Three-point Flexure Research Articles

Effect of heat polymerization conditions and microwave on the flexural strength of polymethyl methacrylate.

Objective:The objective of this study is the effect of different heat polymerization conditions on the strength of polymethyl methacrylate (PMMA) resin base is unknown. Distinguishing one method that provides improved mechanical properties may be beneficial to the clinical success of complete and partial dentures and overdentures. The purpose of this study was to evaluate the effect of different polymerization methods on the flexural strength of a dental PMMA resin.Materials and Methods:Forty PMMA specimens (64 mm × 10 mm × 4 mm) were prepared with 4 different polymerization methods (n = 10); heat polymerization at 74°C for 9 h, at 100°C for 40 min, and with 620 kPa pressure at 100°C for 20 min. The remaining group of specimens was microwave polymerized at 180 W for 6 min. All specimens were thermocycled at 5°C and 55°C for 5000 times. Three-point flexure test was used to measure the flexural strength of specimens. One-way ANOVA and Tukey Honestly Significant Difference were applied to analyze the differences in flexural strengths (α = 0.05).Results:The flexural strength of heat-polymerized groups was similar. The flexural strength of microwave polymerized group was significantly different and lower than the other groups (P < 0.05).Conclusion:Polymerizing conventional heat-polymerizing PMMA resin with microwave energy resulted in a significant decrease in flexural strength. The results of this study suggest that clinicians may benefit from using heat polymerization when processing PMMA denture bases instead of microvawe polymerization when tested brand is used.

Dynamic Mechanical Properties of Hybrid Layered Silicates/Kaolin Geopolymer Filler in Epoxy Composites

Preparation epoxy based hybrid composites were involved kaolin geopolymer filler, organo-montmorillonite at 3phr by using high speed mechanical stirrer. A mechanical behaviour of neat epoxy, epoxy/organo-montmorillonite and its hybrid composites containing 1-8phr kaolin geopolymer filler was studied upon cyclic deformation (three-point flexion mode) as the temperature is varies. The analysis was determined by dynamic mechanical analysis (DMA) at frequency of 1.0Hz. The results then expressed in storage modulus (E�), loss modulus (E�) and damping factor (tan d) as function of temperature from 40 oC to 130oC. Overall results indicated that E�, E�� and Tg increased considerably by incorporating optimum 1phr kaolin geopolymer in epoxy organo-montmorillonite hybrid composites.

The properties of experimental resin-modified glass-ionomer luting cements (RMGICs) containing novel monomers

ObjectivesTo investigate working and setting times, compressive fracture strength (CFS), compressive modulus (CM), three-point flexure strength (TFS) and tensile flexure modulus (TFM) of commercial, control and experimental RMGICs. MethodsRelyX Luting (RX, 3M-ESPE) and Fuji Plus (FP, GC), two control home liquids and eight new liquid compositions (F1-F4 and R1-R4) comprising different percentages of the monomer HPM (hydroxypropyl-methacrylate) and/or THFM (tetrahydrofurfuryl-methacrylate) with the original monomer HEMA (2-hydroxyethyl-methacrylate) were used in this study. The polymerization was initiated chemically (using benzene sulfonic acid sodium-salt in FP powder and potassium persulfate/ascorbic acid in RX powder). Home and experimental liquids were mixed with the corresponding commercial powder. An oscillating rheometer was used to measure the working and setting times (n=6). 20 cylinders per material (6.0±0.1mm height, 4.0±0.1mm diameter) were fabricated for CFS and CM testing, 20bars per material (25.0±0.1mm length, 2.0±0.1mm width, 2.0±0.1mm thickness) were made for TFS and TFM testing. ResultsAll RX compositions showed longer setting times (p≤0.0001) and lower CFS values compared to their FP counterparts (p≤0.0001). The TFS testing showed that commercial and home RMGICs behaved as brittle materials with linear load/deflection curve while experimental materials showed plastic ductile deformation before fracture. F3, F4 and F2 showed significantly higher CFS values compared to the corresponding home material (p≤0.0001). SignificanceAll new experimental compositions demonstrated working and setting times that are clinically acceptable. The new experimental FP compositions containing THFM (especially F3 and F4) demonstrated improved mechanical properties compared to their corresponding home material.

