KIC Values Research Articles

Microstructure and mechanical properties of arc evaporated Ti(Al,Si)N coatings

Ti(Al)SiN protective hard coatings are promising candidates for the metal cutting industry, due to their favorable properties such as a high hardness and good oxidation resistance. Within the scope of this work, the microstructure of cathodic arc evaporated TiN, Ti84Si16N, Ti81Al3Si16N and Ti70Al14Si16N was correlated with their mechanical properties. X-ray diffraction (XRD) as well as scanning electron microscopy investigations of the cross-sections revealed a pronounced grain refinement for Ti(Al)SiN compared to TiN. The texture of the coatings was analyzed by XRD pole-figures, showing a change in the preferred orientation in growth direction from (111) for TiN to (200) for Ti(Al)SiN. Hardness values were found to strongly increase from 29 GPa to 40 GPa upon Si addition, but remained constant for further alloying with Al. Micromechanical bending tests allowed to gain a detailed insight into the fracture properties of the investigated coatings and revealed an enhanced fracture stress and fracture toughness (KIC) for Ti(Al)SiN compared to TiN. Hereby, the KIC value of 2.4 ± 0.3 MPa m1/2 for TiN could be increased to a maximum of 3.3 ± 0.2 MPa m1/2 for Ti70Al14Si16N. The present findings provide a systematic overview of the microstructure and mechanical properties of arc evaporated Ti(Al,Si)N coatings, thus allowing to select the most suitable coatings for different applications in the cutting industry.

Investigation of mechanical and fracture behavior of pure and carbon fiber reinforced ABS samples processed by fused filament fabrication process

Purpose Acrylonitrile butadiene styrene (ABS), as a light and high strength thermoplastic polymer, has found extensive applications in different industries. Fused filament fabrication, known as three-dimensional (3D) printing technique is considered a rapid prototyping technique that is frequently applied for production of samples of ABS material. Therefore, the purpose of this study is to investigate the mechanical and fracture behavior of such materials and the techniques to improve such properties. Design/methodology/approach Experimental and numerical analyses have been conducted to investigate the effects of internal architecture and chopped carbon fiber (CF) fillers on the mechanical properties and mixed mode fracture behavior of the ABS samples made by 3D printing technique. Four different filling types at 70% filling ratios have been used to produce tensile and special fracture test samples with pure and CF filled ABS filaments (CF-ABS) using 3D process. A special fixture has been developed to apply mixed mode loading on fracture samples, and finite element analyses have been conducted to determine the geometric function of such samples at different loading angles. Findings It has been determined that the printing pattern has a significant effect on the mechanical properties of the sample. The addition of 15% CF to pure ABS resulted in a significant increase in tensile strength of 46.02% for line filling type and 15.04% for hexagon filling type. It has been determined that as the loading angle increases from 0° to 90°, the KIC value decreases. The addition of 15% CF increased the KIC values for hexagonal and line filling type by 64.14% and 12.5%, respectively. Originality/value The damage that will occur in ABS samples produced in 3D printers depends on the type, amount, filling speed, filling type, filling ratio, filling direction and mechanical properties of the additives. All these features are clearly dependent on the production method. Even if the same additive is used, the production method difference shows different microstructural parameters, especially different mechanical properties.

Effect of Atmospheric-Pressure Plasma Treatments on Fracture Toughness of Carbon Fibers-Reinforced Composites.

