Work Of Fracture Research Articles

3D printing of continuous metal fiber-reinforced recycled ABS with varying fiber loading

PurposeThe current study aims to develop a 3D-printed continuous metal fiber-reinforced recycled thermoplastic composite using an in-nozzle impregnation technique.Design/methodology/approachRecycled acrylonitrile butadiene styrene (RABS) plastic was blended with virgin ABS (VABS) plastic in a ratio of 60:40 weight proportion to develop a 3D printing filament that was used as a matrix material, while post-used continuous brass wire (CBW) was used as a reinforcement. 3D printing was done by using a self-customized print head to fabricate the flexural, compression and interlaminar shear stress (ILSS) test samples to evaluate the bending, compressive and ILSS properties of the build samples and compared with VABS and RABS-B samples. Moreover, the physical properties of the samples were also analyzed.FindingsUpon three-point bend, compression and ILSS testing, it was found that RABS-B/CBW composite 3D printed with 0.7 mm layer width exhibited a notable improvement in maximum flexural load (Lmax), flexural stress at maximum load (sfmax), flex modulus (Ef) and work of fracture (WOF), compression modulus (Ec) and ILSS properties by 30.5%, 49.6%, 88.4% 13.8, 21.6% and 30.3% respectively.Originality/valueLimited research has been conducted on the in-nozzle impregnation technique for 3D printing metal fiber-reinforced recycled thermoplastic composites. Adopting this method holds the potential to create durable and high-strength sustainable composites suitable for engineering applications, thereby diminishing dependence on virgin materials.

Three-dimensional printing with waste acrylonitrile butadiene styrene: Processing and characterization

Three-dimensional (3D) printing of waste plastic such as acrylonitrile butadiene styrene (ABS) is challenging because multiple heating cycles and irregular cooling cause accumulation of stress in 3D-printed structures, which significantly affects mesostructured and fiber-to-fiber bond strength. Hence, this study demonstrates the ability to print high-quality parts via 3D printing using ABS waste. The different weight proportions (100, 90/10, 80/20, 70/30, 60/40, 50/50) of recycled ABS (RABS)/virgin ABS (VABS) are selected for experimentation. It is found that increasing VABS content in RABS significantly improved the physical properties of samples. Due to VABS blending in RABS, the average enhancement in flexural strength (Sf), flex modulus (Ef), and work of fracture (WOF) are 11.49%, 5.45%, and 17.31%, respectively, when compared with 100% RABS samples. Similarly, the average increase in Young’s modulus (E), tensile strength at yield (Ty), and ultimate tensile strength (UTS) are 7.71%, 5.19%, and 3.51%, respectively. The samples printed with 50% RABS/50% VABS blends show superior mechanical properties than others, also the properties of 90% RABS/10% VABS and 80% RABS/20% VABS are very close to 100% VABS samples. Hence, this study provides unique opportunities for the sustainable use of waste ABS using 3D printing technology.

Notch sensitivity of C/C-SiC composite evaluated by flexural tests

The notch effects on the mechanical behavior of Liquid Silicon Infiltration (LSI) based continuous carbon fiber reinforced silicon carbide (C/C-SiC) was studied. The in-plane (IP) and out-of-plane (OP) flexural properties of notched and unnotched samples with fiber orientations (0°, 45° and 60°) were determined through 3-point-bending (3PB) and single notched beam (SENB) tests. Despite the significant difference in bending modulus, the strength depends only slightly on the fiber orientation and loading direction, which could be explained through the uneven distribution of SiC-matrix within the block-like structure of C/C-SiC. This unique micro-structure also leads to a relatively constant value of notch sensitivity in the IP direction, and the sensitivity to the notch is relatively low for all tested C/C-SiC specimen configurations. Furthermore, due to the large differences of fracture mechanism, the work of fracture (WOF) in the IP direction is significantly smaller than in the OP direction for all fiber orientations.

