Defects In Matrix Research Articles

Investigation on cracking resistance mechanism of basalt-polypropylene fiber reinforced concrete based on SEM test

In order to study the anti-crack mechanism of basalt-polypropylene fiber reinforced concrete (BPFRC), based on the restrained shrinkage test of BPFRC, the anti-crack enhancement mechanism of basalt fiber and polypropylene fiber was discussed through SEM microscopic test, and the sensitivity index of BPFRC's anti-crack performance was studied by combining grey relational theory and entropy weight method. The results show that basalt fiber has a significant inhibitory effect on the initiation and propagation of micro-cracks, and polypropylene fiber has a more obvious inhibitory effect on the propagation of macro-cracks. Mixing basalt fiber and polypropylene fiber into concrete can improve the pore structure of concrete matrix, reduce the initial defects of concrete matrix, enhance the density of the interface transition zone between aggregate and matrix, make concrete play a bridging role in different stages of stress deformation, and enhance the crack resistance of concrete more significantly. Grey relational theory combined with entropy weight method shows that the splitting tensile strength has the most significant influence on the crack resistance of BPFRC. This study can provide a new method for the sensitivity index analysis and crack resistance evaluation of concrete.

Rejuvenating Aged Perovskite Quantum Dots for Efficient Solar Cells.

Perovskite quantum dots (PQDs) have emerged as one of the most promising candidates for next-generation solar cells owing to its remarkable optoelectronic properties and solution processability. However, the optoelectronic properties of PQDs suffer from severe degradation in storage due to the dynamically binding ligands, predominantly affecting photovoltaic applications. Herein, an in situ defect healing treatment (DHT) is reported to effectively rejuvenate aged PQDs. Systematically, experimental studies and theoretical calculations are performed to fundamentally understand the causes leading to the recovered optoelectronic properties of aged PQDs. The results reveal that the I3 - anions produced from tetra-n-octylammonium iodide and iodine could strongly anchor on the surface matrix defects of aged PQDs, substantially diminishing the nonradiative recombination of photogenerated charge carriers. Meanwhile, an DHT could also renovate the morphology of aged PQDs and thus improve the stacking orientation of PQD solids, substantially ameliorating charge carrier transport within PQD solids. Consequently, by using a DHT, the PQD solar cell (PQDSC) yields a high efficiency of up to 15.88%, which is comparable with the PQDSCs fabricated using fresh PQDs. Meanwhile, the stability of PQDSCs fabricated using the rejuvenated PQDs is also largely improved.

Microstructural evolution and properties of He-charged a-Si coatings prepared by magnetron sputtering

The introduction of porosity in nanomaterials via magnetron sputtering in helium atmospheres is an interesting strategy for the design of functional materials. Amorphous silicon coatings, with high concentration of He incorporated in the form of overpressurized nano-bubbles, present modified optical properties in comparison with dense coatings of similar composition.In this work, annealing process in He atmosphere from 300 °C up to 1200 °C is performed to evaluate stability after the release of He from the a-Si:He coatings (thickness ∼1700 nm) and to favor matrix crystallization and defect evolution. The work is focused on these effects on the silicon film and its properties. The composition and microstructural evolution of the coatings annealed to temperatures as high as 1200° were investigated by electron microscopy and X-Ray diffraction. Annealing effects on the optical properties and bandgap of the silicon coatings were evaluated by ellipsometry and UV–Vis spectrometry. Helium release from the coating, densification, defects evolution and ordering due to crystallization have a small effect on the refractive index, but cause a significant change in the material band gap from 1.37 eV to 1.80 eV.

Nonlinear ultrasonic techniques to quantify oxidation damage in carbon/carbon composite material