In this study, nano-scale fillers are added to epoxy matrix-based carbon fibers-reinforced composites (CFRPs) to improve the mechanical properties of multi-scale composites. Single-walled carbon nanotubes (SWCNTs) used as nano-scale fillers are treated with atmospheric-pressure plasma to introduce oxygen functional groups on the fillers’ surface to increase the surface free energy and polar component, which relates to the mechanical properties of multi-scale composites. In addition, the effect of dispersibility was analyzed through the fracture surfaces of multi-scale composites containing atmospheric-pressure plasma-treated SWCNTs (P-SWCNTs) under high load conditions. The fillers content has an optimum weight percent load at 0.5 wt.% and the fracture toughness (KIC) method is used to demonstrate an improvement in mechanical properties. Here, KIC was calculated by three equations based on different models and we analyzed the correlation between mechanical properties and surface treatment. Compared to the composites of untreated SWCNTs, the KIC value is improved by 23.7%, suggesting improved mechanical properties by introducing selective functional groups through surface control technology to improve interfacial interactions within multi-scale composites.

Comparison of Testing Method Effects on Cracking Resistance of Asphalt Concrete Mixtures

As an inherent characteristic of materials, the fracture toughness is an important parameter to study the cracking behavior of asphalt concrete mixtures. Although material compositions and environmental conditions have a significant effect on the fracture toughness, for a certain material and testing environment, the test condition including the specimen configuration and loading type may also affect the obtained fracture toughness. In this paper, the effect of specimen configuration and applied loading type on the measured pure mode-I fracture toughness (KIc) is investigated. In order to achieve this purpose, using a typical asphalt mixture, four different test specimens including Semi-Circular Bend (SCB), Edge Notch Disc Bend (ENDB), Single Edge Notch Beam (SENB) and Edge Notch Diametral Compression (ENDC) disc are tested under pure mode I. The mentioned specimens have different shapes (i.e., full disc, semi-disc and rectangular beam) and are loaded either with symmetric three-point bending or diametral compressive force. The tests were performed at two low temperatures (−5 °C and −25 °C) and it was observed that the critical mode-I fracture toughness (KIc) was changed slightly (up to 10%) by changing the shape of the test specimen (i.e., disc and beam). This reveals that the fracture toughness is not significantly dependent on the shape of the test specimen. However, the type of applied loading has a significant influence on the determined mode I fracture toughness such that the fracture toughness determined by the disc shape specimen loaded by diametral compression (i.e., ENDC) is about 25% less than the KIc value with the same geometry but loaded with the three-point bending (i.e., ENDB) specimen. In addition, the fracture toughness values of all tested samples were increased linearly by decreasing the test temperature such that the fracture toughness ratio (KIc (@−25 °C)/KIc (@−5 °C)) was nearly constant for the ENDB, ENDC, SCB and SENB samples.

Size effect and other effects on mode I fracture toughness using two testing methods

Mode I fracture toughness (KIC) is an intrinsic material property that quantifies its resistance to tensile fracture propagation. The International Society for Rock Mechanics has endorsed four methods to determine the KIC of rock, namely, the short rod, chevron bend, cracked chevron notched Brazilian disc, and semi-circular bend (SCB) methods. In this study, we compare the results of the SCB technique with those of the recently proposed pseudo-compact tension (pCT) test, which has proven to be convenient for the assessment of KIC in both fragile and ductile rocks. We select the SCB as a benchmark method due to its popularity, simplicity, and straightforward testing configuration. We discuss the results of 146 tests performed with different lithologies (Arcera, Pinacas and Corvio sandstones, and Blanco Mera granite), different sample sizes (100, 50 and 38 mm diameter), and a range of notch lengths. We also assess test repeatability and intercomparability of the results obtained using the two techniques. Compared with the SCB test, the pCT test allows for improved control of the specimen behaviour after the peak load, which provides a greater wealth of fracture mechanics information. pCT specimens yield results with higher repeatability than SCB samples. Although we observe that KIC tends to decrease with an increase in the notch length ratio, this effect appears to be non-significant based on statistical assessments. Accordingly, the corresponding mean KIC values are comparable for medium- and large specimens. The influence of specimen size is more pronounced in the SCB tests, while the pCT tests show less dependence for harder lithologies. Therefore, to set up minimum specimen requirements for fracture toughness testing, in addition to geometrical constraints, some key lithology-dependent properties (strength, mineralogy, grain size, etc.) should also be considered. Further methodological considerations related to test execution are also discussed.

