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Fiber-reinforced cementitious matrix (FRCM) and steel-reinforced grout (SRG) have been increasingly applied as externally bonded reinforcement to masonry members in the last few years. Unlike fiber-reinforced polymer (FRP), FRCM and SRG have good performance when exposed to (relatively) high temperature and good compatibility with inorganic substrates, and they can be applied to wet surfaces and at (reasonably) low temperatures. Although numerous studies investigated the mechanical properties and bond performance of various FRCM and SRG, new composites have been developed recently, and their performance still needs to be assessed. In this study, the bond behavior of three FRCM composites and one SRG composite applied to a masonry substrate is investigated. Sixteen single-lap direct shear tests (four tests for each composite) are performed. The FRCM studied comprised one layer of carbon, PBO (polyparaphenylene benzobisoxazole), or alkali-resistant (AR)-glass bidirectional textile embedded within two cement-based matrices. The SRG composite comprised one layer of a unidirectional stainless-steel cord textile embedded within a lime-based matrix. The results show a peculiar bond behavior and failure mode for each composite. Based on these results, the behavior of the carbon and PBO FRCM is modeled solving the bond differential equation with a trilinear cohesive material law (CML).

Rock bolts have been widely used for stabilizing rock mass in geotechnical engineering. It is acknowledged that the bolt profiles have a sound influence on the support effect of the rock bolting system. Previous studies have proposed some optimal rib parameters (e.g. rib spacing); unfortunately, the interface shear behaviors are generally ignored. Therefore, determination of radial stress and radial displacement on the bolt-grout interface using traditional pull-out tests is not possible. The load-bearing capacity and deformation capacity vary as bolt profiles differ, suggesting that the support effect of the bolting system can be enhanced by optimizing bolt profiles. The aim of this study is to investigate the effects of bolt profiles (with/without ribs, rib spacing, and rib height) on the shear behaviors between the rock bolt and grout material using direct shear tests. Thereby, systematic interfacial shear tests with different bolt profiles were performed under both constant normal load (CNL) and constant normal stiffness (CNS) boundary conditions. The results suggested that rib spacing has a more marked influence on the interface shear behavior than rib height does, in particular at the post-yield stage. The results could facilitate our understanding of bolt-grout interface shear behavior under CNS conditions, and optimize selection of rock bolts under in situ rock conditions.

Nanoparticles have advantageous small-size and surface effects that impart them with unique mechanical properties. To evaluate these properties, a constant-volume shear tester that can precisely measure stresses on the shear plane was used. Six samples, namely, hydrophilic and hydrophobic silica, alumina, and titania nanoparticles, were prepared for the shear tests. For each sample, a single shear test provided the void fraction, stress relaxation ratio, stress transmission ratio, powder yield locus, consolidation yield locus, critical state line, shear cohesion, and flow function. All the tests were conducted under ambient conditions using powder beds, in which the void fractions were in the range of 0.89–0.96. A series of analyses demonstrated that the hydrophilic nanoparticles have lower flowability than the hydrophobic nanoparticles, indicating that moisture on the surface increases the cohesion and inhibits the flow.

"Available online 30 September 2021", The assessment and modelling of unreinforced masonry structures require an adequate understanding of ma- sonry behaviour under shear loading. In particular, the behaviour of the interfaces connecting, brick and mortar, are of key importance during seismic actions. This is because the unit-joint interface may act as the main plane of weakness in the masonry composite. It has been observed that the inelastic behaviour of masonry structural elements subjected to shear loading depends largely on this interface behaviour. Hence, different experimental techniques available to observe in-situ or in a laboratory the behaviour of masonry under shear loading are reviewed and a suitable experimental campaign, also employing DIC as optical monitoring system is undertaken and shear tests are performed. After visualisation and discussion of novel displacement and shear strain maps and graphs, the experimental masonry behaviour is replicated via different numerical models based on the finite element approach. Models are used for better characterising the behaviour of the interface between brick and mortar. Further, the main parameters affecting the numerical models are discussed., The experimental part of this research work has received financial support for materials by the European Commission through the FP7- ENV-2007-1 research project “SMooHS - Smart Monitoring of Historical Structures”, (2008–2011) under grant 212939. The experimental facilities and technical personnel of the LISG laboratory of DICAM Department and of CIRI-EC lab both of the University of Bologna are acknowledged. The modelling part of this work was partly financed by FCT/MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE), under reference UIDB/04029/2020.

The objectives of this study were (1) to analyse different testing methods for evaluating face-bonding quality of cross-laminated timber from Eucalyptus grandis timber bonded with a one component polyurethane adhesive and (2) to evaluate the effect of different processing variables on the face-bonding quality of cross-laminated panels. A 3 × 2 factorial design was used to test the effect of clamping pressure, wood density, and presence of stress relief grooves on the bonding quality. Two existing test methods from the EN 16351 standard and two recently developed test methods were used in the evaluation. Among them a combined delamination and shear test, seems to have potential to determine bond quality of cross-laminated timber panels since it evaluates both the durability and shear strength of a joint while minimising the effect of rolling shear. Complex failure behaviour in the different tests and various interactions between the factors evaluated (density, grooves, pressure) make it difficult to reach firm conclusions on the effect of each factor. In general though, the presence of grooves had a negative effect, both increasing the delamination and decreasing the shear strength (whatever the pressure and density used during processing). High clamping pressure was preferable, particularly when high density material was used. Wood density had a positive effect on shear strength when determined on dry specimens, and a negative effect on delamination. Results indicated that the production of Eucalyptus grandis cross-laminated timber could be possible and that face-bonding quality suitable for structural use could be achieved when using a clamping pressure of 0.7 MPa and with no stress relief grooves present.

Base isolation systems reduce the action of earthquakes on buildings by disconnecting the structure from the ground through different devices, being the steel reinforced isolators (SREIs) the most common used. However, due to the high initial costs of SREIs, this technique is mainly implemented in special projects and is rarely used for residential buildings in developing countries with high seismic risk. This paper presented a thorough investigation on novel and unbounded rubber isolators which, based on the satisfactory behavior shown during experimental tests, could be a viable alternative to conventional isolators to be mainly implemented in Colombia for the low-rise residential buildings. Rubber and reinforcement materials employed in the manufacturing of the isolator prototypes were obtained locally to minimize the cost of the new devices. Different isolator configurations, including steel versus nylon/carbon fiber reinforcement (FREI) and bolted versus unbounded connections, were investigated to provide technological competitiveness. In the first phase, a high damping rubber was developed and characterized. In the second phase, prototypes of isolators designed for a real building were built and tested using combined compression and shear test. The results highlight an interesting comparison between vertical and horizontal properties of classical SREIs and unbolted FREIs, both satisfying required design values. Specifically, experimental results show that the behavior of the FREIs, in the horizontal direction, is similar to the SREIs, whereas the damping ratio is higher. Satisfactory results were also obtained with nylon reinforcement. Regarding the connection, the unbonded prototypes showed a better behavior respect to classical SREI, achieving higher deformations without failing. Therefore, this type of unbounded FREIs could represent a very promising option with higher potential to be implemented as a low-cost seismic isolation system in residential low-rise buildings of developing countries.

