Flexural Strength Research Articles

Effects of carbon nanotubes and carbon fibers on the properties of ultra-high performance concrete for offshore wind power generation

Ultra-high performance concrete (UHPC), as one of the most eye-catching building materials, has been the subject of extensive research by scholars. On this basis, to expand the application of UHPC for offshore wind turbine towers in complex marine environments, three different fiber materials - copper-plated microfibre steel fibers, carbon fibers, and carbon nanotubes (CNTs) - have been selected for the study of the possibilities of further improving the mechanical properties of UHPC. This study focused on understanding the impact of various fiber combinations and dosages on the flowability, compressive strength, flexural strength, and tensile strength of UHPC. Our findings indicate that carbon fiber, when present at a concentration of up to 0.5%, the effect on the fluidity of UHPC is only about 1.05%. However, the addition of CNTs significantly diminishes the flowability of UHPC, with a consistent decrease observed as the CNT content increases. Notably, when carbon fiber and CNTs are used in combination, the maximum reduction in flowability reaches 7.8%. Furthermore, as the dosage of these fibers increases, the compressive strength, flexural strength, and tensile strength of UHPC all demonstrate a positive trend of improvement. It is observed that the optimal performance is achieved when both carbon fiber and CNTs are present. In particular, carbon fiber exhibits a more profound impact on enhancing compressive strength and flexural strength, when carbon fibers were doped by volume at 0.5%, the compressive and flexural strengths were increased by 6.7% and 11.7%, respectively, compared to the control group, while carbon nanotubes increased the tensile strength by 7.4% at lower dosage. These findings highlight the potential of fiber combinations to optimize UHPC’s mechanical properties for various engineering applications..

Hybrid machine learning approach to prediction of the compressive and flexural strengths of UHPC and parametric analysis Shapley additive explanations algorithm

Ultra-high-performance concrete (UHPC) is a sustainable construction material; it can be applied as a substitute for cement concrete. Artificial intelligence methods have been used to evaluate concrete composites to reduce time and money in the construction industries. So, this study applied machine learning (ML) and hybrid ML approaches to predict the compressive and flexural strength of UHPC. A dataset of 626 compressive strength and 317 flexural strength data points was collected from the published research articles, where fourteen important variables were selected as input parameters for the analysis of hybrid ML and ML algorithms. This research used XGBoost, LightGBM, and hybrid XGBoost- LightGBM algorithms to predict UHPC materials. Grid search (GS) techniques were used to adjust model hyper-parameters in search of improved high accuracy and efficiency. ML and hybrid ML models were train, and the test stage utilized statistical assessments such as R-square, root mean square error (RMSE), mean absolute error (MAE), and coefficient of efficiency (CE). The results presented hybrid ML algorithm was superior to the XGBoost and LightGBM algorithms in terms of R-square and RMSE values for both compressive strength and flexural strength prediction. A hybrid ML model and two ML models showed CS considerable R-square values above 0.94 at the testing stages and just over 0.97 at the training phase. Hybrid ML model performance accuracy for CS prediction was R-square value found that almost 0.996 for training and 0.963 for testing phases. At the same time, the FS prediction result showed that the R-square value of the Hybrid ML model and two traditional ML models were founded at almost 0.95 for the training phase and around 0.81 for the testing phase. But among them, the hybrid XGB-LGB model prediction performance was high accuracy and lowest error for CS and FS of UHPC trained and its hyperparameters optimized. Additionally, the SHAP investigation reveals the impact and relationship of the input variables with the output variables. SHAP analysis outcome reveals that curing age and steel fiber content input parameter had the highest positive impact on compressive strength and flexural strength of UHPC.

