Polyetherimide (PEI) has recently been used in additive manufacturing as it possesses excellent mechanical and thermal properties. These properties have led to its applications across industries including aerospace, automotive and medical industries. The use of high-performance polymers (HPP) poses attractive properties in relation to medical devices, however, concerns remain with respect to bioactivity. Addition of bioactive fillers to mitigate against this has been considered, such as hydroxyapatite (HA), the main mineral component of human bone. This study considers the preparation and characterisation of PEI-based filaments containing 10, 20, and 30 wt.% of HA and then subsequently printed using fused filament fabrication (FFF). Mechanical, thermal and morphological analysis was performed. Bioactivity was investigated via immersion in simulated body fluid (SBF). PEIHA-20% was recognised as optimal for maintaining acceptable tensile strengths of a mean value of 56.4 MPa and improving Youngs modulus beyond the neat value to a value of 1683 MPa. Scanning electron microscopy (SEM) and SEM- energy dispersion X-rays (EDX) confirmed apatite formation through the detection of calcium and phosphorus elements on the top surface of the samples after 7 days of immersion. Although, mechanical properties are reduced, bioactivity is induced, with values within the threshold for cortical bone/implantable material.

Polymer composites mainly reinforced with continuous fibers manufactured using the material extrusion technique have gained attention due to their light weight and high-performance capabilities. Thermoplastics reinforced with continuous carbon fiber (CCF) offer exceptional mechanical properties. Polymer composites are fabricated using the material extrusion process, adapting various methods. Manufacturing such composites using fused filament fabrication (FFF) with high quality and reduced air void content is challenging due to the complexity of the process. In this study, in-situ co-extrusion with the towpreg process is used to manufacture CCF reinforced composites using the FFF technique. Two important printing parameters (layer thickness and line width) are considered. Mechanical properties (tensile, shear and compressive) were studied after the manufacturing of the composites. The porosity in the composites was observed using X-ray micro computed tomography scan, and the carbon fiber contents were estimated using the dissolution method, while the fracture analysis was performed using SEM. The results obtained suggested that both the printing parameters have a significant impact on the quality and mechanical properties of the additively manufactured composites. The polymer composite fabricated using a layer thickness of 0.4 mm and a line width of 1 mm showed the highest tensile, shear, and compressive strength of 364.69 MPa, 33.89 MPa, and 121.25 MPa, respectively, with a minimum porosity of 16.14 % and a reinforcement content of 26.12 % volume fraction. This thorough research gave insights into how differences in printing settings affect the structural integrity, mechanical properties, and quality of composites, directing future optimizations for improving the performance and quality of 3D-printed thermoplastic composites.

This paper studies the physical and mechanical performance of three main architectures used in 3D woven composites, focusing on their tensile, flexural, and short-beam strength properties. The primary goal of this paper was to investigate the physical and mechanical effects of three different weave architectures, Layer-to-Layer (LL), Angled Interlock (AI), and Orthogonal (ORTH), using a consistent loom set-up. This approach aims to facilitate the seamless manufacture of transitions between weave architectures within a single perform, allowing for tailored properties to meet the requirements of specific applications by evaluating each architecture in warp and weft directions. The results indicate that the AI and ORTH architectures have better tensile properties than the LL architecture in the warp direction, highlighting the importance of warp stuffers in improving tensile strength. On the other hand, the LL architecture showed superior tensile and flexural properties in the weft direction due to 11% and 17% higher directional fibre content compared to AI and ORTH. Additionally, the AI architecture exhibited improved short beam strength in the warp direction due to the angled warp binder tows. This study emphasises how the distribution of resin-rich regions and fibre architecture can influence mechanical properties, with specific architectures providing advantages in different loading conditions. Furthermore, by ensuring a consistent loom set-up across all architectures, this work presents a novel approach to manufacturing 3D woven composites, offering enhanced design flexibility and streamlined fabrication processes.

