Disc Specimens Research Articles

Assessment of fracture toughness in fibrous concrete via Brazilian test: Experimental study with low-clinker cementitious binder

As the predominant and cost-effective material in the construction industry, concrete is susceptible to tension weaknesses, leading to significant flaws such as cracking and brittle fracturing. Recent advancements in fibrous concrete have emerged as a solution to mitigate these issues. Incorporating steel fibers in concrete has emerged as a promising solution to improve crack resistance and structural integrity. This study focuses on developing eco-friendly concrete using a low-clinker cementitious binder and short steel fibers to enhance fracture toughness and mitigate the environmental impact by effectively utilizing lime sludge. Concrete specimens were prepared with three binder types: treated lime sludge (TLS) at 15 % and 30 % and calcined clay (CC) at 15 % and 30 %, replacing conventional clinker. Short steel fibers were added at 1.5 % by volume to enhance mechanical properties. Fracture toughness was evaluated using notched Brazilian disc specimens, assessing mode I, II, and mixed-mode (I/II) fracture at multiple notch orientations (β = 0°, 15°, 28.83°, 45°, 60°, 75°, and 90°). Microstructural analysis during strength development was performed using scanning electron microscopy and X-ray diffraction. The findings revealed that specimens containing 15 % TLS, 30 % CC, and 1.5 % steel fibers exhibited the highest fracture toughness. Mode II fracture toughness exceeded mode I, indicating improved resistance to crack propagation. The addition of fibers to the specimens under mode II demonstrated improved fracture toughness, ranging from 0.44 to 0.53 MPa·m^1/2 compared to the corresponding non-fibrous specimens. The fibrous specimens showed significantly higher ultimate loads at β = 90° compared to β = 0°, indicating superior crack resistance and structural integrity under perpendicular loading conditions. The Brazilian disc specimens demonstrated variability in fracture toughness across different loading orientations, highlighting their suitability for mixed-mode fracture assessment.

Experimental and numerical analysis of Brazilian splitting mechanical properties and failure mechanism for composite discs

The properties of structural planes and the strength of rock matrix significantly influence the splitting characteristics of composite rock masses. To investigate the effects of structural plane and differences in matrix strength on the mechanical behavior and failure characteristics of composite jointed rock bodies, composite jointed disc specimens with varying structural plane roughness and matrix combinations were prepared. These specimens were then subjected to Brazilian split tests under different loading angles ranging from 0° to 90°. Results indicate that the failure mode of the specimens is determined by the angle of the structural plane. As the structural plane angle increases, the failure mode transitions from structural plane failure to combination failure and finally back to structural plane failure. Increased roughness of the structural plane reduces the extent of structural plane failure, while matrix strength has no significant impact on the failure mode. The failure load of the specimens increases with increasing structural plane angle, roughness, and matrix strength. The influence of structural plane roughness and matrix strength on the mechanical properties of the specimens grows with increasing structural plane angle. Increases in structural plane roughness and matrix strength significantly enhance the strain energy and dissipated energy of the disc model. Finally, an analysis of the stress state on the structural planes is combined with an exploration of the failure mechanisms of the specimens.