Fracture toughness, work of fracture, flexural strength and elastic modulus of 3D-printed denture base resins in two measurement environments after artificial aging

ObjectivesTo investigate the fracture toughness (KIC), work of fracture (WOF), flexural strength (FS) and elastic modulus (E) of four additively manufactured denture base resins in two different measurement environments after artificial aging. MethodsRectangular specimens in two different dimensions (n = 480) were 3D-printed with four denture base resins: Denture 3D+ (DEN; NextDent), Fotodent Denture (FOT; Dreve ProDiMed), Freeprint Denture (FRE; Detax), V-Print dentbase (VPR; VOCO)). KIC, WOF, FS and E were measured after (1) water-storage (37 °C; KIC = 7 d; FS = 50 h); (2) water-storage + hydrothermal-aging (20 min, 0.2 MPa, 134 °C); (3) water storage + thermocycling (10,000 cycles, 5/55 °C) in two measurement environments (i) air-23 °C and (ii) water-37 °C. For FS, fracture types were classified, and relative frequencies determined. Univariate ANOVA, Kruskal–Wallis, Mann–Whitney U, and Spearman’s correlation were calculated (p < 0.05, SPSS V.27.0). Weibull modulus (m) was calculated using the maximum likelihood estimation method. ResultsDEN showed the highest KIC (5/6 groups), WOF and highest corresponding m (1/6 groups), while FRE presented the highest FS (2/6 groups) and E values. Hydrothermal-aging and thermocycling reduced KIC and WOF, FS and E, and the number of FS fracture pieces. For 6/8 groups, hydrothermal aging resulted in lower FS than thermocycling. Measurement in air-23 °C led to higher FS for 7/12 groups and a more brittle fracture behavior. A positive correlation between KIC and FS was observed. SignificanceWith measurements in air-23 °C resulting in higher FS than reported in water-37 °C, the measurement environment should be adapted to the clinical situation to allow valid predictions on the mechanical behavior of denture base resins when in situ.

Effect of various methods of pre-treatment of carbon fibers on the mechanical properties of PIP-based ceramics/carbon composites

The purpose of the work was to determine the conditions of CF preparation to obtain carbide composites with favorable mechanical response. The relationships between the interfacial properties of fiber/polymethylsiloxane composite, and mechanical properties of the resulting fiber/carbide composites were investigated. The CF/resin interfacial strength was modified by oxidation of CF surface with nitric acid, silanization, and depositing CNT or a pyrolytic carbon layer (PyC). The study of composite interphases (ILSS and SEM) and surface tests of the modified CF (XPS, FT-IR, wettability measurements) showed different nature of the bonding occurring at the fiber/resin and fiber/ceramics boundary. The CF silanization significantly improved the ILSS between CFs and resin by 38.5%, while reduced flexural properties of carbide composites. The most promising treatment method of CF for PIP-based ceramic composites was modification with PyC, which provided 2 times higher ILSS, 1.5 times higher flexural strength and improved work to fracture (WF) as compared to unmodified CF.

Size effects governing damage resistance of architected PMMA

This study investigates the effect of feature size, volume fraction, and sample size on the damage resistance of an architected brittle Poly(methylmethacrylate) (PMMA) polymer. Holes with varying diameters and number of layers were micro-machined in samples of different sizes in PMMA throughout the beam and tested under bending in the presence of a pre-crack. The initiation and total work of fracture (WOF) are determined for different feature sizes of holes. In the case of a single hole feature ahead of the crack tip, overall fracture resistance increased with increasing diameter of the hole, while no effect was seen on the initiation fracture resistance. This was reflected as increased damage resistance in the fully architected specimen with increasing diameter of holes as well as with increasing number of layers of the features (and hence their volume fraction). However, an increase in sample size led to catastrophic failure and a decrease in damage resistance. These effects are quantifiably explained in terms of crack driving force calculations done through finite element modelling.

