Mixed Mode Research Articles

Impact of surface preparation method on the fracture toughness of adhesive joints subjected to diverse loading modes

While research has explored surface treatment effects on fracture energies in pure modes (I or II), there is a lack of research under mixed-mode loading. The aim of this paper is to investigate the influence of surface treatment approaches on the fracture behaviour and fracture energy of adhesive joints at different loading modes. To achieve this, double cantilever beam (DCB) adhesive joints were manufactured considering two different surface treatment methods namely grit blasting and mechanical bristle blasting. The joints were subjected to five different mode mixities. Fracture energy for each tested condition was calculated based on a compliance-based approach. The fracture energies in mode I reached an increase of 55 % when grit blasting surface treatment was applied, while for mode II the fracture energy reached a value three times higher for mechanical bristle blasting surface treatment, both energies from the mixed mode tests. The failure mechanisms were also evaluated for joints with different surface treatments as a function of loading mode. In all tested conditions, a cohesive failure mode was observed; however, the results underscore the substantial influence of the surface treatment method on the fracture energy of adhesive joints. This is attributed to the distinct failure mechanisms observed under varying surface treatment conditions.

Investigation on the effect of freeze–thaw cycles on damage characteristics of concrete under mixed mode I-II load conditions

In order to investigate the effect of freeze–thaw cycles on the damage characteristics of mixed mode I-II crack propagation in concrete. The three-point bending and three-point shear fracture test were carried out on specimens subjected to different freeze–thaw cycles (0, 50, 100, 150 and 200). The analytical expression of mixed mode I-II damage scale r0(I,II) and ru(I,II) was derived, and the effect of freeze–thaw cycles on damage scale was analyzed. In addition, the critical damage scale of mixed mode I-II fracture was obtained using the numerical simulation method, and the simulation results were compared with the calculation results. Finally, the accumulate energy and tension-shear failure of concrete after freeze–thaw cycles were analyzed based on acoustic emission technology.

Large eddy simulation of a supersonic lifted hydrogen flame: Impacts of Lewis, turbulent Schmidt and Prandtl numbers

Parametric large eddy simulations (LES) of a supersonic lifted hydrogen flame are reported. The emphases are on two aspects: impacts of (1) Lewis number (Lei of the ith species) and (2) turbulent Schmidt and Prandtl numbers (Sct and Prt) on supersonic turbulent flame and flow structures. Five cases are considered: species-specific Lei, Sct=Prt=1.0 (C0); unity Lei, Sct=Prt=1.0 (C1); species-specific Lei, Sct=0.5, Prt=1.0 (C2); species-specific Lei, Sct=1.0, Prt=0.5 (C3); and species-specific Lei, Sct=Prt=0.5 (C4). Numerical results of instantaneous and/or time-averaged species mole fractions, mixture fraction, heat release rate, flame base location, and mixed modes of premixed and diffusion combustion are compared between cases C0 and C1. Differences in auto-ignition locations and strengths and flame structures and stabilization specify the impacts of Lewis number. They are triggered by different predictions of species mass and thermal diffusions at fuel-coflow and/or coflow-ambient air mixing layers. These differences are rationalized by a scale analysis of mass/thermal diffusion and convection for case C0, which suggests the relatively low but non-negligible former against the latter. Cases C0 and C2–C4 barely see differences in terms of instantaneous and/or time-averaged temperature, velocity, and mixed combustion modes except for further downstream areas where combustion occurs. Both Sct and Prt impose less significant influences than Lewis number, as sub-grid scale mass/thermal diffusion is subordinate to its resolved counterpart according to their scale analysis for case C4.