This research applies linear and nonlinear ultrasonic (NLU) techniques to quantify oxidation damage in a carbon/carbon (C/C) composite material cut from an automotive friction disc ring. The oxidation as a result of gasification of carbon at high temperatures (T >∼ 500 °C) is a major degradation mechanism in C/C composites. This is the first research to successfully use a dry-contact mediator wedge setup for nonlinear ultrasonic applications, enabling repeatable in-situ Rayleigh wave measurements on slow wave velocity materials where submersion is impractical. The samples are subjected to thermal damage by exposure to a high temperature atmosphere over multiple holding times, and the oxidation damage is visualized using scanning electron microscopy (SEM). The sample mass is recorded and both linear (velocity and attenuation) and nonlinear (β′) ultrasonic measurements are performed after each holding time. Superior sensitivity to early stage oxidation affirms the suitability of nonlinear Rayleigh wave measurements for the quantification of thermally induced oxidation damage in C/C composites, while the double mediator wedge setup is well suited for high attenuation, slow wave velocity materials, demonstrating potential applicability for in-situ condition monitoring. The results show that a systematic oxidation starts after 3 min of exposure to the temperature in this C/C composite. The oxidation induced fiber–matrix debonding, matrix defects (appearing to be microcracking), and void growth are consistently detected by the Rayleigh wave velocity and acoustic nonlinearity. In addition to the higher sensitivity, the nonlinearity parameter has the capability of selectively measuring the strength related damage such as the observed fiber–matrix debonding, while the wave velocity can detect the oxidation voids. A combined use of these two parameters can provide useful information on the microstructural evolution in C/C composites subjected to high temperatures.

Effect of gamma rays irradiation in the structure, optical, and electrical properties of samarium doped bismuth titanate ceramics

AbstractCeramics have enormous potential in several emerging technologies, including nuclear reactors. Materials with chemical inertness, high-temperature operation, and physical properties stability under applied radiation with high energy are all desired in this field of technology. Given these broad specifications, bismuth titanate ceramics may prove to be a valuable material. Regarding this task, the effect of gamma rays on the structural, optical, and ferroelectric properties of samarium-modified bismuth titanate ceramics was investigated. The Bi3.15Sm0.85Ti3O12(BSmT) compound was irradiated for 0, 50, 100, and 200 kGy using a60Co gamma source at a dose rate of 10 kGy h−1. The phase structure confirmed the orthorhombic, single-phase nature even after gamma irradiation. The results show that the unit cell volume decreases from 966.39 to 962.38 Å3with an increase in gamma dose from 0 to 200 kGy. The X-ray photoelectron spectroscopy study shows an irradiation-induced defect in the host matrix. The results show that the bandgap energy, dielectric constant, Curie temperatures, and remnant polarization slightly decreased with an increase in gamma irradiation. According to the findings of this study, the BSmT exhibits adequate stability against gamma irradiation, which offers tremendous promise in their utilization in nuclear reactor technology.

Assessing the catalytic performance of Cu@Ln (Eu, Sm)-N-C composites as bifunctional electrocatalysts using mesoporous silica-protected calcination

Synthesis of a composite with high technical performance and low cost instead of Platinum-based electrocatalysts has become an investigation hotspot to develop fuel cells and storage technologies. So, in the current investigation, three new bifunctional electrocatalysts incorporating lanthanides into Zeolitic Imidazolate Framework (ZIF)-8 are fabricated and assessed. First, by using a facile protocol, three trimetallic composites consisting of Europium (Eu), Samarium (Sm), Copper (Cu), and ZIF-8 are prepared, and the fabricated samples are labeled as EuCu-ZIF, SmCu-ZIF, and SmEuCu-ZIF. Next, in order to eliminate the irreversible fusion and quick aggregation of metal nanoparticles through the high-temperature carbonization process, the mesoporous-silica-protected calcination technique is investigated. After the Hydrofluoric (HF) etching process, the Cu@Ln (Eu, Sm)-N-C electrocatalysts are formed. Based on the fabricated samples, the Cu@Eu-N-C electrocatalyst exhibited the best Oxygen Reduction Reaction (ORR) performance with an onset potential of −0.06 V vs Ag/AgCl. Additionally, the electron transfer number for this composite is found to be 3.68. The GCD experiments show that the Cu@Eu-N-C electrode has the greatest specific capacitance, measuring 431 F g−1 when tested at 1 A g−1. It is deduced that the introduction of Eu3+ and Sm3+ as metal ions in the ZIF-8 catalyst led to an improvement in defects in the carbon matrix and mass transfer, illustrating the fabricated catalysts have an acceptable efficiency for ORR and storage applications. Indeed, due to the use of metallic ions (Ln and Cu), highly effective active sites were formed, resulting in an outstanding improvement in ORR efficiency. Also, it was found that with the use of mesoporous-silica protection for the fabricated samples, there is a remarkable improvement in the onset potential and specific capacitance parameters.

