Changes In Flexural Strength Research Articles

Changes in the flexural strength of translucent zirconia due to glazing and low-temperature degradation

Statement of problemSurface glazing and low-temperature degradation (LTD) can affect the mechanical properties of zirconia, which is used to fabricate monolithic ceramic crowns. PurposeThe purpose of this in vitro study was to assess the changes in flexural strength of monolithic ceramic crowns fabricated from translucent zirconia due to surface glazing and LTD. Material and methodsSixty plates of zirconia (25×4×1.2 mm) were milled and sintered. They were classified into 4 groups according to glazing and LTD (n=15): control, glazing, LTD, and LTD after glazing. A 3-point flexural test was performed with a universal testing machine. X-ray diffraction (XRD) was used to observe changes in the crystal structures of each group, and field emission scanning electron microscopy was used to observe the sizes of the crystal grains. Two-way analysis of variance was used to evaluate the results of the flexural strength tests, and the Tukey honestly significant difference test was performed for post hoc analysis (α=.05). ResultsThe flexural strength showed significant differences due to glazing (P<.01). No significant differences were found due to LTD (P>.05). The crystal grain size increased with decreasing flexural strength of the specimens. XRD showed monoclinic phases in the groups subjected to LTD. ConclusionsGlazing significantly reduced the flexural strength of translucent zirconia. LTD decreased the flexural strength of glazed translucent zirconia, but not to a significant extent.

Microstructure and mechanical properties of carbon fiber needled felt reinforced sol-derived YAG composite

The study concerning the second phase reinforced YAG matrix composites is few although YAG is well known as a desirable thermo structural ceramic. In this paper, low-cost 3D carbon fiber needled felt was used as reinforcement to improve the fracture toughness of YAG, and the carbon fiber needled felt reinforced YAG (C/YAG) composite was fabricated through vacuum impregnation-drying-heat treatment, using the Y2O3-Al2O3 sol with a high solid content as raw material. The microstructure, mechanical properties, thermal stability and oxidation resistance of C/YAG composite were carefully investigated. Due to the characteristics of reinforcement and the microstructure, the as-fabricated C/YAG composite showed non-catastrophic failure behavior and much higher fracture toughness compared with monolithic YAG ceramic. The flexural strength of C/YAG composite was well retained after annealed at 1700 °C and 1800 °C under inert atmosphere. Although the chemical inertness between carbon fiber and YAG was confirmed up to 1800 °C, the physical bonding of interface was enhanced during annealing, which led to the decrease of fracture work, especially at 1800 °C. The oxidation resistance of C/YAG composite was related to the cracks and pores since YAG is immune to oxidation. The changes of microstructure and flexural strength after oxidation at 1200 °C, 1400 °C and 1600 °C were characterized and analyzed.

Effect of nano-Al2O3 addition on mechanical durability of nickel-yttria stabilized zirconia anode support of solid oxide fuel cells

For anode supported solid oxide fuel cells (SOFCs), the strength and durability of the porous cermet support during long-term operation is critical for the reliability of the cells and stacks. The effect of adding nano-Al2O3 on the long-term durability of the mechanical strength of nickel-yttria stabilized zirconia (Ni-YSZ) based SOFC anode supports was investigated in this study. The SOFC anode support materials, Ni-3YSZ (3 mol% YSZ), Ni-8YSZ (8 mol% YSZ), and nano-Al2O3 added Ni-YSZ composites, were subjected to a long-term degradation test at 900 °C and 30% humidity in an H2 environment and after 1000 h exposure, the flexural strength, phase, and microstructural changes were analyzed. The results suggest that the addition of nano-Al2O3 to Ni-3YSZ improves the long-term strength and durability of the cermet while its addition to Ni-8YSZ cermet did not show any significant changes in the strength degradation behavior of the Ni-8YSZ based anode support. Further analysis by SEM and XRD shows that the tetragonal to monoclinic phase transformation in partially stabilized zirconia was suppressed due to the addition of nano-Al2O3 in Ni-3YSZ resulting in improved long-term stability and higher mechanical strength. Replacing the Ni-8YSZ anode support with nano-Al2O3 added Ni-3YSZ might significantly reduce the material cost of SOFCs without compromising long-term strength durability, thus bringing SOFCs a step closer to commercialization.

