Testing Machine Research Articles

Impact of radiation therapy regimen on the dislodgement resistance of endodontic sealers: A micro push-out test

PurposeThis study aimed to assess the impact of the radiation therapy regimen on the dislodgement resistance of endodontic sealers of different bases through a micro push-out test. Materials and methodsDentin slices were obtained from the cervical and middle root thirds of bovine incisors and distributed into three groups, according to the radiation therapy regimen (n = 30): non-irradiated; 50 Gy; and 70 Gy. Three 1.0 mm diameter root canal-like cavities were made in each dentin slice. Each cavity was filled with the following sealers: AH Plus Jet (epoxy resin), BioRoot RCS (bioceramic) and Endofill (zinc oxide). After 7 days, a micro push-out test was performed in a Universal Testing Machine. Failures were analyzed using a stereomicroscope. Statistical analysis included the application of Three-Way Analysis of Variance (ANOVA) followed by Bonferroni's post-hoc test (α = 5 %). ResultsNon-irradiated specimens filled with AH Plus Jet and BioRoot RCS had higher bond strength than the irradiated ones, regardless of the radiation therapy regimen (p < 0.001). There were no differences between specimens irradiated with 50 Gy and 70 Gy for AH Plus Jet and BioRoot RCS (p > 0.05). There were no differences among non-irradiated and irradiated specimens for Endofill at the cervical third (p = 0.406). Cohesive failure was the most frequent before irradiation. After irradiation, mixed failure was the most frequent. ConclusionRadiation therapy reduced the bond strength of both epoxy resin and bioceramic sealers. The zinc oxide-based sealer exhibited the lowest dislodgement resistance, making it a less suitable option for patients undergoing radiotherapy.

Fabrication of novel halogen-free flame retardant containing functionalized chitosan from fisheries waste through the sol-gel technology and its fire safety performance in polyurethane resin

Chitosan (CS) derived from fisheries waste, such as shrimp and crab shells, was used to fabricate a bio-based, ecofriendly flame retardant. By reacting the –NH2 groups of CS and the NH2 groups of melamine polyphosphate (MPP) with the NCO groups of polymethylene polyphenyl polyisocyanate (PMPI), a novel intumescent flame retardant, CS-PMPI-MPP, was synthesized. Isophorone diisocyanate (IPDI) was reacted with polyol and aminopropyltriethoxysilane (APTS) to form a polyurethane containing silicon (Si-PU), into which the flame retardant was incorporated to produce a high-polymer composite through the sol-gel technology. The structure, thermal properties, flame retardancy, mechanical properties, toxicity, and char formation of the composites were analyzed. Fourier transform infrared spectroscopy, thermogravimetric analysis, limiting oxygen index, cone calorimeter, UL-94, thermogravimetric analysis with infrared spectroscopy, universal testing machine, scanning electron microscopy, X-ray photoelectron spectroscopy, raman spectroscopy, and smoke density test analyses were performed. The thermogravimetric test results indicated an increase in char yield from 0.5 wt% in pristine polyurethane to 25.9 wt% upon the addition of CS-PMPI-MPP, signifying an enhancement in the thermal stability of pristine polyurethane. According to limiting oxygen index and UL-94 data, the incorporation of CS-PMPI-MPP improved the limiting oxygen index and UL-94 ratings from 18.2 % (Fail) to 26.5 % (V-1), demonstrating the exceptional flame-retardant property of CS-PMPI-MPP within the pristine polyurethane formulation.