Understanding the effect of nano‐zirconia on the compressive fatigue performance of cementitious composites

AbstractThe fatigue performance of cementitious composites that affects the service life of structures is particularly sensitive to the initial defects in cementitious matrix and interfacial transition zone. Nano‐ZrO2 (NZ), characterized by high strength and toughness as well as good dispersibility, can improve the compactness of cementitious composites. This paper investigated the modifying effect and mechanisms of NZ on the compressive fatigue performance of cementitious composites, including fatigue life, strength, and deformation behaviors. The experimental results show that adding NZ extends the fatigue life of cementitious composites by an order of magnitude and increases the fatigue failure strain by 11.9%. The microstructural analysis verifies that NZ can deflect the fatigue micro‐cracks, fill the micro‐pores and reduce the growth space of CH crystal size. The modified microstructures potentially lead to fatigue of cementitious composites starting from generating more nano‐cracks in both cementitious matrix and interfacial transition zone, thereby improving the fatigue performance of the composites.

Modulation of vortex pinning by matrix defects in YBa2Cu3O7 nanocomposite film

Nanorods are a very effective pinning center in YBa2Cu3O7 films, and the vortex pinning mechanism should be understood to further improve the critical current density (J c) in the nanocomposite films. Matrix defects are naturally formed during nanocomposite growth, and in this study the effect of matrix defects on the J c in the YBa2Cu3O7 films containing nanorods is discussed. YBa2Cu3O7 + BaHfO3 and YBa2Cu3O7 + BaSnO3 films were prepared by varying the laser repetition frequency to control the matrix defects. All the films contained the nanorods. The YBa2Cu3O7 + BaHfO3 film of 2 Hz exhibits high J c for magnetic field parallel to the c-axis (B//c) due to the nanorods and the isolated random point defects. In the YBa2Cu3O7 + BaHfO3 film of 10 Hz, while the short stacking faults and networked random point defects decreased the J c for B//c, the short stacking faults improved the J c for tilted magnetic field. In the YBa2Cu3O7 + BaSnO3 film of 10 Hz, the isolated random point defects improved J c regardless of the magnetic field direction. While the ab-plane correlated defects are analyzed by the structural observation, the network or isolated nature of the random point defects can be discussed by the normal state resistivity. The matrix defects of YBa2Cu3O7 nanocomposite films should be designed considering the correlated/network/isolated nature which is determined by the morphology and defect concentration.

Physical Properties and Effect of Helium-Vacancy Pair on Tungsten/Graphene Composite as Plasma-Facing Materials from First Principles

Tungsten/graphene composite was developed and demonstrated to have good mechanical and thermal properties. Density functional theory calculations were performed to investigate elastic constants, elastic anisotropies and isotropic elastic moduli, thermodynamic properties and minimum thermal conductivity of tungsten/graphene with and without a helium-vacancy pair, and tungsten/graphane and tungsten/ditungsten carbide (tungsten/W2C) composites. The results show that tungsten/graphene composite has more toughness when compared with pure tungsten metal. It is noticed that the minimum thermal conductivity of tungsten/graphene composite is higher, introducing a potential application in heat dissipation at high temperatures. We give an honest appraisal of the anisotropic and isotropic (polycrystalline) elastic properties of tungsten/graphene, tungsten/graphane, and tungsten/W2C carbide composites. In addition, the results show that the graphene layer is a strong trap for the He atom, while He affinity to the graphene layer is weaker to a single vacancy. The formation of the He-vacancy pair due to trapping effects near the W/graphene interface will help to reduce the concentration of impurities and defects in the tungsten matrix and maintain the inherent heat dissipation properties under irradiation.

Suppressing of secondary electron diffusion for high-precision nanofabrication

Nanopatterning is a well-established approach to fabricating nanostructures in electronics and optics, and exploiting patterning strategy to achieve smaller feature sizes and higher precision is urgently and constantly pursued. State-of-the-art extreme ultraviolet lithography and electron beam lithography have proven to produce smaller sizes. However, for such energetic radiation-based approaches, the serious diffusion behavior of the radiolytic low-energy secondary electrons will result in unpredictable defects in the unexposed matrix, limiting the ultimate resolution and hindering its potential in sub-10 nm patterning. Herein, we report significant progress in high-resolution patterning via suppressing of residues caused by secondary electron diffusion, and 10 nm line-space nanostructures are achieved by utilizing a free radical quencher in patterning a highly sensitive zirconium-containing photoresist. Lithography evaluation combined with theoretical calculation reveals this novel radical quencher approach can effectively suppress undesired electronic excitation and ionization reactions, thereby significantly improving resolution and edge roughness. By inhibiting secondary electron-induced active species, this quenching mechanism is found to increase the onset dose and effectively narrow the energy deposition; thus improving the patterning contrast and facilitating the acquisition of straight lines with sharp edges. This work provides a new perspective on active species diffusion control for higher precision nanoscale fabrication.

