Improvement in ballistic impact resistance of a transparent bulletproof material laminated with strengthened soda-lime silicate glass

This study evaluates the ballistic impact resistance of soda-lime silicate glass strengthened by ion exchange for application in lightweight and thin bulletproof materials. The maximum flexural strength values of the strengthened glass with thicknesses of 3, 4, 8, and 10 mm were 0.63, 0.68, 0.73, and 0.77 GPa, respectively, values that were 3.5 times higher than that of the parent glass. By laminating polycarbonate and multilayer defense film with the strengthened glass, we achieved a ballistic limit velocity of 973.8 m/s, which was 16% higher than the standard. Also, the transmittance satisfied the standard for bulletproof windows.     

Fluorescence properties and relaxation processes of Tb3+ ions in ZnCl2-based glasses

60ZnCl₂–20KCl–20BaCl₂–xTbCl₃ glasses (x = 0.10, 0.25, 0.50, 0.75, 1.00, and 1.25) were prepared by melt-quenching method, and Tb³⁺ fluorescence properties were investigated under 355 nm excitation. Regardless of x values, the electrons that were relaxed from the ⁵D₃ to ⁵D₄ level of Tb³⁺ ions by the multiphonon relaxation, were repressed to 28% of all the excited electrons because the ZnCl₂-based glass had much lower phonon energy than oxide glasses. For 0 < x ≤ 0.34, the cross relaxation, (⁵D₃ → ⁵D₄) → (⁷F₀ ← ⁷F₆), was repressed, and consequently 72% and 28% of all the excited electrons were radiatively relaxed by the ⁵D₃ → ⁷F_J (J = 6, 5, 4, 3, and 2) and ⁵D₄ → ⁷F_J (J = 6, 5, 4, and 3) transitions, respectively. The lifetimes of the ⁵D₃ and ⁵D₄ initial levels were obtained to be 1.1 and 2.1 ms, respectively.     

The effect of reprocessing on the mechanical properties of polypropylene reinforced with wood pulp,flax or glass fibre

Composites of polypropylene, substitutable for a given application and reinforced with: Medium Density Fibreboard fibre (MDF) (40 wt%); flax (30 wt%); and glass fibre (20 wt%), were evaluated after 6 injection moulding and extrusion reprocessing cycles. Of the range of tensile, flexural and impact properties examined, MDF composites showed the best mean property retention after reprocessing (87%) compared to flax (72%) and glass (59%). After 1 reprocessing cycle the glass composite had higher tensile strength (56.2 MPa) compared to the MDF composite (44.4) but after 6 cycles the MDF was stronger (35.0 compared to 29.6 MPa for the glass composite). Property reductions were attributed to reduced fibre length. MDF fibres showed the lowest reduction in fibre length between 1 and 6 cycles (39%), compared to glass (51%) and flax (62%). Flax fibres showed greater increases in damage (cell wall dislocations) with reprocessing than was shown by MDF fibres.     

Novel method for determination of critical fiber length in short fiber carbon/carbon composites by double lap joint

A novel approach is introduced for the experimental determination of critical fiber length in carbon fiber reinforced carbon (CFRC) composites. Critical fiber length is investigated using double lap joint samples. The transition of failure mode from bonding failure to fiber fraction with increasing overlap length correlates with the critical fiber length. Tested overlap lengths were in the range of 4–100 mm. For CFRC at hand, failure mode changes at an overlap length of 26 ± 2 mm. Hence critical fiber length is derived as l_c = 52 ± 4 mm.     

Durability of GFRP nanocomposites subjected to hygrothermal ageing

This paper presents long term durability prediction of 0–5 wt.% nanoclay/vinylester/glass fibre nanocomposites based on their tensile strength retention in accelerated hygrothermal ageing using Arrhenius rate model. The specimens were exposed to 30 °C, 50 °C and 60 °C and 95% relative humidity for 75 days and tested for tensile strength retention as a function of duration of exposure. The predicted tensile strength retentions for one year of ageing of vinylester/glass at 30 °C, 50 °C and 60 °C using Arrhenius rate model were 59%, 48% and 43% respectively. The corresponding strength retentions predicted for 4 wt.% nanoclay/vinylester/glass were 81.1%, 77.9% and 76.4%. Strength retentions for ten years were predicted using the analytical model to assess their long-term performance.     

