Volume 23, Issue 6

The 2,2-bis[4-(3,4)-dicyanophenoxy phenyl]propane (BAPh)/polyarylene ether nitrile (PEN-OH) prepolymers and polymers were prepared by heat polymerization. Firstly, BAPh/PEN-OH systems were characterized using differential scanning calorimetry, dynamic rheological analysis, and thermal gravimetric analysis. The results revealed that the polymerization reaction can be controlled by various concentrations of PEN-OH and postcuring temperatures, and BAPh/PEN-OH prepolymers had low curing temperatures (229.3–300.4°C), large processing windows (∼106.5°C) with low melt viscosities, and excellent thermal stabilities. Then, the polymerization reaction and surface structures of BAPh/PEN-OH systems were investigated using Fourier transform infrared and scanning electron microscopy, respectively. The interpenetrating polymer networks were found in BAPh/PEN-OH polymers, suggesting that the addition of PEN-OH can not only promote the curing behaviors of BAPh but also increase the toughness of the polymers. The flexure strength and modulus of BAPh/PEN-OH polymers increased with the introduction of PEN-OH. The dielectric properties of BAPh/PEN-OH polymers were investigated, which had little dependence on the frequency. BAPh/PEN-OH systems can be used as a good candidate for high-performance polymeric materials.

Many engineering structures such as dam embankments, road way embankments have suffered serious erosion problems and have failed due to the presence of the dispersive soils. Different additives are used to control the dispersivity properties of these soils. In this study, the effects of lime and natural zeolite on the consolidation and swell characteristics of dispersive clay soils were investigated. For this purpose, identification and compaction tests were carried out on the soil samples. Dispersivity, swell and consolidation tests were performed on the specimens prepared by standard Proctor energy and constant lime content levels (2%, as a percentage of dry weight of the soil), the percentage (0%, 1%, 3%, 6%, 10%, 15% and 20%) of a mixture of natural zeolite additives. As a result of this study, it is shown that the dispersive soils can sufficiently be treated using lime and natural zeolite. From the test results, 2% lime and 3% natural zeolite was the most effective stabilizer in decreasing swell and compressibility potential of dispersive soils.

Cu-0.85Cr-0.5Zr-0.5Mo in situ composite was prepared by continuous casting, cold drawing, and aging treatment. By means of the analysis of microhardness, electrical conductivity, and transmission electron microscopy, the aging characteristics and microstructures of the in situ composite were investigated at different aging temperatures and aging times after cold deformation. The results show that the Cu-0.85Cr-0.5Zr-0.5Mo in situ composite has an excellent combination of the microhardness and electrical conductivity aged at 500°C for 4 h, and the microhardness and electrical conductivity reach 171 HV and 81.3% IACS, respectively. Small dispersed particles could strongly pin dislocations and stabilize the substructure from deformation. The main strengthening mechanisms for the in situ composite alloy are the work hardening and the secondary phase or interface strengthening. It was suggested that cold deformation before aging treatment can accelerate the precipitation of the secondary phase and improve the comprehensive properties of the Cu-Cr-Zr-Mo in situ composite.

A particle-based C 3 S hydration model with only three rate constants developed in Part I of this study is further developed and applied to Portland cement paste hydration. Experimental data are obtained with chemical shrinkage tests of cement pastes prepared with different water to cement (w/c) ratios (0.3–0.5), and cured at different temperatures (24°C–63°C) and pressures (0.69–51.7 MPa). The proposed model produces exceptionally good fits to test data. The fitted results indicate that the entire process of cement hydration can be modeled by connecting a nucleation and growth mechanism with a diffusion mechanism. Furthermore, the results reveal that the deceleration period of cement hydration may be due to the gradual transition of the rate-controlling mechanisms of different particles. The fitted rate constants generally follow basic chemical kinetics laws in terms of their dependencies on curing temperature and pressure, and appear to be largely independent of w/c ratio.

Fibre fabrics in liquid composite moulding can be considered as dual-scale porous media. In different gap scales, an unsaturated flow is produced during the mould filling process. This particular flow behaviour deviates from the traditional Darcy’s law, which is used to calculate the filling pressure and will cause errors. To prove the mechanism of this unsaturated flow, an experimental device was set up with a one-dimensional constant flow rate. The influencing factors, such as injected media, flow velocity and fibre fabric, were investigated in this study. Based on the experimental data, several useful conclusions were drawn, providing good references for optimising the process parameters and controlling the product quality.

