome the various challenges remained. Recently, one of the actively researched areas lies in the additive manufacturing of smart materials and structures. Smart materials are those materials that have the ability to change their shape or properties under the influence of external stimuli. With the introduction of smart materials, the AM-fabricated components are able to alter their shape or properties over time (the 4th dimension) as a response to the applied external stimuli. Hence, this gives rise to a new term called ‘4D printing’ to include the structural reconfiguration over time. In this paper, recent major progresses in 4D printing are reviewed, including 3D printing of enhanced smart nanocomposites, shape memory alloys, shape memory polymers, actuators for soft robotics, self-evolving structures, anti-counterfeiting system, active origami and controlled sequential folding, and some results from our ongoing research. In addition, some research activities on 4D bio-printing are included, followed by discussions on the challenges, applications, research directions and future trends of 4D printing.     

Shape memory mechanical metamaterials

Shape memory materials can maintain temporary shapes without external constraints and revert to their permanent shape upon exposure to an external stimulus, such as heat, light, or moisture. This behavior, often named the shape memory effect, has led to the use of shape memory materials in a variety of applications including deployable aerospace structures, biomedical devices, flexible electronics, and untethered soft robots. Most thermally triggered reconfigurable metamaterials using shape memory polymers require a laborious process of thermomechanical programming at high temperature, above their transition value, to maintain a temporary shape. In this paper, we utilize two 3D-printable polymeric materials that do not rely upon their shape memory effect to generate robust shape memory response in a set of mechanical metamaterials. The enabling characteristic is the mismatch of the temperature-dependent moduli of the constitutive materials leveraged in rationally interconnected reconfigurable units, and their hallmark is the freedom to forego the complex programming process of typical shape memory polymers. Their shape reconfiguration and rapid recovery are solely governed by mechanical loading and temperature change, leading to sequentially programmable multistability, hyperelasticity, giant thermal deformations, and shape memory capacity. Theoretical models, numerical simulations, and thermomechanical experiments are performed to demonstrate their functionality, stability transition mechanism, and potential applications.     

3D Printed Photoresponsive Devices Based on Shape Memory Composites

Compared with traditional stimuli‐responsive devices with simple planar or tubular geometries, 3D printed stimuli‐responsive devices not only intimately meet the requirement of complicated shapes at macrolevel but also satisfy various conformation changes triggered by external stimuli at the microscopic scale. However, their development is limited by the lack of 3D printing functional materials. This paper demonstrates the 3D printing of photoresponsive shape memory devices through combining fused deposition modeling printing technology and photoresponsive shape memory composites based on shape memory polymers and carbon black with high photothermal conversion efficiency. External illumination triggers the shape recovery of 3D printed devices from the temporary shape to the original shape. The effect of materials thickness and light density on the shape memory behavior of 3D printed devices is quantified and calculated. Remarkably, sunlight also triggers the shape memory behavior of these 3D printed devices. This facile printing strategy would provide tremendous opportunities for the design and fabrication of biomimetic smart devices and soft robotics.     

Investigating the shape memory properties of 4D printed polylactic acid (PLA) and the concept of 4D printing onto nylon fabrics for the creation of smart textiles

3D printing is an ever growing industry that provides many benefits to the advanced manufacturing and design industry. However, parts tend to be static, rigid, and lack multi-purpose use. Recently, a new technology has emerged that uses 3D printing to print parts with the ability to change shape over time when exposed to different external stimuli. This new technology has been called 4D printing. Creation of a new material that is capable of changing shape when exposed to different stimuli and possess the ability to be 3D printed can be a difficult and a long process. Due to this strenuous process, the potential of a common fused deposition modelling material, poly(lactic) acid (PLA), for use in 4D printing is investigated and the concept of combining PLA with nylon fabric for the creation of smart textiles is explored. PLA possesses thermal shape memory behaviour and maintains these abilities when combined with nylon fabric that can be thermomechanically trained into temporary shapes and return to their permanent shapes when heated.     

Current status of 4D printing technology and the potential of light-reactive smart materials as 4D printable materials

The onset of multi-material 3D printing and the combination of smart materials into the printable material has led to the development of an exciting new technology called 4D printing. This paper will introduce the background and development into 4D printing, discuss water reactive 4D printing methods and temperature reactive 4D printing, modelling and simulation software, and future applications of this new technology. Smart materials that react to different external stimuli are described, along with the benefits of these smart materials and their potential use in 4D printing applications; specifically, existing light-reactive smart materials. 4D printing has the prospective to simplify the design and manufacturing of different products and the potential of automating actuation devices that naturally react to their environment without the need for human interaction, batteries, processors, sensors, and motors.     

