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The changes in mechanical properties, hydrothermal degradation and cell adhesion were studied in 3Y-TZP under two different superficial modification patterns (uni- and multidirectional) with a surface roughness ranging from 16 to 603 nm. In this sense, mechanical properties (i.e. hardness, indentation fracture toughness and scratch) and accelerated tests in water steam were measured to evaluate the influence of the surface treatments on the superficially modified layer. Moreover, a detailed characterization through micro-Raman spectroscopy and X-Ray diffraction was performed. Finally, SaOS-2 osteoblasts were used for the evaluation of the cell adhesion behaviour on the surfaces. Overall, ground/polished specimens increased the mechanical properties and ageing resistance of mirror-like polished specimens, although resistance to degradation was maximum at intermediate conditions (Sa ˜ 40-180 nm). The studied surfaces allowed cell attachment, but promoted contact guidance (i.e. cell alignment) only on unidirectionally ground surfaces above Sa = 150 nm.

International audience; Ceria-stabilized zirconia-based composites have been developed aiming to obtain ceramic materials with enhanced hardness, strength, fracture toughness, and resistance to low temperature degradation. These composites are based on ceria-calcia stabilized zirconia (10 mol% CeO2-1 mol% CaO TZP) and α-alumina (0-15 wt%) as a second phase. Raw materials in the form of powders were dispersed through ball milling, dried by slip casting and subsequently grounded before being pressed and conventionally sintered at 1450ºC. Compared to the strength and hardness of 10Ce-TZP ceramics (typically 500 MPa and 6 GPa), an increase was observed for all compositions, especially for 10Ce-1CaO-5Al2O3 (739 MPa and 10.2 GPa). Single Edge V-Notched Beam fracture toughness values ranged from 5.1 to 6.6 MPa⸱√m, indicating a loss of transformability for all compositions. As in 10Ce-1CaO-TZP co-doped ceramics, the aging resistance of all alumina containing composites was also excellent.

Strain localization analysis for orthotropic-associated plasticity in cohesive–frictional materials is addressed in this work. Specifically, the localization condition is derived from Maxwell’s kinematics, the plastic flow rule and the boundedness of stress rates. The analysis is applicable to strong and regularized discontinuity settings. Expanding on previous works, the quadratic orthotropic Hoffman and Tsai–Wu models are investigated and compared to pressure insensitive and sensitive models such as von Mises, Hill and Drucker–Prager. Analytical localization angles are obtained in uniaxial tension and compression under plane stress and plane strain conditions. These are only dependent on the plastic potential adopted, ensuing, a geometrical interpretation in the stress space is offered. The analytical results are then validated by independent numerical simulations. The B-bar finite element is used to deal with the limiting incompressibility in the purely isochoric plastic flow. For a strip under vertical stretching in plane stress and plane strain as well as Prandtl’s problem of indentation by a flat rigid die in plane strain, numerical results are presented for both isotropic and orthotropic plasticity models with or without tilting angle between the material axes and the applied loading. The influence of frictional behavior is studied. In all the investigated cases, the numerical results provide compelling support to the analytical prognosis.

The simulation of structural problems involving the deformations of volumetric bodies is of paramount importance in many areas of engineering. Although the use of tetrahedral elements is extremely appealing, tetrahedral discretisations are generally known as very stiff and are hence often avoided in typical simulation workflows. The development of mixed displacement–pressure approaches has allowed to effectively overcome this problem leading to a class of locking-free elements which can effectively compete with hexahedral discretisations while retaining obvious advantages in the mesh generation step. Despite such advantages the adoption of the technology within commercial codes is not yet pervasive. This can be attributed to two different reasons: the difficulty in making use of standard constitutive libraries and the implied continuity of the pressure, which makes the application of the method questionable in the context of multi-material problems. Current paper proposes the adoption of the volumetric strain instead of the pressure as a nodal value. Such choice leads to the definition of a modified strain making the use of standard strain-driven constitutive laws straightforward. At the same time, the continuity of the volumetric strain across multimaterial interfaces can be understood as a sort of kinematic constraint (stresses can still remain discontinuous across material interfaces). The new element also opens the door to the use of anisotropic constitutive laws, which are typically problematic in the context of mixed elements. This research has been partly supported by the European Commission (EC) through the project ExaQUte (H2020-FETHPC-2016-2017-800898). The authors also acknowledge financial support from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa Programme for Centres of Excellence in R& D” (CEX2018-000797-S). R. Codina acknowledges the support received from the ICREA Acadèmia Research Program, from the Catalan Government .