Finite-discrete element modelling of fracture development in bimrocks

Block-in-matrix rocks (bimrocks) are a complex geological feature composed of hard blocks in a weak matrix bonded together via a weak interface. The failure mechanism and deformation behavior of the bimrocks is quite complex due to the simultaneous existence of blocks with different shapes, strengths and proportions in a matrix. Therefore, it is of great importance to characterize the bimrocks under different situations. This study employs the combined finite-discrete element method (FDEM) to characterize the failure pattern and load carrying capacity of the bimrocks considering changes in various parameters, including block size, volumetric block proportion (VBP), the strength ratio of block-matrix interface to matrix, and the shape of the blocks (angular, circular, and elliptical shapes). First, the robustness and feasibility of the FDEM in modeling fracture development is verified against an analytical solution as well as a series of experimental tests accompanied with the digital image correlation (DIC) method. Then, the verified model is used to model disc specimens with various block shapes and properties. The results indicate the remarkable influence of VBP, block size and block-matrix interface characteristics on the bimrock mechanical behavior under the same VBP. The results are assessed based on macroscopic observations to investigate the influence of determinative physical properties of bimrocks. The results are also evaluated based on the mode of failure, mode I, II, or mixed mode, to qualitatively elucidate the influence of key factors on the formation of different cracks in different places, including the interface of matrix-blocks or intergrain or intragrain. The results show that since the loading is a quasi-static scheme, all the cracks are intergrain and no intragrain crack is observed for any VBP. The simulations outcomes shows that the block sizes determine the failure pattern, failure mode, and load–displacement behavior, where the larger blocks exhibiting the lowest load carrying capacity due to experiencing more interface breakage in shear. It is found that the VBP is a crucial parameter in the deformation of the bimrocks, showing that the strength of the bimrocks significantly increases with a decrease in the VBPs and the ones with greater VBPs experience more breakage and thus less resistance to loading. The block-interface strength is found to be the most critical factor in the deformation of the bimrocks (regardless of the value of the VBP). Finally, the effect of block shape is shown to have a considerable impact on bimrocks with the higher VBPs (more than 70%).

Research on the Brazilian splitting characteristics and failure mechanism of jointed composite disks

The stress state of composite rock joints has a significant impact on the overall stability of the rock mass. Studying the composite mechanism disk specimens with different matrix strengths and inclination angles under Brazilian splitting state is of great significance for improving the safety of surrounding rock. This research conducted Brazilian tests on different types of jointed composite disk specimens at different inclination angles and explored the effects of inclination angle and material strength on the mechanical properties and deformation characteristics of specimens. Clarified the failure mechanism of joint specimen. The experimental results indicate that the disk specimens under different inclination angles exhibit three typical failure modes. As the inclination angle increases, failure mode changes from Disk matrix failure (DM failure) to Disk matrix and structural failure (DMS failure), and ultimately to Disk structural failure (DS failure). Failure load, input energy, and strain energy of the specimen continue to decrease as the inclination angle increases and the matrix strength decreases. The decrease in matrix material significantly weakens the strength of the specimen, but this effect continues to decrease with the increase of inclination angle. DIC results show that as the inclination angle increases, the position of cracks exists from the loading end to the joint surface. Through theoretical analysis, it is found that as the inclination angle increases, the stress state at the center of the specimens changes from compression-shear state to shear state, and finally to tension state, corresponding to three failure modes: DM failure, DMS failure, and DS failure, respectively.

3D internal crack propagation in brittle solids under non-uniform temperature field: Experimental and numerical simulation

In the field of engineering, elevated temperatures often induce thermal stress. Especially in brittle materials, the propagation of internal cracks under such thermal stress is frequently the primary cause of failure. We utilize the 3D internal laser-engraved crack technology to create internal cracks at various locations inside the half-Brazilian disk specimens. By precisely controlling the power of the heating device, we achieved temperature non-uniformity of the external heat source, resulting in uneven heating of the material’s surface. Simultaneously, by adjusting the geometry of the material and using semi-Brazilian disk specimens, we generated uneven temperature gradients and thermal capacities along different heat conduction paths. The internal cracks at different locations also affect the distribution of thermal stress in the material, further influencing the formation of the non-uniform temperature fields (NUTF). Through the above methods, we successfully conducted physical experiments on the 3D propagation of internal cracks in brittle materials under NUTF. Additionally, we utilized J-integral and the finite element method for thermal analysis to conduct thermo-mechanical coupled 3D numerical simulations. Furthermore, we employed a polarising microscope to analyze the microscopic morphology of 3D internal cracks. Finally, we revealed the mechanism of 3D internal crack propagation under NUTF. The results show that prefabricated internal cracks in group A produce “n-shaped” crack at a height of 15 mm and “u-shaped” cracks at heights of 25 mm and 35 mm. Meanwhile, in group B, the eccentric prefabricated internal cracks ultimately produce “s-shaped” cracks. Through analysis, it was determined that the differential formation occurred due to relative sliding between the upper and lower surfaces of the crack under longitudinal shear stress induced by NUTF. Group A cracks have smooth surfaces, which are mode I-II cracks. group B generated “lance-like” fractures with obvious “anti-binary tree”, which are mixed mode I-II-III cracks. These findings provide an experimental and theoretical basis for the study of 3D internal crack propagation modes under NUTF and deepen the understanding of fracture mechanics in brittle materials.