Honeycomb sandwich panels (HSP) have exhibited significant advantages in light weight and energy absorption, and they have been widely applied in the automotive, aerospace, transportation and defense industries. Rather than restating details of the existing standard regular hexagon HSP (R0-HSP), this paper introduces single-rib reinforced regular hexagon HSP (R1-HSP) and double-rib reinforced regular hexagon HSP (R2-HSP). The mechanical characteristics of these three structures are first investigated by series full-scale elaborator models through LS-DYNA. It is found that the R1-HSP has the best crashworthiness performance under axial impact regarding specific energy absorption per unit ( SEAm and SEAv ) when the peak crashing stress ( σ peak ) is less important. Secondly, the thickness matching effect between stiffener and cell wall is analyzed with equivalent apparent density index to evaluate the contribution of the change of deformation model to the general mechanical properties. Consequently, stiffener thickness of 2.0 times and 1.5 times that of cell wall are found to be the most optimal options for R1-HSP and R2-HSP, respectively. To optimize the crashworthiness of the R1-HSP, optimal Latin hypercube design method is used for selection of sampling design points in the design space. And in the meantime, an accurate surrogate modeling method, or more specifically named as response surface method, is adopted to formulate the SEAm , SEAv and σ peak functions. The results yielded from the optimization indicate that the R1-HSP is superior to R0-HSP both in SEAm and SEAv under the same limitation of σ peak . This research is significant in providing technical support in the extended applications of different HSPs used as crashworthiness structures, and it has essential reference value in low volume and low mass energy absorber design.

The influence of a small amount of magnesium (only 0.01 wt.%) added to the Sn-0.7Cu solder alloy during the aging process of microstructural evolution is studied along with the mechanical properties of the alloy. The experimental results indicate that the addition of magnesium decreases the tensile strength of the solders but improves their elongation. The solidification structure of eutectic Sn-0.7Cu consists of β-Sn, and the eutectic structure, which has extremely fine intermetallic nodules, Cu 6 Sn 5 , is located in the interdendritic region. When the magnesium is added to the Sn-0.7Cu alloy, the Sn dendrites become slightly coarser; in comparison, the melting point of the Sn-0.7Cu-0.01Mg alloy decreased by 2°C for the differential scanning calorimetry results of bulk alloy samples. Sn-0.7Cu-0.01Mg exhibits the lowest contact angles and the widest spreading areas. After aging, the Sn-0.7Cu and Sn-0.7Cu-0.01Mg solders show significant changes in strength, mainly because of the obvious increase in the thickness of the Cu 6 Sn 5 intermetallic layer.

The chip seal is an economical type of asphalt pavement that was constructed for single- or double-layer aggregate-bitumen. Chip seals are applied to prime-sealed granular pavement surfaces in order to waterproof the surfaces of sub-layers, produce smooth and high-skid-resistance surfaces for vehicles and protect pavements against the detrimental effects of traffic and climate. Unlike bituminous hot mixtures, numerous factors can affect the performance of chip seal. One of the most important factors is climate. The aim of this study is to determine the performance variation of chip-sealed pavements under cold climate conditions. Three different chip-sealed roads in Erzurum, which is in one of the coldest regions of Turkey, were examined with non-destructive tests. Sand-patch, British pendulum, light weight deflectometer and dynamic cone penetrometer tests were performed. Chip-sealed pavements’ densities and surface temperature variation and base courses layer’s thicknesses were also measured, and deteriorations were observed and scored by researchers. Test results showed that flushing due to the higher temperatures during the short summer season, deficiency of the base course’s bearing capacity and moisture in the base course are the most important causes of deterioration in this type of chip seal, and the chip seals in this region must be resealed in <1 year because of the premature deterioration.

To investigate the influence of material damage models on machining simulation of unidirectional fiber-reinforced polymer composites (FRP), a two-dimensional (2D) macro-mechanical finite element (FE) model was developed. Four failure criteria in combination with two degradation models were implemented in the machining simulation. The simulation results were compared with experimental data in literature. It is shown that both failure criterion and degradation model have significant influence on the chip shapes, cutting forces and sub-surface damages. The cutting forces and chip shapes predicted by Maximum stress criterion with progressive damage model has a relatively better agreement with experimental observations. The simulated sub-surface damage also agrees with experiments for low fiber orientation angles.

