Controllable interlayer shear strength and crystallinity of PEEK components by laser-assisted material extrusion

Parandoush P., Tucker L., Zhou C., Lin D.

Herein, we proposed a novel laser assisted additive manufacturing (AM) methodology that utilizes prepreg composites (glass fiber-polypropylene) with continuous fiber reinforcement to fabricate 3D objects by implementing laser assisted bonding and laser cutting. The microstructure analysis demonstrated no visible void content and excellent interfacial bonding. The bonding strength of the proposed method was evaluated through lap shear strength and peel strength testing; resulting in 50% higher peel strength than hot compaction method, with lap shear strength up to 96% of compression molding benchmark data. Tensile properties of components printed by our method were superior to those of fused deposition modeling (FDM) printed short fiber composites with 300% and 150% of increase in tensile strength and modulus, respectively. Tensile strength of our printed components was comparable to compression molding and stamping, however, tensile modulus was 50% lower in average. Flexural strength of the laser assisted AM parts was also in the range of stamping and compression molding methods, with flexural modulus up to 100% higher than these methods. Overall, our proposed new technique offers an alternative direction in AM of continuous fiber reinforced thermoplastic polymer composites to solve the issues associated with current techniques.

Yang C., Tian X., Li D., Cao Y., Zhao F., Shi C.

Poly-ether-ether-ketone (PEEK) is a high-performance, temperature-resistant semicrystalline polymer which is frequently used as a replacement for metals in a wide variety of high-performance end-use application. Thermal processing conditions during manufacturing process for PEEK can implement a significant impact on its crystallinity and mechanical properties directly and indirectly. In this paper, we have used a temperature-control 3D printing system to prepare all the PEEK samples for calculating crystallinity and performing tension tests, in order to investigate the relationship between various thermal processing conditions (the ambient temperature, the nozzle temperature and heat treatment methods) in FDM process and crystallinity and mechanical properties (tensile strength, elastic modulus and breaking elongation) of pure PEEK material. All experiment results show temperature-control 3D printing method has tremendous potential to design, control and realize different degrees of crystallinity and mechanical properties for different PEEK parts, even in different regions of the same PEEK part.

Gomes A.C., Soares B.G., Oliveira M.G., Machado J.C., Windmöller D., Paranhos C.M.

Blends of polyamide 6 and nitrile rubber (PA6/NBR) dynamically vulcanized may generate innovative products for special purposes where both high temperature and chemical resistance are key factors. In this investigation, we show that the crystalline nature of the PA6 can be controlled in terms of its morphological aspects (degree of crystallinity, crystal size, and structure) as a consequence of the presence of NBR and processing additives. Our results indicate that this crystalline control is dependent on the plasticization caused by the processing additives. Furthermore, imide-like linkage formation was favored in the presence of ethylene-co-vinyl acetate (EVA)-g-maleic anhydride, resulting in changes in the molecular mobility of the PA6 matrix, crystallization parameters, and viscoelastic properties when compared to the others EVA additives. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45576.

Kishore V., Ajinjeru C., Nycz A., Post B., Lindahl J., Kunc V., Duty C.

The Big Area Additive Manufacturing (BAAM) system can print structures on the order of several meters at high extrusion rates, thereby having the potential to significantly impact automotive, aerospace and energy sectors. The functional use of such parts, however, may be limited by mechanical anisotropy, in which the strength of printed parts across successive layers in the build direction (z-direction) can be significantly lower than the corresponding in-plane strength (x-y directions). This has been primarily attributed to poor bonding between printed layers since the lower layers cool below the glass transition temperature (Tg) before the next layer is deposited. Therefore, the potential of using infrared heating is considered for increasing the surface temperature of the printed layer just prior to deposition of new material to improve the interlayer strength of the components. This study found significant improvements in bond strength for the deposition of acrylonitrile butadiene styrene (ABS) reinforced with 20% chopped carbon fiber when the surface temperature of the substrate material was increased from below Tg to close to or above Tg using infrared heating.

Yan M., Zhou C., Tian X., Peng G., Cao Y., Li D.

