Compressive mechanical properties of closed-cell aluminum foam–polymer composites

The compressive mechanical properties of two kinds of closed-cell aluminum foam–polymer composites (aluminum–epoxy, aluminum–polyurethane) were studied. The nonhomogeneous deformation features of the composites are presented based on the deformation distributions measured by the digital image correlation (DIC) method. The strain fluctuations rapidly grow with an increase in the compressive load. The uneven level of the deformation for the aluminum–polyurethane composite is lower than that for the aluminum–epoxy composite. The region of the preferentially fractured aluminum cell wall can be predicted by the strain distributions in two directions. The mechanical properties of the composites are investigated and compared to those of the aluminum foams. The enhancement effect of the epoxy resin on the Young’s modulus, the Poisson’s ratio and the compressive strength of the aluminum foams is greater than that of the polyurethane resin.     

Influence of refiner fibre quality and fibre modification treatments on properties of injection-moulded beech wood–plastic composites

Thermo-mechanical pulp (TMP) fibres made from beech wood were produced using increasing refiner gap widths and thus with increasing fibre length and coarseness. Fibres (60% by weight) were compounded in an internal kneading mixer using high-density polyethylene as the matrix and injection-moulded. Fibre lengths and length/width ratios were determined (a) before processing and (b) after injection-moulding and Soxhlet extraction using the optical FibreShape system. An increase in fibre length resulted in a decrease in water absorption and an improvement in flexural strength and modulus of elasticity of the wood–plastic composites (WPC). However, flexural strength of the WPC with TMP fibres was not improved compared to WPC with wood flour when maleic anhydride-grafted polyethylene (MAPE) was used as a coupling agent. After injection-moulding, differences in length of the various TMP fibre types were minor. Fibre geometry before processing strongly influences the water absorption and flexural properties of the composite. Fibre treatment with emulsified methylene diphenyl diisocyanate (EMDI) resin before compounding was shown to be equally efficient in reducing water absorption and improving flexural strength as the addition of MAPE during the compounding step.     

The effect of γ-radiation on the mechanical properties of structural adhesive

The modular satellite concept iBOSS (intelligent Building Blocks for On-Orbit Satellite Servicing and Assembly) enables on-orbit servicing and reconfiguration of satellite systems and has the potential to be a game changer in the space industry. Such building blocks have to withstand all environmental loads in space, e.g.: radiation, vacuum and thermal cycling.The present paper investigates the mechanical properties of the two component epoxy adhesive 3M SW9323 under the environmental effect of radiation. This adhesive is part of the building block's primary structure. Furthermore, adhesive bonding is the sole joining technique used in the whole structure. It is therefore critical to know the influence of ionizing radiation on its load-carrying capacity. For this purpose bulk specimens were manufactured and exposed to γ-radiation, generated by a ⁶⁰Co source. Four different doses were achieved by varying the distance to the source and irradiation time. Afterwards the specimen were tested under tensile loading. Using the digital image correlation technique properties like elastic modulus, shear modulus, tensile strength and elongation at break were determined.The results show that the mechanical properties of the bulk specimen of 3M SW9323 are not influenced by γ-radiation up to a dose of 17.6 kGy. This is explained by the phenomena of crosslinking and chain scission which occur simultaneously and cancel each other out. In addition, Fourier-transform infrared spectroscopy (FTIR) was carried out to investigate if one mechanism is predominant. A slight shift in the spectra indicates the supremacy of chain scission.     

Fabrication of corrosion resistant, bioactive and antibacterial silver substituted hydroxyapatite/titania composite coating on Cp Ti

The present work is aimed at developing a bioactive, corrosion resistant and anti bacterial nanostructured silver substituted hydroxyapatite/titania (AgHA/TiO₂) composite coating in a single step on commercially pure titanium (Cp Ti) by plasma electrolytic processing (PEP) technique. For this purpose 2.5 wt% silver substituted hydroxyapatite (AgHA) nanoparticles were prepared by microwave processing technique and were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy and transmission electron microscopy (TEM) methods. The as-synthesized AgHA particles with particle length ranging from 60 to 70 nm and width ranging from 15 to 20 nm were used for the subsequent development of coating on Cp Ti. The PEP treated Cp Ti showed both titania and AgHA in its coating and exhibited an improved corrosion resistance in 7.4 pH simulated body fluid (SBF) and 4.5 pH osteoclast bioresorbable conditions compared to untreated Cp Ti. The in vitro bioactivity test conducted under Kokubo SBF conditions indicated an enhanced apatite forming ability of PEP treated Cp Ti surface compared to that of the untreated Cp Ti. The Kirby-Bauer disc diffusion method or antibiotic sensitivity test conducted with the test organisms of Escherichia coli (E. coli) for 24 h showed a significant zone of inhibition for PEP treated Cp Ti compared to untreated Cp Ti.     