Influence of hydrothermal carbon interphase on mechanical properties of Cf/SiBCN mini-composites after high-temperature treatment

ABSTRACT To investigate the influence of hydrothermal carbon (HTC) interphase on the high-temperature performances of Cf/SiBCN composites, the mechanical properties of Cf/SiBCN mini-composites with HTC interphase and without interphase after high-temperature treatment at 1400–1600°C were studied. The results indicate that, with the increase in heat treatment temperature, Cf/SiBCN mini-composites show a decrease in integrity and interfacial bonding, and the mini-composites with HTC interphase show better integrity and more suitable interfacial bonding. With the introduction of HTC interphase, the corresponding mini-composites show higher tensile strength and work of fracture (WOF) at all temperatures. After heat treatment at 1400 and 1500°C, the tensile strength and the WOF of the mini-composites with HTC interphase are 4.5, 2.6 times and 14.8, 4.3 times higher than the mini-composites without interphase, respectively. After heat treatment at 1600°C, although the mechanical properties of the two mini-composites are comparable, due to the erosion of the fibers and the collapse of the matrix, the tensile strength and the WOF of the mini-composites with HTC interphase are still 2.0 times and 1.7 times higher than the mini-composites without interphase, respectively. Therefore, the HTC interphase is promising to be used to improve the high-temperature performances of Cf/SiBCN composites.

Effect of hydrothermal carbon interphase thickness on mechanical properties of Cf/SiBCN mini-composites

ABSTRACT The carbon fiber/siliconboron carbonitride (Cf/SiBCN) mini-composites exhibit poor mechanical properties due to the strong fiber-matrix bonding, which can be improved by introducing the hydrothermal carbon (HTC) interphase and further engineered by optimizing the HTC interphase thickness. To investigate the effect of the HTC interphase thickness on the mechanical properties of the Cf/SiBCN mini-composites, the tensile properties of the Cf/SiBCN mini-composites with different HTC interphase thicknesses were compared. The tensile test results show that the fracture behavior of the Cf/SiBCN mini-composites changes from brittle fracture to non-brittle fracture after introducing the HTC interphase. In addition, the tensile strength and work of fracture (WOF) of Cf/SiBCN mini-composites first increase and then decrease with the HTC interphase thickness increasing. The corresponding Cf/SiBCN mini-composites with 120 nm HTC interphase exhibits the maximum tensile strength and WOF, which are improved by around 4 times and 18 times, compared with the mini-composites without interphase. This work shows that the introduction of HTC interphase is conducive to improve the tensile properties of the Cf/SiBCN mini-composites, which can provide a preliminary basis for further investigating the effect of HTC interphase on the mechanical properties of the Cf/SiBCN composites.

Reinforcement of Calcium Phosphate Cement with Hybrid Silk Fibroin/Kappa-Carrageenan Nanofibers.

Calcium phosphate cements (CPCs) offer a promising solution for treating bone defects due to their osteoconductive, injectable, biocompatible, and bone replacement properties. However, their brittle nature restricts their utilization to non-load-bearing applications. In this study, the impact of hybrid silk fibroin (SF) and kappa-carrageenan (k-CG) nanofibers as reinforcements in CPC was investigated. The CPC composite was fabricated by incorporating electrospun nanofibers in 1, 3, and 5% volume fractions. The morphology, mineralization, mechanical properties, setting time, injectability, cell adhesion, and mineralization of the CPC composites were analyzed. The results demonstrated that the addition of the nanofibers improved the CPC mixture, leading to an increase in compressive strength (14.8 ± 0.3 MPa compared to 8.1 ± 0.4 MPa of the unreinforced CPC). Similar improvements were seen in the bending strength and work fracture (WOF). The MC3T3-E1 cell culture experiments indicated that cells attached well to the surfaces of all cement samples and tended to join their adjacent cells. Additionally, the CPC composites showed higher cell mineralization after a culture period of 14 days, indicating that the SF/k-CG combination has potential for applications as a CPC reinforcement and bone cell regeneration promoter.

