Alterations In Material Properties Research Articles

Research on the thickness effect and micro-fracture mechanism of graphite sheets with layered structures

Size effect refers to alterations in material properties as their size varies, garnering significant attention as a cutting-edge issue. Graphite sheets, known for their exceptional thermal and electrical conductivity, the thickness effect on their mechanical properties is a notable gap in research. In this paper, the tensile strength, damage rate, and micro-fracture mechanism of graphite sheets with different thicknesses were studied through uniaxial tensile, digital image correlation (DIC) tests, and scanning electron microscope (SEM). The results reveal a significant thickness effect on the tensile strength of graphite sheets: thinner graphite sheets exhibit higher tensile strength and greater resistance to tensile fracture. Additionally, the thickness effect on the tensile strength was elucidated through the modified Weibull scaling law and Bažant size effect law. The thickness effect on the damage rate was revealed through strain evolution measured by DIC and the damage model. Thicker graphite sheets exhibit a more accelerated damage rate. It is noteworthy that the different fracture modes of layered structures are a crucial factor affecting the thickness effect of graphite sheets. Thinner graphite sheets exhibit more layers of stepped-like fracture, longer crack length, and a higher critical energy release rate. This study provides valuable insights for choosing the appropriate thickness of graphite sheets in practical applications and has the potential to enhance the safety performance of devices employing graphite sheets.

Flutter analysis of multi-directional functionally graded sector poroelastic disks

For the first time, in this article, stable/unstable zones of multi-directional functionally graded (MD-FG) sector disks under aerodynamic pressures are sought. Also, because of porous media, the system is modeled as a poroelastic system. The damping matrix, together with the aerodynamic stiffness matrix, is modeled upon Krumhaar's modified supersonic piston hypothesis. For more accuracy of the results, the Series-Fourier expansion of displacement fields in two-dimension is considered. To solve the partial differential equations, the singular convolution integration method with a singular convolution, as a numerical solver, is used. The precision of the outcomes is verified with those available in the other published research. It is demonstrated that the 3D model has great accuracy in predicting the flutter phenomenon and supersonic vibrations of the MD-FG sector disks. Finally, it has been shown that MD-FG power indices, radius ratio, boundary condition, poroelastic media, geometry, Mach number, aerodynamic pressure, and air yaw angle, in addition to Biot's coefficient, have a crucial role in the stable/unstable zones of the MD-FG sector disks under various conditions. One of the most important results of the current report is that the alteration in material properties of the MD-FG sector disk does not alter the yaw angle in which maximum frequency occurs.

Enhancing sensor linearity through the translinear circuit implementation of piecewise and neural network models

<abstract><p>The performance of the control system relies on the linearity of the sensor, which can be influenced by various factors such as aging and alterations in material properties. However, current sensor linearization techniques, such as utilizing neural networks and piecewise regression models in the digital domain, suffer from issues like errors, excessive power consumption, and slow response times. To address these constraints, this investigation employs a translinear based analog circuit to realize neural networks and piecewise regression models for the purpose of linearizing the selected sensors. A conventional feed-forward back propagation network is constructed and trained using the Levenberg-Marquardt algorithm. The developed linearization algorithm is implemented using a translinear circuit, where the trained weights, biases, and sensor output are fed as input current sources into the current-mode circuit. Further in this work, the piecewise regression model is designed and implemented using a translinear circuit and the breakpoint is determined using 'R' language. The simulation results indicate that the implementation of the current-mode circuit with metal-oxide-semiconductor field-effect transistors (MOSFETs) for the neural network algorithm leads to a substantial reduction in full-scale error as compared to the piecewise current mode model. Additionally, a performance analysis was conducted to compare the utilization of current-mode circuits with digital approaches for the linearization of sensors. The proposed translinear implementation surpasses the other researcher's work by delivering notable results. It showcases a significant improvement in linearity, ranging from 60% to 80%, for the selected sensors. Furthermore, the proposed implementation excels not only in linearity but also in terms of both response speed and power consumption. The improvement in the linearity of the sensor can be enhanced further by replacing the MOSFETs with bipolar transistors or any versatile materials such as gallium arsenide or gallium nitride-based transistors.</p></abstract>