Comparative evaluation of desensitizing agents on shear bond strength of zirconia to dentin

BackgroundThe purpose of the study is to evaluate the effect of 7 different desensitizing agents on the shear bond strength (SBS) of zirconia restorations to dentin with a self-adhesive resin cement and determine the failure modes.MethodsEighty molars’ occlusal surfaces were ground to expose dentin and were randomly divided into 8 groups (n = 10): 1. Gluma (HEMA/Glutaraldehyde) 2. Bifluoride (Sodium Fluoride/Calcium Fluoride) 3. Admira (Bis-GMA/HEMA) 4. Smart Protect (Glutaraldehyde) 5. Teethmate (Tetracalcium phosphate, Dicalcium phosphate) 6. Clinpro White (Sodium fluoride) 7. BisBlock (Oxalic acid) and 8. Control (No-treatment). After applying the agent, a self-adhesive resin cement (Rely-X U200) was used to lute zirconia discs (4 mm height and 4 mm diameter) to dentin. After stored in distilled water at 37 °C for 24 h, all groups were thermocycled for 2500 cycles between 5 ± 2 °C and 55 ± 2 °C. Specimens were submitted to SBS test with a universal testing machine at a crosshead speed of 0.5 mm/min until failure. SBS values were compared with ANOVA. Post-hoc multiple comparisons were performed with Dunnett T3. The failure modes of specimens were examined with stereomicroscope at a magnification of 20X and the distribution of the failure modes were evaluated with Pearson Chi-Square test.ResultsRegarding mean SBS values in MPa’s; Admira (10.70 ± 3.99), Smart Protect (9.62 ± 3.93), and Gluma (8.90 ± 3.76) treatments showed higher SBS values compared to control group (p < .05) according to ANOVA. The SBS values of Teethmate (5.31 ± 2.37) and Clinpro White (4.32 ± 2.44) were higher than control group but the difference was not found significant (p > .05). BisBlock (2.33 ± 1.94) and Bifluouride (1.60 ± 1.47) groups showed the lowest SBS values but their difference between control group was not found statistically significant (p > .05). Most specimens showed adhesive failure but no statistically significant difference was found in the distributions of failure modes according to Chi-square test.ConclusionWithin the limitation of the study; Admira, Smart Protect, and Gluma increased the SBS of the zirconia restorations to dentin and can be recommended to use on prepared dentin surfaces prior to the cementation.

The Design and Experimental Research on a High-Frequency Rotary Directional Valve

A directional valve is a core component of the electro-hydraulic shakers in fatigue testing machines, controlling the cylinder or motor that drives the piston for reciprocating linear or rotary motion. In this article, a high-speed rotating directional valve with a symmetrical flow channel layout is designed to optimize the force on the valve core of the directional valve. A comparative analysis is conducted on the flow capacity of valve ports with different shapes. A steady-state hydrodynamic mathematical model is established for the valve core, the theoretical analysis results of which are verified through a Computational Fluid Dynamics (CFD) simulation of the fluid domain inside the directional valve. A prototype of the rotatory directional valve is designed and manufactured, and an experimental platform is built to measure the hydraulic force acting on the valve core to verify the performance of the valve. The displacement curves at different commutation frequencies are also obtained. The experimental results show that the symmetrical flow channel layout can significantly optimize the hydraulic force during the movement of the valve core. Under a pressure of 1 MPa, the hydraulic cylinder driven by the prototype can achieve a sinusoidal curve output with a maximum frequency of 60 Hz and an amplitude of 2.5 mm. The innovation of this design lies in the creation of a directional valve with a symmetric flow channel layout. The feasibility of the design is verified through modeling, simulation, and experimentation, and it significantly optimizes the hydraulic forces acting on the spool. It provides us with the possibility to further improve the switching frequency of hydraulic valves and has important value in engineering applications.

Assessing the Different Nanoparticle-Reinforced Bonding Agents on the Shear Bond Strength of Orthodontic Brackets