Assessing the Influence of Sugarcane Bagasse Ash for the Production of Eco-friendly Concrete: Experimental and Machine Learning Approaches

The innovative utilization of sugarcane bagasse ash (SCBA) in producing lightweight concrete (LWC) needs to be explored experimentally and quantification with machine learning approaches. Therefore, this study aims to investigate fresh, mechanical and microstructural characteristics and machine learning modeling of incorporating SCBA as a partial substitute of cement. In this investigation, OPC was replaced partially by the weight of SCBA in the proportion of 0%, 5%, 10%, 15%, and 20%. The influences of SCBA on the fresh characteristics of concrete were investigated through tests of the slump, compaction factor, Kelly ball, k-slump, density, and air content. In addition, for hardened properties compressive, splitting tensile, flexural strength, and static modulus of elasticity were tested at 7 and 28 days. Furthermore, a microstructural characteristic was carried out for varying content of SCBA. Different machine learning (ML) predictive models were performed utilizing artificial neural network (ANN) and random forest (RF), to predict the fresh and mechanical attributes of the LWC. It was noticed that the workability value of fresh concrete was enhanced almost by 40% to 50% with the incorporation of SCBA content. The hardened test results revealed that a mixture having SCBA up to 10% content SCBA resulted in nearly 10% to 30% better performance to satisfy the requirement of LWC. Regarding the sustainability assessment, the less embodied CO2 (eCO2) is produced in SCBA mixes, whereas it is also economically beneficial to produce SCBA mixes. Models' efficacy was evaluated including mean absolute error (MAE), root mean squared error (RMSE), and coefficient of determination (R2). The maximum R2 and minimum RMSE came across for RF (0.989 and 1.393, respectively) which provides the well estimation of the model.

Thermo-Mechanical Properties of Particulate Banana Epoxy Composite with Fruit Waste (Dragon Fruit Peel) Micro Filler for Household Applications

This study evaluates the thermo-mechanical characteristics of eco-friendly composite made of particulate banana fiber (reinforcement), epoxy resin (matrix) and dragon fruit peel powder (micro filler). The composites were developed using compression moulding technique with 3 factors, 4 variations and Taguchi orthogonal array design (L16). The proposed filler characterization results revealed that the density was 0.97 g/cm3 and combination of C–O, Ca–O, and Ca–Co could improve mechanical strength. Composites with 5 mm fiber length, 40 wt.% fiber weight, and 15 wt.% filler weight have a maximum tensile strength of 25.58 MPa, flexural strength of 44.47 MPa, impact strength 180.33 J/m, and hardness of 82.50 SD. The best composite’s thermal, wear, water and fatigue studies were proposed to suit household applications. The proposed filler improves fiber-resin bonding, which increases thermal stability to 245 °C, wear resistance, decreases water absorption, and results in a fatigue life count of 121000 cycles. Thus, this study concluded that the increasing filler content and decreasing particulate size had an impact on the thermo-mechanical characteristics of banana-reinforced polymeric composites. As a result, an eco-friendly polymeric composite mixer coupler model was developed. Comparative structural and model analyses were performed using ANSYS R17.2. The analysis results confirmed that the proposed composite had higher natural frequencies of 2766.5 Hz and lower deformation values of 0.089293 mm. This proves the proposed eco-friendly composite is a suitable replacement for a synthetic mixer coupler.

Effect of freeze-thaw cycles and chloride salt erosion coupling conditions on fatigue properties of PE-ECC

Engineered cementitious composites (ECC), which are a kind of novel composite building material with high ductility and high toughness, can be utilized in areas susceptible to salt-freezing damage, such as that caused by snowmelt agents, seawater, and saline soils. In this paper, engineered cementitious composites reinforced with polyethylene fibers (PE) are analyzed to study the changes in the flexural static load properties, and flexural fatigue life of PE-ECC specimens after four different freeze-thaw cycles (0, 50, 100 and 150) in fresh water and a 3.5% mass fraction NaCl solution. The results show that upon reaching 150 freeze-thaw cycles, there was a notable disparity in the relative equivalent flexural strength between specimens subjected to chloride salt freeze-thaw and freshwater freeze-thaw environments, with the former exhibiting a 1.07-fold increase in damage compared to the latter specimens. Using the relative dynamic elastic modulus as the damage variable, a relationship model was made between the relative equivalent flexural strength and the freeze-thaw damage degree of PE-ECC in two freeze-thaw environments. The flexural fatigue life of PE-ECC after freeze-thaw obeyed a two-parameter Weibull distribution, and the P-S-N curves at various reliability probabilities correlated well with the test results. The safety coefficient of PE-ECC varied with changes in freeze-thaw conditions, necessitating an increase in the safety coefficient to assure structural safety in locations with more severe freeze-thaw damage. The results of this study can serve as a reference for the development of freeze-thaw-resistant designs for PE-ECC structures in future applications.