The present study evaluates the effects of manufacturing parameters on the tensile properties of a commercial composite material based upon polylactic acid (PLA) with wood fibers known as Timberfill. The specimens are built through fused filament fabrication (FFF), and the influence of four printing parameters (layer height, fill density, printing velocity, and orientation) is considered through a L27 Taguchi orthogonal array. Tensile tests are applied to obtain the response variable used as output results to perform the ANOVA calculations. Results show that fill density is the most influential parameter on the tensile strength, followed by building orientation and layer height, whereas the printing velocity shows no significant influence. The optimal set of parameters and levels is found, being 75% fill density, 0¿Z-axis orientation, 0.4 mm layer height, and 40 mm/s velocity as the best combination. Applying this combination, a 9.37-MPa maximum strength is the highest value obtained for the material. Additionally, five solid injection molded Timberfill specimens were tested as well and the results compared with the FFF samples. The values of the elastic modulus, elastic limit, and maximum strength of the injected samples were almost twofold of those were obtained for the FFF samples, but the maximum elongation of the injected specimens fell sharply.

The article presents the results of a series of compression tests on samples manufactured by means of the mask image projection based on stereolithography additive manufacturing technique (MIP-SL). Recent studies demonstrate the orthotropic nature of the MIP-SL materials. A research is initiated by the authors to attempt to predict the degree of anisotropy from the manufacturing parameters of the MIP-SL parts. The article focuses mainly on the development of the experimental compression tests of the first stage of the research. Special attention is paid to the four methods used to obtain the stress-strain curve of the material: strain gages, 2D Digital Image Correlation, extensometer measurements and crosshead displacement measurements. The article shows the advantages and limitations of each method. Finally, the anisotropic behaviour is verified and a testing procedure is set to obtain the constitutive parameters of the MIP-SL tested materials

The repetitive corrugation and straightening process is a severe plastic deformation technique that is particularly suited to process metallic sheets. With this technique, it is possible to develop nano/ultrafine-grained structured materials, and therefore, to improve some mechanical properties such as the yield strength, ultimate tensile strength, and fatigue lifetime. In this study, an Al-6061 alloy was subjected to the repetitive corrugation and straightening process. A new corrugation die design was proposed in order to promote a heterogeneous deformation into the metallic sheet. The evolution of the mechanical properties and microstructure obtained by electron backscatter diffraction of the alloy showed a heterogeneous distribution in the grain size at the initial cycles of the repetitive corrugation and straightening process. Uniaxial tensile tests showed a significant increase in yield strength as the number of repetitive corrugation and straightening passes increased. The distribution of the plastic deformation was correlated with the hardness distribution on the surface. The hardness distribution map matched well with the heterogeneous distribution of the plastic deformation obtained by finite element simulation. A maximum average hardness (147 HV) and yield strength (385 MPa) was obtained for two repetitive corrugation and straightening cycles sample.

In this study, solid state joining technology of friction stir welding (FSW) was carried out for Al and Mg butt joints. To improve the microstructural characteristics of the banded structure zone, before to the FSW process, a Zn interlayer was also inserted in the butt joints. Optimal conditions for friction stir welding were obtained using a combination of two travel speeds (25 and 35¿mm/min) and three rotation speeds (550, 600 and 650¿rpm). Mg-Zn and Mg-Al-Zn IMCs, Al solid solution and residual Zn were the most common phases in the stirred zone, eliminating Al-Mg intermetallic formation. The joint fabricated at 35¿mm/min and 600¿rpm, in which tensile strength of the weld improved from 141 to 175¿MPa and an elongation from 0.7 to 1.9 was achieved, gave the maximum mechanical properties compared with the Zn free sample FSWed under identical conditions. The fracture micrographs were compatible with the corresponding ductility results and the fracture surfaces of Zn added samples possessed a fine texture combining brittle and ductile fracture features. Meanwhile, the hardness level was lower than that of the Zn free sample because of the change in the IMCs composition of the Zn added samples.

