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Novel analytical solutions with closed-form expressions for the stress and displacement fields of short fiber reinforced composites (SFRCs) and analytical prediction of their effective thermo-elastic properties are presented. The cylindrical SFRC unit-cells with periodic boundary conditions are subjected to axial and transverse stresses as well as thermally induced residual stresses. By comparison with available numerical and analytical solutions, it is revealed that the present closed-form solutions provide accurate stress field variations as well as accurate predictions for the effective thermo-elastic properties of SFRCs in a split second, and thus, the developed model is much more computationally efficient than numerical methods.

When a fiber break occurs in longitudinal tension of a unidirectional composite, dynamic stress concentrations arise, which can be different from the ones found considering only static loading. The current paper analyzes the dynamic stress concentration factors (SCF) around a fiber break in unidirectional carbon fiber/epoxy composites. 3D finite element models with random and hexagonal fiber distributions were analyzed to investigate the evolution of stress concentrations as a function of time and position. The results indicate that dynamic effects result in much higher SCFs with a larger effective area around the broken fiber. The increase of SCFs in the closest fibers was determined to be larger for lower fiber volume fractions due to the presence of dynamic effects. Similar to the static case, a lower volume fraction causes higher maximum dynamic SCF in random packings. Results also support the high prevalence of coplanar cluster breaks observed in the experiments.

Thermoplastic elastomers benefit from high elasticity and straightforward (re)processability; they are widely used across a multitude of sectors. Currently, the majority derive from oil, do not degrade or undergo chemical recycling. Here a new series of ABA triblock polyesters are synthesized and show high-performances as degradable thermoplastic elastomers; their composition is poly(cyclohexene-alt-phthalate)-b-poly(ε-decalactone)-b-poly(cyclohexene-alt-phthalate) {PE–PDL–PE}. The synthesis is accomplished using a zinc(ii)/magnesium(ii) catalyst, in a one-pot procedure where ε-decalactone ring-opening polymerization yielding dihydroxyl telechelic poly(ε-decalatone) (PDL, soft-block) occurs first and, then, addition of phthalic anhydride/cyclohexene oxide ring-opening copolymerization delivers semi-aromatic polyester (PE, hard-block) end-blocks. The block compositions are straightforward to control, from the initial monomer stoichiometry, and conversions are high (85–98%). Two series of polyesters are prepared: (1) TBPE-1 to TBPE-5 feature an equivalent hard-block volume fraction (fhard = 0.4) and variable molar masses 40–100 kg mol−1; (2) TBPE-5 to TBPE-9 feature equivalent molar masses (∼100 kg mol−1) and variable hard-block volume fractions (0.12 < fhard < 0.4). Polymers are characterized using spectroscopies, size-exclusion chromatography (SEC), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). They are amorphous, with two glass transition temperatures (∼−51 °C for PDL; +138 °C for PE), and block phase separation is confirmed using small angle X-ray scattering (SAXS). Tensile mechanical performances reveal thermoplastic elastomers (fhard < 0.4 and N > 1300) with linear stress–strain relationships, high ultimate tensile strengths (σb = 1–5 MPa), very high elongations at break (εb = 1000–1900%) and excellent elastic recoveries (98%). There is a wide operating temperature range (−51 to +138 °C), an operable processing temperature range (+100 to +200 °C) and excellent thermal stability (Td,5% ∼ 300 °C). The polymers are stable in aqueous environments, at room temperature, but are hydrolyzed upon gentle heating (60 °C) and treatment with an organic acid (para-toluene sulfonic acid) or a common lipase (Novozyme® 51032). The new block polyesters show significant potential as sustainable thermoplastic elastomers with better properties than well-known styrenic block copolymers or polylactide-derived elastomers. The straightforward synthesis allows for other commercially available and/or bio-derived lactones, epoxides and anhydrides to be developed in the future., A new series of block polyester thermoplastic elastomers are prepared by a one-pot procedure; they show properties competitive or better than conventional materials and can be fully degraded after use.

The stability and strength of soil aggregates to external forces such as raindrop impact and tillage may be affected by biochar application. In line with this, a three-year field experiment was conducted to investigate the effect of rice straw biochar (0, 15, and 30 t ha(-1)) on the Atterberg limits (plastic limit, PL and liquid limit, LL), water-dispersible clay content (WDC), and the aggregate characteristics of an Acrisol. Aggregate characteristics were measured on four size classes (1-2, 2-4, 4-8, and 8-16 mm). The 30 t ha(-1) treatment significantly (p

Many tubular tissues such as blood vessels and trachea can suffer long-segmental defects through trauma and disease. With current limitations in the use of autologous grafts, the need for a synthetic substitute is of continuous interest as possible alternatives. Fabrication of these tubular organs is commonly done with techniques such as electrospinning and melt electrowriting using a rotational collector. Current additive manufacturing (AM) systems do not commonly implement the use of a rotational axis, which limits their application for the fabrication of tubular scaffolds. In this study, a four axis extrusion-based AM system similar to fused deposition modeling (FDM) has been developed to create tubular hollow scaffolds. A rectangular and a diamond pore design were further investigated for mechanical characterization, as a standard and a biomimicry pore geometry respectively. We demonstrated that in the radial compression mode the diamond pore design had a higher Young's modulus (19,8 ± 0,7 MPa compared to 2,8 ± 0,5 MPa), while in the longitudinal tensile mode the rectangular pore design had a higher Young's modulus (5,8 ± 0,2 MPa compared to 0,1 ± 0,01 MPa). Three-point bending analyses revealed that the diamond pore design is more resistant to luminal collapse compared to the rectangular design. This data showed that by changing the scaffold pore design, a wide range of mechanical properties could be obtained. Furthermore, a full control over scaffold design and geometry can be achieved with the developed 4-axis extrusion-based system, which has not been reported with other techniques. This flexibility allow the manufacturing of scaffolds for diverse tubular tissue regeneration applications by designing suitable deposition patterns to match their mechanical pre-requisites.