Effect of trialkoxysilane/aminosilane-containing universal adhesive on resin-ceramic microtensile bond strength and ceramic wettability: An in-vitro study

BackgroundThe dual-silane (trialkoxysilane/aminosilane) universal adhesive (UA) is claimed for its enhanced priming capacity of glass-ceramics. ObjectiveThis study evaluated the effect of organofunctional trialkoxysilane- and organofunctional trialkoxysilane/aminosilane-containing UAs on the long-term resin–ceramic microtensile bond strength (μTBS) and wettability of ceramic. MethodsHydrofluoric acid-etched lithium disilicate discs were distributed into four groups as follows: (control), no priming was performed; (MBN), primed using a silane-based primer (Monobond N); (SBU), primed using a trialkoxysilane-containing UA (Single Bond Universal Adhesive) and (SBP), primed using a trialkoxysilane/aminosilane-containing UA (Scotchbond Universal Plus Adhesive). Ceramic discs were cemented into blocks then sectioned into microbeams stored in distilled water at 37° for 1 year. The μTBS was evaluated followed by assessment of the failure modes. The contact angle of the two UAs was measured with a goniometer using the sessile drop technique. ResultsMBN significantly improved the resin-ceramic μTBS (31.71 ± 6.33 MPa) compared to the control group. The resin-ceramic μTBS obtained after priming using SBP (22.83 ± 3.42 MPa) was comparable to those of MBN. SBU showed significantly inferior resin-ceramic μTBS (16.02 ± 6.28 MPa) compared with MBN. Mixed failures mode patterns were the most frequent in the groups. The ceramic wettability of both UAs did not significantly differ. ConclusionCeramic priming using a UA with dual-silane monomers (organofunctional trialkoxysilane/aminosilane) resulted in long-term adhesion comparable to a silane-containing primer. Incorporating aminosilane monomer in UA formulation did not affect the wetting of characteristics of the UA solution and enhanced its glass-ceramic priming capacity. Clinical significanceThe use of UA with optimized silane content as a primer for glass-ceramics simplifies clinical adhesive procedures including resin cementation and repair of ceramic restorations.

On group-theoretic eigenvalue vibration analysis of structural systems with C6v symmetry

In considerations of the linear vibration of symmetric systems, group theory allows the space of the eigenvalue problem to be decomposed into independent subspaces that are spanned by symmetry-adapted freedoms. These problems usually feature one or more degenerate subspaces (i.e. subspaces that contain repeating solutions). For such subspaces, the associated idempotents, as calculated from the character table of the symmetry group, are not capable of full decomposition of the subspace. In this paper, and based on group theory, simple algebraic operators that fully decompose the two degenerate subspaces of structural problems belonging to the C6v symmetry group are proposed. The operators are applied to the vibration of a spring-mass system, for which the results for natural frequencies are found to agree exactly with results from the literature. Their application to the vibration of a hexagonal plane grid reveals new insights on the character of the modes of degenerate subspaces. The overall conclusion is that, for problems belonging to the C6v symmetry group, the proposed operators allow the mixed modes of degenerate subspaces to be separated into two distinct symmetry categories, and are very effective in simplifying the actual computation of the repeating eigenvalues of these subspaces.

Bifurcations and mixed mode oscillations in a bi-stable plasma model with slow parametric excitation.

In this study, considering a bi-stable plasma model with slow parametric excitation, the bifurcation of periodic and chaotic responses as well as the resulting fast-slow motions is discussed analytically and numerically. For a nonautonomous fast sub-system, the generalized harmonic balancing method is utilized to obtain an averaged system. Bifurcation analysis about the averaged system shows that the critical manifolds form a S-shape structure. Meanwhile, supercritical and subcritical period doubling (PD) occurs on the upper branch simultaneously. As the frequency of the external excitation changes, bifurcation points on the limit cycle manifolds can present different relative locations. Moreover, an additional bi-stable structure induced by Cusp bifurcation emanates from the upper branch. On the other hand, the existence of a chaotic attractor and the corresponding boundary crisis phenomenon are verified using the Melnikov method and the basin of attraction. The structures of the numerical bifurcation diagram show good agreements with the analytical results. Considering two cases of low-frequency excitation, the corresponding fast-slow dynamics are discussed. It is found that, when the fast-slow flow passing the subcritical PD point, a low frequency with different magnitudes will lead to two patterns of bifurcation delay, i.e., the typical one and the excessive delay, which suppress the PD. As for the boundary crisis point, the slow passage effects show no distinct influence. Thus, three transition mechanisms based on two cases of the bifurcation structure are explained, including "fold of cycle-fold of cycle" type, "fold of cycle-delayed subcritical PD" type, and "fold of cycle-boundary crisis" type.

