Interlayer Voids Research Articles

Study of the development patterns of water-conducting fracture zones under karst aquifers and the mechanism of water inrush

The hydrogeological conditions of the Qianbei coalfield are complex, and karst water in the roof rock frequently disrupts mining operations, leading to frequent water inrush incidents. Taking the representative Longfeng Coal Mine as a case study, research was conducted on the development pattern of the water-conducting fracture zone and the water inrush mechanisms beneath karst aquifers. On the basis of key stratum theory and calculations of the stratum stretching rate, the karst aquifer in the Changxing Formation was identified as the primary key stratum. It was deduced that the water-conducting fracture zone would develop into the karst aquifer, indicating a risk of roof water inrush at the working face. Numerical simulations were used to study the stress field, displacement field, and plastic zone distribution patterns in the overlying roof strata. Combined with similar simulation tests and digital speckle experiments, the spatiotemporal evolution characteristics of the water-conducting fracture zone were investigated. During the coal mining process, the water-conducting fracture zone will exhibit a "step-type" development characteristic, with the fracture morphology evolving from vertical to horizontal. Near the goaf boundary, the strain gradually decreases, and the instability of the primary key stratum significantly impacts the mining space below, leading to the closure of interlayer voids or the redistribution of water-conducting fissure patterns. Field measurements of the water-conducting fracture zone reveal that postmining roof fractures can be classified into tensile-shear, throughgoing, and discrete types, with decreasing water-conducting capacity in that order, the measured development height of the water-conducting fracture zone (51 m) aligns closely with the theoretical height (51.37 m) and the numerical simulation height (49.17 m). Finally, from the perspective of key stratum instability, the disaster mechanisms of dynamic water inrush and hydrostatic pressure water inrush beneath the karst aquifers in the northern Guizhou coalfield were revealed. The findings provide valuable insights for water prevention and control efforts in the Qianbei coalfield mining area.

Printable MXene Ink Hybridized with ZSM-5 for Gas Sensing and CO2 Capturing

In this work we present preparation, characterization and microprinting of Ti3C2/ZSM-5 ink. Printable inks with a viscosity of 5-6 cP were prepared by ultrasonic dispersion of Ti3C2/ZSM-5 nanopowders in DMSO solvent using 1% Polyvinylpyrrolidone (PVP) as dispersant. Brunauer Emmett Teller (BET) results indicate a type IV adsorption isothermal curve for N2 gas with a type H4 retention ring. The data show that the average pore size of the composite material is 23nm, indicating that the material has a micro-mesoporous structure and exhibits excellent adsorption properties for gas sensing applications. However, the adsorption and desorption curves of CO2 shows hysteresis indicating strong interaction between functional groups on the material and CO2 molecules. This material has high CO2 adsorption performance and desorption hysteresis effect, indicating that it can be directly used for CO2 capture. Thermogravimetric (TGA) analysis showed the thermal stability of the composite, with a mass loss of only 5% at 800℃. Ti3C2/ZSM-5 composite ink has excellent anti-oxidation and dispersion properties. When the pure MXene interlayer void is exposed to air, the Ti element in MXene is easily oxidized to TiO2. The introduction of ZSM-5 not only limits the interaction between the functional groups on the surface of MXene, but also fills the layer gap of MXene, effectively reduces the contact with oxygen, and thus shows good oxidation resistance. No characteristic valence signal of TiO2 was observed in XPS results, which confirmed the effectiveness of the method. In addition, imidazole acid molecular sieve frame strengthened MXene adsorption, will have broad prospect of application in gas sensing field. In traditional printing methods, such as drop casting and spin coating, it is difficult to control the uniformity and roughness of coating thickness, which affects the service life and sensing properties of gas sensors. The use of spray atomization technology can maximize the uniform dispersion of ink, and can control the amount of spray, concentration, height and other parameters to control the thickness and roughness of the coating.