The morphology of the joint surface is multi-scale, and it can be divided into first-order asperity (waviness) and second-order asperity (unevenness). At present, the joint roughness characterization formula considers only the morphology contribution of waviness and unevenness components and does not fully consider their mechanical contribution. At same time, the relationship between the mechanical contribution and the morphology contribution is still unclear. Thus, the characterization formula considering the mechanical contribution of waviness and unevenness needs to be further studied. In this study, the standard joint roughness coefficient (JRC) profiles were first decomposed into waviness and unevenness. Then, three types of joint specimens with different asperity orders (flat, the standard JRC profile, and the profile containing only waviness) were prepared by the 3D engraving technique. Finally, direct shear tests were carried out on 39 sets of red sandstone joint specimens under three normal stresses. The mechanical contributions of waviness and unevenness were studied, the relationship between the mechanical contribution and the morphology contribution of waviness and unevenness was analyzed, and the characterization formula considering the mechanical contribution of waviness and unevenness was established. The results showed that the following: (1) the method combining the ensemble empirical mode decomposition (EEMD) and the critical decomposition level could be used to separate the waviness and unevenness from the joint surface, (2) the mechanical contribution of the waviness and unevenness decreased with the increase in normal stress, (3) the relationship between the mechanical contribution ratio and the statistical parameter ratio of the waviness and unevenness can be describe by power function, and (4) the roughness characterization formula considering the mechanical contribution and morphology contribution was established. This study will enhance the accurate evaluation of the roughness coefficient and shear strength of the joint specimen.

The creation of acrylic dentures involves many stages. One of them is to prepare the surfaces of artificial teeth for connection with the denture plates. The teeth could be rubbed with a chemical reagent, the surface could be developed, or retention hooks could be created. Preparation of the surface is used to improve the bond between the teeth and the plate. Choosing the right combination affects the length of denture use. This work focuses on a numerical analysis of grooving. The purpose of this article is to select the shape and size of the grooves that would most affect the quality of the bond strength. Two types of grooves in different dimensional configurations were analyzed. The variables were groove depth and width, and the distance between the grooves. Finally, 24 configurations were obtained. Models were analyzed in terms of their angular position to the loading force. Finite element method (FEM) analysis was performed on the 3D geometry created, which consisted of two polymer bodies under the shear process. The smallest values of the stresses and strains were characterized by a sample with parallel grooves with the grooving dimensions width 0.20 mm, thickness 0.10 mm, and distance between the grooves 5.00 mm, placed at an angle of 90°. The best dimensions from the parallel (III) and cross (#) grooves were compared experimentally. Specimens with grooving III were not damaged in the shear test. The research shows that the shape of the groove affects the distribution of stresses and strains. Combining the selected method with an adequately selected chemical reagent can significantly increase the strength of the connection.

The study was designed to investigate the synergic effect of Ti and Sn in the active metal brazing of Al2O3 ceramic to copper brazed, using the multicomponent Ag-Cu-Zr filler alloy. Numerous fine and hexagonal-shaped rod-like ternary intermetallic (Zr, Ti)5Sn3 phase (L/D = 5.1 ± 0.8, measured in microns) were found dispersed in the Ag-Cu matrix of Ag-18Cu-6Sn-3Zr-1Ti alloy, along with the ternary CuZrSn intermetallic phases. An approximate 15° reduction in contact angle and 3.1 °C reduction in melting point are observed upon the incorporation of Ti and Sn in Ag-18Cu-3Zr filler. Interestingly, the interface microstructure of Al2O3/Cu joints brazed by using Ag-18Cu-6Sn-3Zr-1Ti filler shows a double reaction layer: a discontinuous Ti-rich layer consisting of (Cu, Al)3(Ti, Zr)3O, TiO, and in-situ Cu-(Ti, Zr) precipitates on the Al2O3 side and continuous Zr-rich layer consisting of ZrO2 on the filler side. The shear strength achieved in Al2O3/Cu joints brazed with Ag-18Cu-6Sn-3Zr-1Ti filler is 31% higher, compared to the joints brazed with Ag-18Cu-6Sn-3Zr filler. Failure analysis reveals a composite fracture mode indicating a strong interface bonding in Al2O3/Ag-18Cu-6Sn-3Zr-1Ti filler/Cu joints. The findings will be helpful towards the development of high entropy brazing fillers in the future.

In this study, shear tests and pull-off tests were carried out to investigate the bond performance of glass fibre-reinforced polymer (GFRP) strips bonded to low-grade poplar wood (Populus x euroamericana I-214). Accordingly, 180 shear specimens and 72 pull-off specimens were produced using three different structural epoxy adhesives. These specimens were divided into two joint types (wood-wood and wood-GFRP configurations), which were tested under dry conditions and after exposure to hydrothermal cycles (i.e., accelerated ageing). The results showed that the epoxy adhesives exhibited good behaviour in the wood-GFRP samples exposed to different hydrothermal conditions. The samples exhibited shear strength values between 4.93 MPa and 8.49 MPa and pull-off strength values between 1.72 MPa and 2.69 MPa. Additionally, there were different main failure modes between the dry specimens and the aged specimens. (C) 2020 Elsevier Ltd. All rights reserved., This work was supported by the University of Valladolid through the programme ``Movilidad Doctorandos UVa 2017"and in collaboration with the Laboratory of Structures (LEST) of the University of Minho (Portugal).

This paper presents an experimental material campaign focusing on fiber-reinforced polymers (FRP) to be applied in a novel bridge deck panel. Laminas based on most commonly used fibers, i.e., glass, carbon, basalt and aramid, were prepared and studied in tension, shear and compression. In the subsequent test stages, different fabric reinforcements (uni- and bi-directional fabrics, woven fabrics, CSM layers) were considered for glass laminas only, and finally, a resultant laminate was designed and tested. Such an approach gives a great opportunity to create “tailor-made” laminates, as required in FRP bridge deck panels. Simultaneously with the laboratory tests, analytical calculations were performed using a few micromechanical models that aimed to determine engineering constants and strength parameters. Then, the results obtained from material testing and analytical calculations were compared, and conclusions on the compliance were drawn. Based on this validation, further analytical calculations may replace time-consuming laboratory tests and facilitate FRP deck design.

