Cohesive Bonds Research Articles

Regulation of ash slagging behavior for sewage sludge by rice husk addition: Focusing on control mechanisms

Combustion of sewage sludge (SS) is a promising alternative waste-to-energy process. However the mono-combustion of SS may induce severe ash slagging behavior, which will shorten the life of the combustion reactor. In this study, rice husk (RH) as a clean and high-energy density auxiliary was introduced to improve the slagging characteristics of SS and the underlying mechanism was revealed. The results indicated that RH addition can raise ash fusion temperature (AFT) of SS during co-combustion and the growth rate of AFT increased significantly under high RH dose. Slagging and fouling indices showed that slagging tendency of the co-combustion ashes could be neglected under 50% RH addition. Overall, co-processing of SS and RH is an ideal route to solve ash-related problems. The inhibition mechanism of RH addition to the slagging behavior of co-combusted SS was determined as follows: (1) Insufficient iron-bearing phases caused the formation of refractory co-combustion ash; (2) a reduced liquid phase, which acts as a glue to bond the ash grains, played a significant role in slagging control; (3) fiber-like structures, distributed as discrete particles to form a porous structure, reduced the cohesive bonds in ash agglomerates, which further inhibited ash slagging.

Influence of Silver Addition on Structure, Martensite Transformations and Mechanical Properties of TiNi-Ag Alloy Wires for Biomedical Application.

The microstructural and functional behavior of TiNi-based wires with a silver content of 0–1.5 at.% was evaluated. The concentration range for Ag doping determined for the TiNi wires with potential for the medical industry was 0–0.2 at.%. Microstructure analysis of TiNi wires with different silver contents at room temperature indicated a multiphase structural state. Various internal structures with tangled grain boundaries were formed by intense plastic deformation. The nanocrystalline structure and phase state of wire with the minimum silver content (0.1 at.% Ag) provide full shape recovery, the greatest reversible strain, and optimal strength and ductility. TiNi ingots with a high Ag content (0.5–1.5 at.%) cracked under minimum load due to excess silver that crystallized along the grain boundaries and broke cohesion bonds between the TiNi grains.

Influence of Fraction Particle Size of Pure Straw and Blends of Straw with Calcium Carbonate or Cassava Starch on Pelletising Process and Pellet.

The aim of this study was to investigate the pressure agglomeration process of wheat straw (WS) and the blends of WS with calcium carbonate (CC) or cassava straw (CS) with a ratio of 6% wt./wt. from seven separate fractions with sizes in the range of 0.21–2.81 mm. The agglomeration was performed at a moisture of 30% wb and a material temperature of 78 °C, with a dose of 0.1 g, in a die of diameter 8 mm and height 80 mm. The effects of the process were evaluated based on the compaction parameters and the pellets’ density, tensile strength, and water absorption. The incorporation of additives into the WS improved the pellet process and quality. Refined results were achieved after adding CC, as compared to those achieved after adding CS, and the preferred particle size was in the range of 1.00–1.94 mm. This was because, under the given conditions, the back pressure in the die chamber significantly increased, allowing the achievement of a single pellet density of 800 kg·m−3. The pellets were resistant to compressive loads and cracked only at tensile strength of 6 MPa and a specific compression work of 6.5 mJ·mm−2. The addition of CC to the WS improved the strength of the adhesive and the cohesive bonds between the particles. The water absorption for the uncrushed pellets was considerably less than that for crushed pellets, which results in the safer storage of uncrushed pellets and excellent moisture absorption of crushed pellets. The addition of CC to the WS offers benefits in the form of pellet strength with a high water absorption capability. Notably, a study of crushed pellet litter under broiler rearing conditions and an analysis of the operational costs of using WS additives are required for implementing this study.

Reference Assignment and Character Identification in Mariama Ba’s So Long a Letter

Much scholarly attention has been paid to the works of Mariama Ba, both from the literary and the linguistic perspectives, especially from the literary point of view. This paper contributes to the linguistic study of her works from the pragmatic angle with the adoption of Sperber and Wilson’s Relevance Theory. The aim is simply to explore the role of reference assignment in character identification or indexing in conversation within the text So Long a Letter. The research reveals that the different models of reference serve to aid character presentation toward the achievement of cohesive effects in the advancement of the plot of the novella. The paper shows that a study of reference assignment in the novella of Mariama Ba facilitates good access to a kind of reference and cohesive bond which aids the recovery of meaning in the text.