Advances in artificial intelligence (AI) techniques that can be used for different purposes have enabled it to be used in many different industrial applications. These are mainly used for modeling, identification, optimization, prediction and control of complex systems under the influence of more than one parameter in industrial applications. With the increasing accuracy of AI techniques, it has also obtained a wide application area on friction stir welding (FSW), one of the production methods developed in recent years. In this study, commonly used AI techniques for FSW, results, accuracy and superiority of AI techniques are reviewed and evaluated. In addition, an overview of AI techniques for FSW in different material combinations is provided. Considering the articles examined; It is seen that welding speed, rotational speed, the plunge depth, spindle torque, shoulder design, base material, pin design/profile, tool type are used as input parameters and tensile strength, yield strength, elongation, hardness, wear rate, welding quality, residual stress, fatigue strength are used as output parameters. As can be seen from the studies, it made important contributions in deciding what input parameters should be in order to have the output parameter at the desired value. The most common used materials for FSW are Al, Ti, Mg, Brass, Cu and so on. When FSW studies using artificial intelligence techniques were examined, it was seen that 81% of the most used materials were AL alloys and 23% of them were made with dissimilar materials. The most commonly utilized AI techniques were said to be artificial neural networks (ANN), fuzzy logic, machine learning, meta-heuristic methods and hybrid systems. As a result of the examination, ANN was the most widely used method among these methods. However, in recent years, with the exploration of new hybrid methods it was seen that hybrid systems used with ANN have higher accuracy.

The influence of discrete and randomly distributed polyester (PET) fibers in improving the crack resistance and water-tightness of clay barriers was studied by conducting a series of centrifuge model tests at 40 gravities using a large beam centrifuge available at Indian Institute of Technology Bombay. Model clay barriers with and without fibers were subjected to flexural distress by inducing differential settlements using a settlement simulator. Two types of clay barriers were prepared by using two different types of soil, namely bentonite amended silty soil (Soil A) and kaolin clay-sand mixture (Soil B). Digital image cross-correlation (DIC) technique was used for analyzing the images captured by a digital photo camera and a charged couple device (CCD) camera, mounted along with the model. Unreinforced soil barriers (URSB) were found to lose their water-tightness and integrity at relatively lower distortion levels compared to identical fiber reinforced soil barriers (FRSB). Also, the performance of URSB and FRSB was found to be superior for Soil A compared to Soil B. The capability of PET fibers on preservation of existing unreinforced soil barriers was also demonstrated. The strain at crack initiation, epsilon(c), for FRSB is 2.90 and 2.36 times higher than identical URSB for Soil A and Soil B, respectively. Similarly, the strain at the onset of water breakthrough, epsilon(b), for FRSB is 2.14 and 2.79 times higher than identical URSB for Soil A and Soil B, respectively. There is a significant influence of fiber inclusion in retarding the crack initiation and water breakthrough at the onset of flexural distress for both the soil types. Thus, FRSB can withstand more distortion and strain while maintaining the integrity of the clay barrier. This observed behaviour of restraining cracks and improved performance of FRSB is primarily due to the reinforcement effect achieved due to soil-fiber interactions. (C) 2016 Elsevier B.V. All rights reserved.

A new method is proposed in order to estimate the shear strength of schistosity planes in slate in terms of Mohr-Coulomb cohesion and internal friction angle. The procedure consists in carrying out the Brazilian method under different loading-foliation angles, for which experimental tests were achieved in slates from the northwest of the Iberian Peninsula (Spain). The experimental fracture patterns were analytically studied and justified by simulating the stress field in the discontinuity planes contained in the whole sample, taking into account the first failure registered in the tests. By combining experimental and analytical studies and a procedure based on the representation of the threshold state of stressesin the elastic regimein the failure plane, it is possible to estimate the foliation's strength envelope through a lineal adjustment according to the Mohr-Coulomb criterion and, thus, to characterize the layering. Finally, the proposed procedure was validated by the direct shear test. The cohesion and the internal friction angle obtained with this convenctional test were very close to that calculated by the proposed method, verifying the methodology developed by the authors. This procedure may be interesting in various engineering applications, either in the study of the properties of cleavage in slate, which is commonly used as an industrial rock, or in dam foundations, underground excavations and slope engineering, since one of the main failures in civil engineering is due to sliding along weak planes. The authors of this paper would like to acknowledge the financial support of the PhD fellowship Severo Ochoa Program of the Government of the Principality of Asturias (PA-14-PF-BP14-067). Also, the authors are grateful to editors and reviewers for their suggestions and help us to improve this manuscript.

Triaxial experiments and direct fluid injection experiments have been conducted at confining pressures up to 100 MPa on Mancos shale, Whitby mudstone, Penrhyn slate and Pennant sandstone. Experiments were conducted with sample axes lying both parallel and perpendicular to layering in the materials. During triaxial failure Penrhyn slate was stronger for samples with cleavage parallel to maximum principal stress, but the two orientations in the shales displayed similar failure stresses. Initial flaw sizes of around 40 μm were calculated from the triaxial data using the wing‐crack model, with the shales having shorter initial flaws than the non‐shales. During direct fluid injection, breakdown was rapid, with no discernible gap between fracture initiation and breakdown. Breakdown pressure increased linearly with confining pressure, but was less sensitive to confining pressure than expected from existing models. A fracture mechanics based model is proposed to determine the initial flaw size responsible for breakdown in injection experiments. Flaw sizes determined in this way agree reasonably with those determined from the triaxial data in the non‐shales at low confining pressures. As confining pressure rises, a threshold is reached, above which the fluid injection experiments suggest a lower initial flaw length of around 10 μm. This threshold is interpreted as being due to the partial closure of flaws. In the shales an initial flaw length of around 10 μm was determined at all confining pressures, agreeing reasonably with those determined through the triaxial experiments.