Study on the effect of heating rate and temperature on the fracture properties of flawed granite

The effects of heating rate and temperature on fracture characteristics and mechanical properties of flawed granite were studied by using the cracked straight-through Brazilian disc specimen. Four temperature groups were established, and the specimens were heated in a furnace with different heating rates. After thermal treatment, the specimens were conducted to static compression tests, the compression process was recorded by a camera and the deformation on the specimen surface was calculated by the digital image correlation (DIC) technology. A microscope which can magnify nine times was employed to observe the surface of specimen and the transgranular or intergranular fracture. The results show that: at the same temperature, the thermal cracks increase as the heating rate increases. Within the same temperature group, the mode-I fracture toughness of granite shows a gradual decay characteristic as the rate of heating increases. Due to the DIC results, at the same temperature, when the heating rate increases, the maximum principal strain and the crack tip opening displacement (CTOD) of crack tip show an increasing trend at fracture. At 200 ℃, the maximum principal strain in the range of 0.0781% ∼ 0.237 %, the effect of heating rate is distinct. At 200–400 ℃, the input energy and release energy by fracture decrease with the heating rate. In the same temperature group, the specimen heating rate of 20 ℃/min has more distinct ductile characteristics.

Evaluation of the Effectiveness of Semolina in Improving the Bond Strength of Metal Alloys and Acrylic Resins for the Fabrication of Hybrid Prostheses for Implant Restoration: An In Vitro Study.

Introduction Fixed prosthodontic solutions for restorations of multiple implants are often done using acrylic-metal hybrid prosthesis. These restorations have a high failure rate due to poor bond strength between metal and acrylic, despite using digital attachments and primers. This study has been done to demonstrate an economical yet effective method of increasing shear bond strength between acrylic and metal. Materials and methods Disc specimens of 10 mm diameter and 2 mm thickness were designed using the Meshmixer version 3.5 software (Autodesk Inc., San Rafael, USA). The standard tessellation (STL) file was imported and sent for direct metal laser sintering (DMLS) in cobalt-chromium (CoCr),titanium (Ti), and wax milling. The groups were defined. Ten samples were included in each group. Group 1: Conventional Casting in CoCr; Group 2: Conventional Casting with Opaquer (CoCr); Group 3: DMLS CoCr; Group 4: DMLS CoCr with Opaquer; Group 5: DMLS Ti; Group 6: DMLS Tiwith Opaquer; Group 7: Casting with Semolina (CoCr); and Group 8: Casting with Semolina and Opaquer (CoCr). Wax-up was performed using double wax sheet thickness of modeling wax. Flasking and acrylization were done using the injection moulding technique. A universal testing machine was used for shear bond strength. Results were tabulated and statistical analysis was done usingIBM SPSSStatistics for Windows (IBM Corp., Armonk, USA). The Shapiro-Wilk test was done to confirm the normality of the data, followed by the one-way analysis of variance (ANOVA) test to compare the shear bond strength between metal alloys and heat cure acrylic resin. Results The one-way ANOVA results reveal significant differences in bond strengths among the various groups. Conventional Casting with Opaquer showed no significant difference (p=0.335), but there were notable improvements in bond strength when compared to DMLS CoCr, DMLS CoCr with Opaquer, DMLS Ti, DMLS Ti with Opaquer, Semolina, and Semolina with Opaquer, with DMLS Ti having the largest mean difference (3.368). Conventional Casting with Opaquer significantly outperformed all groups, especially Semolina, which showed the highest mean difference (7.558). Similar trends were seen with DMLS CoCr and DMLS Ti, where Semolina consistently demonstrated superior bond strength. Overall, Semolina produced the highest bond strengths across all conditions. These results underscore the importance of material selection and treatment in enhancing bond strength. Conclusion Semolina can be used as an economicaland reliable method to increase the shear bond strength between acrylic and metal bonding. Its ability to burn out during dewaxing without any remains or remnants in mould deems it a useful material for increasing mechanical bonding.