Fabrication of 100 Centimeter Square Metal-Supported Solid Oxide Fuel Cell Using Thermal Plasma Technique

In this study, the large-scale mold for compression molding process is prepared and a compression load of 120 ton is applied to form a porous alloy specimen with dimension of 12×12×1.2 cm. The carbon is used as pyrolyzable filler in the period of manufacturing processes in order to produce porous interconnected networks of molybdenum (Mo)-containing nickel (Ni)-based alloy. The specimens are sintered in hydrogen at the temperature of 1250°C to obtain porous alloy substrate. The flexural strength of porous alloy supporting component is measured in this work. The strength of porous alloy substrate (Sintered at 1250°C) in three-point flexure at 25°C and 750°C are 188 MPa and 76.5 MPa, respectively. Metal-supported solid oxide fuel cells (MS-SOFCs) are fabricated by thermal plasma spraying technique and the anode (Ce0.55La0.45O2-δ -NiO,LDC-NiO), electrolyte (La0.8Sr0.2Ga0.8Mg0.2O3-δ, LSGM) and cathode (Sm0.5Sr0.5CoO3- δ,SSC) functional layers are deposited onto porous alloy substrate. The 10×10 cm2 MS-SOFC with effective electrode area of 81 cm2 shows the open circuit voltages is 1.09 V at 700°C. The measured maximum output power densities (@0.76V) of this cell has reached 588 mW/cm2 at 700°C by employing hydrogen as fuel and air as oxidant.

Fabrication of 100 Centimeter Square Metal-Supported Solid Oxide Fuel Cell Using Thermal Plasma Technique

In this study, the large-scale mold for compression molding process is prepared and a compression load of 120 ton is applied to form a porous alloy specimen with dimension of 120×120×1.2 mm. The carbon is used as pyrolyzable filler in the period of manufacturing processes in order to produce porous interconnected networks of molybdenum (Mo)-containing nickel (Ni)-based alloy. The specimens are sintered in hydrogen at the temperature of 1250°C to obtain porous alloy substrate. The flexural strength of porous alloy supporting component is measured in this work. The strength of porous alloy substrate (Sintered at 1250°C) in three-point flexure at 25°C and 750°C are 188 MPa and 76.5 MPa, respectively. Metal-supported solid oxide fuel cells (MS-SOFCs) are fabricated by thermal plasma spraying technique and the anode (Ce0.55La0.45O2-δ-NiO), electrolyte (La0.8Sr0.2Ga0.8Mg0.2O3-δ) and cathode (Sm0.5Sr0.5CoO3-δ) functional layers are deposited onto porous alloy substrate. The 10×10 cm2 MS-SOFC with effective electrode area of 81 cm2 shows the open circuit voltages is 1.09 V at 700°C. The measured maximum output power densities (@0.76V) of this cell has reached 588 mW/cm2 at 700°C by employing hydrogen as fuel and air as oxidant.

Effect of the Thickness of Opaque Layer Coating on Strength of Metal-resin Bonding in Repairing PFM

To observe the effect of the thickness of opaque layer coating on strength of metal-resin bonding, by comparing the metal-resin bonding strength of specimen with different opaque specimen thickness. Methods: two metal crown materials: cobalt-chromium alloy, gold alloy. Each material was produced to the same unified specimen. Then divided into three groups: no pre-opaque layer group, thin opaque layer group, thick opaque layer group. Each set had six test specimens. Using three-point flexure test method to test the initial crack pressure, the effect of different opaque layers thickness on the metal-resin bonding strength were compared. Descriptive statistics were used SPSS10.0 software package. Use SNK variance to test. RESULTS: No significant differences on bonding strength between the metal crowns. Thin opaque layer group metal - resin bonding strength was significantly greater than the thick opaque layer group’s (P &lt;0.05); The bonding strength of the two groups’ specimens which coated opaque layer are greater than not coated opaque layer groups’, the differences was significant(P &lt;0.05). Conclusion: Coating a thin opaque layer can increase metal-resin bonding strength, the opaque porcelain layer thickness should be controlled in order to increase the metal - resin bonding strength, in the clinical operation of PFM filling porcelain.

