Influence of different back laminate layers on ballistic performance of ceramic composite armor

This paper mainly reported a new type of ceramic composite armor with a back laminate of Ti6Al4V/UHMWPE/Ti6Al4V against the 12.7 mm armor piercing projectile at a velocity of 818 m/s. The mechanism of the whole ceramic composite armor against the projectile, and the function of each layer in the back laminates were systematically investigated around the experiments and numerical simulations. The results indicated that the outermost Ti6Al4V layer provided support for the UHMWPE layer, leading to the UHMWPE layer displaying the extremely high buffer performance during the impact process. Meanwhile, the middle UHMWPE layer also had an energy balance function between the first and outermost Ti6Al4V layers to cause small damage in the back laminate layers. Thus, this configuration contributed to absorb or dissipate the more energy of the impact projectile, successfully preventing the perforation of the projectile.     

Quasi-static penetration and ballistic properties of kenaf–aramid hybrid composites

In this research, quasi-static penetration and ballistic properties of non-woven kenaf fibres/Kevlar epoxy hybrid laminates with thicknesses ranging from 3.1 mm to 10.8 mm by hard projectile at normal incidence have been experimentally investigated. Hybrid composites were fabricated by hand lay-up technique in a mould and cured at room temperature for 24 h by static load. Hybrid composites consist of Kevlar layers and non-woven kenaf layers at three different configurations, i.e. kenaf at the innermost layers, outermost layers and at the alternating layers. Kevlar/epoxy and kenaf/epoxy composites were also fabricated for comparison purpose. Quasi-static experiments were conducted using a tensile testing machine at the speed of 1.27 mm/min and 2.54 mm/min. Ballistic tests were conducted using 9 mm full metal jacket bullet using a powder gun at speeds varying from 172 to 339 m/s, with the initial and a residual velocity of the projectiles is measured. The tested sample was carefully examined with respect to failure modes. Results showed the effect of hybridization in term of force–displacement curves, energy dissipation and damage mechanisms for quasi-static test. Maximum force to initiate penetration is higher in hybrid composites compared to kenaf/epoxy and Kevlar/epoxy composites. Hybridization of kenaf–Kevlar resulted in a positive effect in terms of energy absorbed (penetration) and maximum load. In the case of ballistic tests, hybrid composites recorded lower ballistic limit (V₅₀) and energy absorption than the Kevlar/epoxy composite. The V₅₀ of hybrid composites with kenaf at the outermost layers is superior to other hybrid composites. These finding inspired further exploration of hybrid composite for ballistic armour spall-liner application.     

Impact strength of a few natural fibre reinforced cement mortar slabs: a comparative study

This paper presents the experimental investigations of the resistance to impact loading of cement mortar slabs (1:3, size: 300 mm × 300 mm × 20 mm) reinforced with four natural fibres, coir, sisal, jute, hibiscus cannebinus and subjected to impact loading using a simple projectile test. Four different fibre contents (0.5%, 1.0%, 1.5% and 2.5%—by weight of cement) and three fibre lengths (20 mm, 30 mm and 40 mm) were considered. The results obtained have shown that the addition of the above natural fibres has increased the impact resistance by 3–18 times than that of the reference (i.e. plain) mortar slab. Of the four fibres, coir fibre reinforced mortar slab specimens have shown the best performance based on the set of chosen indicators, i.e. the impact resistance (R_u), residual impact strength ratio (I_rs), impact crack-resistance ratio (C_r) and the condition of fibre at ultimate failure.     