Low-cost method to reduce interlayer voids in material extrusion: in situ layer-by-layer solvent treatment

Material extrusion (MEX) is worldwide known as one of the most flexible additive manufacturing (AM) technologies for the fabrication of complex polymeric structures. However, the extremely high geometrical freedom has a price to pay: the presence of interlayer voids between consecutive extruded layers is the main backwards of MEX technology. Interlayer voids make 3D printed parts weaker (poor mechanical properties) compared to polymeric components fabricated by means of counterpart processes (i.e., injection molding). The present research work introduces a novel approach for the reduction of voids based on the layer-by-layer application of solvent vapor during the fabrication process, to smooth every single deposited layer. In this way, the new extruded layer has a greater area to bond with the previously extruded layer, resulting in an overall reduction of the porosity. The proposed approach is cost-effective, and it is based on the stop and go method enabled by MEX technologies: the fabrication process is paused after every layer, and when the solvent treatment is performed, the 3D printing process is resumed. The effectiveness of the layer-by-layer solvent vapor approach was evaluated, thereby resulting in a great reduction of the void density and average void area of 96%, and 79% respectively, and an increase of the wetting factor of 34%. Such findings pave the way for the exploitation of the proposed approach for the fabrication of complex structures with a reduced number of voids to be employed as structural components.

A quasi-exponential distribution of interfacial voids and its effect on the interlayer strength of 3D printed concrete

In this work, a novel theoretical model of the void length probability distribution in 3D printed concrete is established based on a zigzag analog of the layer interface. A quasi-exponential distribution of void length is predicted and subsequently validated on both the zigzag analog and the actual 3D printed concrete, with different void ratios that determine the descending rate and node intervals that decide the horizontal scaling of the distribution. Moreover, the relationships between the interlayer strength, void ratio, and quantity of voids are also studied based on the theoretical model. It is found that the quantity of voids is symmetric about a void ratio of 0.5, and the decrease in the interlayer strength against the void ratio is non-linear which is approximated well by combined exponential and linear functions. This work is believed to reveal the nature of the interfacial void distributions and significantly advance the understanding of the layer interface in 3D printed concrete. The code for the zigzag analog with the computation of its interlayer strength is publicly available at: https://github.com/Human-HLW/Layer-interface.

Enhancing interlayer bonding strength of 3D printed ternary geopolymer using calcium carbonate whiskers spray

Weak interlayer bonding, especially induced by a long period of printing interruption, is one of the major concerns for 3D printing concrete. The effect of CaCO3 whiskers suspension (CWS) spray and printing time interval on the interlayer bonding of 3D printing fly ash-granulated blast furnace slag-steel slag based geopolymer was investigated with splitting tensile strength and direct shear strength tests. The underlying mechanisms were explored based on the characterization of micromorphology, porosity, surface roughness and reaction kinetics of interlayer area. It was revealed that the CWS spray at appropriate concentrations can significantly improve the interlayer bonding of geopolymer printed at extended printing intervals, with 0.05 g/mL of CWS increasing the shear strength up to 71% at 60 min and 0.10 g/mL of CWS increasing the splitting tensile strength by 40% at 40 min. The CWS at proper concentrations could replenish the interlayer moisture, fill the interlayer voids and provide nucleation sites for geopolymerization and hydration products, i.e., N(C)-A-S-H and C-S-H gels. However, excessive CaCO3 whiskers or water content was harmful to the interlayer bonding. As the reaction process and microstructure of 3D printed ternary geopolymer were synergistically impacted by the printing time interval, residual water content, compensated moisture and CaCO3 whisker reinforcement, the mix of CWS spray should be carefully designed to optimize its effectiveness on the interlayer strengthening.