Tensile properties of composite metal foam and composite metal foam core sandwich panels

Steel-steel composite metal foam (SS-CMF) and composite metal foam core sandwich panels (SS-CMF-CSP) were manufactured and tested under quasi-static tension. The SS-CMF-CSP were manufactured by attaching stainless steel face sheets to a SS-CMF core using solid-state diffusion bonding. SEM imaging was used to inspect the microstructure of SS-CMF and compare it to that of SS-CMF-CSP. The results indicate a cohesive bond line at the interface of the core and the face sheets. The bare SS-CMF samples had an ultimate tensile strength between 75–85 MPa and a failure strain between 7.5–8%. The normalized tensile strength of the SS-CMF was approximately 24 MPa/(g/cm3), 410% higher than other comparable metal foams, with a specific energy absorption of 0.95 J/g under tension. The uniform porosities and strong bonding between the sphere wall and matrix seem to be the strengthening factor of SS-CMF under tension when compared to other metal foams. The ultimate tensile strength of the SS-CMF-CSP was 115% stronger than the bare SS-CMF at 165 MPa with an average failure strain of 23%. The normalized strength of the SS-CMF-CSP was 52% higher than the bare SS-CMF. The modulus of elasticity was approximated using the rule of mixtures for the SS-CMF and the SS-CMF-CSP and the experimental results were found to lie within the calculated upper and lower bounds.

Collapse analysis of a large plastic pipe using cohesive zone modelling technique

Polypropylene (PP) plastic pipes have recently gained widespread application in non-pressurized gravity pipes used for seawater intake lines in the petrochemical industry. These pipes consist of a solid wall base pipe, on which an outer reinforcement called the omega-profile is spirally winded and hot fusion bonded. The omega-profile is usually filled with grout to provide on-bottom stability for subsea installation. It is of high importance that the bond between the omega-profile and the base pipe has sufficient strength to provide resistance against buckling of the pipeline system. The objective of this study is to investigate the collapse behaviour of such large-diameter PP pipes subjected to a negative internal pressure. The bond is modelled with cohesive zone modelling technique with the aim to determine the failure mode that governs the collapse behaviour of the pipe, e.g. buckling or delamination. Experiments where conducted on single cantilever beam (SCB) specimens cut from the pipe to determine the cohesive bond strength between the omega-profile and base pipe. The findings from the experiments are implemented in a full pipe model, where the surface between the omega-profile and base pipe is assigned bond strength characteristics in accordance with the experimental results. The FEA results of the non-linear collapse analysis of the full pipe model show that for the range of grout stiffness values considered (0 ≤ Eg ≤ 30 GPa), the governing failure mode of the pipe is initiated by buckling and proceeded by delamination. For delamination to govern the failure mode, a grout stiffness greater than 36 GPa in combination with a weaker bond strength than the experimentally measured would be required. The methodology presented in this study gives a rather accurate tool for the design and analysis of this type of structures, and can reliably assess the bond strength level required in view of the governing failure modes, e.g. buckling and delamination.

Discrete element method using cohesive plastic beam for modeling elasto-plastic deformation of ductile materials

This paper introduces a three-dimensional (3D) simulation to model the elasto-plastic deformation of ductile materials by discrete element method (DEM) using cohesive plastic beam approach. The Euler–Bernoulli beam theory is applied to calculate force and torque reactions of the cohesive beam bond that can account for plastic strain. In order to simulate the elasto-plastic behavior of materials, a coupled model of plasticity and damage is proposed for the cohesive beam bond. The von Mises yield criterion, a modified perfectly plastic law and an exponential damage law are implemented to simulate behaviors of ductile materials such as steel and aluminum in tensile tests. It is then further applied to investigate the ductile fracture modes such as localized shear fracture and necking phenomenon with cup-and-cone shape. Finally, the proposed DEM model using cohesive plastic beam is applied to visualize the compression test of cylindrical steel sample and wrinkle deformation of steel tube under bucking due to axial compression. This paper is the first attempt to model ductile materials by DEM with cohesive beam bond in tension, compression and buckling. All of the numerical benchmarks demonstrate the power of DEM using cohesive beam bond to model ductile materials with fracture, large deformation and elasto-plastic behavior.