Hybrid composites combining brittle and ductile reinforcing fibres can be designed to have pseudo-ductile behaviour by controlling their failure mechanisms. The recently developed carbon-fibre/self-reinforced polypropylene (SRPP) hybrids have demonstrated a unique combination of stiffness (7 GPa), toughness (>6% strain) and density (±1000 kg/m³). Here, the influence of a circular notch on their failure mechanisms is investigated. Discontinuous carbon-fibre/polypropylene composites retained 69% of the gross strength and 83% of the net strength. The strength retention of SRPP was highly influenced by the processing parameters, and a notch-insensitive composite could be produced. Pseudo-ductility was obtained even with the notched hybrids. Hybrids that do not achieve the optimal ductility, still exhibit high gross and net strength retentions and can be classified as notch-insensitive. These results illustrate the significant potential of this new hybrid composite for applications with notches or holes.

Significance Small incision lenticule extraction (SMILE) is advanced as the most minimally invasive and least traumatic corneal procedure for correcting refractive errors using a single laser. Although SMILE obtains similar results to femtosecond laser in situ keratomileusis (LASIK) with spherical myopia, it has deficiencies in astigmatism correction. Purpose The purpose of this study was to compare refractive outcomes and high-order aberrations (HOAs) between SMILE and femtosecond LASIK corneal procedures at 1 year post-operative. Methods Ninety-two patients (181 eyes) with myopia/myopic astigmatism underwent either SMILE (group 1) or femtosecond LASIK (group 2). The refractive target was to achieve emmetropia in all cases. Data were analyzed to determine significance of change in refraction and HOAs. Furthermore, astigmatism was subjected to vector analysis using the Thibos (calculation of change, Δ, in J0 and J45 values) and Alpins (calculation of difference, ΔC, between target-induced astigmatism [TIA] and surgically induced astigmatism) methods. Results Forty-five patients (89 eyes) from group 1 and 47 patients (92 eyes) from group 2 completed the study. The main significant (P ≤ .001) findings were as follows: (a) residual astigmatism was greater in group 1; (b) group 1, ΔJ0 = 1.015J0 + 0.040 (R = 0.861), ΔJ45 = 1.082J45 + 0.019 (R = 0.792), ΔC = 0.401TIA + 0.323 (R = 0.489), and mean spherical aberration increased from -0.003 (SD, ±0.059; 95% confidence interval [CI], -0.015 to 0.009) to 0.028 μm (SD, ±0.041; 95% CI, -0.037 to -0.020); and (c) group 2, ΔJ0 = 0.952J0 - 0.005 (R = 0.921), ΔJ45 = 0.962J45 - 0.002 (R = 0.923), ΔC = 0.187TIA + 0.101 (R = 0.272), mean coma reduced from 0.114 (SD, ±0.087; 95% CI, 0.096 to 0.132) to 0.077 μm (SD, ±0.059; 95% CI, 0.065 to 0.089), and trefoil from 0.089 (SD, ±0.049; 95% CI, 0.079 to 0.0990) to 0.056 μm (SD, ±0.047; 95% CI, 0.046 to 0.066). Conclusions In comparison with SMILE, femtosecond LASIK offered better precision in the overall control of astigmatism and HOAs.

Al–Cu alaşımı temel alaşımlar içinde tanımlanması nedeniyle endüstride oldukça fazla kullanım alanı bulmasına rağmen elde edilen alaşımın kontrolsüz döküm hali her zaman istenilen özellik ve performansa sahip değildir. İstenilen özellik ve performansta üretim için katılaştırma koşulları değiştirilir ve bu değişime bağlı olarak elde edilen sonuçların değerlendirilmesi yapılır. Katılaştırma koşullarından katılaştırma hızının etkisi ile mikroyapı özelliklerinin değişimi; malzemelerin mekanik, elektriksel ve ısısal özelliklerini de etkilediği bilinmektedir. Bu nedenle mikroyapı değerlendirmesinin en doğru şekilde yapılabileceği ötektik Al–%33ağ. Cu bileşeninin faz diyagramı yardımıyla belirlenmesinden sonra Bridgman tipi fırın vasıtasıyla sabit sıcaklık gradyenti (G = 8.50 K/mm) ve beş farklı katılaştırma hızında (V = 8.25?164.80 µm/s) kontrollü doğrusal katılaştırma deneyleri yapılmıştır. Böylece katılaştırma hızının mikroyapı üzerine etkisi ve mikroyapıdaki değişimin etkisiyle mekanik özelliklerden mikrosertlik, çekme– dayanım ve elektriksel özdirenç değerlerinin değişimi araştırılmıştır. Mikroyapı, katılaştırma hızı, mikrosertlik, çekme– dayanım ve elektriksel özdirenç değerleri arasındaki ilişkileri ortaya koyabilmek için lineer regrasyon analizi ve Hall– Petch tipi bağıntılar kullanılmıştır. Ayrıca elde edilen sonuçlar benzer deneysel sonuçlarla kıyaslanmıştır., Although it has a lot of usage area in the industry because the Al-Cu alloy is defined among the base alloys, the uncontrolled solidified casting of this alloy does not always have the desired properties and performance. For the production of Al-Cu alloys with superior properties, the solidification parameters known as the solidification rate, temperature gradient and composition ratio are changed and the results of this change are evaluated. It is known that changing the properties of the microstructure by growth rate affects the mechanical, electrical and thermal properties of the materials. For this reason, Al–%33 wt. Cu eutectic composition to carrying out correctly microstructure evaluation was prepared, then controlled solidification experiments were carried out by a Bridgman type furnace at a constant temperature gradient (G = 8.50 K/mm) and at five different growth ratios (V = 8.25?164.80 µm/s). Thus, the effect of the growth rate on the microstructure was investigated and values of microhardness, tensile strength and electrical resistivity were investigated with the effect of change in the microstructure. Both linear regression analysis and Hall-Petch type correlations were used to determine the relationship between microstructure, microhardness, tensile strength and electrical resistivity values. The results obtained in this work were compared with the previous similar experimental results.