Effect of adding natural coconut oil on the antifungal, flexural strength, and hardness properties of heat cure acrylic resin (an in vitro study)

Purpose. This study's objective was to estimate the effect of various quantities of the addition of natural coconut oil according to concentrations (1%, 2%, 3%) on the heat cured denture base material's anti-fungal, flexural strength, and hardness properties. Material and method. A total of 120 samples were created and (divided into three groups each groups contain forty samples) built regarding the attitude test: Candida albicans adherence test, flexural strength test, and hardness test. Next, each group was subdivided into three subgroups (control 0%, 1%, 2% and 3%) based on the various quantities of the added natural coconut oil, with (n=10 samples for each subgroup). Each group was assessed at 48 hours. One-way ANOVA and other statistical methods were used to analyze the data, Duncan and Dunnett’s tests for comparison means among all groups with control at p ≤0.05. Results. A One-way ANOVA showed a significant difference in the mean values of Candida albicans adherence, with the additive of natural coconut oil groups (1%, 2%) showing the highest antifungal effect compare with (3% additive groups). Adding 1% coconut oil had no significant difference on hardness and flexural strength, while adding 2% and 3% additive of coconut oil groups showed a significantly decrease than control groups at p ≤ (0.05). Conclusion. The antifungal properties of heat-cured acrylic resin are enhanced by the addition of coconut oil. However, when used in high concentrations (greater than 1%), it can result in a decrease in hardness and flexural strength.

Strong and Tough MXene Bridging-induced Conductive Nacre.

Nacre is a classic model, providing an inspiration for fabricating high-performance bulk nanocomposites with the two-dimensional platelets. However, the "brick" of nacre, aragonite platelet, is an ideal building block for making high-performance bulk nanocomposites. Herein, we demonstrated a strong and tough conductive nacre through reassembling aragonite platelets with bridged by MXene nanosheets and hydrogen bonding, not only providing high mechanical properties but also excellent electrical conductivity. The flexural strength and fracture toughness of the obtained conductive nacre reach ~282 MPa and ~6.3 MPa m1/2, which is 1.6 and 1.6 times higher than that of natural nacre, respectively. These properties are attributed to densification and high orientation degree of the conductive nacre, which is effectively induced by the combined interactions of hydrogen bonding and MXene nanosheets bridging. The crack propagations in conductive nacre are effectively inhibited through crack deflection with hydrogen bonding, and MXene nanosheets bridging between aragonite platelets. In addition, our conductive nacre also provides a self-monitoring function for structural damage and offers exceptional electromagnetic interference shielding performance. Our strategy of reassembling the aragonite platelets exfoliated from waste nacre into high-performance artificial nacre, provides an avenue for fabricating high-performance bulk nanocomposites through the sustainable reutilization of shell resources.

Strong and Tough MXene Bridging‐induced Conductive Nacre

AbstractNacre is a classic model, providing an inspiration for fabricating high‐performance bulk nanocomposites with the two‐dimensional platelets. However, the “brick” of nacre, aragonite platelet, is an ideal building block for making high‐performance bulk nanocomposites. Herein, we demonstrated a strong and tough conductive nacre through reassembling aragonite platelets with bridged by MXene nanosheets and hydrogen bonding, not only providing high mechanical properties but also excellent electrical conductivity. The flexural strength and fracture toughness of the obtained conductive nacre reach ~282 MPa and ~6.3 MPa m1/2, which is 1.6 and 1.6 times higher than that of natural nacre, respectively. These properties are attributed to densification and high orientation degree of the conductive nacre, which is effectively induced by the combined interactions of hydrogen bonding and MXene nanosheets bridging. The crack propagations in conductive nacre are effectively inhibited through crack deflection with hydrogen bonding, and MXene nanosheets bridging between aragonite platelets. In addition, our conductive nacre also provides a self‐monitoring function for structural damage and offers exceptional electromagnetic interference shielding performance. Our strategy of reassembling the aragonite platelets exfoliated from waste nacre into high‐performance artificial nacre, provides an avenue for fabricating high‐performance bulk nanocomposites through the sustainable reutilization of shell resources.