Reciprocating sliding wear behavior of alendronate sodium-loaded UHMWPE under different tribological conditions

The aim of this study is to investigate the tribological behaviors and wear mechanisms of ultra-high molecular weight polyethylene (UHMWPE) loaded with alendronate sodium (ALN), a potential drug to treat osteolysis, under different normal loads and lubrication conditions. A mixture of UHMWPE powder and ALN (1.0 wt.%) solution was dried and hot pressed. The static and dynamic friction coefficients of UHMWPE–ALN were slightly higher than those of UHMWPE except under normal load as 10 N and in 25 v/v % calf serum. The specific wear rates of UHMWPE–ALN and UHMWPE were the lowest in 25 v/v % calf serum compared to those in deionized water or physiological saline. In particular, the specific wear rate of UHMWPE–ALN was lower than that of UHMWPE at 50 N in 25 v/v % calf serum. The main wear mechanisms of UHMWPE and UHMWPE–ALN in deionized water and UHMWPE in physiological saline were abrasive. The main wear mechanism of UHMWPE–ALN in physiological saline was micro-fatigue. In 25 v/v % calf serum, the main wear mechanism of UHMWPE and UHMWPE–ALN was abrasive wear accompanied with plastic deformation. The results of Micro-XRD indicated that the molecular deformation of UHMWPE–ALN and UHMWPE under the lower stress were in the amorphous region but in the crystalline region at the higher stress. These results showed that the wear of UHMWPE–ALN would be reduced under calf serum lubricated, which would be potentially applied to treat osteolysis.     

Silica–silica polyimide buffered optical fibre irradiation and strength experiment at cryogenic temperatures for 355 nm pulsed lasers

A controlled UV-light delivery system is envisioned to be built in order to study the stability properties of superconducting strands. The application requires a wave guide from room temperature to cryogenic temperatures. Hydrogen loaded and unloaded polyimide buffered silica–silica 100 μm core fibres were tested at cryogenic temperatures. A thermal stress test was done at 1.9 K and at 4.2 K which shows that the minimal mechanical bending radius for the fibre can be 10 mm for testing (transmission was not measured). The cryogenic transmission loss was measured for one fibre to assess the magnitude of the transmission decrease due to microbending that takes place during cooldown. UV-irradiation degradation measurements were done for bent fibres at 4.2 K with a deuterium lamp and 355 nm pulsed lasers. The irradiation tests show that the fibres have transmission degradation only for wavelengths smaller than 330 nm due to the two photon absorption. The test demonstrates that the fibres are suitable for the cryogenic UV applications with 355 nm and 70 μJ pulsed lasers.     

New magnetic phenomena of rare earth ions-modified carbon nanotubes

The preparation and magnetic properties of three rare earth ions-modified multi-walled carbon nanotubes (MWNTs) were discussed. The materials MWNT-X³⁺ (X = Nd, Gd, Er) were prepared by the coordination of rare earth ions and oxidized MWNTs. A novel magnetic phenomena was observed at the applied field of 30 k Oe and at T = 4 K. With the increase of temperature, the value of magnetization decreases from positive to negative, and the magnetic state changes from quasi-ferromagnetism to diamagnetism, which does not follow the behaviors of conventional ferromagnets.     

Manufacturing of lightweight low-current Nb3Sn ADR magnets operating at 10 K

Adiabatic demagnetization refrigerators (ADRs) using superconducting magnets are under development for cooling many NASA instruments. Due to higher efficiency of cryocoolers at 10 K, Nb₃Sn magnets operating at 10 K are favored for space ADRs. Further, magnets need to be as light as possible and have low operating currents. This paper discusses technologies for the manufacture of lightweight, low-current Nb₃Sn magnets and reports on testing of a 35 mm bore by 60 mm long magnet. This magnet weighed less than 1 kg and successfully produced 3 T at 11.5 K with an operating current of 8 A.     

Influence of alkali treatment and fibre length on mechanical properties of short Agave fibre reinforced epoxy composites

Composites based on short Agave fibres (untreated and alkali treated) reinforced epoxy resin using three different fibre lengths (3 mm, 7 mm and 10 mm length) are prepared by using hand lay up and compression mould technique. The materials were characterized in terms of tensile, compressive, flexural, impact, water absorption properties and machinability behaviour. All mechanical tests showed that alkali treated fibre composites withstand more fracture strain than untreated fibre composites. As evidenced by the dynamic mechanical analysis (DMA) tests, the thermo-mechanical properties of the composite with alkali treated Agave fibre were considerably good as alkali treatment had facilitated more sites of fibre resin interface. The machinability and atomic force microscope (AFM) studies were carried out to analyze the fibre–matrix interaction in untreated and alkali treated Agave fibre–epoxy composites.     

