Search

The delayed failure of SiC fibrous reinforcement has continuously been investigated to warrant the long term performances of Ceramic Matrix Composite (CMC). Chiefly assessed on multifilament tow samples to alleviate some handling difficulties, subcritical crack growth (SCG) parameters are however ruled by structural artifacts which hinder the identification of intrinsic filament behavior. In this paper, we propose to estimate the true filament parameters for 5 fiber types from bundle behavior using a recently communicated Monte Carlo algorithm integrating flaw and stress distributions through a deterministic fracture mechanics law under Paris’ formulation. So computed tow lifetime are broadly dispersed, encompassing raw data, and show a structure-dependent scale effect, revealed by nfilament>ntow where n is the stress exponent. The relationship between SCG coefficient and chemical composition of the substrate is discussed and highlights the major effect of doping elements (Ti or Zr), oxygen or hydrogen content.

This paper introduces the analytical solutions of complex behavior analysis utilizing high-order shear deformation plate theory of functionally graded FGM nano-plate content consisting of a mixture of metal and ceramics with porosity. To incorporate the small-scale effect, the non-local principle of elasticity is used. The impact of variance of material properties such as thickness-length ratio, aspect ratio, power-law exponent and porosity factor on natural frequencies of FG nano-plate is examined. Compared to those achieved from other researchers, the latest solutions are. Using the simulated displacements theory, equilibrium equations are obtained. Current solutions of the dimensionless frequency are compared with those of the finite element method. The effect of geometry, material variations of nonlocal FG nano-plates and the porosity factor on their natural frequencies are investigated in this review. The results are in good agreement with those of the literature.

The article presents the methodology of the representative elementary volume definition for 1 m long whole core segments. Scientific articles focused on factors controlling elastic properties are analysed. Terms of additivity and nonadditivity for physical properties of rocks are discussed. The algorithm of core sampling including drilling out of three perpendicular core samples for estimation of elastic anisotropy was used. Porosity values of 1 m long whole core fragment evaluated in two ways using original core samples in the first approach and core samples having volume 133 cm3 in the second way have been compared. Peculiarities of scale effect of porosity in core samples of limestones are analysed.

Based on the generalized nonlocal thermoelastic theory and the memory-dependent differential (MMD) theory, the dynamic response of the inner surface of an infinite hollow cylinder under thermal sho...

A fractal model allowing one to theoretically estimate the shearing strength of the interfacial contact in a polymer-carbon nanotube system is proposed. It takes into account the structure of carbon nanotube surface and describes experimental data accurately enough. This makes the model promising for predicting the polymer/nanofiller contact strength. As a function of nanotube diameter and contact length, this strength showed a strong scale effect.

Pineapple leave fiber (PALF) can be considered as one of the green materials to the industries, which is the potential to replace the non-renewable synthetic fiber. However, the high disparity in the mechanical properties of PALF becomes an issue in structural composite design. Hence, improved Weibull distribution is utilised to quantify the tensile strength variation of PALF in various gauge lengths. The single fiber tensile test was performed after the fiber surface treatment and fiber diameter scanning. The predicted PALF strength by applying the improved Weibull distribution incorporating with conical frustum model is well compromised with experimental data compared to the traditional Weibull model.

The combustible features of wheat dust easily induce a potential hazard in its processing and application. To clearly reveal the effects of porous mesh parameters on the flame propagation of wheat dust, a vertical combustion pipeline together with the data collecting by the high-speed photography and fine thermocouple was built. Results indicate that with the increase in the mesh scale, the dust combustion and peak temperature are intensified first and then decreased with a darker luminescence. The increasing mesh number shows an inhibition effect on both peak temperature and combustion pressure, but an accelerating first and then weakening effect on flame velocity. A smaller particle size contributes to a more complete combustion, causing a higher peak temperature and flame velocity. At the particle mass of 2.5 g, the maximum value of peak temperature, flame velocity and combustion pressure were obtained during the flame propagation.

