ABSTRACT In order to realize the quantitative analysis of the structural integrity and damage evolution of hydroxyl-terminated polybutadiene (HTPB) composite solid propellant under external load, the loading failure experiments were carried out on the macro rectangular specimen and the micro specimen, and the numerical analysis of the strain evolution process in the region of interest (ROI) of the specimen was carried out using digital image correlation (DIC). At the same time, with the help of finite element model updating (FEMU) method, the mechanical and cohesion parameters of the specimen were inversed using the combination of adaptive particle swarm optimization (APSO), back propagation (BP) and Hooke-Jeeves algorithm, and the simulation of the whole process of propellant damage and fracture was realized from the microscopic point of view. The results show that inhibiting the debonding of propellant/liner interface is the key to maintain the structural integrity. It starts with the damage and fracture of the propellant side. A scanning electron microscope (SEM) in-situ dynamic tensile test shows that the initial damage occurs at the strain of 27.368%, and the through-type crack propagates along the interface when the strain reaches 43.276%. In addition, the use of combinatorial optimization algorithm can realize the global optimal inversion of 16 parameters divided into three types in 100 complete calculations, reduce the optimal objective function value to 0.0251, and assist the finite element calculation to realize the quantitative analysis and accurate simulation of the experimental process.

ABSTRACT 3D-Network SiC ceramic was prepared using a polymer sponge replica technique with SiC ceramic slurry (77 wt% solid content). The triangular hole defects in 3D-Network SiC ceramic were reduced and the mechanical properties were improved by high-pressure spraying and vacuum infiltration. The 3D-Network SiC/Cu composite material was fabricated by the gravity casting technique, and the interfacial bonding and abrasion resistance of the composites were tested and analyzed. The results show that the compressive strength of high-pressure sprayed 3D-Network SiC ceramic increased slightly from 0.67 Mpa to 0.74 Mpa due to the triangular hole defects left when the polymer sponge was decomposed at high temperatures. The mechanical properties of 3D-Network SiC ceramics that have been vacuum infiltrated in alumina and a mixture composed of alumina and andalusite were greatly improved, and their compressive strength was increased to 1.02Mpa and 1.57Mpa, respectively. The interface between SiC and Cu in the 3D-Network SiC/Cu composites prepared by different processes shows excellent bonding, and the abrasion resistance of the 3D-Network SiC/Cu composites prepared by different processes was 2.02–9.18 times that of pure copper respectively.

ABSTRACT In order to increase the interfacial adhesion between polybutylene succinate and coconut shell particles, two kinds of chemical treatment of coconut shell particle were carried out. Firstly, a 5% sodium hydroxide treatment and secondly, a 2% sodium hydroxide plus silane coupling agent treatment. The possibility of increasing matrix adhesion has also been explored through addition of polycaprolactone to polybutylene succinate as a matrix. Composites were produced using extrusion prior to injection moulding. The results show that, compared with neat polybutylene succinate, composites with low percentage of particle loading have a higher tensile strength and strain at break despite their lower elastic modulus. A higher elastic modulus can be obtained for composites with higher particle loadings through sacrifice of their ductility. The same trend is observed for composites with the polymer-blend matrix. Scanning electron micrographs show good adhesion between particle and matrix for particles that undergo the second treatment. At low percentage of particle addition, the crystallinity of the composites is higher than the neat polybutylene succinate, however melting temperature is less affected by the addition of reinforcement. Rheological properties such as storage modulus, loss modulus and complex viscosity of the composites are higher than for neat polybutylene succinate.