Penetration of concrete targets with ogive-nose steel rods

We conducted depth of penetration experiments in concrete targets with 3.0 caliber-radius-head, steel rod projectiles. The concrete targets with 9.5 mm diameter limestone aggregate had a nominal unconfined compressive strength of 58.4 MPa (8.5 ksi) and density 2320 kg/m³. To explore geometric projectile scales, we conducted two sets of experiments. Projectiles with length-to-diameter ratio of ten were machined from 4340R_c 45 steel, round stock and had diameters and masses of 20.3 mm, 0.478 kg and 30.5 mm, 1.62 kg. Powder guns launched the projectiles to striking velocities between 400 and 1200 m/s. For these experiments, penetration depth increased as striking velocity increased. When depth of penetration data was divided by a length scale determined from our model, the data collapsed on a single curve. Thus, a single dimensionless penetration depth versus striking velocity prediction was in good agreement with the data at two geometric projectile scales for striking velocities between 400 and 1200 m/s. In addition, we conducted experiments with AerMet 100R_c 53 steel projectiles and compared depth of penetration and post-test nose erosion data with results from the 4340R_c 45 steel projectiles.     

Influence of doped rare earth elements on electronic properties of the R0.25Ca0.75MnO3 systems

The influence of doped rare earth elements on the some electronic properties of perovskite systems R_0.25Ca_0.75MnO₃ (R = La, Nd, Eu, Tb, Ho, Y) is investigated using the density functional theory with Dmol3 code. The density of states, band structure, tolerance factor and Jahn–Teller splitting energy were calculated. By doping the different rare earth elements, the systems show different changing in the crystal structure, hopping amplitude, and electrical resistivity. Among these doping compounds, the Eu_0.25Ca_0.75MnO₃ exhibits the strongest structural change corresponding to the largest Jahn–Teller splitting.     

Optimising industrial hemp fibre for composites

The optimisation of New Zealand grown hemp fibre for inclusion in composites has been investigated. The optimum growing period was found to be 114 days, producing fibres with an average tensile strength of 857 MPa and a Young’s modulus of 58 GPa. An alkali treatment with 10 wt% NaOH solution at a maximum processing temperature of 160 °C with a hold time of 45 min was found to produce strong fibres with a low lignin content and good fibre separation. Although a good fit with the Weibull distribution function was obtained for single fibre strength, this did not allow for accurate scaling to strengths at different lengths. Alkali treated fibres, polypropylene and a maleated polypropylene (MAPP) coupling agent were compounded in a twin-screw extruder, and injection moulded into composite tensile test specimens. The strongest composite consisted of polypropylene with 40 wt% fibre and 3 wt% MAPP, and had a tensile strength of 47.2 MPa, and a Young’s modulus of 4.88 GPa.     

The potential of harakeke fibre as reinforcement in polymer matrix composites including modelling of long harakeke fibre composite strength

Mechanical properties of aligned long harakeke fibre reinforced epoxy with different fibre contents were evaluated. Addition of fibre was found to enhance tensile properties of epoxy; tensile strength and Young’s modulus increased with increasing content of harakeke fibre up to 223 MPa at a fibre content of 55 wt% and 17 GPa at a fibre content of 63 wt%, respectively. The flexural strength and flexural modulus increased to a maximum of 223 MPa and 14 GPa, respectively, as the fibre content increased up to 49 wt% with no further increase with increased fibre content. The Rule of Mixtures based model for estimating tensile strength of aligned long fibre composites was also developed assuming composite failure occurred as a consequence of the fracture of the lowest failure strain fibres taking account porosity of composites. The model was shown to have good accuracy for predicting the strength of aligned long natural fibre composites.     

