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This paper uses a stochastic finite element approach based on perturbation theory to explore the impact of uncertain material properties on the buckling characteristics of functionally graded porous (FGP) beams reinforced with graphene platelets (GPL). The first-order perturbation technique (FOPT) has been employed to accurately quantify diverse sources of uncertainties. A stochastic finite element formulation, ensuring C0 continuity, has been developed to calculate the stochastic buckling behaviour of FG-GPLRC porous beams. Convergence and validation analyses have been performed to validate the formulation's precision, comparing results with those obtained through a conventional Monte Carlo simulation. The Halpin-Tsai micromechanics model and Voigt's mixture rule have assessed the effective material properties at a homogenised level. Ultimately, the study delves into how material uncertainties influence the buckling responses of FG-GPLRC porous beams, particularly focusing on low variability (randomness) in key material design parameters like porosity content, nanofiller quantity, Young's modulus of the metal matrix, and nanofiller properties. The findings underscore that uncertainties in material properties significantly influence the buckling behaviours exhibited by FG-GPLRC porous beams. [ABSTRACT FROM AUTHOR]

The intricate cellular structure within the organ of Corti (OoC) provides the structural basis for how the stereocilia bundles of the hair cells are stimulated, which triggers the mechanoelectrical transduction channels. This intricate process remains elusive, and the stimulation mechanism of the inner hair cell (IHC) stereocilia is under heated debate. Recent experimental data on micromechanics of the OoC and IHC stereocilia motion motivate modeling studies to understand the detailed cellular motion within OoC. However, such a model is not computationally feasible for a full-length model of the cochlea. Current work develops and examines a slice modeling technique that considers the stimulation input location and wavenumber at the slice location. This slice model is compared to results from a full-length box model. [ABSTRACT FROM AUTHOR]

In this paper, the relation between the current and displacement responses due to an external mechanical stimulus on the outer hair cell (OHC) hair bundle (HB) is studied using a theoretical approach. We seek to understand the interplay between the time constants of the external loading and those intrinsic to the HB. To incorporate HB adaptation and channel gating, we used the model of an isolated HB, denoted as the TMJ model. We solved the nonlinear equations for the bundle dynamic response due to an externally applied force that consisted of an exponential temporal rise to a constant value. We determined the dependence of the bundle displacement over which the current continued to increase (the apparent operating range (OR)) on the rise time (τF) of the applied force. In addition, we developed a model linearized about the resting open probabilities for a given static, biasing load to provide closed-form approximations of the dependence on the stimulus rise time, τF, and bundle adaptation time constants. Finally, we wanted to determine if the inclusion of more precise kinematics of the tip link motion relative to the stereociliary rotation influenced model predictions of the channel opening and bundle stiffness. Hence, we developed geometrical relations between the two rows of stereocilia to establish coupled kinematic relations for inclusion in our HB kinetic model. We predict an OR of 30−50 nm for small τF and an overestimation by a factor of 10 in the OR for τF higher than the slow adaptation time constant. Finally, with accurate bundle kinematics, lower HB displacement, current, and adaptation motor displacement were predicted in contrast to the TMJ model. We are exploring the implications of this model on nanoscale mechano-electrical transduction. [ABSTRACT FROM AUTHOR]

Stimulus frequency otoacoustic emissions (SFOAEs), which are sounds emitted by the cochlea at the frequency of the stimulus, have been used as a noninvasive measure of cochlear function. The gradient of the SFOAE phases characterizes the latency of emission and is associated with the frequency selectivity and sharpness of tuning of the mammalian cochlea. However, whether the phase-gradient delay of SFOAE can be used as a indicator of cochlear tuning and sensitivity reliably when the proper-ties of the cochlea change remains unclear. The objective of this study is to address this question by varying cochlear model activity, tectorial membrane (TM) properties and organ of Corti (OoC) micromechanical properties to change cochlear tuning. In this work, a three-dimensional gerbil cochlear model that couples mechanical, electrical and acoustic domains with cochlear roughness has been used. The roughness is implemented on outer hair cells (OHCs) force acting on the basilar membrane (BM). Parameters that control the activity levels, TM longitudinal coupling and OoC impedance are varied. The results show that changes in sharpness of tuning due to reduction in cochlear activity and TM longitudinal coupling can be detected by using SFOAE phase-gradient delay. However, changes in cochlear tuning due to changes in OoC impedance are not necessarily reflected by corresponding changes in SFOAE phase-gradient delay. [ABSTRACT FROM AUTHOR]

There have been prior efforts characterizing hemp fiber reinforced composites but not hemp stem reinforced composites. Here, we investigate preparation of hemp stem reinforced concrete specimens for analysis and testing. To align the hemp stems in a specific direction, we have devised a method using a plastic u-tube to hold the hemp stems materials in place. Without the u-tube, hemp stems can shift from their desired positions while pouring the concrete. Stems were arranged in a 0 and 0/90/0 orientations. A representative bunch of stems and their cross sections are provided. Based upon micromechanical models of predicting effective properties of stems, we have aligned and used NDSANDS module of ASCA. Effective properties of five representative stem volume elements are calculated using constituent properties. A set of hemp stem reinforced concrete composite specimens are prepared and presented towards conducting flexure tests and relevant analysis. [ABSTRACT FROM AUTHOR]