This paper presents the results of three dimensional finite element analysis of laterally loaded pile groups of configuration 1×1, 2×1 and 3×1, embedded in two-layered soil consisting of soft clay at liquid limit overlying dense sand using Plaxis 3D. Effects of variation in pile length (L) and clay layer thickness (h) on lateral capacity and bending moment profile of pile foundations were evaluated by employing different values of pile length to diameter ratio (L/D) and ratio of clay layer thickness to pile length (h/L) in the analysis. Obtained results indicated that the lateral capacity reduces non-linearly with increase in clay layer thickness. Larger decrease was observed in group piles. A non-dimensional parameter Fx ratio was defined to compare lateral capacity in layered soil to that in dense sand, for which a generalized expression was derived in terms of h/L ratio and number of piles in a group. Group effect on lateral resistance and maximum bending moment was observed to become insignificant for clay layer thickness exceeding 40% of pile length. For a fixed value of clay layer thickness, lateral capacity and bending moment in a single pile increased significantly with increase in pile length only up to an optimum embedment depth in sand layer which was found to be equal to three times pile diameter and 0.21 times pile length for pile with L/D 15. Scale effect on lateral capacity has also been studied and discussed. Doi: 10.28991/cej-2021-03091686 Full Text: PDF

This research concentrates on pull-in behavior of a micro-plate laminated with a novel material: light activated shape memory polymer (LASMP). Under light exposure, this material can realize dynami...

We explored the microstructure-related scale effect on the tensile failure of coal. Disc specimens with different diameters (25 mm, 38 mm, 50 mm, and 75 mm) were processed for the Brazil split test. The influence of microstructures on fracture initiation and propagation was detected and analysed by the combination of X-ray computed tomography scanning, digital image correlation approach, and acoustic emission monitoring. The investigation indicated that tensile strength decreased with increasing specimen diameter, and the relationship can be described by an exponential equation. Four tensile failure modes were observed in specimens with different diameters, namely central, non-central, central edge, and central multiple pattern. Larger specimens exhibited more complicated failure patterns (central edge and central multiple failure patterns) and a greater percentage of shear failure fractures. Strain concentration and strain reversal were observed, respectively, in mineral—inclusion-rich regions and pre-existing discontinuities regions. This possibly contributed to fracture initiation, propagation, and coalescence. Fractures tended to grow along with the interface of mineral inclusion and coal matrix, and they could have propagated into and connect the pre-existing discontinuities. The greater volume of microstructure in larger specimens resulted in fractures that were more complex and may have increased the number of shear failure cracks and led to failure modes that were more complicated.

Coal mass strength estimation has attracted broad attentions for decades. Investigating the effect of scale and anisotropy on the Uniaxial Compressive Strength (UCS) estimation via P-wave velocity ...

In this manuscript, Electrochemical Micromachining (ECM) is well designed with the important concept called scale effect. The main objective is to evaluate the scale effects that occur when the mac...

The effects of flexoelectricity on thickness-twist waves propagating in the nanoplates are analytically investigated. Detailed calculations are performed for nonpiezoelectric material using the met...

The hydrodynamic performance of a ship with and without a stern flap was comprehensively investigated based on model tests and model- and full-scale simulations. The stern flap led to an increase i...

The paper describes the effect of the size of parts on their strength properties, in particular, on the value of the true tensile strength of steels. The use of the obtained dependence for the scale factor allows using the method developed by the authors for determining the true tensile strength of steels for parts of various sizes.

In this paper, multi-junction clamp was used for junction strength evaluation under 20, 50 and 100 mm/min of strain rate at ambient condition. One~eight rib specimens were gripped in the clamps and each gage length was 50 mm, 100 mm and 150 mm, respectively. Warp knitted and woven type geogrids were used to compare the effects of multi-junction clamping on junction and tensile strength, respectively. The results indicate that junction strength decreased while the number of junctions increased. When the strain rate was increased, junction strength of woven type increased, but there was no effect of strain rate on warp knitted type. The newly designed clamp test for geogrid junction strength in this research is more accurate than the single-junction test, considering the scale effect of specimens.