Investigation on preparation and spectroscopic properties of Yb2+-doped silica-based glass prepared by the oxyhydrogen flame fusing process

In this paper, we report the preparation and spectroscopic properties of Yb²⁺-doped silica-based glass prepared by the solid state reaction using the oxyhydrogen flame fusing process. The glass exhibits broadband emission in the visible region due to a 5d–4f transition of the rare earth ions. The emission peak wavelength and bandwidth are especially 505 nm and 147 nm for Yb²⁺-doped silica-based glass at the room temperature. The color coordinate calculation shows that the Yb²⁺-doped silica-based glass has a better color coordinate (0.28, 0.37) in the white light region.     

Computational design of electrostatic potential to maximise or minimise adhesion to surfaces

The free energy of adsorption based on electrostatic interactions only has been optimised for glycine on a (111) diamond surface in continuum water to show maximum adhesion or maximum repulsion by adjusting the partial point charge distribution in the diamond surface model. It has been found that the free energy of adhesion is readily maximised by means of increasing the polarity of the electrostatic surface potential in a distinctive dipolar pattern. The maximum adhesion obtained in the present calculations was ? 21.02 ± 0.49 kJ mol^? 1. The surface with the maximum repulsion, which would be of particular interest for designing novel surfaces with low protein adsorption, had a mostly uniform, slightly positive, surface electrostatic potential with a specific irregular pattern. The maximum free energy of repulsion achieved in the present simulations was 0.08 ± 0.01 kJ mol^? 1. These values suggest that most real surfaces are more likely to be overall attractive due to electrostatic interactions of the partial surface charges, and that the overall energy of repulsion, although theoretically possible, is likely to be small.     

Effect of short nylon-6 fibres on natural rubber-toughened polystyrene

Composites based on polystyrene and natural rubber at a ratio of 85/15 were prepared by melt mixing with nylon-6 fibres using an internal mixer. The loading of short nylon-6 fibre, untreated and resorcinol formaldehyde latex (RFL)-treated, was varied from 0 to 3 wt.%. Tensile and flexural test samples were punched out from sheets and tested to study the variation of mechanical and dynamic mechanical properties. The tensile behaviour of the composite has been determined at three different strain rates (4.1 × 10⁻⁴ s⁻¹, 2 × 10⁻³ s⁻¹ and 2 × 10⁻² s⁻¹). Both the tensile strength and Young’s modulus of the composite increased with strain rate. The tensile strength, tensile modulus, flexural strength and flexural modulus increased with the increase in fibre content up to 1 wt.%, above which there was a significant deterioration in the properties. The RFL-treated fibre composites showed improved mechanical properties compared to the untreated one. Dynamic mechanical analysis (DMA) showed that the storage modulus of the composite with RFL-treated fibre was better compared to the untreated one. The fibre–matrix morphology of the tensile fractured specimens was studied by scanning electron microscopy (SEM). The results suggested that the RFL treatment of nylon fibre promoted adhesion to the natural rubber phase of the blend, thereby improving the mechanical properties of the composite.     

Mechanical properties of soil buried kenaf fibre reinforced thermoplastic polyurethane composites

A study on mechanical properties of soil buried kenaf fibre reinforced thermoplastic polyurethane (TPU) composites is presented in this paper. Kenaf bast fibre reinforced TPU composites were prepared via melt-mixing method using Haake Polydrive R600 internal mixer. The composites with 30% fibre loading were prepared based on some important parameters; i.e. 190 °C for reaction temperature, 11 min for reaction time and 400 rpm for rotating speed. The composites were subjected to soil burial tests where the purpose of these tests was to study the effect of moisture absorption on the mechanical properties of the composites. Tensile and flexural properties of the composites were determined before and after the soil burial tests for 20, 40, 60 and 80 days. The percentages of both moisture uptake and weight gain after soil burial tests were recorded. Tensile strength of kenaf fibre reinforced TPU composite dropped to ∼16.14 MPa after 80 days of soil burial test. It was also observed that there was no significant change in flexural properties of soil buried kenaf fibre reinforced TPU composite specimens.     