Fatigue behaviour assessment of flax–epoxy composites

The present study focuses on the characterisation and evaluation of the fatigue behaviour of flax–epoxy composites. A better understanding of this behaviour allows the prediction of long-term properties to assess the viability and long-term durability of these materials. The purpose of this work is to systematically compare the tension–tension fatigue behaviour of flax fibre composites for one random mat, six textile architectures and two laminate configurations, which are used in a wide range of applications. The fibre architecture was found to have a strong effect on the fatigue behaviour, where higher static strength and modulus combinations present the best fatigue characteristics. They have a delayed damage initiation and increased fatigue life as well as a reduced damage propagation rate combined with higher energy dissipation in the early stages of fatigue loading.     

Semi-rigid biopolyurethane foams based on palm-oil polyol and reinforced with cellulose nanocrystals

In this study, water-blown biopolyurethane (BPU) foams based on palm oil were developed and cellulose nanocrystals (CNC) were incorporated to improve the mechanical properties of the foams. In addition, the foams were compared with petroleum polyurethane (PPU) foam. The foam properties and cellular morphology were characterized. The obtained results revealed that a low-density, semi-rigid BPU foam was prepared using a new formulation. CNC as an additive significantly improved the compressive strength from 54 to 117 kPa. Additionally, cyclic compression tests indicated that the addition of CNC increased the rigidity, leading to decreased deformation resilience. The dimensional stability of BPU foams was increased with increasing CNC concentration for both heating and freezing conditions.Therefore, the developed BPU nanocomposite foams are expected to have great potential as core material in composite sandwich panels as well as in other construction materials.     

In situ assessment of carbon nanotube flow and filtration monitoring through glass fabric using electrical resistance measurement

Filtration of nanofillers into porous fabric media is still an issue during the preparation of advanced fiber-reinforced composites. The assessment of resin/multiwall carbon nanotube (MWCNT) flow, MWCNT filtration, and the cure monitoring of glass fiber/carbon nanotube-polyester composites by means of the measurement of the electrical resistance was introduced. The vacuum-assisted resin transfer molding technique was used. The electrical resistances measured over the span of a composite were qualitatively correlated with MWCNT flow and the degree of MWCNT filtration. It was found that while the complexity of the fabrics could likely introduce preferential deposition of MWCNTs, their filtration is mainly affected by their dispersion state in the resin suspension. Relationships among critical parameters such as the lengths and diameters of MWCNTs, the inter- and intra-tow dimensions of glass fabrics, the dispersion level of MWCNTs, and the viscosity of nanocomposite samples are discussed and correlated to the filtration, cure, and flow phenomena. We showed that our method can also serve as an early warning to obviate defects in the resulting composite.     

Relation between repeated uniaxial compressive pressure and electrical resistance of carbon nanotube filled silicone rubber composite

Carbon nanotube filled polymer composite can be used as sensitive material of flexible pressure sensor. By using solution mixing method, carbon nanotubes are dispersed into silicone rubber matrix to fabricate the composite. The piezoresistivities of the composite with different carbon nanotube concentrations under repeated compressions are researched quantitatively. The monotonicity of the piezoresistivity is dependent on the content of carbon nanotube and the range of the applied pressure. The reproducibility error of the piezoresistivity decreases with the increase of the compression cycles. The experimental data of the piezoresistivity are fitted by the linear combination of two exponential functions. The piezoresistive mechanism is studied qualitatively by analyzing the changes in the carbon nanotube network.     

Enhanced strength and excellent transport properties of a superaligned carbon nanotubes reinforced copper matrix laminar composite

Superaligned carbon nanotube (SACNT) reinforced copper matrix laminar composites have been fabricated by means of the traditional copper sulfate electroplating process. The mechanical properties and transport properties of the Cu/SACNT composites with different SACNT content have been studied systematically, and the experimental results show that the as-prepared composites possess a better comprehensive performance than pure copper. The simple rule of mixtures (ROM) has been used to estimate the potential maximum properties of the Cu/SACNT composites. The Cu/SACNT composite is considered to be a promising material for electronics and communications applications.     

In situ monitoring of structural changes in nonwoven mats under tensile loading using X-ray computer tomography

Changes in the internal structure of nonwoven mats during tensile testing were investigated in situ with micro X-ray computer tomography (CT). Fiber orientation and volume fraction, as well as fiber–fiber contact, were quantitatively characterized at several strain levels. These parameters are apt to change under tensile loading and are important in determining the mechanical properties of nonwoven mats. The reorientation of fibers along the tensile direction was restricted at large deformations due to interlocked structures, which formed as a result of inherent entanglements in the nonwoven mats. In addition, contact efficiency, which describes the relative degree of fiber–fiber contact and was shown to be a suitable geometrical parameter for characterizing the microstructure of nonwoven mats, decreased at low strain and then increased with increasing strain until failure.