Study of rocks under high temperature and strain-rate condition can serve as vital information in the restoration process of fire damaged buildings. In this study, the mechanical response of thermally treated fine-grained Dholpur sandstone was observed under increasing strain rates. Dholpur sandstone, a popular construction material, has been used to build some of the iconic monuments in India, a list which includes the Parliament, House of Indian President and the Buddhist Stupas of Sanchi. Thermal treatment spanned across ten days which included heating of the samples (200, 400, 600, 800 and 1000 degrees C) for five days followed by cooling, in room condition, for the exact same duration. The samples were then tested to failure at three different strain rates (2 x 10(-5), 1 x 10(-4) and 2 x 10(-4)S(-1)). The elastic modulus was measured using non-contact laser extensometer. Acoustic emission (AE) technique was used to observe the microcrack development under compressive loading. The results from AE were used to demarcate the various stress thresholds and the stress regimes. The result of the experimental analysis suggests that the strength and elastic properties of rocks tend to increase till 400-600 degrees C followed by a fall in the mechanical characteristics. Onset of plasticity can be observed at high temperature. Strength of the rocks decrease at high strain rates due to the influence of strain rate dependency. The threshold values follow the behaviour of the mechanical properties under the influence of temperature and strain rate. (C) 2018 Elsevier Ltd. All rights reserved.

Efficiency of fiber reinforcements to ensure the sealing efficiency of the landfill cap soil barriers so as to isolate the waste from the environment was demonstrated in the present study. Evaluation of hydraulic conductivity of soil barrier materials with different types of fibers, fiber dosage and fiber lengths are very important to ensure the sealing efficiency of the fiber reinforced soil barriers. An attempt was made to evaluate the hydraulic conductivity of the soil barrier material at a known effective stress using a flexible wall permeameter. Soil samples of 100 mm diameter and 100 mm height were prepared and tested in the present study. In all the cases, the hydraulic conductivity test phase was started after the completion of initialisation, saturation and isotropic consolidation phases of the soil samples. In the present study, seventeen (17) hydraulic conductivity tests were conducted on two different soil types for studying the influence of fiber content, fiber length and fiber type on the hydraulic conductivity of fiber reinforced soil. The fiber content, f used were 0.25%, 0.50% and 0.75% and the fiber lengths, l were 30 mm, 60 mm and 90 mm. Two types of fibers namely polyester (PET) fibers and polypropylene tape (PP-T) fibers were used for hydraulic conductivity tests. The repeatability of test results was also demonstrated. As the fiber content and fiber length were increased, initially there was a marginal decrease in hydraulic conductivity of the soil and thereafter marginally increased. Short fibers and low fiber contents were found to have greater influence in reducing the hydraulic conductivity of the soil and the variation was found to depend on the soil type also. Even with long fibers, the hydraulic conductivity of selected barrier material remained within the permissible limit required for a barrier material. The hydraulic conductivity of PP-T fiber reinforced soil is more, compared to hydraulic conductivity of PET fiber reinforced soil at all the fiber contents varied in the present study. The use of Scanning Electron Microscopy (SEM) is also attempted for the interpretation of the results.

The paper presents experimental observations of the anisotropic effect of dry and saturated lineated schistose rock on deformational behaviour and fracture patterns under indirect tensile loading conditions. Dry mylonitic quartz-mica schist (M-QMS) shows strength minima in between lineation orientation of 20 degrees-30 degrees with loading direction, whereas dry crenulated quartz-mica schist (C-QMS) shows strength minima in between 45 degrees and 60 degrees. Water saturation significantly reduces the failure strength and shifts the strength minima towards a higher angle. In addition, the water saturation effect induces plasticity along the lineation direction. P-wave velocity is found to be maximum along lineation direction, which continuously decreases to a minimum value across the lineation. Three types of fracture patterns, namely layer activation, central and non-central, are observed for both the rock types. For both the rock types, tensional fractures occur when the lineation is inclined at 0 degrees and 90 degrees to the loading direction, whereas shear and mixed-mode fractures occur at all other orientations. Fracture through the layer activation is prominent in saturated specimens compared to the dry specimens for beta angle range of 15 degrees-60 degrees and 15 degrees-45 degrees in the case of M-QMS and C-QMS, respectively.

