Band 19, Heft 2

Sputtered films were deposited over glass and silicon (Si) substrates by using homemade centrifuged aluminum (Al) targets containing boron (B) AlB 2 and AlB 12 particles as their constituents. Additional films were produced with an as-received aluminum target for comparison purposes. The composite targets were mounted in the magnetron sputtering system working at varying discharge powers, ranging from 200 to 450 W, to produce films with the smallest surface roughness. This roughness analysis showed that films deposited from the composite targets (fabricated by centrifugal casting) possessed lower surface roughness than the pure aluminum films if they were deposited over silicon substrates. Also, preliminary studies of film structure and mechanical properties revealed that the films produced with the composite targets had smaller grain size, dominant compression stresses, higher disorder in the crystalline structure, and higher hardness and elastic modulus, when compared with the films produced with the pure aluminum target.

Aluminum is a light metal and is widely used in a variety of industries. Aluminum-silicon has good casting properties but does not offer any suitable tribological properties. Therefore, in this study surface composite coating was performed by the gas tungsten arc welding (GTAW) process, which increased hardness up to 34 HV, which is nearly two times compared to untreated specimens. This process is done by composite manufacturing with the silicon carbide reinforcement particles in the matrix of eutectic aluminum-silicon alloy. The mixed powder is deposited on the surface during melting by travelling the arc of GTAW. The desired optimum performance condition is achieved by arc current 75 amp, 1 g of poly vinyl alcohol (PVA) binder, 65 wt.% of aluminum powder and 15 wt.% of silicon carbide.

Nanophase hydroxyapatite (HAP) particles were coated with silica via the hydrolysis of tetraethyl orthosilicate after a dodecyl alcohol based esterification reaction. The nanocomposite particles were characterized by transmission electron spectroscopy, scanning electron microscopy, X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, thermogravimetry and differential scanning calorimetry, sedimentation time and zeta potential (ζ) studies. A sequential change in infrared spectral features characteristic of HAP was accompanied by an increase in features characteristic of silica as revealed by FTIR. The silica coating enhanced the colloidal stability of HAP in aqueous suspensions. This behavior can be explained based on a heterocoagulation coating mechanism in which silica clusters adsorb onto the HAP particle surface.

(SiO 2 ) f /SiO 2 composites reinforced with three-dimensional (3D) six-directional preform were fabricated by the silicasol-infiltration-sintering method. The nominal fiber volume fraction was 47%. To characterize the mechanical properties of the composites, mechanical testing was carried out under various loading conditions, including tensile, flexural, and shear loading. The composite exhibited highly nonlinear stress-strain behavior under all the three types of loading. The results indicated that the 3D six-directional braided (SiO 2 ) f /SiO 2 composites exhibited superior flexural properties and good shear resistant as compared with other types of preform (2.5D and 3D four-directional)-reinforced (SiO 2 ) f /SiO 2 composites. 3D six-directional braided (SiO 2 ) f /SiO 2 composite exhibited graceful failure behavior under loading. The addition of 5th and 6th yarns resulted in controlled fracture and hence these 3D six-directional braided composites could possibly be suitable for thermal structure components.

In this article, Carrera’s Unified Formulation (CUF) is combined with a radial basis function collocation technique. A higher-order theory that considers deformations in the thickness direction was developed under CUF to predict the buckling behaviour of laminated plates. The obtained governing equations and boundary conditions are then interpolated by collocation with radial basis functions. The accuracy and efficiency of the combination of the two techniques for buckling problems of laminated plates are demonstrated through numerical experiments.

A formulation of element-based Lagrangian 9-node shell element based modified first-order shear deformation theory is improved for non-linear behaviors of composite laminates containing matrix cracking. Using the refined ANS (assumed natural strain) shell elements either show the optimum combination of sampling points with an excellent accuracy or remove the locking phenomenon. The multi-directional stiffness degradation caused by matrix cracking, which was proposed by Duan and Yao, is conducted. Natural coordinate based higher-order transverse shear strains are used in the present shell element. Numerical examples demonstrate that the present element behaves reasonably satisfactorily either for the linear or geometrical non-linear analysis of laminated composite structures. The results of laminated composite shells with matrix cracking may be the benchmark test for the non-linear analysis of damaged composite laminates.

This research paper establishes the relationship between fabric parameters and fiber volume fraction through analyzing the representative unit cell of the 2.5D shallow straight-joint preform. The effect of fabric parameters on the fiber volume fraction by theoretical study is also investigated. The 2.5D shallow straight-joint fabric was manufactured by quartz fiber to verify the fiber volume fraction by theoretical and experimental study. The errors between predicted and measured results is only 2.12% and 1.13%. It was also found that as warp density and linear yarn density of yarn decrease and fabric thickness increases, the overall fiber volume fraction and weft yarn fiber volume fraction increase, but warp yarn fiber volume fraction decreases. Weft yarn has greater influence on fiber volume fraction of fabric than warp yarn in the structure of shallow straight-joint.