A novel method to prepare porous resin mould for pressure slip casting was proposed by using Selective Laser Sintering (SLS), which is one of Additive Manufacturing (AM) processes. The mixture of polyamide and salt (NaCl) were designed as raw materials, in which polyamide acted as matrix material and NaCl as pore-foaming agent. To investigate the feasibility of the pressure slip casting with the mould, the compressive strength and porosity of the porous specimens were measured. Experiments showed a compressive strength of 7.19 MPa and an elastic modulus of 32.26 MPa were reached. Meanwhile, the porosity of the specimens was 59.75%, and the aperture concentrated in 25–75 μm. The water permeability was verified and the maximum permeability reached to 0.921 mL/(mm2·s). Pressure slip casting with porcelain slurry was performed using SLS porous specimens as the mould. Results showed the moisture content of the green body was about 23% and the relative density was 68.4%–74.1%. At last, a green body of whiteware with complex surface was prepared by the proposed method to demonstrate the feasibility of pressure slip casting with this mould. This method could be used in porcelain industry to realize rapid development of new products and customized production with further improvements.

Zalaznik M., Kalin M., Novak S.

The main aim of this research was to investigate the influence of different processing temperatures on the properties of pure poly-ether-ether-ketone (PEEK). In order to do this, we used a variation of compression moulding, which enabled us to use different processing temperatures, including temperatures below the melting point of PEEK. The PEEK samples were produced at temperatures below, around and above the melting point of PEEK and were compared to a commercially available PEEK material produced with a conventional procedure. The results of the dry-sliding tribological tests, the hardness measurements and the XRD analyses show that the processing temperature greatly influences the hardness and the crystallinity, which in turn affects the tribological behaviour.

Vaezi M., Yang S.

ABSTRACT There has been a trend in recent years to develop polyetheretherketone (PEEK)-based medical devices due to the excellent cell biocompatibility and desirable mechanical properties of PEEK, which has elastic modulus comparable to cortical bone. Different manufacturing techniques such as injection moulding, particulate leaching, compression moulding, and selective laser sintering (SLS) have been used to produce porous PEEK for biomedical applications. Despite a large number of publications on extrusion-based additive manufacturing (AM) of porous structures using various materials, there have been very few general reports on extrusion AM of low quality small PEEK parts without defects such as warpage and delamination and no further assessment of mechanical properties. Successful low-cost 3D printing of PEEK structures using filament-based extrusion AM process is reported in this paper for the first time. Hot extrusion head design, extrusion temperature, and ambient temperature were identified as important factors need to be taken into consideration for printing PEEK structures without warpage, delamination, and polymer degradation. Compression and tensile tests were conducted to investigate mechanical properties of these new 3D printed PEEK structures. The air gap between infill pattern and entrapped micro-bubbles inside filaments were identified as the main source of mechanical properties reduction. In addition, three-point flexural test was performed on the 3D printed PEEK and compared with flexural specimens printed using other AM materials and techniques.

Garcia-Gonzalez D., Rusinek A., Jankowiak T., Arias A.

This paper deals with the mechanical behavior of polyether–ether–ketone (PEEK) under impact loading. PEEK polymers are the great interested in the field of medical implants due to their biocompatibility, weight reduction, radiology advantage and 3D printing properties. Implant applications can involve impact loading during useful life and medical installation, such as hip systems, bone anchors and cranial prostheses. In this work, the mechanical impact behavior of PEEK is compared with Ti6Al4V titanium alloy commonly used for medical applications. In order to calculate the kinetic energy absorption in the impact process, perforation tests have been conducted on plates of both materials using steel spheres of 1.3 g mass as rigid penetrators. The perforation test covered impact kinetic energies from 21 J to 131 J, the equivalent range observed in a fall, an accidental impact or a bike accident. At all impact energies, the ductile process of PEEK plates was noted and no evidence of brittle failure was observed. Numerical modeling that includes rate dependent material is presented and validated with experimental data.

Magalhães L.C., Volpato N., Luersen M.A.