The purpose of this research is to develop innovative techniques and combinations of constituents to use composites in agricultural, infrastructural and other relevant industries. Industrial, infrastructural, and biodegradable structural applications using hemp fibers are of interest to enhancing environmental sustainability. The products including graphite or hemp reinforced polymers with different volume fractions and orientations are considered. While a large number of products could be used in the commercial production, we explore only two laminates in this investigation. In this paper we are analyzing interlaminar stress components contributing to delamination of composite laminate. Using analytical techniques, effective response characteristics and interlaminar stresses of representative composites are predicted and given in this paper. Based upon this research a set of influencing factors will be identified, specific number of composite laminates will be chosen, manufactured, analyzed and tested for their performance characteristics. This is a step towards further research in progress for comparative studies between predicted and experimental values. We have used hemp fiber properties from reference [2]. For hemp fiber the Young’s modulus varies from 2.9 msi to 5.8 msi and Poisson ratio is 0.15. The matrix material properties of EPON 828 with Young’s modulus 0.42 msi and Poisson ratio 0.35 are used from reference [1]. For computation of effective properties of (0/90)s hemp reinforced composite laminates, we have used Young’s modulus values 2.9 msi and 5.8 msi separately. Dr. Pagano [3] was the first to recognize the importance of interlaminar phenomena in high-performance composite materials. His discovery of the “stacking sequence phenomenon” led to new practices to reduce the potential for delamination. [ABSTRACT FROM AUTHOR]

The Mori-Tanaka (MT) framework is utilized to develop a micromechanics model to predict the effective Young's modulus of a hybrid fiber-reinforced composite (HFRC) lamina reinforced with carbon nanotubes (CNT) nanofiller. The influence of waviness of CNTs on the effective Young's modulus of HFRC is investigated by considering the waviness of CNTs. Our findings indicate that wavy CNTs can be employed to tailor the material properties of HFRC lamina effectively. Due to the CNT waviness, we observed that transverse Young's modulus enhanced significantly, while the longitudinal Young's modulus degrades drastically. Out fundamental study highlights on development of high-performance and efficient multiscale composite material that can be effectively used in engineering applications to meet modern engineering demands. [ABSTRACT FROM AUTHOR]

Industrial, infrastructural, and biodegradable structural applications using hemp fibers are of interest to enhancing environmental sustainability. The purpose of this research is to develop innovative techniques and combinations of constituents to use composites in agricultural, infrastructural and other relevant industries. The products including graphite or hemp reinforced polymers with different volume fractions and orientations are considered. While a large number of products could be used in the commercial production, we explore only two laminates in this investigation. Broad aspects of mechanical response for composites and their products are provided in the user manual of a software package developed at AdTech Systems Research in collaboration with Air Force Research Laboratory. After identifying important constituents for composites and desirable applications, an attempt was made to investigate a set of sample cases by running ASCA Code for 2 representative composite laminates. Using analytical techniques, effective response characteristics of representative composites are predicted and given in this paper. Based upon this research a set of influencing factors will be identified, specific number of composite laminates will be chosen, manufactured, analyzed and tested for their performance characteristics. Further research is in progress for comparative studies between predicted and experimental values. [ABSTRACT FROM AUTHOR]

The paper investigates the mechanism of microplastic deformation during pulsed laser treatment of Armco-iron. It is shown that under conditions of ultrafast heating and cooling, deformation occurs with the participation of the grain boundary slip (GBS) mechanism. The characteristic features of GBS, revealed by high-resolution electron microscopic examination, are presented. A technique is proposed for measuring the magnitude of deformation by the GBS mechanism under the assumption of the statistical equality of the strain vector components for cubic lattices. The strain vector components were measured using the secants method; a statistical analysis of the measurements was performed. Its results made it possible to determine the values of the relative deformation by the GBS mechanism in Armco-iron in the range of 1.2-5.9%. [ABSTRACT FROM AUTHOR]

Particle Size Distribution (PSD) is one of the prime guiding factors of granular media response. Degradation via weathering is a process, which brings about a gradual shift in the PSD. In nature, chemically sensitive material like calcite undergoes chemo-mechanical degradation bringing about variations in their behaviour. In the present study, an experimental investigation is carried out to get insight into the mechanical response during the coupled chemo-mechanical process. The experiments were carried out at two different rates of dissolutions in a custom made 1D compression mould. From the experiments, it is clear that the higher rate of dissolution reduces the lateral earth pressure more than the lower rate. Discrete Element Method (DEM) analyses the micromechanical process behind the observed response from experiments. The results showed a reduction in lateral stress as soon as the dissolution starts. DEM analysis confirms the competing mechanism between grain size reduction and grain rearrangement as the guiding element for the granular media response. [ABSTRACT FROM AUTHOR]

The frictional behaviour of a series of numerical 2D granular mass flows down a model topography is analysed. Effective friction coefficients estimated from final deposits are compared with data from documented natural geophysical flows, and show a consistent behaviour as far as run-out distances are concerned. The latter is used to estimate effective friction coefficients which capture well the frictional behaviour derived from the computation of micro-mechanical stress tensors near the gravity centre. Distinguishing between the different parts of the mass while spreading, we show that the downstream part of the flow exhibits a much larger friction than the core and the tail. A dependence between friction and flow volume is however observed in each region. [ABSTRACT FROM AUTHOR]