Detailed simulations on the mixed modes of premixed and diffusion combustion in supersonic hydrogen flames

Detailed simulations on the mixed modes of premixed and diffusion combustion in supersonic hydrogen flames

Covid-19 Pandemic & Post Pandemic-Technology and Education

The COVID-19 pandemic, was occurred in 2019. It is a worldwide pandemic which effect the whole world. The disease is mainly pass through the respiratory track; Infected people transmit the COVID-19 virus when they are Come in contact with other non-infected persons. However, infection can also be occurred in longer distances, particularly indoors. This pandemic has drastically changed the use of digital technologies in the field of education due to the social distancing norms and nationwide lockdowns. People and organizations all over the world have had to adjust to new ways of work and life. Education is field in which there is a dramatic shift to the online mode of transacting. Since the beginning of the lockdown, schools, colleges and universities around the world have shifted their classes to video conferencing platforms like Zoom, goggle classroom, Microsoft and goggle meet Suit. This increases the on-screen community. Some universities are now shifting entirely to the online mode, with the exception where require a physical presence is necessary. Due to Covid-19 pandemic we imagine a largest shift of digital usage on all fields of work and life. These changes are largely depended on our responses to and shaping of the emerging trends (e.g., Some School App). The Covid-19 pandemic has led to online revolution in education fields to shift to work-from-home (WFH). The Covid-19 post pandemic introduce a new mode of education i.e. hybrid or blended mode of learning.

Validation of LC-MS/MS method for opioid monitoring in Valencia City wastewater: Assessment of synthetic wastewater as potential aid

In this study, a comprehensive and sensitive method for the simultaneous detection of 17 opioids (OPs) and their human metabolites in wastewater using high-performance liquid chromatography coupled to tandem mass spectrometry was validated. The chromatographic separations of opioids were carried out on a Kinetex® Biphenyl column (1.7 μm, 100 Å, 50 × 2.1 mm). A synthetic wastewater approach was used for recovery studies to mimic a contaminant-free matrix. Two solid-phase extraction (SPE) sorbents (hydrophilic-lipophilic balance and mixed mode with the previous phase and a weak cationic exchange) were studied to optimize sample treatment and obtain higher recoveries. The mixed mode was chosen because the recoveries of 17 target analytes at three spiked concentrations (25, 50, and 100 ng mL−1) were > 80 % for 75 % of the analytes in a simulated wastewater. The intra- and inter-day relative standard deviations (RSDs) were between ±1 % and ±20 %. The method limits of quantification ranged from 5 to 25 ng L−1, the only exceptions being heroin (275 ng L−1) and morphine-3β-glucuronide (250 ng L−1). Suppression/enhancement is comparable between the synthetic and the influent wastewater. The analytical method was applied to the OPs analysis in twenty-one influent samples collected from the treatment plants treating the wastewater of Valencia City (Spain). Twelve OPs were detected with total daily concentrations ranging from 1 ng L−1 to 2135 ng L−1. The widespread presence of these compounds in water suggests potential widespread exposure, highlighting the need for increased environmental awareness. Furthermore, the estimated daily intake results raise concerns about opioid use as a potential future health and social issue.

Under the Blended Teaching Mode based on OBE Concept in Undergraduate Universities in Shandong Province Research on the Development Strategy of Teacher's Teaching Ability

With the advent of the digital age, the deep integration of cutting-edge technology and education continues to innovate, driving the transformation of teaching models. Compared with traditional teaching methods, blended teaching mode reshapes the entire process of education and teaching, and is of great significance in promoting educational fairness, improving educational quality, and building a high-quality education system. In response to the current situation of blended teaching mode with OBE concept among university teachers, how to effectively accelerate the development of teachers' teaching abilities in the digital era has become an important task in the field of higher education. Based on this, this article clarifies the specific connotation of the OBE concept blended teaching model, constructs a professional teaching ability system for university teachers, and proposes strategies to update education and teaching concepts in a timely manner, comprehensively optimize teaching design capabilities, actively improve information literacy of university teachers, and continuously improve training and incentive mechanisms. The aim is to promote university teachers to adapt to the development of the digital era and educational innovation and transformation.