Thermomechanical and thermophysical characteristics of alumina-carbon monolithic refractory containing surface-modified graphites in matrix

The thermophysical and thermomechanical behavior of graphite-containing refractory castable matrix with 20.0 wt% of graphite had been compared with graphite-free high alumina based castable matrix analogous to it. The thermomechanical properties of similar type of castables with and without 5.0% of graphite had also been evaluated. Graphite was incorporated both as coated and as-received forms, the former having a thin sol-gel derived calcium aluminate coating on graphite flakes. The influence of thermal conductivity, thermal diffusivity and pore size distribution had been critically estimated. The changes in flexural strength, porosity and density of the matrices had also been determined to interpret the castable performance, namely refractoriness under load (RUL), spalling resistance and conventional physical properties. The role of coated graphite on improved densification and thermal tolerance of refractories was further explored by microstructure and phase evolution studies of all kinds of fired samples at 1500 °C. It was further supplemented with the scanning electron microscope (SEM) studies of surface-modified graphites at uncalcined and calcined condition.

Influence of carbon nanofiber clustering in cement pastes exposed to sulfate attack

The effects of CNFs and CNF clustering on the microstructural evolution and mechanical response of cement pastes subjected to sulfate attack were studied. Portland cement pastes with and without 0.5% CNFs were exposed to sodium sulfate for a total duration of 550 days. The presence of CNFs and CNF clusters led to pore refinement, limited sulfate-induced microstructural changes, and provided a reinforcing network that delayed the onset of cracking and spalling and increased the cement paste expansion capacity. At all stages of exposure, the cement paste with CNFs experienced less sulfate-induced changes in flexural strength than the reference cement paste.

Low temperature degradation of single layers of multilayered zirconia in comparison to conventional unshaded zirconia: Phase transformation and flexural strength.

The aim of this study was to evaluate the transformation of yttrium stabilized tetragonal zirconia (Y-TZP) to monoclinic phase and its change in flexural strength of the various layers of multilayered zirconia (enamel layer, transition layer 1, transition layer 2 and body layer) in comparison to two conventional zirconia ceramics. Additionally, the ball-on-three-balls test was compared with a conventional biaxial flexural strength test. The crystallographic structure of the four layers of Katana Zirconia ML (Kuraray), e.max ZirCAD (Ivoclar Vivadent) and Lava Plus (3M ESPE) was investigated by x-ray-diffraction before and after hydrothermal aging in an autoclave for 5, 10, 15 and 20h. The biaxial flexural strength was examined with a piston-on-three-ball test and a ball-on-three-balls test. There was a significant difference of the ratio of transformation with respect to the tested materials, also between the four different layers of multilayered zirconia. After 20h of hydrothermal aging the mean ratio of monoclinic phase ranged from 9.9vol% (LAVA Plus) to 44.2vol% (Katana Zirconia ML, enamel layer). However, hydrothermal aging had no significant influence on the flexural strength of any material. Furthermore, the flexural strength measured by the ball-on-three-balls test was higher than that measured by the piston-on-three-ball test. A ratio of 40% monoclinic phase at the surface did not significantly influence the biaxial flexural strength. Both test methods provide reliable results. However, as the ball-on-three balls test is less dependent on surface roughness, it might be preferred for investigations adapted to clinical reality.

Influence of Water Infiltration and Flexural Strength Change with Glazing Treatment of Dental Porcelain

Influence of Water Infiltration and Flexural Strength Change with Glazing Treatment of Dental Porcelain

Microstructure evolution and phase transformation of TiB2/SiC/B4C composites synthesized from Ti‐SiC‐B4C ternary system

AbstractBulk TiB2/SiC/B4C composites have been synthesized from Ti‐SiC‐B4C ternary system with different Ti weight percentages via reactive hot pressing at 1800°C under an applied pressure of 30 MPa for 1.5 h. By Ti amount increasing, the flexural strength curve exhibited an “M‐like” tendency reaching the maximum value of 512.36 MPa for 30 wt.% Ti. Microstructural evolution of the composites from conterminously large matrix grains to finely clear‐edged particles was observed by scanning electron microscopy. The phase transformation and element diffusion were analyzed by XRD and Energy Disperse Spectroscopy. A hybrid reinforcing mechanism of fracture and crack deflection is proposed to illustrate the change in flexural strength.

