Reactive powder concrete reinforced with steel fibres exposed to high temperatures

An experimental investigation was carried out to assess the mechanical properties of reactive powder concrete (RPC) reinforced with steel fibres (2% in vol.) when exposed to high temperatures. The compressive, flexural and tensile strength, modulus of elasticity and postcracking behaviour were assessed after specimens’ exposure to different high temperatures ranging from 400 to 700ºC. The mechanical properties of the RPC were assessed for specimens dried for 24 hours at 60 ºC and 100 ºC. Partially dried specimens (60 ºC) exhibited explosive spalling at nearby 450 ºC, while fully dried RPC specimens (100 ºC) maintained their integrity after heating exposure. In general, the mechanical properties of RPC significantly decreased with the increase of the temperature exposure. The rate of decrease with temperature of the compressive, tensile and flexural strengths, as well the corresponding post-cracking residual stresses was higher for exposure temperatures above the 400 ºC.The authors would like to acknowledge the Zhejiang Boen Company and MAPEI Company for providing gratuitously, respectively, the steel fibers and micro silica fume. The first author would also like to acknowledge the grant obtained under the scope of the Erasmus Mundus - Marhaba project. The third author wishes to acknowledge the grant SFRH/BSAB/114302/2016 provided by FCT.info:eu-repo/semantics/publishedVersio

4D printing of multifunctional and biodegradable PLA‐PBAT‐Fe3O4 nanocomposites with supreme mechanical and shape memory properties

4D printing magneto-responsive shape memory polymers (SMPs) using biodegradable nanocomposites can overcome their low toughness and thermal resistance, and produce smart materials that can be controlled remotely without contact. This study presented the development of 3D/4D printable nanocomposites based on poly (lactic acid) (PLA)-poly (butylene adipate-co-terephthalate) (PBAT) blends and magnetite (Fe3O4) nanoparticles. The nanocomposites are prepared by melt mixing PLA-PBAT blends with different Fe3O4 contents (10, 15, and 20 wt%) and extruded into granules for material extrusion 3D printing. The morphology, dynamic mechanical thermal analysis (DMTA), mechanical properties, and shape memory behavior of the nanocomposites are investigated. The results indicated that the Fe3O4 nanoparticles are preferentially distributed in the PBAT phases, enhancing the storage modulus, thermal stability, strength, elongation, toughness, shape fixity, and recovery of the nanocomposites. The optimal Fe3O4 loading is found to be 10 wt%, as higher loadings led to nanoparticle agglomeration and reduced performance. The nanocomposites also exhibited fast shape memory response under thermal and magnetic activation due to the presence of Fe3O4 nanoparticles. The 3D/4D printable nanocomposites demonstrated multifunctional multi-trigger shape-memory capabilities and potential applications in contactless and safe actuation

4D printing of polyethylene glycol‐grafted carbon nanotube‐reinforced polyvinyl chloride–polycaprolactone composites for enhanced shape recovery and thermomechanical performance

4D printing with carbon nanotube (CNT)-reinforced polymers enables advanced shape-changing materials but faces challenges in CNT dispersion and performance. This study addresses these limitations by functionalizing CNTs with polyethylene glycol (PEG), significantly enhancing dispersion and interfacial bonding within biocompatible polyvinyl chloride (PVC)-polycaprolactone (PCL) composites. The composites, tailored for biomedical applications with a glass transition temperature (Tg) of 37–41 °C, exhibit enhanced mechanical, thermal, and shape-memory properties. At 0.5 wt% CNT, the composite achieves a 25% increase in tensile strength, 95.78% shape fixity, and a 5-s recovery time, offering an optimal balance of strength, flexibility, and rapid shape recovery. Higher CNT concentrations (5 wt%) further improve thermal stability, increasing the decomposition temperature by 20 °C and storage modulus by 670 MPa, although ductility is reduced. PEG grafting prevents CNT agglomeration, enabling high filler loading without compromising printability, as confirmed through uniform nanoparticle dispersion and defect-free fused deposition modeling (FDM)-printed structures. These intelligent composites combine biocompatibility, durability, and excellent shape-memory performance, making them suitable for diverse structural and biomedical applications, such as adaptive medical devices, ergonomic shoe soles, and wearable biosensors. This novel material provides a versatile platform for high-performance, 4D-printed intelligent systems that address current challenges in polymer nanocomposites and advance engineering and biomedical innovations