Molecular basis and genetic testing strategies for diagnosing 21-hydroxylase deficiency, including CAH-X syndrome.

Congenital adrenal hyperplasia (CAH) is a group of autosomally recessive disorders that result from impaired synthesis of glucocorticoid and mineralocorticoid. Most cases (~95%) are caused by mutations in the CYP21A2 gene, which encodes steroid 21-hydroxylase. CAH patients manifest a wide phenotypic spectrum according to their degree of residual enzyme activity. CYP21A2 and its pseudogene (CYP21A1P) are located 30 kb apart in the 6q21.3 region and share approximately 98% of their sequences in the coding region. Both genes are aligned in tandem with the C4, SKT19, and TNX genes, forming 2 segments of the RCCX modules that are arranged as STK19-C4A-CYP21A1P-TNXA-STK19B-C4B-CYP21A2-TNXB. The high sequence homology between the active gene and pseudogene leads to frequent microconversions and large rearrangements through intergenic recombination. The TNXB gene encodes an extracellular matrix glycoprotein, tenascin-X (TNX), and defects in TNXB cause Ehlers-Danlos syndrome. Deletions affecting both CYP21A2 and TNXB result in a contiguous gene deletion syndrome known as CAH-X syndrome. Because of the high homology between CYP21A2 and CYP21A1P, genetic testing for CAH should include an evaluation of copy number variations, as well as Sanger sequencing. Although it poses challenges for genetic testing, a large number of mutations and their associated phenotypes have been identified, which has helped to establish genotype-phenotype correlations. The genotype is helpful for guiding early treatment, predicting the clinical phenotype and prognosis, and providing genetic counseling. In particular, it can help ensure proper management of the potential complications of CAH-X syndrome, such as musculoskeletal and cardiac defects. This review focuses on the molecular pathophysiology and genetic diagnosis of 21-hydroxylase deficiency and highlights genetic testing strategies for CAH-X syndrome.

Repeated impact resistance of steel fibre-reinforced dry UHPC: Effects of fibre length, mixing method, fly ash content and crumb rubber

Dry concrete exhibits significantly different mechanical properties and failure patterns under dynamic loads from those under static conditions. Considering the practical applications of dry concrete, the flexural impact load renders its units/structures susceptible to unpredictable damage or even failure. In this study, the modified low-velocity drop-weight impact test was conducted on steel fibre-reinforced dry UHPC (FR-DUHPC) beam samples to simulate the frequent and multiple impact loads. The effects of steel fibre length, mixing method, fly ash content and crumb rubber addition on the impact resistance of FR-DUHPC were evaluated based on dynamic responses. Weibull distribution was then conducted to analyse the failure hit number of concrete samples in consideration of the large value variation. Test results indicated that the flexural impact performance was markedly improved with longer steel fibres, but deteriorated with increased fly ash content (especially at early ages) and considerably degraded with the inclusion of rubber aggregate. Hybrid medium/long fibre reinforcement was proposed for DUHPC that were mainly subjected to impact loads during service, while the fly ash content utilized to partially replace cement was not recommended to exceed 40%. Rubber aggregate was not proposed to be added to dry concrete mixtures since the impact load would greatly accentuate the initial matrix defects caused by the weak bonding. Additionally, the two-parameter Weibull distribution was verified to be a desirable statistical method for analysing the failure blow number of FR-DUHPC under repeated low-speed drop-weight impacts. The impact energy for the practical structural design could be preliminarily computed utilizing the derived Weibull parameters at different levels of reliability.

Evaluation of room temperature creep deformation of in situ Fe-based bulk metallic glass nanocomposites by instrumented indentation

In the present work, Fe57Cr9Mo5B16P7C6 (at. %) in situ bulk metallic glass nanocomposites of varying crystallinity, i.e. 0 to 80 vol. %, were synthesized by spark plasma sintering. Room temperature indentation creep behaviour of these composites was evaluated with nanoindentation technique. Effect of crystalline phase content on overall creep behaviour of the BMG composites was evaluated. Creep resistance of the BMG composites was improved with increase in the amount of crystalline phases up to 40 vol. %. Improved creep resistance is attributed to the presence of nanocrystalline phases in amorphous matrix and lower defect concentration in the BMG composite samples. However, excess crystallinity imparted brittleness and resulted in poor creep performance of the BMG composites. Derived stress exponent values are significantly lesser for the BMG composite sample in comparison to the amorphous compact indicating the transition in the mode of plastic deformation from inhomogeneous to nearly homogeneous. Loading rate has more pronounced influence on final creep displacement of fully amorphous sample in comparison to that of BMG composite.

