Search

Fracture toughness, bending strength, Young's modulus, hardness and subcritical crack growth were determined for six different alumina/zirconia composites. The bending strength was modelled using Weibull distribution. The fracture toughness, bending strength and resistance to subcritical crack growth increase as a function of ZrO 2 content (stabilized with 3 mol% Y 2 O 3). The authors claim that a threshold stress in a three-parameter Weibull distribution may correspond to a threshold stress intensity factor in which the subcritical crack growth is negligible. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Functionally Graded Material concept applied for Autoclaved Aerated Concretes (AAC). • Functionally Graded Autoclaved Aerated Concretes (FGAAC) with gradient in porosity. • A numerical model to describe the mechanical behaviour of FGAAC is developed. • AAC with different bulk densities tested in: 3-PB, compact shear, Brazilian test. • Numerical model describes behaviour of notched specimens subjected to 3-PB test. Abstract The paper proposes a new concept for the Functionally Graded Autoclaved Concrete (FGAAC) and provides a numerical model to describe its mechanical behaviour. The model contains several material parameters describing damage growth and cracks propagation. They were assessed for the FGAAC by several laboratory tests like: 3-point bending, compact shear and modified Brazilian test done for homogeneous Autoclaved Aerated Concretes (AAC) with bulk densities in the range 400 ÷ 700 kg/m3. To achieve the goal efficient experimental procedures for the AACs testing were elaborated. The first step of this numerical model creation is description of the AAC gradual degradation and further cracks propagation in the above specified tests using XFEM approach. A good correlation with experiments was achieved. In second step the numerical model for theoretical FGAACs with using the material parameters describing damage growth in the AAC was build. The mechanical behaviour of the FGAAC was analysed in virtual 3-point bending (3-PB) test. Comparison to the experimental 3-PB test for the homogeneous AACs leads to conclusion that the mechanical behaviour of the FGAAC is correctly modelled. Moreover, the proposed numerical model has potential application in civil engineering concerning designing of structural elements with build-in thermal protection. [ABSTRACT FROM AUTHOR]

Abstract WC/Co composite is a standard hard material used for the production of cutting tools. It has both very good thermo-mechanical and wear properties. During the cutting, process tools are subjected to impact loading and gradual degradation due to high-stress concentrations. This loading induced deterioration is complex process still not well investigated and explained. Up till now the dynamic response of the WC/Co composite was analysed under dynamic impulse compressive loading [1]. However, the behaviour of the above two-phase composite under impacts conditions was not investigated in details. In the presented micromechanical approach the real material structure geometry of the internal structure can be performed including spatial distribution of: (1) WC grains and their dimensions, (2) volume content of plastic Co binder with their thickness, (3) system of grain/binder interfaces and (4) cracks initiated and developed during impulse loading, (5) possible brittle grains rotation. The results reveal the dependence of the microcracking processes and the stress distribution on impact velocity and presence of discontinuities in the Co binder and the interface zone between the binders and the grains. The microcracks system was evaluated by the damage parameter according to Kachanov, 1986 [62]. [ABSTRACT FROM AUTHOR]

Abstract Many computational problems in machine learning can be represented with near-separable matrix factorization models. In a geometric approach, linear separability means that the entire set of data points can be modeled as a conical combination of a few data points, referred to as the extreme rays that express meaningful features. In this study, we propose segmented convex-hull algorithms for estimating the extreme rays of the simplicial cone generated by observations in the near-separable and inconsistent non-negative matrix factorization (NMF) and non-negative tensor factorization (NTF) models. The segmentation is based on the concept of hierarchical convex-hull NMF. The proposed algorithms are used to solve near-separable noisy blind source separation problems and classification problems. For the former, the experimental results demonstrate that they significantly outperform the state-of-the-art geometry-based NMF algorithms and the basic hierarchical alternating least squares NTF, if observations are noisy with signal-to-noise ratio lower than 100 dB. For the latter, the classification results also provide strong evidence for the effectiveness of the proposed approach with respect to existing geometry-based NMF algorithms. [ABSTRACT FROM AUTHOR]