New technologies known as additive manufacturing (AM) are now available for producing prototypes directly from a 3D CAD model. However, prototypes made by AM usually have mechanical characteristics inferior to those of the final product. AM technologies are in increasing demand for use in the development of functional prototypes and the manufacture of final products. The main aim of this work was to evaluate the influence of deposition strategies on the mechanical behavior of the AM process known as fused deposition modeling (FDM) and to gain a better understanding of the stiffness behavior of the parts. Specimens with different raster orientations in each layer (sandwich-like configurations) were built. The final stiffness and strength of the specimens were determined in tensile and bending tests, and the stiffness was predicted using classical lamination theory. The stiffness in the two main directions for the specimens manufactured with the sandwich deposition configurations was higher than or at least equal to the stiffness of the specimens produced with the default FDM configuration. However, the results indicate that the analytical model used did not accurately predict the behavior in the experimental tests.

Grouve W.J., Vanden Poel G., Warnet L.L., Akkerman R.

Fibre reinforced thermoplastic tapes are subjected to high heating and cooling rates during the tape placement process. Such high cooling rates can significantly inhibit the crystallisation of the thermoplastic polymer and thereby affect its mechanical properties, such as strength or toughness. In the present work, the crystallisation of poly(phenylene sulphide) (PPS) subjected to high cooling rates was investigated using a fast scanning calorimeter. The PPS was found to be unable to crystallise when subjected to cooling rates higher than 20°C s−1. The influence of the degree of crystallinity on fracture toughness was investigated using an essential work of fracture approach. The amount of plastic work during the fracture process was found to decrease after moderate annealing

Grouve W.J., Warnet L.L., Rietman B., Visser H.A., Akkerman R.

The interrelation between process parameters, material properties and interlaminar bond strength is investigated for the laser assisted tape placement process. Unidirectionally carbon reinforced poly(phenylene sulfide) (PPS) tapes were welded onto carbon woven fabric reinforced PPS laminates. The laminate and tape temperature distribution was measured during the welding process. The mandrel peel test method was applied to quantify the bond strength. The experiments demonstrated that an excellent bond quality can be obtained at high velocities and low input power in case the laser is primarily aimed at the tape. For these settings, the tape temperature exceeds the laminate temperature, while the latter stays well below the melt temperature of the PPS

Lovald S., Kurtz S.M.

Publisher Summary This chapter summarizes the historical development of polyetheretherketone (PEEK) and other isoelastic prostheses for fracture fixation, cranial defect repair, and arthroscopy. It discusses the continuously morphing understanding of the ideal environment for fracture healing and explores the benefits and drawbacks of using semirigid fixation, including materials such as PEEK, for internal fixation. Semirigid fixation for trauma and arthroscopy has been finding favor as the fracture healing and stress shielding literature continues to develop. Although PEEK fracture fixation has a number of proposed benefits for fracture healing, it remains to be seen whether a PEEK solution can provide better clinical and functional outcomes relative to metallic fixation. PEEK has, however, found early clinical success in arthroscopic and cranial defect markets. It is expected that performance of PEEK implants for each of these applications will continue to improve as product design methodologies innovate to optimize and capitalize on the unique material property advantages inherent in this material. Bones provide structural support for the body, protect internal organs, facilitate movement, produce blood cells, and store minerals. When a bone absorbs energy above its ultimate strength, a fracture occurs along line or lines of least resistance. Open reduction and internal fixation is the preferred method to treat most bone fractures. The necessary requirements for a polymer implant material for internal fixation are sufficient strength and stiffness, long-term stability, the ability to be sterilized without degradation, and biocompatibility. PEEK possesses a number of properties that make it suitable for certain trauma applications. PEEK is biocompatible, meaning there are no toxic, inflammatory, or allergic reactions. Clinical studies of customized PEEK cranioplasty implants have reported promising results.

Jaekel D.J., MacDonald D.W., Kurtz S.M.