Studies conducted by several researchers suggest that a large variance exists in the morphological integrity of rocks when subjected to thermal treatment. The extent of thermal damage, D(T), can be quantified by analyzing the change in either the elastic modulus, ultrasonic wave velocities or the acoustic emission signals. However, these require the use of sophisticated laboratory equipment, which may not be readily available. Additionally, the shape and size of the sample has to adhere to the specifications that have been mandated for the corresponding experiments. This would further introduce delay in the process of assessing the damage. Therefore, in this study, new predictive models have been developed, which can predict the extent of damage (D(T)) from the physical properties of thermally-modified fine-grained Dholpur sandstone. The sandstone is a primary construction material, and has been widely used in several Indian monuments of historic and political importance. The models have been developed using statistical and soft-computing tools such as multivariate regression analysis (MVRA), artificial neural network (ANN) and adaptive neuro-fuzzy inference system (ANFIS). The physical properties viz. temperature (T), density (D), porosity (P), thermal expansion coefficients (E-L and E-v) and ultrasonic wave velocities (V-P and V-S), serve as predictor variables. The efficacy of the models has been tested by calculating the performance indices, namely, coefficient of determination (R2), mean absolute percentage error (MAPE), root mean square error (RMSE) and variance account for (VAF). The results suggest that the ANFIS model has the best prediction capacity.

The inherent brittleness of conventional high-performance composites can be addressed by the use of discontinuous fibres or hybridisation of fibre-types. In this paper, we propose the first models in the literature to predict the stress-strain curve of hybrid discontinuous composites, with either a brick-and-mortar or an intermingled-fibre microstructure. The models consider a shear-lag stress-transfer between the hybrid reinforcement units, and show that this stress transfer becomes less efficient with hybridisation. The model for intermingled-fibre hybrids also considers stochastic fibre strengths and fibre fragmentation, and can therefore predict a brittle or pseudo-ductile response of hybrid discontinuous composites as observed experimentally, as well as hybrid effects. These models can be used to perform virtual testing and microstructural design of hybrid aligned discontinuous composites.

Electroless plating is used as an alternative approach to alloying the commercially pure titanium powders. Two types of irregularly shaped powders, which differ in particle size distribution, are coated with nickel-phosphorus (Ni-P) and nickel-boron (Ni-B). A novel method, combining aspects of the Kawakita and Alderbom approaches, has been employed in order to understand compaction behaviour. The overall consolidation is described by a Kawakita-Ludde relationship, and the transition pressures which demarcate the limits of rearrangement only and plastic deformation only are identified using a modification of the Alderborn relationship. A significant increase in green strength is achieved with the Ni-B coated powders, and this is attributed to a modification of friction conditions and the number of possible contacts, which lead to an increased contribution from plastic deformation. The Mohr-Coulomb model and Ohyane equations are used to describe the contribution of the number of contacts on green strength. (C) 2015 Elsevier B.V. All rights reserved.

This work reports the production process of bi-layered ceramics tiles, formed from two layers with different densities - dense and porous - and with adjustable thickness. The novel production method comprises a double pressing action, fast and easy to implement industrially, that ensures the development of a perfect interface bonding between layers. The bi-layered ceramic tile is formed by an upper layer with density similar to a conventional porcelain stoneware tile, and a porous bottom layer, which promotes weight reduction of the product maintaining suitable mechanical strength. The introduction of porosity is achieved by means of the incorporation of pore forming agent - polypropylene (PP) - into the ceramic formulation, which undergoes complete and non-harmful thermal decomposition during firing. For comparison, polymethyl methacrylate (PMMA) was also tested as porogen. The rapid and complete combustion of PP is suitable for fast-firing ceramic products, such as porcelain stoneware. In addition, the polymer decomposition does not induce defects in the ceramic pieces, and is environmentally acceptable. The produced tiles are lighter than conventional porcelain stoneware tiles, thus decreasing their transport and distribution costs. Additionally, the thermal attenuation provided by the porous layer could be valuable in innovative applications, such as ventilated facades. (C) 2014 Elsevier B.V. All rights reserved.

Unidirectional composites under longitudinal tension develop damage through the accumulation and clustering of fibre–breaks, which may lead to catastrophic failure of an entire structure. This paper uses a hierarchical scaling law to predict the kinetics of fibre–breakage and its effect on the stress–strain response of composites under longitudinal tension; due to its analytical formulation based on the statistical analysis of hierarchical fibre–bundles, the scaling law predicts the response of composite bundles up to virtually any size in less than one second. Model predictions for the accumulation and clustering of fibre–breaks are successfully validated against experiments from the literature. These results show that the present model is a much more computationally–efficient alternative to other state–of–the–art models based on Monte–Carlo simulations, without sacrificing the accuracy of predictions when compared against experiments.

本論文は、紙管の製造における技術の継承に関する研究と、紙管の主材料である板紙の特性と紙管の物性との関係、および紙管の破壊の研究が、主たる内容である。目的としては、どのような物性を持つ板紙が、紙管の強度に寄与できるかという事を探ることで、最適な紙管用の原紙を作成することと、紙管のどの部分にどのような物性を持った板紙を使用することで強度アップにつながるかを研究することである。

A key aspect of the longitudinal tensile failure of composites is the stress redistribution that occurs around broken fibres. Work on this topic has focussed mainly on the stress field surrounding a single broken fibre; however, this is an important limitation as unstable failure in carbon fibre bundles occurs when a cluster of about 16 or more broken fibres is formed. Therefore, we have developed a detailed Finite Element (FE) model to investigate how stress redistribution varies with the number of broken fibres in a cluster. The results show that both the recovery length and stress concentration factor increase significantly with increasing number of broken fibres in a cluster. We have also developed an analytical model, suitable to be included in existing or new fibre bundle models, that captures how the recovery length and stress concentration factor vary with the broken cluster size, and validated its predictions against our FE simulations. Finally, we extended our FE model to predict the survival probability of fibre bundles using Monte Carlo simulations, and found that these predictions were in good agreement with experimental and analytical results on microcomposites.