PLA bio-blends with a predominantly biosourced PA10.10 in the composition range 10-50wt.% were prepared by melt blending in order to overcome the advanced brittleness of PLA. Due to the inherent immiscibility of the blends, 30 wt.% of PA was needed to achieve a brittle-to-ductile transition and a co-continuous morphology was predicted at 58 wt.% of PA. The initial enhancement of the PLA rheological behaviour through the environmentally friendly reactive extrusion process yielded a finer and more homogeneous microstructure and hence enhanced the mechanical properties of the bio-blends at much lower PA contents. The brittle-to-ductile transition could be achieved with only 10 wt.% and co-continuity was observed already at 44 wt.% of PA. Results indicate the significant potential of modifying PLA flow behaviour as a promising green manufacturing method toward expanding PLA-based bio-blends applications.

Zr 1−x Mo x thin films were synthesized on glass substrates by co-sputtering molybdenum and zirconium targets in the presence of argon with x in the 0.32–0.95 range. From X-ray diffraction analyses and transmission electron microscopy images it was possible to observe an evolution of the samples structure from a nano-crystalline solid solution of Zr in the bcc lattice of Mo to clusters of Zr(Mo) nano-crystalline in an amorphous matrix. The coherence length deduced from X-ray diffractograms was around 1 nm–8 nm depending on the composition. Mechanical measurements show that the films exhibited high hardness H , low Young's modulus E and therefore high H ∕ E ratio compared with the bulk of Zr and Mo. We also found a low friction coefficient values for all the samples. Finally, an inverse Hall-Petch effect was observed for coherence length lower than 6 nm.

Purpose The aim of this paper is to analyze the mechanical properties of acrylonitrile-butadiene-styrene (ABS) parts manufactured through fused filament fabrication and compare these results to analogous ones obtained on polylactic acid (PLA) and PLA–wood specimens to contribute for a wider understanding of the different materials used for additive manufacturing. Design/methodology/approach With that aim, an experimental based on an L27 Taguchi array was used to combine the specific parameters taken into account in the study, namely, layer height, nozzle diameter, infill density, orientation and printing velocity. All samples were subjected to a four-point bending test performed according to the ASTM D6272 standard. Findings Young’s modulus, elastic limit, maximum stress and maximum deformation of every sample were computed and subjected to an analysis of variance. Results prove that layer height and nozzle diameter are the most significant factors that affect the mechanical resistance in pieces generated through additive manufacturing and subjected to bending loads, regardless of the material. Practical implications The best results were obtained by combining a layer height of 0.1 mm and a nozzle diameter of 0.6 mm. The comparison of materials evidenced that PLA and its composite version reinforced with wood particles present more rigidity than ABS, whereas the latter can experience further deflection before break. Originality/value This study is of interest for manufacturers that want to decide which is the best material to be applied for their application, as it derives in a practical technical recommendation of the best parameters that should be selected to treat the material during the fused filament fabrication process.

Made available in DSpace on 2019-10-06T15:50:52Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-08-30 Centro Nacional de Pesquisa em Energia e Materiais Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Laboratório Nacional de Nanotecnologia Petrobras In this work, the influence of hydrogen on the microstructure and fracture toughness of API 5L X80 high strength pipeline steel welded by friction stir welding was assessed. Samples were hydrogenated at room temperature for a duration of 10 h in a solution of 0.1 M H2SO4 + 10 mg L−1 As2O3, with an intensity current of 20 mA cm−2. Fracture toughness tests were performed at 0 °C in single-edged notched bending samples, using the Critical Crack Tip Opening Displacement (CTOD) parameter. Notches were positioned in different regions within the joint, such as the stir zone, hard zone, and base material. Hydrogen induces internal stress between bainite packets and ferrite plates within bainite packets. Besides, hydrogen acted as a reducer of the strain capacity of the three zones. The base metal had a moderate capacity to resist stable crack growth, displaying a ductile fracture mechanism. While the hard zone showed a brittle behavior with CTOD values below the acceptance limits for pipeline design (0.1–0.2 mm). The fracture toughness of the stir zone is higher than that of the base metal. Nevertheless, the stir zone displayed higher data dispersion due to its high inhomogeneity. Hence, it can also show a brittle behavior with critical CTOD values. State University of Ponta Grossa UEPG Brazilian Nanotechnology National Laboratory LNNano Brazilian Center for Research in Energy and Materials Center for Engineering Modeling and Applied Social Sciences (CECS) Universidade Federal do ABC (UFABC) State University of Campinas UNICAMP Metallurgical and Materials Engineering University of São Paulo USP Petrobras CENPES UNESP – São Paulo State University UNESP – São Paulo State University