The Effect of Resin Interleafing on the Wedge Peel Strength of CF/PEEK Manufactured by Laser-Assisted In Situ Consolidation

In this work, a novel approach involving coating fine PEEK powder on prepreg is introduced to improve wedge peel strength and reduce interlaminar voids. CF/PEEK laminates with resin interleaving are in situ consolidated by laser-assisted fiber placement. The morphology of the powdered surface is obtained using an optical profilometer, and the surface roughness and volume of added resin are calculated accordingly. Interface and surface temperature are measured during the layup process. Thermal history indicates that very short bonding time is the dominating factor for voids and limited interlayer strength. Laminate porosity and microscopic features are characterized with an optical microscope. The porosity of resin-interleaved laminates decreases to 3.7%, while the resin content only increases by 4.5% in the meantime. This is because interlayer resin particles rapidly melt under laser heating and quickly fill the voids between layers. The wedge peel strength of resin-interleaved laminates can increase by 30.1% without a repass treatment. This could be attributed to the increase in resin intimate contact and reduction in interlayer voids.

Additive manufacturing of yttria-stabilized zirconia using digital light processing: Green density and surface roughness analysis

The amalgamation of digital light processing (DLP) technology and pressureless sintering has emerged as a promising method for producing delicate, complex, and custom-made yttria-stabilized zirconia (YSZ) components. The procedure consists of fabrication of green part using DLP, debinding to remove the binders and sintering to densify the parts. Explorations in the parameter selection in each step are still far from maturity for producing defect-free densified parts. This study addresses the effect of DLP print parameters on the density of green parts and surface irregularities. DLP printing parameters, such as layer thickness, orientation, and light intensity, were selected, and a central composite design methodology was adopted for the design of experiments to investigate the impact of individual parameter as well as their interactions. The density of the green part decreased with an increase in layer thickness from 10 μm to 70 μm, whereas an increase in density was observed when the part orientation changed from 0 ° to 90°, and the intensity changed from 10 to 50 mW/cm2. The variations in layer thickness and part orientation substantially impact the surface roughness, but variations in intensity have comparatively less influence on the surface roughness. The in-layer and inter-layer voids of the samples fabricated with varying parameters were analyzed using scanning electron microscopy. The minimum surface roughness and maximum green part density responses were obtained using regression equations and a multi-objective optimization strategy. Subsequently, the samples were debinded and sintered to produce high-density zirconia components. To establish the importance of parameter optimization, a comparison of the specimen density and surface irregularity in the green and sintered states was performed for specimens fabricated with optimized parameters and a randomly chosen set of parameters. The novel study provides the parametric relation to fabricate as desired green and sintered density parts along with tuned surface roughness.

Multiscale porosity characterization in additively manufactured polymer nanocomposites using micro-computed tomography

Extrusion-based additive manufacturing (AM) of polymer composites exhibits complex thermally driven phenomena that introduce severe discontinuities in the internal structure across length scales, especially voids or porosity. This study utilizes a high-throughput porosity characterization technique to analyze large datasets from numerous micro-computed tomography (μCT) scans to capture the influence of AM print parameters on the size, shape, and location of porosity across multiple print layers (up to a few cm) on fused granular fabrication (FGF) printers. The materials investigated include nanocomposite formulations based on commercially relevant nylon-12 and polyether ketone ketone (PEKK) materials comprising nano- or micro-sized fillers. The estimated global porosity follows an inverse linear correlation against the bulk density of the printed samples. Increasing the extrusion multiplier (EM) and the nozzle temperature while decreasing the print speeds reduces the global porosity. Outlier analyses (local porosity morphology) show that faster print speeds and higher extrusion rates result in long, slender inter-layer voids, while lower nozzle temperatures lead to large, symmetrical, inter-bead voids (at the bead junction). Lack of active chamber temperature increases inter-layer and intra-bead voids with a two-fold increase in global porosity. Overall, the micro filler-reinforced composites exhibit higher global porosity than nanofiller-reinforced composites, which is attributed to the increased mismatch in the thermal expansion coefficient between the filler and the polymers used in the study.