Effect of the curing process on the thermomechanical properties of calcium aluminate cement paste under thermal cycling at high temperatures for thermal energy storage applications

Future perspectives to improve the energy efficiency of concentrating solar power (CSP) plants are focused on increasing temperatures above 600 °C. Among the different components of a CSP plant, the thermal energy storage (TES) medium must withstand high operating temperatures. Concrete was identified as an exciting candidate for its mechanical and thermal properties, needing further experimental research about this specific application. A fundamental concrete element is the cement binder, bringing cohesion to the composite components. As a requisite, the cement needs to be heat-resistant, and calcium aluminate cement (CAC) suits this demand. This cement is characterised by curing temperature-driven crystallisation changes, triggering an alteration of material properties. Considering that at 60 °C, the metastable hexagonal crystallisation is converted into a stable cubic crystallisation, seven curing cases were proposed in this study. After the curing process, thermo-mechanical properties of calcium aluminate cement paste were tested before and after thermal cycles from 290 °C to 650 °C. The results showed that, despite thermal cycling, the immediate hydration at 60 °C results in a higher thermal conductivity and compressive strength than standard curing at 20 °C.

Material property alterations for phenotypes of heart failure with preserved ejection fraction: A numerical study of subject-specific porcine models.

A substantial proportion of heart failure patients have a preserved left ventricular (LV) ejection fraction (HFpEF). This condition carries a high burden of morbidity and mortality and has limited therapeutic options. left ventricular pressure overload leads to an increase in myocardial collagen content, causing left ventricular stiffening that contributes to the development of heart failure patients have a preserved left ventricular ejection fraction. Although several heart failure patients have a preserved left ventricular ejection fraction models have been developed in recent years to aid the investigation of mechanical alterations, none has investigated different phenotypes of the disease and evaluated the alterations in material properties. In this study, two similar healthy swine were subjected to progressive and prolonged pressure overload to induce diastolic heart failure characteristics, providing a preclinical model of heart failure patients have a preserved left ventricular ejection fraction. Cardiac magnetic resonance imaging (cMRI) scans and intracardiac pressures were recorded before and after induction. In both healthy and disease states, a corresponding finite element (FE) cardiac model was developed via mesh morphing of the Living Heart Porcine model. The material properties were derived by calibrating to its passive and active behavior. The change in the passive behavior was predominantly isotropic when comparing the geometries before and after induction. Myocardial thickening allowed for a steady transition in the passive properties while maintaining tissue incompressibility. This study highlights the importance of hypertrophy as an initial compensatory response and might also pave the way for assessing disease severity.

Analysis of vertical roller mill performance with changes in material properties and operating conditions using DEM

The vertical roller mill (VRM) is commonly used for secondary and tertiary crushing processes in numerous industries. In this study, the discrete element method (DEM) was employed to explore the crushing in an overflow VRM without air involved via the bonded-particle model (BPM). Particle crushing experiments on a laboratory-scale VRM were compared with simulated results and good agreement was obtained indicating the accuracy of the numerical model. Then, effects of the material properties and the operating conditions on the overflow VRM performance were systematically investigated. It was found that trends in the particle size distribution of product and changes in throughput and crushing rate could be identified with alterations in material properties and the operating conditions. These two aspects are of great significance to the equipment performance. By increasing the rotation, the residence time decreases, which helps increase the throughput. However, this will lead to a higher proportion of coarse level particles in the finished products. The crushing behavior of materials is related to their physical size as well as sphericity. The research on the crushing characteristics of VRM is effective in optimizing the process and operation parameters of the crushing equipment.

Fouling of mammalian hair fibres exposed to a titanium dioxide colloidal suspension.