Social Enterprises in Poland in the Face of Recent Crises

Background: The research problem addressed in this study concerns the activities of social enterprises (SEs) within the framework of the social market economy (SME) in Poland during the crises triggered by the COVID-19 pandemic and the war in Ukraine. Research objectives: The article aims to verify the hypothesis that SEs situated within the SME can mitigate the negative effects of crises by undertaking additional actions for recipients during the pandemic and Ukrainian refugees. Research design and methods: An interdisciplinary research model helped examine the stated problem. It synthesizes both the concepts of SME and SE. Moreover, part of the research was a nationwide quantitative study using the CAWI method supported by the CATI method and Dilman’s prompting method (mixed mode). Results: During the pandemic in Poland, 56% of SEs took additional actions for recipients, even though the situation worsened for 41% of them. During the war in Ukraine, 68% of SEs took action for refugees, while the situation worsened for 29% of SEs. Conclusions: Social enterprises experiencing the consequences of crises are also able to minimize their effects. Simultaneously, to an equal extent, they support environmental issues and sustainable development.

Effectiveness of Gamified Cooperation and Competition in Blended Learning Environment for EFL Business Writing in TVET

This research investigated the effectiveness of gamified blended learning environments in fostering EFL writing skills among technical and vocational education and training (TVET) trainees in Saudi Arabia. It compared three distinct learning strategies achieved through gamification design in a blended delivery mode: gamified cooperation, gamified competition, and gamified cooperation-competition. Each strategy leveraged a specific category of gamification features that evoke different goal structure: cooperation, competition, or a combination of both. A quasi-experimental design with a pre-test and post-test was employed. Forty-five trainees were purposively selected and randomly assigned to three groups, each receiving instruction using a different gamified blended learning program for teaching business writing. The findings revealed significant improvement in English as a Foreign Language business writing skills for all three groups. However, a one-way ANOVA and post-hoc Tukey HSD test indicated that the gamified cooperation-competition strategy yielded the greatest improvement compared to the gamified cooperation and gamified competition strategies alone. This suggests that a combination of cooperative and competitive elements within a gamified blended learning environment might be the most effective approach for enhancing English as a Foreign Language business writing skills among Technical and Vocational Training and Education learners.

The application of 2-(3-nitrophenyl)imidazo[1,2-α]pyridine as an effective corrosion-defender for steel in acidic environment

Metal corrosion in acidic settings presents serious problems for many industrial areas. The creation of corrosion inhibitors that are efficient, long-lasting, and ecologically benign is essential. This study introduces a novel corrosion inhibitor, 2-(3-nitrophenyl)imidazo[1,2-α]pyridine (NIP), which was synthesized for protecting mild steel in 1 M HCl. The synthesized NIP was evaluated using Electrochemical Impedance Spectroscopy (EIS), Potentio-dynamic Polarization (PDP), Scanning electron microscopy (SEM), Energy X-ray analysis (EDX), and theoretical approache, including Density Functional Theory (DFT) and Monte Carlo simulations (MCs). NIP demonstrated outstanding protection behavior, reaching a peak of 91.47 % at a concentration of 1.00 mM. PDP studies classified NIP as a mixed-type inhibitor that effectively mitigated both anodic and cathodic reactions. SEM and EDX analysis confirmed the formation of a protective layer on the surface of the structural steels, composed mainly of nitrogen and oxides, indicating the presence of the inhibiting agent. DFT calculations identified the imidazole ring and heteroatoms (N and O) as the active sites for corrosion inhibition. The adsorption behavior of NIP on the metal surface has been studied by means of Monte Carlo simulations. The inhibitory efficiency of NIP was evaluated across a temperature range of 298–323 K, and the results showed a decrease in efficacy with increasing temperature, which provides crucial information for practical applications. The Langmuir model fit indicated a mixed mode of physical and chemical adsorption, with a calculated ΔG°ads value of −33.76 kJ/mol. This novel approach pinpointed reactive sites within the NIP, enhancing our understanding of its protective mechanism at the molecular level.