Effect of span length on micromechanics of fracture under flexure load in CFRP composites

ABSTRACTUnidirectional (UD) and bidirectional (BD) woven carbon fiber reinforced plastic (CFRP) composites were tested under three-point flexure at different span lengths ranging from 20 to 60 mm. Expectedly, flexure load decreases with increasing span length. A sharp change in flexure load is observed at a span length of 30 mm with a transition in failure mechanism. Analysis suggests that crack initiation occurs at compression side and tension side, respectively, in UD and BD woven composites. In case of UD composites, at a span length of 20 mm, the failure was governed by kink band initiation (two fractures per fiber) followed by tension side delaminations, and at other span lengths, microbuckling (multiple fiber fractures) together with compression side delaminations led to failure. On the other hand, the failure in BD composites at a span length of 20 mm is controlled predominantly by thickness crack propagation with tensile fiber pullouts, whereas for other span cases the failure occurs due to the development of delaminations at interlace regions. The stress analysis by finite element modeling (FEM) also supports the experimental observations in an attempt to correlate the failure mechanisms under flexure loads in CFRP composites.

저/고분자량 키토산에 의한 종래형 치과용 글라스아이오노머 시멘트의 강화

The aim of this study was to investigate the effects of chitosan powder addition on the strengthening of conventional glass ionomer cement. Two types of chitosan powders with different molecular weight were mixed with conventional glass ionomer cement (GIC): low-molecular weight chitosan (CL; 50∼190 kDa), high-molecular weight chitosan (CH; 310∼375 kDa). The chitosan powders (CL and CH) were separately added into the GIC liquid (0.25-0.5 wt%) under magnetic stirring, or mixed with the GIC powder by ball-milling for 24 h using zirconia balls. The mixing ratio of prepared cement was 2:1 for powder to liquid. Net setting time of cements was measured by ISO 9917-1. The specimens for the compressive strength (CS; 4 x 6 mm), diametral tensile strength (DTS; 6 x 4 mm), three-point flexure (FS; 2 x 2 x 25 mm) with flexure modulus (FM) were obtained from cements at 1, 7, and 14 days after storing in distilled water at (37±1)℃. All mechanical strength tests were conducted with a cross-head speed of 1 mm/min. Data were statistically analyzed by one-way ANOVA and Tukey HSD post-hoc test. The mechanical properties of conventional glass ionomer cement was significantly enhanced by addition of 0.5 wt% CL to cement liquid (CS, DTS), or by addition of 10 wt% CH (FS) to cement powder. The CL particles incorporated into the set cement were firmly bonded to the GIC matrix (SEM). Within the limitation of this study, the results indicated that chitosan powders can be successfully added to enhance the mechanical properties of conventional GIC.

Effects of Long-Term Water-Aging on Novel Anti-Biofilm and Protein-Repellent Dental Composite.

The aims of this study were to: (1) synthesize an anti-biofilm and protein-repellent dental composite by combining 2-methacryloyloxyethyl phosphorylcholine (MPC) with quaternary ammonium dimethylaminohexadecyl methacrylate (DMAHDM); and (2) evaluate the effects of water-aging for 180 days on protein resistance, bacteria-killing ability, and mechanical properties of MPC-DMAHDM composite. MPC and DMAHDM were added into a resin composite. Specimens were stored in distilled water at 37 °C for 1, 30, 90, and 180 days. Mechanical properties were measured in three-point flexure. Protein attachment onto the composite was evaluated by a micro bicinchoninic acid approach. An oral plaque microcosm biofilm model was employed to evaluate oral biofilm viability vs. water-aging time. Mechanical properties of the MPC-DMAHDM composite after 180-day immersion matched those of the commercial control composite. The composite with 3% MPC + 1.5% DMAHDM had much stronger resistance to protein adhesion than control (p < 0.05). MPC + DMAHDM achieved much stronger biofilm-eradicating effects than MPC or DMAHDM alone (p < 0.05). Biofilm colony-forming units on the 3% MPC + 1.5% DMAHDM composite were three orders of magnitude lower than commercial control. The protein-repellent and antibacterial effects were durable and showed no loss in water-aging from 1 to 180 days. The novel MPC-DMAHDM composite possessed strong and durable resistance to protein adhesion and potent bacteria-eradicating function, while matching the load-bearing ability of a commercial dental composite. The novel MPC-DMAHDM composite represents a promising means of suppressing oral plaque growth, acid production, and secondary caries.