Environment dependence of KIc of glass

The role of temperature (T) and moisture on fracture toughness (KIc) of glasses, as measured by the single-edge precracked beam method (SEPB), is investigated. The brittle to ductile temperature, shown by an increase of KIc, is ~Tg. At T below 0.9Tg, the decrease of the bond strength with T results in the decrease of both the fracture surface energy and Young's modulus, so that KIc decreases with T. From above Tg to below 1.1Tg, the work of fracture increases because of dissipative processes, including confined viscoplasticity and blunting at the crack front. From 1.1Tg, viscous flow extends to the whole specimen and becomes more uniform, resulting in the macroscopic deformation of the specimen, eventually preventing against fracture. The results on humidity sensitive glasses show that both precracking and final fracture steps need to be performed in inert environment to meet the intrinsic KIc value, unless the test is fast enough.

Fracture toughness of flax braided yarn woven PLA composites

Flax fiber braided yarn plain woven fabric reinforced Poly Lactic Acid (PLA) bio-composites are fabricated using film stacking and hot-press compression molding method. Effect of fiber weight fraction on tensile and fracture properties of the bio-composites is studied and fractured surfaces are analyzed using scanning electron microscope (SEM) images. It is found that tensile modulus and strength increases by 62.11 and 59.75% respectively for 35 wt.% of the braided fabric reinforcement compared to pristine PLA. Fracture toughness study is performed on single-edge-notched-bend (SENB) specimens using three point bending method. It is found that plane-strain fracture toughness (KIC ) and strain energy release rate (GIC) values of the PLA composites are 71.61 and 124% higher than pure PLA for 35 wt.% braided fabric reinforcement. KIC values of the braided fabric reinforced PLA composites are much high compared to similar natural fiber composites reported in literature. This is attributed to high resistance offered by the interweaving yarns of the braided fabric hence more energy is required to begin crack propagation compared to other typical forms of reinforcement.

Determination of Fracture Toughness and KIC-CVN Correlations for BM, HAZ, and WB in API 5L X60 Pipeline

This paper presents a study to determine the fracture toughness for the API 5L X60 pipeline in the base metal (BM), the heat-affected zone (HAZ), and the welding bead (WB) by SE(B) specimens in the short transverse direction in an API 5L X60 pipeline. Also, a comparison of the KIC results from SE(B) specimens and KIC-CVN (Charpy V-notch) correlation equations using CVN energy values was done. SE(B) specimens were machined and tested according to ASTM E339. Standard Charpy specimens were machined and tested according to ASTM E23. The notch remained within the evaluation zone to obtain KIC and Charpy specimens at the HAZ and WB. The KIC and CVN values are higher for the BM, followed by the HAZ and the WB. These KIC and CVN values are similar to those reported by other authors in API 5L pipelines. The decrease in KIC and CVN values is due to the microstructure present in the temperature transformations. For BM, the ferrite matrix with pearlite colonies could be presented, while for the WB zone, martensite and finer bainite are detected. In some regions of the HAZ temperatures are reached that promote the transformation of the ferritic/pearlitic structure of the BM into austenite. KIC-CVN correlation equations values should be used only to estimate KIC values when KIC data cannot be obtained from standard specimens.

Epoxidized soybean oil modified using fatty acids as tougheners for thermosetting epoxy resins: Part 2—Effect of curing agent and epoxy molecular weight

