Fractured Specimens Research Articles

The Effects of Reusing Cobalt-Chromium Alloy Powder on Its Mechanical Properties and Grain Size: An In Vitro Study.

To characterize material changes that may occur in virgin cobalt-chromium (Co-Cr) alloy powder when it is blended with alloy powders that have been reused multiple times. Initially, 20 kg of virgin Co-Cr powder was loaded into a laser-sintering device. The tensile test specimens were fabricated in the first (Group 1), fourth (Group 2), seventh (Group 3), tenth (Group 4), and thirteenth (Group 5) production cycles (N = 15). Prior to fabricating the specimens, powder alloy samples were collected from the powder bed for analysis. The tensile strength, elastic modulus, and percent elongation were calculated with tensile testing. Scanning electron microscopy and energy dispersive x-ray spectroscopy (SEM/EDS) and laser particle size distribution (LPSD) were used to analyze the alloy powder samples. The fracture surface of one tensile test specimen from each group was examined via SEM/EDS. One-way ANOVA followed by Dunnett T3 test was used for statistical analysis (α = .05). No difference was observed between groups in terms of tensile strength. A statistically significant difference was observed between Groups 1 and 2 in terms of percent elongation. Groups 2 and 4 were statistically significantly different in terms of both elastic modulus and percent elongation (P ≤ .05). SEM images of the powder alloy showed noticeable differences with increasing numbers of cycles. SEM images and the EDS analysis of the fractured specimens were in accordance with the strength data. Reusing Co-Cr alloy powder increased the particle size distribution. However, there was no correlation between increased cycle number and the mechanical properties of the powder.

Integrated laser additive manufacturing of high-strength steel and Ti6Al4V: Experimental investigations and thermodynamic calculations

This work focuses on the challenging task of joining high-strength steels and titanium alloys, which are extensively utilized in the defense and aerospace industries. The study presented the fabrication of bimetals comprising high-strength steel (HSS)and Ti6Al4V (TC4) using laser-directed energy deposition (LDED) technology. The research elucidated the interface bonding mechanism of LDEDed HSS/TC4 bimetals and analyzed various bonding strategies for achieving superior properties of steel/titanium joints based on thermodynamic calculations. Due to the limited compatibility between Fe and Ti, a large amount of Fe-Ti intermetallics, especially Fe2Ti, were formed at the interface of LDEDed HSS/TC4 bimetals. The presence of Fe2Ti intermetallics caused a significant enhancement in interfacial hardness, ultimately leading to the fracture of tensile specimens during the wire cutting. Thermodynamic calculations indicated that utilizing a composition gradient processing strategy does not yield a high-quality metallurgical bonding interface between HSS and TC4. Interlayer engineering is an effective building strategy to obtain high-performance LDEDed HSS/TC4 bimetals. Moreover, these compatible interlayers should ensure a reasonable match of thermophysical properties and have a certain thickness. The findings provide valuable insights into bonding and failure behavior, building strategies, and potential future directions for joining high-strength steels and titanium alloys.

Study on fracture characteristics and mechanisms of red sandstone under high-voltage pulse discharge

To investigate the influences of geometrical size and discharge voltage of the pulse discharge equipment on the fracture characteristics and mechanisms of sandstone under high-voltage pulses, a series of experiments was conducted using a high-voltage pulse discharge device on sandstone circular disc specimens of sandstone with a thickness of 10 mm. These experiments covered a range of disc diameters ranging from 50 mm to 142 mm and discharge voltages from 15 kV to 40 kV. Through these experiments, the fracture characteristics of sandstone at both macroscopic and microscopic levels were investigated. In the experiments, a quantitative analysis of surface fracture was undertaken based on fracture density and fractal damage. Additionally, using the principle of energy equivalence, numerical simulation methods were used to study the damage evolution process in sandstone. The research results indicate that the formation and distribution of fractures in the sandstone specimens are significantly affected by geometrical size and discharge voltage. By analyzing the interaction between stress waves and fracture propagation, combined with indoor experimental results, the fracture mechanism was revealed. The high temperature and shock wave generated by the plasma channel leads to the crushing zone near the electrode, while the circumferential tensile component of the stress wave can result in radial fractures, and the reflected tensile wave leads to circumferential and radial fractures near the boundary.