An AA6082 alloy deformed by equal channel angular pressing (ECAP) was studied. Microstructural evolution of the alloy processed by ECAP with different passes were evaluated by using optical microscope, scanning electron microscopy coupled with an electron backscattered diffraction (EBSD) detector and X-ray diffraction. Texture analysis showed the apparition of two types of textures, one associated with shearing deformation and the second due to the recrystallization phenomena. Mechanical strength properties measured by tensile tests increased in the first ECAP pass, and then progressively diminished due to the presence of concurrent softening phenomena. Calorimetric analysis indicated a slightly increase in the recrystallization temperature of the deformed specimens. Also, the stored energy increased with increasing ECAP passes due to the production of new dislocations. The average geometrically necessary dislocation density, measured by EBSD, increased with increasing ECAP passes. However, the rate of increase slows down with the progress of ECAP passes. Fil: Khelfa, T.. Northwestern Polytechnical University; China. University of Sfax; Túnez Fil: Muñoz Bolaños, Jairo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina. Universidad Politécnica de Catalunya; España Fil: Li, F.. Northwestern Polytechnical University; China Fil: Cabrera -Marrero, J. M.. Universidad Politécnica de Catalunya; España Fil: Khitouni, M.. University of Sfax; Túnez

cited By 22; Although the atomic structure of amorphous alloys, which lacks long-range translational symmetry, may appear homogeneous at the macroscopic scale, their local dynamic and/or static properties however vary significantly according to the recent experimental and simulation results. In the literature of amorphous alloys, the nature of such local heterogeneities is currently an issue under debate. More importantly, since amorphous alloys are in a thermodynamically nonequilibrium state, their local structures constantly evolve during structural relaxation, physical aging and mechanical deformation. As such, local structural heterogeneities, which vary with the thermal and mechanical history of amorphous alloys, could provide a key to understand the structural origin of their mechanical behavior, such as anelasticity, viscoelasticity, plasticity and fracture. In this review article, we first review mechanical spectroscopy or dynamic mechanical analyses as an important tool to study the relaxation dynamics in amorphous alloys, with a focus on the possible correlation between the secondary (also called β)relaxation and the local structural heterogeneities of amorphous alloys. After that, we discuss the recent advances on the understanding of structural heterogeneities in metallic supercooled liquids and the influence of the structural heterogeneities on the overall mechanical properties of the corresponding amorphous alloys. Finally, we briefly discuss the further development of research on this subject. © 2019 Elsevier Ltd

The plastics industry is increasingly oriented towards the use of bio-based polymers replacing the fossil-based ones. Bio-based polyamides (PAs) in the film packaging application are not still used and need enhancement to overcome some drawbacks. In this scenario, fully (PA10.10) and partially (PA6.10) bio-based PAs were extruded in a laboratory sheet-casting machine. The materials used to obtain films were previously melt blended with modified clay in a twin-screw extruder. The resulting films were morphologically investigated through the scanning electron microscope. The magnifications show agglomerated particles and the packed layers are preferentially aligned in the extrusion machine direction. X-rays confirm that 5 wt% of clay content is difficult to exfoliate in such matrices. The crystallinity was studied by using X-ray diffraction (XRD) and differential scanning calorimetry. The XRD results show coexisting a and ¿ phases in the PA6.10 while the presence of only ¿ in the PA10.10. The presence of clay platelets constrains the crystallites formation, especially in the more polar PA6.10, resulting in changes in the type and the amount of crystals. The mechanical analysis data showed that 5 wt% of clay induced significant improvement in Young's modulus (+68 and + 14%), a slight increase in the tensile yield stress (+21 and + 5%) and only a surprisingly small decrease in the deformation at break (-15 and -24%) for PA10.10 and PA6.10, respectively. Furthermore, the addition of clay gave the best oxygen barrier properties reaching a value of 1.8 ± 0.2 cm3 × mm/m2 × day × atm comparable to a commercial PA6 film used in the packaging field.