Abstract Degradation of Cermet Materials (CM) under impact and pulse pressure is not thoroughly investigated. In this study, we qualitatively compare the behaviour of WC/Co samples under these types of loading. The new models of impact and dynamic compressive load of a WC/Co plate were investigated. We developed two models of the composite plate, namely, a continuous model and a model with crack appearance possibility in the interfaces/binders. We noted a qualitative difference of the shapes of the deformed structure due to different models and kind of loading. The differences also concern the Mises stress, equivalent plastic strains and damage parameter. The proposed models are suitable for both impact and pressure load. The possibility of cracks appearance should not be neglected. In case of the model with discontinuities, for both kinds of loads, the grains rotation and sliding is more distinct than in case of the continuous model. Highlights • Impact and compressive pressure load are qualitatively compared, • FEA model with discontinuities and FEA continuous model are suitable for impact and dynamic pressure loading, • In the impact and dynamic pressure loading cases, the possibility of cracks formation should not be neglected, • In the impact and dynamic pressure cases, plastic strains develop stronger at the edges of the binders than in their interior, • In the impact and dynamic pressure cases, damage parameter develops stronger in the interior of binders that at their edges, [ABSTRACT FROM AUTHOR]

Abstract Cutting tools are manufactured among others from cermet (e.g. WC/Co) having excellent mechanical properties. Geometry of the internal microstructure is complex and mechanical response due to quasi-static or dynamic loading is difficult to be described. Particularly, the dynamic loading is not investigated enough precise up till now. Experimental evidences, e.g. Siegl and Fischmester (1988), Ravichandran (1994), indicate that the fracture energy of WC/Co is expended through ductile failure of the Co: (1) near the binder/tungsten carbide interface or by (2) dimple rupture across the interphase. Concentrations of stresses around grain boundaries lead to initiation of microcrack system, which is dispersed for dynamic loading. The aim of the paper is to extend the previously formulated models (Sadowski et al., 2005, 2006, 2007, Dębski and Sadowski, 2014, 2017) of the polycrystalline composite towards more advanced finite element formulation, applicable for description of the cermet behavior under dynamic pulses. The model takes into account: (1) spatial distribution of the cermet constituents, (2) system of grain boundaries/binder interfaces modeled by interface elements, (3) rotation of brittle grains. The obtained results show that stress distributions and gradual microcracking processes are quite different for quasi-static and dynamic loadings. It was revealed by damage parameter indicating concentration of microcracks. [ABSTRACT FROM AUTHOR]

A novel method is proposed to create a TBC on the CFRP/epoxy laminate surface in a single technological process by formation of one additional layer made of a commercially available alumina fiber mat. Both materials: the CFRP/epoxy laminate made of four layers and the ceramic mat were joined during prepreg curing. The quick thermal heating tests of the TBC system were conducted for different times with a propane-butane torch. Changes of material strains due to temperature influence are determined experimentally in uniaxial tensile tests via the Digital Image Correlation (DIC) method. A numerical model corresponding to the experimental quick heating test is built in Abaqus standard finite element software to determine temperature distribution in the CFRP/epoxy laminate. The experimental and numerical investigations lead to a conclusion that the alumina fiber mat is an effective protection of the CFRP/epoxy laminate against temperature degradation and can be used in industrial practice. [ABSTRACT FROM AUTHOR]