Evaluation of Antimicrobial Efficiency, Shear Bond Strength, and Adhesive Remnant Index of TiO2 Infiltrated Orthodontic Adhesive - An In Vitro Study.

Enamel demineralization is an unavoidable adverse effect encountered with bonding brackets in orthodontic therapy. Introducing nanoparticles into the composite adhesive paste can prevent enamel demineralization. Titanium dioxide (TiO2) is known to exhibit direct antimicrobial efficiency. This study aimed to assess the antibacterial efficiency and shear bond strength (SBS) of an orthodontic bonding composite infiltrated with TiO2 nanoparticles. This in vitro study evaluated the efficiency of TiO2 nanoparticle-incorporated light-curing orthodontic composite paste (ENLIGHT, ORMCO). Twenty extracted premolars were randomly and equally allocated to the two study groups, N = 10. While a conventional composite was utilized for the bonding brackets in Group I, a TiO2-incorporated composite was used in Group 2. The adhesive remnant index (ARI) scores given by Artun and Bergland et al. and SBS were determined. Furthermore, the antimicrobial efficiency was estimated using the minimum inhibitory concentration (MIC)/minimum bactericidal concentration (MBC) and agar well diffusion assay for six composite disc specimens. The results were statistically analyzed using the chi-square test and Student's t test, at P < 0.05. After 24 h of curing, no statistical mean difference was observed between the two groups in terms of ARI or SBS scores (P > 0.05). However, there was a significant increase in the antimicrobial efficiency of Group II when compared with Group I (P < 0.05). TiO2 nanoparticle-incorporated orthodontic composites improve the antimicrobial efficiency with no significant change in the SBS. The ARI scores indicate the presence of 50% remnant orthodontic composite on the tooth enamel surface post debonding.

Effect of Blood Decontamination Procedures on the Microshear Bond Strength of Resin-modified Glass Ionomer Cement to Resin Composite.

To investigate the effect of decontamination procedures on the microshear bond strength (μSBS) of blood-contaminated resin-modified glass ionomer cement (RMGIC) bonded to resin composite (RC). Eighty RMGIC disc specimens were allocated into 5 groups (n=16). All groups except Group 2 were contaminated with blood. Group 1 had no decontamination procedure, Group 3 was decontaminated by rinsing, Group 4 was decontaminated by 34% phosphoric acid etching, and Group 5 was decontaminated by 5% sodium hypochlorite application. RMGIC specimens were subsequently bonded with RC using a universal adhesive in self-etch mode. μSBS tests were conducted using a universal testing machine at a crosshead speed of 1 mm/min. Failure mode analysis was conducted on RMGIC fracture surfaces under a scanning electron microscope. μSBS results indicated that Group 4 had the highest mean μSBS value of 6.22 ± 2.14 MPa, while Group 1 had the lowest mean μSBS value of 3.53 ±1.67 MPa. Significant differences were observed in the μSBS of Group 2 with no contamination (p=0.023) and Group 4 with decontamination by phosphoric acid-etching (p=0.003) when compared to Group 1 with blood contamination. No statistically significant differences (p>0.05) were observed between all other groups' μSBS. For all groups, the predominant mode of failure was adhesive failure between the RMGIC-RC interface, with a few mixed failures in RMGIC for Groups 2-5. Blood contamination before adhesive application significantly reduced the μSBS between RMGIC and RC. Phosphoric acid etching was the most effective blood decontamination procedure to improve the μSBS.