The relationship between the spatial parameter of the development of a localized plastic flow (the length of the localized plasticity autowave) and the length of the deformed sample is studied. According to experiments carried out on polycrystalline samples of a zirconium alloy and commercial purity aluminum, these quantities are related to each other by a logarithmic law valid at the stage of parabolic strain hardening.

An indentation technique for measuring and comparing the microhardness of hardening coatings, which takes into account the scale factor, is proposed and explained. This technique is experimentally shown to be more valid in terms of estimation and comparison of the microhardness of thin hardening coatings.

The classical method for evaluating the waveguide ability only focuses on the optical loss coefficient. However, for the micro- or submicroscale, an organic waveguide is demonstrated by the present study whose scale effect should not be neglected. We found that the optical loss coefficient increased remarkably when decreasing the sectional size of the microfibers. Furthermore, simulations based on Finite-Difference Time-Domain also demonstrated the size-dependent effect of the waveguide. Both the experimental and simulating results showed that the optical loss coefficient converges to a certain value, which means that the scale effect can be neglected as the sectional size is large enough. On the basis of the present study, we suggest that the scale-dependent effect on the sectional size of the waveguide should be investigated by evaluating the waveguide ability by the optical loss coefficient.

We quantitatively explore and explain the different time behavior of anomalous solute transport in three-dimensional (3D) porous media with different cementation degrees. We find that the temporal evolution of the breakthrough curves (BTCs), spatial moments and propagators representing the time behavior of the transport varies significantly in each case with rising cementation degree. For example, the early breakthrough and long tail in the BTCs are enhanced simultaneously when the cementation degree increases, implying that the solute transport is anomalous. Correspondingly, instead of both the first and second central moments growing linearly with time as described by the traditional advection-dispersion equation (ADE), the relationship between the second central moment M₂ and time gradually transitions from an approximate linear relationship into a nonlinear relationship. This indicates that the scale effect is enhanced in the porous media with larger cementation degree. In addition, the propagator is characterized by a more remarkable and more persistent stagnant concentration peak when the cementation degree rises. Our simulations also demonstrate that the CTRW model can capture the simulated BTCs and quantitatively predict the temporal evolution of the first two moments of the solute plume. Finally, we explain the mechanism of the different time behavior of solute transport via the characteristics of the flow field.

A numerical study has been carried out for ring and circular footings resting on unreinforced and fibre-reinforced layered sand beds. The sand bed consists of two layers. The top layer of sand has ...

Existing studies confirmed that the response of geocell-reinforced beds is directly affected by contributory factors, including soil's grains, geocell's characteristics, and surface loading geometries. In this paper, a series of plate load tests has been carried out for the further understanding of the behaviour of geocell-reinforced soil. Four different soil grains sizes, two different geocell's opening sizes and three different loading plate sizes were the considered variables. During the tests, the applied loading and soil surface settlements were recorded to evaluate the systems' response. As it was expected, the geocell-reinforced soil exhibited higher bearing capacity than the unreinforced status, up to 524%. The results further focused on the important role of scale effect on the response of reinforced foundations. The optimum nominal cells size of geocells was obtained about 15 times of medium grain size of soil. Also, it was found that in order to obtain the highest reinforcement benefits, the footing's width should be in the range 13–27 (20 in average) times of medium grain size of the backfill. Finally, to provide more stable and reliable geocell-reinforced backfill, it is recommended that the cells size of geocells should be selected smaller than 0.67 times of footing width.