Casting methods for the production of rotationally symmetric copper bimetals

ABSTRACT Multiple-material products are characterised by a complex property profile which is achieved by combining the particular advantages of at least two different materials. Bimetal casting is an energy- and material-efficient technology for the production of multi-metallic objects. This paper describes the development of a semi-continuous casting process for the formation of a rotationally symmetric bimetal with a cohesive bonding character at the interface of a copper–tin alloy (CuSn6) and pure copper (Cu99.5). Initial experiments are conducted by static casting to evaluate the thermal process window. Based on the results of the initial experiments, a vertical semi-continuous compound casting process is developed. A stable cohesive bond between the joining partners is accomplished by forming a solid solution at the interface. This paper is part of a Thematic Issue on Copper and its Alloys.

Micro-Foundations of the Vanguard: The Origins of Revolutionary Leftist Rebel Groups

What explains the emergence of leftist national liberation rebel groups? I present one causal pathway that unfolded in the early-to-mid-20th century and involved out-group individuals uprooting to imperial metropoles for assimilatory education programs. Once there, out-group individuals experienced discrimination by in-group members of the empire. Discriminatory experiences by imperial in-group members, despite out-group expectations of similar privileges, prompted a series of psychological and behavioral responses that made out-group individuals more likely to accept national liberation—independence and social revolution—as a political goal and adopt leftist ideologies while forming cohesive bonds with other out-group individuals and participating in political agitation. The combination of psychological and behavioral responses resulted in a cohesive, experienced and relatively well-equipped vanguard seeking leftist national liberation. Exploiting as-if random variation in educational experiences of rebel leaders in Eritrea’s Independence War, I quantitatively and qualitatively test mechanisms using archival and primary materials and an original dataset. Results are robust to multiple specifications including out-of-sample qualitative tests that include archival data from four countries. The project illustrates the formation of a highly consequential type of insurgency with implications for the formation of revolutionary jihadist groups.

Šafā‘a. La cohesión de una sociedad

Se presenta en este trabajo la doctrina de la šafā‘a, esto es, la intercesión escatológica del Profeta por su comunidad, desde la perspectiva de los nuevos vínculos de cohesión social de la sociedad religiosa instaurada por el islam que sustituían a la aṣabiyya tribal, constituyéndose la šafā‘a en el colofón y broche final de esos nuevos vínculos. Tras estudiar dicha doctrina se constata la seguridad de la salvación final que ofrece, elemento valiosísimo de cohesión social, y se destaca la exclusividad de la šafā‘a para solo el musulmán a través de la comparación de La disputa entre los animales y el hombre de los Ijwān al-Ṣafā’ con La disputa de l’ase de Turmeda y a través de la verdadera causa de la muerte de al-Ḥallāŷ según al-Rūmī. Hay, sin embargo, una excepción a esa exclusividad ya que existen musulmanes que quedan excluidos de la šafā‘a. Son estos, los herejes, quienes con la divulgación de sus nuevas doctrinas ponen en peligro la unidad y la cohesión de la comunidad. Se termina sugiriendo el posible calco de esta doctrina islámica en la devoción a la intercesión de la Virgen, pues la devoción mariana que con tanta fuerza irrumpe en el Occidente cristiano a partir del siglo XII, y que aparece reflejado en la Cantigas de Alfonso X el Sabio y en los Milagros de Nuestra Señora de Gonzalo de Berceo, es un fenómeno cuyo origen es todavía discutido.

The influence of temperature and component proportion on stability, sensitivity, and mechanical properties of LLM-105/HMX co-crystals via molecular dynamics simulation.