The evaluation of the shear behavior of masonry walls is a first fundamental step for the assessment of existing masonry structures in seismic zones. However, due to the complexity of modelling experimental behavior and the wide variety of masonry types characterizing historical structures, the definition of masonry’s mechanical behavior is still a critical issue. Since the possibility to perform in situ tests is very limited and often conflicting with the needs of preservation, the characterization of shear masonry behavior is generally based on reference values of mechanical properties provided in modern structural codes for recurrent masonry categories. In the paper, a combined test procedure for the experimental characterization of masonry mechanical parameters and the assessment of the shear behavior of masonry walls is presented together with the experimental results obtained on three stone masonry walls. The procedure consists of a combination of three different in situ tests to be performed on the investigated wall. First, a single flat jack test is executed to derive the normal compressive stress acting on the wall. Then a double flat jack test is carried out to estimate the elastic modulus. Finally, the proposed shear test is performed to derive the capacity curve and to estimate the shear modulus and the shear strength. The first results obtained in the experimental campaign carried out by the authors confirm the capability of the proposed methodology to assess the masonry mechanical parameters, reducing the uncertainty affecting the definition of capacity curves of walls and consequently the evaluation of seismic vulnerability of the investigated buildings.

International audience; The granular Bond number, defined as the ratio between interparticle attractive forces and particle's weight, can be computed to predict the flow behavior of powders. Previous studies used this dimensionless number to predict the flowability of various pharmaceutical or ceramic powders, exhibiting polydispersed particle size distributions. In this paper, we employ a multi-component population-dependent granular Bond number in order to apply this model to powder mixtures. Some binary and ternary mixtures are prepared using two different techniques: a Turbula® mixer and a ball mill. The flowability predictions appear to be in very good agreement with the empirical measurements, carried out with a powder shear tester. However, the model parameters seem to be slightly different between milled and raw powders. The model discussed in this paper allows a prediction of the flowability of powder mixtures according to their composition and serve as a guide for product formulation and equipment design.

Energy consumption and the emission of harmful particles have increased significantly in recent decades. The constant development of transport poses an increasing threat to the environment. The search for alternative energy-saving solutions is closely linked to the development and improvement of new vehicles, reducing their negative impact on the environment. Fiberglass or carbon fiber are among the most promising materials that can reduce weight in all types of vehicles. They are also much easier to recycle than steel. Fiberglass or carbon fiber composite materials are widely used in a variety of applications: construction, ships, and trains. Vehicles and buses are no exception. These innovative materials are used not only for interior elements but also in constructional units for the production of light duty vehicles. Meanwhile in buses these material are not yet used in safety frame. Bus safety frames are made out of steel. Therefore, in this work the fiberglass composite material from which the tubes are made by pultrusion process would replace the steel tube in the safety frame construction of the bus. Such technology could reduce the weight of the bus safety frame by about 20%. Other parameters would also be affected by weight reduction: safety: bus would be less overloaded, the braking distance would be reduced, the center of gravity position would be closer to the ground; environmental: lower air pollution due to lower CO2 emissions; economic: lower fuel consumption. However, before using such technology, it is necessary to determine the properties of the composite material. Properties were determined by tensile and shear tests (ISO 527-2:2012 and ASTM D5379/D5379M-19). Comparison tests of different materials (tensile and crushing tests) were also performed. According to the experimental results, conclusions were drawn regarding the possibility of using fiberglass for the bus frame.

The rise of digital fabrication has increased the use of wood-wood connections inspired by traditional carpentry in modern timber constructions. With recent developments on standard construction systems, the mechanical behavior of such joints for in-plane loading configurations is an essential parameter for the structural design. However, only few design guidelines exist on this topic in building codes such as Eurocode 5 and research has been mainly focused on the rotational behavior, which is important for free-form structures. Therefore, this work presents an experimental campaign on the load-carrying capacity of digitally produced through tenon connections for commonly available engineered timber products such as oriented strand board, laminated veneer lumber, and multiply solid wood panels. Shear and compression failure modes were studied and two test setups were developed. The scope of the study was limited to five different materials, a grain orientation parallel to the joint, and three different tenon lengths. The test results showed significant differences between the product specifications given by manufacturers and real performances observed for oriented strand board and cross laminated timber, while laminated veneer lumber had more accurate specifications. Nonetheless, a spreading of the compression strength was highlighted only for the OSB material and was also observed for the shear strength of laminated veneer lumber specimens. The existing Eurocode 5 guidelines generally underestimated the load-carrying capacity of the connections by 25% and only the capacity of oriented strand board connections was overestimated. Finally, the study demonstrates that different design approaches can be defined according to the material employed in through tenon connections. Design diagrams based on tests are preferred for materials with a high variability between product specifications and real performances while design criteria from building codes can be applied for the others., Engineering Structures, 213, ISSN:0141-0296

[EN] Continuous reinforced concrete (RC) beams may develop significant plastic rotations to enable the redistribution of bending moments. These rotations occur at plastic hinges, which are subject to high shear forces. The influence of rotations on the shear strength for statically determined beams without shear reinforcement failing in shear after yielding of the flexural reinforcement has already been experimentally verified. However, this influence has not been studied in continuous members with shear reinforcement. An innovative tests system has been specially designed to develop shear failures before and after yielding of the flexural reinforcement in both statically determinate and indeterminate structures. Nine beams (9000 mm long, 250 mm wide, 450 mm high) with a shear reinforcement of phi 8/30 (rho(w) = 0.13%) and different longitudinal reinforcement ratios were tested under different load and support conditions. The shear strength provided by shear reinforcement and that provided by the other mechanisms of resistance (shear strength provided by concrete) for each specimen were calculated based on the critical shear crack width measurements performed by Digital Image Correlation (DIC). Bending rotation and crack rotation along the development length of the critical shear crack were also obtained by DIC. Based on the test results, the shear strength provided by concrete was studied in relation to the bending rotation and the average crack width in reinforced concrete beams with shear reinforcement. It was confirmed that the shear strength provided by concrete decreased with increasing both bending rotations and crack widths. The shear strength values predicted by different design codes (ACI 318-19, Eurocode 2 and Model Code 2010) were compared with the test results, and showed that these formulations did not properly capture the loss of shear strength caused by bending rotation., This research was funded with grants from the Spanish Ministry of Economy and Competitiveness to Research Project BIA2015-64672-C4-4-R. The experimental programme was developed in the Laboratory of Concrete of the Institute of Concrete Science and Technology (ICITECH) of the Universitat Politecnica de Valencia (UPV), with concrete supplied by Caplansa. Andrea Monserrat was supported by the Conselleria d'Educacio, Investigacio, Cultura i Esport of the Generalitat Valenciana (Order 6/2015, DOCV no. 7615 15.09.2015) with European Regional Development Funds (ERDF) allocated by the EU.