[EN] The current study investigates the influence of carbon addition on the microstructural and micromechanical properties of Ti(C,N)-FeNi cermets with different ceramic/metal phase ratios. Evaluation of small-scale hardness is conducted by using high speed nanoindentation in conjunction with statistical analysis. It allows to gather extremely large data sets (40,000 imprints per grade and condition); and thus, detailed hardness mapping at the microstructure length scale. Subsequent statistical analysis was done by considering three mechanically distinct phases: Ti(C,N) particles, the metallic binder, and one exhibiting the composite behaviour (i.e. imprints probing two-phase regions). In general, it is found that porosity amount is reduced as ceramic/metal phase ratio decreases and carbon is added. Carbon addition is also observed to rise small-scale hardness, but only for two of the defined phases: metallic binder and the composite one. Similar trends are observed regarding the influence of ceramic/metal phase ratio and carbon addition on the inverse hardness-fracture toughness correlation measured under high applied loads., This investigation was supported by the Spanish Ministerios deEconomía y Competitividad MINECO through grant MAT2015-70780-C4-P. J.J. Roa acknowledges the Serra Hunter programme of the Generalitat de Catalunya.

In this work, the mechanical behavior of the coated ADI system is studied. For this purpose, single layer Ti and bilayer Ti/TiN and TiAl/TiAlN coatings, with different thicknesses, were deposited by the PVD technique of cathodic arc deposition on high strength ADI substrates using industrial and experimental devices. The characterization of the coatings includes the measurement of the layer thicknesses by the spherical abrasion method, the determination of existing phases and residual stresses by x-ray diffraction and the evaluation of the surface topography using a stylus profilometer. The analysis of the mechanical properties of the coatings comprises the measurement of the surface hardness by micro indentation tests and the evaluation of the scratch resistance. The scratch tests were performed on a scratch tester equipped with a Rockwell indenter. A progressive load from 1 to 100 N, a load rate of 99 N/min, a speed of 5 mm/min and a scratch length of 5 mm were employed. The influence of the coatings characteristics on the scratch resistance of the coated samples and the friction coefficients obtained are evaluated. The results show that Ti coated samples had tensile residual stresses, the lowest surface hardness and the lowest critical loads for scratch adhesion strength. The samples coated with Ti/TiN and TiAl/TiAlN had highly compressive residual stresses and the highest critical loads, while the hardness was higher for TiAl/TiAlN. On the other hand, the evolution of the friction coefficient was similar for all the coated samples. Fil: Colombo, Diego Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Márquez, Adriana Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física del Plasma. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física del Plasma; Argentina Fil: Marro, Fernando García. Universitat Politécnica de Catalunya; España Fil: Llanes, Luis Miguel. Universitat Politécnica de Catalunya; España Fil: Sosa, Amadeo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina

The aim of this work is to evaluate the feasibility of small punch test as a tool for analysing the mechanical response of small plastic parts or specimens. Here, the small punch test was used to study the possible influence of ultraviolet radiation exposure on the mechanical properties of outdoor furniture made from recycled polyethylene terephthalate in the frame of an industrial project with participants from both industry and academia. The industrial project partners prepared four types of masterbatches in order to stabilize the recycled polyethylene terephthalate and to minimize photodegradation as well as colour change in the final product. The masterbatches contained red pigments, antioxidants and ultraviolet absorbers. Flat sample plates were injection moulded from recycled polyethylene terephthalate and these masterbatches. Some sample plates were used as-moulded, some samples received a thermal treatment in order to post-crystallize the bottle-grade recycled polyethylene terephthalate and some other samples were subjected to ultraviolet radiation for 900 h. In the frame of an industrial project, the ultraviolet ageing was performed superficially only on one side of the plates in order to evaluate the colour change. The three sets of samples were analysed by means of tensile tests, differential scanning calorimetry and intrinsic viscosity. However, the irradiated samples could not be tested with tensile tests due to their small size. Therefore, the small punch test was used to accurately characterize these small samples. The feasibility of the small punch test as a valid mechanical characterization method for these types of materials was demonstrated by comparing the small punch test results from the unradiated samples with the tensile test ones. The mechanical parameters obtained from both types of tests showed the same results. Although the used industrial ultraviolet ageing process produced a colour change in the studied recycled polyethylene terephthalate samples, it was possible to verify via small punch tests that the mechanical properties were not affected.