ABSTRACT Background: The strength of the binding between brackets and tooth surfaces has a major impact on how well orthodontic therapy works. The shear bond strength of orthodontic brackets may be strengthened by the invention of bonding agents supplemented with nanoparticles, thanks to recent developments in nanoparticle technology. Materials and Methods: In order to perform a randomized controlled experiment, 90 human premolars were excised for orthodontic purposes. Three groups of 30 teeth were randomly assigned to each group: Group A used a bonding agent augmented with nanoparticles of titanium dioxide (TiO2), Group B used nanoparticles of zirconium dioxide (ZrO2), and Group C used a standard bonding agent as a reference. The appropriate bonding chemicals were used to attach the brackets to the teeth, and a universal testing equipment was used to measure the shear bond strength. Stereomicroscopic analysis was used to evaluate the failure mechanisms. To do statistical analysis, Tukey’s post hoc test and analysis of variance were used. Results: There were significant differences (P &lt; 0.05) in the mean shear bond strength values across the groups. The average shear bond strength for Group A (TiO2) was 18.5 ± 2.3 MPa, that for Group B (ZrO2) was 17.2 ± 2.6 MPa, and that for Group C (control) was 14.8 ± 2.4 MPa. In comparison to Groups B and C, Group A exhibited a statistically greater bond strength, although Group B also showed an improvement over the control. According to the failure mode analysis, the control group had mostly adhesive failures, whereas the nanoparticle groups saw mixed failures. Conclusion: When TiO2 and ZrO2 nanoparticles are added to bonding agents, the shear bond strength of orthodontic brackets is greatly increased in comparison to traditional bonding agents. TiO2-reinforced materials performed better, pointing to possible benefits for orthodontic applications. It is advised that further study be done to examine the long-term impacts and therapeutic implications of these results.

PENGUJIAN CUTTER ENDMILL HSS DIAMETER 12 MM DENGAN PEMOTONGAN DEPT OF CUT TERHADAP BAJA AMUTIT DI MESIN MILLING LAGUN FU 100 (LFR 25)

This study aims to analyze the relationship between machining parameters and tool wear (flank wear) in the milling process of amutite steel (SKS3) using a 12 mm diameter High-Speed Steel (HSS) endmill cutter. The machining parameters studied included cutting speed (Vc = 14 m/min and 18 m/min), feed rate (F = 30 mm/min and 75 mm/min), and depth of cut (Doc = 0.5, 1, 1.5, 2 and 2.5 mm). The linear regression method was used to build a mathematical model relating these parameters to tool wear. Experimental data were obtained through a series of machining tests with predetermined parameter variations. The regression analysis results showed that tool wear or flank wear (Vb) was significantly affected by cutting speed (Vc), feed rate (F), and depth of cut (Doc), with constant and exponent values obtained through logarithmic transformation and regression analysis. The regression model obtained has a good level of accuracy in predicting tool wear, although there is a difference between the theoretical and actual Vb values. This discrepancy may be caused by factors not measured in the experiment, such as variations in workpiece material or environmental conditions. This research also provides that the 12 mm diameter HSS endmill cutter is proven to be capable of carrying out the depth-of-cutting process on amutite steel material in the Lagun FU 100 milling machine with the specified depth-of-cut.

Miniaturized Shear Testing: In-Plane and Through-Thickness Characterization of Plywood.

This study addresses the challenges associated with conventional plywood shear testing by introducing a novel miniaturized shear test method. This approach utilizes a controlled router toolpath for precise sample fabrication, enabling efficient material use and data acquisition. Miniaturized samples, designed with double shear zones, were tested for τxy, τxz, and τyz configurations using a universal testing machine. Results revealed a mean ultimate shear strength ranging from 5.6 MPa to 7.3 MPa and a mean shear modulus ranging from 0.039 GPa to 0.095 GPa, confirming the orthotropic nature of plywood. The resulting shear behavior was determined with stress-strain curves correlated with failure patterns. The miniaturized tests effectively captured the material's heterogeneous behavior, particularly at smaller scales, and demonstrated consistent load-bearing capacity even after substantial stress reduction, suggesting suitability for bracing applications. This method allows for increased sample sizes, facilitating robust data collection for developing and validating finite element models. Future work will focus on evaluating the scalability of the observed orthotropic behavior and data scatter at larger scales and assessing the potential for this method to replace conventional full-scale plywood shear testing.

Trends of drug-resistant tuberculosis and risk factors to poor treatment-outcome: a database analysis in Littoral region-Cameroon, 2013-2022.