Study on the influence of coarse aggregate distribution uniformity on the compaction characteristics of gap-graded gravels

There has yet to be a quantitatively characterised study that relates the degree of uniformity of aggregate distribution to the compaction of gap-graded gravels. The particle tracking technique was used to calibrate the vibrational compaction discrete element model, which was used to simulate the vibratory compaction of gap-graded aggregates at varying coarse aggregate contents (25 %, 50 %, and 75 %) and different coarse aggregate distribution uniformities ranging between 0.0 and 1.0. The results showed that with an increase in the coarse aggregate distribution uniformity, the amount of void ratio of gap-graded gravels under three coarse aggregate contents decreased significantly. The mechanism of variation in the effect of gap-graded aggregates with coarse aggregate distribution uniformity was found to be due to the variation of the local coarse content between layers: the disparity in the depth range of coordination number, stress transfer, distribution of strong and weak force chains and interlayer void ratio decreases with increasing coarse aggregate distribution uniformity. Hence, it improves the overall compaction effect and the homogeneity of the specimen. Local variations in coarse content between layers are considered to be the main cause of this effect.

Enhancing the sensitivity of 3D printed sensors via ironing and void reduction

ABSTRACT Material Extrusion (MEX) Additive Manufacturing (AM) has risen as a promising technology to monolithically manufacture smart structures with embedded sensors. Despite all the benefits of MEX AM, 3D printed piezoresistive sensors still suffer from low sensitivity, making them unsuitable for the detection of low values of force, displacement and bending angle. In the present paper, a simple, effective, and inexpensive method to increase the sensitivity in 3D printed sensors is proposed, based on the leveraging of the ironing strategy, which resulted in an improvement in the sensitivity of 83% compared to traditional process parameter selection. The ironing strategy reduced intralayer porosity by 59%, as verified by X-Ray CT. Additionally, the ironing strategy involves an increased healing time, which promotes the polymer chain diffusion between layers, which translated into a greater stability of the sensor when cyclically stressed. Smart structures capable of detecting small forces (0.19 N of resolution against 1.96 N for traditional MEX scenario) and smart auxetic devices have been manufactured, demonstrating the potential of the proposed approach. The present research demonstrates the ability to reduce interlayer voids by using an intrinsic feature of the MEX process and consequently improve electrical performance of 3D printed sensors.

Nondestructive Evaluation of Nylon/carbon-Fiber Additively Manufactured Components Using Rotational Eddy Current Testing

ABSTRACT This work applies high-frequency rotational Eddy Current Testing (ECT) to characterize various material and manufacturing properties of fiber-filled fused filament fabrication (FFF) components. Using the FFF process, multilayer coupons were produced with varying filament feedstock materials, extrusion multipliers, and raster orientation patterns. With extrusion multiplier being used to adjust interlayer void content, these manufacturing variables were investigated given their significant influence on the mechanical performance of FFF samples. A custom 15 MHz transmit-receive (TR) ECT probe demonstrated sufficient sensitivity to visualize the phenomena of the swept variables. Furthermore, the extraction of simple features from the rotational ECT scans produced clustering and trendlines consistent with observations from X-Ray computed tomography (CT). Thus, this novel approach to nondestructive evaluation (NDE) of fiber filled FFF components is effective for detection and characterization of impactful AM material properties.

Effect of raster and layer characteristics on tensile behavior and failure of FFF printed PLA samples by representative volume element model

In the fused filament fabrication (FFF) based additive manufacturing process, finding optimum printing parameters for achieving the required mechanical properties of the FFF-built part is challenging. In this study, a representative volume element (RVE) based mesoscale approach was developed to describe the influences of printing parameters on the mechanical behaviors of the 3D printed parts. It was shown that the stress-strain curves up to failure obtained from RVE simulations were well verified by experimental tensile test data of printed PLA samples. Then, effective tensile properties of samples manufactured using different raster angles (0°, 45°/−45°, and 90°) and a wide range of layer heights and widths were predicted and correlated with their respective local damage occurrences. The raster angle strongly affected the elastic modulus and tensile strength. The orientation between interlayer voids and loading direction governed local stress distribution, interface failure, and total deformation of FFF samples. An increased layer height and decreased layer width resulted in a more significant fraction of voids between layers and thus lowered stiffness and tensile strength. The introduced RVE model can serve as a simple tool for determining homogenized responses and studying local stress-strain developments and failure of complex printed parts according to the used printing parameters.