Based on molecular dynamics (MD) simulation, the binding energy, cohesive energy density (CED), bond length, and mechanical parameters were calculated for 2,6-diamino-3,5-dinitropyrazine-l-oxide (LLM-105) crystal, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) crystal, and their co-crystals under different temperatures. Three LLM-105/HMX patterns were constructed to investigate the influence of component proportion on structures and properties of co-crystals, in which the mole ratios of LLM-105 and HMX are 1:1, 1:2, and 2:1. The effect of temperature and components on the stability and sensitivity were investigated as well. The results show that the binding energies, CED and mechanical parameters of all the co-crystals, decrease when the temperature increases from 248 to 398K, while their maximum N-NO2 bond length (Lmax) increases with rising temperature, indicating that the sensitivities increase and stabilities decrease when temperature rises. At all temperatures, co-crystals exhibit larger CED and shorter bond length than that of single explosive, demonstrating that they are more stable and less sensitive than single crystal, where the stability of co-crystals was ordered as 2:1>1:1>1:2. Moreover, the bulk modulus (K) and shear modulus (G) of co-crystals are lower than that of HMX, conversely, the Cauchy pressure and K/G are higher than that of HMX, implying co-crystals have better ductility. Finally, the 2:1 ratio of LLM-105/HMX co-crystal was identified as the excellent one, owning to the highest binding energy, highest CED, shortest Lmax, and greatest ductility. Graphical Abstract Models of LLM-105/HMX and one of the properties.

Silver nanoparticles decorated α-alumina as a hybrid filler to fabricate epoxy-based thermal conductive hybrid composite for electronics packaging application

Silver-alumina hybrid fillers (Ag/α-Al2O3) were synthesized by a simple ‘heat and mix’ technique to increase the thermal conductivity of epoxy resin. The nano and micro coalition of Ag/α-Al2O3 could facilitate the effective 3 D phonon transfer system throughout the insulative epoxy resin and consequently reduced the interfacial Kapitza resistance. The Ag/α-Al2O3hybrid filled epoxy composite with 55 wt % (Ag/αA-55Ep) expressed the 9.8 fold thermal conductivity improvement than pristine epoxy. The filler content was optimized to maximize the interfacial and cohesive bond strength of composites through lap shear tests. The Ag/αA-55Ep hybrid composite demonstrated glass transition temperature (Tg) of 118 °C evaluated through dynamic mechanical analysis (DMA). At 5% weight loss, the thermal stability of the Ag/αA-55Ep composite was 324 °C as measured using thermo-gravimetric analysis (TGA). The logarithm of electrical conductivity of Ag/αA-55Ep composite was 0.023 (Ω cm)−1 which signified the semiconducting material range. Surface morphology and conductive networks were determined from the fracture surface analysis of the composites. Agari’s empirical model was adopted to analyze the obtained experimental thermal conductivity results. The Horowitz and Metzger method was also considered for activation energy analysis of optimized composite.

Decoupling the Role of Inertia, Friction, and Cohesion in Dense Granular Avalanche Pressure Build‐up on Obstacles

Understanding the physical processes involved in snow avalanche‐obstacle interaction is essential to be able to estimate the pressure exerted on structures. Although avalanche impact pressure has been measured in field experiments for decades, the underlying physical principles are still elusive. Previous studies suggest that pressure is increased due to the formation of an influenced flow region around the structure, the mobilized domain, which varies in size depending on snow properties such as snow cohesion. Here, we aim to better understand how cohesion, friction, velocity, and their interplay affect avalanche pressure buildup on structures. This is achieved by simulating the avalanche‐obstacle interaction with a newly developed numerical model based on the discrete element method, using a cohesive bond contact law. The relevance of the model is tested by comparing simulated impact pressures with field measurements from the Vallée de la Sionne experimental site. Our results show that at the macroscale, impact pressure consists of the inertial, frictional, and cohesive contributions. The inertial and frictional contributions arise due to the existence, shape, and dimension of the mobilized domain. The cohesive contribution increases the particle contact forces inside the domain, leading up to a doubling of the pressure. Based on these physical processes, we propose a novel scaling law to reduce the problem of calculating the pressure induced by cohesive flows, to the calculation of cohesionless flows. These findings enhance our understanding of the interaction of cohesive granular flows, such as snow avalanches, and structures at the microscale and macroscale.