The paper describes a micromechanical approach that explores the anisotropic nature of the capillary stress tensor and its evolution in pendular granular materials via Discrete Element Modeling (DEM) simulations. Dimensionless parameters are used to address the conditions under which the contribution of capillarity (or cohesive interparticle forces) to the stress transmission within a Representative Elementary Volume (REV) is expected to be considerable. From a series of suction-controlled conventional triaxial tests, numerical results show that the significance of the capillary stress and the relative magnitude of its mean to deviatoric components is directly connected to the characteristic particle size and applied stress. In addition, it is shown that the anisotropic character of the capillary stress tensor intensifies with increasing suction. Furthermore, a simple shear test is conducted at constant mean stress to reveal the development of deviatoric capillary stresses in the absence of any change in mean stress, which cannot be captured by the commonly used Bishop's stress expression. [ABSTRACT FROM AUTHOR]

The micromechanical behaviour of sand-rubber mixtures (SRMs) under monotonic triaxial shear were investigated using X-ray micro-tomography. The localisation of sand particle rotations that occurred in a pure sand sample under shear was inhibited in the sand mixed with 30% rubber grains by mass. Meanwhile, the SRMs exhibited an evolution of sand-sand contact coordination number that is not negatively correlated with sample porosity, dramatically different from that was observed in pure sands. Substantially increasing anisotropy degree of sand-rubber contacts compared with minor changes of sandsand contact fabric was observed, implying the increasingly important role of sand-rubber contacts in the transmission of deviatoric loads as the shear of SRMs progressed. [ABSTRACT FROM AUTHOR]

Knowledge transfer from micromechanics of granular media failure to geohazard forecasting and mitigation has been slow. But in the face of a rapidly expanding data infrastructure on the motion of individual grains for laboratory samples – and ground motion data at the field scale – opportunities to accelerate this knowledge transfer are emerging. In particular, such data assets coupled with data-driven approaches enable 'new eyes' to re-examine granular failure. To this end, effective strategies that can jump scales from bench to field are urgently needed. Here we demonstrate one strategy that focusses on the study of deformation patterns in the precursory failure regime using kinematic data. Unlike previous studies which focus on regions of high strains, here we probe the development and evolution of near-undeforming regions through the lens of explosive percolation. We find a common dynamical signature in which undeforming regions, which are initially transient in the precursory failure regime, become persistent from the time of imminent failure. We demonstrate the robustness of these findings for data on individual grain motions in a classical laboratory test and ground motion in two real landslides at vastly different scales. [ABSTRACT FROM AUTHOR]

We present the results of both experimental and numerical investigations of the silo discharge for a cohesive granular material. In our study, thanks to a cohesion-controlled granular material (CCGM) we propose to investigate the effect of the cohesive length lc, on the discharge of a silo for two different configurations, one axisymmetrical, and one quasi-2D rectangular silo. In both configurations, an adjustable bottom is used to control the size of the orifice. As observed for cohesionless granular material by previous studies, the mass flow rate and the density through an orifice are mostly controlled by the diameter of the orifice D. The experimental results of the quasi-2D silo are compared with continuum numerical simulations. [ABSTRACT FROM AUTHOR]

This paper summarises the numerical and experimental studies of brittle, hollow, cylindrical particles, called shells. It addresses the influence of shell properties both at the particle and assembly scales. Extreme compressibility has been recorded in the oedometer tests. Due to the large internal porosity of the shell, the breakage phenomena lead to highly compressive deformations with a significant stress dissipation. Using the Discrete Element Method (DEM), we have investigated in depth the micro-mechanical phenomena governing this macroscopic response. By quantifying the breakage and separating the double-porosity of the material, the foundations of a future constitutive model have been established throughout a simple prediction model applicable to the engineering practice. [ABSTRACT FROM AUTHOR]

We use bi-dimensional non-smooth contact dynamics simulations to analyze the isotropic compaction of mixtures composed of rigid and deformable incompressible particles. Deformable particles are modeled using the finite-element method and following a hyper-elastic neo-Hookean constitutive law. The evolution of the packing fraction, bulk modulus and particle connectivity, beyond the jamming point, are characterized as a function of the applied stresses for different proportion of rigid/soft particles and two values of friction coefficient. Based on the granular stress tensor, a micro-mechanical expression for the evolution of the packing fraction and the bulk modulus are proposed. This expression is based on the evolution of the particle connectivity together with the bulk behaviour of a single representative deformable particle. A constitutive compaction equation is then introduced, set by well-defined physical quantities, given a direct prediction of the maximum packing fraction φmax as a function of the proportion of rigid/soft particles. [ABSTRACT FROM AUTHOR]

It has been contemplated for a long time that dense granular materials flow in a stick-slip manner, and large fluctuations in the stresses are associated with it. However, the particle scale mechanics for this type of macroscopic motion has not been understood so far. We have analyzed the time evolution of contact networks from particle dynamics simulations and found that the rate of change of elastic energy of the packing can distinguish the stick regimes and the slip events. The isostatic criterion (number of contacts for a minimally stable particle) has been used to construct a cascade failure mechanism which reveals that the effect of the random breaking of contacts due to applied shear can be system-spanning for some cases. The size of the cascade failures follows a power law that explains experimentally observed large fluctuations is stresses. We expect that this power law distribution can connect the microstructure of a granular packing to its mechanical response. [ABSTRACT FROM AUTHOR]