AbstractA series of bio‐rubber (BR) tougheners for thermosetting epoxy resins was prepared by grafting renewable fatty acids with different chain lengths onto epoxidized soybean oil at varying molar ratios. BR‐toughened samples were prepared by blending BRs with diglycidyl ether of bisphenol A resins, Epon 828 and Epon 1001F, at different weight fractions and stoichiometrically cured using an amine curing agent, 4, 4′‐methylene biscyclohexanamine (PACM). Fracture toughness properties of the unmodified and BR toughened polymer samples—including critical strain energy release rate (GIc), and critical stress intensity factor (KIc)—were measured to investigate the toughening effect of prepared BRs. It was found that the degree of phase separation and toughening were more controllable relative to similar polymers cured using the aromatic curing agent Epikure W, and the use of higher molecular epoxy resins produces a synergistic effect increasing the toughness much more than similar polymers made with lower molecular weight epoxy resins. Average BR domain sizes ranging from 200 to 900 nm were observed, and formulations with GIc, values KIc as high as 1.0 kJ/m2 and 1.4 MPa m1/2 were attained respectively for epoxy systems with Tg greater than 130°C.

Strategy for improving the wear-resistance properties of detonation sprayed Fe-based amorphous coatings by cryogenic cycling treatment

Abstract Fe-based amorphous coating is deposited on invar steel substrates using detonation spray and then through the cryogenic cycling (CCT) treatment from 0 to 60 cycles with the interval 10 cycles. Effects of CCT on microstructure, thermal properties, mechanical and tribological properties were investigated. It was found that, all the coated samples with CCT are still well bonded with the invar steel substrate, except for the surface of C60 appears local cracks. Moreover, it also found that although CCT did not significantly change the phase structure of the amorphous coating, CCT promoted the rejuvenation behavior in the amorphous coating, which also led to the heterogeneity of the internal structure. Attributed to this heterogeneity, it promotes the generation of a large amount of free volume in the amorphous coating, which results in a significant change in the toughness and resistance to crack propagation of the amorphous coating. And after 50 CCT cycles, the amorphous coating has undergone an obvious ductile-brittle transition, which has the highest fracture toughness KIC and plastic work Wp value. The COF and wear rate of coatings increased initially, then followed by a decrease, but then again increased with the increase of CCT cycles. The 50-cycles coatings exhibited the lowest COF (0.60) and wear rate (0.56 × 10−5 mm3N−1 m−1). The wear mechanism of all the samples is mainly delamination wear with oxidative wear, but the degree of delamination wear is obviously different, showing a trend corresponding to the tribological behavior of the amorphous coating. Therefore, the CCT method could be an effectively strategy to ameliorate the toughness and then enhance the wear performance of the Fe-based amorphous coating.

Determination of concrete strength and toughness from notched 3 PB specimens of same depth but various span-depth ratios

Notched three-point-bending (3 PB) tests of small concrete samples with a fixed depth/size but various span/depth ratios can be performed in almost every laboratory. Additional usefulness is added to the flexibility of those fixed-depth 3 PB tests in this study by providing a simple closed-form solution for determination of the depth and span independent tensile strength ft and fracture toughness KIC measurable from 3 PB samples with any span-depth ratio. Material constants, ft and KIC, only existed asymptotically for large concrete structures are determined by the simple fracture mechanics model regardless the span-depth ratio. Recent results of notched 3 PB tests with 6 span-depth ratios (2, 2.5, 3, 4, 5 and 6) were analysed again by the closed-form model and compared with the effective fracture toughness in the previous study (without ft). A good agreement in KIC values was obtained. That is the two different fracture models have affirmed the usefulness of small notched 3 PB tests of a fixed depth/size but with flexible choices of the span/depth ratio. Moreover, the weight of specimens is suggested to be considered when the span/depth ratio is greater than 4.0 for 3 PB tests. Finally, fracture statistics analysis, not considered by the previous method, was included in this study, which provided the 95% reliability band besides the mean ft and KIC values.