This study demonstrates a new constant-volume shear test configuration to analyze the stresses in powder beds and evaluate powder flowability. A novel cylindrical shear cell geometry and load cell arrangement allowed precise measurement of the normal stress acting on the shear planes of the powder beds. The stress transmission ratio between the top and shear planes decreased with increasing ratio of the powder bed height in the upper section of the shear cell to the shear cell diameter. This was due to friction between the powder bed and the side wall of the upper section of the shear cell. Using the measured values of the normal stress on the shear planes, the effects of the powder bed height and shear cell diameter were eliminated from the data. In addition, to evaluate the shear properties of the powder beds, the powder yield locus, consolidation yield locus, critical state line, shear cohesion, and void fraction were obtained from a single shear test. The powder yield locus data were used to obtain flow functions.

In this paper, the authors discuss dissimilar materials joining structures fabricated by friction-stir forming (FSF) and easily decomposable. Dissimilar-materials-joining has been successfully studied as a key for new producing light-weight parts; however, it can be a barrier to recycling in the future. The authors suggested the concept of easily separable joining of dissimilar materials employing friction-stir forming (FSF). A joined plate having a keyhole was prepared and put into a mold having a hook cavity. An aluminum alloy plate was put on and friction stirring was conducted on its back surface. Due to the massive heat and compression force generated by the friction stirring, a hook-like joint was successfully generated, and the substrate and joined member are sheared to disconnect them by hitting with a plastic hammer; however no room was observed between the hook and joined material after forming. Opposite hooks generated by the above approach join dissimilar materials tightly, but the materials can be separated smoothly after cutting them between the hooks. In the experiment, a pair of a 0.8mm-thick JIS SPCC steel sheets and a 3mm-thick JIS A5083P-O aluminum alloy plate was joined. The authors evaluated the joints by tensile and shear tests and discuss their mechanical behavior and failure. The tensile strength of the joint was 652N (average). In the tensile tests, the deformation of the keyhole of 0.8mm-thick SPCC steel sheet caused the failure of the joint. The shear strength was affected by the shear direction, i.e. 1010N at 0deg, 705N at 45deg, and 1320N at 90deg (average) for the connecting line between hooks. It was thought that the hook-like joints had enough strength for the cross-sectional area of their stems (i.e. 4.16mm2).

International audience; This study concerns the characterization of the mechanical properties of the cement paste and of the cement-aggregate interface in the degraded state by a chemical leaching mechanism. This study is carried out within the framework of the MIST laboratory. The experimental tests were carried out on cement paste and composites consisting of aggregates bound by the same cement paste prepared with a water/cement ratio of 0.5. The particular experimental devices, designed and produced for the purposes of this study, made it possible to directy solicit the composites at the cement-aggregate interface. As the process of leaching with the deionized water occurs very slowly, the experimental study is accelerated in the laboratory by replacing water by ammonium nitrate solution. To quantify the development and kinetics of chemical degradation at the cemented bond, the concrete leaching fronts are characterized at different times of degradation by using phenolphthalein. The local mechanical tests (tensile and shear) are performed on cement paste and composite at different degradation rate. The experimental results show a fast drop in shear or tensile strength of about 45% at the beginning of degradation. These results confirm the effect of the cement paste-aggregate interface degradation on the mechanical properties.

BackgroundPrecious metal alloys can be supplied in traditional plate form or innovative drop form with high degree of purity.ObjectiveThe aim of the present work is to evaluate the influence of precious metal alloy form on metallurgical and mechanical properties of the final dental products with particular reference to metal-ceramic bond strength and casting defects.MethodA widely used alloy for denture was selected; its nominal composition was close to 55 wt% Pd – 34 wt% Ag – 6 wt% In – 3 wt% Sn. Specimens were produced starting from the alloy in both plate and drop forms. A specific test method was developed to obtain results that could be representative of the real conditions of use. In order to achieve further information about the adhesion behaviour and resistance, the fracture surfaces of the samples were observed using ‘Scanning Electron Microscopy (SEM)’. Moreover, material defects caused by the moulding process were studied.ResultsThe form of the alloy before casting does not significantly influence the shear bond strength between the metal and the ceramic material (p-value=0,976); however, according to SEM images, products from drop form alloy show less solidification defects compared to products obtained with plate form alloy. This was attributed to the absence of polluting additives used in the production of drop form alloy.ConclusionsThis study shows that the use of precious metal denture alloys supplied in drop form does not affect the metal-ceramic bond strength compared to alloys supplied in the traditional plate form. However, compared to the plate form, the drop form is found free of solidification defects, less expensive to produce and characterized by minor environmental impacts.

This paper investigates the explicit use of rock reinforcement in a discontinuous stress analysis model. A series of numerical experiments was undertaken to evaluate the performance of local and global reinforcement models implemented in universal distinct element code (UDEC). This was made possible by calibrating the reinforcement models to the laboratory behavior of a fully-grouted rebar bolt tested under pure pull and pure shear loading conditions. The model calibration focuses on matching different loading stages of the force–displacement curve including the initial elastic response, the hardening behavior and the bolt rupture. The paper concludes with a discussion on the suitability of the different reinforcement models in UDEC including their advantages and limitations. Finally, it addresses the choice of input parameters required for a realistic simulation of fully-grouted rebar bolts.

The adhesively bonded 3-point bending specimen has been recently considered for evaluating the adhesive shear stress-strain behaviour. Its main advantage is avoiding the spurious end effects typical of lap-joints. A previous beam model proved to be fairly accurate for thin bondlines typical of structural joints. The present study extends such model to thick bondlines and achieves improved shear strain results. Model predictions were in very good agreement with finite element analyses of specimens with metal adherends and adhesive elastic-perfectly plastic behaviour. The present model will facilitate the inverse method needed to evaluate the parameters of a piecewise linear approximation to the adhesive shear stress-strain curve. Furthermore, two simplified models were shown to provide useful bounds for the shear stress-strain curve using only the basic load-displacement data.