Tuberculosis(TB), currently has limited treatment options, and faces worldwide threat of drug-resistance(DR). In 2022, the DR-TB prevalence in Cameroon was 1.4% among new-cases and 8.3% among retreatment-cases. We analyzed the DR-TB database to descript the trends and DR-TB profile, treatment-outcome and associated risk-factors so-as-to propose measures to enhance program performance in Cameroon. We conducted a retrospective cohort study, analysed the DR-TB database of the Littoral region from 2013 to 2022. We appreciated the data-quality using zero-reporting, completeness, consistency, and validity indicators. We categorized DR-TB into Rifampicin-resistant-TB(RR-TB), multi-drug-resistant-TB(MDR-TB), pre-extensive-drug-resistant-TB(pre-XDR-TB), and XDR-TB and performed descriptive statistics. We assessed DR-TB treatment outcome targeting > 80% cure and/or completed treatment. Multiple logistic regression was used to determine risk factors related to poor treatment outcomes, and adjusted relative risk(RR) was considered significant at p < 0.05. Overall database quality was 93.7% with uniqueness 100%, data-completeness 82.5%, consistency 97% and validity 95.1%. A total of 567 DR-TB cases were reported, with median age of 34 (1-80) years, male-to-female sex ratio (3:2). Cases were classified as 19(3.4%) RR-TB, 536(94.6%) MDR-TB, 7(1.3%) pre-XDR-TB, and 4(0.7%) XDR-TB. Case-reporting increased from 2013, reaching their peak in 2018. The overall treatment refusal rate was 123(11.9%) and treatment outcomes of 270(60.8%) cured, 116(26.4%) completed, 32(7.2%) deaths, 19(4.3%) lost-to-follow-up, and 6(1.4%) failure were recorded. We identified 84 dead (CFR:14.8%) amongst whom 52(62%) refused treatment, 17(20%) occurred during the first month of therapy and 13(15.5%) HIV-TB co-infected. Male gender [p = 0.006, RR = 2.5 (95% CI: 1.3-4.7)], HIV positive status [p = 0.012, RR = 2.1 (95% CI: 1.2-3.7)], and previous DR-TB status [p = 0.02, RR = 3.9 (95% CI: 1.3-12.0)] were statistically associated to poor treatment outcomes. In the Littoral Region-Cameroon, cases of DR-TB increased from 2013, reaching their peak in 2018 befor dropping right up to 2022. RR-TB, MDR-TB, Pre-XDR-TB and XDR-TB represented 3.4%, 94.6%, 1.3% and 0.7% of all reported DR-TB cases. Overall, DR-TB treatment success rate was 87.2%. Male-gender, HIV-positive status, and previous DR-TB are associated with poor TB treatment outcomes. We recommend universal drug susceptibility testing to ensure early/maximum DR-TB case-detection and proper pre-treatment counselling to limit the high death rates and anti-TB treatment refusal rates which are setbacks from achieving end-TB strategies.

Notch fatigue behaviour of friction stir welded AA6061-T651 aluminium alloy joints: Role of microstructure, and residual stresses

The main objective of this study was to investigate the combined effect of microstructure and residual stresses on notch fatigue behaviour of friction stir-welded (FSW) AA 6061-T651 aluminium alloy joints. Two different microstructures of FSW joints were produced at different welding speeds. A completely reverse-rotating fatigue testing machine was utilized to investigate the fatigue properties of notched specimens. The test results showed that the notch fatigue strength of a welded joint made at a speed of 25 mm/min was 33 % of the welded joint’s yield strength and 23 % of its tensile strength. To understand the overall fatigue behaviour of the welded joints, fatigue data were further analyzed using the Basquin equation variables. Microstructure investigation using optical and orientation imaging microscopy, transmission electron microscopy, and X-ray diffraction analysis of the joints was analyzed and discussed. The microstructure complexity and the weld zone tensile residual stress significantly affect the welded joints fatigue behaviour. It was found that the notch fatigue properties of the joints were extremely sensitive to their microstructural characteristics and residual stresses. An increase in tensile residual stresses decreases the notch fatigue life of the welded joints. The results of electron backscattered diffraction analysis indicated that joints with a fine grain microstructure exhibit higher microstructural stability and less initial damage. A fractography investigation showed that joints with fine grain microstructure have increased crack resistance in stage I and lower crack propagation in stage II.