Aligned-discontinuous-fibre reinforced polymers have the potential to combine (i) the high specific stiffness and strength and light weight of conventional continuous-fibre composites with (ii) increased damage tolerance, improved manufacturability, and the ability to close the life-cycle loop of composites by using recycled fibres. However, predicting the mechanical response of discontinuous composites is a challenge for which no universally accepted and computationally-efficient solution exists yet. This paper presents a model for aligned discontinuous-fibre reinforced composites considering (i) a generic constitutive law for the matrix, (ii) stochastic fibre failure under non-uniform stress fields due to the presence of fibre-ends, and (iii) unstable final failure from a critical cluster of damage. Results show good agreement with experiments from the literature, and the model also stresses the importance of considering the stochastic nature of both the fibre-end locations and the fibre-strengths to model aligned discontinuous composites. Parametric studies suggest that failure of aligned discontinuous composites depends on (i) the overlap length between fibres for short-fibre composites, and (ii) the fibre strength for long-fibre composites; intermediate-length fibres would result in discontinuous composites with maximum stiffness, strength, and failure strain simultaneously.

Fracture toughness (FT) and tensile strength (TS) indicate a rock's susceptibility to fracturing. Past studies showed that mechanical properties and FT of homogeneous rocks can be correlated well. In the present study, this capability has been extended to the jointed sedimentary rocks. Sandstone with a wide combination of analogue joints were tested in the laboratory, and the control of joint geometrical properties on the FT, TS, and development of fracture process zone (FPZ) were investigated. A FT prediction model was developed based on the TS of the jointed specimens. Multifractal scaling law (MFSL) was utilized to extend the laboratory results to the field scale. Further, the interaction of propagating crack with the already existing joints were investigated and post-peak behavior were studied. Results show that FT and TS decrease with decreasing joint spacing, but they are more sensitive at higher joint spacing. It is also possible to construct a linear prediction model between the FT and TS of rock. FPZ of jointed rock is less sensitive to joint orientation and more related to joint spacing. A negative correlation between the FPZ size and joint spacing is established in this study. Post-peak behavior of the jointed specimens indicate that crack-joint interaction increases the frictional resistance and dissipated fracture energy of the specimens. Further, comparison of mixed-mode fracture criteria with the experimental results show that Maximum Tangential Stress (MTS) criterion can successfully predict the mixed-mode fracture behavior of jointed sandstone.

Teeth are generally used for actions in which they experience mainly compressive forces acting toward the base. The ordered tooth enamel(oid) and dentin structures contribute to the high compressive strength but also to the minor shear and tensile strengths. Some vertebrates, however, use their teeth for scraping, with teeth experiencing forces directed mostly normal to their long axis. Some scraping suckermouth catfishes (Loricariidae) even appear to have flexible teeth, which have not been found in any other vertebrate taxon. Considering the mineralized nature of tooth tissues, the notion of flexible teeth seems paradoxical. We studied teeth of five species, testing and measuring tooth flexibility, and investigating tooth (micro) structure using transmission electron microscopy, staining, computed tomography scanning, and scanning electron microscopy-energy-dispersive spectrometry. We quantified the extreme bending capacity of single teeth (up to 180 degrees) and show that reorganizations of the tooth (micro) structure and extreme hypomineralization of the dentin are adaptations preventing breaking by allowing flexibility. Tooth shape and internal structure appear to be optimized for bending in one direction, which is expected to occur frequently when feeding (scraping) under natural conditions. Not all loricariid catfishes possess flexible teeth, with the trait potentially having evolved more than once. Flexible teeth surely rank among the most extreme evolutionary novelties in known mineralized biological materials and might yield a better understanding of the processes of dentin formation and (hypo) mineralization in vertebrates, including humans.

The role of notches in the fracture strength of metal foams has been studied using a multiscale model based on a two-dimensional Voronoi representation of the cellular architecture. The effect of the crack length to the specimen width ratio on the net section strength of double edge notch (DEN) specimens and central crack panels (CCP) has been investigated in two ways: (i) by fixing the number of cells in the width and (ii) by fixing the number of cells in the ligament. Notch strengthening has been observed in DEN specimens in excellent agreement with experiments. Analysis of the strain fields suggests that in the DEN configuration, the constraint imposed on the rotation fields in the notch tip zones of the ligament enhances the net section strength. In CCP specimens, stress concentration and free-edge effects produced a small level of notch weakening. Our results show that both the ligament length as well as the notch length (normalized by the cell size) influence the notch behaviour in two-dimensional metal foams. (C) 2011 Published by Elsevier Ltd. on behalf of Acta Materialia Inc.

Submitted by Guilherme Lemeszenski (guilherme@nead.unesp.br) on 2014-02-26T17:02:28Z No. of bitstreams: 1 WOS000256794400005.pdf: 76769 bytes, checksum: 065d9aa05242f821fff1386ee64a5657 (MD5) Made available in DSpace on 2014-02-26T17:02:28Z (GMT). No. of bitstreams: 1 WOS000256794400005.pdf: 76769 bytes, checksum: 065d9aa05242f821fff1386ee64a5657 (MD5) Previous issue date: 2007-07-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T15:19:31Z No. of bitstreams: 1 WOS000256794400005.pdf: 76769 bytes, checksum: 065d9aa05242f821fff1386ee64a5657 (MD5) Made available in DSpace on 2014-05-20T15:19:31Z (GMT). No. of bitstreams: 1 WOS000256794400005.pdf: 76769 bytes, checksum: 065d9aa05242f821fff1386ee64a5657 (MD5) Previous issue date: 2007-07-01 Purpose: To evaluate the bond strength between human dentin and composites, using two light-activated single-bottle total-etch adhesive systems with different pHs combined with chemically activated and light-activated-composites. The tested hypothesis was that the dentin bond strength is not influenced by an adhesive system of low pH, combined with chemically activated or light-activated composites. Material and Method: Flat dentin surfaces of twenty-eight human third molars were allocated in 4 groups (n=7), depending on the adhesive system: (One Step Plus-OS and Prime & Bond NT-PB) and composite (light-activated Filtek Z-100 [Z100] and chemically activated Bisfil 2B [B2B]). Each adhesive system was applied on acid-etched dentin and then one of the composites was added to form a 5 mm-high resin block. The specimens were stored in tap water (37 degrees C/24 h) and sectioned into two axes, x and y. This was done with a diamond disk under coolant irrigation to obtain beams with a cross-section area of approximately 0.8 mm(2). Each specimen was then attached to a custom-made device and submitted to the microtensile test (1 mm.min(-1)). Data were analyzed using two-way ANOVA and Tukey's tests (p