4D printing of composite thermoplastic elastomers for super‐stretchable soft artificial muscles

This study explores the development of soft, super-stretchable artificial muscles by 4D printing of composite thermoplastic elastomers. A propylene-based elastomer, combined with carbon black (CB) nanoparticles, is utilized to develop nanocomposite elastomers with enhanced mechanical properties. A pellet-based material extrusion technique is employed to overcome the challenges of filament buckling in traditional filament-based printing methods. The pure elastomer exhibits an elongation at break of 4048% and a tensile strength of 3.71 MPa, while the optimal nanocomposite (2% CB) achieves an elongation of 2665% and a tensile strength of 5.58 MPa. Scanning electron microscopy confirms that high-quality printing with well-bonded layers is achievable. The shape memory properties of printed elastomers are assessed through cyclic tests. It demonstrates the material's ability to recover its original shape after deformation with a drop in mechanical properties after each cycle controllable by CB reinforcements. Innovative artificial muscles are inspired by the chameleon's tongue, achieving significant strain recovery and lifting capabilities. Objects with varying weights are lifted by these muscles, showcasing potential for soft robotics and actuators. The potential of 4D printed composite elastomers in creating highly stretchable, efficient artificial muscles is highlighted, offering promising applications in fields requiring high elasticity and mechanical performance

3D and 4D printing of PETG–ABS–Fe3O4 nanocomposites with supreme remotely driven magneto-thermal shape-memory performance

This study introduces novel PETG–ABS–Fe3O4 nanocomposites that offer impressive 3D- and 4D-printing capabilities. These nanocomposites can be remotely stimulated through the application of a temperature-induced magnetic field. A direct granule-based FDM printer equipped with a pneumatic system to control the output melt flow is utilized to print the composites. This addresses challenges associated with using a high weight percentage of nanoparticles and the lack of control over geometry when producing precise and continuous filaments. SEM results showed that the interface of the matrix was smooth and uniform, and the increase in nanoparticles weakened the interface of the printed layers. The ultimate tensile strength (UTS) increased from 25.98 MPa for the pure PETG–ABS sample to 26.3 MPa and 27.05 MPa for the 10% and 15% Fe3O4 nanocomposites, respectively. This increase in tensile strength was accompanied by a decrease in elongation from 15.15% to 13.94% and 12.78%. The results of the shape-memory performance reveal that adding iron oxide not only enables indirect and remote recovery but also improves the shape-memory effect. Improving heat transfer and strengthening the elastic component can increase the rate and amount of shape recovery. Nanocomposites containing 20% iron oxide demonstrate superior shape-memory performance when subjected to direct heat stimulation and a magnetic field, despite exhibiting low print quality and poor tensile strength. Smart nanocomposites with magnetic remote-control capabilities provide opportunities for 4D printing in diverse industries, particularly in medicine, where rapid speed and remote control are essential for minimally invasive procedures

Effects of TPU on the mechanical properties, fracture toughness, morphology, and thermal analysis of 3D‐printed ABS‐TPU blends by FDM

In this paper, blends of ABS-TPU with two different weight percentages of TPU were prepared using fused deposition modeling technology. The effect of adding TPU on the fracture toughness of ABS and mechanical properties was comprehensively studied. Tensile, compression, fracture toughness, and shear tests were conducted on the 3D-printed samples. Thermal and microstructural analyses were performed using dynamic mechanical thermal analysis (DMTA), and scanning electron microscope (SEM). The DMTA results showed that adding TPU decreased the storage modulus and the glass transition temperature of ABS, as well as its peak intensity. The mechanical test results showed that adding TPU decreased the strength but increased the formability and elongation of the samples. Fracture tests showed that the addition of TPU decreased the maximum force needed for a crack to initiate. The force required for crack initiation decreased from 568.4 N for neat ABS to 335.3 N for ABS80 and 123.2 N for ABS60. The ABS60 blend exhibited the highest strength against crack growth, indicating that TPU can change the behavior of ABS from brittle to ductile. Shear test results and SEM images also showed good adhesion strength between the printed samples for all three specimens, indicating their good printability. Adding TPU resulted in a reduction in the size and number of voids and holes between the printed layers

Development of pure poly vinyl chloride (PVC) with excellent 3D printability and macro‐ and micro‐structural properties