Granular matter, particulate matter and granular materials are generic terms to refer to systems composed of many macroscopic bodies (grains or particles) where the contact interaction (which is non-conservative) plays a crucial role in the behavior of the system. This contrasts with other systems (e.g., atomic or molecular systems) where the constituent bodies (e.g., atoms or molecules) interact via conservative forces. The non-conservative contact interactions come from inelastic collisions (due to plastic deformation, sound or heat production) and also from friction. This makes the study of granular matter a major challenge to scientists and the handling/storage/processing of granular materials a major challenge to engineers. Particulate matter covers a very broad range of systems, from those formed by fine particles (powders) to those formed by large rocks (derbis), from soft bodies (cotton balls) to hard grains (glass beads), from those we eat (muesli) to those we play with (beach sand), from those used to build our houses (cement) to those used to grow our crops (soil). Needless to say, any new knowledge in this area has a tremendous potential to impact our lives and our economy. Powders & Grains is a conference held every four years to bring together researchers working both in fundamental aspects of granular matter and in technological applications. This volume collects the 195 papers presented during the 2021 edition of P&G, which provide an excellent overview of the current state-of-the-art in granular matter and new trends with contributions form six continents. [ABSTRACT FROM AUTHOR]

A micromechanical model is developed to predict the deformation behavior of additively manufactured aluminum alloys. Three-dimensional models of grain structures typical for different microregions of the melt pool are generated by the step-by-step packing method. A crystal plasticity-based constitutive model accounting for the elastic-plastic anisotropy of face-centered cubic crystals is employed to simulate the microscale deformation in an additively manufactured aluminum alloy under loading. The grain shape and texture effects on the plastic strain localization patterns are analyzed. [ABSTRACT FROM AUTHOR]

The Gurson–Tvergaard–Needleman (GTN) model, is widely used to predict the failure of materials based on lab specimens, The direct identification of the GTN parameters is not easy and its time and money consuming. The Gurson model is based on micro-mechanical behavior of ductile fracture, containing void nucleation, growth and coalescence The most used method to determine the GTN parameters is the combination between the experimental and FEM results In this paper we are going to determine the GTN parameters for the SENT specimen based on the fracture toughness test of CT specimen. The reason behind choosing the SENT specimen is because it can be very good representative of the pipe for both uniaxial and biaxial loading conditions. [1] The Results show that the GTN parameters concluded from CT simulations, predict very well the crack initiation and propagation of SENT specimen which confirm the validity of this model, as already proved in the literature. [ABSTRACT FROM AUTHOR]

This paper presents an investigation of engineering failure modes for INCONEL601 tested after exposure to annealed heat-treatment (1.5 hour duration) and as received prior to annealing. Microstructural and failure surfaces were tested for chemical composition and examined by metallographic techniques and fatigue fractography. Scanning electron microscopy and enginery dispersive spectroscopy (SEM-EDS) revealed the presence of voids, dimples, and striations associated with fatigue crack propagation. The microstructural characterization of annealed INCONEL601 is notable for triangular voids that congregate along grain boundaries in contrast to the as received INCONEL601. In addition, the tensile and fatigue strengths of as-received samples were greater than annealed heat-treated INCONEL601. [ABSTRACT FROM AUTHOR]

Bioactive glass (BG) is a bioceramic materials widely used as bone regenaration. However, BG has low mechanical strength to use at load bearing part. In this study, cordierite was added into BG to form BG-cordierite composite. The objective of this study is to study the effect cordierite addition into BG on mechanical and bioactivity properties. BG and cordierite were synthesized through melt-quench method. BG and cordierite powders obtained were mixed together with different amounts (10 – 30 wt.%) of cordierite. The mixtures were pressed to form pellets. Then, the mechanical and bioactivity properties of the pellets were tested. The BG-cord composites were soaked in Hank’s Balance Salt Solution (HBSS) for 7 days to test the bioactivity. The Vickers hardness was used to test the physical properties. The morphology of BG-cord composite was analysed using scanning electron microscope (SEM) and X-ray diffraction (XRD) was used to analyse the phases present. The results show that BG-cord has shown good bioactivity but the its hardness is lower than the pure BG. [ABSTRACT FROM AUTHOR]

The paper consists of two parts united by the central idea of the random field of the microstructure of the material. The first part addresses a discrete static approach to describing the localization effect of plastic deformation known with the help of finite-element analysis under the assumption that the deformation of each of the grains obeys a bilinear law with a normal distribution of the yield stress over the grains. The result is a surface relief in the form of diagonally directed strips, which allows one to treat the deformed surface as Panin’s "chessboard". The second part is concerned with a dynamic continuum approach to the description of the random microstructure of materials. The problem of the propagation of stochastic waves modeled by waves in media with random elastic and mass properties is solved by means of the integral decomposition of the wave amplitude over the wave numbers. [ABSTRACT FROM AUTHOR]

In the context of the classical Biot theory for acoustic waves in a fully-saturated granular material, we improve upon the constitutive relation of the solid phase by means of micro-mechanical modeling. This is needed to explain discrepancies on the dependency of the frequency with the sound speed attenuation and dispersion between present models and experiment. As first step, we provide a more detailed description of the interaction between the particles and water. A Standard Linear Solid model is proposed to represent the behavior at contact level between particles immersed in a compressible fluid. [ABSTRACT FROM AUTHOR]

The design of composites is a crucial stage that needs to be systematically considered before its fabrication take place especially when it relates to complex and micromechanics interaction. The purpose of this paper is to develop and optimize the micromechanical mechanism of rhombus unit cell using different types of materials by using finite element analysis integrated with the Taguchi method and principal component analysis (PCA). In this study, three different fibres were selected such as E-glass, Kevlar and Boron and as for matrix materials were epoxy, polyester and aluminium, respectively. Different parameters were controlled and statistically analysed in the optimization phase. The findings showed that the set of optimal parameters in designing the rhombus model related to micromechanics properties were identified as fibre volume fraction of 20%, the vertex angle for rhombus model is 75º, the thickness for a unit cell model is 0.03 mm and the load applied to the model is 100N. As for the best combination of materials were identified as Boron/Aluminium composite. [ABSTRACT FROM AUTHOR]