International audience; Granular materials are used in many industrial processes among various fields, such as pharmaceutical, food, metallurgy or nuclear fuel production. However, compared to other commonly used media, such as liquids, powders are known to behave unpredictably, leading to uncontrolled process operations. Since the flow behavior of the powders originates from interparticle forces, we suggest a model, linking the macroscopic flowability of powder beds, and the properties of the microscopic particles constituting the powder. A population dependent granular Bond number (Capece et al., 2016), that takes into account the particles properties such as the particles’ true density, surface energy, rugosity and the whole particle size distribution, is used. This non-dimensional number was found to correlate well with the flowability of polydispersed powder bed, which can be measured by shear testing with a Freeman FT4® powder rheometer. The results found in previous studies (Bernard-Granger et al., 2019; Capece et al., 2016) are extended and discussed using five different oxide powders exhibiting various flow behaviors. In particular, a short sensitivity analysis of the model is carried out. The results show that the fraction of fine particles within a polydispersed powder is a critical parameter for the flowability of the powder bed. Finally, the Rumpf’s theory is used to suggest a physical meaning for the model parameters.

In this study, the effects of different shear rates during direct shear tests on variations in the strength characteristics were investigated for the sand samples of various particle size distribution. Direct shear tests were carried out at nine different shear rates ranging from 0.05 to 5 mm/min under normal stresses of 54.5, 109, and 218 kPa. Both sample groups were tested under a condition of defined water content and in a water-filled condition. Results show that with increasing shear rate, the internal friction angle and peak shear strength values increased. The increase in the internal friction angles and peak shear strengths were particularly evident for shear rates higher than 1 mm/min. Even though the effect of grain size on the variation in strength parameters due to shear rate is limited for the soils examined in this study, the effect should be considered. C1 [Beren, M.; Undul, O.] Istanbul Univ Cerrahpasa, Istanbul, Turkey. [Cobanoglu, I.; Celik, S. B.] Pamukkale Univ, Denizli, Turkey.

International audience; CLT-concrete composite floor systems are a solution for timber buildings with a long-span floor. It yields a reduction of carbon footprint and even eco-friendly structure at the end of its service life. This study will evaluate the structural performance of notched connectors in the CLT-concrete composite floor, comprised of the serviceability sti ness, maximum load, and behavior at failure. The parameters of the test plan are the loaded edge length, the notch depth, the concrete thickness, and the screw length. Other secondary variables are also assessed, such as di erent loading sequences, speed of test, and timber moisture content. Experimental results prove that the performance of the connector depends significantly but not linearly on the notch depth and the length of the loaded edge. The connector with a deeper notch and a shorter heel will be sti er and more robust, but it also tends to have a brittle rupture. The test results also help validate a solution for deconstructable connector systems. A nonlinear finite element model of the connector is built and validated versus the experimental results. It yields reasonably good predictions in terms of resistance and can capture the load-slip relationship.

In this paper, a novel transient liquid phase bonding material was fabricated by consequent electroless plating of Cu and Sn on a multi-walled carbon nanotube (MWCNT). The resulting Sn-Cu-MWCNT composites were used to join the Cu interconnects at 260&deg, C. After 8 min of reflow time, a complete transformation of Cu3Sn intermetallic compound (IMC) occurred, leaving a Cu/MWCNT-Cu3Sn /Cu joint capable of withstanding the high operating temperature. Due to flake-like morphology, the Sn-Cu-MWCNT composite particles were well packed with lesser voids. The shear strength of the Cu/Cu3Sn-MWCNT/Cu joint was measured as 35.3 MPa, thus exhibiting the scope for replacing conventional transient liquid phase (TLP) powders in the future.

International audience; Undesired agglomeration of powders, known as caking, results in the loss of product quality and is unacceptable in many powder industries. Information on how ambient conditions influence the cake strength is essential to prevent caking. Although there are a lot of existing methods to form caked samples and even more to characterize them, there is still no consensus regarding these methods. Repeatability is rarely evaluated and the comparative studies remain infrequent. As a deliquescent powder, sucrose is characterized by a threshold Relative Humidity (RH), called Deliquescence Relative Humidity (DRH), above which it turns into an aqueous solution. Partially deliquesced crystals are linked by liquid bridges of aqueous solution. When the RH is decreased below the DRH, these liquid bridges recrystallize into solid bridges to form a hard cake. In this study, an accelerated caking device was developed to obtain homogeneous caked samples of sucrose under controlled conditions. Three mechanical tests were compared on the basis of their sensitivity and repeatability: the uniaxial compression test, the diametrical compression test (tensile test) and the shear test. The varying parameter was the amount of water uptaken before drying, and the data were fitted by cross-validated local linear nonparametric regression. The best mechanical test was found to be the shear test, giving a sharp failure of the cake along a predetermined failure surface and a linear relationship between the cake strength and the amount of water uptaken.

The effectiveness of new shear test methods for evaluating the face-bonding quality of Cross-Laminated Timber (CLT) panels was examined by comparing experimental data and numerical modelling. The common characteristic of the specimens was the loading with angle of 45° with respect to the wood grain, in order to avoid rolling shear during test. In addition, the sampling methodology along the panel was investigated, as well as the relation between shear and delamination tests, and the possibility of coupling them using the same specimen. The results demonstrated that all the proposed shear test methods were effective for evaluating the quality of bonding among layers in CLT panels; however, the practical applicability of the methods led to elect the most suitable for inclusion in technical standards. Shear and delamination results proved not to be correlated, and the results showed that the size of the specimen is a crucial factor in determining the outcomes of delamination tests. Therefore, while it is feasible to propose the coupling of accelerated aging procedures with shear tests, the size of the samples need to be higher than the one tested here.

One of the primary concerns about the design aspects is that how to deal with the shear reinforcement in the ultra-high performance fiber reinforced concrete (UHPFRC) beam. This study aims to investigate the shear behavior of UHPFRC rectangular cross sectional beams with fiber volume fraction of 1.5 % considering a spacing of shear reinforcement. Shear tests for simply supported UHPFRC beams were performed. Test results showed that the steel fibers substantially improved of the shear resistance of the UHPFRC beams. Also, shear reinforcement had a synergetic effect on enhancement of ductility. Even though the spacing of shear reinforcement exceeds the spacing limit recommended by current design codes (ACI 318-14), shear strength of UHPFRC beam was noticeably greater than current design codes. Therefore, the spacing limit of 0.75d can be allowed for UHPFRC beams.

The analysis of the connection steel/Al/steel made by resistance welding was performed. The used low-carbon steel had low content of carbon and other elements, aluminum was of 99.997 wt.% Al purity. Formation of various FeAl intermetallic phases found in the phase diagram depending on the duration of the process was analyzed. Two distinctively different types of structure depending on time of welding were observed: 1) hypoeutectic structure for samples processed for 5 s, and 2) eutectic structure for samples processed for 10 s and more. The shear test showed increase of mechanical properties of the connection for the samples welded 10 s.