The effect of post-cure duration on the mode I interlaminar fracture toughness of glass-fibre reinforced vinylester

The effect of different post-cure conditions on the mode I fracture toughness of a vinylester resin and its glass-fibre reinforced composite counterpart has been studied. Two sets of parameters were investigated. The first was the post-cure duration at constant temperature; 90°C for 1, 4 and 24 h. The second, for resin toughness only, was a combination of post-cure temperature and duration; 90°C/4 h, 80°C/8 h and 70°C/16 h. The results show that the post-cure increases toughness. This trend is consistent between the pure resin and the fibre composite for all treatments, except at 90°C/24 h. It is believed that the prolonged post-cure duration of 24 h has weakened the bond strength at the fibre–matrix interface, thus reducing the effectiveness of toughness transfer from the matrix to the composite. The study concludes that the post-cure enhances the toughness of the glass-fibre/vinylester composite, mainly due to the increase of resin toughness.     

Three kinds of charcoal powder reinforced ultra-high molecular weight polyethylene composites with excellent mechanical and electrical properties

Highly filled charcoal powder reinforced ultra-high molecular weight polyethylene (UHMWPE) composites with tunable electrical conductivity and good mechanical properties were prepared using extrusion and hot-compression techniques. Three kinds of charcoal carbonized under various temperatures were used in this study. The scanning electron microscopy showed that charcoal powder was dispersed uniformly in the UHMWPE matrix and strong interfacial interaction was achieved. The tensile test results showed that with the incorporation of charcoal powder, the tensile strength increased by 325%, 262% and 203% respectively compared to neat UHMWPE. Furthermore, the composites containing 70 wt.% charcoal powder (above 700 °C) exhibited good electrical conductivity, which is adequate for many electrical applications. It was obvious that the storage modulus of all the composites increased remarkably with the incorporation of charcoal powder, E′ reached 30.2, 26.8 and 25.9 GPa for samples PC1100/UHMWPE, AC1100/UHMWPE and BC1100/UHMWPE at − 150 °C respectively.     

Effects of Si addition on microstructure and mechanical properties of Mg–8Gd–4Y–Nd–Zr alloy

Effects of Si addition (1.0 wt.%) on microstructure and mechanical properties of Mg–8Gd–4Y–Nd–Zr alloy have been investigated using scanning electron microscopy (SEM) equipped with energy dispersive spectrum (EDS), X-ray diffraction (XRD), hardness measurements and tensile testing. The results indicated that the addition of Si led to the formation of Mg₂Si and (RE + Si)-rich particles, which enhanced the Young’s modulus of the alloy by 7 GPa while decreased the yield strength and ultimate strength by 10 MPa and 31 MPa, respectively. The tensile properties of the Mg–8Gd–4Y–Nd–Zr–Si alloy are as follows: Young’s modulus E = 51 GPa, yield strength σ_0.2 = 347 MPa, ultimate strength σ_b = 392 MPa and elongation δ = 2.7%. The increase in Young’s modulus was attributed to the formation of particles with high Young’s modulus, while the decrease in strength was ascribed to the decrease in volume fraction of metastable β′ precipitates caused by the consumption of rare earth atoms due to the formation of the rare earth containing particles.     

Aramid fibers reinforced silica aerogel composites with low thermal conductivity and improved mechanical performance

Aramid fibers reinforced silica aerogel composites (AF/aerogels) for thermal insulation were prepared successfully under ambient pressure drying. The microstructure showed that the aramid fibers were inlaid in the aerogel matrix, acting as the supporting skeletons, to strengthen the aerogel matrix. FTIR revealed AF/aerogels was physical combination between aramid fibers and aerogel matrix without chemical bonds. The as prepared AF/aerogels possessed extremely low thermal conductivity of 0.0227 ± 0.0007 W m⁻¹ K⁻¹ with the fiber content ranging from 1.5% to 6.6%. Due to the softness, low density and remarkable mechanical strength of aramid fibers and the layered structure of the fiber distribution, the AF/aerogels presented nice elasticity and flexibility. TG–DSC indicated the thermal stability reaching approximately 290 °C, can meet the general usage conditions, which was mainly depended on the pure silica aerogels. From mentioned above, AF/aerogels present huge application prospects in heat preservation field, especially in piping insulation.