The motivation of this work is to derive a means of monitoring the structural integrity of components used in nuclear power plants since there are a diverse range of materials, under variable loading, with a range of prior loading histories under complex environmental conditions. An experimental technique has been developed to characterize brittle materials which, using linear elastic fracture mechanics, has given accurate measurements of the global quantity fracture toughness. Here we extend this geometry to X-ray measurements in order to track the crack front as a function of loading parameters as well as to determine the crack surface area as loads increase. We have applied these advances to fracture in beryllium, to determine the onset of damage within the target as strain increases. Further, visualization of crack front advance and the correlated strain fields that are generated during the experiments, have allowed determination of the fracture surface generated as a function of load. This accurate tracking of the micromechanics controlling the energy balance in dynamic failure will provide a vital step in validating multiscale predictive modelling. By these means we aim to produce a micro- and mesoscale justification for macroscale concepts such as KIC. [ABSTRACT FROM AUTHOR]

In order to describe the meso-damage of the refractories more accurately, and to study of the relationship between the mesostructured of the refractories and the macro-mechanics, this paper takes the magnesia-carbon refractories as the research object and uses the molecular dynamics method to instead the traditional sequential algorithm to establish the meso-particles filling model including small and large particles. Finally, the finite element software-ABAQUS is used to conducts numerical simulation on the meso-damage evolution process of refractory materials. From the results, the process of initiation and propagation of microscopic interface cracks can be observed intuitively, and the macroscopic stress-strain curve of the refractory material is obtained. The results show that the combination of molecular dynamics modeling and the use of Python in the interface to insert the cohesive element numerical simulation, obtaining of more accurate interface parameters through parameter inversion, can be more accurate to observe the interface of the meso-damage evolution process and effective to consider the effect of the mesostructured of the refractory material on its macroscopic mechanical properties. [ABSTRACT FROM AUTHOR]

Our understanding of cochlear amplification has been mainly informed by observations of the high-frequency basal region. Results from the few existing in vivo studies from the low-frequency apical region have suggested that cochlear amplification may be more broadly tuned and not as nonlinear as in the base. The current study explored micromechanics via sound evoked vibrations of the cochlear partition, including the organ of Corti (OoC), the basilar membrane (BM) and the tectorial membrane (TM), within the 2nd apical turn, corresponding to the 2.5 kHz best frequency region, of the gerbil cochlea using volumetric optical coherence tomography vibrometry (VOCTV), imaged non-invasively through the otic capsule bone in vivo. Sound induced radial displacements below 4 kHz showed similarities and differences to the well-established BM transverse responses at high-frequency basal region. Responses showed broader tuning, but similar gains at the best frequency and similar phase accumulation. The distinct difference found was the presence of compressive nonlinear growth with SPL below the best frequency down to 0.1 kHz observed at the outer hair cell (OHC) and reticular laminar (RL) locations but not in the BM or inner hair cell regions. These relative motions provide further insight on how OHC somatic forces are distributed within the cochlear partition. [ABSTRACT FROM AUTHOR]

Designing flat roofs has many issues and decisions. This can be, for example, the decision on how to close the flat roof. By default, roofs are terminated at the periphery by means of attics or by creating a so-called rigid edge of the roof. This paper focuses on the first option, and therefore the termination of the flat roof using the atics. The author is dealing with the findings with regard to the way the proposal is implemented and the subsequent realization of the details. As a major waterproofing layer, films of soft polyvinyl chloride are considered for all cases. As part of the flat roof implementation, many situations can occur which may result in a shorter life of the detail of flat roof atics. One of these aspects may be the built-in moisture in the roof cladding during construction. This work is focused on the description of the knowledge about the individual methods of implementation of details and their suitability from the perspective of the possible incorporation of moisture in the roof casing composition within the roof realization. [ABSTRACT FROM AUTHOR]

The article describes behavior of ternary gypsum-based composites, especially the changes of properties caused by the influence of moisture. The ternary mortars are composed from gypsum, hydraulic lime, different types of pozzolan and standard sand. Pozzolans in the mixture react with hydraulic lime and form CSH and CAH phases. Presence of these phases improves resistance of gypsum against the moisture. The way of samples storage affects the development of materials structure and properties of gypsum-based mortars. The basic physical, mechanical and thermal properties of samples stored in the laboratory environment and under the water are compared. The storage in the water has the greatest impact on the properties of all materials, especially on the mechanical properties. While the strength of pure gypsum mortar, stored in the water, decreased significantly and after one year in the water environment the samples were nearly destroyed, the samples with pozzolan admixtures evinced the improvement of mechanical properties, when stored in water. [ABSTRACT FROM AUTHOR]

This work is initially devoted to study the cracking behaviour of a small composite wind turbine blade. In order to choose material, the blade is manufactured by different materials (glass/epoxy, carbon/epoxy, Aluminium, and PVC). Considering loads and boundary condition, we study in static analysis the stress, strain and displacement, in dynamic analysis the modes shape and naturals frequencies, in fracture analysis the stress intensity factor, crack initiation and crack growth in order give the results by finite element method, then follow the evolution of the displacement, strain, stress SIF and first six naturals frequencies a function as crack propagation. As results we provide the best and idol materials versus the fatigue life of blade. [ABSTRACT FROM AUTHOR]