Effects of the Fiber Diameter on Mechanic Properties in Polymethyl-Methacrylate Composites Reinforced with Goose Feather Fiber

The polymethyl-methacrylate (PMMA)-based composites were prepared using goose feather fibers at different diameters. The fibers, which were washed and dried, cut through the shaft, and their sizes were shrunk to short fiber form. Then the obtained short fibers were added into acryl matrix in portions of 2%, 4%, 6%, and 8% in volume. The mixture containing goose feather fiber was shaped via free casting method, and the goose feather fiber/PMMA composites were obtained. The samples, which were processed in accordance with the standards of test to be implemented after the thermal curing process, were characterized in terms of the mechanical properties after being evaluated by using three-point flexure test and impact test. For the goose feather-added composites, a significant increase was observed in rupture resistance, flexural strength, and flexure module. The flexure test curves of composites clearly revealed the slow and stable crack enlargement. Micro mechanisms of toughening and rupture processes were observed under the light of microstructure of rupture surfaces. The results of present study showed that the goose feather can be used as an important reinforcing material for bio-composites.

Monitoring fracture of steel corroded reinforced concrete members under flexure by acoustic emission technique

Acoustic emission (AE) technique is used for monitoring and evaluating the influence of corrosion on the structural behaviour of steel reinforced concrete (RC) beams under three-point flexure test. In this study, steel corrosion was accelerated by electro-chemical method utilising a direct current (DC) power supply and 5% sodium chloride (NaCl) solution. The steel corrosion that was induced into beam specimens casting were estimated at 0%, 4.55% and 32.37%, respectively, according to mass loss of steel reinforcement. Based on observations during static load test, the damage developed in the specimens could be classified into four different stages, namely, micro-cracking, first visible cracks, cracks distribution, as well as damage localization and yielding. Analysis of the AE data reveals distinguishable trends for RA value and average frequency (AF) registered for different corrosion levels, respectively. Moreover, the index of damage (ID) derived from the AE energy parameters obtained during the first stage of damage was found to be useful as an indicator for evaluating the extent of corrosion damage of RC beam specimens at initial loadings. In addition, to provide a practical application of AE toward life span estimation of corroded beam specimen, a Weibull damage function was introduced to estimate the remaining flexural capacity of the beam specimens. Based on analysis as well, it is noted that tensile fracture became more dominant with an increase in corrosion level.

An efficient methodology for the experimental characterization of mode II delamination growth under fatigue loading

Crack growth rate curves provide information about the delamination resistance of composite materials under cyclic loading. The existing methodologies for mode II fatigue testing using three-point bending end-notched flexure (3-ENF) under constant cyclic displacement conditions yield discontinuous delamination growth rate curves, therefore requiring a batch of several specimens to be tested under different severity conditions in order to fully characterize the crack growth. This work describes a variable cyclic displacement test procedure that, in combination with the real time monitoring of the specimen’s compliance, allows the crack growth rate to be measured for the desired range of severities with a single specimen, thus avoiding any human intervention during the test.

One-year water-ageing of calcium phosphate composite containing nano-silver and quaternary ammonium to inhibit biofilms.

Dental composites are commonly used restorative materials; however, secondary caries due to biofilm acids remains a major problem. The objectives of this study were (1) to develop a composite containing quaternary ammonium dimethacrylate (QADM), nanoparticles of silver (NAg), and nanoparticles of amorphous calcium phosphate (NACP), and (2) to conduct the first investigation of the mechanical properties, biofilm response and acid production vs water-ageing time from 1 day to 12 months. A 4 × 5 design was utilized, with four composites (NACP-QADM composite, NACP-NAg composite, NACP-QADM-NAg composite, and a commercial control composite), and five water-ageing time periods (1 day, and 3, 6, 9, and 12 months). After each water-ageing period, the mechanical properties of the resins were measured in a three-point flexure, and antibacterial properties were tested via a dental plaque biofilm model using human saliva as an inoculum. After 12 months of water-ageing, NACP-QADM-NAg had a flexural strength and elastic modulus matching those of the commercial control (P>0.1). Incorporation of QADM or NAg into the NACP composite greatly reduced biofilm viability, metabolic activity and acid production. A composite containing both QADM and NAg possessed a stronger antibacterial capability than one with QADM or NAg alone (P<0.05). The anti-biofilm activity was maintained after 12 months of water-ageing and showed no significant decrease with increasing time (P>0.1). In conclusion, the NACP-QADM-NAg composite decreased biofilm viability and lactic acid production, while matching the load-bearing capability of a commercial composite. There was no decrease in its antibacterial properties after 1 year of water-ageing. The durable antibacterial and mechanical properties indicate that NACP-QADM-NAg composites may be useful in dental restorations to combat caries.