3D architecture reduced graphene oxide-MoS2 composite: Preparation and excellent electromagnetic wave absorption performance

High-performance electromagnetic absorbers with wide absorption band, strong absorption and lightweight are necessary for industry and military application. To obtain the desired materials, two-dimensional (2D) atomic layers structure nanosheets, such as graphene and graphene-like, were adopted due to its unique structure and properties. Here, 3D architecture reduced graphene oxide-molybdenum disulfide (RGO-MoS₂) composite was prepared by one-pot hydrothermal reaction. MoS₂ generated on graphene oxide intercalation through hydrothermal process and rGO is obtained in the meanwhile. 3D architecture RGO-MoS₂ composite can effectively prevent two-dimensional nanosheets re-stacked and can be applied in electromagnetic wave absorption field. In this paper, composites consist of RGO and various MoS₂ were prepared and their electromagnetic performances were investigated for the first time. Maximum absorption bandwidth (R_L < −10 dB) is 5.92 GHz with thickness of 2.5 mm. We may reasonably conclude that RGO-MoS₂ composite can serve as excellent light-weight electromagnetic wave absorbers and can be widely used in practice.     

Engineering properties of lightweight aggregate concrete made from dredged silt

Silt dredged from reservoirs can be hydrated and sintered into lightweight aggregate for producing lightweight aggregate concrete (LWAC). The densified mixture design algorithm (DMDA) was employed to manufacture LWAC using 150 kg/m³ of water at different water-to-binder ratios (w/b = 0.28, 0.32 and 0.4) using lightweight aggregates of different particle densities (800, 1100 and 1500 kg/m³). The engineering properties of the LWAC thus obtained were examined. Results show that the fresh concrete meets the design requirement of having slump of 250 ± 20 mm and slump flow of 600 ± 100 mm. With respect to hardened properties, the compressive strength, ultrasonic pulse velocity and thermal conductivity were found to decrease with increasing w/b ratio but increase with increasing aggregate density. Moreover, higher aggregate density also resulted in less shrinkage. The surface resistivity exceeding 20 kΩ-cm also matched the design objective. The experimental results prove that LWAC made from dredged silt can help enhance durability of concrete.     

Bifunction in Er3+/Yb3+ co-doped BaTi2O5–Gd2O3 glasses prepared by aerodynamic levitation method

Novel Er³⁺/Yb³⁺ co-doped BaTi₂O₅–Gd₂O₃ spherical glasses have been fabricated by aerodynamic levitation method. The thermal stability, upconversion luminescence, and magnetic properties of the present glass have been studied. The glasses show high thermal stability with 763.3 °C of the onset temperature of the glass transition. Red and green emissions centered at 671 nm, 548 nm and 535 nm are obtained at 980 nm excitation. The upconversion is based on a two-photon process by energy transfer, excited-state absorption, and energy back transfer. Yb³⁺ ions are more than Er³⁺ ions in the glass, resulting in efficient energy back transfer from Er³⁺ to Yb³⁺. So the red emission is stronger than the green emissions. Magnetization curves indicate that magnetic rare earth ions are paramagnetic and the distribution is homogeneous and random in the glass matrix. Aerodynamic levitation method is an efficient way to prepare glasses with homogeneous rare earth ions.     

Scaling resistance of high performance concretes containing a small portion of pre-wetted lightweight fine aggregate

The subject of the investigation was the influence of pre-wetted lightweight aggregate on damage of the concrete surface due to cyclic freezing and thawing in the presence of de-icing salts tested according to the Swedish Standard SS 13 72 44 (the Borås method). Six series of concrete specimens were made with the same water/binder (w/b) ratio 0.32, cement volume 400 kg/m³ and content of superplasticiser 8.8 kg/m³. One series, S3/2, contained an air-entraining agent. Series S4/7 and S4/8 were made with water/cement ratio equal to 0.45 and a lower cement content 340 kg/m³. In a few series the sand fraction 0–2 mm and basalt fraction 2–4 mm were partly or totally replaced by wetted lightweight aggregate. Concretes S3/1, S3/3, S4/7 and S4/8, failed the test. The best results were obtained for concrete S3/6 (with the 2–4 mm fraction replaced by half) and S3/2 (air-entrained). The application of an air-entraining agent is more expensive than LWA, and at a construction site it is not always easy to control. It seems that the replacement of a part of aggregate by LWA could be a more effective way to improve the scaling resistance.     