Fracturing behavior and mechanism of flawed disc specimens under compressive loading using geometry‐constraint‐based nonordinary state‐based peridynamics

AbstractA geometry‐constraint‐based nonordinary state‐based peridynamic (GC‐NOSBPD) model is developed to investigate the fracture characteristics of flawed brittle disc specimens under compressive loading as well as its fracturing mechanism. The bond‐associated horizon (BAH) size is directly defined based on the kinematic constraint (KC). This proposed model can well mitigate the numerical oscillation. The failure criteria based on the bond‐associated stress state are utilized to simulate the fracture of materials. Two stress effects can offer an insight into the fracturing mechanism of flawed specimens. The failure modes of flawed specimens are controlled by the tensile failure, and the crack growth trajectories acquired by the present numerical model are equivalent to those obtained by the experimental observations. The effects of size and crack inclination angles on the fracture toughness of brittle materials are assessed. The GC‐NOSBPD model is competent for evaluating the fracture damage of flawed brittle materials and understanding its failure mechanism.

The Effect of Brand, Thickness, and Abutment Substrate on the Masking Ability of Monolithic Zirconia Ceramics

The goal of the present study was to determine the minimum thickness of monolithic zirconia required to achieve an acceptable masking ability and to examine how brand, thickness, and abutment substrate influenced that masking ability (∆E). Seventy-two A2-shade monolithic zirconia disc specimens in various thicknesses (1.0, 1.5, and 2.0 mm) were fabricated using three brands: Nacera® Pearl 1, DD cubeX2 and XTCERA TT. A spectrophotometer was used to determine the CIELab values of the specimens, which were placed on a D4-shade resin composite and white acrylic (control) substrates. The ∆E was calculated and compared with the acceptable (AT = 5.5) and perceptible (PT = 2.6) tolerance thresholds. Further investigation was conducted on 72-disc specimens from the monolithic zirconia brand with the best masking ability on D3-shade resin composite and semi-precious alloy. Using two-way ANOVA, the interaction of thickness, brand, and abutment substrate on ∆E was investigated. Nacera® Pearl 1 at 1.5 mm thickness was sufficient to achieve AT on a D4-shade resin composite substrate, whereas 2.0 mm of DD cubeX2 and XTCERA TT were required. Nacera® Pearl 1 further testing on two other substrates requires thicknesses of 1.5 mm and 1.0 mm, respectively. Only the Nacera® Pearl 1 group achieved PT on D3- and D4-shade resin composite (2.0 mm) and semi-precious alloy substrates (1.5 mm). Brand, thickness, and abutment substrate influenced the ∆E (p &lt; 0.001). To achieve an acceptable masking ability, the minimum thickness of monolithic zirconia tested on D3- and D4-shade resin composite and semi-precious alloy should be around 1.5 mm to 2.0 mm.

Influence of specimen configuration on mode I and mode II fracture toughness of sandstone

In order to investigate the impact of cracked specimen configurations on the apparent fracture toughness of the green sandstone, a series of fracture experiments were conducted utilizing four distinct types of specimens. The experimental results show that the cracked straight-through Brazilian disk (CSTBD) specimens observed the minimum mode I fracture toughness KIC and the maximum mode II fracture toughness KIIC. The KIC measured by notched semi-circular bending (NSCB) specimens is nearly twice that of CSTBD specimens, while the KIIC is only 77% of CSTBD specimens. It indicates that both the specimen configurations and loading conditions are significant factors influencing the apparent fracture toughness, which may be attributed to the different T-stress for different specimens. Furthermore, several fracture criteria were employed to evaluate the experimental results. Simultaneously, a theoretical framework based on the generalized maximum tangential strain (GMTSN) criterion was proposed to investigate the impact of T-stress on apparent fracture toughness. The results indicate that positive T-stress can improve the KIC, while negative T-stress can decrease the KIC. In addition, we also found that the dependence of KIIC on T-stress is exactly opposite to that of KIC. The study provides theoretical references for systematically evaluating experimental results and selecting specimens reasonably.

Effective delivery of miR-150-5p with nucleus pulposus cell-specific nanoparticles attenuates intervertebral disc degeneration.