The current stage in the development of the construction industry is associated with improving the consumer properties of composite materials, increasing their operational efficiency, increasing production volumes and service lives. One of the ways to solve the problem associated with increasing the durability and reliability of materials from plant raw materials is to create compositions based on the synthesis of ceramic materials with an ordered structure by mineralization of the wood matrix with sol-gel surface heating. Basically, this technology consists in processing materials from wood with a soluble complex obtained from the natural polysaccharide arabinogalactan and nanoscale quartz-containing minerals of rocks of various genesis. However, the mechanism of formation of such a complex compound and its composition has not been studied so far. Therefore, the purpose of this work was to determine the composition of the organomineral complex arabinogalactan-quartz-containing polymineral sand for its further use in the process of accelerated petrification of wood. Arabinogalactan is isolated from Siberian larch wood by aqueous extraction using a liquid extractor for accelerated extraction of water-soluble substances. As a mineral component, quarry polymineral sand with a silica content of 91% was used. The quartz-containing component was preliminarily ground in a planetary ball mill. Experimentally, the conditions for mechanical dispersion of the experimental samples were chosen, which make it possible to obtain reproducible results on the dimensional characteristics of particles with a normal polydispersity index value. Thus, the average volume of sand particles was 186 nm. The resulting fine-dispersed system was characterized by the specific surface area by nitrogen sorption. This parameter is equal to 7532 m2 / kg. The complexation process was studied by calorimetry, by measuring the thermal effect of the interaction reaction of an organic substrate with a mineral additive. It is established that the complexation process is characterized by the following time parameters: the induction period is 30-35 minutes, active complexation during the interaction of the components proceeds for 8 - 10 minutes. The change in the temperature of the reaction mixture for different series of experiments varies within 0.6 ° C. The obtained experimental data made it possible to calculate the enthalpy change of complexation in the arabinogalactan - quartz-containing polymineral sand system and determine the composition of the obtained organomineral complex. [ABSTRACT FROM AUTHOR]

Modern satellite design requires fibers with a high elastic modulus to ensure that satellite systems have a high resonant frequency at a low launch weight. High-modulus carbon fibers have a limited number of suppliers and end users, representing less than 1% of the total carbon fiber market. Recently, domestic carbon fiber producer Hexcel introduced HM63, a new, made in the United States, high-modulus carbon fiber. Harris is qualifying HM63 to reduce the risk to U.S. satellite manufacturing from the current high-modulus carbon fiber market which primarily resides in Japan. The effort to qualify and fully characterize HM63 is a combined micro- and macromechanics based building block approach that minimizes testing complexity and cost, while allowing for downstream design flexibility. In pursuing this, Harris created and validated new prepreg specifications, developed micromechanical modeling results, carried out prepregging trials, laid up lamina panels, and conducted lamina testing to create a validated micromechanics model. Additional efforts included laminate design and testing for a variety of application targets. Application laminate designs will prepare HM63 for use as a drop-in or redesign replacement for a range of legacy fibers on Harris' next-generation electro-optical imaging systems. [ABSTRACT FROM AUTHOR]

Material placement at the ideal nip point temperature over complex surfaces with uniformity across the width of the compaction rollers results in optimized part properties for Automated Fiber Placement (AFP) processes. However, current AFP systems utilize heat control models and methodologies, based on multiple process parameters such as feed-rate and orientation, that are mostly open-loop. Here, infrared (IR) heater input is calibrated as a function of process parameters during machine qualification. This work presents a numerical simulation to predict arrayedinfrared (AIR) emitter radiation onto a substrate that includes view factor implementation, IR radiative heat flow calculation, energy rate balance, and a transient heat transfer model. The purpose of this numerical model is to predict nip point temperature on complex surfaces , serving as a baseline for a new arrayed-infrared (AIR) thermoset heater to improve AFP process control.. It is anticipated that this simulation will accurately control the temperature for high-speed AFP layup of complex geometries. An anticipated result of an AIR heater system is that material calibration and testing will be reduced as temperature is instantaneously monitored and controlled. Therefore, temperature across the roller width will be uniform during placement of complex parts, independent of their geometry. [ABSTRACT FROM AUTHOR]

Continuous fiber reinforced polymer matrix composite materials are growing in applications across multiple industries as a light-weight structural component solution. It is well-known that the selection of polymer matrix affects the ultimate mechanical properties and structural performance of a composite. In this study, a micromechanics modeling approach in Digimat MF based on Mori-Tonaka mean-field homogenization theory was adopted to investigate the impact of thermoset matrices on the mechanical performance of unidirectional composites. Progressive failure analysis of longitudinal tension, transverse tension, and shear tests of continuous carbon fiber (CF) reinforced unidirectional (UD) composites with an epoxy matrix (Baseline) and a ductile thermoset matrix with higher elongation and lower modulus (Improved) were modeled and compared. In addition, the effects of void content in the composites are also accounted for by adding an additional phase. The study of unidirectional composites reveals the following: • The evolutions of fiber and matrix failure indicators from the progressive failure analysis show that fiber fails much faster than matrix under longitudinal tension while an inverse trend is predicted under transverse tension and shear. • Using a ductile matrix with higher elongation and lower modulus can enhance the transverse tensile and shear properties of the final composites by delaying matrix failure. • Void sensitivity shows a trend similar to experimental results from literature: void content has larger negative effects on transverse and shear properties than on longitudinal properties as void content increases. However, the model underpredicts the magnitude in transverse strength reduction by a factor of 5 at a void volume fraction of 5%, which may be related to the assumptions and the underlying homogenization theory utilized in the model. [ABSTRACT FROM AUTHOR]