The small punch test is widely used to characterize the ductility and fracture resistance in metals and ceramics, when only a small volume of material is available. This study was conducted to investigate the suitability of the small punch test for characterizing polyetheretherketone (PEEK) polymeric biomaterials for changes in material grade, crystallinity, and molding process. The small punch test reproducibly characterized the mechanical behavior of PEEK and was able to distinguish differences induced by molding process alterations and annealing. Peak load was most sensitive to changes in crystallinity, grade, molding process, and increased with increasing crystallinity, but decreased with the addition of image contrast materials. The ultimate displacement was negatively correlated with crystallinity. Molding process conditions had the greatest influence on metrics of the small punch test, when compared with the effects of annealing and the addition of a radiopacifier. The results of this study validate the small punch test as a repeatable method for measuring the mechanical behavior of PEEK biomaterials.

Grouve W.J., Warnet L., Akkerman R., Wijskamp S., Kok J.S.

A mandrel peel set-up is developed to assess the peel fracture toughness of fibre reinforced thermoplastic tapes welded on a woven laminate using a laser-assisted tape placement robot. A comprehensive experimental programme was designed to investigate the influence of nip point temperature and placement velocity on weld strength. The results indicated that the weld strength improves with increasing temperature and placement velocity. Moreover, the applicability of the method is demonstrated.

Zhang G., Schlarb A.K.

The tribological behaviors of three poly-ether-ether-ketones (PEEKs) with different molecular weights and their SCF (short carbon fiber)/graphite/PTFE (polytetrafluoroethylene) filled composites were examined using a block-on-ring apparatus under dry sliding conditions. Tensile tests, hardness measurements and dynamic mechanical thermal analysis (DMTA) of the PEEK based materials were also performed. The tribological behaviors of PEEK based materials were correlated with their mechanical properties and the tribological mechanisms were discussed based on scanning electron microscope (SEM) inspections of worn surfaces and wear debris. Under a low apparent pressure, a high material ductility seems to reduce the wear rate of pure PEEK through alleviating the microcutting effect exerted by the protruding regions of the counterpart. Under a high pressure, however, a high stiffness seems to improve the wear resistance of pure PEEK by reducing the plastic flow occurring in the PEEK surface layer. After incorporating SCF/graphite/PTFE fillers, the wear rate of PEEK was decreased significantly. Thinning and cracking of SCF are supposed to be the important factors determining the tribological behaviors of the composites.

Li J., Wang C., Fu Y., Xia D., Xu P., Xiang C., Wu J., Li J., Li Y., Li F., Shi H., Sun B., Fu S.

AbstractMechanical properties of 3D printed continuous fiber reinforced polymer composites (CFRPCs) are generally lower than expected due to unavoidable voids and weak interfacial adhesion. However, previous research work has rarely been reported on introducing carbon nanofillers such as carbon nanotubes (CNTs) and graphene oxide (GO) to reduce internal void defects and improve interfacial adhesion of CFRPCs. In this work, an innovative means of introducing CNTs and GO is proposed to reduce internal void defects and improve interfacial adhesion for enhancing the mechanical properties of 3D printed hybrid CFRPCs. Polyethylene terephthalate glycol (PETG) is employed as a polymer matrix due to its excellent processability for the 3D printing process. Continuous basalt fiber (CBF) is selected as a microscale filler due to its high mechanical properties, low cost and availability for additive manufacturing. It is shown that introducing carbon nanofillers into PETG leads to notably reduced porosity and greatly improved interfacial adhesion between CBF and PETG. As a result, the mechanical properties of 3D printed hybrid CFRPCs are significantly enhanced by introducing carbon nanofillers into the polymer matrix. Finally, the mechanisms of CNTs and GO are analyzed for enhancing the mechanical properties of 3D printed hybrid CFRPCs. The multiscale filler enhancement method has the characteristics of low cost and easy implementation. This approach contributes a novel idea for preparing high‐performance 3D printed CFRPCs by reducing internal void defects and enhancing interfacial adhesion by simply introducing carbon nanofillers. This method can expand material systems and provide a new development idea for industrial applications.Highlights Proposed a new means to improve the mechanical properties of 3D printed CFRPCs. The performances of PETG composites are enhanced by optimal CNT or GO content. Combination of carbon nanofillers with PETG enhances interfacial adhesion.