Synergistic Enhancement of the Mechanical Properties of Epoxy-Based Coir Fiber Composites through Alkaline Treatment and Nanoclay Reinforcement

This study explores the synergistic effects of incorporating coir fibers and nanoclay into epoxy resin composites. Coir, a renewable and cost-effective natural fiber, undergoes an alkaline treatment to influence its ability to form strong interfacial bonding with the epoxy matrix. To further enhance the mechanical properties of the composite, montmorillonite nanoclay, surface-modified with aminopropyltriethoxysilane and octadecyl amine, is introduced. The research investigates different combinations of coir fiber content (20, 30, and 40 wt%) and nanoclay loading (0, 2, and 4 wt%) with epoxy resin. The composites are fabricated through an open molding process, and the mechanical properties are evaluated using tensile and flexural tests according to the ASTM D638 and D7264 standards, respectively. The tensile and flexural strengths of the 40 wt% coir fiber-reinforced epoxy composite are found to be 77.99 MPa and 136.13 MPa, which are 44% and 23% greater than pure epoxy, respectively. Furthermore, the strengths displayed a 23% improvement in tensile strength with 4 wt% and a 31.4% improvement in flexural strength with 2 wt% nanoclay as additional reinforcement. Scanning electron microscopy is employed for fractographic analysis of the fractured specimens from the tensile test. The study underscores the importance of understanding the interplay between natural fibers, nanoclay, and epoxy resin for optimizing the composite’s performance in real-world applications.

Miswak-Infused Glass Ionomer Cement: A Comparative In Vitro Analysis of Antibacterial Efficacy and Compressive Strength.

Glass ionomer cement (GIC) restorations are commonly used in primary dentition, due to their aesthetic appeal, self-adhesive nature, and biocompatibility. However, the material's limited antibacterial activity and inadequate mechanical strength highlight the necessity for modifying the material. The study aims to evaluate and compare the antimicrobial potency and compressive strength of GIC-incorporated Miswak extract with that of conventional GIC. After obtaining the Miswak extract, a modified GICwas formulated by combining the extract with the conventional GIC powder and liquid components, in three different ratios (Powder: Extract and Liquid), Group I (2:1:1), Group II (3:1:2), Group III (3:2:1), and the Group IV as control, which consist of unmodified/conventional GIC. To evaluate and compare the antibacterial efficacy of the modified and unmodified GIC, standard strains of Streptococcus mutans and Lactobacillus were utilized. For each group, the minimal inhibitory concentration (MIC) assay was tested. For the evaluation of compressive strength, cylindrical moulds were utilized in compliance with ISO 9917-1:2007 standards and tested using the universal testing machine (Instron, ElectroPuls®, Bangalore, IND). The highest force exerted at the point of specimen fracture was recorded to calculate the compressive strength values in MPa. The data obtained were analyzed using the StatisticalPackage for the Social Sciences (IBMSPSSStatisticsforWindows,IBMCorp., Version 24.0, Armonk,NY)software. The statistical analysis was conducted utilizing repeated measures of analysis of variance (ANOVA) to calculate the mean MICvalues and compressive strength, with pairwise comparisons assessed using Tukey's post hoc test. The results provedthat the antimicrobial properties of Miswak containing GIC performed better against S. mutans and Lactobacillus with a statistically significant difference when compared with group IV (p<0.05), it has been found that an increase in the concentration of extract increased the antimicrobial potency. Significant results were obtained in compressive strength where GroupII (41.49±3.6) and Group III (15.23±4.96) proved to be weaker than the control (62.69±2.58), while Group I showed no differences from the control group (p>0.05). It can be concluded that Group I was found to be better in terms of both antimicrobial properties and compressive strength, where no significant difference in compressive strength was identified when comparing Group I with Group IV. Thus, the overall study depicts that a lesser concentration of extract can be the best option in terms of good antimicrobial properties without altering its strength. Hence, the Miswak containing GIC could be a promising restorative material; further studies should include considering intraoral variables such as masticatory stress, moisture levels and in-vivo tests of this combination.