Cermet Materials (CM), for example, WC/Co, have very good mechanical, thermal and wear properties. They are used for manufacturing of cutting tools. However, their behavior under dynamic loads is still not properly understood. Experiments, e.g. Siegl and Fischmester (1988) and Ravichandran (1994), indicate that the fracture energy of WC/Co is expended through ductile failure of the Co: (1) close to the binder/tungsten carbide interface (Liu et al., 2017) [64] or by (2) dimple rupture across the interphase (Sigl and Exner, 1987) [22] . Stress concentrations around grain boundaries lead to initiation of microcracks which are dispersed by dynamic loading. The main goal of the paper is to investigate the previously formulated models of the two-phase composite (Sadowski et al., 2005, 2006, 2007; Dębski and Sadowski, 2014, 2017) [47–51] in the case of dynamic compressive pulses that are common in the case of cutting tools. We have taken into account complex spatial distribution of cermet phases, grain/binder interfaces modeled by interface elements, possibility of cracks appearance within binders using interface elements as well, and rotation of brittle grains. The obtained results show that microcracking process and stress distributions are different for quasi-static and dynamic loadings. Early development of microcracks distribution revealed by damage parameter was observed. [ABSTRACT FROM AUTHOR]

The paper deals with analysis of relationships between the microgeometry and mechanical properties of fiberglass i.e. epoxy resin composites with random fibers distribution. The mechanical properties (e.g. a flexural modulus E f , taking into account shear effects) of the material were determined in bending by Short Beam Shear Tests (SBST). Microgeometry of the structure was characterized on the basis of microscopic images of test specimens. The paper proposes a new measure of irregular reinforcement distribution expressed as an area ratio of the matrix surrounding the single fiber to the circuit of the fiber. The measure, denoted by G AB , is expressed in microns. In particular the relationship between the results obtained in the test samples with random distribution of fibers and theoretical regular structures of square (K) and hexagonal (H) type is presented. Specimens of the investigated composite (E-glass fibers and Epidian 5 epoxy resin), supplied by industrial partner, were cut out from raw material of helicopter blades girders. The obtained experimental results for the analyzed composite corresponded to approximation by the theoretical model of the square (K) type. The results can be used to estimate the flexural elastic modulus E f of the unidirectional composites with irregular arrangement of fibers, made manually or using the molding apparatus. Based on those results, it can be concluded that the square distribution model (K) is appropriate for numerical estimation of the strength composites properties reinforced with glass fibers of circular cross-section, having the diameter in the range of 10–16 μm. [ABSTRACT FROM AUTHOR]

Abstract: Hybrid joints obtained by a combination of two simple techniques, e.g. by spot welding and adhesive, are relatively modern joints developed especially for application in aerospace industry. This contribution describes the modelling and testing of structural elements by application of an angle bar and spot welding techniques with the introduction of adhesive layers between adherends. Numerical modelling of the mechanical response using the Finite Element Analysis requires a description of 3 different damage processes: (1) plastic degradation of the spot welded points, (2) plastic deterioration of the joined parts around the regions of spot points and (3) degradation of the adhesive layer. The whole uniaxial deformation process of samples was experimentally investigated with the application of 2 Digital Image Correlation systems to monitor the development of deformation up to the final failure. The first damage process starts within the adhesive layer, much below the maximum force that can be carried by the specimen. The second damage process activated in the joined adherends surrounding the spot welded points – near the maximum of the carrying force. The failure of the specimens took place when the adhesive layer was almost totally degraded and the welded spots were subjected to intensive plastic degradation. [Copyright &y& Elsevier]

Highlights: [•] The XFEM and the R&T techniques were exploited in damage analysis of the WC/Co microstructure. [•] Damage propagation analysis was performed with 2-D numerical models. [•] The Gurson–Tvergaard material porosity was used for the description of the Co interface. [•] Traction–Separation and Ductile Damage Criterions were used to model the WC/Co composite damage process. [Copyright &y& Elsevier]

Highlights: [•] FEM-based numerical analyses of road pavement cracking were conducted. [•] 2D model of a pavement layer structure was devised. [•] ANNs were applied to classify pavement condition. [•] Effect of particular bituminous layer parameters on road pavement cracking sensitivity was determined. [ABSTRACT FROM AUTHOR]