Interest in the use of beech wood in construction is growing steadily. Considering its high mechanical performance, it has a large potential to be used for the production of glued timber structural products. However, the issue of structural bonding remains to be solved before effective production and safe use of beech wood in these products can be achieved. Three adhesives (one-component polyurethane – PUR, PUR + primer and melamine-urea–formaldehyde – MUF) and two press systems (hydraulic and vacuum press) were explored in the production of pure beech and combined beech-spruce-beech cross laminated timber (CLT). An evaluation of the bonding quality was performed with both standardized and optimized (the specimen layers were oriented with the wood grain forming an angle of 45° with respect to the load application) delamination and shear test methods. None of the adhesives that were tested met the requirements for delamination tests provided by the current standard for softwood. Specifically, PUR yielded the poorest performance in the production of the CLT panels entirely made of beech; the addition of a primer improved the bonding, achieving results comparable to those observed for MUF. On the contrary, in the production of beech-spruce panels, the three adhesives showed similar results. The press system was not a relevant factor in terms of bonding quality. In regard to testing, a size effect was noticed in the delamination test: the larger the specimen the greater the delaminations that were observed. The shear tests on dry specimens proved to be less efficient in determining the influence of the several bonding parameters, even if a 45° grain orientation seemed to reduce the rolling shear during the shear test and to improve the response of the test in this regard. Combining delamination pretreatment and shear made the test more sensitive and objective.

Friction surfacing offers a means of producing coatings between dissimilar materials through a solid state process; a union that would otherwise be classed as incompatible for liquid state coating processes. A method of using a rotating consumable friction rod supplemented by inductive heating was employed to produce conditions necessary for a sound bond between a stainless steel coating and an aluminium substrate. The rotational speed of and load on the coating rod influenced the bond strength significantly with low rotational speeds and high load values producing a good bond quality; however, cavitations at the coating-substrate interface showed a detrimental effect on the bond quality. Mechanical interlocking could be identified from images of longitudinal cross-sectional slices which were recorded using optical microscopy. An image recognition software tool was used to generate an interfacial roughness profile graph which described the coating-substrate interface. Additional filtering of the profile graph showed the depth of mechanical interlocking of the stainless steel coating into the aluminium substrate with the degree of this interlocking quantified by roughness values calculated from the profile graph. Large roughness values can be related to high coating push-off strengths (up to 107 MPa), and also were a result of low rotational speeds and high load values during friction surfacing. Dovetail shaped mechanical interlocks identified in the profile produced both high push-off and shear strength when compared with wedge-shaped interlocks; which, overall, provided good shear strengths up to 126 MPa.

Base isolation system is one of the most commonly used technologies implemented around the world for seismic protection of infrastructure. Its objectives are the protection of human life and the reduction of damage to buildings as a result of earthquakes. However, the system is rarely used in developing countries such as Colombia, due to its relatively high costs, including the cost of importing the devices. The development of an isolation system using local technology therefore eliminates the latter expense. This paper focuses on the experimental assessment and analytical modeling of low-cost seismic isolators for low-rise buildings, which represent most construction projects worldwide. Two types of unbonded isolator with a high damping rubber matrix and different reinforcement fibers were employed: carbon and polyester. Scaled prototypes were manufactured and tested under compression and shear loads . Despite the lower mechanical properties of polyester, the results revealed an adequate comparison between the vertical and horizontal properties of the two isolators, with both satisfying minimum required design values. Nevertheless, when taking into account the fact that the price of polyester fiber is one order of magnitude less than of carbon, this seems to be the option with greater potential to be implemented as a low-cost seismic isolation system. Based on the experimental results, an analytical model was proposed to estimate the horizontal stiffness of unbounded isolators, taking into account the reinforcement characteristics, the effective area and the shear modulus of the rubber. In comparison with other formulations, the proposed model was found to be sufficiently accurate to be used in the preliminary design of unbonded fiber-reinforced elastomeric isolators.

The joining of materials is essential to many industrial applications used today. However, it still lacks a reliable and true single step method to join different types of materials including polymers. Laser welding was primarily employed for metals until some decades ago, but with the rise of high power solid state lasers, applications have emerged in the polymer field. With the recent addition of fiber lasers, true clear to clear welding, joining two of the same transparent polymer layers, has become feasible at a different wavelength range, which benefits the sealing of microfluidic devices. A number of research efforts were made at performing welds of thermoplastics at this wavelength range, however without attempts at offering elaborate explanation of the observations. In our work, a laser welding system using a Thulium fiber laser at 1940 nm was used to join a variety of thermoplasts, without the use of additives or prior processing. By optically and chemically characterizing the materials, a basis was established that links intrinsic material properties to observed welding performance, as determined by mechanical shear tests on the welded materials. We found that four of the ten considered thermoplastic polymers lend themselves to sufficiently strong bonding to allow the creation of leak-proof microfluidic devices by use of laser welding at this wavelength.

Conventional tunnelling methods (i.e., the drill and blast tunnelling method or the new Austrian tunnelling method) have been frequently applied for the construction of tunnels/caverns under a high overburden and with a large cross section. Under such adverse conditions, tunnel support materials may yield because of ground pressure and tunnel deformation. As a result, a tunnel may lose its stability due to a reduced effectiveness of the tunnel supports. Rock bolts have been widely used as an essential component of tunnel support, and many studies have been conducted on the performance of rock bolts in strengthening the jointed rock mass. However, there is a lack of understanding on the interface behaviour between the rock bolt and the bond material, especially the crack initiation and propagation inside the bond material. This study aims to investigate the interface behaviour between rock bolts and bond materials using laboratory tests (shear tests) and numerical simulations (Discontinuous deformation analysis). By assessing the impact of the key parameters in the rock bolting system, such as the ribs, rib angle, strength of the bond material and the confining pressure, we are able to better understand the supporting mechanism and the effects of rock bolting.