Degradation behavior and lifetime estimation of fiber reinforced plastics tanks for hydrochloric acid storage

Abstract Fiber reinforced plastics (FRPs) are often used for chemical equipment because of their high chemical resistance, especially their resistance to acidic conditions. However, serious accidents have been reported when using such tanks with hydrochloric acid (HCl). We gathered FRP tanks used for 35% HCl storage from various chemical companies, and analyzed their changes in appearance, HCl penetration and residual flexural strength. We found that residual strength of FRP decreased to

Durability of Partially mixed GGBS concrete exposed to acid and base attack

This thesis investigates the effects of aggressive Hydrochloric acid attack and sodium sulfate attack on the concrete mixtures prepared by partial replacement of cement with Ground granulated blast furnace slag GGBS&nbsp; at 20%, 35% and 50%&nbsp; replacement levels. The Hydrochloric acid solutions and sodium sulfate solutions with concentrations of 3% were used for examining behaviour of concrete for a total exposure period of 3days, 7days and 28 days. The performance of the degraded specimens was evaluated by measuring &nbsp;change in compressive strenght, tensile strength,&nbsp; flexural strength and visual assessment. The mixtures with ternary binders of OPC and GGBS experienced the lowest strength loss after exposure to high concentrations of Hydrochloric acid attack and sodium sulfate attack.

Unsaturated polyester resin toughening with very low loadings of GO derivatives

Graphene oxide (GO) and its derivatives with vinyl and alkyl functional groups (mGO) were synthesized and dispersed into unsaturated polyester resin (UPR) to prepare nanocomposites. Successful chemical modification of the GO sheets was confirmed by infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction. In contrast to unmodified GO, mGO was easily dispersed in UPR, even without sonication, making the process scalable. The few-micrometer GO sheets and aggregates in the resin composite were characterized by transmission electron microscopy and visible light microscopy. Compact tension testing of the resin composites with mGO showed that, with a remarkably low loading of only 0.04 wt% mGO, a 55% improvement in fracture energy (GIC) was obtained with little change in flexural strength or modulus. This high effectiveness renders mGO economically viable. Analysis of fracture surfaces by scanning electron microscopy suggests that mGO particles interact with the propagating crack, the main toughening effect being crack pinning.

Effect of alkali treatment on the flexural properties of a Luffa cylindrica-reinforced epoxy composite

Abstract This experimental study was conducted to investigate the effect of NaOH concentration and treatment time on the flexural properties of Luffa cylindrica fiber-reinforced epoxy composites. Significant improvement (up to 84.92%) in the flexural properties for the treated fiber composite compared with the untreated fiber composite was observed. Both treated and untreated fiber composites were then subjected to different environmental treatments (saline water, distilled water, and subzero temperature). To find out the changes in flexural strength immediately after treatment, the same test was carried out on the composites. Degradation in the flexural strength of both treated and untreated fiber composites, when subjected to environmental treatments, was observed. They were found within the range of 2%–20% and were found to be least in subzero treatment. The SEM micrograph indicates that alkali treatment is effective in improving the adhesion between the fiber and matrix.

Influence of aging on flexural strength of translucent zirconia for monolithic restorations

Statement of problemConcern has been raised with regard to the low-temperature degradation (LTD) of translucent yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) for monolithic zirconia restorations. PurposeThe purpose of this in vitro study was to assess the LTD behavior of 4 commercially available translucent Y-TZP materials by accelerated aging specimens in steam at 134°C, 0.2 MPa. Material and MethodsThin bars (22×3×0.2 mm) of Y-TZP, including Katana ML (Kuraray Noritake Dental Inc), Katana HT13 (Kuraray Noritake Dental Inc), Prettau (Zirkonzahn), and BruxZir (Glidewell Laboratories) (n=30 for each group), were machined from sintered blocks. Control specimens were assessed in the nonaged condition. Artificially ageing (n=5 per group at 5, 50, 100, 150, and 200 hours) was conducted in steam at 134°C at 0.2 MPa. The specimens were characterized, tested in 4-point flexure, and the fracture surfaces were analyzed. The monoclinic-to-tetragonal (m/t) peak intensity ratio measured by x-ray diffraction was used to calculate the monoclinic phase fraction and monitor LTD. Linear regression with heteroscedasticity-consistent robust standard errors was used to test for the effect of LTD (aging time) on (σf) and m/t. The Spearman rank correlation coefficient was used to assess the relationship between σf and monoclinic phase fraction (α=.05). ResultsArtificial aging resulted in LTD as shown by an increase in the monoclinic phase fraction for all specimens. After aging for 200 hours, the mean ±SD monoclinic phase fraction increased from 2.90 ±0.34% to 76.1 ±0.64% for Prettau, 2.69 ±0.18% to 76.0 ±0.26% for BruxZir, 4.6 ±0.19% to 35.8 ±0.80% for Katana HT13, and 3.57 ±0.35% to 33.2 ±1.1% for Katana ML (all P<.001). Flexural strength changed from a mean ±SD of 1612 ±197 MPa to all fractured during aging for Prettau (P<.001); 1248 ±73.5 MPa to all fractured during aging for BruxZir (P<.001); 1052 ±84.2 to 1099 ±70 MPa ±130 for Katana HT13 (P=.45); and from 875 ±130 to 909 ±70 MPa (P=.82) for Katana ML. The mean flexural strength values of Prettau and BruxZir decreased with an increase in the monoclinic phase with Spearman rank correlation coefficients of −0.80 (P=.001) for Prettau and −0.63 (P=.022) for BruxZir. No significant changes in flexural strength were measured for Katana ML or Katana HT13 (P>.05). ConclusionsThe LTD of Y-TZP resulted in a significant decrease in flexural strength of Prettau and BruxZir, whereas Katana ML and Katana HT13 exhibited less LTD and no significant decrease in flexural strength.