Printing with high-performance polymers such as polyether ether ketone (PEEK) and polyetherimide (PEI) presents issues regarding shrinkage and warpage due to elevated temperatures. One method highlighted to mitigate against this is through polymer blending. This study explores the development and characterization of PEEK and PEI blends as filament for fused filament fabrication (FFF) in additive manufacturing. Filaments were produced via melt extrusion using PEEK/PEI weight ratios 100/0, 80/20, 70/30, 60/40, 50/50, 40/60, 20/80, and 0/100 (wt.%). The aim is to identify an optimum blend which enhances printability and maintains mechanical and thermal integrity. The extruded filaments were first characterized through differential scanning calorimetry (DSC) to determine miscibility with all ratios presenting a single glass transition temperature. Samples were then 3D-printed and assessed through mechanical testing, DSC, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The PEEK/PEI 80/20 (wt.%) blend was recognized as the optimum blend for maintaining crystallinity (35%) as well as good mechanical properties, averaging ultimate tensile strengths (UTSs) of 75.6 MPa and a Young's modulus of 1338 MPa. Thermal properties also improved while warpage reduced and printability improved.

Recently, high-performance polymers (HPP) have been exploited in the world of additive manufacturing (AM) as a result of improved techniques and the ability to process these materials which require higher processing temperatures. These materials present enhanced mechanical properties, chemical resistance, and thermal stability, increasing AM potentials beyond prototyping applications. Polyether ether ketone (PEEK) has been recognised for its mechanical properties due to its semi crystalline nature and established itself as a biomaterial, possessing biocompatibility and chemical resistance. Polyetherimide (PEI) is renowned for its thermal stability and has been utilised in high temperature-dependent applications. PEEK and PEI are one of the few miscible blends of HPPs, characterized through the presence of a single glass transition temperature. Both materials individually present properties which make them ideal for biomedical applications and through the blending of these materials the biomedical industry could benefit from the synergistic outcome. This review paper will look at PEEK, PEI, and their blends, focusing on the printing parameters, crystallinity and reinforcements. It will also take a look at some of the areas which PEEK and PEI are currently being used, including, implants, prosthetics, and Tissue Engineering.

In this study, a nacre-inspired carbon-polypropylene 3D woven composite is developed. The biomimetic 'brick-and-mortar' design is implemented by interlacing softer polypropylene yarns with brittle carbon fibres. This novel composite was benchmarked against a standard carbon fibre 3D woven composite with identical weave architecture, examining tensile properties, impact resistance, and shear strength. The comparative analysis was supported by micrographs and mu CT scans. Results showed that the hybrid composite absorbed 16% more impact energy in the weft direction than its purely carbon counterpart. The presence of polypropylene yarns increased crimp within the weave contributing to reduced tensile and shear properties. The study identifies the bulk factor of polypropylene yarns as critical in minimising crimp and structural flaws in the hybrid design. In summary, this work presents a nature-inspired hybrid composite, with an increased impact resistance but with trade-offs in tensile and shear properties.

This study focuses on evaluating the fatigue life performance of 3D-printed polymer composites produced through the fused deposition modelling (FDM) technique. Fatigue life assessment is essential in designing components for industries like aerospace, medical, and automotive, as it provides an estimate of the component’s safe service life during operation. While there is a lack of detailed research on the fatigue behaviour of 3D-printed polymer composites, this paper aims to fill that gap. Fatigue tests were conducted on the 3D-printed polymer composites under various loading conditions, and static (tensile) tests were performed to determine their ultimate tensile strength. The fatigue testing load ranged from 80% to 98% of the total static load. The results showed that the fatigue life of the pressed samples using a platen press was significantly better than that of the non-pressed samples. Samples subjected to fatigue testing at 80% of the ultimate tensile strength (UTS) did not experience failure even after 1 million cycles, while samples tested at 90% of UTS failed after 50,000 cycles, with the failure being characterized as splitting and clamp area failure. This study also included a lap shear analysis of the 3D-printed samples, comparing those that were bonded using a two-part Araldite glue to those that were fabricated as a single piece using the Markforged Mark Two 3D printer. In summary, this study sheds light on the fatigue life performance of 3D-printed polymer composites fabricated using the FDM technique. The results suggest that the use of post-printing platen press improved the fatigue life of 3D-printed samples, and that single printed samples have better strength of about 265 MPa than adhesively bonded samples in which the strength was 56 MPa.