Influence of the process parameters on the mechanical properties of engineering biocomposites using a twin-screw extruder

The utilization of bio-based engineering polymers as a matrix material for cellulosic fiber reinforced composites has become an important focus in materials research. This is due to a rising demand for sustainable materials from renewable resources. In addition to this aspect, the bio-based materials provide an advantage for lightweight applications with their lower density. In this investigation, the completely bio-based polyamide 10.10, with a melting point above 200 °C, was used as a polymer matrix. Chopped man-made cellulose fibers (Cordenka CR-Type) were investigated as reinforcement for use in injection molded applications. A co-rotating twin-screw extruder with a screw-diameter of 18 mm was used for compounding. It was verified that reinforcing polyamide 10.10 with 20 wt% and 30 wt% cellulosic fibers is possible, resulting in an increase of impact and tensile properties. Furthermore, it was shown that the temperatures and screw-configurations of the twin-screw extruder only result in different fiber length distributions but in minor differences of the morphological structure and mechanical properties of PA 10.10 with 20 wt% fibers. Compounds with 30 wt% cellulose fibers show significant higher impact properties that those with 30 wt% glass fibers.     

Fabrication of polypyrrole/nano-exfoliated graphite composites by in situ intercalation polymerization and their microwave absorption properties

Polypyrrole/nano-exfoliated graphite composites were synthesized using an in situ intercalation polymerization of pyrrole into the layers of expanded graphites. The morphologies and nanostructures of obtained composites were characterized by field emission scanning electron microscopy, transmission electron microscopy and X-ray diffraction analysis. Results showed that the in situ intercalation polymerization of pyrrole cation into the layers of expanded graphites could separate graphite into nano-exfoliated graphite sheets. The interactions between polypyrrole and the graphite sheet were also confirmed by Fourier transformed infrared spectroscopy. The fabricated nanocomposites polypyrrole/nano-exfoliated graphite-1.5 showed obvious improvement in microwave absorption compared with those of the polypyrrole or the expanded graphite itself. With a thickness of 2.7 mm, the optimal absorption peak reached −48 dB at 13.4 GHz and the bandwidth corresponding to the reflection loss at −10 dB was 3.4 GHz (from 13.2 to 16.6 GHz). The minimum RL reached −34 dB with a thickness of 2.5 mm for Polypyrrole/nano-exfoliated graphite-1.5. Moreover, it could be observed that the absorption bandwidth with RL below −10 dB was obtained in the frequency range of 5–18 GHz for polypyrrole/nano-exfoliated graphite-1.5 with a thickness of 2–5 mm. This would open a path toward the fabrication of microwave absorption materials of light-weight.     

Broad bandwidth of thin composite radar absorbing structures embedded with frequency selective surfaces

The three-layer ultrathin radar absorbing structure (RAS) involving a frequency selective surface (FSS) exhibiting excellent broad bandwidth properties is designed and fabricated. The EW and flaky carbonyl iron powders were used to produce two kinds of silicone rubber matrix magnetic composites for the top and the bottom layer, respectively. The electromagnetic parameters of the composites were measured in the frequency range of 2–18 GHz. The middle layer is an FSS in the form of double-square loops with four micro-split gaps in the middle of the outer loop. The results show that the proposed RAS can provide a 10 dB absorbing bandwidth of 13.2 GHz from 4.8 to 18 GHz (1.7 mm thickness) and a 10 dB absorbing bandwidth of 14.1 GHz from 3.9 to 18 GHz, covering C-band, X-band and Ku-band (2.0 mm thickness). A good match between simulation and measurement results demonstrates the validity of our design.     

