Quasi-static axial compression behavior of constraint hexagonal and square-packed empty and aluminum foam-filled aluminum multi-tubes

The axial crushing behavior of empty and Al close-cell foam-filled single Al tubes and Al multi-tube designs (hexagonal and square) were investigated through quasi-static compression testing. The effects of foam filling on the deformation mode and the crushing and average crushing loads of single tubes and multi-tube designs were determined. The foam filling was found to shift the deformation mode of empty single tube and empty multi-tube designs from diamond into concertina. In multi-tube designs the constraint effects and the frictional forces were found to increase the average crushing loads over those of single tubes. It was also found that foam filling induced a higher strengthening coefficient in multi-tube than single tubes. Although foam filling increased the energy absorption in single tubes and multi-tube designs, it was not effective in increasing the specific absorbed energy over that of the empty tubes. However, multi-tube designs were found to be energetically more effective than single tubes at similar foam-filler densities, proving a higher interaction effect in multi-tube designs.TÜBİTAK for Grant #MISAG-22

Thermal and acid treatment of diatom frustules

Purpose: Diatoms, belonging to Bacilariophyta family, are single-celled microscopic (1-100 micron) plants living in aquatic environment. The diatom cell is protected inside a shell (frustule) constructed from amorphous nano-silica particles. It is proposed that the frustules and purified silica powders obtained from frustules can be used to reinforce composites. In this study, microstructural properties of two diatom frustules were determined and different methods were investigated for silica powder processing from diatom frustules. Design/methodology/approach: Natural (ND) and calcined (CD) diatom frustules were used in this study. The chemical and microscopic properties of the diatom frustules were determined using Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), Fourier Transform Infrared Spectrometry (FTIR) and energy dispersive X-Ray Florescence spectrometer (XRF). Two different processing routes were applied to process silica powder from diatom frustules. These included (i) leaching the frustules directly in HF, (ii) incorporating thermally treated frustules in to the liquid nitrogen. Findings: At increasing HF concentrations, the variety of shapes, nanopores and open voids were seen on the surface of frustules as silica particles were removed from the surface. SEM micrograph results showed that HF significantly etched inside the existing pore structure of the diatom frustules. HF concentration was found more effective in mass loss than the leaching time. Thermal treatment induced several cracks propagated between macro pores and nanopores of the frustules. Practical implications: Results show that thermal and acid treatments were not effective for obtaining silica powder from frustules. Ball milling can be used for silica powder processing from frustules in the further study. Originality/value: In this paper, the microstructural properties of ND and CD frustules were determined. The effect of thermal and acid treatment on frustules was investigated with SEM.TÜBİTAK (106M186) and İYTE-BAP for support to 2008İYTE04 projec

High strain rate testing of a unidirectionally reinforced graphite epoxy composite

Since accurate, reproducible methods of testing polymer composites are not very well developed or standardized, this research forms part of a program to gain a better understanding of the mechanical properties and failure mechanisms of polymer composites at high strain rates. Since failure modes differ markedly depending on fiber architecture, orientation, fiber/matrix combination and so forth, these initial tests were carried out using a simple unidirectionally reinforced composite. Beginning with testing in the longitudinal and transverse directions, reported here, future experiments are being carried out to determine how the high strain rate properties vary with angle of testing, and then move on to other simple fiber lay-ups, ±90◦, ±45◦, etc

High strain rate behavior of a SiC particulate reinforced Al2O3 ceramic matrix composite

The high strain rate deformation behavior of composite materials is important for several reasons. First, knowledge of the mechanical properties of composites at high strain rates is needed for designing with these materials in applications where sudden changes in loading rates are likely to occur. Second, knowledge of both the dynamic and quasi-static mechanical responses can be used to establish the constitutive equations which are necessary to increase the confidence limits of these materials, particularly if they are to be used in critical structural applications. Moreover, dynamic studies and the knowledge gained form them are essential for the further development of new material systems for impact applications. In this study, the high strain rate compressive deformation behavior of a ceramic matrix composite (CMC) consisting of SiC particles and an Al{sub 2}O{sub 3} matrix was studied and compared with its quasi-static behavior. Microscopic observations were conducted to investigate the deformation and fracture mechanism of the composite

Calcined and natural frustules filled epoxy matrices: The effect of volume fraction on the tensile and compression behavior

The effects of calcined diatom (CD) and natural diatom (ND) frustules filling (0–12 vol.%) on the quasistatic tensile and quasi-static and high strain rate compression behavior of an epoxy matrix were investigated experimentally. The high strain rate testing of frustules-filled and neat epoxy samples was performed in a compression Split Hopkinson Pressure Bar set-up. The frustules filling increased the stress values at a constant strain and decreased the tensile failure strains of the epoxy matrix. Compression tests results showed that frustules filling of epoxy increased both elastic modulus and yield strength values at quasi-static and high strain rates. While, a higher strengthening effect and strain rate sensitivity were found with ND frustules filling. Microscopic observations revealed two main compression deformation modes at quasi-static strain rates: the debonding of the frustules from the epoxy and/or crushing of the frustules. However, the failure of the filled composites at high strain rates was dominated by the fracture of epoxy matrix

Processing and compression testing of Ti6Al4V foams for biomedical applications

Open cell Ti6Al4V foams (60% porosity) were prepared at sintering temperatures between 1,200 and 1,350 °C using ammonium bicarbonate particles (315–500 μm) as space holder. The resulting cellular structure of the foams showed bimodal pore size distribution, comprising macropores (300–500 μm) and micropores (1–30 μm). Compression tests have shown that increasing sintering temperature increased the elastic modulus, yield and compressive strength, and failure strain of foams. The improvements in the mechanical properties of foams prepared using smaller size Ti64 powder with bimodal particle distribution were attributed to the increased number of sintering necks and contact areas between the particles. Finally, the strength of foams sintered at 1,350 °C was found to satisfy the strength requirement for cancellous bone replacement.Technology Development Foundation of Turkey (TTGV) for the grant #TTGV-102/T1