Due to the complex structure of three-dimensional (3D) woven fabrics, their mechanical properties and failure modes tend to differ to those of equivalent two-dimensional woven and unidirectional composites. The application of 3D woven composites in advanced structural components is limited by a lack of understanding of the influence of textile weaving parameters on the final fibre architecture. This chapter provides a comprehensive review of the influence of microstructural parameters on the physical, mechanical, in-plane, and out-of-plane impact performance of 3D woven composites. It highlights the motivation for using 3D woven composites for various structural applications. Potential modifications and improvements to 3D Jacquard weaving looms are also discussed, in order to minimise fibre damage.

This research investigated the ballistic response of homogenous and hybrid multi-ply fabrics toward developing a full-scale hybridized soft armor system. Fabrics with varying yarn and thread counts were manufactured from para-aramid and ultra-high molecular weight polyethylene yarns through a plain-woven architecture. Homogeneous fabrics used the same yarn and thread count for two- and three-ply systems. For hybrid systems, two- and three-ply stacks were assembled in various sequences including increasing and decreasing cover factor ( C fab ) and varying yarn types as the strike face and rear face. Ballistic impact testing was performed on all fabrics at low (340 m s −1 ) and high velocity (620 m s −1 ). Observations and measurements were performed to determine failure mechanisms, energy absorption, transverse wave propagation, and system effects of multi-ply systems. Hybrid systems showed significant differences in specific energy absorbed (SEA), dependent on the layer order. The para-aramid hybrid systems impacted at 340 m·s −1 showed a significantly greater SEA when the fabrics were ordered with an increasing rather than a decreasing cover factor. At 620 m·s −1 the difference in SEA was less pronounced or absent entirely. It was concluded that hybridization would enhance the performance of a soft armor system and was likely to be most effective for the rear layers of the system where fabrics with a progressively increasing cover factor that were manufactured of fine (550 dTex) para-aramid yarns would offer an advantage. The front layers of the system, subjected to higher strain loading, would benefit from low cover factor fabrics (0.76), which maximize the dissipation of strain from the point of impact.

Tufting has been shown to improve the mechanical properties of composites. Unlike other published works which rely on commercially available materials, for this study, continuous polymer yarns with diameters ranging from 160 μm to 720 μm of unfilled PPSU and PPSU nanocomposites with 1 wt.% of carbon nanotubes (CNT) were prepared using a twin-screw extruder. The tensile properties of these yarns generally improved with the addition of CNT at higher values of ‘screw speed to haul-off’ ratio. This effect is correlated with the yarn draw down ratio and attributed to the nanofiller orientation induced in the thermoplastic matrix. The fibres exhibited as much as a 23% increase in Ultimate Tensile Strength (UTS) for the same parameter set when loaded with CNT. Depending on filler and processing parameters set, yarns varied in UTS from 96.4 MPa to 206.2 MPa for unfilled PPSU and PPSU-CNT, respectively.

Poly ether ether ketone (PEEK)/Fe composites were prepared by a twin-screw extruder in which 30 and 35 %wt. of iron microparticles were dispersed into medium viscosity PEEK polymer. Samples for further characterisations were manufactured by an injection moulding process. The PEEK crystallinity decreased at these loadings of iron particles due to the reduction of chain movement in the polymer. The temperatures of chain-scission and thermo-oxidation at two decomposition stages of the composites showed a subtle change compared to the pure PEEK polymer, which suggests an influence of the additive material on the thermal properties of the material. This was studied by differential Scanning Calorimetry (DSC) and Thermal Gravimetrical analysis (TGA)

