Influence of crack initiation length on fracture behaviors of reinforced concrete

For the purpose of discussing the fracture features of high strength reinforced concrete, under the conditions of the fundamental assumptions to reinforced concrete, the calculating process of fracture parameters for three point bending beam of high strength reinforced concrete is given, and through a total of 16 specimens with the same sizes, with the different initial crack length 40 mm to 100 mm on three point bending beam of high strength reinforced concrete, it is performed to examine the calculation method. The results show that the fracture features of high strength reinforced concrete are different from normal concrete, both the initiation toughness and the unstable toughness of high strength reinforced concrete gradually increase with the crack-to-depth ratios, and the ratios of initial load to maximum load are different depending on the initial crack length, the bigger the crack-to-depth ratios, the lower the ratio, and the ductility is best to the high strength reinforced concrete.     

Improved manufacturing method and mechanical performances of carbon fiber reinforced lattice-core sandwich cylinder

Filament winding and twice co-curing processes were applied to make advanced carbon fiber reinforced composite (CFRC) sandwich cylinder with lattice cores. Split metallic moulds were designed and adopted for easy demoulding after winding the lattice core. The cylinders were designed with a small tapering to assure tight contact between the lattice core and the inner skin. To avoid local failure at the end of the cylinder, flange structures were placed continuously from the fibers of skins and lattices. Axial compression was carried out to reveal the mechanical behaviors of the fabricated sandwich cylinder. The experiment shows that the advanced making technology shows the promise of lattice sandwich cylinder (LSC) avoiding instability, local buckling, local cracking and debonding.     

Molecular dynamics and atomistic based continuum studies of the interfacial behavior of nanoreinforced epoxy

In this study, we investigate the interfacial mechanical characteristics of carbon nanotube (CNT) reinforced epoxy composite using molecular dynamics (MD) simulations. The second-generation polymer consistent force field (PCFF) is used in the MD simulations. In particular, we compare MD results with those obtained by atomistic-based continuum (ABC) multiscale modeling technique, which makes use of the appropriate constitutive relations derived solely from interatomic potentials. The results of our comparative investigation suggest that (i) the ABC multiscale model and MD simulation provides almost identical predictions for the interfacial properties of the nanocomposite for smaller diameter of CNTs, (ii) the ABC model slightly over predict the interfacial properties of the nanocomposite for larger diameter of CNTs, and (iii) the MD simulations represents the real nanocomposite structure with the minimum assumptions compared to that of the ABC multiscale model but with much greater computer requirements and limited length scale.     

Study of ion cluster reorientation process of geopolymerisation reaction using semi-empirical AM1 calculations

In this paper all the possible reaction pathways involved in ion clusters reorientation process of metakaolin based Geopolymeric cement were systemically investigated according to thermodynamic theory. The reaction energy of every possible reorientation pathway was also calculated using computational chemistry method-semi-empirical AM1 calculation. The optimum reorientation pathway was analyzed based on the energy-minimized principle. The calculation results showed that Si–Al hybrid reorientation should be primary reorientation pathway of Geopolymeric cement made with NaOH or KOH activated metakaolin. This viewpoint was also verified by Nuclear Magnetic Resonance Spectroscopy equipped with Magic Angle Spinning technique (MAS-NMR). In addition, the semi-empirical AM1 calculations revealed that the reorientation reaction is easier and stronger in NaOH solution than in KOH solution.     

Sulphuric acid corrosion of ultrafine-grained mild steel processed by equal-channel angular pressing

A bulk ultrafine-grained (UFG) mild steel with a ferrite grain size of approximately 200 nm and a dispersed distribution of iron carbide particles was fabricated by equal-channel angular pressing (ECAP) at 400 °C. The corrosion behaviour of the ECAP-processed mild steel and pure iron was investigated in a 0.5 mol/L H₂SO₄ solution. They exhibited a higher corrosion rate and better anodic passivity properties due to the presence of more crystalline defects. As a result of the refinement of the iron carbide particles, the forming ability of a continuous dense passive film was improved.     

ZnWO4–TiO2 composite nanofilms: Preparation,morphology, structure and photoluminescent enhancement

ZnWO₄–TiO₂ composite nanofilms on a glass slide were prepared by means of the dip-coating method, in which collodion was used as a dispersant and film-forming agent. The nanofilms are characterized through SEM, XRD, TG/DTA, PL and IR, respectively. SEM and XRD characterization of these films indicated that ZnWO₄ and TiO₂ particles crystallized in a monoclinic wolframite-type structure and Anatase phase, respectively, and both of these were well dispersed in the nanofilms. Compared with nanoparticles, when TiO₂ nanoparticles were added in 3.61% ratio, the PL intensities of ZnWO₄ nanofilms were obviously enhanced. FTIR spectra further confirmed the presence of ZnWO₄ on the nanofilms.     