Tamburrino F., Aruanno B., Neri P., Paoli A.

Additive Manufacturing (AM) of Polyether ether ketone (PEEK) via Fused Filament Fabrication (FFF) presents a versatile and effective solution for producing complex, lightweight, and customized parts with intriguing mechanical properties. PEEK, known for its high-temperature resistance, chemical stability, and biocompatibility, finds applications in diverse fields, from aerospace component manufacturing, benefiting from its lightweight nature to biomedical engineering, requiring patient-specific implants or prostheses. However, AM of PEEK via FFF poses significant challenges, and conventional low-cost 3D printers may not always be well-equipped for this demanding task. In the present study, a low-cost solution was proposed and evaluated through simulations and experimental measurements to enhance the performance of a 3D printer valued at less than $ 6.000. The solution entails designing an accessory that utilizes the printer’s second nozzle, incorporating a basic aluminum plate. Through simulations and experimental measurements, it is demonstrated that this accessory provides localized heating in the printing area, thereby increasing the average temperature and improving temperature uniformity. Additionally, specimens printed using this proposed solution show no interlayer delamination and exhibit higher crystallinity compared to parts printed on the same machine without the heating plate.

da Conceição M.D., Anaya-Mancipe J., Bastos D.C., Pereira P.S., Libano E.V.

The rise of Industry 4.0 has introduced challenges and new production models like additive manufacturing (AM), enabling the creation of complex objects previously unattainable. However, many polymers remain underutilized due to the need for improved mechanical properties and reduced process-induced anisotropy. ME-based part construction involves successive filament deposition, akin to welding. Upon exiting the nozzle, the polymer solidifies within seconds, limiting the time and temperature available for diffusion and efficient bonding with the adjacent filament. Therefore, optimizing this welding process is essential. The primary objective of this review was to report on the equipment utilized to enhance the bonding between filaments deposited during manufacturing. While higher temperatures improve welding, most equipment cannot endure prolonged high-heat operations, limiting the use of engineering-grade polymers. Modifying polymer matrices by incorporating low-molar-mass molecules can boost welding and mechanical strength. Significant gains in mechanical properties have come from matrix modifications and new in situ welding devices. Reported devices use light (laser, UV IR), electric current, radio frequency and heat collection from the nozzle. The simplest device is a heat collector, while a double laser beam system has achieved the highest mechanical properties without matrix modification. There was an improvement in properties ranging from 20% to 200%.

Conceição M.D., Fonseca H.M., Thiré R.M.

Fused Filament Fabrication (FFF) is the most used additive manufacturing (AM) technique. Understanding the behavior of the in situ temperature profile during the cooling stage is crucial to enhancing the mechanical properties of the parts manufactured by FFF since adhesion between printed layers is strongly related to the polymer cooling rate. However, only some studies analyze each layer in detail. For such analysis, infrared thermographic cameras can be used as a tool for non-contact temperature measurement. Numerous variables in constructing the part offer potential for such investigation. This study may lead to the enhancement of the part manufactured and improvements in the 3D printer itself. In addition, the polymer matrix and the manufacturing software can also be optimized. This work aims to systematically evaluate the temperature profile along the deposited layers during the fabrication of three-dimensional parts using poly(lactic acid) (PLA) filament. An infrared camera was used for real-time temperature measurements, and the data were processed with MATLAB® as a function of time and part length. A difference of up to 30 °C was observed between the edges, and non-uniform temperature profiles were also observed at the beginning, middle, and end of the part manufacturing. The highest temperatures were observed at the side where the print nozzle positions itself for the base to descend to the next layer. Several strategies are proposed to enhance the temperature distribution during the cooling process.

Wang Z., Zhou K., Xu P.