Cost-efficient, easy processing antistatic PEEK/Expanded graphite (EG) composites were prepared via twin-screw extrusion and injection moulding. 0.5, 1, 3 vol% of unfunctionalized EG with a diameter of 600 gm were melt mixed with PEEK and the rheological, electrical, and thermal properties of the composites were investigated. The storage modulus (G') of the composite containing 1 vol% EG was almost independent of the angular frequency at low frequencies. Zero-shear viscosity exhibited an earlier shear thinning behavior at low shear rates for EG loadings of 1 vol%. However, it did not increase much with the addition of EG in comparison with other nanofillers such as carbon nanotube. Also, with an increase of the EG loading to 3 vol%, DC electrical conductivity exhibited an abrupt increase to 2e-6 S/m which is in the required range of electrical conductivity for antistatic materials. Therefore, the rheological and electrical percolation thresholds of the PEEK/EG composites occur at the EG loadings of 1 and 3 vol%. The PEEK crystallinity in the composite containing 3 vol% EG was enhanced by 12%.

A novel finite element modelling approach is presented which incorporates representative binder yarn compaction, for simulating the low-velocity impact (LVI) and compression after impact (CAI) response of 3D woven layer-to-layer carbon/epoxy composite architectures. Simulations of out-of-plane drop-weight impact tests were performed at energies of 32 J and 42 J. Warp and weft layers were modelled as continuous plies and three different approaches were explored to model the binder reinforcement; (i) with a rectangular cross-section and non-compacted, (ii) with an elliptical cross-section and non-compacted, and (iii) an elliptical cross-section which accounts for compaction. Predictions were compared with experimental results from literature and it is shown that modelling the binder reinforcement as an elliptical cross-section with compaction leads to a predicted damage area, on the impacted side, which is within 2%, and the non-impacted side within 6% of experimental measurements. The predicted CAI strength is within 11% of the experimental values.

This work discusses the development and refinement of a polymer/fibre through thickness reinforcement method. Similar in initial concept to the traditional metalworking process of riveting this allows the manufacture of through thickness reinforced 2-D preforms. Pins are placed with deliberate excess length using a veterinary needle to part in-plane fibres. A layup with an array of pins is then subjected to a hot-press process flattening the pin ends resulting in a consolidated preform. This preform exhibits useful characteristics such as the ability to be cut and reformed to a new topology, with the through thickness reinforcement also conforming to the new shape. Refinements to the process introduce a multi-stage press process aimed at improving pin orientation with both original and refined processes evaluated using ASTM D5528 to determine the effect on interlaminar fracture toughness.

A common theme in the application of through-thickness reinforcement is the desire to minimize/eliminate any reduction in in-plane properties. In this work a novel method of reinforcement is introduced using a polymer/fibre pin. Similar in concept to the traditional metalworking process of riveting these pins are placed through the thickness with deliberate excess length. The application of heat and pressure deforms the exposed ends of the pin against the part surface. The resultant preform maintains its shape and may be re-formed with further heat and pressure with the reinforcement conforming to the desired shape. Samples manufactured using this method are tested under quasi-static tensile loading and show no significant change in properties due to the pin addition. Samples tested under mode 1 show further refinement of the manufacture method is required, with shallow pin angles resulting in sub-optimal performance.

Fused deposition modelling (FDM) is one of the most popular additive manufacturing (AM) technique which is used to investigate the elastic properties of 3D printed polyamide-based polymer composites structures. The aim of this work is to study the mechanical properties of continuous carbon fibre reinforced polyamide polymer composite samples using tensile and flexural testing by varying the fibre volume contents with applying pressure, temperature and holding the samples for 60 minutes in the platen press. The results showed that the strength and stiffness increased with the increase in fibre volume content (fraction). Hot pressed samples exhibited the increase in tensile strength by about 27 % and elastic modulus by 11 % because of increasing the fibre volume fraction from 29 % to 35%. Synergetic effect of both short and continuous carbon fibre was also studied, and it was observed that the tensile properties were higher for the samples reinforced with short and continuous fibre than only continuous fibre polymer composites. Effects of voids on 3D printed continuous carbon fibre-reinforced polymer composites were quantified. A microstructure study of the 3D printed polymer composites was carried out using scanning electron microscope (SEM). Following SEM analysis on the tested specimens, it was observed that there was a strong correlation between the mechanical properties and the microstructure. Fibre volume fraction was measured using acid digestion method to determine the amount of fibre contents before and after hot pressing (compaction). From Micro- Computed Tomography (mu CT) it was confirmed that hot pressing reduced the void content which in return increased the strength and modulus.