Mechanical properties of ceramic composites based on ZrO2 co-stabilized by Y2O3–CeO2 reinforced with Al2O3 platelets for dental implants

ObjectivesThe objective of this work was the development and characterization of a ceramic composite based on (Ce,Y)-TZP/Al2O3 aiming an application on dental implants, comparing it with conventional monolithic 3Y-TZP ceramics, currently used for the same type of application. MethodsCeramic samples, 3Y-TZP (n = 40) and (Ce,Y)-TZP/Al2O3 (n = 40), were sintered at 1500 °C - 2h and characterized by relative density, X-Ray diffraction (XRD) and microstructure. Then, the samples of both materials were divided into two groups: 1) samples with original (as sintered) surfaces; 2) samples with conditioned, polished, surfaces. All samples were submitted to hydrothermal degradation tests, on an autoclave (134 °C - 2 bar), for 10 h in artificial saliva. The degraded samples were characterized by XRD and the polished group were also characterized by their elastic moduli, Vickers hardness and fracture toughness (Vickers indentation method). Both groups were also submitted to a flexural strength test, 3B–P testing, for which the data were interpreted using Weibull statistics. ResultsAll sintered specimens presented nearly full densification. After the hydrothermal degradation tests, 3Y-TZP samples presented 16.4% of monoclinic (m)-ZrO2 phase while the composite samples withheld 100% of tetragonal (t)-ZrO2 phase. Both materials presented equiaxial ZrO2 grains with an average size of 0.48 ± 0.17 μm and 0.75 ± 0.22 μm, respectively, for the monolithic and composite ceramics. In the composites, is observed the presence of well distributed Al2O3 grains on the ZrO2 matrix, in two distinct morphologies: equiaxial grains and platelets. The composites (Ce,Y)-TZP/Al2O3 presented average values of elastic moduli, Vickers hardness and fracture toughness of 228.3 ± 6.5 GPa, 1427 ± 46 HV e 11.3 ± 0.4 MPa m1/2, respectively. An inversely proportional relationship is observed between the roughness and the bending strength, since the 3Y-TZP samples presented a average strength of 860.7 ± 81 MPa (as-sintered) and 965.4 ± 93 MPa (polished) while the (Ce,Y)-TZP/Al2O3 composites presented average strength of 810.6 ± 147 MPa (as-sintered) and 952.6 ± 88 MPa (polished). ConclusionsThe composites (Ce,Y)-TZP/Al2O3 showed high resistance to degradation in saliva and adequate properties for use as dental implants. Values of flexural strength (>950 MPa) and Weibull modulus (m > 10) were similar to the conventional 3Y-TZP ceramics. Moreover, its hardness, elastic modulus and fracture toughness were higher than those obtained for 3Y-TZP. The expressive values of KIC obtained for (Ce,Y)-TZP/Al2O3 composites are results of association of different toughening mechanisms acting simultaneously in the material.

Influence of specimen geometry on mode I fracture toughness of asphalt concrete

Determination of fracture toughness (KIc) for the asphalt mixture concrete requires employment of suitable testing methods and specimens. Disc-shape specimens are among the favorite test geometries for conducting the fracture toughness experiments on asphalt concrete materials since they can be manufactured easily from those samples obtained by the gyratory compactor machine. Semi-circular bend (SCB) and edge notch disc bend (ENDB) specimens are two suitable and well-known specimens in this regard, and both of them are tested using three-point bend setup. In order to compare the consistency of fracture toughness results obtained from these two specimens, an experimental study is performed herein on a typical asphalt concrete mixture. In the experiments, the thickness of SCB and ENDB specimens and also the loading rate and test temperature are considered as variable. It is found that the KIc values obtained from both SCB and ENDB testing methods are in good agreement. The corresponding value of KIc obtained from the SCB specimen being slightly smaller than the data obtained from the ENDB specimen. Using a two term KI + T strain-based fracture model, that the critical normal strain value for both specimens is shown to be nearly the same and constant for both SCB and ENDB specimens. In addition, it is found that the fracture toughness value and load carrying capacity of asphalt mixture increases by increasing the specimen thickness (from 30 to 70 mm) and the loading rate (from 1 to 6 mm/min), and by decreasing the test temperature (from −15 °C to −25 °C).