Fouling of surfaces in prolonged contact with liquid often leads to detrimental alteration of material properties and performance. A wide range of factors which include mass transport, surface properties and surface interactions dictate whether foulants are able to adhere to a surface. Passive means of foulant rejection, such as the microscopic patterns, have been known to develop in nature. In this work, we investigate the anti-fouling behaviour of animal fur and its apparent passive resistance to fouling. We compare the fouling performance of several categories of natural and manufactured fibres, and present correlations between contamination susceptibility and physio-mechanical properties of the fibre and its environment. Lastly, we present a correlation between the fouling intensity of a fibre and the cumulative impact of multiple interacting factors declared in the form of a dimensionless group. Artificial and natural hair strands exhibit comparable anti-fouling behaviour in flow, however, the absence of flow improves the performance of some artificial fibres. Among the plethora of factors affecting the fouling of fur hair, the dimensionless groups we present herein provide the best demarcation between fibres of different origin.

Study of severe plastic deformations of metallic materials:- A move towards Amorphization

This review highlights one of the amorphization processes of metals, alloys as well as metal matrix composites (MMCs) and its benefits towards strength enhancements. The need for material properties such as low weight, improved strength, enhanced wear, and corrosion resistance along with sensible ductility instigated the researchers to investigate the effect of different reinforcements as well as processing techniques on light metals. Developments in different primary, as well as secondary processing techniques, partly resulted in the enhancement of material properties. Different severe plastic deformation (SPD) technologies consequence the formation of ultra-fine grain structures as well as even nano-crystalline materials hence resulting in alteration of material properties. The numerous techniques are high-pressure torsion (HPT), accumulative roll bonding (ARB), equal channel angular pressing (ECAP), repetitive corrugation and straightening (RCS), etc. The operational principles of different SPDs, microstructural revolutions, mechanical properties are reported here. Implementation of the SPD techniques for the property enhancement of aluminium matrix composites (AMC) is the limelight here. Furthermore, this article highlights the recent achievements and current developments in determining the deformation mechanisms.

REVIEW OF INTELLIGENT MATERIALS AND THE POSSIBILITY OF THEIR USE IN ROCKET AND SPACE TECHNOLOGY

A new generation of materials – «intellectual» materials – is rapidly developing. Intelligent materials are materials that react in a certain way to changes in the state of the environment or the influence of force fields, vibrations or oscillations and radiation. This reaction results in the alterations of material properties, geometry and its adaptation to changes in operating conditions. Constructions are made of intelligent materials, in addition to the traditional functions of taking operational loads and ensuring load and strength, can provide self-monitoring, identification and localization of the fatigue damage. The material in such constructions can contain a set of electronics, built into the structure, which performs the function of receiving, processing and transmitting information in different frequency ranges. Intellectual material requirements are defined by the purpose and conditions of use of the structures and their components. The objective of this work is to give an overview of intellectual materials, in order to introduce the main information about their properties and their applicability in space and rocket technology. Furthermore, in this article data processing and analysis were carried out, which allowed to formalize the properties of the considered intellectual materials. Moreover, the application of intellectual materials can improve existing design schemes and elements or create entirely new design solutions in the future. For instance, the use of magnetostrictive materials allows to reduce the longitudinal oscillations of the launch vehicle on an active part of the trajectory along with absorbing vibrations and regulating the stringency of the stage separation. Structural analysis of the special properties of intellectual materials and their application not only will solve existing problems, but also enable further development of the space rocket industry.

Brillouin and Raman Micro-Spectroscopy: A Tool for Micro-Mechanical and Structural Characterization of Cortical and Trabecular Bone Tissues.

Human bone is a specialized tissue with unique material properties, providing mechanical support and resistance to the skeleton and simultaneously assuring capability of adaptation and remodelling. Knowing the properties of such a structure down to the micro-scale is of utmost importance, not only for the design of effective biomimetic materials but also to be able to detect pathological alterations in material properties, such as micro-fractures or abnormal tissue remodelling. The Brillouin and Raman micro-spectroscopic (BRmS) approach has the potential to become a first-choice technique, as it is capable of simultaneously investigating samples’ mechanical and structural properties in a non-destructive and label-free way. Here, we perform a mapping of cortical and trabecular bone sections of a femoral epiphysis, demonstrating the capability of the technique for discovering the morpho-mechanics of cells, the extracellular matrix, and marrow constituents. Moreover, the interpretation of Brillouin and Raman spectra merged with an approach of data mining is used to compare the mechanical alterations in specimens excised from distinct anatomical areas and subjected to different sample processing. The results disclose in both cases specific alterations in the morphology and/or in the tissue chemical make-up, which strongly affects bone mechanical properties, providing a method potentially extendable to other important biomedical issues.