ABSTRACT Amphiphilic Silane coupling agent (SCA) improves the weak bond between the two phases of rubber and hydration products, fills the interfacial gaps and effectively repairs the interfacial defects between rubber and hydration products. The addition of PVA fibers mainly improves the cracking performance and durability of concrete. However, most of the studies addressing this issue have been limited to phenomenology, ignoring the mechanism of action at the atomic structure level. Therefore, this study investigates the strengthening mechanism of the interfacial properties of KH-560 coupling agent-reinforced PVA fiber-rubber concrete from the multi-scale analysis of macro-mechanical properties, micro and fine structure, chemical composition and nano-optical level. Based on the results of macro-mechanical tests, it was found that the KH-560 coupling agent could improve the compressive, flexural and shear strength of PVA-rubber concrete, so that the damage morphology also changed from brittle damage to plastic damage, and the compressive strength of concrete was slightly reduced due to the addition of PVA, but the durability and cracking resistance were enhanced. XRD (X-ray diffraction), FT-IR (Fourier transform infrared spectroscopy) and SEM (scanning electron microscopy) tests observed the presence of some gels and polymers that filled the interfacial slits and effectively repaired the interfacial defects. The two-phase interface was simulated by molecular dynamics at the nano level, and it was found that KH560 molecules could be closely connected with C-S-H gel collectively through Si-O-Si chemical bonding, and KH560 molecular bonds were unevenly distributed between the C-S-H and rubber interfaces, while the addition of modifier KH560 and PVA fibers caused more hydrogen and ionic bonds at the interface, which enhanced the interfacial interaction energy. Systematic experiments were conducted on PVA fiber-rubber soil materials before and after SCA modification under macroscopic, microscopic, fine and nano-level multi-scale analyses, which ultimately lead to the design and performance improvement of SCA modification of PVA-rubber cement-based materials in a multi-scale framework. The graphic summary is shown in Figure 1.

ABSTRACT Basalt fibers (BF)-reinforced double-layered resin composite with excellent absorption performance in X band (8.2–12.4 GHz) has been designed, choosing carbon black (CB) and nano-Fe3O4 as absorbent for absorbing layer and matching layer, respectively. The electromagnetic parameters of the composites were measured by vector network analyzer using waveguide method. The calculated result suggests that an increased amount of absorbent could significantly improve the microwave absorbability of the single-layered composites in the measured frequency. For double-layered composites, the optimum microwave absorption performance can be obtained by tailoring the electromagnetic parameters and thicknesses of each layer. The minimum reflection loss of −43.97 dB and full X band effective absorption can be achieved when the thickness of the matching layer (BF/Fe3O410) and absorbing layer (BF/CB7.5) were 0.3 mm and 2.7 mm, respectively. Therefore, utilization of dielectric loss, magnetic loss absorbent and BF/resin double-layered structure has designed flexibility, and contributes to promote the development of high-performance microwave absorbing composites.

ABSTRACT Natural fiber-reinforced polymer composites are presently receiving the attention of scholars and industrialists due to their specific properties, such as being naturally eco-friendly, biodegradable, economical, viable, available, and sustainable. The key problems associated with natural fiber polymer composites, including fiber/matrix compatibility, high moisture absorption, and, especially, thermal degradation in engineering plastics (high-temperature plastics), constitute the most critical thrust of this review. It is noted that at high temperatures, natural fibers degrade and this has adversely restricted their usage with only commodity thermoplastics having relatively low melting temperatures, such as polypropylene (PP) and polyethylene (PE). This review paper, therefore, provides valuable research highlights on utilizing and improving the mechanical and thermal properties of natural kenaf fibers as reinforcement in engineering polymer composites for high-temperature engineering applications using polymer matrices, such as polyethylene terephthalate (PET), acrylonitrile butadiene styrene (ABS), and polyphenylene ether (PPE). The initial and various chemical treatments of natural fibers, their effect on the thermal and performance properties of natural fiber engineering thermoplastic composites, and the advanced treatment of epoxy coatings are reviewed. Applications of natural fiber-reinforced thermoplastic composites in the construction and automotive industries, as well as in other applications, are outlined. It was established that the adhesion and thermal stabilities between polymer matrix and natural fibers are better improved by surface coating with diluted epoxy resin thermoset. This eventually improved the overall thermal and performance properties of the resultant composites and will serve as a data bank and guide for manufacturers and future research directions using high-end engineering polymers with higher processing temperatures.

ABSTRACT The interface characteristics and formation mechanism of explosive welded waveform structures still lack a detailed and in-depth research. Thus, a combination of advanced characterization and numerical simulation methods were performed in this study to investigate the phase constitution, texture distribution, 3D interface morphology and wave formation mechanism of Sn/Cu explosive welded interface. The microstructure analyses indicated that the typical waveform structures composed of fine crystal band and elongated grains zone were formed at the Sn/Cu joining interface. The dynamic recrystallized structures and local high strain at the waveform were attributed to severe rheological deformation and rapid solidification of liquid metals. In addition, the S, copper, brass and fiber deformation textures and the cube and gross recrystallization textures were found. The CT results indicated the 3D Sn/Cu joining interface morphology presents a regular convex waveform feature, which is related to periodic pulse load caused by explosive detonation. Furthermore, based on the simulation results, the 2D joining interface presents similar experimental waveform structure, and the 3D interface evolution characteristic was consistent with the shock wave propagation characteristics on the flying plate to some extent, which was in good agreement with the experimental results.