Wellbore stability analysis based on geomechanical modeling using finite element method

The analysis and prediction of the wellbore stability is considered as one of the sensitive and critical factors in oil wells’ drilling operations. Parameters affecting well stability include region’s in situ stresses, pores’ water pressure, rock strength, drilling fluid pressure and drilling direction, respectively. In general, in situ stresses and rock resistance are some of the uncontrollable parameters affecting the wellbore and will become possible only by adjusting controllable parameters such as fluid pressure and drilling direction to avoid well instability problem occurrence. This paper has tried to investigate well instability problem in one of the Asmari Reservoir wells in one of the southwestern Iran fields in different ways and present the necessary approaches and suggestions for better promotion of drilling operations in the aforesaid field. To achieve induced stresses around the wellbore, numerical method and Phase 2 software have been used. Rock mechanical parameters including modulus of elasticity, Poisson's ratio, cohesive bond, friction angle, over-burden floor stress amount, minimum and maximum horizontal stresses along the well depth have been investigated and their variations have been shown and then, to simulate the wellbore stability, these data were entered at a cross-section (2380 m) into the Phase 2 software and the output of this software including stresses, displacements around the wellbore has been analyzed finally after solving with finite element method.

Cognitive, Motor and Social Factors of Music Instrument Training Programs for Older Adults' Improved Wellbeing.

Given emerging evidence that learning to play a musical instrument may lead to a number of cognitive benefits for older adults, it is important to clarify how these training programs can be delivered optimally and meaningfully. The effective acquisition of musical and domain-general skills by later-life learners may be influenced by social, cultural and individual factors within the learning environment. The current study examines the effects of a 10-week piano training program on healthy older adult novices’ cognitive and motor skills, in comparison to an inactive waitlisted control group. Fifteen participants completed piano training led by a music facilitator in small groups (max n = 4 per lesson class; two experimental, two waitlisted control groups). Data was collected using an explanatory sequential design: quantitative data from a battery of cognitive and motor tests was collected pre/post-test on all participants, with further post-test data from the waitlisted control group (n = 7). Qualitative data included weekly facilitator observations, participant practice diaries, and an individual, semi-structured, post-experiment interview. Bayesian modelling demonstrated moderate evidence of a strong positive impact of training on part A of the Trail Making test (TMT), indicating improved visuo-motor skills. Moderate evidence for negative impacts of training on part B of the Trail Making Test (and difference score delta) was also found, suggesting no benefit of cognitive switching. Qualitative results revealed that the group learning environment motivated participants to play in musical ensembles and to socialize. Motivation was optimal when all participants were happy with the chosen repertoire (participants reported they were motivated by learning to play familiar music) and when the facilitator observed that groups had formed cohesive bonds. Informed by these factors, exploratory analyses demonstrated strong evidence that a participant’s lesson class had an impact on post-test scores (TMT part A). These results not only demonstrate the extent of cognitive benefits of a short-term piano training intervention for older adults, but also the importance of considering the group dynamics in the learning environment.

Numerical Simulation of Corroded Reinforced Concrete Beam Strengthened by a Steel Plate with Different Strengthening Schemes

This paper proposes 3D nonlinear finite element (FE) models to predict the response of corroded reinforced concrete (RC) beam strengthened using a steel plate. Five FE models are developed based on the tests carried out by the authors in a previous investigation, in which three models are used to simulate the corroded RC beams with different schemes. The FE models use the coupled damaged‐plasticity constitutive law for concrete in tension and compression and consider the bond‐slip between the corroded tensile steel bar and concrete. The cohesive element is also used to model the cohesive bond between the steel plate and concrete. The FE results of load‐deflection and the crack distribution are compared with the test data. The FE results are consistent with the test results. The influence of the thickness of the steel plate, the thickness, and location of the U‐shaped steel strip on the bearing capacity of the strengthened corroded beam is analyzed through FE models. The results show that the thickness of the steel plate on the bottom surface should not exceed 4 mm for the flexure‐strengthened and combined strengthened beams with a 10% corrosion rate. It is most reasonable to improve the bearing capacity using the 3 mm and 2 mm of thick U‐shaped steel strips for the shear‐strengthened and combined strengthened beams, respectively. The most reasonable location of the U‐shaped steel plate is at the end of the steel plate for beams with a 10% corrosion rate.