Effect of cellulose nanocrystals on the mechanical and free vibration behavior of hybrid glass/kenaf fiber reinforced polyurethane core-based sandwich structures

ABSTRACT Engineering applications widely use foam-core-based sandwich structures. The study incorporated cellulose nanocrystals (CNC) into a hybrid glass/kenaf fiber-based polymeric sandwich structure with a 65 kg/m3 polyurethane foam core. Four unique face sheets (S1, S2, S3, and S4) were made using glass, kenaf, and CNC. Three-point bending, Charpy impact testing, and free vibration testing were used to characterize sandwich structures. The inclusion of CNC in the matrix of face sheets improved the hybrid composite’s bending strength and impact resistance. One layer of Kenaf fabric and two layers of glass make up the hybrid composite, which is stronger in both flexural strength and impact resistance, with 14.56 MPa and 8.1 J, respectively. These improvements are 44.84% and 57.49% compared to the pure glass/epoxy composite face plate. Nevertheless, the incorporation of Computer Numerical Control (CNC) failed to result in a substantial enhancement in vibration characteristics. Both matrix modification and natural fiber (kenaf) can effectively substitute glass fabric in sandwich structures.

A Sustainable Revolution in Sisal Fiber with Enhanced Mechanical Properties of Concrete

Introduction This study provides a comprehensive comparative analysis of conventional concrete (CC) and Sisal Fiber Concrete (SFC) and incorporates sisal fiber into a concrete blend for the M25 grade concrete mix. Methods In order to evaluate the efficacy of both variations of concrete, mechanical and durability parameters were examined. As compared to CC, the results indicated that SFC had a substantially greater compressive strength. The average compressive strength of SFC at the 28-day was 29.47 N/mm2, which signified a significant incremental percentage growth of 9.58% in comparison to CC. In the same way, SFC exhibited an exceptional flexural strength, as evidenced by its mean value of 7.81 N/mm2, which represented a significant 34.42% improvement in comparison to CC. The Bayesian factor independent sample test yielded a t-test value of 12.495 for compressive strength, accompanied by a p-value below 0.001. These results suggest that the observed difference was statistically significant. Conversely, a t-test value of 19.380 and a p-value below 0.001 were produced by the Bayesian factor independent sample test for flexural strength, both of which further supported the existence of a significant difference. The mean disparity in compressive strength between CC and SFC was 5.1522 N/mm2, with a 95% confidence interval encompassing values between 4.2856 and 6.0188 N/mm2. In a similar manner, the mean discrepancy in flexural strength was 2.0000 N/mm2, accompanied by a 95% confidence interval that varied between 1.7831 and 2.2169 N/mm2. Results The obtained results provide further evidence that SFC is stronger than CC in both compressive and flexural strength, which is consistent with the results obtained from the frequentist statistical analysis. Conclusion With its eco-friendly properties, sisal fiber concrete could indeed play a significant role in the future of sustainable construction.

Quality of comply boards from the industrial waste of palm and bamboo

Requisite of boards as a material for furniture is increasing. Therefore, alternative materials are needed to replace wooden boards such as comply boards. This study aims to determine the quality of comply board from palm and bamboo waste using PVAc adhesives. The treatment used is 12% and 14% adhesive percentages. Parameter tests of comply board of physical properties include moisture content, density, and thickness development; mechanical properties include modulus of elasticity (MOE) and modulus of rupture (MOR). The mechanical properties of adhesive content have a significant effect on the mechanical properties of comply board palm and bamboo namely MOE and MOR the Physical Properties of the resulting comply board meet SNI 03-2105-2006 standards, namely for the parameters of Water Content, Density, Water Absorption. The mechanical properties of comply boards, namely Modulus of fracture (MoR) are not included in these standards. The condition of the results of this study is thought to be.