Effect of flow velocity on cavitation erosion behavior of HVOF sprayed WC-10Ni and WC-20Cr3C2–7Ni coatings

WC-10Ni and WC-20Cr₃C₂–7Ni coatings were deposited successively using high-velocity oxygen-fuel (HVOF) spraying. The microstructures and mechanical properties of the coatings were evaluated by X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), Vickers microhardness tester, and Ultra nanoindentation tester. The cavitation erosion behaviors of the coatings at different flow velocities were investigated by a rotating disk rig facility with bolt cavitator and circulating system. The results showed that the main phases in the WC-10Ni and WC-20Cr₃C₂–7Ni coatings were WC, W₂C, W, and WC, (W,Cr)₂C, respectively. Both coatings were dense and well bonded to the steel substrate. Despite higher porosity and elastic modulus (E) as well as slightly lower hardness (H), the WC-10Ni coating showed lower H/E, H³/E² and η values as well as cavitation erosion resistance at each flow velocity compared to the WC-20Cr₃C₂–7Ni coating. Both coatings exhibited an increase in the volume loss rates with increasing flow velocity, and the critical flow velocity of the WC-20Cr₃C₂–7Ni coating was in the region of 33.5 to 41.9 m·s⁻¹. The cavitation erosion failure mechanism of the WC-10Ni coatings was the brittle detachment of the WC particles, while cavitation pinholes, pits, cracks, craters, and massive exfoliation contributed to the evolution of the cavitation erosion processes of the WC-20Cr₃C₂–7Ni coating with the increase of the flow velocity.     

Hybrid carbon fiber composite lattice truss structures

Carbon fiber reinforced polymer (CFRP) composite sandwich panels with hybrid foam filled CFRP pyramidal lattice cores have been assembled from linear carbon fiber braids and Divinycell H250 polymer foam trapezoids. These have been stitched to 3D woven carbon fiber face sheets and infused with an epoxy resin using a vacuum assisted resin transfer molding process. Sandwich panels with carbon fiber composite truss volumes of 1.5–17.5% of the core volume have been fabricated, and the through-thickness compressive strength and modulus measured, and compared with micromechanical models that establish the relationships between the mechanical properties of the core, its topology and the mechanical properties of the truss and foam. The through thickness modulus and strength of the hybrid cores is found to increase with increasing truss core volume fraction. However, the lattice strength saturates at high CFRP truss volume fraction as the proportion of the truss material contained in the nodes increases. The use of linear carbon fiber braids is shown to facilitate the simpler fabrication of hybrid CFRP structures compared to previously described approaches. Their specific strength, moduli and energy absorption is found to be comparable to those made by alternative approaches.     

Concrete porosimetry: Aspects of feasibility,reliability and economy

The opening operator of mathematical morphology is applied to section images in this paper for the assessment of pore characteristics, such as the size distribution, and critical pore size, in cement pastes. Moreover, the mean free spacing parameter is demonstrated as reflecting pore depercolation during cement maturation. This approach is compared with other popular methods for serving this purpose, encompassing the experimental technique of mercury intrusion porosimetry (MIP), Wood’s metal intrusion porosimetry (WMIP), the conventional method of image analysis by area histogram and a direct 3D approach by a simulation model. The comparison study reveals that the opening distribution technique is superior in terms of feasibility, reliability and economy; realistic and relevant structural information on pore space in cement pastes is obtained. Nevertheless, star volume measurements applied to section images are referred to as an interesting alternative to the proposed method. The proper characterization of pore size distribution, and assessment of critical pore size, and delineation of percolated porosity zones are of significant importance to permeability prediction of cementitious materials and thereby to durability studies of the materials.     

Mechanical property of lattice truss material in sandwich panel including strut flexural deformation

Lattice truss materials are usually assumed to be stretching dominated neglecting the bending resistance of struts. In this paper, bending resistance of struts is considered for lattice truss sandwich panels. The mechanical behaviors are not only decided by the relative density of the lattice and the strut inclination, but also the slenderness ratio of the strut. For stout and hierarchical struts, the slenderness ratio turns to smaller, and the shear force and the bending moment are comparable to the strut axial force. Compared with the stretching dominated theory, the stiffness of the lattice material should be improved while the strength reduced, which has been proved to be more consistent with experimental results.