Fracture toughness of different monolithic zirconia upon post-sintering processes.

BackgroundSurface treatments are expected to be a reason for alteration in fracture resistance of zirconia. This study evaluated the effect of post-sintering processes on the fracture toughness of different types of monolithic zirconia. Material and MethodsClassical- (Cz) and high-translucent (Hz) monolithic zirconia discs (1.2 mm thickness, 14 mm in Ø) were prepared, and randomly divided for surface treatments with 1) as-glazed (AG); 2) finished and polished (FP); 3) finished, polished, and overglazed (FPOG); and 4) finished, polished, and heat-treated (FPHT) technique (n=15/group). Fracture toughness (KIC) was determined with indentation fracture toughness method at load 1 kg for AG, FPOG and 10 kg for FP, FPHT with 15 sec dwelling time. Weibull analysis was applied for survival probability, Weibull modulus (m), and characteristic toughness (K0). Microstructures were examined with SEM and XRD. ANOVA and multiple comparisons were determined for significant differences (α=0.05). ResultsThe mean±sd value of KIC (MPa.m1/2), m, and K0 were 1.60±0.19, 7.27, 1.71 for CzAG; 9.57±0.89, 9.97, 10.96 for CzFP; 1.61±0.15, 10.56, 1.68 for CzFPOG; 6.45±0.31, 20.31, 6.60 for CzFPHT; 1.45±0.13, 10.91, 1.51 for HzAG; 6.58±0.24, 27.00, 6.70 for HzFP; 1.24±0.05, 23.90, 1.27 for HzFPOG; and 5.07±0.16, 30.51, 5.15 for HzFPHT. The KIC was significantly affected by the post-sintering process, type of zirconia (p<0.05). The Cz indicated a significantly higher KIC than Hz. The FP significantly enhanced KIC, while OG was unable to raise KIC. HT reduced KIC due to reverse phase transformation. ConclusionsPost-sintering processes caused alteration in fracture resistance of zirconia. Fracture toughness was enhanced with FP, but not with either OG or HT process for both Cz and Hz. Surface treatment of zirconia through a finished-polished process is recommended, while glazing and heat-treated are not suggested. Key words:Fracture toughness, glazing, heat treatment, polishing, post-sintering process, zirconia.

Mechanical and Thermal Properties of Epoxy Resins Modified by a Novel Thermoplastic-polyimide

In this paper, a novel polyimide with trifluoromethyl group (PIS) was synthesized successfully and used to improve the toughness of epoxy resins. Five modified epoxy resins (5, 7.5, 10, 12.5 and 15 wt%) were prepared and investigated, respectively. The structure, thermal properties, tensile properties, viscoelastic properties, toughness and morphology of modified epoxy resins were studied by Fourier Transform Infrared Spectroscopy (FT-IR), thermogravimetric analysis (TGA), Instron 5967, Dynamic Mechanical Analysis (DMA), and Scanning Electron Microscopy (SEM). The results showed that the epoxy resins modified with PIS exhibited good thermal stability which the glass transition temperatures increased from 135.9 °C to 146.4 °C. Tensile strength of modified epoxy resins increased from 40.4 MPa to 92.3 MPa. The KIC values increased from 0.86 MPa·m1/2 to 1.56 MPa·m1/2 indicated that the toughness enhancement was markedly. The fracture modes also were examined by SEM images and exhibited the fracture mode changed from the brittle one to ductile fracture with varied weight of the novel trifluoromethyl-polyimide.