The use of gene therapy to deliver microRNAs (miRNAs) has gradually translated to preclinical application for the treatment of intervertebral disc degeneration (IDD). However, the effects of miRNAs are hindered by the short half-life time and the poor cellular uptake, owing to the lack of efficient delivery systems. Here, we investigated nucleus pulposus cell (NPC) specific aptamer-decorated polymeric nanoparticles that can load miR-150-5p for IDD treatment. The role of miR-150-5p during disc development and degeneration was examined by miR-150-5p knockout (KO) mice. Histological analysis was undertaken in disc specimens. The functional mechanism of miR-150-5p in IDD development was investigated by qRT-PCR assay, Western blot, coimmunoprecipitation and immunofluorescence. NPC specific aptamer-decorated nanoparticles was designed, and its penetration, stability and safety were evaluated. IDD progression was assessed by radiological analysis including X-ray and MRI, after the annulus fibrosus needle puncture surgery with miR-150-5p manipulation by intradiscal injection of nanoparticles. The investigations into the interaction between aptamer and receptor were conducted using mass spectrometry, molecular docking and molecular dynamics simulations. We investigated NPC-specific aptamer-decorated polymeric nanoparticles that can bind to miR-150-5p for IDD treatment. Furthermore, we detected that nanoparticle-loaded miR-150-5p inhibitors alleviated NPC senescence in vitro, and the effects of the nanoparticles were sustained for more than 3months in vivo. The microenvironment of NPCs improves the endo/lysosomal escape of miRNAs, greatly inhibiting the secretion of senescence-associated factors and the subsequent degeneration of NPCs. Importantly, nanoparticles delivering miR-150-5p inhibitors attenuated needle puncture-induced IDD in mouse models by targeting FBXW11 and inhibiting TAK1 ubiquitination, resulting in the downregulation of NF-kB signaling pathway activity. NPC-targeting nanoparticles delivering miR-150-5p show favorable therapeutic efficacy and safety and may constitute a promising treatment for IDD.

SiRNA incorporated in slow-release injectable hydrogel continuously silences DDIT4 and regulates nucleus pulposus cell pyroptosis through the ROS/TXNIP/NLRP3 axis to alleviate intervertebral disc degeneration.

In this investigation, we administered oxidative stress to nucleus pulposus cells (NPCs), recognized DNA-damage-inducible transcript 4 (DDIT4) as a component in intervertebral disc degeneration (IVDD), and devised a hydrogel capable of conveying small interfering RNA (siRNA) to IVDD. An in vitro model for oxidative stress-induced injury in NPCs was developed to elucidate the mechanisms underlying the upregulation of DDIT4 expression, activation of the reactive oxygen species (ROS)-thioredoxin-interacting protein (TXNIP)-NLRP3 signalling pathway, and nucleus pulposus pyroptosis. Furthermore, the mechanism of action of small interfering DDIT4 (siDDIT4) on NPCs in vitro was validated. A triplex hydrogel named siDDIT4@G5-P-HA was created by adsorbing siDDIT4 onto fifth-generation polyamidoamine (PAMAM) dendrimer using van der Waals interactions, and then coating it with hyaluronic acid (HA). In addition, we established a rat puncture IVDD model to decipher the hydrogel's mechanism in IVDD. A correlation between DDIT4 expression levels and disc degeneration was shown with human nucleus pulposus and needle-punctured rat disc specimens. We confirmed that DDIT4 was responsible for activating the ROS-TXNIP-NLRP3 axis during oxidative stress-induced pyroptosis in rat nucleus pulposus in vitro. Mitochondria were damaged during oxidative stress, and DDIT4 contributed to mitochondrial damage and ROS production. In addition, siDDIT4@G5-P-HA hydrogels showed good delivery activity of siDDIT4 to NPCs. In vitro studies illustrated the potential of the siDDIT4@G5-P-HA hydrogel for alleviating IVDD in rats. DDIT4 is a key player in mediating pyroptosis and IVDD in NPCs through the ROS-TXNIP-NLRP3 axis. Additionally, siDDIT4@G5-P-HA hydrogel has been found to relieve IVDD in rats. Our research offers an innovative treatment option for IVDD.