Microstructure and mechanical property of CoCrFeNiAlxMn(1-x) dual-phase gradient high-entropy alloy coatings prepared by laser cladding

High-entropy alloy (HEAs), known for their balanced strength and ductility, are promising candidates for impact wear-resistant applications. In this study, CoCrFeNiAlxMn(1-x)(x = 0, 0.2, 0.8, 1.0) dual-phase gradient coatings with a layered structure were prepared using laser cladding technology to explore the microstructure evolution, tensile properties and fracture mechanism of gradient coating. As the Al content increased, the single-phase face-centered cubic (FCC) HEA coatings transitioned to dual-phase of FCC+ body-centered cubic (BCC) solid-solution, and finally to a single BCC phase. The remarkable improvement of microhardness is attributed to the dominance of the BCC phase and the impeding effect of the second phase particles on dislocation movement. The gradient coating exhibited a gradual change in internal element composition, microhardness, and structure along the depth direction, with the highest hardness value reaching 530 HV. Compared with the minimum tensile strength (69.03 MPa) and the minimum elongation (0.14 %) of single-layer coating, the gradient coatings exhibited a balance of high tensile strength and good plastic toughness, with a tensile strength of 597 MPa and an elongation of 4.08 %. Fracture analysis indicated a transition from ductile to brittle fracture in single-layer coatings as x values increased. The double-layer and four-layer gradient coatings displayed a mixed mode of brittle and plastic fracture. The study provides valuable insights into the design and fabrication of HEA gradient coatings, offering a novel approach to enhance the durability and performance of laser-clad coatings for various applications.

Mechanical characteristics and damage model for rock-like specimen with two parallel grout-filled cracks

To investigate the mechanical properties of rock-like specimens with two parallel cracks filled with grout, uniaxial compression tests in combination with digital image correlation (DIC) and acoustic emission (AE) techniques have been performed on grout-filled cracked specimens with different rock bridge dip angles β. Results indicated that with the increase of β, the uniaxial compression strength, cumulated AE count, AE energy, as well as shear crack proportion initially decreases and subsequently increases. The overall AE b-value and the DIC-based maximum principal strain initially increases and subsequently decreases as β increases. The failure mode also varies from tensile to mixed tensile-shear mode. Furthermore, a particle flow code (PFC) model, which considers the grout filling, grout-rock interface, and rock, has been proposed. Numerical results showed that the range of microcracks inclination angle first decrease from 70°−100° to 70°–90° and then increases to 70°–110°. Besides, existence of grout filling and changes of bridge angle leads to significant difference in PFC particle displacement, which can cause the changed of crack initiation positions and failure modes. Finally, a damage model considering stress intensity factor for the grout-filled specimen was established. Both of pre-crack damage and loading damage were considered in this model, and a damage repair factor was proposed to describe effect of grout filling. The results showed that grouting could can effectively suppress stress concentration caused by pre-existing crack, thereby changes the strength of cracked specimen.

In-depth research on azole corrosion inhibitors - effect of N atoms position and quantity on copper corrosion inhibition performance in alkaline environments: Experimental evaluation and theoretical analysis

Copper's superior electrical properties make it ideal for multi-layer interconnections in integrated circuits. Chemical mechanical polishing (CMP) is the main method for achieving copper wiring flatness. However, copper is susceptible to corrosion in glycine-based alkaline polishing solutions. This study examines benzimidazole, indazole, and benzotriazole as corrosion inhibitors for copper in an alkaline environment (pH=9), focusing on the impact of nitrogen atom arrangement on inhibition efficiency. Through electrochemical, contact angle, static corrosion, and surface characterization tests, it's demonstrated that these inhibitors protect copper surfaces effectively. The adsorption of these inhibitors follows the Langmuir equation with a mixed adsorption mode. X-ray photoelectron spectroscopy (XPS), UV–vis spectroscopy tests, and density functional theory calculations elucidate the adsorption configuration and corrosion inhibition mechanism. The scope of this research extends beyond merely analyzing the performance of the three corrosion inhibitors; more importantly, it has yielded novel insights that are broadly applicable to the field of corrosion inhibitors. The findings are as follows: 1. The coupled structure of dinitrogen and trinitrogen facilitates charge accumulation, manifesting as the formation of additional Cu-N bonds, which prevents desorption; 2. The multi-nitrogen coupled structures provide sites for the formation of intermolecular hydrogen bonds, which is essential for the establishment of an orderly and dense passivation layer. It is expected that this study will provide valuable insights into the development and design of new and efficient copper corrosion inhibitors.