Polyurethane foams crush in compression and have a brittle fracture in tension, so their failure could be evaluated based on Linear Elastic Fracture Mechanics. Fracture toughness in mixed mode loading is of particular interest because foam cracking weakens the structure's capacity for carrying loads. Four fracture criteria (Maximum circumferential tensile stress, Minimum strain energy density, Maximum energy release rate, Equivalent stress intensity factor) were considered for evaluation of mixed mode fracture of three closed cell rigid polyurethane foams with densities: 100, 145 and 300 kg/m3. Mixed mode fracture tests were performed using asymmetric semi-circular specimen. The equivalent stress intensity factor criterion looks to give the better prediction of mixed mode fracture. Also the effect of cell orientation and the crack propagation angle were investigated. [ABSTRACT FROM AUTHOR]

Abstract: Blades of combustion turbines are elements which transfer an operative energy to an engine rotor. The blade consists of two pieces: a working piece called a profile covered by Thermal Barrier Coating (TBC) and a footer. The most dangerous parts of the blades are subjected to very high stress concentrations. They are situated in the profile section with the footer connection, where the maximum values of bending moments occur resulting from centrifugal forces and pressure of a working medium on the profile section. In the work we propose an extension of the turbine blade design strategy (in comparison to ) by application of submodeling technique to perform more detailed analysis of damage process and progressive fracturing of the most efforted cross sections of the blade. In particular cracking direction of the TBC was analyzed numerically with application of the XFEM technique. The critical values of rotor speeds were estimated at which damage process initiates and further develops. The damage of TBC can lead to destruction of protective covering and exposures the whole turbine blade core (made of alloys) to sudden thermal shock. [Copyright &y& Elsevier]

Abstract: The work presents a theoretical study (an asymptotic analytical and a semi-analytical) of the interaction of two parallel cracks under Mode II loading corresponding to the loading in the Compact Shear Specimen. Approximate analytical formulas for the stress intensity factors at the crack tips are derived. A numerical calculation for the corresponding integral equations is presented. The influence of geometry of the problem, i.e. the crack inclination angle to the remote shear loading and the distance between the cracks, on the SIFs and on the angles of the initial propagation direction of the cracks is investigated. [Copyright &y& Elsevier]

Abstract: The influence of impregnation on mechanical properties of polyurethane foams at room temperature has been experimentally evaluated in both static and impact loading conditions. The impregnation layer increases the flexural modulus and changes the foam behaviour at impact. For un-impregnated foam the energy absorbed to fracture is equal to the impact energy, while for the impregnated specimens the energy absorbed to fracture is approximately 80% of the impact energy, which indicated that the other part of the impact energy was consumed for internal damage. The same amount of energy was reached for both static and impact tests, but different shapes of energy versus displacement curves were obtained. For notched specimens under impact load, the effect of impregnation is cancelled and identical behaviour was obtained for un-impregnated and impregnated specimens. [ABSTRACT FROM AUTHOR]

Abstract: The dynamic behavior of partially delaminated at the skin/core interface sandwich plates with flexible cores is studied. The commercial finite element code ABAQUS is used to calculate natural frequencies and mode shapes of the sandwich plates containing a debonding zone. The influence of the debonding size, debonding location and types of debonding on the modal parameters of damaged sandwich plates with various boundary conditions is investigated. The results of dynamic analysis illustrated that they can be useful for analyzing practical problems related to the non-destructive damage detection of partially debonded sandwich plates. [ABSTRACT FROM AUTHOR]

Abstract: This paper is a first attempt to determine the dynamic fracture toughness of polyurethane foam and to study the effect of impregnation on the fracture toughness. Instrumented impact tests were performed using notched specimens. In order to study the effect of impregnation on the impact properties two different resins were used. The obtained results show that the impregnation increases the dynamic fracture toughness by 27%. [Copyright &y& Elsevier]