The Effect of Exposure to Candida Albicans Suspension on the Properties of Silicone Dental Soft Lining Material.

While functioning in the oral cavity, denture soft linings (SL) are exposed to contact with the microbiota. Dentures can offer perfect conditions for the multiplication of pathogenic yeast-like fungi, resulting in rapid colonisation of the surface of the materials used. In vitro experiments have also shown that yeast may penetrate SL. This may lead to changes in their initially beneficial functional properties. The aim of this work was to investigate the effect of three months of exposure to a Candida albicans suspension on the mechanical properties of SL material and its bond strength to the denture base polymer, and to additionally verify previous reports of penetration using a different methodology. Specimens of the SL material used were incubated for 30, 60 and 90 days in a suspension of Candida albicans strain (ATCC 10231). Their shore A hardness, tensile strength, and bond strength to acrylic resin were tested. The colonization of the surface and penetration on fractured specimens were analysed with scanning electron and inverted fluorescence microscopes. Exposure to yeast did not affect the mechanical properties. The surfaces of the samples were colonised, especially in crystallized structures of the medium; however, the penetration of hyphae and blastospores into the material was not observed.

Effect of strain rate on the stress corrosion cracking of TP439 stainless steel in water vapor environment at 500 ℃

The effect of water vapor on the stress corrosion cracking (SCC) behavior of TP439 stainless steel at 500 °C was investigated using slow strain rate tensile tests at three strain rates of 2 × 10–5/s, 2 × 10–6/s, and 2 × 10–7/s. Air was selected as a comparative blank test environment for the water vapor environment. The results showed that the tensile strength of the specimens increased significantly in air when the strain rate was decreased from 2 × 10–5/s to 2 × 10–7/s, while it decreased in water vapor. Dynamic strain aging (DSA) and SCC are the main factors contributing to the difference in tensile strength of the specimens in air and water vapor. The SCC of TP439 stainless steel in water vapor at 500 °C occurs at a strain rate of 2 × 10–7/s or even lower. Based on the SCC susceptibility index and SEM observation of specimen fracture, TP439 stainless steel exhibits a slight transgranular SCC in water vapor with low SCC susceptibility.

Combined vertical and external rotational force in plantarflexion position produces posterior pilon fracture: A preliminary cadaveric study

BackgroundPosterior pilon fracture is speculated to occur by a combination of rotation and axial load, which makes it different from rotational posterior malleolar fracture or pilon fracture, but is not validated in vitro. The aim of the current study is to investigate the injury mechanisms of posterior pilon fracture on cadaveric specimens. MethodsEighteen cadaveric specimens were mounted to a loading device to undergo solitary vertical loading, solitary external rotational loading, and combined vertical and external rotational loading until failure, in initial position of plantarflexion with or without varus. The fracture characteristics were documented for each specimen. ResultsVertical loading force combined with external rotation force diversified the fracture types resulting in pilon fracture, tibial spiral fracture, rotational malleolar fracture, talar fracture or calcaneal fracture. Vertical violence combined with external rotational loading in position of 45° of plantarflexion and 0° of varus produced posterior pilon fracture in specimens No. 13 and 14. ConclusionCombination of vertical and external rotational force in plantarflexion position on cadaveric specimens produce posterior pilon fracture.

Investigation of dynamic three–point bending fracture properties of SCB sandstone

The stress intensity factor (SIF) is not only an important parameter in the field of fracture mechanics but also a key indicator reflecting the strength of the stress field at the crack tip. Therefore, this paper uses the Split–Hopkinson–Pressure–Bar (SHPB) device to conduct dynamic fracture experiments on semi–circular bend (SCB) sandstones of different fracture modes and then uses an experimental–numerical method to simulate the dynamic loading process to explore the changes law in SIF. Finally, combined with the high–speed digital image correlation (HS–DIC) technology, the fracture characteristics of SCB sandstones are studied. The results show that the rising rate of dissipated energy acting on the specimen fracture and damage increases rapidly when it is close to dynamic fracture, which makes the dynamic SIF also get a substantial increase, and the influence of dissipated energy on dynamic SIF is seen to be very strong. Moreover, prior to the occurrence of dynamic initiation fracture, the damage to the specimen is primarily triggered by microscopic tensile effects at the tip of the preset crack, which results in the value of KI always being greater than KII before the dynamic fracture occurs. Meanwhile, the distribution curve of dynamic SIF exhibits better symmetry or a trend towards symmetry compared to the distribution curve of static SIF. This suggests that the tip of the preset crack distributes with more uniform tensile and shear stresses during dynamic loading. Using the HS–DIC technique, when the specimen occurs dynamic pure mode I initiation fracture, there was a good symmetrical trend in both the vertical strain around the fracture crack and the horizontal displacement field at the specimen. However, when specimens occur dynamic mixed mode I/II initiation fracture, the horizontal displacement fields showed asymmetry, and the specimens all suffered varying degrees of shear damage.