The notch strengthening effect is studied experimentally in closed cell aluminum foams. The limit loads, net section strength were found for a set of double-edge-notched (DEN) and single-edge-notched (SEN) specimens loaded in compression. In addition, the evolution of the deformation is monitored through a digital image correlation procedure. The influence of independently varying the net section width, b. and the crack length to width ratio, a/W is examined. The DEN specimens showed notch-strengthening behavior, while the SEN specimens were found to be notch-insensitive. From the plastic deformation measurements the dominant deformation mode for the SEN specimens was found to be a crushing/twinning mode. The constraint imposed on this twinning mode by the DEN geometry leads to the observed notch-strengthening behavior. A phenomenological model is developed to ratiorialize the observed strength enhancement for the DEN-specimens, featuring a dependence on the ligament width to cell size ratio, b/d. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The mechanical properties of tablets compacted from blends are generally not directly predictable from the mechanical properties of the individual components. This paper introduces a structure-dependent fit, which gives a prediction of two major mechanical properties (elastic modulus and tensile strength) of compacts consisting of two particulate components. The structure-dependent fit takes into account the properties of the individual materials, macroscopic changes in the compact structure, and, if necessary, an interfacial interaction between particles of both components. Firstly, the relationship between the solid volume fraction and mechanical properties of compacts of single materials was fitted by the percolation theory. From these fits, the mechanical properties at zero porosity and the volume fraction of particles coupled in parallel were obtained. The material characteristics were applied into the structure-dependent fit to predict the maximal values (the upper boundary) and minimal values (the lower boundary) of the mechanical property of compacts made from the blends. It has been shown that the elastic modulus of the blends can be predicted by the upper boundary of the structure-dependent fit. The calculated tensile strengths result into a relative estimation of the adhesive interfacial interaction between particles of both components. In the end, all steps of the structure-dependent fit are included into a block diagram for the prediction of mechanical properties of compacts consisting of a blend. (C) 2004 Elsevier B.V. All rights reserved.

An experimental investigation into size effects in notched [45/90/-45/0](4s) carbon/epoxy laminates is carried out. The in-plane dimensions of the quasi-isotropic laminates are scaled up by a factor of up to 8. Larger Scale 16 specimens with only their width and notch length being doubled were also tested as a further comparison. Interrupted tests and X-ray Computed Tomography (CT) scanning are carried out to study the damage at the crack tips. Sharp centre-notched tensile tests are compared to open-hole tests of the same notch length (hole diameter), material and stacking sequence. A similar strength reduction scaling trend is found for both configurations at the small sizes, except with higher tensile strength for the centre-notched specimens than the open-hole specimens. However, there is a cross-over point when the sizes increase, with the sharp notched results approaching an asymptote based on Linear Elastic Fracture Mechanics (LEFM), and the open hole results approaching an asymptote based on Weibull theory.

The void fractions of loosely packed and tapped beds of particles of continuous size distributions are correlated by means of a proposed new semi-empirical relation. In this relation four parameters describing the following particle properties are included: (i) mean particle size, (ii) spread of the particle size distribution, (iii) particle density and (iv) particle shape. The adjustable constants in the relation were optimised using experimental void fractions and particle characteristics for a wide variety of powders mainly gathered from the published literature. The optimised relation correlated the loosely packed and tapped bed void fractions with correlation coefficients of 0.955 and 0.973, respectively, the correlation thus removing virtually all the scatter in the original data. A discussion is provided.

The content of water-dispersible colloids (WDC) in a soil can have a major impact on soil functions, such as permeability to water and air, and on soil strength, which can impair soil fertility and workability. In addition, the content of WDC in the soil may increase the risk of nutrient loss and of colloid-facilitated transport of strongly sorbing compounds. In the present study, soils from the Bad Lauchstädt long-term static fertilizer experiment with different management histories were investigated to relate basic soil properties to the content of WDC, the content of water-stable aggregates (WSA), and aggregate tensile strength. Our studies were carried out on soils on identical parent material under controlled management conditions, enabling us to study the long-term effects on soil physical properties with few explanatory variables in play. The content of WDC and the amount of WSA were measured at a series of time steps giving a colloid release and aggregate disaggregation rate and a quantification of the content of WDC and WSA at a given time for each of the six investigated experimental field plots. The content of WDC in the moist soil was linearly correlated (r = 0.82* [P < 0.05]) to the part of the total clay not associated with organic matter. No significant difference in release rate was found for air-dry aggregates. The low-carbon soils initially had a higher content of WSA but were more susceptible to disaggregation than the high-carbon soils. Furthermore, the application of NPK fertilizer had a destabilizing effect on the WSA and also caused a decrease in the cation exchange capacity of the soils. The mean tensile strength was positively correlated to the colloid release rate and the content of WDC after 2 min of shaking and therefore to the amount of clay not associated with organic carbon. The content of water-dispersible colloids (WDC) in a soil can have a major impact on soil functions, such as permeability to water and air, and on soil strength, which can impair soil fertility and workability. In addition, the content of WDC in the soil may increase the risk of nutrient loss and of colloid-facilitated transport of strongly sorbing compounds. In the present study, soils from the Bad Lauchsta¨dt longterm static fertilizer experiment with different management histories were investigated to relate basic soil properties to the content of WDC, the content of water-stable aggregates (WSA), and aggregate tensile strength. Our studies were carried out on soils on identical parent material under controlled management conditions, enabling us to study the long-term effects on soil physical properties with few explanatory variables in play. The content of WDC and the amount of WSA were measured at a series of time steps giving a colloid release and aggregate disaggregation rate and a quantification of the content of WDCand WSA at a given time for each of the six investigated experimental field plots. The content of WDC in the moist soil was linearly correlated (r = 0.82* [P G 0.05]) to the part of the total clay not associated with organic matter. No significant difference in release rate was found for air-dry aggregates. The low-carbon soils initially had a higher content of WSA but were more susceptible to disaggregation than the high-carbon soils. Furthermore, the application of NPK fertilizer had a destabilizing effect on the WSA and also caused a decrease in the cation exchange capacity of the soils. The mean tensile strength was positively correlated to the colloid release rate and the content of WDC after 2 min of shaking and therefore to the amount of clay not associated with organic carbon.