Unmodified polyvinyl chloride (PVC) has low thermal stability and high hardness. Therefore, using plasticizers as well as thermal stabilizers is inevitable, while it causes serious environmental and health issues. In this work, for the first time, pure food-grade PVC with potential biomedical applications is processed and 3D printed. Samples are successfully 3D printed using different printing parameters, including velocity, raster angle, nozzle diameter, and layer thickness, and their mechanical properties are investigated in compression, bending, and tension modes. Scanning electron microscopy is also used to evaluate the bonding and microstructure of the printed layers. Among the mentioned printing parameters, raster angle and printing velocity influence the mechanical properties significantly, whereas the layer thickness and nozzle diameter has a little effect. Images from scanning electron microscopy also reveal that printing velocity greatly affects the final part's quality regarding defective voids and rasters’ bonding. The maximum tensile strength of 88.55 MPa is achieved, which implies the superiority of 3D-printed PVC mechanical properties compared to other commercial filaments. This study opens an avenue to additively manufacture PVC that is the second most-consumed polymer with cost-effective and high-strength features

Simultaneous 4D printing and in-situ foaming for tailoring shape memory behaviors in polylactic acid foams

This study introduces an innovative 4D printing technique combined with in-situ foaming to enhance the shape memory properties of polylactic acid (PLA) foams. By melt mixing PLA with azodicarbonamide (AZO) below its decomposition temperature, followed by direct pellet printing, the research achieves uniform microporous structures and tailored shape memory behaviors. The findings demonstrate that higher AZO content improves shape fixity (∼96 %) but reduces shape recovery. Moreover, the programming temperature significantly influences performance, with hot programming enhancing shape fixity and cold programming boosting shape recovery. This novel approach offers potential applications in lightweight, thermally insulative, and shock-absorbing materials with programmable properties

4D printing-encapsulated polycaprolactone–thermoplastic polyurethane with high shape memory performances

There are a few shape memory polymers (SMPs) like polylactic acid (PLA) and polyurethane (PU) that are 4D printable, and other SMPs must be synthesized with a complicated chemical lab effort. Herein, considering dual-material extrusion printing and microscopic mechanism behind shape memory effect (SME), bilayer-encapsulated polycaprolactone (PCL)–thermoplastic polyurethane (TPU) shape memory composite structures are 4D printed for the first time. The SME performance is investigated by assessing fixity, shape recovery, stress recovery, and stress relaxation under bending and compression loading modes. PCL, TPU, and melting temperature of PCL play the role of switching phase, net point, and transition temperature, respectively. Due to the destruction and dripping of molten PCL in contact with water, PCL is encapsulated by TPU. Encapsulation successfully solves the challenge of bonding/interface between printed layers, and the results show that the SME performance of the encapsulated structures is higher than bilayer PCL–TPU one's. Experiments reveal that maximum stress recovery in 4D-printed composites remains constant over time. This is a great achievement compared to the previous extrusion-based SMP structures that have great weakness in stress relaxation due to weak and low crystalline fractions and the unraveling of molecular entanglements in semicrystalline and amorphous thermoplastic SMPs, respectively

4D printing of polyvinyl chloride (PVC): a detailed analysis of microstructure, programming, and shape memory performance

In this research, polyvinyl chloride (PVC) with excellent shape-memory effects is 4D printed via fused deposition modeling (FDM) technology. An experimental procedure for successful 3D printing of lab-made filament from PVC granules is introduced. Macro- and microstructural features of 3D printed PVC are investigated by means of wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA) techniques. A promising shape-memory feature of PVC is hypothesized from the presence of small close imperfect thermodynamically stable crystallites as physical crosslinks, which are further reinforced by mesomorphs and possibly molecular entanglement. A detailed analysis of shape fixity and shape recovery performance of 3D printed PVC is carried out considering three programming scenarios of cold (Tg −45 °C), warm (Tg −15 °C), and hot (Tg +15 °C) and two load holding times of 0 s, and 600 s under three-point bending and compression modes. Extensive insightful discussions are presented, and in conclusion, shape-memory effects are promising, ranging from 83.24% to 100%. Due to the absence of similar results in the specialized literature, this paper is likely to fill a gap in the state-of-the-art shape-memory materials library for 4D printing, and provide pertinent results that are instrumental in the 3D printing of shape-memory PVC-based structures