General Finite-Element Framework of the Virtual Fields Method in Nonlinear Elasticity

This paper presents a method to derive the virtual fields for identifying constitutive model parameters using the Virtual Fields Method (VFM). The VFM is an approach to identify unknown constitutive parameters using deformation fields measured across a given volume of interest. The general principle for solving identification problems with the VFM is first to derive parametric stress field, where the stress components at any point depend on the unknown constitutive parameters, across the volume of interest from the measured deformation fields. Applying the principle of virtual work to the parametric stress fields, one can write scalar equations of the unknown parameters and solve the obtained system of equations to deduce the values of unknown parameters. However, no rules have been proposed to select the virtual fields in identification problems related to nonlinear elasticity and there are multiple strategies possible that can yield different results. In this work, we propose a systematic, robust and automatic approach to reconstruct the systems of scalar equations with the VFM. This approach is well suited to finite-element implementation and can be applied to any problem provided that full-field deformation data are available across a volume of interest. We also successfully demonstrate the feasibility of the novel approach by multiple numerical examples. Potential applications of the proposed approach are numerous in biomedical engineering where imaging techniques are commonly used to observe soft tissues and where alterations of material properties are markers of diseased states.

Mechanical Properties of Materials for Stem Cell Differentiation.

Recent findings about cell fate change induced by physical stimuli have expedited the discovery of underlying regulatory mechanisms that determine stem cell differentiation. Progress with regards to micro-/nanofabrication technology have led to the development of advanced materials that can mimic biophysical features of in vivo related circumstances of the human body. Since the cellular microenvironment directly defines cellular structure and function, diverse material properties including stiffness, topology, and surface chemistry are investigated to regulate multiple signaling cascades involved in stem cell differentiation for the development of innovative tools that can be widely utilized in various fields ranging from basic research to medical applications. This progress report addresses essential biophysical regulation and alteration of material properties applied to control stem cell differentiation. It also presents novel strategies to regulate stem cell differentiation based on relationships between recently discovered mechanotransduction pathways and cell differentiation signaling. A new perspective on stem cell physiology will further provide a framework of biomedical applications such as regenerative medicine and stem cell therapy.

Altered mechanical behavior of demineralized bone following therapeutic radiation.

Post-radiotherapy (RTx) bone fragility fractures are a late-onset complication occurring in bone within or underlying the radiation field. These fractures are difficult to predict, as patients do not present with local osteopenia. Using a murine hindlimb RTx model, we previously documented decreased mineralized bone strength and fracture toughness, but alterations in material properties of the organic bone matrix are largely unknown. In this study, 4 days of fractionated hindlimb irradiation (4 × 5 Gy) or Sham irradiation was administered in a mouse model (BALB/cJ, end points: 0, 4, 8, and 12 weeks, n = 15/group/end point). Following demineralization, the viscoelastic stress relaxation, and monotonic tensile mechanical properties of tibiae were determined. Irradiated tibiae demonstrated an immediate (day after last radiation fraction) and sustained (4, 8, 12 weeks) increase in stress relaxation compared to the Sham group, with a 4.4% decrease in equilibrium stress (p < .017). While tensile strength was not different between groups, irradiated tibiae had a lower elastic modulus (-5%, p = .027) and energy to failure (-12.2%, p = .012) with monotonic loading. Gel electrophoresis showed that therapeutic irradiation (4 × 5 Gy) does not result in collagen fragmentation, while irradiation at a common sterilization dose (25 kGy) extensively fragmented collagen. These results suggest that altered collagen mechanical behavior has a role in postirradiation bone fragility, but this can occur without detectable collagen fragmentation. Statement of Clinical Significance: Therapeutic irradiation alters bone organic matrix mechanics and which contribute to diminished fatigue strength, but this does not occur via collagen fragmentation.