Forward Modeling and Model Test of Ground-Penetrating Radar toward Typical Asphalt Pavement Distresses

As the total mileage of roads with asphalt concrete pavement is increasing rapidly, using ground-penetrating radar (GPR) to estimate the dimension of internal distresses of the asphalt pavement is of great significance for pavement maintenance. However, the relationship between the dimension of road distress and the characteristics of road distress’s radar echo has not been quantified. Therefore, in this paper, a GPR forward modeling toward base cracks and interlayer voids is conducted to investigate the relationship, and a model test is conducted to verify the forward modeling. The results indicate that it is feasible to use a GPR image to estimate the dimension of interlayer voids and base cracks. For vertical dimension estimation, the vertical dimension of the distressed area has a positive relationship with the difference in the return time of radar echoes from the top and bottom of the distressed area. However, the area’s vertical dimension must be at least a quarter of the length of the electromagnetic wave used in the GPR to be correctly identified. Otherwise, it is not easy to distinguish the overlapping echoes from each other. For horizontal dimension estimation, the base crack’s horizontal dimension has a quadratic correlation with the echo’s amplitude, and the horizontal dimension of an interlayer void is approximately equal to the length of its echo’s flat segment.

Constructing bilayer-mesoporous structure in molecularly imprinted nanocomposite membranes for efficient separation of acteoside

The main active component of Cistanche tubulosa is acteoside (ACT), which is difficult to separate due to its low content. Therefore, it is important to develop an efficient method for efficient separation of ACT. Herein, the ACT-based molecularly imprinted nanocomposite membranes (A-MINMs) doped with bilayer-mesoporous carbon nanospheres (BMCNs) were fabricated for efficient separation of ACT. The designed BMCNs mixed with polyvinylidene fluoride (PVDF) powders to prepare the hybrid membranes (BMCNs@PVDF) by a phase inversion method. Then, a sol–gel method was used to synthesize the ACT-imprinted layer on the BMCNs@PVDF. The A-MINMs-400 synthesized under the given conditions demonstrated an excellent rebinding capacity of 114.94 mg/g, the brilliant permselectivity of 7.15, and the rebinding selectivity of 4.48. It mainly attributed to the following three reasons: (i) The designed BMCNs possessed a well-defined bilayer-mesoporous structure composed of the mesoporous carbon shell, interlayer void, and mesoporous carbon core. This bilayer-mesoporous structure can construct the efficient shell@void@core@void@shell pathways in A-MINMs for intercepting ACT molecules through the A-MINMs. (ii) The interlayer void structure can provide a large space for accommodating ACT molecules, thereby enhancing the rebinding capacities of A-MINMs. (iii) The introduced BMCNs nanofillers facilitated to form the abundant ACT-imprinted sites and cavities, improving the selectivity of A-MINMs for ACT. Therefore, the development and design of A-MINMs with bilayer-mesoporous nanofillers had a great potential for efficient separation of bioactive active constituents from natural products.

Yielding and post-yielding behavior of FDM parts under compression stress at different strain rates

AbstractThe present study investigates the compression behavior of components made by material extrusion, also known as fused filament fabrication (FFF) or fused deposition modeling (FDM). An experimental plan was conducted by adopting a high-density fulfillment and varying the material flow. Additional tests were performed by thermomechanical compaction to produce full-density samples. Compression tests were performed at various strain rates ranging between 5 × 10−4 and 5 × 10−1 s−1. Yielding and post-yielding behaviors were analyzed. Morphological analysis was carried out to determine the mesostructural features (interlayer neck and void sizes) and how they behave during the compression test. The results indicated that the principal dimension of the voids ranged between 65 mm and 170 mm depending on the adopted value of the extrusion multiplier. On the other hand, thermomechanical compaction enabled the restriction of the voids of printed samples to 10 mm. The cross-sectioning of samples at different strains indicated the formation of shear banding strain localization. In addition, printed samples behaved like porous media during the compression tests and showed different characteristic regions with different void dimensions. The samples printed at the higher material extrusion showed similar behavior to compacted samples. Post-yielding analysis indicated that strain softening observed on compacted samples was more severe as compared to that observed on printed samples. This behavior is dramatically reduced by decreasing the extrusion multiplier.