Clustering in ZnBVI-rich SrxZn1−xOyBVI1−y (BVI = S, Se, Te) highly mismatched alloys

Abstract The clustering properties of dilute highly mismatched semiconductor alloys attract considerable interest recently. Non-homogeneity of clusters and strong internal strains are the main disadvantages of such alloys. 4O10Sr clustering in ZnBVI-rich SrxZn1−xOyBVI1−y (BVI = S, Se, Te) up to 800 °C are presented. Reduction of the internal strains is a cause of the cluster formation. The cohesive energies, stiffness coefficients, bond stretching and bond bending elastic constants of zinc blende SrS and SrSe are estimated. All or almost all oxygen atoms should be in 4O10Sr clusters up to 800 °C in SrxZn1−xOyS(Se)1−y if alloy content is y > 1 × 10−3 (5 × 10−4) and x > 4y. SrxZn1−xOyTe1−y are completely 4O10Sr cluster ordered with contents from the ultra dilute limit (x > 1 × 10−4, y = 1 × 10−4) up to 800 °C. The densities of 4O10Sr clusters were calculated by minimization of the free energy. The binding energy of the electron bound to the oxygen tetrahedron in ZnTe:O at RT is estimated. The obtained results demonstrate that SrxZn1−xOyBVI1−y are promising semiconductors with the reduced internal strains and identical polyatomic clusters containing oxygen tetrahedrons.

DEM simulation of grain-coating type methane hydrate bearing sediments along various stress paths

This study explores the mechanical behaviors of grain-coating type methane hydrate bearing sediments (MHBS) using the discrete element method (DEM) under four typical compression conditions, i.e. triaxial, isotropic, constant stress ratio, and true triaxial. The particle-scale mechanism of grain-coating type MHBS is taken into account in the DEM contact model. The numerical results show that MH saturation and bond result in increased structural yield stress. The mean stress and volumetric change are larger under lower stress ratio in the constant stress ratio compression tests. The yield envelop obtained from the true triaxial compression test agrees well with the Lade-Duncan criterion. The shear strain contours in deviatoric plane can be described by changing the size of Lade-Duncan yield surface. Grain-coating type MHBS behaves like weakly-bonded sand, as cohesive MH bonds break at the very early stage of loading. Upon loading, the frictional properties of MH host sands evolve according to the change in grain morphology (i.e., particle enlargement and angulation). The simulation results and revealed particle-scale mechanism are useful in future development of constitutive models for MHBS.

Acoustic-Emission Monitoring of Airframe Failure under Cyclic Loading

The structural–phenomenological approach used to classify and split acoustic-emission signals into energy clusters, together with the parameters of detection frequency and weight content of location pulses in the clusters, allows real-time monitoring of main trends in damage accumulation at different structural levels and makes it possible to isolate signals generated during the failure of a structural material from accompanying mechanical interference and electromagnetic noise. An example of applying new criterion parameters to determining the moment of delamination of stringer runoffs from the shelves of the MC-21 airframe support strut under conditions of fatigue tests with a symmetric loading cycle is provided. Using the new criterion parameters and developed cluster-analysis techniques, employed, among other things, to discriminate location pulses in the field of spectral characteristics, an interconnection has been established between the process of breaking cohesive and adhesive bonds in the adhesive layer at the boundary between the stringer runoff fastening and the support strut shelves and the generated acoustic signals by their energy, waveform, and spectrum.

Study on filtration rules of horizontal fracturing liquid based on fluid-solid coupling

A three-dimensional finite element model of layered porous media containing interlayers and reservoirs was established with ABAQUS software and the three-dimensional fluid-solid coupling solid element and cohesive bond element were adopted to describe the damage behaviors of rock and fracture, stimulate the initiation and propagation of horizontal fractures and the fluid filtration process, analyze and obtain the effect of geological and engineering factors on propagation parameters of the horizontal fracture and on the filtration distance, and analyze the significance of the parameters, including elastic modulus, construction displacement, permeability, viscosity of pressure liquid, ground stress, pore pressure and amount of construction fluid. Finally, the simulated rules were adopted to guide the design of fracturing parameters in actual wells, which has obtained remarkable effect after fracturing.