Non-destructive ultrasonic evaluation of construction variability effect on concrete pavement performance

It is commonly recognized that non-uniformity of as-constructed Portland Cement Concrete (PCC) pavement may negatively affect long-term pavement performance. Conventional wisdom states that PCC thickness deficiency is the most important factor causing premature pavement failures. To address it, transportation agencies often impose strict penalties for not meeting the designed slab thickness requirements, thus contractors build slightly thicker slabs to avoid fines. However, other aspects of construction variability on pavement performance are mostly ignored by studies because conventional methods for construction uniformity assessment fail to provide sufficient information to quantify their effect. This study utilized a non-destructive ultrasonic test to evaluate in-situ pavement construction variability. To investigate the correlation between construction variability and surface distresses, a combination of non-destructive ultrasonic thickness measurements and visual distress surveys were performed in highways prior to rehabilitation. PCC slab thicknesses and shear wave velocities were computed from recorded ultrasound signals. An in-depth statistical analysis was performed to investigate possible relations between thickness or shear wave velocity and distresses using various pavement performance parameters. The main results of this analysis illustrate the importance of material quality and uniformity control during construction, since alterations in material properties significantly influence the presence of distresses. Shear wave velocity variations significantly correlate to cracked and broken slab panels in two sections, and, more importantly, to any type of distress in all tested pavement sections.

Thermal degradation of citrus pectin in low-moisture environment – Investigation of backbone depolymerisation

Thermal degradation of modified pectin samples with varying molecular structure during storage was recently studied at 60 °C and 80% relative humidity (rh) for 28 days. Demethoxylation and depolymerisation were identified as main degradation reactions. The present paper aims on improving the understanding of the different depolymerisation reactions and their interplay with demethoxylation during storage. Therefore, thermal degradaton of acidic and alkaline demethoxylated pectins was studied at a further reduced rh of 40%. The alterations were examined in detail via molecular parameters and were reflected by differential scanning calorimetry and attenuated total reflectance Fourier-transformation infrared spectroscopy. The impact of thermal degradation on pectin particle structure was studied via particle surface area and microscopy.At low relative humidity (rh) demethoxylation and depolymerisation were reduced, and the formation of brown reaction products, resulting from further decomposition of intermediate uronides and neutral sugars, was restricted. By comparing thermal degradation at different humidity, eliminative decarboxylation was identified as the main depolymerisation reaction.Reduction of rh affected also the alteration of pectin material properties, particle surface reduction was less pronounced. Molecular alterations were stronger in case of acidic demethoxylated samples, and alterations of material properties were higher in case of alkaline demethoxylated samples.

Electrically powered motions of toron crystallites in chiral liquid crystals

Malleability of metals is an example of how the dynamics of defects like dislocations induced by external stresses alters material properties and enables technological applications. However, these defects move merely to comply with the mechanical forces applied on macroscopic scales, whereas the molecular and atomic building blocks behave like rigid particles. Here, we demonstrate how motions of crystallites and the defects between them can arise within the soft matter medium in an oscillating electric field applied to a chiral liquid crystal with polycrystalline quasi-hexagonal arrangements of self-assembled topological solitons called "torons." Periodic oscillations of electric field applied perpendicular to the plane of hexagonal lattices prompt repetitive shear-like deformations of the solitons, which synchronize the electrically powered self-shearing directions. The temporal evolution of deformations upon turning voltage on and off is not invariant upon reversal of time, prompting lateral translations of the crystallites of torons within quasi-hexagonal periodically deformed lattices. We probe how these motions depend on voltage and frequency of oscillating field applied in an experimental geometry resembling that of liquid crystal displays. We study the interrelations between synchronized deformations of the soft solitonic particles and their arrays, and the ensuing dynamics and giant number fluctuations mediated by motions of crystallites, five-seven defects pairs, and grain boundaries in the orderly organizations of solitons. We discuss how our findings may lead to technological and fundamental science applications of dynamic self-assemblies of topologically protected but highly deformable particle-like solitons.