Evaluation of flexural strength of additively manufactured resin materials compared to auto-polymerized provisional resin with and without hydrothermal aging

PurposeAdditive manufacturing (AM) technologies are used to fabricate 3D-printed provisional dental restorations. The purpose of this study was to investigate the flexural strength of 3D-printed resins and compare their mechanical performance with those of conventional resins indicated for provisional restorations. Materials and methodsThis study included six different 3D-printed resin materials, namely (Nextdent (ND); Temp PRINT (TP); Optiprint temp (OT); 3Delta Etemp (DE); Saremco print | CROWNTEC (SA); MED690 (ST)), and one conventional (Protemp (PT)) (Control) provisional resin material. Specimens (N = 168) were prepared (25x2x2 mm3) following ISO 10477:2018 guidelines for temporary materials using a printer (Asiga MAX 3D). Post-processing was accomplished following each manufacturer's recommendation. While half of the specimens were tested after 24 H without aging, the other half was subjected to thermomechanical aging in a custom-made chewing simulator (1.200.000 cycles, 5 °C and 55 °C). Flexural strength of the specimens was determined using a Universal Testing Machine. Data were analyzed using two-way ANOVA followed by Tukey's post-hoc test (α = 0.05). Weibull modulus for each group was calculated based on parametric distribution analysis of censored data for maximum fracture load. ResultsNo significant difference was observed in mean flexural strength (MPa) when non-aged and aged conditions were compared in the OT and PT groups (p>0.05). Groups ND, SA, TP, DE, and ST presented significant differences ranging between 12.67 and 57.39 MPa (p<0.05). All groups presented lower shape and scale values in aged groups compared to their non-aged counterparts. While OT and PT maintained their flexural strength after aging, ND exhibited the highest decrease (30%), followed by DE (23.8%), SA (16.2%), TP (12%), and ST (8.6%) in descending order. Weibull modulus decreased as a function of aging except in group ST. ConclusionSignificant effect of themomechanical aging especially on ND and DE materials should be considered with caution when such materials are indicated as interim or long-term interim provisional restorations. SA and TP exceeded the expectations from a provisional material compared to that of the conventional control material PT.

Experimental Analysis of the Mechanical Properties of Carbon Foams Under Quasi-Static Compressive Loads.

This article sought to determine the response of a carbon foam material derived from polyurethane foam when subjected to a quasi-static compression load. The effects of the foam pore densities and additives (solvents) on the compression strength, compressive modulus, and surface morphology of the carbon foam were investigated. In this study, three different carbon foam pore densities (20, 40, and 60 ppi) and three solvents for the phenol-formaldehyde resins that coated the polymer foam (acetone, ethanol, and methanol) were used. Carbon foams were derived from polyurethane foams by carbonization. Quasi-static compression testing was carried out using a universal testing machine. The compressive strength, compressive modulus, and relative density of these different carbon foams were computed and compared. Two-way ANOVA analyses were performed to compare the significance of solvents and pore density. These results showed that pore density and solvents significantly affected the compressive strength, compressive modulus, and surface morphology of the fabricated polyurethane-derived carbon foam. Finally, the maximum compressive strength and maximum compressive modulus were observed in carbon foam (60 ppi) with 40% methanol as the solvent. Conversely, a minimum compressive strength was observed for a 20 ppi carbon foam with a 20% acetone solvent, and a minimum compressive modulus was observed for a 20 ppi foam with 40% methanol. Lastly, the chemical composition of the polyurethane foams was investigated, and these results indicated that the polyurethane-derived carbon foam had 96% carbon atoms after carbonization.