High-value utilization of boron mud waste: preparation of magnesium oxysulfate cement after primary blank roasting and secondary (NH4)2SO4 roasting

Boron mud, as a typical industrial solid waste, calls for value-added use because of environmental problems caused by stockpiling and waste of considerable magnesium resource. In this work, the primary blank roasted boron mud, as well as the secondary (NH4)2SO4 roasted boron mud were used to prepare magnesium oxysulfate (MOS) cement, then, its characterization and mechanical properties were analyzed and compared systematically. Results showed that the primary blank roasted boron mud can replace 45 % of light burned MgO to prepare MOS cement, whose compressive and flexural strength are 59.0 MPa and 8.0 MPa after curing for 28 d. During the secondary (NH4)2SO4 roasting process of boron mud, MgO and Mg2SiO4 in the primary roasted boron mud transform into MgSO4. The secondary roasted boron mud can replace MgSO4 completely, MOS cement rich in 5Mg(OH)2·MgSO4·7 H2O (517) phase can be obtained with compressive and flexural strength of 70.0 MPa and 9.0 MPa after curing for 28 d. When both of the primary blank roasted and secondary (NH4)2SO4 roasted boron mud are used for preparing MOS cement which compressive and flexural strength are higher than the requirements of the national standard, MgSO4 can be completely derived from the secondary roasted boron mud, the primary blank roasted boron mud can replace up to 35 % of light burned MgO at most, and the total utilization ratio of boron mud is 53.3 wt%. This process not only achieves the high-value utilization of boron mud, but also provides a new thought to prepare MOS cement with high mechanical properties.

Green bio-derived epoxidized linseed-oil plasticizer improves the toughness, strength, and dimensional stability of furfuryl alcohol-modified wood

Furfuryl alcohol (FA) modification represents a sustainable approach to wood modification; however, it significantly reduces the toughness of the wood, limiting its practical applications. This study introduced epoxidized linseed oil (ELO) as an environmentally friendly and bio-derived plasticizer to enhance the toughness and mechanical properties of FA-modified wood. Microstructural analyses confirmed the integration of FA and ELO into the cellular structure of the wood. The chemical interactions between the epoxy groups of ELO and hydroxyl groups of FA were characterized using Fourier-transform infrared spectroscopy and nuclear magnetic resonance spectroscopy, illustrating that a ring-opening reaction occurred that grafted the long flexible aliphatic chains of ELO onto the FA chains, thereby enhancing the chain mobility and flexibility. This interaction significantly decreased the crosslinking density, thereby achieving toughening. FA–ELO modification resulted in significantly enhanced dimensional stability and mechanical properties. Specifically, the anti-swelling efficiency exceeded 80 %, while the modulus of elasticity, modulus of rupture, and along-grain compressive strength increased by up to 35.0 %, 36.8 %, and 45.7 %, respectively. Additionally, significant enhancements in the elongation at break and impact strength were achieved, at 369.1 % and 72.4 %, respectively. The loss factor also increased. The optimal ELO content was 20 wt%. This study effectively demonstrated how ELO mitigates the brittleness of FA-modified wood and supports its application in high-value fields such as construction.