Ceramic composites (CCs) are mixtures of different phases, and their development is often regarded as a milestone in technological progress. They are used in practically all significant industries. Frequently, CCs are exposed to variable dynamic loads, impacts or high temperatures [1–3]. In this paper, the impact of thin plates fabricated from Al 2 O 3 /ZrO 2 is analyzed. The plates are made of the above CC with different proportions of its components. Damage progression is analyzed using peridynamics, similarly to quasi-static tension [4]. The purpose of the study is to describe the impact damage development in the CC plates and determine the role of phase contents. It has been found that phase ratios in the tested CC are vital for the behavior of the plates. In conclusion, it can be claimed that the employed peridynamic approach is suitable for solving the problems under study and that the impacting plates should be treated as real three-dimensional structures. [ABSTRACT FROM AUTHOR]

Abstract: The paper is the extension of the previous article , dealing with multiscale modelling of two-phase Ceramic Matrix Composites (CMCs), but now – subjected to compression state. It presents an unified multiscale approach to modelling of the CMC behaviour at different scales: micro- meso- and macro-. Within this approach cracks nucleation mechanisms and further growth along grain boundaries of the polycrystalline structure can be precisely described. A capability of the method was presented in numerical examples for two-phase composite made of alumina and zirconia. The main conclusion leads to the statement, that multiscale approach is a convenient tool for description of the CMC behaviour comprising gradual degradation, i.e. gradual decreasing of elastic material properties due to microdefects growth. [Copyright &y& Elsevier]

WC/Co metal-matrix ceramic composites (MMCs) are used for manufacturing cutting and drilling tools, surgical tools, mill inserts, jet engines, and other high-responsibility structures. The combination of a phase of hard wolfram carbide (WC) grains with a metallic ductile interface of cobalt (Co) yields a complex microstructure with significantly different mechanical properties of the phases. The aim of this study is to investigate the thermomechanical behavior of the MMC polycrystalline material with ductile binders under impact conditions. An adiabatic and coupled thermomechanical analysis of the WC/Co composite under impact loading is performed using FEM. The heat conduction is considered in the analysis in order to capture heat transfer in the polycrystalline structure, i.e. between the grains and the grain boundaries (GBs). The Johnson-Cook yield function is used in the constitutive model of the ductile Co interface, while the WC phase is linear elastic. The motivation comes from the observation that the heat conductivity effect is often omitted, even in recent papers **[75]. Significant differences between temperatures and plastic strains in the adiabatic and coupled solutions are observed, which leads to the main conclusion that the adiabatic solution should not be used for assessing the impact response of the composite material. [ABSTRACT FROM AUTHOR]

• Novel technology of 3D-printed cement based material. • Complex layered structure reinforced by polymeric interlayer mesh and short polymeric fibers. • 3-PB fracture process of 3D-printed layered beams. Technological processes and materials related to Additive Manufacturing (AM) are gaining popularity in civil engineering 3D concrete printing is aimed mainly at the process of rising the inner and outer walls of buildings. In these elements, the main load is axial compression with a low fraction of bending. The 3D-printing process of cement-based materials provides the construction elements with appropriate compressive strength. Although creating elements, which can carry the tensile loading is necessary to make the 3D-printing process used in civil engineering. Therefore, this paper aims to show the response of the 3D-printed cement-based composites to the bending process to find the effect of complex layered structures on their effective properties. Instead of the standard use of an extensometer to obtain Crack Mouth Opening Displacement results, novel Digital Image Correlation measurement technology was used during research. This technology allows for continuous real-time measurements that are extremely difficult when testing brittle materials such as concrete and avoids the additional introduction of external forces caused by the classical measuring device. The proposed AM material contains the interlayer polymeric net and smeared polymeric reinforcement to enhance flexural strength. The use of the polymeric net and smeared reinforcement introduces residual strength into the composite allowing for its further work after brittle phase failure. However, the obtained results showed that analysed layered beams had decreased interlayer resistance. The process of layer cracking occurs subsequently layer by layer and the failure in different layers developed as an independent process including cracks arresting. [ABSTRACT FROM AUTHOR]