4D打印复合软材料力学性能预测研究进展

4D打印是一门新兴的制造技术,所打印结构的形状、属性或功能在外部环境的刺激下会随着时间的推移而变化。智能软物质材料由于变形大,激励响应机制多,响应速度快等特点被广泛使用于4D打印中,尤其是形状记忆水凝胶和形状记忆聚合物。目前对复合软材料的刚度和弯曲形状的控制是4D打印在应用上的两个难题,建立4D打印复合结构的等效模量和曲率预测模型对复合软材料的力学性能的设计具有指导意义。本文对现有的4D打印复合结构的等效模量及弯曲曲率模型进行了概述,首先介绍了4D打印结构在静态和动态下的弹性模量预测模型,然后,重点综述了Stoney理论,Timoshenko理论和复合材料力学在复合软材料弯曲曲率建模上的应用。最后探讨了现有4D打印复合软材料力学预测模型存在的问题及主要发展的方向。      

3D Printing of Liquid Crystal Elastomeric Actuators with Spatially Programed Nematic Order

Liquid crystal elastomers (LCEs) are soft materials capable of large, reversible shape changes, which may find potential application as artificial muscles, soft robots, and dynamic functional architectures. Here, the design and additive manufacturing of LCE actuators (LCEAs) with spatially programed nematic order that exhibit large, reversible, and repeatable contraction with high specific work capacity are reported. First, a photopolymerizable, solvent‐free, main‐chain LCE ink is created via aza‐Michael addition with the appropriate viscoelastic properties for 3D printing. Next, high operating temperature direct ink writing of LCE inks is used to align their mesogen domains along the direction of the print path. To demonstrate the power of this additive manufacturing approach, shape‐morphing LCEA architectures are fabricated, which undergo reversible planar‐to‐3D and 3D‐to‐3D′ transformations on demand, that can lift significantly more weight than other LCEAs reported to date.     

Selective laser melting of NiTi alloy with superior tensile property and shape memory effect

It is a challenge to develop complex-shaped NiTi shape memory alloy parts by traditional processing methods, due to the poor machinability of NiTi alloy. It is reported that selective laser melting (SLM) of additive manufacturing could overcome this problem. However, the reported SLM-produced NiTi exhibits poor tensile ductility due to the inner defects and adverse unidirectional columnar grains from SLM process. In this work, the defect-less SLM-NiTi with nondirective columnar grains was fabricated by optimizing the intraformational laser scanning length and interformational laser scanning direction. The obtained lath-shaped SLM-NiTi sample exhibits tensile strain of 15.6%, more than twice of the reported maximum result (˜7%). Besides, the SLM-NiTi part with complex geometry displays a shape memory recovery of 99% under compressive deformation of 50%.     

Shape Memory Materials for Biomedical Applications

Shape memory properties provide a very attractive insight into materials science, opening unexplored horizons and giving access to unconventional functions in every material class (metals, polymers, and ceramics). In this regard, the biomedical field, forever in search of materials that display unconventional properties able to satisfy the severe specifications required by their implantation, is now showing great interest in shape memory materials, whose mechanical properties make them extremely attractive for many biomedical applications. However, their biocompatibility, particularly for long‐term and permanent applications, has not yet been fully established and is therefore the object of controversy. On the other hand, shape memory polymers (SMPs) show promise, although thus far, their biomedical applications have been limited to the exploration. This paper will first review the most common biomedical applications of shape memory alloys and SMPs and address their critical biocompatibility concerns. Finally, some engineering implications of their use as biomaterials will be examined.     

Development of Bioimplants with 2D, 3D,and 4D Additive Manufacturing Materials

Over the past 30 years, additive manufacturing (AM) has developed rapidly and has demonstrated great potential in biomedical applications. AM is a materials-oriented manufacturing technology, since the solidification mechanism, architecture resolution, post-treatment process, and functional application are based on the materials to be printed. However, 3D printable materials are still quite limited for the fabrication of bioimplants. In this work, 2D/3D AM materials for bioimplants are reviewed. Furthermore, inspired by Tai Chi, a simple yet novel soft/rigid hybrid 4D AM concept is advanced to develop complex and dynamic biological structures in the human body based on 4D printing hybrid ceramic precursor/ceramic materials that were previously developed by our group. With the development of multi-material printing technology, the development of bioimplants and soft/rigid hybrid biological structures with 2D/3D/4D AM materials can be anticipated.     

Smart polymers and nanocomposites for 3D and 4D printing

Smart materials, also known as intelligent materials, which are responsive to the external stimuli including heat, moisture, stress, pH, and magnetic fields, have found extensive applications in sensors, actuators, soft robots, medical devices and artificial muscles. Using three-dimensional (3D) printing techniques for fabrication of smart devices allows for complex designs and well-controlled manufacturing processes. 4D printing is attributed to the 3D printing of smart materials that can be significantly transformed over time. Herein the smart materials including hydrogels and polymeric nanocomposites used in 4D printing were reviewed and the fundamental mechanisms responsible for the functionalities were discussed in detail. In this report, 4D printing of smart systems and their applications in sensors, actuators and biomedical devices were reviewed to provide a deeper understanding of the current development and the future outlook.     