A composite beam with single delamination under the action of moving load has been modeled accounting for the Poisson’s effect, shear deformation, and rotary inertia. The existence of the delamination changes the stiffness of the structure, and this affects the dynamic response of the structure. We have used a constrained mode to simulate the behavior between the delaminated surfaces. Based on this mode, eigensolution technique is used to obtain the natural frequencies and their corresponding mode shapes for the delaminated beam. Then, the Ritz method is adopted to derive the dynamic response of the beam subjected to a moving load. The obtained results for the free and forced vibrations of beams are verified against reported similar results in the literature. Moreover, the maximum dynamic response of such beam is compared with an intact beam. The effects of different parameters such as the size, depth, and spanwise location of the delamination, the load velocity, the different ply configurations, and the Poisson’s effect on the dynamic response of the beam are studied.

The main objective of this investigation is to assess the feasibility of strengthening square hollow steel tubular sections subjected to compression and to develop or predict the suitable wrapping scheme of fibre reinforced polymer (FRP) to enhance the structural behaviour of it. For this study, compact mild steel tubes were used with the main variable being FRP characteristics. Carbon fibre has been considered and used as strips with several other parameters such as the number of layers, width and spacing of strips, the sectional area of strips, and wrapping scheme. Experiments were undertaken until column failure to fully understand the influence of FRP characteristics on the compressive behaviour of square hollow steel tubes including their failure modes, stress-strain behaviour, enhancement in load carrying capacity and effect of distribution of CFRP layers. The behaviour of externally bonded hollow steel tubular sections was compared with one another and also with the control specimen. From the test results, it was found that CFRP strengthening significantly increases the load carrying capacity and ductility of the hollow steel tubular members further.

Determination of fracture load and displacement values that might be formed in a reinforced concrete (RC) construction having different overhang types by artificial neural network (ANN) modeling was investigated in this study. Nonlinear static pushover analysis of the key parameters in change defined in Turkish earthquake code (TEC) [1] for columns and beams was carried out, and the capacity curves, failure loads, and displacements were obtained. In total, 64 RC buildings were analyzed according to the change intervals of the parameters chosen. In addition, regression analysis was performed with Statistical Packages for the Social Sciences (SPSS) statistical program (SPSS Inc., Chicago, IL, USA) by using the same parameters for the same model types. Consequently, separate equations were obtained for displacement and load values, and their R 2 values were calculated. As a result of ANN modeling, 91.77% convergence for displacement values and 90.61% convergence for load values were obtained. The graphs between the calculated values and expected values are given.

Based on a self-assembly mechanism, a co-precipitation method was utilized to fabricate bone-like biomimetic nanocomposite with a simplified preparation approach and accessible materials to investigate in depth some characteristics of hydroxyapatite/collagen(HAp/Col) nanocomposite for the elucidation of performances in some respects. The as-prepared composite was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transformation infrared spectroscopy, and thermal analysis. The results show that HAp nanocrystals formed as preferentially oriented slender needles 50–100 nm in length on a felt-like Col matrix which is composed of large numbers of randomly oriented Col fibers and showed polycrystalline behavior. The as-prepared cellular composites are analogous in both composition and nanostructured architecture to native bone, longer aging time promotes the growth and purification of nano-HAp on Col, and characterization confirms that chemical interaction occurs and causes intimate bonding between HAp and Col.

Woven polymer-based composites exhibit highly non-linear behavior, which often results in very high strains to failure. A micromechanical model is developed to represent the large deformation kinematics of woven composites, and develop predictions for failure strain components in specific cases of multiaxial loading. Failure functions are proposed for macromechanical analyses of arbitrary cases of large deformation loading. The approach is validated against basic tension experiments performed using both digital image correlation and with specially designed instrumentation for large strain measurement. Predicted failure strains correspond well with experimental observations. The proposed failure functions are well suited for finite element applications involving user-defined material models.

Lightfast color filters (intensively and brightly colored) can be easily produced by dying optical plastics with the surface plasmon resonance (SPR) of metal nanoparticles such as silver and gold. Here, color filters based on silver nanoparticles embedded in amorphous polystyrene have been prepared by dissolving and thermally decomposing (1,5-cyclooctadiene)(hexafluoro-acetylacetonate)silver(I) in amorphous polystyrene. The metal precursor quickly decomposes (10 s, at 180°C), leading to silver atoms that clusterize and produce a non-aggregated dispersion of silver particles in the polymer matrix. The intensity of the yellow coloration due to the SPR of nanoscopic silver can be widely tuned simply by varying the cluster numerical density in the polymer matrix that depends on the silver precursor concentration. The obtained nanocomposite films have been characterized by X-ray power diffraction, transmission electron microscopy, and UV-Vis spectroscopy.

The influence of water/cementitious material ratio, silica fume, and fly ash as partial Portland cement replacement materials on the properties, pore structure, and durability of cement-based composites was evaluated by conducting compressive strength test, mercury intrusion porosimetry test, water absorption, rapid chloride penetration test, and scanning electron microscopy (SEM). Water/cementitious material ratio, and replacement percentage of silica fume and fly ash have significant effects on the pore structure and durability of cement-based composites. Composites with silica fume or fly ash have a denser structure than the control composite on SEM micrographs. Silica fume has about 5–10 times as much effect as fly ash, according to results of multiple linear regression analyses of testing data.