Size dependence of concrete fracture energy determined by RILEM work-of-fracture method

The paper analyzes the size dependence of the fracture energy of concrete obtained according to the existing RILEM recommendation proposed by Hillerborg and based on the work-of-fracture method of Nakayama, Tattersal and Tappin, in which the energy dissipated at the fracture front is evaluated from the measured load-displacement curve. The analysis is based on the size effect law proposed by Baant, which has been shown to be applicable to the size ranges up to about 1:20 and apply in the same form for all specimen geometries. The analysis utilizes the previously developed method for calculating the R-curve from the size effect, and the load-deflection curve from the R-curve. The R-curve is dependent on the geometry of the specimen. The results show that the fracture energy according to the existing RILEM recommendation is not size-independent, as desired, but depends strongly on the specimen size. This dependence is even stronger than that of the R-curve. When the specimen size is extrapolated to infinity, the fracture energy according to the RILEM recommendation coincides with the fracture energy obtained by the size effect method. It is also found that, in fracture specimens of usual sizes, the pre-peak contribution of the work of the load to the fracture energy is relatively small. Finally, as a by-product, the analysis also verifies the fact that, in three-point bend fracture specimens, the fracture energy according to the RILEM definition is dependent on the notch depth.     

On the choice of creep function for standard recommendations on practical analysis of structures

In the proposed revision of the C.E.B. International Recommendations, the unit creep curves for various ages t′ at loading are approximated in the form f(t-t')+g(t)-g(t') where t = time. Using optimization techniques to find functions f and g which give optimum fits of experimental data, it is shown that, by contrast with the present form, the proposed from of the C.E.B. creep function cannot reasonably approximate experimental creep curves over the full range of t′ of interest. In addition, the simplification of creep structural analysis intended by this formulation of creep function can be achieved, even to a greater extent, by another recent method. Therefore, the creep function of form ?(t')F(t-t'), which is presently used by C.E.B., should be retained, although improvement in the definition of functions ? and F is in order.     

Formation and Distribution of Rubbery Phase in High Impact Poly(propylene) Particles

This paper reconstructs the principle of rubber incorporation in high impact poly(propylene) (hiPP) particles. The detailed information about the pores and rubber distribution inside and on the surface of hiPP particles is obtained by micro‐computed tomography and atomic force microscopy. The strong effect of homopolymer origin on hiPP particle morphology and rubber distribution is demonstrated. To obtain the most homogeneous rubber distribution, the low homopolymer porosity is required. The initial particle porosity has a negligible effect on the thickness of the rubber layer on the particle surface at the medium rubber content. The rubber forms not only along the iPP primary particles and directly or close to the pores but also on or close to the particle surface rather than it flows there. The evidence for these claims is based on the systematic investigation in dependence on EPR content, homopolymer particle porosity (prepared by different catalysts) and antistatic agent deactivating catalyst close to particle surface.

     

Efficient Synthesis of a Maghemite/Gold Hybrid Nanoparticle System as a Magnetic Carrier for the Transport of Platinum-Based Metallotherapeutics

The preparation and thorough characterization of a hybrid magnetic carrier system for the possible transport of activated platinum-based anticancer drugs, as demonstrated for cisplatin (cis-[Pt(NH₃)₂Cl₂], CDDP), are described. The final functionalized mag/Au–LA–CDDP* system consists of maghemite/gold nanoparticles (mag/Au) coated by lipoic acid (HLA; LA stands for deprotonated form of lipoic acid) and functionalized by activated cisplatin in the form of cis-[Pt(NH₃)₂(H₂O)₂]²⁺ (CDDP*). The relevant techniques (XPS, EDS, ICP-MS) proved the incorporation of the platinum-containing species on the surface of the studied hybrid system. HRTEM, TEM and SEM images showed the nanoparticles as spherical with an average size of 12 nm, while their superparamagnetic feature was proven by ⁵⁷Fe Mössbauer spectroscopy. In the case of mag/Au, mag/Au–HLA and mag/Au–LA–CDDP*, weaker magnetic interactions among the Fe³⁺ centers of maghemite, as compared to maghemite nanoparticles (mag), were detected, which can be associated with the non-covalent coating of the maghemite surface by gold. The pH and time-dependent stability of the mag/Au–LA–CDDP* system in different media, represented by acetate (pH 5.0), phosphate (pH 7.0) and carbonate (pH 9.0) buffers and connected with the release of the platinum-containing species, showed the ability of CDDP* to be released from the functionalized nanosystem.     