Additively manufactured composite specimens exhibit anisotropic properties, meaning that the elastic response changes with respect to orientation. Both in-plane and out-of-plane mechanical properties are important for designing purpose. Recent studies have characterised the in-plane performance. In this study, however, through-thickness tensile strength of 3D polymer composites were determined by printing of continuous carbon fibre reinforced thermoplastic polyamide-based composite, manufactured using a Markforged Two 3D printer. This paper discusses sample fabrication and geometry, adhesive used, and testing procedure. Test standards used to determine out-of-plane properties are tedious as most of the premature failures occur between the specimens and the tabs. Two types of samples were printed according to ASTM flatwise tension standard and the results were compared to determine the geometry effect on the interlaminar strength. This test method consists of subjecting the printed sample to a uniaxial tensile force normal to the plane. With this method, the acceptable failure modes for tensile strength must be internal to the structure, not between the sample and the end tabs. Micro-computed tomography (µCT) was carried out to observe the porosity. Surface behaviour was studied using scanning electron microscopy (SEM) to see the voids and the distribution of the fibres in the samples. The results showed consistent values for tensile strength and elastic modulus for Araldite glue after initial trials (with some other adhesives) to determine a suitable choice of adhesive for bonding the samples with the tabs. Circular specimens have higher tensile strength and elastic modulus as compared to rectangular specimens.

Semi-crystalline polymers develop higher amounts of residual stress and part distortion (warpage) compared to amorphous polymers due to their crystalline nature. Additionally, the FDM processing parameters such as ambient temperature play an important role in the resulting residual stresses and part distortion of the printed part. Hence, in this study, the effect of ambient temperature on the in-built residual stresses and warpage of amorphous acrylonitrile-butadiene-styrene (ABS) and semi-crystalline polypropylene (PP) polymers was investigated. From the results, it was observed that increasing the ambient temperature from 50 °C to 75 °C and further to 120 °C resulted in 0.22-KPa and 0.37-KPa decreases in residual stress of ABS, but no significant change in the amount of warpage. For PP, increasing ambient temperature from 50 °C to 75 °C led to a more considerable decrease in residual stress (0.5 MPa) and about 3% increase in warpage. Further increasing to 120 °C resulted in a noticeable 2 MPa decrease in residual stress and a 3.4% increase in warpage. Reduction in residual stress in both ABS and PP as a result of increasing ambient temperature was due to the reduced thermal gradients. The enhanced warpage in PP with increase in ambient temperature, despite the reduction in residual stress, was ascribed to crystallization and shrinkage.

In fused deposition modelling (FDM) based on the selected raster pattern, the developed internal thermal residual stresses can vary considerably affecting the mechanical properties and leading to distinct part distortions. This phenomenon is more pronounced in semi-crystalline than amorphous polymers due to crystallisation. Hence, this study focuses on the simulation of the FDM process of a semi-crystalline polymer (polypropylene) with raster patterns such as line (90°/90°), line (0°/90°), zigzag (45°/45°), zigzag (45°/−45°), and concentric from Cura (slicing software). The simulation provides visualisation and prediction of the internally developed thermal residual stresses and resulting warpage with printing time and temperature. The sample with a line (90°/90°) raster pattern is considered as the reference sample in order to compare the relative levels of residual stress and warpage in the other printed/simulated samples. Among the considered raster patterns, the concentric pattern displays the lowest amount of warpage (5.5% decrease) along with a significant drop in residual stress of 21%. While the sample with a zigzag (45°/−45°) pattern showed the highest increase of 37% in warpage along with a decrease of 9.8% in residual stresses. The sample with a zigzag (45°/45°) pattern, exhibited a considerable increase of 16.2% in warpage with a significant increase of 31% in residual stresses. Finally, the sample with a line (0°/90°) raster pattern displayed an increase of 24% increase in warpage with an increase of 6.6% in residual stresses.