In this study, the mechanical property of copper microwire, a widely used material in our daily life, is investigated by subjecting it to in situ scanning electron microscope twisting based on a self-developed nanorobotic manipulation system. First, copper microwire is assembled on the nanorobotic system inside the scanning electron microscope, and then twisted clockwise and anticlockwise continuously from 0° to 360° until fracture. After that, the mechanical properties of elastic modulus, microhardness, yield stress, and the strain hardening exponent of the twisted sample are investigated by nanoindentation. The change in elastic modulus and indention hardness showed strong indentation size effects, because a large number of geometrically necessary dislocations were generated around the indenter. In addition, the fracture analysis indicated that the smaller the scale of the material, the more sensitive it was to surface cracks or defects. Ductile fracture features of the twisted sample appear due to the nucleation, growth, and coalescence of the microvoids.

Accurate assessment of anisotropy and scale effect of rock joint roughness is essential for evaluating the mechanical behaviour of rock joints. However, in previous studies, how to quantify roughness anisotropy of rock joints remained largely unsolved, and the research on the scale effect on roughness anisotropy is not conclusive. A statistical analysis on the joint roughness coefficient of different sized profiles was implemented to investigate the scale dependence of joint roughness. The scale effect on the roughness anisotropy was investigated based on the class ratio transform approach. The roughness anisotropy was characterized by local anisotropy and global anisotropy. The global anisotropy tends to be almost constant when the sample size exceeds the stationarity threshold length of 70 cm. The result shows that the global anisotropy is scale dependent. However, the scale effect on local anisotropy is less apparent. The case study indicates that the class ratio transform approach is of value in roughness anisotropy investigation.

The micro-surface asperity scale of grinding metal parts is within several microns. When two grinding surfaces are in contact, the unevenness of the plastic deformation of the asperities at the micro-scale leads to greater plastic hardening strength of the material. The results of the nano-indentation experiment conducted in this paper confirmed this phenomenon. Based on conventional mechanism-based strain gradient (CMSG) plasticity theory, the micro-scale plastic constitutive equation of materials is given and then is verified by the nano-indentation experiment. Finite element software abaqus and the user-defined element (UEL) subroutine are used to build three-dimensional rough surface elastoplastic contact models. By calculating the grinding rough surface contact in the macro-scale constitutive model based on J2 theory and in the CMSG plasticity constitutive model, the influence law of plastic micro-scale effect on contact performance is obtained.

An electrothermal microgripper is an important actuator in microelectromechanical and micro-operating systems, and its temperature field analysis is the core problem in research and design. Because of the small size of an electrothermal microgripper, its microscale heat transfer characteristics are different from those of the macrostate. At present, only a few studies on the heat transfer scale effect in electrothermal microgrippers have been conducted, and the heat transfer analysis method under the macrostate is often used directly. The temperature field analysed and simulated is different from the actual situation. In the present study, the heat transfer mechanism of an electrothermal microgripper in the microscale was analysed. The temperature field of a series of microscale heating devices was measured using microthermal imaging equipment, and the heat transfer parameters of the microscale were fitted. Results show that the natural convective heat transfer coefficient of air on the microscale can reach 60–300 times that on the macroscale, which is an important heat transfer mode affecting the temperature field distribution of the electrothermal microgripper. Combined with the finite element simulation software, the temperature field of the electrothermal microgripper could be accurately simulated using the experimental microscale heat transfer parameters measured. This study provides an important theoretical basis and data support for the optimal design of the temperature controller of the electrothermal microgripper.

Bridging the mechanical response of rockfill materials with laboratory grading curves and field grading curves is of obvious importance in rockfill dam engineering and has been a great cha...

S-shaped characteristics in turbine mode are prone to instabilities in associated transient processes. A single value of the speed factor corresponds to multiple values of the discharge factor, having the possibility of changing the operating point among the turbine, turbine brake, and reverse pump modes. Because of this characteristic, the S-shaped curves induce instability in transient processes. Understanding the hydraulic behavior of a turbine on the four-quadrant characteristic is important since it provides detailed performance information through the whole discharge range of the turbine. This study was numerically and experimentally investigated the scale effect on the S-shaped characteristics in the turbine transition region. The four-quadrant characteristic curves (full- and laboratory-scale) in the turbine mode were predicted by numerical simulations. To verify the predicted results, a laboratory-scale experiment was performed in the turbine, turbine brake, and reverse pump modes. Although the full-scale experiment was performed in the normal operating head range, the scale effect can be validated by comparing steady operating points between the two models. Based on the verified results, the internal flow and pressure pulsation characteristics were determined at the operating point in a specific transition region.