Effect of build orientation on fracture behaviour of AlSi10Mg produced by selective laser melting

PurposeA key challenge found in additive manufacturing is the difficulty to produce components with replicable microstructure and mechanical performance in distinct orientations. This study aims to investigate the influence of build orientation on the fracture toughness of additively manufactured AlSi10Mg specimens.Design/methodology/approachThe AlSi10Mg specimens were manufactured using the selective laser melting (SLM) technology. The fracture toughness was experimentally determined (under ASTM E399-09) using C(T) specimens manufactured in different orientations. The microstructure of the specimens was examined using metallography to determine the effects of grain orientation on fracture toughness.FindingsThe fracture toughness magnitude of manufactured specimens ranged between 36 and 50 MPam, which closely matched conventional bulk material and literature values regarding AlSi10Mg components. The C(T) specimens printed in the T-L orientation yielded the highest fracture toughness. The grain orientation and fracture toughness values confirm the anisotropic nature of SLM parts where the T-L-oriented specimen obtained the highest KIC value. A clear interaction between the melt pool boundaries and micro-slipping during the loading application was observed.Originality/valueThe novelty of this paper consists in elucidating the relationship between grain orientation and fracture toughness of additively manufactured AlSi10Mg specimens because of the anisotropy generated by the different melting pool boundaries and orientations in SLM. The findings show that melt pool boundaries can behave as easier pathways for cracks to propagate and subsequently reduce the fracture toughness of specimens with cracks perpendicular to the build direction.

Fracture Toughness of Resin Based Composites, Impregnated with Silver Nanoparticles and Bioactive Glass

OBJECTIVE: To investigate the effect, on fracture toughness (KIc), of impregnating silver nanoparticles (AgNPs) and bioactive glass (BAG) in resin based composites (RBCs). METHODOLOGY: During the period from August 2016 to May 2018, this study was performed at Peshawar Dental College (Pakistan) and Montreal University (Canada), using; a commercial RBC and experimental RBCs with or without BAG content (5-15wt%), and AgNPs (0.009%). Standardized specimens (n=6) were made in each of five RBCs (G1-G5). AgNPs were synthesized and characterized by uv-vis spectroscopy. With universal testing machine, the KIc for RBCs specimens was computed. SEM and dynamic light scattering (DLS) was used to assess the size and form of the prepared silica. One-way ANOVA and Tukey post hoc test were used for data analyses. RESULTS: KIc values varied both within and between RBCs groups. The commercial RBC had highest mean KIc (G1=1.03+0.24). Mean KIc values for the experimental RBCs were; G2=0.69±0.14, G3=0.9±0.13, G4=0.9±0.14 and G5=0.69±0.13. The only RBC groups that had statistically significant variations between their mean KIc values were; G1-G2 (p=0.017) &amp; G1-G5 (p=0.017). SEM and DLS analysis of synthesized silica particles having round shape and sizes of 0.9-1µm. Uv-vis spectroscopy of AgNPs showed round shape with size up to 20nm. CONCLUSION: The KIc of the experimental RBCs with BAG (5-10 wt%) and AgNPs (0.009%) was not significantly different than the commercial RBC. KEYWORDS: Resin based composites, RBCs, Silver nanoparticles, AgNPs, Bioactive glass, BAG, Re-mineralizing resin based composite, Fracture toughness, KIc HOW TO CITE: Hanif A, Ghani F. Fracture toughness of resin based composites, impregnated with silver nanoparticles and bioactive glass. J Pak Dent Assoc 2020;29(4):179-184.

Resonance Raman Scattering Spectra of Co(II)- and Cu-5,10,15,20-Tetrakis[4-(N-methylpyridyl)]porphyrin in the dd Excited State and Mechanisms of Its Deactivation in a Solution and in Complexes with DNA