Combined and alone addition effect of nano carbon black and SiC on the densification and fracture toughness of SPS-sintered ZrB2

ZrB2-nano-size carbon black (C.Bn), ZrB2-SiC, and ZrB2-SiC-C.Bn specimens were fabricated by spark plasma sintering (SPS) at 1850 °C for 8 min under 35 MPa pressure. The bulk density (B.D) was measured by the Archimedes method. The single-edge notched beam (SENB) method was applied to investigate the fracture toughness and work of fracture (WOF). It was found that the combined addition of C.Bn and SiC modified the densification behavior to reach full-densified samples. Also, it was found that the fracture toughness and WOF were improved by the addition of C.Bn to the monolithic ZrB2 continuously, and they reached 5.1 ± 0.1 MPa·m1/2 and 433 ± 20 J·m−2, respectively for the sample containing 15 vol% C.Bn. Compared to monolithic ZrB2, the fracture toughness and the WOF for the composite with 30 vol% SiC and 15 vol% C.Bn increased nearly 26 % and 57 %, respectively. It was noteworthy that the alone addition of C.Bn to the pure ZrB2 had more effect in improving the fracture toughness than the simultaneous addition of C.Bn and 30 vol% SiC. The predominant mechanisms in fracture toughness improvement can be related to the observed crack deflections, branching, and bridging in scanning electron microscopy (SEM) images.

Fracture toughness of conventional, milled and 3D printed denture bases

ObjectivesThe aim of this study was to determine and compare fracture toughness (KIC) and work of fracture (WOF) of a conventional (C) denture base, using the notchless triangular prism (NTP) specimen KIC test, with CAD/CAM (milled, M) and 3D-printed (P) materials at 7 d and 90 d. MethodsLucitone 199 (C), Lucitone 199 CAD (M) and Lucitone Digital Print (P) (Dentsply, USA) were used to fabricate NTP specimens. Samples were stored in 37 °C water for 7 d (20/group) and 90 d (20/group) and conditioned in 23 °C water for 1 h prior to testing. For testing, samples were secured in custom-made jigs and loaded in tension until crack arrest/failure. The maximum-recorded load was used to calculate KIC. The results were analyzed by two-way ANOVA, Scheffé multiple mean comparisons (α = 0.05), independent t-tests and Weibull. WOF (in KJ/m2) was calculated by dividing the area under the load-displacement graphs by twice the corresponding crack-arrested cross sectional area of the fractured surfaces. ResultsThe results have shown that: 1) the tested materials had significantly different KIC (P > C > M; p < 0.005) and WOF at both 7d and 90d; 2) ageing in 37 ºC water for 90 d resulted in a significant decrease of KIC in the C and M groups (p < 0.001) and of WOF in all groups. SignificanceThe tested P denture base exhibited significantly higher KIC and WOF, suggesting that it could be more resistant to crack propagation than the C and M materials tested. Water storage for 90 d significantly decreased KIC of C and M materials and WOF of all.

An assessment of the effect of Na2SiO3/NaOH ratio, NaOH solution concentration, and aging on the fracture properties of ultra-high-performance geopolymer concrete: The application of the work of fracture and size effect methods

This experimental study deals with the effects of Na2SiO3 to NaOH solution ratio (SS/SH) (at three levels of 1, 2, and 3), NaOH solution concentration (at three levels of 8, 12, and 16 M), and aging (at three levels of 3, 7 and 28 days) on the fracture characteristics of ultra-high-performance geopolymer concrete (UHPGC) based on ground granulated blast furnace slag (GGBFS) and silica fume. So, five mix proportions were selected. Fracture parameters, including total fracture energy (GF), initial fracture energy (Gf), characteristic length (Lch), the effective size of process zone (Cf), brittleness number (β), fracture toughness (KIC), and critical effective crack- tip-opening displacement (δc), were calculated based on the work-of-fracture (WF) method and size effect (SE) method, and a comparison was made among the results. So, sixty notched beams were subjected to the three-point bending test. The results showed that with increasing SS/SH ratio, molarity, and aging, fracture energy increased and ductility decreased. The specimens up to the age of 7 days could obtain over 90% of the total fracture energy obtained at the age of 28 days. Furthermore, fracture energy increased with the improvement of mechanical properties. The specimen with an SS/HS ratio of 3 and morality of 16 exhibited the highest fracture energy and the lowest ductility. Finally, GF/Gf ratio was calculated as an important parameter in fracture mechanics, which decreased with increasing total fracture energy and initial fracture energy. The mix proportion with the highest fracture energy had the lowest GF/Gf ratio.