In this note the problem of thermoelasticity in composite made of two different materials is presented. The macroscopic properties of this composite are changing continuously along one direction. In this work three models are presented: the tolerance and the asymptotic-tolerance model, taking into account the effect of the microstructure size and the asymptotic model, which neglects this effect. The equations of these three models were obtained by using the tolerance averaging technique and solved by the finite difference method. Then the results obtained by tolerance modelling were verified by the finite element method. [ABSTRACT FROM AUTHOR]

Laboratory tests of concrete composite concrete T-shaped beams with variously arranged interface were performed. In the particular series the interface between concrete parts was reinforced or non-reinforced. Additionally the interface conditions varied as follows: existence of adhesion in the interface, adhesion partly broken using chemical agent and adhesion completely broken with PVE membrane put in the interface. The paper presents the compiled results of all tests and the first stage of FEM analysis concerning the series of beams, where the adhesion was broken. Results of numerical analysis are compared with the crack pattern observed during tests. [ABSTRACT FROM AUTHOR]

The paper presents an optimal design of UAV wing, made of composite materials. The aim of the optimization is to improve strength and stiffness together with reduction of the weight of the structure. Three different types of functionals, which depend on stress, stiffness and the total mass are defined. The paper presents an application of the inhouse implementation of the evolutionary multi-objective algorithm in optimization of the UAV wing structure. Values of the functionals are calculated on the basis of results obtained from numerical simulations. Numerical FEM model, consisting of different composite materials is created. Adequacy of the numerical model is verified by results obtained from the experiment, performed on a tensile testing machine. Examples of multi-objective optimization by means of Pareto-optimal set of solutions are presented. [ABSTRACT FROM AUTHOR]

Mechanical joints (e.g. bolted) used for decades are proved to be reliable. They can be assembled and applied in very rough conditions since they are less sensitive to environmental effects than other types of joints (e.g. adhesive). Therefore, they are still employed in aircraft design. High specific stiffness and strength of composite materials (especially CFRP) cause a continuous increase in their usage in aircraft structures. In general, composites are brittle materials and more notch sensitive than metal alloys. Hole making is a necessary stage in manufacturing of a mechanical joint. Holes vicinities are the areas of high stress concentrations and determine load capability of the whole structure. Therefore, mechanical joints of composite parts require a special focus during both a designing and a manufacturing process. The aim of the paper is analysis of potential local material weakness/deterioration caused by a drilling process and its influence on the global response of a mechanical joint. The specimen in the form of a double-shear joint was analyzed. The weakened areas were identified on the basis of NDT ultrasonic analysis. A simple gradient material model was proposed to describe the hole vicinity. Numerical simulations were performed and compared to experimental results. [ABSTRACT FROM AUTHOR]

The paper is devoted to the optimal design of pores in microstructure with respect to thermal and mechanical properties. Porous material was modeled by means of two-scale analysis with numerical homogenization method. In order to model the shape of the pores closed B-Spline surfaces were used. It allowed for optimization in which pores may have almost arbitrary shape. The task of optimal design of pores was performed with respect to mechanical, thermal and geometrical properties. Three different criteria, which depend on stresses, ability to conduct heat and porosity were defined. In-house implementation of multiobjective evolutionary algorithm was used as an optimization tool. Numerical examples of optimization were included. [ABSTRACT FROM AUTHOR]

The paper aims to model the performance of the Glass Fibre Reinforced Epoxy (GRE) composite pipe under multiaxial loading via system identification approach. System identification modelling depends on the input and output data of the experimental result. In this study, the experimental data used are obtained from a pressurised test rig. The model is based on pure hydrostatic (2H: 1A) loading using GRE pipes with three different winding angles (±45 °, ±55 °, ±63 °). Several models based on different model structures are derived for comparison to obtain the best modelling accuracy. The result shows that the transfer function method could model and has the highest efficiency compared with the experimental result. The ±45 ° pipe model have achieved 92.41% and 85.13% for both its hoop and axial model. The ±55 ° pipe model has achieved 96.64% and 86.1%. Follow by the ±63° which the best fit is 92.41% and 94.26%. At the last part of this research, the ±55° pipe model and experimental data has been use to identified when the damage occur and found that the axial strain of 78 bar can damage the experimental pipe in this research. [ABSTRACT FROM AUTHOR]

The effects of elevated temperature on the tensile strength of Napier/glass-epoxy hybrid reinforced composites and its morphology of fractured surfaces are discussed. Napier/glass-epoxy hybrid reinforced composites were fabricated by using vacuum infusion method by arranging Napier fibres in between sheets of woven glass fibres. Napier and glass fibres were laminated with estimated volume ratios were 24 and 6 vol. %, respectively. The epoxy resin was used as matrix estimated to 70 vol. %. Specimens were tested to failure under tension at a cross-head speed of 1 mm/min using Universal Testing Machine (Instron) with a load cell 100 kN at four different temperatures of RT, 40°C, 60°C and 80°C. The morphology of fractured surface of hybrid composites was investigated by field emission scanning electron microscopy. The result shows reduction in tensile strength at elevated temperatures. The increase in the temperature activates the process of diffusion, and generates critical stresses which cause the damage at first-ply or at the centre of the hybrid plate, as a result lower the tensile strength. The observation of FESEM images indicates that the fracture mode is of evolution of localized damage, from fibre/matrix debonding, matric cracking, delamination and fibre breakage. [ABSTRACT FROM AUTHOR]