This study investigates the impact of infrared heating and annealing on the mechanical properties of carbon fiber-reinforced polyphenylene sulfide (CF-PPS) and graphene nanoplatelet (GNP)-reinforced CF-PPS composites in Material extrusion (MEX) additive manufacturing. GNP/CF-PPS composites are prepared by mechanically mixing CF-PPS plastic particles with GNP particles and subjecting them to infrared heating and annealing treatments during the three-dimensional (3D) printing process. Three-point bending tests assess the mechanical properties of the samples. The results reveal that the 0.03 wt.% GNP/CF-PPS sample, subjected to infrared heating followed by annealing, exhibits a 30% increase in bending strength compared to pure CF-PPS, demonstrating that the combined treatment significantly enhances mechanical performance. Microscopy observations using a Keyence VH7000 digital optical microscope and a scanning electron microscope (SEM) confirm that GNP addition and infrared irradiation lead to reduced surface roughness and fewer fracture cross-sectional pores. The interlayer bonding improves notably, indicating enhanced internal density and structural stability. Furthermore, differential scanning calorimetry analysis shows a 20% increase in crystallinity for heat-treated samples, contributing to better interlaminar bonding and reduced temperature gradients during printing. Finite element simulations using MATLAB and ABAQUS software corroborate these findings, demonstrating that infrared heating proves more effective than varying GNP content alone in reducing deformation, residual stress, and temperature differences during the MEX process. These results provide valuable insights into improving the mechanical properties and stability of MEX-manufactured large-dimensional composite materials through optimized thermal management.

Potapov Andrey A., Volgin Vladimir M., Malakho Artem P., Gnidina Inna V.

The application of additive technologies to the manufacture of polymer and composite products is now actively expanding. The FDM printing process is popular because of its ability to adapt to specific tasks and to bring products with complex geometries into production quickly and at minimal cost, and is seen as a technology that can compete with injection molding. However, due to the nature of the process, FDM printed parts are significantly inferior in quality to injection molded parts. Much attention is now being paid to research into supplementary treatment methods to improve the properties of FDM printing parts. However, there is no complete and clear description of such methods, nor are there any recommendations on the choice of treatment methods aimed at improving the specific parts properties. The aim of this review is to analyse the research in the field of post-treatment of parts in order to systematise their advantages and limitations, which will allow a more reasoned choice of a post-treatment method to improve specific properties of FDM printing parts.The bibliography includes 120 references.

Zhang J., Chen J., Peng J., Qiu Y., Zuo Z., Zhang Z.

A multiscale topology optimization model of anisotropic multilayer periodic structures (MPS) is proposed using the isogeometric analysis (IGA) method. The integrative design of multiscale structures was realized in two stages: the distribution optimization of multilayer periodic materials, which determines the types, distribution, and volume fraction of microstructures, and parallel topology optimization, which optimizes the macrostructure and various microstructures simultaneously. To implement the multilayer periodic constraint, the relative density and sensitivity of the IGA control points were equally redistributed. The correctness and advantages of the proposed model were confirmed by comparing its results with those obtained using finite element methods, and the optimal IGA microstructures displayed smoother boundaries. In addition, the multiscale MPS of the cantilever was 3D printed, confirming the practicality of the proposed model. The influences of the regularization scheme, multilayer periodic constraints, and Poisson's ratio factor on the results of the multiscale multilayer periodic optimization were explored, and recommendations for proper values of these parameters were provided to enhance the structural stiffness.

Gümrük R., Vatandaş B.B., Uşun A.

Wang Y., Wu T., Huang G.

Traditional ceramic manufacturing is typically done using molds or by hand, which limits the design complexity, and reduces production efficiency. Ceramic 3D printing technology enables the direct manufacturing of intricate ceramic products tailored to design requirements, leading to revolutionary changes in the ceramic industry. The advanced ceramics are widely used in automotive, aerospace, electronic communications, and medical fields due to their high strength, low density, corrosion resistance, electrical insulation. In view of the use of 3D printing is not affected by the fragility of ceramics and does not require molds, which allows for the quick and accurate creation of complex product structures. To fully utilize the excellent properties and broad application areas of ceramics, 3D printing technology will become crucial, and which will also lead to an increasing demand for ceramics in various fields. Therefore, this paper reviews the application and development of ceramic 3D printing technology in recent years. It also introduces the characteristics of ceramic 3D printing related technologies in detail, compares and analyzes the advantages and disadvantages of different types of ceramic 3D printing technology. In addition, the limitations and practical challenges of ceramic 3D printing technology are also put forward, which hoped that the review can provide a dependable and practical strategy for the development and market implementation of new ceramic 3D printing technology.