Effect of Alkylation Chain Length on Inhibiting Performance of Soluble Ionic Liquids in Water-Based Drilling Fluids.

This work investigated the effect of the alkyl chain length of soluble methylimidazolium bromide ionic liquids (ILs) on their inhibition performance. The IL with a shorter alkyl chain length showed superior inhibition performance by suppressing clay swelling, mitigating clay dispersion, at room temperature. Particularly, the IL with an alkyl chain length of two (EmBr) reduced the sodium bentonite (Na-BT) swelling degree to 89% and achieved a cutting recovery of 81.9% after being rolled at room temperature, performing the best among all ILs. To systematically analyze the inhibition mechanism of ILs, X-ray diffraction (XRD), ζ potential, and particle size distribution have been carried out. The results revealed that the methylimidazolium with shorter alkyl chain length had better ability to enter the interlayer void by ion exchange and decrease interlayer distance, suppress the electrical double layer of the Na-BT particles and decrease the ζ potential, and promote the aggregation of Na-BT in water. It is also observed that high hot rolling temperature reduced the shale inhibiting performance of all ILs, and ILs with longer alkyl chain length had better ability to prevent cutting disintegration at high temperature. It is attributed to the variation of the hydrophilic characteristic of Na-BT at high temperature where EmBr no longer adsorbed the most on the surface and entered the interlayer voids of Na-BT. This study can be used as a reference to systematically explore the effect of the structure of shale inhibitors on their inhibiting performance and develop effective shale inhibitors.

Three-Dimensional Sulfonated Graphene Oxide Proton Exchange Membranes for Fuel Cells

During the last decades, graphene oxide (GO)-based materials have been extensively studied as low-cost efficient solid electrolytes for fuel-cell application. However, the observed limited proton conductivity of GO in the out-of-plane directions and associated lower fuel-cell performance largely limit their practical application. Herein, we have demonstrated a sulfate ion-intercalated three-dimensional graphene oxide (3DSGO) showing an exceptionally high out-of-plane proton conductivity of 0.74 S cm–1 at room temperature and 90% RH, and an in-plane proton conductivity of 3.19 S cm–1. Additionally, measurement of cell performance using the prepared membrane as the electrolyte of the proton exchange membrane fuel cell (PEMFC) showed an optimum power density of 112.65 mW cm–2 at 100% RH and 30 °C, which is more than double that achieved for 3DGO (50 mW cm–2). This efficient proton conduction ability and PEMFC performance of the 3DSGO is linked with the 3D interconnected ionic highways and substantial interlayer void space, which provide the higher water retention capacity in the 3D spongy architecture and a facile proton conduction pathway.

Fabrication Temperature-Related Porosity Effects on the Mechanical Properties of Additively Manufactured CFRP Composites

The use of additive manufacturing in fabricating composite components has been gaining traction in the past decade. However, some issues with mechanical performance still need to be resolved. The issue of material porosity remains a pertinent one which needs more understanding to be able to come up with more viable solutions. Different researchers have examined the subject; however, more research to quantitatively determine fabrication temperatures effects at the micro-scale are still needed. This study employed micro-CT scan analysis to quantitatively compare fabrication temperatures effect at 230 °C, 250 °C, 270 °C, and 290 °C on the mechanical properties of AM fabricated carbon-fiber-reinforces plastic (CFRP) composites, testing carbon fiber-reinforced polyamide (CF-PA) and carbon fiber-reinforced acrylonitrile butadiene styrene (CF-ABS) samples. This micro-CT examination followed an SEM evaluation, which was used to determine temperature effects on interlayer and intralayer porosity generation. The porosity volume was related to the mechanical properties, in which it was determined how temperatures influence porosity volumes. It was also determined that fabrication temperature generally affects semicrystalline composites more than amorphous composites. The overall porosity volumes from the interlayer and intralayer voids were determined, with the interlayer voids being more influential in influencing the mechanical properties.