Resonance Raman scattering (RRS) spectra of the complexes of 5,10,15,20-tetrakis[4-(N-methylpyridyl)]porphyrin with Co(II) and Cu(II) (CoIITMpyP4 and CuTMpyP4) in various solvents and in complexes with DNA are studied. Under nanosecond pulsed excitation, additional lines have been found in the RRS spectra of CoIITMpyP4 in a dimethylformamide (DMF) solution containing formic acid as an impurity and in a complex with DNA. At the same time, such lines are absent in the spectra of CoIITMpyP4 in pure DMF, dimethyl sulfoxide, water, and alcohols under the same excitation conditions. To interpret the experimental data, we have calculated the structure and vibrations of the solvate complexes of CoIITMpyP4 and CuTMpyP4 with water, methanol, and formic acid in the ground and in excited states. Based on the obtained data, additional lines in the Raman spectra are assigned to the dd excited state corresponding to the d(z2) → d(x2 – y2) transition, the lifetime of which increases with the formation of complexes of CoIITMpyP4 with formic acid. According to the calculation results, this correlates with a decrease in rate constant kic of the internal conversion due to an increase in energy gap ΔE between the ground and dd states of CoIITMpyP4. A decrease in the kic value in the case of binding of CoIITMpyP4 and CuTMpyP4 to DNA is caused by the additional interaction of the extra-ligand water molecule with one of its bases directly or via several water molecules immobilized on DNA surface. This complicates the conformational rearrangement of the water molecule in the dd excited state, which gives rise to an increase in the ΔE value.

Fracture and mechanical behavior of vacuum-assisted microwave cured unidirectional carbon woven fabric reinforced epoxy composite

Woven fabric reinforced epoxy composite shown inherent favorable characteristics for aerospace industry applications. This paper comprehensively investigated the mechanical and fracture behavior of unidirectional carbon woven fabric reinforced epoxy composite using experimental and computational techniques. The composites were fabricated with two, four, and six ply laminates with cross-ply and inclined ply (45/–45) orientations. Laminates were fabricated using Vacuum-Assisted Resin Infusion Microwave Curing technique with a high fiber volume fraction of 50% for each laminate. Experimental analyses were performed to predict the behavior of composites under tensile, shear, and impact loading environment. Further, the mean-field homogenization technique coupled with the finite element method was employed to predict orthotropic material properties, fracture energy, and fracture parameters ( KICand GIC) of the composite. The results showed that fracture energy obtained by the computational technique was in good agreement with experimental results. The values of GICincreased with the number of plies both for cross and inclined plies orientation composites. KICvalues were higher for cross plies laminates than the inclined plies laminates.

Electrochemical Properties and Excited-State Dynamics of Azaperylene Derivatives.

A series of azaperylene derivatives such as monoazaperylene (MAPery), 1,6-diazaperylene (1,6-DiAPery), 1,7-diazaperylene (1,7-DiAPery), 1,12-diazaperylene (1,12-DiAPery), triazaperylene (TriAPery), and tetraazaperylene (TetAPery) was synthesized by changing the position and number of nitrogen atoms at the bay region of a perylene skeleton in 1, 6, 7, and 12 positions. The density functional theory (DFT) calculations and electrochemical measurements suggested that the energies of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) states significantly become stabilized with increasing the number of nitrogen atoms, whereas the estimated HOMO-LUMO gaps approximately remain constant. This result is in good agreement with the absorption and fluorescence spectral measurements. Additionally, these steady-state spectroscopic measurements demonstrate the broadened spectra as compared to pristine perylene (Pery). In photophysical measurements, the fluorescence quantum yields (ΦFL) significantly decreased as the number of nitrogen atoms increased, whereas much enhanced quantum yields and rate constants of internal conversion (ΦIC and kIC) were observed. Especially, the increased kIC values of TriAPery (kIC: ∼108 s-1) and TetAPery (kIC: ∼109 s-1) are much larger than those of diazaperylene and monoazaperylene derivatives (kIC: ∼107 s-1). These photophysical trends were successfully explained by time-dependent DFT (TD-DFT) calculations. Finally, the characteristic protonated and deprotonated processes of nitrogen atoms in azaperylenes under acidic conditions were monitored utilizing absorption and fluorescence measurements. The binding constants demonstrate that the nitrogen atoms at 1 and 12 positions of a perylene skeleton are essential for the increased values.