Review: Recent advancement and research possibilities in 4D printing technology

The development of smart materials has provided a new technology in the field of 3D printing which is termed as 4D printing technology. Such development has allowed the researchers to design a material and component which can respond to external stimuli. The present review focuses on an overview of the advancement in 3D printing technology and 4D printing technology and possibilities for further development. Apart from 3 dimensions of 3D printing, 4D printing uses time as fourth dimension to create or modify shape when exposed to stimuli. The parameters which change with time include temperature, water, light, humidity, pH etc. The invention of smart materials, development in fabrication process and deformation model, advancement in printing methods have led to development of 4D printing technology. The ability of smart material to change the shape and design according to their environment and as per the application have enhanced degree of freedom of parts during application. The effect of major components including smart materials, printing methods and stimuli on 4D printing technology have been reviewed. Some recent discoveries have shown promising results but still need to overcome certain impediments.     

连续纤维增强热塑性复合材料3D打印研究进展

连续纤维增强热塑性复合材料(Continuous Fiber Reinforced Thermoplastic Composites,CFRTPCs)具有强度高、寿命长、耐腐蚀和绿色可回收等优点,广泛应用于航空航天、交通运输和高精密加工装备等领域.传统复合材料制造工艺较为复杂、生产周期长且成本较高,先进的3D打印技术可...     

Curing characteristics of shape memory polymers in 3D projection and laser stereolithography

The radical shift in 3D printing to fabricate soft active materials such as shape memory polymers (SMPs) has brought along other techniques in realising 4D printing. Stereolithography (SL) process has recently been one of the popular systems for printing SMPs. In this paper, the curing characteristics and behaviour of the SMPs fabricated via projection-type and laser-scanning-type SL process were analysed. Factors such as the UV exposure of the projection type and variation in resin compositions have significant differences in terms of energy density and curing depths when compared to the laser scanning type. Hence, theoretical calculations were made to determine the critical energy density and threshold penetration depth attainable, which enables newly developed SMP materials to be successfully printable using different types of UV-based 3D printing systems.     

Finite element simulation of low velocity impact on shape memory alloy composite plates

Delamination of composite materials due to low velocity impacts is one of the major failure types of aerospace composite structures. The low velocity impact may not immediately induce any visible damage on the surface of structures whilst the stiffness and compressive strength of the structures can decrease dramatically.

Shape memory alloy (SMA) materials possess unique mechanical and thermal properties compared with conventional materials. Many studies have shown that shape memory alloy wires can absorb a lot of the energy during the impact due to their superelastic and hysteretic behaviour. The superelastic effect is due to reversible stress induced transformation from austenite to martensite. If a stress is applied to the alloy in the austenitic state, large deformation strains can be obtained and stress induced martensite is formed. Upon removal of the stress, the martensite reverts to its austenitic parent phase and the SMA undergoes a large hysteresis loop and a large recoverable strain is obtained. This large strain energy absorption capability can be used to improve the impact tolerance of composites. By embedding superelastic shape memory alloys into a composite structure, impact damage can be reduced quite significantly.

This article investigates the impact damage behaviour of carbon fiber/epoxy composite plates embedded with superelastic shape memory alloys wires. The results show that for low velocity impact, embedding SMA wires into composites increase the damage resistance of the composites when compared to conventional composites structures.     

高分子基功能复合材料的熔融沉积成型研究进展

3D打印又称增材制造技术,是基于材料、机械控制、计算机软件等多学科交叉的先进制造技术,可得到传统加工不能制备的形状复杂制件。熔融沉积成型(FDM)是目前最通用的3D打印技术之一,具有设备简单、成本低、操作便捷等特点,广泛应用于航空航天、医疗、汽车工业等领域。本文介绍了国内外3D打印技术的整体布局、发展和规划,总结了常见3D打印技术的特点和分类。系统地介绍了FDM加工技术的原理和优势,阐明了 FDM加工对高分子材料的基本要求,介绍了碳基高分子复合材料在FDM加工中的应用。此外,详细综述了国内外基于FDM打印技术制造功能化高分子复合材料及器件的最新研究进展,其中包括FDM打印制造导电高分子复合材料、导热高分子复合材料及生物医用高分子复合材料等,以期为FDM制造高性能多功能高分子复合材料的研究及应用提供借鉴。并对FDM加工面临的挑战及需要解决的关键问题提出了思考并做出展望。      

3D‐Printable Photochromic Molecular Materials for Reversible Information Storage

The formulation of advanced molecular materials with bespoke polymeric ionic‐liquid matrices that stabilize and solubilize hybrid organic–inorganic polyoxometalates and allow their processing by additive manufacturing, is effectively demonstrated. The unique photo and redox properties of nanostructured polyoxometalates are translated across the scales (from molecular design to functional materials) to yield macroscopic functional devices with reversible photochromism. These properties open a range of potential applications including reversible information storage based on controlled topological and temporal reduction/oxidation of pre‐formed printed devices. This approach pushes the boundaries of 3D printing to the molecular limits, allowing the freedom of design enabled by 3D printing to be coupled with the molecular tuneability of polymerizable ionic liquids and the photoactivity and orbital engineering possible with hybrid polyoxometalates.