An assessment of the fracture parameters of ultra-high-performance fiber-reinforced geopolymer concrete (UHPFRGC): The application of work of fracture and size effect methods

This research aimed to study the effects of a certain volume of fiber on the fracture characteristics of ultra-high-performance geopolymer concrete (UHPGC) based on the ground granulated blast furnace slag and silica fume. To this end, seven mixtures were selected and three different volume fractions were used in them. Three mixtures were used to study the effect of steel fiber (SF) volume fraction and the other three mixtures were used to assess the effect of replacing 0.25% of the SF volume fraction with polypropylene fiber (PPF). Fracture parameters, including total fracture energy (GF), initial fracture energy (Gf), characteristic length (Lch), the effective size of process zone (Cf), brittleness number (β), fracture toughness (KIC), and critical effective crack-tip-opening displacement (δc) were calculated by the work of fracture (WF) method and size effect (SE) method, and the results were compared. Furthermore, the relationship between the fiber’s volume fraction with GF, Gf, Lch, Cf, and KIC was individually obtained in the form of polynomial functions. For this purpose, 84 notched beams were tested by three-point bending. The results show that increasing SF volume fraction significantly increased the fracture properties of UHPGC and increased fracture energy and ductility. On the other hand, partial replacement of SF with PPF slightly affected fracture characteristics adversely versus the specimens containing only SF. Finally, the GF/Gf ratio, which is an important parameter in fracture mechanics, was calculated. This ratio was increased with increasing fiber fraction so that it reached from 2.84 for UHPGC to 13.64 for UHPFRGC.

Size-controllable synthesis of dendritic porous silica as reinforcing fillers for dental composites

ObjectivePorous materials, especially porous silica particles are of great interest in different areas, and have applied in dental composites as inorganic fillers, due to their potential in constructing micromechanical interlocking at the filler-resin matrix interfaces. However, the facile and precise synthesis of hierarchical porous silica with graded sizes is still a great challenge. MethodsHere, we synthesized dendritic porous silica (DPS) with center-radial hierarchical pores and controllable size ranging from 75 to 1000nm by varying simultaneously the amounts of silica precursor and template in the microemulsion. A plausible nucleation-growth mechanism for the structural formation and the size tunability of the DPS particles was further put forward. These DPS particles were then formulated with Bis-GMA/TEGDMA resin. ResultsThe particle size and morphology influenced the mechanical properties of dental composites. Particularly, DPS-500 particles (average size: 500nm) exhibited the superior reinforcing effect, giving large improvements of 32.0, 96.7, 51.9, and 225.6% for flexural strength (SF), flexural modulus (EY), compressive strength (SC), and work of fracture (WOF), respectively, over the DPS-75 filled composite. All DPS filler sized exhibited similar degree of conversions and curing depths. Furthermore, the DPS-500 filled composite presented better cytocompatibility than commercial Z250 XT. SignificanceThe facile synthesis of DPS particles developed here and the understanding of the influence of the filler size and morphology on the composite properties provide a shortcut to design porous silica with precise size control and dental composites with superior performance. These DPS particles could also have promising applications in biomedicine, catalysis, adsorption, and cancer therapy.