Effect of TiO2-SiO2-SnOx sol-gel coating on the bonding strength of titanium-porcelain

Effect of TiO2-SiO2-SnOx sol-gel coating burnt at 300°C on the cpTi-porcelain bond strength was investigated in this study. Before the porcelain was fused, the phase, surface morphology, and static water contact angle of the intermediate layer were evaluated. The cpTi-porcelain bond strength was measured using the three-point flexure test according to ISO 9693 standard. The surface morphology of titanium surface debonded from porcelain was evaluated with a scanning electron microscope. Statistical analysis was made with an independent samples t test. No rutile phase was found in the tested specimen coated with TiO2-SiO2-SnOx sol-gel coating. The cpTi-porcelain bond strength of coated group (35.7±2.65MPa) was significantly higher than that of noncoated group (31.7±3.52MPa). Statistical difference of static water contact angle was found between the two groups. The surface morphology of the intermediate layer was compact and homogeneous with visible cracks. Sn element was found in the titanium surface after the porcelain was debonded, which indicated that the fracture mode of titanium-porcelain system might have been changed. The results show that the TiO2-SiO2-SnOx sol-gel coating burnt at 300°C can improve the bond strength of titanium to porcelain.

Fracture Performance of GFRP Bars Embedded in Concrete Beams with Cracks in an Alkaline Environment

AbstractAn experimental and analytical investigation of the fracture performance of glass fiber-reinforced polymer (GFRP) bars embedded in concrete beams with cracks is presented. Beams with cracks were conditioned with sustained flexural loads in outdoor, 60°C-alkaline solution, and tap water environments for up to 9 months, after which they were subjected to eccentric three-point flexure tests to evaluate fracture performance and microscopic tests to analyze the changes in microscopic structures through scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). The results showed that the cracks aggravated the influence of the environments on GFRP-RC beams but did not change the mechanisms of mechanical degradation of the GFRP bars. Based on the research conclusions, the same durability tests and eccentric three-point flexure tests were conducted to determine the permissible crack values and treatment recommendations for GFRP-RC beams...

Effect of microwave curing process on the flexural strength and interlaminar shear strength of carbon fiber/bismaleimide composites

Microwave heating has been conceived as a rapid and cost-effective method for curing carbon fiber composites. In this paper, microwave radiation was used to cure carbon fiber/bismaleimide composites aiming at shortening the production cycle time. Through controlling the microwave power, vacuum bagged laminates were fabricated under one atmosphere pressure without arcing. Degree of cure, void content and fiber volume fraction were measured to evaluate part quality. Three-point flexure and short beam shear testing were employed for mechanical assessment. Variation in the microwave cure cycle had a significant effect on the material properties. The optimum processing parameters for microwave curing were established based on analysis of the mechanical performance. A cycle time reduction of nearly 63% was obtained compared to thermal processing. The physical and mechanical properties of microwave cured samples were found to be superior to those cured in a conventional oven. The composite panels manufactured by the optimized microwave cure process exhibited a slight decrease in flexural strength but equivalent interlaminar shear strength in comparison with those produced by autoclave curing.

Comparative study of flexural strength test methods on CAD/CAM Y-TZP dental ceramics.