Silver Nanoparticles in Blends of Polyethylene and a Superabsorbent Polymer: Morphology and Silver Ion Release

Antimicrobial properties of polymer materials are required in many applications. The polyethylene/superabsorbent polymer (PE/SAP) blends containing silver nanoparticles were successfully prepared via thermal reduction during melt mixing. It was found that in situ formed silver nanoparticles are preferentially located at the interface between PE matrix and SAP particles. The expectation was that the low water uptake of the PE will be enhanced by blending with a SAP and thus the silver ion release from the material will increase. Surprisingly, the silver ion release was markedly suppressed by the addition of SAP. This finding is explained by the preferential sorption of silver ions by the SAP particles.

     

Microplane Model M5 with Kinematic and Static Constraints for Concrete Fracture and Anelasticity. II: Computation

Following the formulation of the constitutive model in the preceding Part I in this issue, the present Part II addresses the problems of computational algorithm and convergence of iterations. Typical numerical responses are demonstrated and the parameters of the model are calibrated by test data from the literature.     

Combined Approach Supporting Integrated Furnace Design and Retrofit

Existing complicated and complex calculation procedures for the design of process tubular furnaces create the main reason why the connection of targeting and detail design stage of furnaces (i.e., the continuous design and/or retrofit approach) is a serious problem in design practice. A complex, newly developed approach of furnace design and/or retrofit is presented in this paper. This comprehensive approach involves the application of heat transfer (radiation and convection) in equipment design, thermodynamic analysis for process design from the point of view of furnace integration, and the latest approach consisting in involving process fluid flow and hydrodynamic analysis to avoid potential problems in operation. This new methodology bridges existing gaps between modern targeting methods based on pinch analysis (providing optimized parameters such as the temperature of preheated air, stack temperature, and excess air) and the detailed design of furnaces. It is partly interactive and based on three stages of design: targeting, synthesis, and detailed design. It can be applied for both grassroots and retrofits problems.     

Short form of creep and shrinkage prediction model B3 for structures of medium sensitivity

TC Membership: Chairman: Zdeněk P. Bažant, USA;Secretary: Bernard Espion, Belgium;Members: Paul Acker France; Michel Auperin, France; Ignacio Carol, Spain; Domingo Carreira, USA; José M. R. Catarino, Portugal; Jenn-Chuan Chern, Taiwan; Mario Chirino, Italy; John W. Dougill, UK; Christian Huet, Switzerland; Jan Erik Jonasson, Sweden; Jin-Keun Kim, Korea; Vladimir Kristek Czech Republic; Harald S. Muller, Germany; Byung-Hwan Oh, Korea; Josko Ozbolt, Germany; Stuart G. Ried, Australia; Hans Reinhardt, Germany; Peter Schwesinger, Germany; Bretislav Teply, Czech Republic; Heinrich Trost, Germany; Tatsuya Tsubaki, Japan; Robert F. Warner, Australia; Folker H. Wittmann, Switzerland; J. Francis Young, USA.     

Partially pyrolyzed composites with basalt fibres – Mechanical properties at laboratory and elevated temperatures

Mechanical properties of partially pyrolyzed at 650 °C or 750 °C unidirectional basalt fibre composites with polysiloxane matrix were studied at laboratory and elevated temperatures. Ten pyrolysis processes differing mutually in heating courses and ultimate temperatures were compared. The material treated at 650 °C revealed at laboratory temperature flexural strength around 850 MPa. Fracture toughness of this material exceeded that of the cured only (at 250 °C) and treated at 750 °C composites. However, the composite pyrolyzed at 750 °C is more suitable for applications at elevated temperatures because of its slower degradation in hot air.