The Influence of Electromagnatic Field Microwave on Physical and Mechanical Characteristics of CFRP (Carbon Fiber Reinforced Polymer) Structural

Based on the analysis of the development trends of modern transport equipment the prospect of structural composite materials usage, for example CFRP structural, is shown. In this regard, the expediency of conducting research to improve the strength characteristics of these materials is established. It is shown that, despite the large amount of scientific publications on the application of electro-technological methods and microwave technologies for modification of composite materials, applied to heterogeneous materials, such as carbon fiber, in Russia and abroad there are still some unsolved theoretical and practical questions. The studies of the effect of microwave electromagnetic field power density on different physical and mechanical characteristics of laminated composite materials in order to establish the opportunities to improve their performance, in particular their strength, were made. The example of carbon is used to show that the microwave electromagnetic field power density of 17.5 W/cm3 at a frequency of 2450 MHz exposure time of 2 minutes causes an increase in the shear strength of 38 – 40 % and an increase in the duration of the construction operation of carbon under the action of the peak load of 1.5 up to 4.5 times, wherein the change in flexural strength and modulus of elasticity was 2.6 %.

Fabrication of Mullite Coating and its Oxidation Protection for Carbon Fiber Reinforced SiC Composites

To protect carbon fiber-reinforced SiC (C/SiC) composites against oxidation,mullite coating was prepared on C/SiC composites by dip-coating method with high solid content Al2O3-SiO2 sol as raw materials. X-ray diffraction and scanning electron microscopy were employed to analyze the phase and microstructure of the coating. The results show that the as-prepared coating is SiO2-rich, monolithic and well bonded with substrate without penetrating crack, giving rise to good oxidation-resistance. After soaked at 1400°C for 30min under static air, the coated C/SiC composites possess 87% of original flexural strength. As a result of sealing and filling of cracks and pores by viscous SiO2 in coating, the coated C/SiC composites exhibit improved oxidation resistance at 1500°C and 1600°C. There is no change in flexural strength after oxidized at 1500°C and 1600°C for 30min, respectively. Nevertheless, the carbothermal reduction between viscous SiO2 and free carbon in C/SiC substrate would occur obviously when oxidation temperature was elevated or oxidation time was prolonged, leading to local foaming in coating and decreasing in oxidation resistance.

Damage evaluations of oven-dried mortar subjected to one-directional fire

Concrete structures can be damaged by various factors in extreme service conditions. Analytical methods that can predict the strength of structural concrete after exposure to fire are needed to facilitate decisions regarding whether to repair, strengthen, or demolish fire-damaged buildings. However, appropriate and widely applicable material models have not yet been proposed. This paper presents an experimental study in which we assess damage, including changes in flexural strength, porosity and residual cement hydrates, to oven-dried mortar that has been fired and immediately cooled in the air. Mortars were made from calcareous and siliceous aggregates, and one face of each specimen (100×100×400 mm) was exposed to fire curves of ISO 834 and ASTM E119. Specimens for quantitative assessment were hewed to ten layers from the original specimens. Experimental results indicate that the in-depth flexural strength of a thin specimen is substantially diminished by fire exposure, especially for specimens with existing fire cracks. In addition to the loss in strength, changes in porosity and chemical properties occur. Based on the experimental evidence obtained from this study, the relationships between each property are discussed.