In this study Magnesium- Hydroxyapatite (Mg-HA) composites were prepared by powder metallurgy method using pure magnesium and synthesized hydroxyapatite powders. HA was synthesized in nano and micro scales powder by wet chemistry precipitation method and Mg-HA composites made in ; 1, 3, 5 and 10 wt. % nano and 1, 5, 10 and 15 wt. % micro scale HA powders .The effects of particle size and amount of HA on microstructure and mechanical behavior of composites were investigated. Significant improvement in mechanical properties was observed by using nano HA for reinforcing Mg matrix because the HA distribution were better in nano-scale composites than the micro scale. The theoretical density of the composite prepared by adding 3 wt. % HA nano particles reached to 96 %, with 80.88 V hardness, and 131.52 MPa Ultimate shear stress, as optimum mechanical properties. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) grafted on carbon surfaces can be used to reinforce composite materials. During an industrial process of CNTs production and composite processing, friction stresses will be applied on CNTs. This study showed that CNTs formed a transfer film under friction stresses and that the wear of the CNTs has no influence on the wettability of the surface, so we can predict no decrease in the properties of composites. [ABSTRACT FROM AUTHOR]

Titanium alloy profiles are widely applied as airframe parts due to its excellent mechanical properties and high compatibility of electrical potential with resin composite material. The electrical assisted forming is recognized as the effective approach to improve plasticity of titanium alloy profile. In this work, the electo- thermal uniaxial tension was performed to investigate the mechanical properties. The experiment results show that, the stress-strain curves increases sharply to the peak and declines quickly, exhibiting no stable deformation occurring. On basis of the obtained curves, a constitutive equation was established with consideration of the characteristic of self resistance heating, and the microstructure evolution was predicted. A comparison of the calculated stress- strain curves with the experimental ones was conducted, showing a reasonable agreement. [ABSTRACT FROM AUTHOR]

With the development of net-shape forming technology, hot forming process is widely applied to manufacturing gear parts, during which, materials suffer severe plastic distortion and microstructure changes continually. In this paper, to understand and model the flow behavior and microstructure evolution, SAE 8620H, a widely used gear steel, is selected as the object and the flow behavior and microstructure evolution are observed by an isothermal hot compression tests at 1273-1373 K with a strain rate of 0.1-10 s-1. Depending on the results of the compression test, a set of internal-state-variable based unified constitutive equations is put forward to describe the flow behavior and microstructure evaluation of SAE 8620H. Moreover, the evaluation of the dislocation density and the fraction of dynamic recrystallization based on the theory of thermal activation is modeled and reincorporated into the constitutive law. The material parameters in the constitutive model are calculated based on the measured flow stress and dynamic recrystallization fraction. The predicted flow stress under different deformation conditions has a good agreement with the measured results. [ABSTRACT FROM AUTHOR]

A comprehensive knowledge about the material flow stress is a key parameter for a reliable design of hot forming processes using Finite Element (FE) software codes. Due to the microstructure evolution caused by the interaction of hardening and softening phenomena that take place during hot forming operations, the material flow stress is influenced by strain rate and temperature. While transient strain rates and temperatures typically characterize the industrial forming processes, the flow curves used in FE simulations are normally determined at arbitrary constant temperatures and strain rates. To calculate the flow stress evolution in between the measured strain rates, FE programs use linear interpolation. Hence, the material relaxation behavior caused by the microstructure evolution during transient strain rates is not considered. Previous investigations by various authors have shown that for a rapid strain rate change by one order of magnitude significant deviations between measured flow stress and linear interpolation appear before the flow stress approximates the flow curve obtained at the new constant strain rate again. However as mentioned before, industrial forming processes are characterized by more or less smooth than instantaneous changes in strain rate. Therefore, in this study, changing strain rates with different linear slopes are investigated. For this purpose, isothermal cylinder compression tests of an industrial case hardening steel are conducted at elevated temperatures. The resulting flow stress is compared with the linear interpolation of the flow curves determined at constant strain rates. Additionally, the grain size evolution during the strain rate change is analyzed to better understand the microstructural changes. The current investigation shows that the slope of the strain rate increase significantly influences the deviation from the linear interpolation. This observation can be explained by the time dependent microstructure evolution during deformation at elevated temperatures. [ABSTRACT FROM AUTHOR]

Quality parameters such as firmness and susceptibility to mechanical damage are affected by the mechanical properties of fruit tissue. Fruit tissue is composed of turgid cells that keep cell walls under tension, and intercellular gas spaces where cell walls of neighboring cells have separated. How the structure and properties of these complex microstructures are affecting tissue mechanics is difficult to unravel experimentally. In this contribution, a modelling methodology is presented to calculate the deformation of apple fruit tissue affected by differences in structure and properties of cells and cell walls. The model can be used to perform compression experiments in silico using a hygromechanical model that computes the stress development and water loss during tissue deformation, much like in an actual compression test. The advantage of the model is that properties and structure can be changed to test the influence on the mechanical deformation process. The effect of microstructure, turgor pressure, cell membrane permeability, wall thickness and damping) on the compressibility of the tissue was simulated. Increasing the turgor pressure and thickness of the cell walls results in increased compression resistance of apple tissue increases, as do decreasing cell size and porosity. Geometric variability of the microstructure of tissues plays a major role, affecting results more than other model parameters. Different fruit cultivars were compared, and it was demonstrated, that microstructure variations within a cultivar are so large that interpretation of cultivar-specific effects is difficult. [ABSTRACT FROM AUTHOR]