Estimation of Tensile and Flexure Strength of Hybrid Composites along with Epoxy as Matrix and Jute &amp; E-Glass as Reinforcements

The natural fibers have the good properties such as mechanical and physical than artificial fibers in a many cases during the fabrication of composite materials that are used in many engineering applications. Also hybridization of fibers leads to impotent of mechanical properties these composites used in interior of aerospace vehicles, automobiles bumpers, decorative items, window panels, interior paneling, etc. where application pf load is very less. This research work is concentrated on the evolution of hybrid composite of Jute/E-glass reinforced with matrix epoxy using Hand layup method. Laminated composites specimens are prepared by calculating the required number of fiber layers and quantity of matrix based on the different volume fraction. The testing specimens are prepared for Tensile and Bending test as per standard of ASTM. The Universal Testing Machine is used to conducted Tensile and Bending test and results are plotted the graphs.

Investigation of mechanical characteristics and sustainable practices in concrete incorporating recycled marble waste

Due to the rapid expansion of infrastructure, urbanization, and industry, there is a constant need for concrete worldwide. However, the expansion of the concrete sector increases pressure on natural resources, endangering the balance of the ecosystem. Thus, it would be advantageous to meet current concrete needs without reducing production quality by incorporating recycled materials into concrete mixes. In this work, we investigate the mechanical characteristics of environmentally friendly concrete using recycled marble powder (WMP) partially replacing cement and marble coarse aggregates (MCA) as an alternative to natural coarse aggregates. The qualities of the concrete were evaluated using a combination of destructive and non-destructive testing techniques. In this study, three series of mixes were prepared. The first series (S1) is composed of 100% natural coarse aggregates. In the second series (S2), 50% of the natural coarse aggregates are substituted for marble coarse aggregates, while the third series (S3) is composed of 100% marble coarse aggregates. In each of the three series, Marble powder was used in place of cement at a percentage ranging from 5% to 20%, increasing by 2.5%. Concrete mixes were developed and evaluated with different levels of marble waste substitution to compare their compressive strengths and workability to those of traditional concrete made from 100% natural aggregates. Simultaneously, the strength characteristics were measured using the Schmidt hammer and ultrasonic velocity tests. As was mentioned, in the three series, when Cement is replaced with marble powder, the slump decreases, even though the incorporation of marble coarse aggregates tends to increase this workability, while the compressive strength shows an increase of 28.66% and 31.63% compared to the control mix for 50% and 100% substitute of natural coarse aggregates with marble coarse aggregates, respectively. It is also noteworthy that concrete containing marble waste exhibits normal ultrasonic velocity. For concrete mixtures of series (S1), (S2), and (S3), respectively, the velocity of ultrasonic pulses increased by 18.20%, 27.44%, and 27.98%, while the Schmidt Rebound Number increased by 10.13%, 14.52%, and 21.37%, respectively, in contrast to the values of the control mixture. Additionally, the reliability of results from the universal testing machine (UTM) was validated through correlation analysis of compressive strength measurements obtained by various methods. The study's findings are intriguing and underscore the potential of employing marble waste as an alternative to natural aggregates.

Investigation of the Effect of Al2O3 Nanoparticle-Added MQL Lubricant on Sustainable and Clean Manufacturing

In this study, in order to improve the characteristics of the vegetable-based cutting fluids used in the MQL technique and increase the machining performance of MQL and its positive effects on sustainable manufacturing, the effects of the MQL method with nano-Al2O3 additives on surface roughness (Ra) and cutting temperature (Ctt) were examined through turning experiments carried out by adding nano-Al2O3 to the vegetable-based cutting fluid. For this purpose, machining tests were carried out on hot work tool steel alloyed with Cr-Ni-Mo that has a delivery hardness of 45 HRC. In hard machining experiments, three techniques for cooling and lubricating (dry cutting, MQL, and nano-MQL), three cutting speeds (V) (100, 130, 160 m/min), three feed rates (f) (0.10, 0.125, and 0.15 mm/rev), and two different ceramic cutting tools (uncoated and TiN-coated with PVD methods) were used as control factors. For Ra, the nano-MQL method provided an average of 21.49% improvement compared to other cooling methods. For Ctt, this rate increased to 26.7%. In crater wear areas, the nano-MQL method again exhibited the lowest wear values, decreasing performance by approximately 50%. The results of this research showed that the tests conducted using the cooling of nano-MQL approach produced the best results for all output metrics (Ra, Ctt, and crater wear).