Effect of Processing Parameters on Microstructure and Mechanical Properties of Friction Stir Welded 6061 Aluminium Alloy Joints

In this research, friction stir welding was successfully conducted on 6 mm thick Al6061 plates, employing rotation speeds of 1200, 1400, and 1600 rpm, along with a constant traverse speed of 66 mm/min. Microstructural analyses of welded joints were performed using optical and scanning electron microscopy techniques. Notably, joints fabricated at a welding speed of 1600 rpm exhibited superior tensile properties. A discernible transformation occurred in the microstructure, wherein coarse grains within the parent material underwent a morphological change, transitioning into fine equiaxed recrystallized grains specifically within the nugget zone. Hardness assessments revealed that the hardness values of the nugget zones in all welded joints surpassed those of the parent material, with the lowest recorded hardness values observed in the heat-affected zone (HAZ). This observed microstructural refinement and hardness variation signify the successful alteration of material properties, particularly within the nugget zone, as a consequence of the FSW process.

A transparent three-layered laminate composed of poly(methyl methacrylate) and thermoplastic polyurethane subjected to low-velocity impact

Experimental and numerical results of a novel polymeric laminate consisting of poly(methyl methacrylate) (PMMA) and thermoplastic polyurethane (TPU) are presented. The laminate was subjected to low-velocity impact loadings using clamped three-point bending and dart impact tests at different temperatures and velocities in order to investigate the highly strain-rate and temperature dependent characteristics of a purely polymeric laminate. An investigation of the adiabatic heating of the highly strained interlayer in the post-breakage phase was performed with high-speed infrared thermography. A significant temperature rise of the interlayer in the impacted area and in the vicinity of cracks of the broken PMMA was observed, which facilitates temperature-based alteration of material properties during the test. Material and Finite Element modelling techniques are proposed and discussed, which are able to represent the mechanical and thermal behaviour of the laminate qualitatively and quantitatively.

Rolling contact fatigue assessment of repair rail welds

A repair welding procedure is numerically simulated. To validate the numerical model, analyses of the temperature evolution in a repaired rail are compared to existing full-scale test results. Thermomechanical simulations are carried out to evaluate the residual stress formation during welding and how the residual stress field is influenced by subsequent wheel passages during operations. The risk of rolling contact fatigue (RCF) is analysed and results discussed. It is found that tensile stress magnitudes resulting from welding decrease substantially during rolling contact loading. The influence of the residual stresses on RCF is found to be minor on the surface and somewhat more severe in a layer at the bottom of the repair weld. In addition to residual stresses, there is also a risk that welding introduces material defects and alters material properties. The influence of these factors on the risk of RCF is discussed.

Modeling Porosity Evolution Throughout Reaction‐Induced Fracturing in Rocks With Implications for Serpentinization

AbstractNumerical modeling based on the discrete element method was used to explore the kinetics and mechanics of fractures induced by mineral volumetric expansion during rock hydration. Two systems were considered: the hydration of periclase into brucite and the hydration of peridotite into serpentine. We modeled the coupling between mineral transformation, stress, volume increase, and deformation by simulating the volumetric growth of discrete elements based upon an Avrami‐type kinetics equation. The model was implemented to consider the effects of stress and temperature on reaction kinetics as well as the alteration of material properties during hydration reactions. We were able to reproduce experimental evidences observed during the transformation of periclase into brucite, including volume growth, fracturing of periclase, formation of a porosity pulse, as well as the slow‐down effect of effective stress on the kinetics of the transformation. The model was also applied to study the serpentinization process. We estimated a bell‐shaped relationship between temperature and reaction rate of peridotite transformation following observations made during serpentinization experiments. For both periclase and peridotite systems, we characterized a relationship between the formation of a porosity pulse and the rate of fracture development within the medium. During serpentinization, the amplitude of the porosity pulse and the duration of this pulse depend on the reaction rate and, therefore, on the temperature. Our investigations provide geomechanical explanations on how native dihydrogen formed during serpentinization can be expelled and initiates its migration process.