A Ti3C2Tx@PANI core-shell heterostructure assembled into a 3D porous hydrogel as a free-standing electrode for high-energy supercapacitors.

Although Ti3C2Tx MXenes have attracted attention in electrochemical energy storage devices due to their excellent electronic conductivity, controllable layer structure, and huge redox active surface area, the application of Ti3C2Tx as supercapacitor (SC) electrode materials is severely limited by the ineffective chemical ion transport kinetics caused by self-restacking. In order to increase the interlayer spacing of Ti3C2Tx, the intercalation method is hailed as an effective process. Herein, polyaniline (PANI) nanorods as intercalators were synthesized by the polymerization of an aniline (ANI) monomer chemisorbed onto Ti3C2Tx wrinkled nanosheets, and the formation of a Ti3C2Tx@PANI heterostructure is conducive to the large interlayer voids. Then, the heterostructure was integrated into a three-dimensional (3D) porous cross-linked framework via a simple graphene oxide (GO)-assisted self-convergence hydrothermal strategy with low temperatures. Due to the synergistic effect among each component and 3D porous interconnected structure, the hierarchical Ti3C2Tx@PANI-reduced graphene oxide (RGO) heterostructure hydrogel possesses the advantages of excellent electrical conductivity, high specific capacitance, repressive aggregation, and large electrochemical active area. Heterostructure hydrogel electrodes (without binders) display excellent electrochemical performance with a specific capacitance as high as 301.0 F g-1 at 1 A g-1, 90.74% capacitance retention over 10 000 cycles, and a maximum energy density of 44.6 W h kg-1 at a power density of 504.7 W kg-1. Our study provides a fresh strategy for constructing a 3D Ti3C2Tx-based framework applicable to other MXenes in the design of hybrid structures for maximizing their potential applications in energy storage.

Experimental study on interface failure behavior of 3D printed continuous fiber reinforced composites

Additive manufacturing (or 3D printing) for continuous fiber composite exhibits great potential for fabrication of next-generation lightweight sophisticated structural components. Nevertheless, understanding of interface characteristics of printed parts has remained an open research question for broader applications of this new technology in engineering practice. This study aimed to evaluate the interfacial quality of 3D-printed carbon fiber reinforced plastic (CFRP) composites from two aspects: interlaminar fracture toughness in a pure mode and interfacial failure mechanism in a mixed mode. Prior to the experimental tests, the microstructural quality of the 3D printed specimens was characterized, which showed that the void content and shape of different materials are different. There is a clear boundary line where the short fiber matrix layer and the continuous fiber reinforced layer are in contact, while the interface formed between the same material layers has no evident connection traces. The standard specimens were printed for testing pure mode I and mode II interlaminar fracture toughness, through which the G Ι C and G IIC of interface between continuous carbon fiber layers was characterized. It was found that the fiber bridging phenomenon presented in the double cantilever beam (DCB) experiments, resulting in a higher initial mode I fracture toughness. The end notched flexure (ENF) tests found that the fracture toughness of initial mode II in between the 0° continuous carbon fiber layers was relatively low. The scanning electron microscope (SEM) analysis revealed that the separated surface had only a small area of the matrix being sheared. The single lap specimen printed directly was proposed as a simplified model for simulating complex structural parts subjected to mixed stress of peel and shear. The mechanical responses and failure characteristics of the interfaces composed of different materials and different fiber angles under mixed stress were studied. It is found that each specimen presented some mixed failure modes, and the interface characteristics of different materials and different fiber orientations were completely different. The results gained in-depth understanding on the interfacial properties of 3D printing fiber reinforced structures, thereby providing key data and knowledge for practical applications. • Different layering methods with different interlayer morphology and void shape. • The critical strain energy release rates of type I and typeⅡwere obtained. • Continuous fiber bridging enhances type I fracture toughness. • The shear resistance of the interface between continuous fibers and matrix is very weak. • Reinforcement materials and fiber angles affect the interfacial bond strength and failure.