Ding Y., Gracego A.X., Wang Y., Dong G., Dunn M.L., Yu K.

A new embedded 3D printing method is developed that enables the printing of high-quality continuous fiber composites with variable fiber volume fractions, matrix materials, and composite structures with large-hollow features.

Huang C., Lv D., Zhu Y., Chen G., Chen M., Zhang Y., Han Y., Wu H.

AbstractFused deposition modeling (FDM) process with laser assistance can effectively enhance the interfacial strength of short carbon fiber/poly‐ether‐ether‐ketone (SCF/PEEK) composites. However, excessive crystallization of the semi‐crystalline matrix generally results in irregular shrinkage, which seriously deteriorates dimensional accuracy of composite specimens. To overcome this issue, we establish a novel heat treatment technique by the combinations of laser assistance and post‐treatment to improve the interlayer properties and dimensional accuracy simultaneously. It is found that lateral cracks at the interlayer interfaces can be completely eliminated at laser pre‐heating temperature , due to the reduction of temperature gradient and residual stresses. The further increased evidently promotes molecular diffusion and crystallization behaviors, thus increasing the interlaminar shear strength of FDM‐printed specimens. The post‐treatment temperature visibly promotes mutual diffusions of the molecules and formations of the perfect crystals, strengthening the interlayer adhesion of specimens. The proposed combination technique can increase the interlayer strengths of composite specimens by approximately 22.5%, while their warpage deformations are suppressed simultaneously.Highlights Pre‐heated temperature was a threshold for eliminating lateral cracks at interlayer interfaces. Post‐treatment significantly promoted molecular diffusion and crystallization behaviors. A novel technique was established to improve interlayer strength while suppressing warpage. The combination technique could increase the interlayer shear strength by approximately 22.5%.

Uşun A., Vatandaş B.B., Gümrük R.

The field of additive manufacturing encounters an innate challenge regarding insufficient interlayer adhesion and anisotropy, which consequently constrains the mechanical properties of printed materials. Continuous fiber-reinforced thermoplastic composite (CFRTP) printing allows ultra-high mechanical properties using a material extrusion (ME) platform but is still significantly affected by the mentioned inherent challenges. The expansion of the usage spectrum for composites manufactured with additive methods depends on overcoming these challenges. Achieving higher fiber volume fractions is a primary method for enhancing the mechanical properties of CFRTP parts. However, it has been proven that high fiber volume fractions can adversely affect mechanical properties due to lower impregnation and reduced interlayer strength. In this study, a high fiber volume fraction of 50% was utilized, and interlayer strength was further improved by employing an infrared heater to preheat the previous layers. This approach resulted in better interlaminar strength and overall mechanical properties, demonstrating the effectiveness of infrared heating in mitigating the challenges associated with high fiber volume fractions. The infrared heater was positioned in a rotating printing head so it could continuously stay in front of the print path. Mechanical tests showed a flexural strength of 1304 MPa and tensile strength of 995 MPa, with high fiber volume fraction and infrared assistance. As far as we know, these values represent the highest achieved in the literature for CFRTP printing without any post-processing. Optical images and differential scanning calorimeter (DSC) tests were used to investigate the microstructure and thermal properties of the printed samples.

Tian X., Li D., Lian Q., Wang L., Lu Z., Huang K., Wang F., Liang Q., Zhang H., Meng Z., He J., Sun C., Liu T., Huo C., Wu L., et. al.