A timespace of zero‐COVID in Southwest China: Building community, governing time

AbstractIn this article, I take the organization of universal COVID testing as a point of departure for understanding the lived experiences of China's zero‐COVID policy and look at “the Community” (shequ) as a dynamic interface between the state and urban residents during the liminal time of a global pandemic. Drawing on Bryant and Knight's notion of “vernacular timespace” (2019), I analyze the timespace of zero‐COVID as a state‐regulated future orientation interwoven with collective anticipation of crisis, bureaucratic temporal governance, and contestations over time as a form of agency in everyday life. Instead of assuming a unitary form of present‐future relationship that was homogeneous and unchallenged, I argue that the collective anticipation of a public health crisis was constantly shaped, managed, and contested throughout the processes of pandemic community building. This research hopes to enrich reflections on the interplays of time, power, and legitimacy in post‐pandemic urban governance.

Energy distribution in 1D chains of foam disks subjected to low-velocity impact at different temperatures

A series of experiments is conducted to study energy transfer in a chain of foam disks as a function of temperature. These experiments use two different densities of closed-cell Polyvinyl Chloride foams as an array. A puncture testing machine impacts the chain at a velocity of 1 m/s at five different temperatures. Piezoelectric sensors capture the output and input forces of the chain during the impact, while high-speed cameras record the disk deformations. The chain’s energy retention is computed using disk deformations and loading forces. Results indicate that high-density foam chains exhibit significantly higher force and energy retention than low-density counterparts. Notably, the foam’s stiffness decreases with rising temperature, more prominently in higher-density foam. However, the proportion of energy retained by the chains remains relatively consistent across different temperatures. Additionally, both foam types show a pattern of exponential decay in energy retention along the chain. These insights offer implications for designing and optimizing energy-absorbing foam systems, paving the way for enhanced energy mitigation in low-velocity impact applications.

Experimental study of fractures of the posterior pelvic ring C1.1 using LC-II screws and internal fixation by plate

IntroductionTo compare the biomechanical outcomes of C1.1 posterior pelvic ring fractures treated with different numbers of LC-II screws and plate internal fixation.Materials and methodsNine adult preserved pelvic specimens were used. After being measured by bone densitometry, the specimens were randomly divided into 3 groups of 3 pelvic specimens each. The C1.1 pelvic fractures were generated by iliac osteotomies and anterior pelvic ring osteotomies. The fractures were fixed and randomly divided into three groups: (1) one LC-II screw, (2) two LC-II screws, and (3) two reconstruction plates. The anterior pelvic rings were all fixed with pubic branch screws. A biomechanical testing machine loaded all specimens vertically, recording the displacement and ultimate load of the specimens to quantify the stiffness.ResultsWhen loads up to 1000 N were applied, the displacement of the iliac bone was close between the one LC-II screw and the two LC-II screw group specimens; (P > 0.05); when loads such as 1000 N, 1200 N and 1400 N were applied, there was no significant difference in displacement between the plate fixation group and the two LC-II screw fixation group (P > 0.05), both of which were superior to the one LC-II screw fixation group (P < 0.05). There was no significant difference in compressive stiffness between the two LC-II screw fixation groups and the plate fixation group (P > 0.05), and both were superior to the one LC-II screw fixation group (P < 0.05) the ultimate load of both the two LC-II screws and the steel plate is greater than that of one LC-II screw (1.74 times the ultimate load of one LC-II screw for the two LC-II screws and 1.83 times the ultimate load of one LC-II screw for the steel plate).ConclusionFor posterior pelvic ring fractures of type C1.1, placement of two LC-II screws provides comparable posterior pelvic ring stability compared to reconstructed plates. At loads below 1000 N, one LC-II screw fixation and two LC-II screws were comparable in restoring posterior pelvic ring stability.