Made available in DSpace on 2018-12-11T16:47:41Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-09-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) This study aimed to evaluate the effect of various zirconia surface pretreatments on the adhesion between full contour 3Y-TZP zirconia and glaze, and the shear bond strength (SBS) between glazed/3Y-TZP and resin cement. Specimens were allocated into groups: GL-glaze; AL+GL-sandblasting with Al2O3+GL; CJ+GL-tribochemical silica coating (Cojet®/CJ)+GL; PS+GL-piranha solution+GL; and CJ. Adhesion between 3Y-TZP and GL was evaluated using the scratch test. Surface topography and glaze thickness were evaluated by using a scanning electron microscope (SEM). For SBS, glazed/3Y-TZP surface was etched with hydrofluoric acid and a silane was applied. For CJ only the silane was applied. Samples were tested after 24 h (24 h wet) or after 15,000 thermal cycles and 90 days storage (thermocycled). After SBS, the type of failure was classified as: adhesive, mixed or cohesive. The data were analyzed using two-way ANOVA and Tukey's test. SEM analysis after scratch test revealed circular cracks in the GL group and conformal cracks in the others groups. SEM micrographs suggested that zirconia specimens submitted to airborne-particle abrasion presents rougher and porous surface when compared to surfaces treated with GL and PS. The glaze layer was approximately 1.86 µm thick in all groups. After 24 h, SBS test showed highest values for AL+GL and CJ+GL and were significantly higher when compared to the GL group. Differences were not significant between PS+GL and the other groups. After aging (thermocycling+storage), groups GL and CJ presented no statistically significant difference compared to 24 h and aged AL+GL, CJ+GL and PS+GL groups. The predominant type of failure was mixed. 3Y-TZP surface treatment with glaze application could be considered as an alternative treatment, since it yielded a similar resin bond strength without the need for airborne-particle abrasion. Department of Biomedical and Applied Sciences Division of Dental Biomaterials Indiana University School of Dentistry Department of Dental Materials and Prosthodontics Institute of Science and Technology Universidade Estadual Paulista–UNESP Materials Science and Technology Center Institute for Energy and Nuclear Research IPEN São Paulo Department of Restorative Dentistry Division of Prosthodontics Federal University of Santa Maria Department of Dental Materials and Prosthodontics Institute of Science and Technology Universidade Estadual Paulista–UNESP CAPES: 18922/12-0 FAPESP: 2012/02945-0

The adhesive shear stress-strain behaviour is an essential input for the design of structural adhesive joints. Relative to current standard tests, the main advantage of bonded beams is reducing spurious adhesive joint end effects on strength measurements. A beam model was developed in this work for the three-point bending test considering metal adherends, support effects and adhesive elastic-perfectly plastic stress-strain behaviour. Model predictions were in good agreement with finite element analyses for specimens with the thin bondlines typical of structural joints. The present results show that the adhesively bonded three-point bending test can be an interesting approach for the thin bondlines used in structural joints. Nevertheless, there are limitations on the range of measurable properties and data analysis requires models such as the one developed herein.

Natural sintering in ice is a fundamental process determining mechanical properties of various ice forms. According to the literature, limited data are available about the complex subjects of snow sintering and bond formation. Here, through cold laboratory mechanical tests with a new shear apparatus we demonstrate time-dependent effects of isothermal sintering on interface strengthening at various normal pressures. Measurements showed that interfacial strength evolved rapidly, conforming to a power law (mean exponent ≈0.21); higher pressure corresponded to higher initial strength and sintering rates. Our findings are consistent with observations on homogeneous snow, provide unique records essential for slope stability models and indicate the significant importance of normal load on data interpretation.

The contact state between layers of asphalt pavement not only has a significant effect on the mechanical response of road structure but is also the bottleneck of research on the mechanical behavior of pavement structure at present. In this paper, the effects and laws of different water−salt entry modes, salt solution concentrations, and temperatures coupling on the contact state between base and surface layers are studied by a 45° inclined shear test. The simulation and verification of each working condition are carried out by ABAQUS (Dassault, Paris, France) the friction coefficient between layers is reversed, and the actual contact state between layers is characterized in order to realize comprehensive evaluation and reasonable expression. The results show that different modes have different effects on contact characteristics. At the same temperature and concentration of the salt solution, bonding of water and salt erosion is the best, followed by direct erosion, with the worst being from bottom to top, and the interlayer bonding condition is weakened with increase in temperature. The relative accuracy of the software simulation and test analysis was as high as 92% and the friction coefficient of the water-free salt erosion test piece was found to be about 0.85 at 25 °C, while after the bottom-up erosion of the 14% salt solution the friction coefficient was found to be about 0.43, which indicates that the corrosion of the water−salt will have a great effect on the bonding condition between the structural layers of the road.

The developed study aimed at investigating the mechanical behavior of a new type of self-insulating concrete masonry unit (SCMU). A total of 12 full-grouted wall assemblages were prepared and tested for compression and shear strength. In addition, different axial stress ratios were used in shear tests. Furthermore, numerical models were developed to predict the behavior of grouted specimens using simplified micro-modeling technique. The mortar joints were modeled with zero thickness and their behavior was applied using the traction–separation model of the cohesive element. The experimental results revealed that the shear resistance increases as the level of precompression increases. A good agreement between the experimental results and numerical models was observed. It was concluded that the proposed models can be used to deduct the general behavior of grouted specimens.

8th RILEM International Conference on Mechanisms of Cracking and Debonding in Pavements, NANTES, FRANCE, 07-/06/2016 - 09/06/2016; Poor bond between two asphalt layers is one of the main causes of premature failure of pavement surface layers, such as slippage cracking, fatigue cracking, shoving or surface layer delamination. These distresses become more serious in pavement areas often adversely affected by horizontal loads due to traffic wheels. There are many factors affecting the quality of bond between asphalt layers including temperature and application rate of tack coat. In an elemental study, the modified Leutner shear test, which allows determining shear strength and shear stiffness modulus at the interface of double-layered cylindrical specimen, was used. Tests were carried out at a range of temperatures between 20 and 60 °C and with different application rates between 0.0 and 0.9 l/m2 (non-residual) using a Cationic Rapid Setting 1 (CRS-1) emulsion. Results of the elemental study are then used to establish regression equations, relating bonding strength, temperature and application rate which are used as part of larger studies to investigate the influence of interface bond on premature failures in pavement structures, such as premature fatigue cracking or rutting. Some interesting results of these studies cast additional light on the behavior of bonding between asphalt layers.

International audience; The chemical modification of tannin through epoxidation is a way to develop new applications for tannins and to improve tannin resins performances. In this paper the influence of reaction conditions was studied. Commercial tannin bark extract was epoxidized. The resulting products were characterized by FT-IR Spectroscopy, 13C NMR and MALDI-TOF mass spectrometry. Tannin epoxidation has been confirmed by 13C NMR and FT-MIR. Wood specimens were bonded with mixed diglycidyl ether of bisphenol A (DGEBA) and glycidyl ether tannin (GET) epoxy resin formulations. The bonded joints were tested for block shear strength. The results obtained indicated that such formulations, based on up to 75% commercial natural materials are capable of satisfying the shear strength requirements of relevant international standards.