Scientists and engineers are looking forward to new manufacturing technologies to realize the integrated fabrication of macro shape and microstructure for the components with a short production chain, which can also save materials and reduce energy consumption. Additive manufacturing (AM) technology is a new fabrication pattern with a character of a lay-by-lay material deposition. The components are fabricated in a bottom-up way, from points, lines, to layers and volume, which provided a capability to solve the impossible integrated fabrication problem for micro- and macro-structure by using conventional manufacturing technologies. Thus, based on integrated fabrication of micro- and macro- structures, research team in Xi'an Jiaotong University has been focusing on technological innovations and applications of advanced additive manufacturing technologies. Novel additive manufacturing principles have been proposed and explored, by which new AM processes and equipment for metals, composites, ceramics, and biomaterials have been developed to support the industrial applications. Additive manufacturing and cutting-edge applications of advanced composite structure, metamaterials, bio-implants, and monocrystal alloy components have been investigated to push the new development of integrated fabrication of micro- and macro- structures.

Lei M., Ren S., Xiong Y., Xiao J., Wen L., Lu H., Hou X.

The dynamic crystallization during extreme thermomechanical history under producing or service strongly influences the dimensional stability of the semi-crystalline thermoplastic polymers. To produce high-precision structural components, the proper thermomechanical history needs to be carefully designed to eliminate the crystallization-induced shrinkage. On the contrary, the rapidly developed four-dimensional (4D) printing technology tries to amplify the crystallization-induced shrinkage to directly produce the complex curvatures without supporting materials. However, the crystals formed at different deformation states might have different orientations, leading to an anisotropic residual deformation. Therefore, tracing of all crystals formed with different initial configurations is the key issue to ensure the geometric accuracy of both the high-precision and the deformable components. In this study, we developed a continuous phase-evolution model for both the cold and the strain-induced crystallization in semi-crystalline thermoplastics. The irreversible cold crystallization is analogized as the raindrop falling into the pool, and the reversible strain-induced crystallization is analogized as the nonequilibrium liquid-gas phase transformation. Using the continuous phase-evolution concept, the crystal growth is described by a series of continuously formed crystal phases sequentially added into the initial amorphous medium. Each newly formed crystal phase is in a stress-free state at the formation moment, and therefore the crystallization history coupled with the whole deformation history can be memorized. By introducing the oriented growth tensor representing the stress-free state of all formed crystals, the deformation-history dependent anisotropic crystallization and the corresponding residual deformation can be traced. The developed model is validated by comparing with the experimental data of the dynamic crystallization in amorphous poly l-lactide polymers under thermomechanical loading cycles. Finally, the predictive capability of the model is illustrated by several demonstrations, to show the influences of deformation-history dependent crystallization orientations and the corresponding anisotropic residual deformation.

Lv X., Yang S., Pei X., Zhang Y., Wang Q., Wang T.

AbstractMaterial extrusion additive manufacturing provides an effective solution for fabrication of highly customized polyether ether ketone (PEEK) composite parts with any complex shape. Nevertheless, compared with conventional methods, the mechanical strength of 3D printed carbon fiber reinforced PEEK (CF/PEEK) composites is unsatisfactory due to the weak interface bonding strength and high voids content induced by the temperature difference. To overcome this challenge, a temperature‐control 3D printer was used to investigate the effects of ambient temperature and annealing temperature on the microstructure, crystallization behavior and mechanical properties of 3D printed parts. Moreover, the tribological properties of parts printed at different ambient temperature were also studied under various contact pressure. Experimental results showed that the ambient temperature and annealing treatment directly affected the interfacial bonding (fiber/matrix, filament/filament, layer/layer), crystallinity of printed samples, thus affecting their mechanical and tribological properties. The CF/PEEK parts printed at high ambient temperature of 200°C exhibited outstanding mechanical and tribological properties. This study has positive significance for promoting the application of 3D printed PEEK composites in the field of structural load‐bearing and friction materials.Highlights Structure–property relationships for 3D printed CF/PEEK composites. The ambient temperature strongly affects the thermal and microstructural properties Interaction between crystallization and molecular interface diffusion. Interfacial bonding and crystallinity determine the mechanical properties. Tribological properties are highly dependent on applied pressures.