The changes in grinding parameters have direct influences on the characteristics of surface morphology of workpieces during grinding. On the basis of the application of particle-reinforced aluminum silicon carbide (SiCp/Al), this paper analyzes the surface morphology of SiCp/Al after being ground by an electroplated diamond-grinding wheel by integrating studies on grinding processes. The typical morphology of grinding surfaces of SiCp/Al is elaborated, and the general principles of evaluating the grinding surfaces of particle-reinforced SiCp/Al are summarized by considering the surface morphology and formation mechanism. Comparison is made on the surface morphology between ultrasonic vibration-assisted grinding and traditional grinding. It indicates that the surface morphology can be evaluated in terms of the root mean square deviation of three-dimensional profiles, crushing ratio, and fractal dimension. Studies show that the surface morphology of workpieces after ultrasonic-assisted vibration grinding is better than that of the traditional machining.

Polyester tire cord is often used as reinforcement in the production of chloroprene rubber (CR) composite materials. This study investigated the influences of polyester tire cord layers and arrangement directions on the mechanical properties and vibration isolation of CR composite materials. The experimental results indicate that the optimal molding condition for bonding tire cord with CR composites is 170°C for 30 min, which enables tire cord-reinforced CR composites to exhibit maximum pull-out strength. The compression set, tensile strength, and tear strength of CR composites increased with the increasing number of tire cord layers, and the stretching direction parallel to the arrangement direction of the tire cord produced optimal reinforcement effect. Moreover, the storage modulus of CR composites is better than that of pure CR at low temperature, although it reduced the tan delta at glass transition temperature. Regarding the vibration isolation properties, the transmissibility ratio decreased at resonance frequency, while the damping ratio increased when the CR is reinforced with increasing number of tire cord layers.

An identification algorithm based on an isoparametric graded finite element model is developed to identify the material parameters of the plane structure of functionally graded materials (FGMs). The material parameter identification problem is formulated as the problem of minimizing the objective function, which is defined as a square sum of differences between measured displacement and calculated displacement by the isoparametric graded finite element approach. The minimization problem is solved by using the Levenberg-Marquardt method, in which the sensitivity calculation is based on the differentiation of the governing equations of the isoparametric graded finite element model. The validity of this algorithm is illustrated by some numerical experiments. The numerical results reveal that the proposed algorithm not only has high accuracy and stable convergence, but is also robust to the effects of measured displacement noise.

The effects of hygrothermal conditioning and moisture on the impact resistance of carbon fiber/epoxy composite laminates were investigated. Specimens were fabricated from carbon fiber/epoxy woven prepreg materials. The fabricated specimens were either immersed in water at 80°C or subjected to hot/wet (at 80°C in water for 12 h) to cold/dry (at -30°C in a freezer for 12 h) cyclic hygrothermal conditions, which resulted in different moisture contents inside the laminates. It was found that the absorbed moisture did not migrate out from composite materials at -30°C. Neither of the hygrothermal conditions in this study had detrimental effects on the microstructure of the laminates. Low-velocity impact testing was subsequently conducted on the conditioned specimens. When attacked by the same level of impact energy, laminates with different moisture levels experienced different levels of impact damage. Moisture significantly alleviated the extent of damage in carbon fiber/epoxy woven laminates. The elastic response of the laminate under impact was improved after hygrothermal conditioning. The mechanism behind the improved impact resistance after absorbing moisture was proposed and deliberated.

Fiber Bragg grating (FBG) sensors provide excellent capability for the structural health monitoring (SHM) of load-bearing structures by allowing for local internal strain measurements within structures. However, the integration of these sensors to composite materials is associated with several challenges that have to be addressed to have the correct strain measurement and in turn to perform reliable SHM. One of the most important issues is the presence of uneven strain fields around FBGs, which significantly affect the response of the sensors and hence the reliability of the acquired data. The uniformity of the strain fields around sensors is important for dependable data acquisition; however, to generate such a condition, tow width-to-FBG length relationship, optical fiber configuration with respect to reinforcement fiber orientation, and crack density resulting from fatigue loading are very important factors that have to be considered. In this paper, these issues are addressed by investigating the signal properties of FBG sensors with 1 and 10 mm lengths embedded within the composite specimens during the manufacturing process. After fatigue testing of the specimens, it is shown that 1-mm-long FBGs embedded in-line with adjacent reinforcement fibers with tow widths of ∼2 mm provide much more reliable signals than 10-mm-long FBGs embedded perpendicular to adjacent tows.