Study on Fracture Characteristics of Layered Sandstone under Asymmetric Loading.

In engineering practice, layered rock masses often display obvious anisotropy while deforming and failing, and the failure mode directly impacts the engineering construction stability. In this study, the fracture failure load, fracture toughness, crack deflection angle, and failure mode of a layered rock mass under different fracture modes were analyzed by utilizing improved asymmetric semi-circular disc specimens. According to the constitutive model of transversely isotropic materials, the maximum tensile stress (MTS), maximum energy release rate (MERR), and maximum strain energy density (MSED) calculation formulas were modified, and the calculation formulas of the three prediction criteria under anisotropic materials were derived. The calculation results were compared with the experimental results. The results show that the fracture toughness and crack deflection angle were significantly affected by the weak bedding plane. As a result of applying the MTS criterion, the results are closer to the experimental results, providing a solid foundation for engineering deformation, failure, and fracture analyses.

Effect of crack surface friction on stress intensity factor for double-edge cracked Brazilian disk specimens under parabolic distribution load

The weight function method was employed to derive the closed-form solutions of stress intensity factors (SIFs) for double-edge cracked Brazilian disk (DECBD) specimens subjected to parabolic distribution loads, taking into account the influence of crack surface friction. Additionally, the accuracy and validity of these solutions were discussed in comparison with previous numerical results. Furthermore, the impact of friction coefficient and load distribution angle on SIFs was further investigated. The results indicate that the effect degree of load distribution angle on SIFs is closely correlated with both the loading angle θ and crack length α. Both the mode I and mode II SIFs increase with increasing load distribution angle γ for θ = 15° and α < 0.4. However, when α ≥0.60, the impact of load distribution angle γ on SIFs becomes negligible. Furthermore, the friction between crack surfaces of DECBD specimens significantly affects the dimensionless mode II SIF YII, leading to a decrease in dimensionless mode II SIF YII as the friction coefficient μ increases. Moreover, it further demonstrates that both the relative crack length α and friction coefficient μ play important roles in determining the critical loading angle θIIc for crack sticking. The critical loading angle θIIc for crack sticking increases with an increasing relative crack length; however, an increase in the friction coefficient leads to a reduction of this critical loading angle θIIc.

Effect of high temperature on the mixed mode I-II fracture characteristics of hot-dry rock

To investigate the variation law of rock fracture characteristics with temperature in hot-dry reservoirs, the pure mode I, pure mode II and mixed mode I-II loading experiments were carried out on sandstone and granite at room temperature and after high-temperature (100 °C, 300 °C, 500 °C and 700 °C) treatment by using the central cracked Brazilian disk (CCBD) specimen. The changes of parameters such as failure load, fracture toughness and fracture envelope with temperature were discussed, and the changes of rock mineral composition and fracture surface morphology were analyzed by X-ray diffractometer (XRD) and scanning electron microscope (SEM), respectively. The results showed that the influence of temperature on the fracture characteristics of sandstone and granite presents different evolution laws.With the increase of temperature, the failure modes of sandstone and granite all change from brittle failure to ductile failure, but the critical temperature of the transition is different. Granite shows obvious ductile failure characteristics at 500 °C, while sandstone shows slight ductile failure characteristics at 500 °C.The failure load and fracture toughness of sandstone increase first and then decrease with the increase of temperature, which indicates that within a certain range, the temperature has a toughening effect on sandstone, and can improve its failure resistance. However, the failure load and fracture toughness of granite always decrease with the increase of temperature, which indicates that the temperature only has a deteriorating effect on granite. In the range of 100 °C to 500 °C, the temperature enhances (sandstone) or weakens (granite) the mode I fracture toughness of rocks more than it enhances or weakens the mode II fracture toughness. However, when the temperature is 700 °C, the temperature weakens the mode II fracture toughness more than the mode I fracture toughness. The area enclosed by the fracture envelope of sandstone first increases and then decreases with the increase of temperature, while the area enclosed by the fracture envelope of granite decreases with the increase of temperature. As the temperature increases, the tortuosity of the crack paths in sandstone and granite increases, the cross-section morphology becomes rougher, and the internal fissures and fragmentation increase.