Soil organic carbon (OC) influences clay dispersibility, which affects soil tilth conditions and the risk of vertical migration of clay colloids. No universal lower threshold of OC has been identified for satisfactory stabilization of soil structure. We tested the concept of clay saturation with OC as a predictor of clay dispersibility and soil friability. Soil was sampled 3 yr in a field varying in clay content (∼100 to ∼220 g kg−1 soil) and grown with different crop rotations. Clay dispersibility was measured after end-over-end shaking of field-moist soil and 1- to 2-mm sized aggregates either air-dried or rewetted to −100 hPa matric potential. Tensile strength of 1- to 2-, 2- to 4-, 4- to 8-, and 8- to 16-mm air-dried aggregates was calculated from their compressive strength, and soil friability estimated from the strength–volume relation. Crop rotation characteristics gave only minor effects on clay dispersibility and no detectable effects on soil friability. Dispersed clay correlated to soil content of clay, but the correlation increased if subtracting a fraction assumed protected by OC. This trend was less convincing for soil tensile strength and friability. Increased clay dispersibility and reduced soil friability for 1 yr of measurements could be ascribed to wet conditions for potato (Solanum tuberosum L.) harvest and tillage the preceding year. Literature data indicate soils’ content of clay and silt (Fines20) to be a better predictor of specific surface area than clay. We conclude that a clay/OC ratio of 10 and a Fines20/OC ratio of 20 may serve as corresponding thresholds for clay dispersibility, the latter probably best reflecting organo-mineral interactions of importance to the soil physical properties. Soil organic carbon (OC) influences clay dispersibility, which affects soil tilth conditions and the risk of vertical migration of clay colloids. No universal lower threshold of OC has been identified for satisfactory stabilization of soil structure. We tested the concept of clay saturation with OC as a predictor of clay dispersibility and soil friability. Soil was sampled 3 yr in a field varying in clay content (∼100 to ∼220 g kg−1 soil) and grown with different crop rotations. Clay dispersibility was measured after end-over-end shaking of field-moist soil and 1- to 2-mm sized aggregates either air-dried or rewetted to −100 hPa matric potential. Tensile strength of 1- to 2-, 2- to 4-, 4- to 8-, and 8- to 16-mm air-dried aggregates was calculated from their compressive strength, and soil friability estimated from the strength–volume relation. Crop rotation characteristics gave only minor effects on clay dispersibility and no detectable effects on soil friability. Dispersed clay correlated to soil content of clay, but the correlation increased if subtracting a fraction assumed protected by OC. This trend was less convincing for soil tensile strength and friability. Increased clay dispersibility and reduced soil friability for 1 yr of measurements could be ascribed to wet conditions for potato (Solanum tuberosum L.) harvest and tillage the preceding year. Literature data indicate soils’ content of clay and silt (Fines20) to be a better predictor of specific surface area than clay. We conclude that a clay/OC ratio of 10 and a Fines20/OC ratio of 20 may serve as corresponding thresholds for clay dispersibility, the latter probably best reflecting organo-mineral interactions of importance to the soil physical properties.

Detachment is one of the major processes determining the physical structure and microbial functionalities of biofilms. To predict detachment, it is necessary to take the mechanical properties of the biofilm and the effect of both hydrodynamic and growth conditions into account. In this work, experiments were conducted with biofilms developed under various shear stresses and with various substrate natures. In addition, two cases were considered in order to differentiate between the effect of hydrodynamic factors and growth factors: the biofilms were directly grown under the targeted shear stress (tau) condition or they were precultivated under very low shear stress (0.01 Pa) and then exposed to high shear stress in the range of 0.1-13 Pa. An exponential and asymptotic decrease of the biofilm thickness and mass with increasing tau was observed in both cases. On contrary density, expressed as the biofilm dry mass on a known substratum divided by the average thickness increased with tau. Denitrifying biofilms always showed greater thickness and density than oxic biofilms. These results showed the presence of a compact basal layer that resisted shear stresses as high as 13 Pa whatever the culture conditions. Above this basal layer, the cohesion was lower and depended on the shear stress applied during biofilm development. The application of shear stress to the biofilms resulted in both detachment and compression, but detachment prevailed for the upper part of the biofilms and compression prevailed for the basal layers. A model of biofilm structure underlying the stratified character of this aggregate is given in terms of density and cohesion. (C) 2012 Elsevier Ltd. All rights reserved.