In this experimental study, the impact response of unidirectional hybrid composite laminate was investigated. Hybrid laminates with different stacking sequences were fabricated, using unidirectional glass and carbon fiber as reinforcement and epoxy resin as matrix. ASTM standard D5628 was followed to conduct the experiment using the instrumented drop weight impact test apparatus. All the square specimens were tested at an impact velocity of 3.43 m/s and the time histories of force and energy absorbed were recorded. The impacted specimens and their X-ray images were visually inspected to understand the failure pattern. The experimental results showed that the addition of carbon fiber increases the impact strength by absorbing more force and energy. Furthermore, the laminate can be stiffened with the carbon fiber layers by interfacing glass fiber layers on either side.

This paper presents a simple design analysis and performance evaluation of rectangular, slotted, microstrip feed patch antenna. The design processes are performed by employing the finite element method (FEM)-based commercial EM simulation software High-Frequency Structural Simulator (HFSS). The proposed multiband antenna is composed of a rectangular, slotted radiator formed with four arc slots and central square slot, reduced ground plane, and microstrip line for feeding. The patch antenna is excited through the standard 50 Ω RF transmission line, impedance-compliant SMA connector that is connected to the microstrip line. The optimal parametric dimensions from the numerical simulations are used for constructing the physical prototype on a custom-made, ceramic-filled biopolymer substrate of ε r =10.0. Based on simulation results, the experimental data are collected, analyzed, and compared; the surface current distributions on the patch, gain, and radiation patterns are critically discussed. The measured results show the impedance bandwidths for S11 less than -10 dB are 712 MHz at 0.788 GHz band, 1.38 GHz at 3.34 GHz band, and 2.46 GHz at 8.01 GHz band. The good radiation pattern performances, almost stable gain over the bands, and appreciable bandwidths recommend the antenna for operating in RFID, WiMAX, and C/X-band applications.

Laser cladding of the TiAl/Fe+Co-coated WC+TiB 2 pre-placed mixed powders on a Ti-6Al-4V alloy substrate can be used to form TiB 2 /α-W 2 C-reinforced composite coating, which improved the wear resistance of the substrate. To further improve the TiB 2 /α-W 2 C-reinforced composite coating, yttria partially stabilized zirconia (YPSZ) was added into the pre-placed powders. A metallurgical bonding was formed between the YPSZ-infused composite coating and the substrate. Many amorphous alloys were produced in this composite coating due to the action of YPSZ, and such coating showed fine microstructure. Thus, it is feasible to further improve the wear resistance of the laser clad TiB 2 /α-W 2 C-reinforced composite coating through the addition of YPSZ.

In this study, the effects of the particle reinforcement ratio on cutting forces and surface roughness were investigated when milling particle-reinforced metal matrix composite (MMCp) produced by hot pressing with different cutting tools. Alumix 123 alloy as the matrix material and B 4 C particles with an average size of 27 μm and 5%, 10% and 15% ratio as reinforcing elements were used for the manufacture of composite materials. The experiments were carried out in dry cutting conditions with four different cutting speeds, constant feed rate and depth of cut. Changes depending on the increased reinforcement ratio in cutting forces and surface roughness values were investigated; the effects of 10% B 4 C reinforced composite on tool wear were also examined. It was observed that cutting forces increased with the increase in cutting speed and particle ratio with carbide cutting tools, and it was seen that the cutting forces on the cutting tools decreased when cutting speed decreased and the cutting forces increased as the reinforcement ratios increased. In addition, with increasing the cutting speed, the surface roughness of the machined surfaces of composite samples increased with the carbide tools, while the cubic boron nitride (CBN) tools have the opposite effect. While it was seen that flank and crater wear occurred on the cemented carbide cutting tools, abrasive, adhesive and other wear mechanism tools in addition to the main wear mechanism, no remarkable flank and crater wear occurred on CBN cutting tools.

The microstructure of the interface in a Gr f /Al composite after exposure at high temperature was investigated. The graphite fiber reinforced aluminum matrix composite was prepared by the pressure infiltration method. After being heat treated at 550°C, 600°C and 640°C for different times, the microstructure of the interface in the composite was studied by using transmission electron microscopy (TEM). Furthermore, the content of Al 4 C 3 in the interface was examined using X-ray diffraction (XRD). The results showed that not only the micro morphology but also the content of Al 4 C 3 in the interface varied with the increase in temperature. When the composite was heat treated at 550°C and 600°C, Al 4 C 3 with a big length-to-diameter ratio was observed in the interface, while Al 4 C 3 with a small length-to-diameter ratio was found when the heat treatment temperature was 640°C. With the increase in the time, the content of Al 4 C 3 in the interface increased rapidly when the composite was heat treated at 640°C. Based on the dynamic calculation, the interface reaction diffusion rate constant of the Gr f /Al composite increases rapidly when the temperature is higher than 600°C.