Effect of stitch density on fatigue characteristics and damage mechanisms of stitched carbon/epoxy composites

The effect of stitch density (SD) on fatigue life, stiffness degradation and fatigue damage mechanisms in carbon/epoxy (T800SC/XNRH6813) stitched using Vectran thread is presented in this paper. Moderately stitched composite (SD = 0.028/mm²; ‘stitched 6 × 6’) and densely stitched composite (SD = 0.111/mm²; ‘stitched 3 × 3’) are tested and compared with composite without stitch thread (SD = 0.0; ‘unstitched’). The experiments show that the fatigue life of stitched 3 × 3 is moderately better than that of unstitched and stitched 6 × 6. Stitched 3 × 3 pattern is also able to postpone the stiffness degradation onset. The improvement of fatigue properties and postponement of stiffness degradation onset in stitched 3 × 3 is primarily due to an effective impediment of edge-delamination. Quantification of damage at various cycles and stress levels shows that stitch density primarily affects the growth rate of delamination.     

Chemical bonding and optoelectrical properties of ruthenium doped yttrium oxide thin films

Highly infrared transparent conductive ruthenium doped yttrium oxide (RYO) films were deposited on zinc sulfide and glass substrates by reactive magnetron sputtering. The structural, optical, and electrical properties of the films as a function of growth temperature were studied. It is shown that the sputtered RYO thin films are amorphous and smooth surface is obtained. The infrared transmittance of the films increases with increasing the growth temperature. RYO films maintain greater than ∼65% transmittance over a wide wavelength range from 2.5 μm to 12 μm and the highest transmittance value reaches 73.3% at ∼10 μm. With increasing growth temperature, the resistivity changed in a wide range and lowest resistivity of about 3.36 × 10⁻³ Ω cm is obtained at room temperature. The RYO thin films with high conductivity and transparency in IR spectral range would be suitable for infrared optical and electromagnetic shielding devices.     

Exploring mechanical property balance in tufted carbon fabric/epoxy composites

The paper details the manufacturing processes involved in the preparation of through-the-thickness reinforced composites via the ‘dry preform–tufting–liquid resin injection’ route. Samples for mechanical testing were prepared by tufting a 5 harness satin weave carbon fabric in a 3 mm × 3 mm square pitch configuration with a commercial glass or carbon tufting thread, infusing the reinforced preforms with liquid epoxy resin and curing them under moderate pressure. The glass thread reinforcement increases the compression-after-impact strength of a 3.3 mm thick carbon fabric laminate by 25%. The accompanying drop-downs in static tensile modulus and strength of the same tufted laminate are below 10%. The presence of tufts is also shown to result in a significant increase in the delamination crack growth resistance of tufted double-cantilever beam specimens and has been quantified for the case of a 6 mm thick tufted carbon non-crimped fabric (NCF)/epoxy composite.     

Characterization of friction stir welded boron carbide particulate reinforced AA6061 aluminum alloy stir cast composite

Development of welding procedures to join aluminum matrix composite (AMCs) holds the key to replace conventional aluminum alloys in many applications. In this research work, AA6061/B₄C AMC was produced using stir casting route with the aid of K₂TiF₆ flux. Plates of 6 mm thickness were prepared from the castings and successfully butt joined using friction stir welding (FSW). The FSW was carried out using a tool rotational speed of 1000 rpm, welding speed of 80 mm/min and axial force of 10 kN. A tool made of high carbon high chromium steel with square pin profile was used. The microstructure of the welded joint was characterized using optical and scanning electron microscopy. The welded joint showed the presence of four zones typically observed in FSW of aluminum alloys. The weld zone showed fine grains and homogeneous distribution of B₄C particles. A joint efficiency of 93.4% was realized under the experimental conditions. But, FSW reduced the ductility of the composite.     