Effects of plasma surface quenching on strength and crack resistance property of PCrNi3 Mo steel

Plasma surface quenching technology uses a high-energy beam to rapidly heat the PCrNi3Mo steel material. Simultaneously, the treated workpiece is rapidly cooled by its own heat transfer to realize surface quenching. The metallographic structure showed that the grains of the PCrNi3Mo steel treated by plasma quenching were significantly refined. The DEFORM software was utilized to simulate the heat treatment process, and the results showed that the martensitic volume fraction of the plasma quenching treatment of PCrNi3Mo steel was as high as 83.6%~95.9%, and the simulated hardness value was HRC55~57. The actual hardness of the specimen after plasma surface quenching was HRC54~56, which was in good agreement with the simulation value. The plasma was employed to treat the PCrNi3Mo steel tensile specimen, the processing depth was only 1/10 of the thickness of the specimen. Through the MTS tensile experiment, it was observed that the tensile strength of specimens treated with plasma increased by 9.2% when compared to the untreated specimens. Despite the high hardness of the treated specimen, fracture strain exceeded 7%. Furthermore, before the fracture of the tensile specimen occurred, the plasma quenching part effectively prevented crack propagation and delayed fracture, and the fracture necking phenomenon of the specimen was not obvious.

Tensile properties of welded joints with delayed hydride crack

In this work, a procedure for producing tensile coupon specimens with naturally delayed hydride cracks was proposed, and the tensile properties of the specimens were studied. Firstly, a delayed hydride crack was prefabricated on the welded plate according to the relevant specification, and the crack type was determined by microstructure and macrostructure observation and analysis. Secondly, the tensile coupon specimens of welded joints with or without delayed hydride cracks were cut from the welded plate. Finally, tensile tests of welded joints were carried out, and the strain and displacement were monitored by a digital image correlation system. The test phenomena, fracture mode and the tensile properties of the welded joint were analysed according to the stress-strain curve, the strain cloud map and the tensile property parameters. When the specimen fractured at the base metal, the effect of delayed hydride crack on the strength and deformation of the welded joints was insignificant. The cracked area ratio was relatively small (e.g. 1.91% to 22.5%). When the specimen fractured at the cracked region, the cracked area ratio was relatively large (e.g. 16.77% to 39.62%). The fracture modes could be divided into two types: the full-sectional yield fracture and the low stress fracture. The remaining ultimate strength, yield-to-tensile ratio and elongation of low stress fracture specimens showed a linear decline with the increase of cracked area ratio. For specimens with cracked area ratio between 16.77% and 22.5%, the differences in fracture locations might be caused by the pattern and angles of the crack.

Fracture characterization of structural steel S690Q by using mini-CT specimens

Mini-CT specimens are an interesting alternative when characterising the fracture behaviour of structural materials and there are issues with regard to, for example, the amount of available material, the irradiation level (in nuclear materials) or material inhomogeneities. Furthermore, in ferritic-pearlitic steels, the characterisation of the fracture behaviour within the ductile-to-brittle transition zone (DBTZ) is of particular interest, given that the material may behave very different, in terms of fracture toughness, when operating at different but relatively close temperatures within this zone. In many occasions, the definition of the DBTZ behaviour is performed through the Master Curve (MC) methodology and, thus, by testing standardised fracture specimens (e.g., CT, SENB) and determining the material Reference Temperature (T0). The use of mini-CT specimens to define T0 has been validated in a wide range of steels used in nuclear industry, but its application to structural steels has been scarce. Thus, this work gathers the fracture characterisation results (T0) obtained in structural steel S690Q, comparing them to those obtained by using conventional standardized SENB specimens. It is shown that, for this particular structural steel, the use of miniaturized specimens provides a T0 value (-89.3°C) which is comparable to the value obtained from conventional larger specimens (-110°C).