Thermal energy storage materials are carriers of thermal energy. The physical and chemical properties of these materials dictate their thermal storage performance. Accurate modeling of them under both ideal and industrially relevant conditions is valuable in terms of predicting influences of materials properties on device and system level performances, and understanding potential constrains and methods for overcoming the limitations of the materials. Recent years have seen the development and applications of new composite materials for thermal energy storage, which bring difficulties to the modeling of these materials. Examples include the strong scale effect due to the doping of nanoscale particles to thermal storage materials. Therefore, microscopic modeling is needed for in-depth understanding of these phenomena. In this chapter, density functional theory (DFT) and molecular dynamics (MD) methods are introduced in detail for modeling thermal energy storage materials from a microscopic aspect.

The objective of this chapter is to show the modelling of composite materials at the micro-meso level, involving the nonlinearities associated with the damage that may appear in a composite laminate. The potential damage includes debondings between the fibres and matrix where the initial damage occurs in the weakest lamina of a laminate, and the cracking of the matrix that appears when a debonding abandons the fibre–matrix interface, kinking and penetrating into the matrix. Integrated multiscale models based on the boundary element method are developed, allowing us to analyze the whole laminate in a model while also having the possibility of modelling the damage object of study at the micromechanical level in this chapter. The incidence of the features of the model in the representativity of the results is first analyzed, correlating the predictions with the experimental observations from testing laminates. The models carried out will follow a line of association with particular problems regarding the use of composites, with a special emphasis on the study of the scale effect in composite laminates, emphasizing the correspondence between the model performed to simulate the damage and the actual mechanism of damage that a laminate experiences.

SiC-fibers are subjected to a predictable premature failure, consequence of a slow crack growth mechanism. This has chiefly been studied through static fatigue testing of multifilament tows. The discrepancy existing between experimental results, broadly dispersed, and the bundle theory (solely considering the filament strength distribution) has been interpreted by discrete stochastic phenomena. In this work, the uncertainty on applied stress caused by fiber misalignment (slack) was rather investigated through Monte Carlo simulation, ascribing to each filament of the tow a strength and a stress among established distributions. If a coherent lifetime range could this way be obtained, a scale effect on stress exponent was also revealed: equal to 12.6 on filament it falls to 8.4 on bundle, in agreement with experimental results. The same would apply to larger scale (woven tow).

Masonry columns often exhibit a lack of load-carrying capacity that is due to overloads and do not provide any ductility or dissipation capacity under seismic forces. Column confinement has been extensively studied as an effective technique, which could mitigate these structural vulnerabilities. The confinement of masonry columns will be studied in this paper, by considering fabric-reinforced cementitious matrix (FRCM) materials as external jackets. Due to the lack of information in the scientific literature, a new analysis-oriented model (AOM) for the prediction of the axial stress-strain law will be presented and discussed in this paper. The proposed AOM consists of a system of equations that make several assumptions: crossing the predicted peak point (strength and relative strain), crossing the ultimate point (80% residual strength and relative strain), and the horizontal tangent at the peak point and the initial (linear elastic) slope derived from the geometry and mechanical properties of the materials involved. The AOM was demonstrated to be simple and accurate, based on Pearson's test (χ2); therefore, the proposed approach could be considered for future design equations. In addition, this paper will illustrate and discuss the validation of two available design-oriented models (DOMs), which could predict the axial strength of FRCM jacketed columns, by comparing the theoretical results with a database of experimental results that is available in the scientific literature. Novel formulas for the computation of both the peak and ultimate axial strains will be further proposed, as the basis for a design procedure. Their accuracy was demonstrated by considering an experimental versus theoretical comparison.