Clinically, fractures are the main cause of computer-aided design and computer-aided manufacturing (CAD/CAM) 3 mol%-yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) all-ceramic dental restorations failure because of repetitive occlusal loading. The goal of this work is to study the effect of test methods and specimen’s size on the flexural strength of five ceramic products. Both bi-axial flexure test (BI) and uni-axial flexure tests (UNI), including three-point flexure test (3PF) and four-point flexure test (4PF), are used in this study. For all five products, the flexural strength is as follows: BI > 3PF > 4PF. Furthermore, specimens with smaller size (3PF-s) have higher values than the bigger ones (3PF). The difference between BI and UNI resulted from the edge flaws in ceramic specimens. The relationship between different UNI (including 3PF-s, 3PF and 4PF) can be explained according to Weibull statistical fracture theory. BI is recommended to evaluate the flexural strength of CAD/CAM Y-TZP dental ceramics.

An automated methodology for mode II delamination tests under fatigue loading based on the real time monitoring of the specimen’s compliance

This work introduces a procedure based on the real time monitoring of the specimen’s compliance for the experimental characterization of the fatigue behaviour of interlaminar cracks in composites. The methodology was applied to a mode II loading in a three-point end notch flexure test. The onset point for fatigue damage was determined with a precision of one cycle by establishing a threshold on the compliance variation from its initial value. On the other hand, the crack growth rate curve was derived from the continuous monitoring of the compliance and an experimental calibration of said compliance. The precision of this methodology allowed the effect of commonly neglected phenomena such as the thermal expansion of the testing system or the friction between the specimen and the fixture, to be unveiled.

In-plane shear behaviour of multiscale hybrid composites based on multiwall carbon nanotubes and long carbon fibres

Both in-plane shear modulus and in-plane shear strength of multiscale hybrid composites have been studied. Carbon fibre-based laminates have been fabricated including functionalized multiwall carbon nanotubes by means of solvent spraying method and hot compression process. Mechanical in-plane shear characterization has been carried out using off-axis three-point flexure test. Fibre volume fraction of multiscale hybrid composites has been determined through thermogravimetric analysis and fracture surfaces after testing have been imaged by scanning electron microscopy. Results reveal that the inclusion of functionalized multiwall carbon nanotubes on laminates has a small influence on in-plane shear modulus, although it increases up to 15% of the in-plane shear strength. Multiwall carbon nanotube functionalization improves shear stress transmission between matrix and carbon nanotubes, which represents a reinforcement effect responsible for the increase in in-plane shear strength. Scanning electron micrographs have confirmed in-plane shear tests results.

Effect of TiO2-SiO2-SnOx film with different firing temperatures on bond strength of low-fusing dental porcelain to pure titanium

To evaluate the influence of TiO(2)-SiO(2)-SnOx nano-coatings with different firing temperatures on the bond strength of low-fusing dental porcelain to pure titanium. The surface of pure titanium was coated uniformly with TiO(2)-SiO(2)-SnOx nano-coatings by solution-gelatin (Sol-Gel) technology and then fired at 300 °C (group A) or 750 °C (group B) for 1 h. The specimens without any coatings were the control group (group C). There were 10 specimens in each group. Dental porcelain was sintered on the surface of titanium specimens. Surface roughness and contact angle of the coatings were also detected. The titanium-porcelain bond strength was investigated according to YY 0621-2008 standards using three-point flexure bond test. The phase composition of the TiO(2)-SiO(2)-SnOx nano-coatings was characterized by X-ray diffraction(XRD). The interface of titanium-porcelain and TiO(2)-SiO(2)-SnOx nano-coatings were observed using scanning electron microscope (SEM). No rutile phase was found in these specimens of group A and group B. The surface roughness of group A, B, C was (0.97 ± 0.06), (0.99 ± 0.03), (0.96 ± 0.07) µm, respectively. No significant difference was found among the three groups. Compared with that of group C (64.37° ± 3.01°), contact angles detected in group A (52.04° ± 3.15°) and group B (85.27° ± 4.17°) were significantly different (P < 0.05). The bond strength of titanium-porcelain in group A [(35.66 ± 2.65) MPa] was significantly increased compared with those in group B [(26.18 ± 2.22) MPa] and group C [(31.66 ± 3.52) MPa]. SEM photomicrographs of titanium-porcelain interface morphology of the specimens before porcelain sintering showed that TiO(2)-SiO(2)-SnOx nano-coatings in group A were compact and homogeneous with petty cracks and those in group B was loose and arranged disorderly. TiO(2)-SiO(2)-SnOx nano-coating fired at 300 °C is significantly effective in improving the titanium-porcelain bond strength.