Exploring the impact of red mud on the mechanical, durability, and microstructure properties of concrete

Purpose This study investigated the potential of partially replacing cement with red mud (RM) in concrete and examined its effects on its mechanical properties and microstructure. This study aims to explore sustainable alternatives to traditional cement and evaluate the performance of concrete mixtures with varying percentages (%) of RM as cement replacement. Design/methodology/approach This research aims to comprehensively understand the impact of RM on concrete, aiming for both environmental sustainability and improved construction materials. Subsequently, concrete mixtures were prepared with varying RM contents, ranging from 0% to 21% in increments of 3%, replacing cement. The workability of these mixtures was evaluated using the Slump Cone Test, whereas their mechanical properties (compressive strength, flexural strength and split tensile strength) were assessed through standardized tests. The durability was further investigated via water absorption, acid attack, rapid chloride permeability tests, open porosity test and Sorptivity test. To gain deeper insights into the internal structure of concrete, microstructure analysis was conducted using X-ray diffraction and scanning electron microscopy. Finally, the results were analyzed and quantified. Findings The finding demonstrates that substituting 12% of cement with RM not only boosts the mechanical characteristics of concrete but also mitigates waste disposal. The microstructural analysis identified a denser cement matrix and improved bonding between the cement paste and the aggregates, suggesting potential improvements in strength and durability. Originality/value These results suggest that RM can be efficiently used to produce sustainable concrete with potential applications in construction projects with environmental considerations.

Internal Curing Utilising Recycled Concrete Aggregate: A Sustainable Approach for Improving High-Strength Concrete’s Performance

AbstractHigh-strength concrete (HSC) makes up the vast majority of materials used in the construction sector due to its exceptional mechanical characteristics and outstanding long-term behaviour. However, in cement-based materials with a low water-to-binder ratio (w/b), excessive autogenous shrinkage has become a prevalent issue. This work suggests the sustainable use of recycled concrete aggregate (RCA) to internally cure HSC in order to reduce autogenous shrinkage during the hydration and curing processes. RCA was employed with various volumetric replacement percentages with natural coarse aggregate as a water storage agent (0%, 8%, 16%, 24%, 32%, 50%, 75%, and 100%) under sealed and unsealed conditions. The efficiency of the adopted materials for internal curing was investigated by determining the autogenous shrinkage in addition to unconfined compressive and flexural strength. The laboratory results reveal that the studied properties significantly improved by incorporating RCA into HSC, and the improvement depends on the substitution rate of the coarse aggregate. A better shrinkage behaviour can be obtained by raising the substitution percentage of coarse aggregate with RCA; in contrast, the strengths decrease with increased RCA. RCA can be utilised as an internal curing material for HSC to alleviate autogenous shrinkage with a percentage of around 40%, with the adopted ambient conditions in the early age of HSC with full replacement of virgin coarse aggregate. It is recommended to use 24% RCA as a substitution for natural coarse aggregate for internal curing to improve the characteristics of HSC and the sustainability advantages and reduce its negative environmental impacts.

Comparison of Mechanical Properties of Bulk NiAl-Re-Al2O3 Intermetallic Material Manufactured by Laser Powder Bed Fusion and Hot Pressing

AbstractThe low fracture toughness of NiAl at room temperature is one of the critical issues limiting its application in aircraft engines. It has been previously shown that a small addition of rhenium and alumina significantly improves the fracture toughness of hot-pressed NiAl. In this work, NiAl with an admixture of rhenium and alumina was produced by laser powder bed fusion additive technology (LPBF). The purpose was to compare the fracture toughness, bending strength, and microhardness of the NiAl-Re-Al2O3 material produced by LPBF and hot pressing (HP). Our results show that the LPBF material has lower fracture toughness and bending strength compared to its hot-pressed equivalent. Microcracks generated by thermal stresses during the LPBF process were the primary cause of this behavior. To improve the LPBF material, a post-processing by HP was applied. However, the fracture toughness of the (LPBF + HP) material remained at 50% of the KIC of the HP material. This study supports hot pressing as a suitable processing method for NiAl with rhenium and alumina additions. However, a hybrid approach combining LPBF and HP proved to be highly effective on the raw NiAl powder, resulting in superior fracture toughness of the final material compared to that consolidated by singular HP.