TiO2 nanotubes (TNTs) are a potential candidate for the photoelectrode in dye-sensitized solar cells (DSSCs). In this review, emphasis is given to the fabrication methods of the TNT photoelectrode, including the anodic oxidation method, the hydro/solvothermal method, and the template method. Modification of TNTs to improve the power conversion efficiency (PCE) and the long-term stability of DSSCs is also covered. The active area of the DSSC strongly correlates with the PCE. Therefore, evaluating and comparing cell efficiencies with the same active area would be important. Reducing the material and manufacturing costs of TNT-based DSSCs will be an important future target.

Based on small scale laboratory experiments on artificially created discontinuous Pendeli marble specimens, the strength and stability scale effects in uniaxial compression were investigated. Large scale field measurements confirmed the laboratory results. A fractal scaling analysis was further performed on strength, specific surface energy and strain energy release parameters of rock fracture in uniaxial compression. In this experimental and theoretical analysis the effect of : a) the nature of the crack spatial distribution and b) the relative importance of small cracks compared to large cracks, on the scale behaviour of rock-like materials, were established. Several scaling relations were obtained which explain some previous experimental results of various researchers.

High-damping rubber bearing (HDRB) is one of the most popular devices used for seismic isolation of structures. In order to clarify the mechanical characteristics of HDRB, various loading tests have been conducted on the bearings and obtained data have been applied to practical design of isolation systems. In this study, in order to investigate the scale effect on the physical characteristics of HDRB, dynamic loading tests were conducted with full scale and scaled model isolators, which have diameters of 1,000 and 225 mm, respectively. The test program covers shear strain dependence tests, frequency dependence tests, and repeated loading dependence tests. Special attention is paid in the differences of shear characteristics caused by the specimen scale. Repeated loading test was conducted only with a scaled model, and the relationship of temperature increase of the specimen and shear characteristics was evaluated. In parallel, finite element analysis (FEA) of the isolator under repeated loading was conducted. After the constitutive model of FEA was identified by the results, the FEA was extrapolated to simulate repeated loading of 1,000- and 1,600-mm-diameter isolators, which cannot be tested realistically by dynamic loading. Change of properties along the increasing number of cycles and temperature distribution of full scale and scaled down isolators were investigated. Necessity of consideration for the scale effect in the evaluation of HDRB properties by dynamic testing is discussed.

The aim of this paper is to discuss the unrecognized problem of the scale effect in compressive strength tests determined for cored specimens of lightweight aggregate concrete (LWAC) against the background of available data on the effect for normal-weight concrete (NWAC). The scale effect was analyzed taking into consideration the influence of slenderness (&lambda, = 1.0, 1.5, 2.0) and diameter (d = 80, 100, 125, and 150 mm) of cored specimens, as well as the type of lightweight aggregate (expanded clay and sintered fly ash) and the type of cement matrix (w/c = 0.55 and 0.37). The analysis of the results for four lightweight aggregate concretes revealed no scale effect in compressive strength tests determined on cored specimens. Neither the slenderness, nor the core diameter seemed to affect the strength results. This fact should be explained by the considerably better structural homogeneity of the tested lightweight concretes in comparison to normal-weight ones. Nevertheless, there were clear differences between the results obtained on molded and cored specimens of the same shape and size.

An analytical study to predict the behaviour of clamped FGM nanoplates based on Winkler-Pasternak’s elastic foundations using hyperbolic shear deformation theory. non-local elasticity theory is used to introduce the small-scale effect. This model has a forward displacement field which includes the effect of transverse shear deformation without using shear correction factors. The winkler-Pasternak medium is introduced by considering the damping effect of the foundation model. It’s modeled by the linear Winkler coefficient and the Pasternak foundation coefficient (shear). The influences of many parameters such as the non-local parameter, the geometric ratio, the Winkler-Pasternak coefficients, the damping parameter and the mode numbers on the vibrational response are studied and discussed.