Micromechanical properties of a polycrystalline cubic boron nitride (PcBN) composite have been assessed by statistical analysis of data gathered from experimental massive nanoindentation. The mechanical study was complemented with electron probe X-Ray microanalysis, aiming to correlate relative B/N ratio and local hardness for individual cBN particles. Best-fit of experimental and deconvoluted data is achieved by considering five mechanically different phases, defined on the basis of chemical nature, TiN/cBN interface presence, ratio between residual imprint dimension and microstructural length scale as well as phase stoichiometry. In-depth local micromechanical and chemical analysis permitted to propose and validate, for the first time, the existence of a correlation between intrinsic hardness and phase stoichiometry for cBN phase. Finally, based on experimental data measured by nanoindentation and analyzed in terms of plastic index, toughness for the PcBN composite studied is estimated to range between 4 and 6¿MPa·vm.

Already for fifteen years many researchers have been trying to discover metallic materials with unusual combinations of strength and ductility: with high strength and enhanced ductility . This combination may be achieved through different ways: alloying, nanostructuring, etc. This report is an attempt to analyze the influence of inhomogeneity of different types (structural, phase and space) on mechanical properties of commercially pure ti tanium (bulk and powder) subjected to high- pressure torsion. Experimental results for HPT bulk and powder titanium have demonstrated that mechanical behavior of CP titanium strongly depends on phase inhomogeneity (alpha + omega phases), structural inhomoge neity (bimodal grain size distribution) and space inhomogeneity (retained porosity) in case of cold consolidated Ti powder. High strength in HPT bulk titanium due to the formation of hard omega phase during HPT processing at room temperature was detected. The strong omega phase transforms back to nanograined alpha phase domains during short annealing at elevated temperature. HPT consolidation of titanium powder leads to the formation of brittle specimens showing high strength but almost zero plasticity

The aim of this work is to test the mechanical properties of dental zirconia surfaces patterned with Nd:YAG laser interference (¿¿=¿532¿nm and 10¿ns pulse). The laser treatment produces an alteration of the topography, engraving a periodic striped pattern. Laser-material interaction results mainly in thermal effects producing microcracking, phase transformation and texturization. The role of such microstructural modifications and collateral damage on the integrity and mechanical performances has been assessed. Laser patterned discs of zirconia doped with 3% mol yttria (3Y-TZP) have been tested before and after a thermal treatment to anneal residual stresses and revert phase transformation. Both groups of samples behave in a similar manner, excluding residual stresses and phase transformation from the origin of properties modification. Result show that laser patterning induces a minor decrease in mechanical properties and surface integrity of 3Y-TZP surfaces. The biaxial strength decreases as a consequence of the damage induced by laser patterning. Fractographic observations identify preexisting defects enlarged by local laser interaction as the fracture origins. The Hardness and Young modulus of treated surfaces tested with nanoindentation also decrease slightly after laser treatment and this may be attributed to laser-induced microcracking.

A series of low density, highly porous clay/poly(vinyl alcohol) composite aerogels, incorporating ammonium alginate, were fabricated via a convenient and eco-friendly freeze drying method. It is significant to understand rheological properties of precursor gels because they directly affect the form of aerogels and their processing behaviors. The introduction of ammonium alginate impacted the rheological properties of colloidal gels and improved the mechanical performance of the subject aerogels. The specific compositions and processing conditions applied to those colloidal gel systems brought about different aerogel morphologies, which in turn translated into the observed mechanical properties. The bridge between gel rheologies and aerogel structures are established in the present work.