One of the fundamental criteria in the design of air structures is to achieve required strength at the highest possible reduction of structure weight w . However, it is necessary to keep the second design parameter i.e. stiffness of the air structural element on the proper level in order to satisfy durability and reliability of aircrafts. This paper presents the application of an integrated system based on artificial neural networks and calculations by the finite element method (FEM) for the optimization of geometry of a thin-walled element of an air structure. The main criterion of optimization was to reduce the structure’s weight w at the lowest possible deformation (high stress level) of the tested object. The objective of the analyses – using artificial neural networks (ANN) – was to investigate the effect of 4 individual variables defining geometry of the model (including: system of ribs and their inclination, system of holes in ribs and side walls) on its deformation and final value of the reduced weight w . Numerical analysis showed that the most important variable is the diameter of holes in the side walls of the model. [ABSTRACT FROM AUTHOR]

Highlights: [•] Digital Image Correlation was used to measure R-curve of clay brick blocks. [•] DIC allows to collect data from crack propagation up to the total rupture of samples. [•] An average K IC of clay brick blocks equal to 0.36MPam1/2 was estimated. [•] A quite accurate R-curve of clay brick blocks was traced. [ABSTRACT FROM AUTHOR]

Abstract: Analysis and fracture interpretation (using the strain energy density criterion) of Compact Shear specimen for Mode II fracture testing of materials is presented in the paper. Two approaches are used. One is based on singular integral equations for the problem of the interaction of two parallel cracks under Mode II loading corresponding to the loading in the Compact Shear specimen (CS specimen). Approximate analytical formulas for the stress intensity factors at the crack tips are derived. A numerical calculation using Gauss-quadrature formulae for the corresponding integral equations is presented. The influence of geometry of the problem on the stress intensity factors and on the angles of the initial propagation direction of the cracks is investigated. The other approach is Finite Element Method implemented in FRANC2D/L code. Numerical analysis was done for plain strain conditions. Different geometries of the specimen are considered for two models of the CS specimen and compared with results available in the literature. Analytical and FEM calculations are also compared and discussed. [Copyright &y& Elsevier]

Abstract: The fracture behaviour of unfired dry earth has been investigated by means of an experimental approach supported by some numerical simulations. Three-points bending tests, both with monotonic and cyclic loads, have been performed experimentally, and the related force–displacement diagrams are interpreted theoretically to characterize the fracture parameters of the considered material. Both Linear Elastic Fracture Mechanics and a Two Parameter Model are considered. In the latter case, based on the post-peak softening behaviour, the R-curve is determined, which shows how the critical stress intensity factor depends on the fracture length. [Copyright &y& Elsevier]

Abstract: Cemented tungsten carbide is the most popular material for making cutting tools. During machining process the cutting tools are subjected to varying high mechanical and thermal stresses leading to initiation and propagation of the crack in the material. The aim of this paper is to develop a new methodology in order to estimate crack resistance and R-curve behavior of WC/Co composite. The measurement was done by compact tension (CT) specimen test. Obtained results lead to the conclusion that the shielding effect in the cermet is in the region behind crack tip. The increase of the fracture toughness in comparison to pure WC is very high and reaches plateau of 12.6MPam1/2 after overall crack extension of 310μm. [Copyright &y& Elsevier]