Spatial self-organization of plastic flow localization depends on the work hardening law. At the parabolic hardening stage the most important parameter of stationary dissipative structures existence is their spatial period (autowave length). This study attempts to determine the dependence of autowave spatial period on the object size under loading. The investigations were performed using commercially pure aluminum (1050A) which has prolonged parabolic hardening stage. Exponential dependence of autowave length on tested specimen size was revealed. Minimum size of tested specimen for autowave pattern occurrence has been defined.

This paper deals with the study of the actual progression of the damage in the 90 degrees lamina of a composite. It has been proved and observed that isolated debondings between fibres and matrix are the first manifestation of damage in the weakest lamina, the 90 degrees lamina in a [0,90]S laminate. It was also numerically supported that this first phase was independent of the thickness of the 90 degrees lamina, not being then affected by the “scale effect”. The continuation of this first phase of damage is the objective of the present paper. To this end, a multiscale model is created involving the debonding between fibre and matrix and studying the kink of this crack, abandoning the fibre-matrix interface and entering into the matrix to produce a meso-transverse crack in the 90 degrees ply. The study is based on the application of Fracture Mechanics to an incipient kinked crack that starts from a debonding between fibre and matrix. It is concluded that this second phase of damage, playing with the thickness of the 90 degrees lamina, is not affected by the scale effect, as the variation of the energy release rate of the kinked crack is not significantly influenced by the variation of the thickness of the lamina.

Composite laminates are materials where different scales are required for the understanding of the damage and for the calculation of structures made of these materials. The appearance of ultra thin plies of composites has opened the possibility of delaying the onset of damage, which at a first stage appears at a micromechanical level, debondings in between fibre and matrix in the weakest lamina of the laminate. A multiscale BEM model is developed in the present paper with the final purpose of being able to study the effect that the relative size of the laminas of the laminate plays in the appearance of this initial damage. The model presents many difficulties derived from the different scales involved in it and from the non-linear nature of the problem under study. The approach followed involves the solution of the whole problem, with the different scales involved in it, at once. The solution obtained is checked with another already obtained with a much simpler model. The multiscale model developed has been proved to be very efficient, accurate and robust, having been applied to simulate the first stages of damage in the light of the scale effect that is trying to be studied.

Quantitative estimation of scale effect is a complex problem which contained many uncertainties and should be solved using probability calculus and statistical approach. This paper aims to derive the structural factor according statistical strength theory involving discontinuity surface conditions account to estimate the design rock mass strength. A short review of scale effect estimation techniques based on statistical strength theory is given. A new method of structural factor evaluation is proposed. This technique allows accounting discontinuity conditions by changing the variation of tested specimen random sample. A function that describes the decreasing of strength due to poor discontinuity surface quality is introduced to correct the initial and central statistical moments of strength random distribution. The evaluation of the joints condition function based on analysis of the results of uniaxial compressive strength tests and petrographic structure of specimens is shown. Improving the statistical approach of structural factor evaluating increase the accuracy of the rock mass strength assessment and allow avoiding costly modifications of the mining excavation support design. A case of rock mass strength estimation under conditions of coal mine “Komsomolets Donbassa” according to proposed statistical method is studied.

The variation in the apparent strength of a lamina in a laminate depending on the stacking sequence and thicknesses of the laminas of the laminate has been a matter of interest since the initiation of the extension of the applicability of composites. This fact led to the concept of in-situ strength, the problem itself being covered as a scale effect. In this paper this question is revisited moving towards the level where the damage appears, that is the micromechanical level. As the origin of the effect under consideration, the variation of thickness, takes place at a different level (mesomechanical), a multi-scale model is developed. It is possible in this model to vary the thickness of the lamina under consideration and to observe its effect on the damage. In this paper, only the first stage of damage, which appears in form of debondings between fibres and matrix, is taken into consideration. The analysis carried out shows that there is no scale effect at this first stage of the damage, which is corroborated by experimental evidences.