ABSTRACT Banana fibers are cost-effective, abundantly available and environmentally sustainable, but they often have some drawbacks, such as hydrophilicity and performance variations. The experimental approach is intended to be used in this work to examine the effects of cold glow discharge argon plasma modification on the surface of banana fibers. The emphasis is on examining the mechanisms that underlie the morphological and chemical changes observed in banana fibers, as well as identifying the mechanisms that enhance the fiber–matrix interface and, as a consequence, the mechanical properties of the laminates. Significant improvements were observed for epoxy matrix laminates reinforced with banana fibers when the surface of the banana fibers was modified by plasma of argon gas (Ar) gas with varying power densities of 80,120 W for 30 min, which changed the surface chemical characteristics. The FTIR and XRD investigations revealed that plasma treatment imparted active functional groups onto the surface of the banana fiber, establishing chemical interactions with the epoxy resin. As a result, banana fibers and modified BFREC composites can be used to manufacture interior panels, headliners, seatbacks, dashboards, automobile industry, and industrial applications in order to nurture self-sustaining biodegradable natural resources.

ABSTRACT The current research aimed to investigate the different aspects of novel nanocomposites based on carboxylated acrylonitrile butadiene rubber (XNBR), carboxylated styrene butadiene rubber (XSBR), graphene oxide (GO), and glycidyl methacrylate-grafted XNBR compatibilizer (XNBR-g-GMAC) blend. For this purpose, the novel nanocomposites of GO-XNBR-g-GMAC/XNBR/XSBR with different XNBR, XSBR, and GO composition and with and without XNBR-g-GMAC were synthesized. The related characteristics including curing properties, swelling behavior, morphological, electrical and mechanical characteristics were studied through rheometry, swelling test, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) observation, electrical resistivity, mechanical test, dynamic mechanical thermal analysis (DMTA), etc. Results of rheometric tests revealed that the addition of XNBR-g-GMAC and increasing GO content reduces the scorch time (t 5) and optimum cure time (t 90) and increases the crosslink density (CLD). So that the addition of 5 phr of compatibilizer and 1 phr of GO to the XNBR75/XSBR25 blend reduced the t 5 and t 90 by 29% and 34%, respectively. TEM micrograph confirms the GO dispersion in rubber matrix and SEM observation shows that incorporation of XNBR-g-GMAC and GO reduces dispersed-phase droplet size due to the improved compatibility of XNBR and XSBR. According to the DMTA result, all the samples except XNBR/XSBR (without XNBR-g-GMAC) show one glass transition temperature (T g) which means XNBR-g-GMAC successfully enhanced the compatibility of XNBR/XSBR. The mechanical properties of samples showed that by the increase of GO concentration tensile strength, elongation at break, modulus, fatigue life, and hardness increased. Testing surface temperature changes in constant voltage (75 V) showed that the addition of 0.3 phr GO showed the best result and the further increase of GO up to the value of 1 phr revealed the opposite result and caused a decrease of about 54%. The results of practical tests also confirm the theories.

ABSTRACT The use of additives as supplementary cementitious materials (SCM) from waste materials in concrete helps to improve its properties and protects the environment from hazardous impacts. This study is focused to use waste materials like silica fume and fly ash with steel fibers (SFs) in production of SCC. Two mixes with 5%SF&15%FA and 10%SF&15%FA were used. The dosage of steel fibers with aspect ratio 20 was used in the dosage of 0.1, 0.15, and 0.2% by volume of concrete. To test fiber’s impact on workability, a lower aspect ratio is chosen. From test results, it was observed that lower dosage of additive shows better performance of SCC both at fresh and hardened state. Significant improvement in the flexural strength of concrete mix containing 0.15% SFs, 5%SF&15%FA was recorded. In addition the specimens with the steel fibers during split tensile and bending test did not split completely in two pieces at collapse due to the presence of fibers, which act as locking medium in concrete matrix. This indicates some sort of ductile fracture and sign of impending warning time before the complete failure of high-strength SCC.