Temperature Effects on Critical Energy Release Rate for Aluminum and Titanium Alloys

This work investigates temperature’s effect on the critical energy release rate using damage mechanics material models and the element deletion method. The energy release rate describes the decrease in total potential energy per increase in crack surface area. The critical energy release rate is widely used as the failure criterion for various elastic and plastic materials. In real-life scenarios, fractures may occur at different temperatures. The temperature dependency of the critical energy release rate for aluminum 2024-T351 and titanium Ti-6Al-4V is studied in this work. We utilized test-data-based advanced material models of these two alloys, considering the strain rate, temperature, and state of stress for plasticity and failure. These material models are used to simulate a three-dimensional fracture specimen to find the critical energy release rate at different temperatures. A new method to calculate the critical energy release rate with the element deletion method is introduced and verified with the virtual crack opening method. This method enables the calculation of the energy release rate in a classical damage mechanics simulation for dynamic cack propagation. The simulation result indicates that the critical energy release rate increases with rising temperatures for these alloys.

Microstructural evolution and mechanical properties of Ti55531–0.5Nb fabricated by selective laser melting under different heat treatments

The metastable Ti55531–0.5Nb alloy was deposited by selective laser melting (SLM) technology. The microstructure and phase orientation along different deposition directions were analyzed, and the microstructural evolution and mechanical properties of the alloy with different heat treatments have been investigated. It is indicated that the microstructures of the as-build samples were β phase without α phase, and the β phase orientation was dominated by 〈100〉 texture. The volume fraction of primary α decreases with increasing of solution temperature, while the secondary α exhibits an opposite trend, which is mainly related to the growth rate and dissolution rate α phase. The relatively higher ultimate tensile strength of 1300 ± 20 MPa and lower elongation of 2.4 ± 0.1% was observed when solution temperature is 790 °C, and the lower ultimate tensile strength of 1190 ± 8 MPa with higher elongation of 8.40 ± 0.6% was obtained at solution temperature of 700 °C. The tensile fracture exhibits a mixture fracture mode dominated by ductile fracture when there is primary α phase in the microstructure, while the brittle fracture was obtained owing to the absence of primary α phase. The crack nucleation mode is mainly microvoid coalescence, which mainly nucleate grain boundaries α phase and propagates along the grain boundary observed from the tensile fracture and cross-sectional microstructure near the fracture of tensile specimens. There results can provide some theoretical support for metastable β titanium alloys fabricated by additive manufacturing technology and subsequent heat treatment in the future.

Lap shear properties of CF/PEKK composites through nanoparticle-enhanced adhesive joints

This study investigates the effects of incorporating halloysite nanotubes (HNTs) into polyetherimide (PEI) adhesive for carbon fiber/polyetherketoneketone (CF/PEKK) composite joints. The CF/PEKK substrate is fabricated through an oven consolidation process, while PEI adhesive films with varying HNTs loadings (0.5, 1 and 3[Formula: see text]wt.%) are prepared using solvent casting with [Formula: see text]-butyrolactone. Homogeneous dispersion of HNTs in PEI is achieved through magnetic stirring and IR heating. The resulting film is hot pressed to form a 100[Formula: see text][Formula: see text]m thick film, and adhesive lap shear joint specimens are manufactured through oven consolidation. Morphology and dispersion of HNTs in PEI are analyzed using SEM and EDS, revealing favorable dispersion at 0.5[Formula: see text]wt.% HNTs and aggregation at higher loadings. Differential scanning calorimetry (DSC) is employed to study the glass transition temperature (Tg) of PEI, showing decreased Tg for solvent-cast PEI and increased Tg with HNTs incorporation. This increase is attributed to the constrained mobility of polymer chains due to HNTs’ influence. Lap shear strength (LSS) is evaluated, demonstrating enhancement with HNTs incorporation: 0.5[Formula: see text]wt.% HNTs (+12.5%) &gt; 1[Formula: see text]wt.% HNTs (+8.33%) &gt; Pure PEI &gt; 3[Formula: see text]wt.% HNTs (−12.5%). The study attributes this enhancement to HNTs’ reinforcement and chemical interactions with PEKK. Aggregation tendencies at 3[Formula: see text]wt.% HNTs lead to decreased LSS. SEM-EDS analysis of fractured specimens indicates a multifaceted bonding joint interface involving PEKK, PEI and HNTs. CF/PEKK composites show adhesive, cohesive and adherend failure modes, with adherend failure being dominant. Notably, fabric-like textures and plastic deformations in PEI with 0.5[Formula: see text]wt.% HNTs contribute to enhanced LSS, while higher HNTs content leads to cohesive failure due to aggregation. This study provides insights into optimizing composite adhesive systems by harnessing nanotube reinforcement and controlling dispersion, thereby influencing interfacial strength.