This work reports the out-of-plane crushing response of aluminum honeycomb (HC) filled with polyurethane (PU) foams. For the filling of the HC, two types of PU foams were manufactured: unreinforced PU (UR/PU) foam and PU foam reinforced (GR/PU) with reduced graphene oxide (rGO) flakes. In this investigation, the static and low velocity impact compressive tests were performed on the separate constituents (UR/PU foam, GR/PU foam and empty HC) and their combinations (UR/PU foam-filled HC and GR/PU foam-filled HC). By the addition of 0.02% rGO flakes, to UR/PU, an increase (over 41%) of the strength and energy absorption properties was obtained. Moreover, due to the interaction effect, the foam-filled HC composite highlights better properties (up to 61%) than the empty HC structure. Further, it has been observed that exposure of the specimens to ultraviolet (UV) radiation do not change the foam density, but their properties increase by up to 30%. Finally, it was noticed that the in-situ foam-filled HC manufacturing technique is clearly superior to the ex-situ method, while the foam material dictates the filled HC collapse mechanisms considerably. [ABSTRACT FROM AUTHOR]

Due to the high economic and environmental benefits, researchers have considered recycling metal chips, especially for the more valuable alloys of copper, brass, aluminium, etc. Several methods have been used including casting and solid-state techniques for recycling the metal chips, wasted annually in large quantities by machining processes. This work examines the sustainability of the Friction Stir Extrusion (FSE) technique, as one of the most recently developed methods for recycling metal chips, comparing it to six different casting methods. Four sustainability indicators of economic, environmental, social, and mechanical performance are calculated and compared for the FSE and casting methods, using a multi-dimensional sustainability methodology. In terms of environmental, social, and mechanical indicators, the FSE method gained significantly the highest levels and in overall sustainability, it achieved the best score of 0.78, while the worst casting technique for recycling was 0.514. However, economically, the FSE has not yet gained a foothold in the industry and needs more attention from manufacturers, environmentally friendly craftsmen, and recycling firms side. Despite the higher investment required for the FSE process (compared to conventional casting techniques) and its lower economic feasibility, the FSE is expected to become more economically viable in the future by further research and development in its tools. [ABSTRACT FROM AUTHOR]

The modern polycrystalline composite materials have a complex internal structure consisting of different phases and interfaces with random distribution. Relevant examples are Al 2 O 3 /ZrO 2 , i.e. alumina/zirconia composites, widely used as structural materials with applications ranging from aerospace to bio-engineering. Depending on the phases content and on the grain size a broad range of material characteristics, among which elastic constants, can be obtained. With the aim of characterizing this class of materials, we exploit a numerical Fast Statistical Homogenization Procedure (FSHP) in order to both estimate the size of the Representative Volume Elements (RVE) and the effective elastic properties, assuming a linear elastic material behaviour. The 2-D analyses are performed considering a microstructure inspired by images of real portions of the Al 2 O 3 /ZrO 2 composite obtained from a scanning electron microscope. The recent Virtual Element Method is used in combination with the FSHP approach to numerically solve boundary value problems. Different volume contents of phases are considered ranging from pure Alumina to pure zirconia. The results are useful to reliably characterize such materials in the elastic range taking into account the role played by random distribution of grains. [Display omitted] • Homogenization of random Ceramic Matrix Composites (CMC). • Fast identification of the homogenized moduli with the Virtual Element Method. • Parametric analysis. [ABSTRACT FROM AUTHOR]

Many efforts have been made in recent years to determine the fracture toughness of different types of foams in static and dynamic loading conditions. Taking into account that there is no standard method for the experimental determination of the fracture toughness of plastic foams different procedures and specimens were used. This paper presents the polyurethane foam fracture toughness results obtained for different foam densities. Two types of specimens were used for determining fracture toughness in modes I, II and a mixed one, and also the size effect, loading speed and loading direction were investigated. The paper proposed correlations for density, cell orientation and mixed mode loading based on the experimental testing results. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents a correlation between dynamic and static fracture toughness of polyurethane rigid foams. Static three point bend tests and instrumented impact tests were performed using single edge notch specimens. The obtained results show that for all foam densities the dynamic fracture toughness is higher than the static toughness. Density appears to have the main influence on both static and dynamic fracture toughness. A quasi brittle fracture without plastic deformations and cushioning was observed for all foam densities. [Copyright &y& Elsevier]