This paper presents results of experimental and mathematical analysis of stiffness characteristics of a composite timber-concrete structure. The composite timberconcrete structure presented herein is non-typical compared to similar types of building structures. The interaction between the timber and concrete part of the composite cross-section is not based on metal connecting elements, but it is ensured by a glued-in perforated mesh made of plywood. The paper presents results of experimental and mathematical analysis for material alternatives of the solution of the glued joint. The slip modulus values were determined experimentally. Data obtained from the experiment evaluated by means of regression analysis. Test results were also used as input data for the compilation of a 3D model of a composite structure by means of the 3D finite element model. On the basis of result evaluation, it can be stated that the stress-deformation behaviour at shear loading of this specific timber-concrete composite structure can be affected by the type of glue used. Parameters of the 3D model of both alternative of the structure represent well the behaviour of the composite structure and the model can be used for predicting design parameters of a building structure.

The article presents a prototype of a new device for measuring the shear strength of snow specimens in situ. The resistance to sliding of a snow slab on a mountain slope is a key parameter in snow mechanics. The proposed apparatus acts as a sampler, to obtain a nearly undisturbed specimen, and as a shear box, similar to those used in the laboratory, with complete control of the test procedure. The main components of the device are a pneumatic system, for the application of normal and shear forces to the specimen, a real-time controller for commanding and recording of the data, and a computer. The apparatus can be carried to the place of the experiments and operated by a team of two researchers. Calibration and preliminary tests are also described in the article.

Adhesion is one of the most important parameters which influences the development of thermal spray coatings. Therefore, the level of adhesion should be known for a given application. Apart from the standardized Tensile Adhesive Test (TAT), more than 80 methods are reported to measure the coating adhesion. Most of them are energy consuming in terms of time, cost and equipment. Moreover, they do not fulfil the necessary requirements of accuracy, confidence and representation of the real delamination process observed in service. To address this problem, the interfacial indentation test is used here to initiate and propagate a crack at the interface between the substrate and the coating. Studying the extension of the crack, an interfacial toughness is defined and deduced analytically from the experimental results. The new shear test, developed in the frame of the EU-CRAFT-project “Shear Test for Thermally Sprayed Coatings”, is also employed to assess the coating adhesion. Both tests are compared to the standardized TAT for various spraying systems, materials, substrate roughness and coating thickness. Advantages and disadvantages of the three tests are discussed. Correlations between the tests results obtained for different coating–substrate combinations are presented and general trends are described.

International audience; The jerky flow in an Al-Mg alloy is studied during simple shear tests for various shear strain rates at room temperature. Direct observations of the sample surface using digital image correlation allow the study of the type and the dynamics of bands associated to plastic instabilities as a function of shear strain and shear strain rate. The paper features that both Piobert-Lüders and Portevin-Le Chatelier phenomena can be observed for a simple shear stress state at room temperature. The nucleation, growth and movement of the bands are described: it is shown that the kinematics of the bands is similar to those oberved in tension but that the orientation of the bands varies with the shear strain.

International audience; By means of 3D contact dynamic simulations, the behavior of a viscoelastic granular material under shear loading is investigated. A viscoelastic fluid phase surrounding the solid particles is simulated by a contact model acting between them. This contact law was implemented in the LMGC90 software, based on the Burgers model. This model is able to simulate also the effect of creep relaxation. To validate the proposed contact model, several direct shear tests were performed, experimentally and numerically using the Leutner device. The numerical samples were created using spheres with two particle size distribution, each one identified for two layers from a road structure. Our results show a reasonable agreement between experimental and numerical data regarding the strain-stress evolution curves and the stress levels measured at failure. The proposed model can be used to simulate the mechanical behavior of multi-layer road structure and to study the influence of traffic on road deformation, cracking and particles pull-out induced by traffic loading.

Section : Particle simulations and particle-based methods.; International audience; Calibration of powder mixing simulation using Discrete-Element-Method is still an issue. Achieving good agreement with experimental results is difficult because time-efficient use of DEM involves strong assumptions. This work presents a methodology to calibrate DEM parameters using Efficient Global Optimization (EGO) algorithm based on Kriging interpolation method. Classical shear test experiments are used as calibration experiments. The calibration is made on two parameters - Young modulus and friction coefficient. The determination of the minimal number of grains that has to be used is a critical step. Simulations of a too small amount of grains would indeed not represent the realistic behavior of powder when using huge amout of grains will be strongly time consuming. The optimization goal is the minimization of the objective function which is the distance between simulated and measured behaviors. The EGO algorithm uses the maximization of the Expected Improvement criterion to find next point that has to be simulated. This stochastic criterion handles with the two interpolations made by the Kriging method : prediction of the objective function and estimation of the error made. It is thus able to quantify the improvement in the minimization that new simulations at specified DEM parameters would lead to

International audience; Particle shape is a major parameter for the space-filling and strength properties of granular materials. For a systematic investigation of shape effect, a numerical benchmark test was set up within a collaborative group using different numerical methods and particles of various shape characteristics such as elongation, angularity and nonconvexity. Extensive 2D shear simulations were performed in this framework and the shear strength and packing fraction were compared for different shapes.We show that the results may be analyzed in terms of a low-order shape parameter h describing the degree of distortion from a perfectly circular shape. In particular, the shear strength is an increasing function of h with nearly the same trend for all shapes, the differences being of second order compared to h. We also observe a nontrivial behavior of packing fraction which, for all our simulated shapes, increases with h from the random close packing fraction for disks, reaches a peak considerably higher than that for disks, and subsequently declines as h is further increased. Finally, the analysis of contact forces for the same value of h leads to very similar statistics regardless of our specific particle shapes.

The paper presents the experience of a working group within the Rilem Technical Committee 223-MSC ‘Masonry Strengthening with Composite materials’, aimed at developing a standardized, reliable procedure for characterizing the bonding mechanism of masonry elements strengthened with composite materials under shear actions. Twelve laboratories from European universities and research centers were involved. Two different set-ups were compared, for single-lap and double-lap shear tests (the latter in two versions). Four kinds of fiber fabrics, i.e., glass, carbon, basalt and steel, were applied with epoxy resins (wet lay-up system) to clay brick units, for a total of 280 monotonic tests. The results provided information regarding the response of externally bonded-to-brick composites in terms of observed failure mechanisms, load capacity, effective transfer length, and bond shear stress-slip behavior. The test results of the twelve laboratories constitute a set of statistically representative data which may conveniently be used for setting appropriate design provisions and guidelines.