Comparison between Explosive Welding and Roll-Bonding Processes of AA1050/Mg AZ31B Bilayer Composite Sheets Considering Microstructure and Mechanical Properties

In this article, the effect of the manufacturing process on the microstructure and mechanical properties of AA1050/Mg-AZ31B bilayer composite sheets has been studied experimentally. In multilayer composite sheets, the interface bond strength plays a significant role in the mechanical properties of the composite. The most important factor affecting the bond strength is the manufacturing process of these sheets. So, two processes of explosive welding and roll bonding have been used to manufacture the bilayer composite sheets. The results show that the atomic diffusion in the interface is 6.5 microns in the explosive welding and 6.7 microns in the roll bonding. No intermetallic compounds have been observed in the interface of the studied bonding methods. The wavy and straight interface morphologies have been observed for explosive welding and roll bonding, respectively. Also, recrystallization has been observed in the microstructure of both methods. In the magnesium microstructure of rolled sample, twinning and deformation bands have been seen, while adiabatic shear bands have been formed in the explosive-welded sample. The ultimate tensile strength, elongation, and work of fracture (WOF) of explosive-welded sheets have been increased by 145%, 31%, and 407% relative to the rolled sheets, respectively. Besides, considering the separation of layers in the tensile test of rolled sheets compared to explosive welded ones, it can be stated that the structural failure in explosive welding occurs simultaneously for all layers. However, for roll bonding, the layer failure is independent of the entire structure failure. In this case, first, necking and fracture of the magnesium layer occur, and then, after the separation of the interface, the fracture of the aluminum layer happens.

Influence of Sodium Alginate on Properties of Tetracalcium Phosphate/Nanomonetite Biocement

Abstract The tetracalcium phosphate/nanomonetite (TTCPMH) biocements with the addition of sodium alginate were prepared by mechanical homogenization of powder mixture with hardening liquid containing sodium alginate. The effect of various viscosity of different alginates on properties of TTCPMH cement mixture was investigated. The medium viscous (MED) alginate had a more negative effect on setting process and compressive strength than low viscous (LOW) alginate. An approx. 50% decrease in mechanical properties (compressive strengths, Young´s modulus, work of fracture (WOF)) was revealed after an addition of 0.25 wt % with rapid fall above 1 wt % of LOW alginate in biocement. A statistically significant difference in the WOF was found between of 0.25 and 0.5 LOW alginate biocements (p&lt;0.035) whereas no statistical differences were revealed between WOF of 0.5 and 1 LOW alginate biocements (p˃0.357). In the microstructure of composite cements, the increased amounts of granular or finer needle-like nanohydroxyapatite particles arranged into the form of more separated spherical agglomerates were observed. A low cytotoxicity of cement extracts based on measurement of cell proliferation was revealed.

An investigation into the three-point bending properties and the vickers microhardness of dental composites reinforced with nylon 66 nanofibers

The aim of this research work is to study the reinforcement effect of nylon 66 nanofibrous mats on the mechanical properties of the three different dental composites, termed as Nanohybrid, Microhybrid and, Microfill. Nylon 66 nanofibrous mats were prepared by using the electrospinning technique at different spinning dope concentrations (17%, 20% and 23% wt.) and characterized by a scanning electron microscopy and a mechanical tester. The obtained mats were added to the dental composites in a laminate form with the weight fraction of 0, 0.5, 1.5, 3 and 6%. The flexural strength (FS), elastic modulus (EY), and work of fracture (WOF) of the dental composites were evaluated using three-point bending test and the Vickers hardness of the composites was studied using microhardness test. Obtained results showed that by increasing the spinning solution concentration, the diameter of the resultant nanofibers increased which further increased the tensile strength of the nanofibrous mats. The results of the three-point bending test indicated that FS, EY, WOF of the nanofiber reinforced composites were all significantly increased by the addition of nylon 66 nanofibers; as an illustration, the addition of 6% nanofibrous mats (23% wt) improved FS of the Microhybrid composite by 68.08%, EY of the Nanohybrid composite by 509%, and WOF of the Microfill composite by 106.08%, as compared to those of the pure dental composite. Furthermore, the incorporation of the nanofibers within the resin matrix increased the microhardness value of the reinforced resin, as compared to the unreinforced resin, for all three different dental composites.