Investigation on tribo‐properties of twaron pulp‐reinforced brake friction composites

AbstractDetermining the appropriate formulation in designing and developing brake friction materials is one of the most complex tasks. This study investigates the synergistic effect and optimization of twaron fiber on the fade and recovery performance of brake friction composites. For this purpose, a series of friction materials containing varying amounts of twaron between 1 and 9 wt% were developed, and their characterization and tribo evaluation were carried out. The tribo performance of the composites was evaluated in a Krauss‐type friction test machine in line with the ECE R90 procedure in terms of their fade and recovery behaviors. It was noted that the fade‐recovery friction response of composites was affected when fiber is added; that is, an increase in fiber content improved the fade performance, friction fluctuations decreased, and a higher recovery response was observed. The fade and average coefficient of friction were found to be the main determinants, while recovery was found to be the stabilizer. Analytical hierarchy process (AHP) was used to determine the priority of importance of criteria in the performance evaluation, and VIKOR (multi‐criteria optimization compromise solution) was used for ranking evaluation. The formulation with a concentration of twaron 7 wt% was found to have exhibited an optimal braking performance. The worn surfaces scanning electron microscope (SEM) study confirms the general friction and wear mechanisms of friction layers with fiber content.Highlights Development of twaron pulp‐reinforced eco‐friendly brake friction composites. Use of MCDM approach in the development of BFCs for braking applications. VIKOR optimization positioned 7 wt% twaron‐addition BFC as the optimal choice. It was observed that fiber amount is effective on the behaviors of composites.

Laboratory experimental of ballast–bituminous–latex–roving (Ballbilar) layer for conventional rail track structure

Abstract Ballast structures continue to be utilized in Indonesia’s railway system. They are essential for conventional railway lines, which experience high levels of stress and are susceptible to damage from train traffic. This study examined the utilization of a pressure test machine and sieve analysis to determine the abrasion value of ballast made of 60/70 penetration asphalt with a binder and stabilizer material consisting of a mixture of latex and roving fiber. The test results revealed that the compressive strength of the ballast structure was positively affected by the addition of asphalt, latex, and roving fiber. However, when comparing the compressive strengths of the two ballast structures, the ballast structure with 2% asphalt and 3% latex generated superior results to that with 4% asphalt and 1% latex. In other words, asphalt, as opposed to latex, was more effective in protecting ballast material from abrasion.

Effects of precuring heating modalities on the shear bond strength and adhesive remnant index of orthodontic adhesive

Aim: This study aimed to investigate precuring adhesive and bracket heating\cooling protocol on shear bond strength (SBS) and adhesive remnant index (ARI). Methods: 70 newly extracted lower premolars categorized randomly into 7 groups (n = 10 (ten teeth each)) according to adhesive and/or brackets temperatures. Pre-curing, the 3M Transbond PlusTM XT adhesive temperature was adjusted to 5, 22, 40, 70°C, while the brackets were stored at 5, 55°C before bonding. Also, adhesive and brackets were heated by tooth dryer before curing representing the seventh group. The samples were stored in deionized water for 24h at 37°C in dark incubator before debonding by universal testing machine. Analysis of variance (ANOVA) and post Hoc Tukey statistical tests were performed for SBS analysis, while Kruskal Wallis test analyzed ARI data (α=0.05). Results: Significant differences were found among the groups regarding SBS and ARI where p = 0.00, 0.024 respectively. SBS significantly increased when the adhesive temperature modified to 5°C and 70°C and brackets temperature adjusted to 5°C and 55°C. Also, heating the adhesive and brackets by tooth dryer generated peak SBS. While, heating the adhesive to 40°C declined SBS significantly. Conclusions: Lowering the temperature of the adhesive and/or brackets to 5°C and elevation their temperature above 55°C pre-curing has favorable effects on SBS. Storing the adhesive at 40°C before bonding showed reductions in SBS. Also, heating both the adhesive and brackets pre-curing formed all-out SBS with reduced ARI.