Alkaline aluminum phosphate glasses for thermal ion-exchanged optical waveguide

Alkaline aluminum phosphate glasses (NMAP) with excellent chemical durability for thermal ion-exchanged optical waveguide have been designed and investigated. The transition temperature Tg (470 °C) is higher than the ion-exchange temperature (390 °C), which is favorable to sustain the stability of the glass structure for planar waveguide fabrication. The effective diffusion coefficient D_e of K⁺–Na⁺ ion exchange in NMAP glasses is 0.110 μm²/min, indicating that ion exchange can be achieved efficiently in the optical glasses. Single-mode channel waveguide has been fabricated on Er³⁺/Yb³⁺ doped NMAP glass substrate by standard micro-fabrication and K⁺–Na⁺ ion exchange. The mode field diameter is 9.6 μm in the horizontal direction and 6.0 μm in the vertical direction, respectively, indicating an excellent overlap with a standard single-mode fiber. Judd–Ofelt intensity parameter Ω₂ is 5.47 × 10⁻²⁰ cm², implying a strong asymmetrical and covalent environment around Er³⁺ in the optical glasses. The full width at half maximum and maximum stimulated emission cross section of the ⁴I_13/2 → ⁴I_15/2 are 30 nm and 6.80 × 10⁻²¹ cm², respectively, demonstrating that the phosphate glasses are potential glass candidates in developing compact optoelectronic devices. Pr³⁺, Tm³⁺ and Ho³⁺ doped NMAP glasses are promising candidates to fabricate waveguide amplifiers and lasers operating at special telecommunication windows.     

Magnetic properties of nanocrystalline ɛ-Fe3N and Co4N phases synthesized by newer precursor route

Nanocrystalline ɛ-Fe₃N and Co₄N nitride phases are synthesized first time by using tris(1,2-diaminoethane)iron(II) chloride and tris(1,2-diaminoethane)cobalt(III) chloride precursors, respectively. To prepare ɛ-Fe₃N and Co₄N nitride phases, the synthesized precursors were mixed with urea in 1:12 ratio and heat treated at various temperatures in the range of 450–900 °C under the ultrapure nitrogen gas atmosphere. The precursors are confirmed by FT-IR study. The ɛ-Fe₃N phase crystallizes in hexagonal structure with unit cell parameters, a = 4.76 Å and c = 4.41 Å. The Co₄N phase crystallizes in face centred cubic (fcc) structure with unit cell parameters, a = 3.55 Å. The estimated crystallite size for ɛ-Fe₃N and Co₄N phases are 29 nm and 22 nm, respectively. The scanning electron microscopy (SEM) studies confirm the nanocrystalline nature of the materials. The values of saturation magnetization for ɛ-Fe₃N and Co₄N phases are found to be 28.1 emu/g and 123.6 emu/g, respectively. The reduction of magnetic moments in ultrafine materials compared to bulk materials have been explained by spin pairing effect, lattice expansion, superparamagnetic behaviour and canted spin structures at the surface of the particles.     

Synthesis and properties of sandwiched films of epoxy resin and graphene/cellulose nanowhiskers paper

Graphene (GN)-based composite paper containing 10 wt.% cellulose nanowhiskers (CNWs) exhibiting a tensile strength of 31.3 MPa and electrical conductivity of 16 800 S/m was prepared by ultrasonicating commercial GN powders in aqueous CNWs suspension. GN/CNWs freestanding paper was applied to prepare the sandwiched films by dip coating method. The sandwiched films showed enhanced tensile strength by over two times higher than the neat resins. The moduli of the sandwiched films were around 300 times of the pure resins due to the high content of GN/CNWs paper. The glass transition temperature of the sandwiched films increased from 51.2 °C to 57.1 °C for pure epoxy (E888) and SF (E888), and 49.8 °C to 64.8 °C for pure epoxy (650) and SF (650), respectively. The bare conductive GN/CNWs paper was well protected by the epoxy resin coating, which is promising in the application as anti-static materials, electromagnetic interference (EMI) shielding materials.     

The effect of processing temperature and placement rate on the short beam strength of carbon fibre–PEEK manufactured using a laser tape placement process

The ability of a modern near infra-red laser tape placement system to produce high-quality laminates is investigated by performing short beam strength tests on samples manufactured at different process temperatures from 400 °C to 600 °C at placement rates of 100 mm/s and 400 mm/s. The temperature history in tape placement is highly dynamic and the correlation between the process control temperature, laser power and the consolidation temperature is not well understood. The complete temperature history was therefore estimated with a previously developed optical-thermal model and validated using long wave infra-red imaging. Short beam strengths equivalent to conventional manufacturing methods were found for placement rates of 400 mm/s. Failure modes of the samples were elucidated by scanning electron microscopy of the fracture surfaces. Signs of degradation were observed on samples prepared with a 600 °C process temperature at 100 mm/s, however none was evidenced at 400 mm/s for the same process temperature.