Low density composites of sodium montmorillonite and poly(amide-imide) polymers have been created using an ice templating method, which serves as an alternative to the often-difficult foaming of high temperature/high performance polymers. The starting polymer was received in the poly(amic acid) form which can be cured using heat, into a water insoluble amide-imide copolymer. The resulting materials have densities in the 0.05 g/cm3 range and have excellent mechanical properties. Using a tertiary amine as a processing aid provides for lower viscosity and allows more concentrated polymer solutions to be used. The concentration of the amine relative to the acid groups on the polymer backbone has been found to cause significant difference in the mechanical properties of the dried materials. The synthesis and characterization of low density versions of two poly(amide-imide) polymers and their composites with sodium montmorillonite clay are discussed in the present work.

ARMCO iron processed by ECAP up to a maximum equivalent strain of sixteen ECAP passes following route Bc was investigated by Electron Back Scattering Diffraction (EBSD), Transmission Electron Microscopy (TEM), TEM-EBSD and X-ray Diffraction Line Profile Analysis (XRDLPA). Different values of grain size were obtained with each technique. The lower values were obtained by XRDLPA whereas, the higher values were achieved by TEM-EBSD. Dislocation densities were also calculated by different techniques obtaining values of statistically stored and geometrically necessary dislocations as a function of the deformation. All differences in values allowed a better understanding of the nature of microstructures of the materials processed by severe plastic deformation (SPD). Mechanical properties showed a considerable increment in the material strength due to the progressive reduction of the grain size because of the Continuous Dynamic Recrystallization (CDRX) mechanism and the increment in the dislocation density.

Ground tire rubber from car and truck was modified using microwave irradiation at variable time. The irradiated ground tire rubber was used as filler in composites based on natural rubber. The composites, with high content of ground tire rubber, were prepared using an internal batch mixer and subsequently cross-linked at 160℃. The influence of the ground tire rubber source (car/truck) and irradiation time on structure, physico-mechanical behaviour, thermal properties and morphology of natural rubber/ground tire rubber composites was studied. The interfacial interactions between ground tire rubber and natural rubber as function of ground tire rubber source and irradiation time were evaluated by Fourier transform infrared spectroscopy, thermogravimetric analysis, tensile tests, swelling measurements and scanning electron microscopy. The results showed that irradiation of ground tire rubber slightly enhanced tensile properties and cross-link density of natural rubber/ground tire rubber composites. This effect was more evident in the case of ground tire rubbertruck because of its higher content of natural rubber and was reflected in changes in the interfacial adhesion, which were confirmed by the results of Fourier transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy analysis.

This article is focused on the characterization of the lack of homogeneity in the dispersive acoustic properties of polymeric materials used in industrial pipes. Usually, the parameter of interest associated to dispersion is the variation in the propagation velocity as a function of the frequency or the temperature. Nevertheless, this paper, studies the variation in the propagation velocity, as a function of the intensity of the acoustic signal. In these cases, pipes made of PVC, PP and PVDF, which are commonly used in industrial installations, have been characterized. For each type of pipe, high and low acoustic intensity signals have been applied in order to reproduce working conditions that typically appear in the pipe wall below the transducers in commercial Clamp-on ultrasonic flowmeters (UFMs). Under these conditions, acoustic velocity maps have been created for the three materials under test. These maps reveal two effects that are not usually taken into account. The first one is the variation of the propagation velocity with the power density of the ultrasonic signal and the second one is the nonhomogeneous behaviour along the pipe surface. Finally, the acoustic maps reflect how a stronger acoustic signal produces greater behaviour differences in the materials under test. The characterized phenomenon of lack of homogeneity in dispersive acoustic properties, produces a variation in the zero flow error in Clamp-on UFM caused, so as not to fulfil the reciprocity criterion.

In order to understand the mechanical behaviour of Al2O3 inverse opals, nanoindentation techniques have been implemented in material layers with three different microstructures, in terms of hollow or polystyrene spheres, with Al2O3 shells of distinct wall thickness. Different indenter tip geometries as well as contact loading conditions have been used, in order to induce different stress field and fracture events to the layers. Field emission scanning electron microscopy and focused ion beam have been employed to understand accommodation of plastic deformation induced during the indentation process. Results show that materials with polystyrene spheres exhibit higher hardness and modulus under sharp indentation, and cracking resistance under spherical indentation. Furthermore, deformation is discerned to be mainly governed by the rotation of the microspheres. In the case of the inverse opals made of hollow spheres, the main deformation mechanisms activated under indentation are the rearrangement and densification of them