Structural design and energy absorption mechanism of laminated SiC/BN ceramics

The laminated silicon carbide/boron nitride (SiC/BN) ceramics with different structural designs were fabricated by pressureless sintering at 1900 °C for 1 h in argon flow. The alumina (Al2O3)-and yttrium(III) oxide (Y2O3)-doped SiC ceramic exhibited a significant intergranular fracture behavior, which could be attributed to the yttrium aluminum garnet (YAG) phase located at the grains boundaries. The bending strength and fracture toughness were used to characterize the crack propagation including the delamination cracking, crack kinking, and crack deflection. The energy absorption in the process of crack propagation was characterized by the work of fracture (WOF) and damping capacity. The mode of crack propagation changed with the change in the structure and variation of BN content in the BN layer. The delamination cracks occurred inside the BN layer or at the interface between SiC and BN layers. The sample with a gradient structure exhibited the combination of delamination cracks occurring at the interface and inside the BN layer, which showed the maximum WOF of 2.43 KJ m−2, bending strength of 300 MPa, and fracture toughness of 8.5 MPa m1/2. The damping capacity varied with the change of the structure and the amplitude. The sample with a gradient structure exhibited the damping capacity of 0.088 and the maximum loss modulus of 9.758 GPa.

The influences of carbon nanotubes introduced in three different phases of carbon fiber/pyrolytic carbon/silicon carbide composites on microstructure and properties of their composites

The influences of carbon nanotubes (CNTs) introduced in three different phases of carbon fiber/pyrolytic carbon/silicon carbide (Cf/PyC/SiC) composites on the microstructure and properties of the composites were investigated in this paper. The results showed with CNTs introduced at PyC-PyC interface, tensile strength and work of fracture (WOF) of a Cf/PyC/SiC composite had the largest increase, and significantly improved 54.9% and 130.3% respectively from those of the CNTs-free composite. Multiple interfaces (CF-PyC interface, CNT-PyC interface, PyC-PyC interface) failure and a great number of carbon fiber and carbon nanotube pull-outs were observed from tensile fracture morphology of the composite, which indicated weakening of PyC-PyC interface due to CNTs and accounted for the remarkable improvement in WOF of the composite. The increase of tensile strength of the composite was resulted from the reduction of residual stress of the composite.

Fracture behavior improvement of TaC-based ceramic composites by fibrous structure

Tantalum carbide (TaC) has monopolized properties making it suitable for aerospace applications. However, its extensive usages have been confined by its catastrophic fracture as a ceramic material. Accordingly, in this research, a fibrous monolithic structure based on TaC-20vol% HfC composite as cell materials and porous graphite as cell boundary phase was produced by co-extrusion processing. Then, fibrous specimens were sintered using hot pressing at the temperature of 1800°C for 1h at a pressure of 40MPa. Monolithic TaC- HfC composites also with the cell composition were manufactured by hot pressing at the same conditions and their fracture behavior and mechanical properties were compared to fibrous specimens. TaC-based fibrous monoliths showed graceful failure in flexural testing because of sufficient difference in strength between the cell and the cell boundary phases. In addition, fibrous monolithic specimens with three values of 25:75, 30:70, and 35:65 cell boundary to cell (CB:C) volume ratios were prepared and its influence on the mechanical properties was investigated. On increasing the cell boundary to cell volume ratio, the work of fracture (WOF) and the fracture toughness enhanced remarkably and reached maximum values of 2145±56J/m2 and 6.6±0.4MPam1/2, respectively in ratio of 30:70, because the wide crack interactions with the weak and porous graphite such as crack deflection and delamination occurred. Crack propagation patterns were also studied by scanning electron microscopy.