Comparative evaluation of microhardness of three restorative materials after immersion in chlorhexidine mouthwash: An in vitro study

Aim: To evaluate and compare the microhardness of Filtek Z250XT, Beautifil II, and Neo Spectra ST HV after immersion in chlorhexidine mouthwash. Materials and Methods: Thirty disc specimens (10 for each group) made of three different restorative materials, Group 1 – Filtek (3M ESPE), Group 2 – Beautifil II (Shofu), and Group 3 – Neo Spectra ST HV (Dentsply). To simulate 1 year of daily mouthwash use, 10 specimens from each group were immersed in chlorhexidine, kept in an incubator at 37°C for 12 h, and later subjected to microhardness measurement using Vicker’s hardness test. Finally, analysis of variance and post hoc tests were used to analyze the results statistically. Results: A significant reduction in microhardness was observed after immersion in chlorhexidine in Groups 1 and 3 compared to Group 2. Conclusions: Filtek Z250XT exhibits the highest microhardness compared to the other two materials. However, Beautifil II is more resistant to chlorhexidine mouthwash and does not show a significant reduction compared to the other two restorative materials.

Average grain size evaluation using scattering-induced attenuation of coda waves

Grain size is one of the key microstructural factors affecting the mechanical properties of polycrystalline metal materials. In this study, a novel method for grain size evaluation using ultrasonic coda waves is proposed. Different from conventional bulk wave methods that require a point-by-point scanning of the structure, the proposed method allows for a rapid evaluation of the average grain size of the whole part from a single inspection location using one-pass testing data. A piecewise energy attenuation function dealing with different attenuation mechanisms is proposed to obtain the effective attenuation coefficient of coda waves. A power-law model is constructed to correlate the effective attenuation coefficient with the average grain size. Ultrasonic testing on nickel-based superalloy plate specimens with different average grain sizes is performed for model calibration and method verification. The applicability and robustness of the proposed method are further validated using a realistic turbine disk specimen with an irregular shape and non-uniform grain sizes. Results show that the proposed method yields a reliable and accurate estimation of the average grain size with a maximum relative error less than 20 %.

Glutamine Mitigates Oxidative Stress-Induced Matrix Degradation, Ferroptosis, and Pyroptosis in Nucleus Pulposus Cells via Deubiquitinating and Stabilizing Nrf2.

Aims: Intervertebral disc degeneration (IDD) is closely related to low back pain, which is a prevalent age-related problem worldwide; however, the mechanism underlying IDD is unknown. Glutamine, a free amino acid prevalent in plasma, is recognized for its anti-inflammatory and antioxidant properties in various diseases, and the current study aims to clarify the effect and mechanism of glutamine in IDD. Results: A synergistic interplay was observed between pyroptosis and ferroptosis within degenerated human disc specimens. Glutamine significantly mitigated IDD in both ex vivo and invivo experimental models. Moreover, glutamine protected nucleus pulposus (NP) cells after tert-butyl hydroperoxide (TBHP)-induced pyroptosis, ferroptosis, and extracellular matrix (ECM) degradation in vitro. Glutamine protected NP cells from TBHP-induced ferroptosis by promoting the nuclear factor erythroid 2-related factor 2 (Nrf2) accumulation by inhibiting its ubiquitin-proteasome degradation and inhibiting lipid oxidation. Innovation and Conclusions: A direct correlation is evident in the progression of IDD between the processes of pyroptosis and ferroptosis. Glutamine suppressed oxidative stress-induced cellular processes, including pyroptosis, ferroptosis, and ECM degradation through deubiquitinating Nrf2 and inhibiting lipid oxidation in NP cells. Glutamine is a promising novel therapeutic target for the management of IDD.