Formation of Models for Registering Systemic Processes in The Digital Educational Environment of the University Based on Log File Analysis

It has been demonstrated that technologies and methods of intelligent data analysis (IDA) in the educational domain, particularly based on the analysis of digital traces (DT) of students, offer substantial opportunities for analyzing student activities. Notably, the DT of students are generated both during remote learning sessions and during blended learning modes. By applying IDA methods to DT, one can obtain information that is beneficial for both the educator in a specific discipline and for the educational institution's management. Such information might pertain to various aspects of the functioning of the digital educational environment (DEE) of the institution, such as: the student's learning style; individual preferences; the amount of time dedicated to a specific task, among others. An algorithm has been proposed for constructing a process model in the DEE based on log analysis within the DEE. This algorithm facilitates the description of a specific process in the DEE as a hierarchy of foundational process elements. Additionally, a model based on cluster analysis methods has been proposed, which may prove beneficial for analyzing the registration logs of systemic processes within the university's DEE. Such an analysis can potentially aid in detecting anomalous behavior of students and other individuals within the university's DEE. The algorithms proposed in this study enable research during log file analysis aimed at identifying breaches of information security within the university's DEE.

Interest, Collaboration, Autonomous Learning and satisfaction in the Blended Teaching of Martial Arts

This study involves two classes of education majors taking a general Martial Arts course, using traditional teaching methods for one class and blended teaching methods for the other over a semester. It aims to compare the learning outcomes in terms of student interest in Martial Arts, cooperative learning abilities in sports, and independent learning abilities. The goal is to explore the feasibility and effectiveness of the online and offline blended teaching mode in university Martial Arts instruction. The result showed that compared to traditional teaching methods, the implementation of blended learning based on online teaching platforms complements students' interest in learning martial arts, as well as their ability to learn independently and collaboratively. With the implementation of personalized learning, interest has increased, and the abilities to learn independently and through hands-on learning have been cultivated, resulting in improved satisfaction.

Stress based fracture criteria for mixed-mode I/II delamination of unidirectional composite laminates

Mixed mode delamination is prone to occur in composite laminates subjected to complicated loading. In current study, the modified maximum principal stress (M-MPS) criterion and the modified maximum shear stress (M-MSS) criterion considering the effect of mode ratio on the critical distance are developed to predict the mixed mode delamination of unidirectional laminates. The accuracy of the proposed fracture criteria is validated by the comparison of the predicted fracture locus curve with extensive experimental data available in the literatures, a higher correlation is observed between the predicted results and the experimental data. Finally, comprehensive discussion on the capability of the proposed M-MPS and M-MSS criteria is conducted, a dimensionless parameter named fracture index composed of the difference of elastic properties and the difference of pure mode fracture toughness is proposed to reveal the fracture mechanisms of the unidirectional composites.

Investigation on the interaction evolution and growth behavior of multiple cracks under fatigue loading

In this study, the cracks interaction is investigated on plates with different crack geometry parameters through finite element analysis and experiments. The presence of multiple cracks may lead to an enhancement or shielding effect on stress intensity factors (SIFs) depending on crack relative positions and sizes, thereby potentially accelerating or decelerating the crack propagation rate. When the crack tips of double parallel non-collinear cracks begin to overlap, the interaction between cracks transitions from an enhancement effect to a shielding effect, and the KII values reach their peak at this point, which are explained by the stress field distributions surrounding the cracks. For non-collinear double cracks with an inclined angle α, the shielding effect of inclined cracks becomes increasingly pronounced in comparison to horizontal cracks as the angle α increases. To verify the numerical results, fatigue crack propagation experiments were carried out on Al–Li alloy samples with double non-collinear cracks with different crack vertical distance. The experimental results show that growth direction of two non-collinear cracks underwent a transition when they overlapped, leading to load mode I changing into mixed mode of I + II. Based on both numerical simulations and experimental results, the material parameters C and m in Paris equation are modified, and then a new method for predicting the multiple cracks growth life is presented. By comparing with the experimental values, it was found that this method exhibits high accuracy and reliability.