Experimental study on slow tensile, fatigue, and impact on X42 steel and #20 carburizing steel

Hydrogen embrittlement is a common phenomenon in high-strength steels and presents a significant challenge in the research and development process. This study aims to analyze the mechanism of hydrogen embrittlement, investigate the causes of crack growth in steel, and conduct experiments at mesoscopic and microscopic scales to gain a deep understanding of the relationship between hydrogen embrittlement and defects in high-strength steels. The research includes a slow tensile test to study the shrinkage and ductility of X42 steel and 20# carburizing steel under air and hydrogen environments. Furthermore, fatigue testing is conducted to comparatively investigate the crack growth of CT specimens in nitrogen and hydrogen environments at different pressures. Additionally, impact testing is performed to examine the fracture of V-notched specimens in air and hydrogen at different pressures. The findings reveal that 20# carburizing steel exhibits better fracture toughness than X42 steel during the slow tensile process, and its hydrogen embrittlement sensitivity is lower. Moreover, the fatigue crack growth process of 20# carburizing steel is less affected by hydrogen embrittlement, resulting in better fatigue rupture resistance compared to X42 steel. Furthermore, the impact toughness value of 20# carburizing steel is higher than that of X42 steel in the impact toughness test. Both steels show varying effects on crack growth under different hydrogenation pressures. Importantly, the impact toughness of both steels is less affected by different hydrogenation pressures.

Uniaxial Compressive Damage Characteristics of Rock-like Materials with Prefabricated Conjugate Cracks

Joined fractures are an important factor affecting natural rock masses’ mechanical and deformation properties. In this paper, indoor uniaxial compression experiments reproduce prefabricated cracks’ generation, extension, and coalescence in rock-like specimens. For the fractured specimens, a single crack with an inclination of α = 45° was placed on the left and right sides, and a third crack with an angle of β = 30°, 45°, 60°, and 90° to the single crack on the right side was placed in groups III–VI, respectively. All cracks extended in the thickness direction. Vertical pressure was applied at a constant loading rate of v = 0.1 mm/min until the stress dropped dramatically. In addition, numerical calculations were performed on the rock specimens using PFC2D, a sub-module of the Discrete Element Method (DEM). The experimental results agree with the numerical simulations in that the strength of the specimens containing a conjugate crack is significantly reduced, and the mechanical and deformation properties of the specimens are related to the internal angle of the conjugate crack, with the lowest peak strength and lowest percentage energy dissipation at β = 45°.

Optimization design of porthole die and study on microstructures and mechanical properties for an Al–Li alloy hollow profile

In this paper, a hollow Al–Li alloy profile was taken as an example, and the optimization design method of Al–Li alloy porthole die was given. Compared with the basic die design, the optimized die reduces the standard deviations of velocity and temperature as well as the maximum equivalent stress, resulting in a significant reduction of the distortion degree of the extruded profile, and the optimized die meets the strength requirements. The microstructures, mechanical properties and strain distributions of the longitudinal welds and matrices of the extruded profile were analyzed. It is found that the longitudinal welds are well welded without macro/micro defects. The fracture of tensile specimens all occurred at the matrices instead of welds, and the mechanical properties in the thick-walled matrices are much lower than those in the thin-walled matrices. The grain size in the thick-wall matrices is much coarser and more ununiform than that in the thin-walled matrices, which is caused by the low strain in the thick-walled matrices. For increasing the strain amount and uniformity of local zone of the extruded profile, an innovative method through adding baffle-blocks in the portholes was proposed.