Accelerated aging of polymer composite from Pennisetum purpureum fibers with recycled low-density polyethylene

The use of natural fibers (NF) as reinforcement in polymer composites have been an interesting option to improve their mechanical properties and to decrease production costs since several crops can produce large amounts of NF with low cost. This is particularly attractive for polymer waste recycling that depends of the production of cheap materials to be economically viable. Elephant grass ( Pennisetum purpureum schum) is a tropical climate plant of fast growth with high potential for production of NF. However, studies on the use of P. purpureum fibers as reinforcement in polymers, mainly for recycled polymers, have been restricted. The aims of this study was to evaluate the action of the P. purpureum fibers on the properties of composites using matrix of low-density polyethylene waste (LDPE-w) as well as to verify the behavior of recycled polymer when submitted to the accelerated photochemical aging using UVA radiation. LDPE-w and LDPE-w composite with P. purpureum fibers (LDPE-composite) were analyzed at different aging times by tensile and impact tests, melt flow rate, scanning electron microscopy and Fourier transform infrared. It was verified that P. purpureum fibers induce defects in matrix of LDPE-w, decreasing the performance of mechanical properties. Similar effect also occurs when LDPE-w is submitted to the first hours of accelerated aging. On the other hand, effects of stabilization of the degradation on the polymer matrix can be attributed to the P. purpureum fibers at high aging times. Thus, P. purpureum presents high potential for use as reinforcement in recycled thermoplastic waste.

Morphology mediated photocatalysis and room temperature ferromagnetism in cerium oxide

Present work is focused on fine-tuning of magnetic and photocatalytic properties of three samples of cerium oxide nano/micro-sized particles synthesized via different chemical routes. X-ray diffraction measurement infers the growth of single phase cubic fluorite structure of pure CeO2 with a space group of Fm3‾m. The route of synthesis significantly altered the morphology and particle size as evident from high resolution transmission electron microscopy. Raman spectra and XPS confirmed the existence of oxygen vacancies defects in CeO2 matrix. In this article, investigations of magnetic properties and photocatalytic activity of rose Bengal dye in the presence of UV light have been carried out. For SG, CO, and HB samples, room temperature ferromagnetism was observed with small magnetizations of 2.21, 16.8, and 3.58 emu/g × 10−4 respectively. The photocatalytic efficiency of CO sample was 76.3% for degradation of rose Bengal dye on UV illumination for 140 min. Thus, morphology dependent enhanced ferromagnetic and superior photocatalytic behavior of CeO2 make it a multifunctional material for its use as a photocatalyst for organic dye decomposition and in spintronics devices.

Effect of CNT-FA hybrid on the mechanical, permeability and microstructure properties of gangue cemented rockfill

Solid waste resource reuse, such as fabricating cemented rockfill material, plays a central role in underground reinforcement projects and construction waste recycling. However, the cement applied in the cemented rockfill material still brings massive CO2 emissions and energy consumption. Hence, we take the 0.009 wt% carbon nanotubes (CNTs) combining fly ash(FA) to replace 20% cement to explore a more sustainable improvement for cemented rockfill material. The results demonstrated that CNTs modified specimens exhibited a 17.6% reinforcement in elastic modulus, while the compressive strength remains almost unchanged. The modified specimen also shows fewer and sparser acoustic emission activities, indicating lower destruction intensity. Furthermore, with the help of CNTs filling the pores, water sorptivity and gas permeability tests showed that the impermeability improved by 8.4%-19.7%. By calculating the fractal dimension of the fracture surface SEM images, the CNTs reinforced specimens show better integrity and less structural damage. Metal intrusion measurements indicated that CNTs minify the ITZ width, split micropores in ITZ to reduce porosity under all equalized diameters significantly, especially at 65–70 μm, and form a network skeleton in the pores at the edge of the ITZ to prevent pores from connecting with microscopic defects in the cement matrix. The findings of this work can enhance the understanding of CNTs in composites fabrication and guide the application of CNTs in construction, transportation and mineral engineering in the future.