Mechanical properties of steel fiber RPC, basalt fiber RPC, and hybrid fiber RPC: A review of research progress

AbstractBased on an analysis of the literature on fiber‐reinforced concrete (FRC), especially the development and formation of various types of FRC combined with reactive powder concrete (RPC) in recent years, this paper systematically expounds the research progress, particularly the mechanical properties, of steel fiber RPC, basalt fiber RPC and hybrid fiber RPC. This paper concludes the improvement in the mechanical properties of RPC under common curing methods, elaborates on the influence of steel fiber on the compressive, tensile, and flexural strength of RPC, and outlines the principle of fiber enhancing the mechanical properties of RPC. Additionally, it discusses the research progress in basalt FRC, and further examines the impact of basalt fiber on the mechanical properties of RPC. Referring to the research on single fiber reinforced RPC, the mechanical properties of hybrid fiber RPC are analyzed and summarized; based on the characteristics of steel fiber and basalt fiber, research on steel‐basalt hybrid fiber RPC is proposed.

High-Performance One-Component Epoxy Adhesive Based on the Synergistic Effect of Lignin-Derived Triaryl-Imidazole and Phytic Acid.

Latent curing agents are essential in the formulation of one-component epoxy resins, yet they are seldom derived from fully biobased chemicals. In the present work, a fully biobased latent curing agent for epoxy resins (BIMPA) was produced by synthesizing an ionic complex of lignin-derived triaryl-imidazole (BIM) and phytic acid (PA). Benefiting from the synergistic effect of BIM and PA, the one-component epoxy resin, composed of BIMPA and commercially available E51, exhibits a storage stability of over 90 days. Upon heating, the ionic complex undergoes decomposition, liberating the active imidazole to cure the precursor. The resulting epoxy resins exhibited a flexural modulus of 3.09 GPa, a flexural strength of 107.47 MPa, a notched izod impact strength of 2.47 kJ/m3, and a shear strength of 41.02 MPa. The outcome can provide an effective supplement for the development of biobased epoxy resins.

Prediction of residual stress depth profiles in case-carburized gears

Residual stresses have a significant influence on the load carrying capacity of gears. High near-surface compressive residual stresses can increase pitting strength and tooth root bending strength up to 50%. Tooth flank fracture (TFF) is a gear fatigue failure mode, which is in contrast to pitting or tooth root breakage not initiated at the surface or close to the surface but in larger material depths beneath the active gear flank. Therefore, the residual stresses in larger material depths are decisive for TFF. In these larger material depths, the residual stress conditions are almost unknown up to now. It is assumed that tensile residual stresses are present in these areas, which can negatively influence the TFF load carrying capacity. So far, no validated methods are known to estimate or predict these tensile residual stresses. As a result, the tensile residual stresses could not be considered in the calculation methods for the risk of TFF at all until recently.This paper presents a method to predict the residual stresses in case-carburized gears based on comprehensive numerical simulations of case-carburizing processes of different-sized gears. The calculated residual stress profiles also consider the tensile residual stresses in larger material depths.

Effect of Graphene Oxide Incorporation on the Strength of Denture Repair Resin

To evaluate the effect of incorporating graphene oxide nanoparticles (GO NPs) and graphene sheets on the flexural strength of an auto-polymerized (AP) acrylic resin-repaired denture. 60 heat-activated (HA) resin specimens were fabricated and randomly divided into 6 groups (n = 10). The specimens in Group I were kept intact. 50 specimens were cut into two parts with a 45-degree bevel. Group II specimens were repaired with AP resin and Group III specimens were repaired with HA resin. In the repair of Group IV, Group V, and Group VI specimens, 1%, 2% GO NPs, and graphene sheets were added to AP resin, respectively. A 3-point bending test with a universal test device measured the flexural strength. Statistical analyses of the results were performed with the Kruskal Wallis H-test. (α = 0.05) The flexural strength of Group I (130.05 ± 20.20 MPa) was the highest among all groups. The flexural strength of Group IV (67.49 ± 12.70 MPa) was significantly higher than Group V (50.87 ± 15.02 MPa) and Group VI (44.77 ± 10.70 MPa). The lowest strength value was obtained in Group VI. Adding 1% GO NPs to AP acrylic resins increases flexural strength. However, the increase in nanoparticle concentration and the addition of graphene sheets negatively affect strength.