Composition, phase analysis, biaxial flexural strength, and fatigue of unshaded versus shaded Procera zirconia ceramic

Statement of the ProblemRecent interest in shaded zirconia has raised questions about the relative stability of the tetragonal phase after colorant oxide additions. PurposeThe purpose of this in vitro study was to evaluate the effects of fatigue cycling on the stability of a commercially available dental zirconia (Procera) in both unshaded and shaded compositions by measuring the change in biaxial flexural strength (BFS) after 500 000 cycles at 80-N loads and in phase composition as detected by x-ray diffraction (XRD). Material and MethodsPartially stabilized zirconia disks (NobelProcera) were fabricated in unshaded and shaded forms (12 mm diameter × 0.8 mm thick). Specimens were analyzed by energy-dispersive x-ray spectroscopy (EDS) and by wavelength-dispersive x-ray spectroscopy (WDS) for oxide compositions which indicated the presence of small amounts of Fe-O (0.13 ±0.10 wt %) in the shaded specimens. XRD focused on the tetragonal (T) and monoclinic (M) peaks in the 20 to 40 degrees 2θ range. The disks were polished on 1 side, cyclically loaded (80N, 500 000 cycles, custom 4-station fatigue test machine), and tested for residual BFS after cycling. Unshaded (U) and shaded groups (S) were compared before (U1, S1) and after (U2, S2) load cycling with XRD and residual BFS. ResultsResidual BFS (MPa) for specimens before (U1=856 ±99 versus S1= 842 ±40) and after fatigue (U2=772 ±65 versus S2= 718 ±68) were statistically different (U1 versus U2; S1 versus S2; U2 versus S2, P<.05). The XRD of U1 and S1 specimens revealed tetragonal and cubic zirconia. U2 and S2 specimens contained tetragonal zirconia, with the initial appearance of small amounts of monoclinic zirconia after fatigue cycling. Monoclinic detection was measured on the tension side of the tested specimens and varied between tests at the center and radially at 4 mm. ConclusionsThe results indicated shaded materials more readily transform the tetragonal to the monoclinic phase during load cycling than unshaded ones. However, extrapolating the effects of any shortening of the service life of zirconia compositions is difficult. The potential mitigating effects of other factors such as the thermal postprocessing of porcelain veneers, stains on zirconia, or effects of water have yet to be investigated.

The effect of different fiber reinforcement on the thermal and mechanical properties of autoclaved aerated concrete

In this study, the changes in thermal conductivity value, compression and flexural strength of autoclaved aerated concrete were investigated experimentally by adding polypropylene, carbon, basalt and glass fibers into the G3/05 and G4/06 class autoclaved aerated concrete used as wall elements in buildings and the commercial production of which is made. Fibers were substituted with the aggregate in autoclaved aerated concrete in equal amounts volumetrically. The produced samples were subjected to autoclaved cure as in non-fibrous autoclaved aerated concrete. As a result of the experimental study; it has been seen the thermal conductivity of fiber substituted autoclaved aerated concrete changes linearly with thermal conductivity of the substituted fibers and basalt fiber reinforced autoclaved aerated concrete gives the highest thermal conductivity. But, it has been seen that the best compression and flexural strength was given by the carbon fiber reinforced samples.

Changes in Properties of Cement and Lime Mortars When Incorporating Fibers from End-of-Life Tires

This paper studies the addition of fibers from end-of-life tires to commercial mortar mixtures. Two different types of mortar, one lime-plastic and other cement-fluid, are mixed with different percentage of fibers ranging from 0% to 1%. The changes in bulk density, consistency, compressive and flexural strength, dynamic Young modulus and water absorption are studied. According to the results, consistency is the property that shows more relevant changes for an addition of 0.25% fibers. Consistency is related to workability and affects the water absorption and the Young modulus values. On the contrary, bulk density and mechanical properties did not change with the addition of fibers. The results prove that this fiber, considered a waste from recycling of end-of-life tires, can be used in commercial mixtures without losing strength. On the other hand, mortar workability limits the amount of fibers that can be included in the mixture and this parameter determines the performance of the mortar.

Processing of alumina-coated clay–diatomite composite membranes for oily wastewater treatment

Crack-free alumina-coated clay–diatomite composite membranes were successfully prepared by a simple pressing and dip-coating route using inexpensive raw materials at a temperature as low as 1000°C in air. The changes of porosity, flexural strength, pore size, flux, and oil rejection rate of the membranes were investigated while changing the diatomite content. A simple burn-out process subjected to the used membranes in air completely recovered the specific surface area, steady state flux, and oil rejection rate of the virgin membranes. The recycled membranes showed an exceptionally high oil rejection rate (99.9%) with a feed oil concentration of 600mg/L at an applied pressure of 101kPa. The typical porosity, pore size, flexural strength, oil rejection rate, and steady state flux of the recycled alumina-coated clay–diatomite composite membrane were 36.5%, 0.12μm, 32MPa, 99.9%, and 6.91×10−6m3m−2s−1, respectively, at an applied pressure of 101kPa.