Preparation and characterization of nanocrystalline titania

Nanokristal seramikler, ileri seramiklerin gelecekteki uygulamalannda önemli etkileri olabilecek özgün kimyasal, fiziksel ve mekanik özelliklere sahiptir. Bu çalışmada, tItanyum; izopropoksit'ten titan seramikleri hazırlanması ve karakterizasyonu incelendi. Şekillendirilmiş yapılar 650-850 C aralığında hava ortamında sinterlendi. Sol-jel prosesi ve jellerin kontrollü kurutulması ile elde edilen seramiklerin yoğunluklan teorik yoğrunluğun %79-99' u olarak bulundu. Sollar, jeller ve çökertme yöntemleriyle hazırlanan tozlardan preslenen peletlerin sinterlerne işlemi öncesi ve sonrası yoğunlukları sırasıyla teorik yoğunluğun %40-52 ve %55-83' ü olarak bulundu.Nanocrystalline ceramics possess unique chemical, physical and meehanical properties which may have a significant impact on the future applications of advanced cemmies. The preparatiion and characterization of titania ceramics from titanium isopropoxide precursor was investigated in this work. Green bodies were air gintered in the 650-850°C range for the determination of the sintering behaviour. The sintered densities of the cerainics prepared by sol-gel processing and controlled drying of the gels were in the 79-99% of theoretical density. The green and sintered densities of the pellets prepared by uniaxial pressing of powders derived from sols, gels and precipitation were in the 40-52% and 55-83% respectively

Room temperature foaming of glass powder in aqueous environment

Foam glass is a cellular material that is used in thermal insulation applications due to its low thermal conductivity. The high crushing resistance, low moisture absorption, high temperature and corrosion resistance of foam glass are considered to be key advantages over polymer and cement based cellular structures that are used in the construction industry. Foam glass technology has been thoroughly documented from both scientific and industrial perspective. Conventional processing of this material utilizes either recycled or chemically controlled glass as its main source of raw material, which is formed into a controlled cellular structure using foaming reactions at high temperatures (typically between 700-1000C) [1, 2]. Different from the conventional production methods, this study has focused the formation and its mechanisms of formation of cellular structures at room temperature conditions using recycled glass as the starting raw material. Foaming was achieved in aqueous suspensions of glass particles using the reaction between aluminum metal powder and calcium hydroxide as the gas forming (foaming) mechanism. This route allows the formation of the pores, their size and size distributions at room temperature using slurry rheology as a critical parameter. This article will present the foaming behavior of slurries prepared using recycled soda-lime silica glass that was milled and screened to three different size distributions and mixed with water between 50 and 60 weight % solids content. Carboxymethyl cellulose (CMC) was used as a binder and stabilizer at 2 and 4 weight % of the slurry composition. The results on the dynamic expansion behavior (Figure 1) and the rheology of the suspensions will be presented discussing the critical relation between these two and their effects on the control over the pore formation and structure of the green body. This study aims to provide a new insight for foam glass production by combining the established methodologies utilized in the processing of aerated concrete and conventional foam glass production. Although the study has used recycled soda-lime silica glass as the main ingredient, the discussed method lends itself to using other forms and chemistries of recycled glass making it a viable green technology candidate. Please click Additional Files below to see the full abstract

Foaming behavior of Ti6Al4V particle-added aluminum powder compacts

The foaming behavior of 5 wt.% Ti6Al4V (Ti64) particle (30–200 μm)-added Al powder compacts was investigated in order to assess the particle-addition effects on the foaming behavior. Al compacts without particle addition were also prepared with the same method and foamed. The expansions of Ti64 particle-added compacts were measured to be relatively low at small particle sizes and increased with increasing particle size. At highest particle size range (160–200 μm), particle-added compacts showed expansion behavior similar to that of Al compacts without particle addition, but with lower expansion values. Expansions studies on 30–45 μm size Ti64-added compacts with varying weight percentages showed that the expansion behavior of the compacts became very similar to that of Al compact when the particle content was lower than 2 wt.%. However, Ti64 addition reduced the extent of drainage. Ti64 particles and TiAl3 particles formed during foaming increased the apparent viscosity of the liquid foam and hence reduced the flow of liquid metal from cell walls to plateau borders. The reduced foamability in the compacts with the smaller size Ti64 addition was attributed to the relatively high viscosities, due to the higher cumulative surface area of the particles and higher rate of TiAl3 formation between liquid Al and Ti64 particles.TÜBİTAK for the grant #106M18

Predicting energy absorption in a foam-filled thin-walled aluminum tube based on experimentally determined strengthening coefficient

The energy absorption in a foam-filled thin-walled circular Al tube was investigated based on the experimentally determined strengthening coefficient of filling using Al and polystyrene closed-cell foams with three different densities. Foam filling was found to change the deformation mode of tube from diamond (empty tube) into concertina, regardless the foam type and density used. Although foam filling resulted in higher energy absorption than the sum of the energy absorptions of the tube alone and foam alone, it was not effective in increasing the specific energy than simply thickening the tube wall. It was shown that for efficient foam filling an appropriate foam-tube combination must be selected by taking into account the magnitude of strengthening coefficient of foam filling and the foam filler plateau load.TÜBİTAK for the Grant # MISAG-22