When indenting a brittle material with a sharp indenter, cracks can be generated at the corners of the imprint. From the length of these cracks, the fracture resistance can be estimated. This technique is simple and allows characterizing small volumes of materials, especially if nanoindentation cube-corners tips are used. For evaluation of fracture resistance, a number of different models based on crack morphology have been proposed. However, the morphology of the cracks is difficult to determine due to the small scales involved. In this work, indentation fracture with a cube-corner nanoindentation tip on different materials is investigated by FIB tomography to obtain the generated crack morphology. Experimental observations are rationalized in terms of applied load, tip geometry and crystal anisotropy. Once the crack morphology is visualized, the two most commonly used equations for calculating the fracture resistance are discussed. Finally, guidelines for better estimation of fracture resistance are proposed. (C) 2015 Elsevier Ltd. All rights reserved.

This paper presents a study of the mechanical properties and an evaluation of damage mechanisms of nanocolumnar TiO-SiO multilayer coatings prepared by physical vapour oblique angle deposition at different configurations (slanted, zigzag or chiral) and two zenithal evaporation angles (70°or 85°). The characterization at micro- and nanometric length scales of the mechanical properties of the multilayers has been carried out by nanoindentation and nanoscratch tests, while the morphological evaluation of the surface and sub-surface damages produced with a sharp indenter and the adhesive and/or cohesive failures between coating and substrate have been investigated by field emission scanning electron microscopy and focused ion beam, respectively. The obtained results have shown that the main processing parameters controlling the mechanical response of the different multilayers is the zenithal angle of deposition and the number of layers in the multilayer stack, while the coating architecture had only a minor effect on the mechanical response. This analysis also revealed a higher resistance to scratch testing and a brittle failure behaviour for the low zenithal angle coatings as compared with the high angle ones., Furthermore, we would like to thank the support received from Direcció General de Recerca del Comissionat per a Universitats i Recerca de la Generalitat de Catalunya through recognition of CIEFMA as Grup de Recerca Consolidad (2014-SGR-130) and the MINECO (projects MAT2014-60720-R, MAT2013-40852-R and RECUPERA 2020, this latter co-funded with structural funds of the EU). J J R would like to thank the Juan de la Cierva Programme for its financial support (grant number: JCI-2012–14454). MINECO/ICTI2013-2016/MAT2013-40852-R

Mask Image Projection based on Stereolithography (MIP-SL) is an Additive Manufacturing (AM) system which it is based on a Frontal Photopolymerization Process (FPP) to manufacture parts made of photocurable materials. In this paper, a FPP numerical model is used to analyse the printability of different reinforced photocurable materials for MIP-SL manufacturing process. Consequently, optimal printing parameters could be defined to increase the material photoconversion ratio. Two different reinforcements are used to analyse the influence of fillers on FPP material coefficients. The results show the use of reinforcement could significantly enhance the mechanical properties obtained by means of experimental compression tests

A Fe–20.1Mn–1.23Si–1.72Al–0.5C TWIP steel with ultrafine grain structure was successfully processed through equal channel angular pressing (ECAP) at warm temperature up to four passes following the B C route. The microstructure evolution was characterized by electron backscattered diffraction to obtain the grain maps, which revealed an obvious reduction in grain size, as well as a decrease in the twin fraction, with increasing number of ECAP passes. The texture evolution during ECAP was analyzed by orientation distribution function. The results show that the annealed material presents brass (B) as dominant component. After ECAP, the one pass sample presents A 1* and A 2* as the strongest components, while the two passes and four passes samples change gradually toward $$ B/\bar{B} $$ components. TEM analysis shows that all samples present twins. The twin thickness is reduced with increasing the number of ECAP passes. Nano-twins, as a result of secondary twinning, are also observed in the one and two passes samples. In the four passes sample, the microstructure is extensively refined by the joint action of ultrafine subgrains, grains and twins. The mechanical behavior was studied by tensile samples, and it was found that the yield strength and the ultimate tensile strength are significantly enhanced at increasing number of ECAP passes. Although the ductility and strain hardening capability are reduced with ECAP process, the present TWIP steel shows significant uniform deformation periods with positive work hardening rates.