Bond Strength to Lithium-Disilicate Ceramic after Different Surface Cleaning Approaches.

To evaluate the effect of different lithium-disilicate (LiSi) glass-ceramic surface decontamination procedures on the shear bond strength (SBS) to resin cement. Seventy CAD/CAM LiSi ceramic specimens (IPS e.max CAD, Ivoclar) were cut and sintered. Fifty specimens were treated with 5% hydrofluoric acid (HF) for 20 s, while 20 were left untreated. All 70 specimens were then contaminated with human saliva and try-in silicone paste. The following surface cleaning methods were investigated (n = 10): C: water rinsing (control); PA: 37% H3PO4 etching for 20 s; E: 70% ethanol applied for 20 s; CP: cleaning paste (Ivoclean, Ivoclar) brushed for 20 s; HFSEP: self-etching ceramic primer (Monobond Etch&Prime, Ivoclar) rubbed for 20 s; HF: 5% HF applied for 20 s or no HF etching prior to contamination; SEP: self-etching ceramic primer rubbed for 20 s and no HF etching prior to contamination. Composite cylinders were created and luted with an adhesive resin cement to the decontaminated surfaces. After storage for 24 h at 37°C, the SBS test was conducted. Two fractured specimens per group were observed under SEM to perform fractographic analysis. The data were statistically analyzed with p set at <0.05. The type of surface cleaning approach influenced bond strength (p < 0.001). HFSEP, SEP, and HF attained higher SBS (p < 0.001) compared to other groups. None of the approaches were able to completely remove contaminants from the ceramic surfaces. SEM images showed residual traces of contaminants on CP-treated surfaces. The self-etching ceramic primer enhanced bond strength to contaminated LiSi ceramic surfaces, irrespective of previous treatment with hydrofluoric acid.

Comparative analysis of flexural strength of 3D printed and milled 4Y-TZP and 3Y-TZP zirconia

Statement of problemThe mechanical properties of 3 dimensionally (3D) printed zirconia have been reported to be comparable with those of milled zirconia, except for the flexural strength. However, most previous studies tested 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP), making it necessary to study 3D printed zirconia with 4 mol% yttria content (4Y-TZP). PurposeThe purpose of this in vitro study was to compare the flexural strength of 3D printed 4Y-TZP with 3Y-TZP materials and milled 4Y-TZP. Material and methodsA total of 80 disk specimens (Ø15×1.5 mm) were fabricated and divided into 4 groups (n=20) using the fabrication method and yttria content: milled 3Y-TZP (Katana HT; Kuraray Noritake), 3D printed 3Y-TZP (TZ-3Y-E; Tosoh), milled 4Y-TZP (Katana STML; Kuraray Noritake), and 3D printed 4Y-TZP (3DMAT; Genoss). The biaxial flexural strength was determined with a piston-on-3-ball test (n=15). The flexural strength of each specimen was measured, and the Weibull modulus (m) and characteristic strength (σ0) were estimated from the fracture load distribution. Two intact and fractured specimens were examined with scanning electron microscopy (SEM). The crystalline phase of the specimens in each group was identified through X-ray diffraction (XRD) analysis (n=5). A 1-way ANOVA was used to compare the flexural strength among different groups. Subsequently, pairwise comparisons were conducted with the Tukey post hoc method (α=.05). ResultsThe flexural strength of 3D printed 4Y-TZP was significantly higher than that of milled 4Y-TZP (P<.001). In contrast, the flexural strength of 3D printed 3Y-TZP was significantly lower than that of milled 3Y-TZP (P<.001). X-ray diffraction (XRD) analysis revealed that the tetragonal phase was the dominant phase in all groups, with the identification of some cubic phase peaks. ConclusionsThree dimensionally printed 4Y-TZP showed significantly higher flexural strength than milled 4Y-TZP and exhibited a clinically acceptable flexural strength exceeding 800 MPa.