MOF-Derived Tourmaline@ZnO Nanostructure as a High-Response Sensing Material of Gas Sensors toward n-Butanol

Herein, in order to efficiently enhance the sensing properties based on zinc oxide (ZnO) sensors toward n-butanol, a series of MOF ZIF-8 (zeolite imidazolate framework-8)-derived Tourmaline@ZnO core–shell nanostructures were prepared with a facile solution mixing method and an after-treatment calcination process, and the gas sensing performances were systematically characterized. The results exhibited that the paucity of tourmaline introduction could significantly improve the gas sensitivity for n-butanol, simultaneously increasing the gas selectivity and reducing the response–recovery times. In particular, the sensor based on 5 wt % Tourmaline@ZnO nanocomposites achieved a superior response value, reaching up to 294.4 for 100 ppm n-butanol at 320 °C. Through the integrated testing and analyses of BET, XPS, PL, and UV, it has been confirmed that the introduction of tourmaline can not only enlarge the specific surface area and enrich the surface defects of the ZnO matrix, but its unique spontaneous polarization electric field can also reduce the recombination rate of electron–hole pair efficiency, promoting the efficiency of electron transport and accelerating the gas sensing process ultimately. The enhancement mechanism of the nanostructured Tourmaline@ZnO core–shell gas sensing material was also elucidated from the perspective of the energy band theory at length.

Distributed Bragg Reflector–Mediated Excitation of InAs/InP Quantum Dots Emitting in the Telecom C‐Band

Herein, it is demonstrated that optical excitation of InAs quantum dots (QDs) embedded directly in an InP matrix can be mediated via states in a quaternary compound constituting an InP/InGaAlAs bottom distributed Bragg reflector (DBR) and native defects in the InP matrix. It does not only change the carrier relaxation in the structure but could also lead to the imbalanced occupation of QDs with charge carriers, because the band structure favors the transfer of holes. Thermal activation of carrier transfer can be observed as an increase in the emission intensity versus temperature for excitation powers below saturation on the level of both an inhomogeneously broadened QD ensemble and single QD transitions. That increase in the QD emission is accompanied by a decrease in the emission from the InGaAlAs layer at low temperatures. Finally, carrier transfer between the InGaAlAs layer of the DBR and the InAs/InP QDs is directly proven by the photoluminescence excitation spectrum of the QD ensemble. The reported carrier transfer can increase the relaxation time of carriers into the QDs and thus be detrimental to the coherence properties of single and entangled photons. It is important to take it into account while designing QD‐based devices.

Hydrostatic, strike-slip and normal stress true triaxial hydrofracturing testing of Blanco Mera Granite: breakdown pressure and tensile strength assessment

We have designed and built a versatile testing device to perform hydraulic fracturing experiments under true triaxial conditions. The device, based on a stiff biaxial frame that can be installed in a servocontrolled press, can accommodate cube rock samples of up to 150 mm-edge. Using a low-permeability rock known as Blanco Mera granite, we have performed a series of tests across a range of confining pressures including hydrostatic, normal, and strike-slip regimes. We have verified the applicability of two simple fracture mechanics-based models for the interpretation of experimental results, and we have determined the value of tensile strength of the rock from the injection curves recorded. The orientation of the hydraulically-triggered fractures with respect to the applied stress has also been analyzed. Although the models proposed by Rummel and Abou-Sayed provided reasonably satisfactory results, especially for hydrostatic and strike-slip tests, the presence of heterogeneities and defects in the rock matrix may have a strong influence on the fracture behavior and, therefore, affect the interpretation of hydrofracturing tests.

Monotonic crack propagation in a notched polymer matrix composite reinforced with continuous fiber and printed by material extrusion

The study presents the crack mouth opening and propagation of cracks in a composite material printed by material extrusion subjected to monotonic loading. The composite material is made out of a nylon matrix (with embedded short carbon fiber—called Onyx®) and reinforced with continuous Kevlar fibers. Three-point bending tests were performed on notched specimens built according to ASTM-E399. Tests were digitally recorded to extract crack opening displacement (COD) and crack length data through image treatment techniques (using ImageJ), and results were analyzed using linear elastic fracture mechanics parameters through the use of COD. Therefore, the crack mouth opening was established, and fracture toughness was found to be 46 MPa√m. Additionally, microscopy analysis identified fracture zones, crack initiation, transition, and final rupture. The observed failure mechanisms were matrix cracking, fiber pull-out, fiber breakage, and defects such as non-proper fiber-matrix bonding.