Volume 25, Issue 3

Variable stiffness design (VSD) has been paid more attention for its capability of further exploiting the potential of fiber-reinforced composite in composite structure design. VSD under different mechanical property indexes is reviewed in this paper. The review mostly focuses on strength, buckling, frequency, and other more common mechanical indices. Subsequently, the usage of VSD method for several years is briefly summarized. Some successful tests about variable stiffness composite parts are introduced and the experiment results are also addressed. The article summarizes the research situation from both perspectives based on a number of papers about the VSD of composite materials in recent years and provides theoretical reference and basic knowledge to new researchers.

In the present article, static analysis of thin functionally graded micro-plates, based on Kirchhoff plate theory, is investigated. Utilizing the strain gradient theory and principle of minimum total potential energy, governing equations of rectangular micro-plates, subjected to distributed load, are explored. In accordance with functionally graded distribution of material properties through the thickness, higher-order governing equations are coupled in terms of displacement fields. Introducing a novel methodology, governing equations are decoupled, with special privilege of solving analytically. These new equations are solved for micro-plates with Levy boundary conditions. It is shown that neutral plane in functionally graded micro-plate is moved from midplane to a new coordinate in thickness direction. It is shown that considering micro-structures effects affects the governing equations and boundary conditions. Finally, the effects of material properties, micro-structures, boundary conditions and dimensions are expounded on the static response of micro-plate. Results show that increasing the length scale parameter and FGM index increases the rigidity of micro-plate. In addition, it is concluded that using classical theories for study of micro-structures leads to inaccurate results.

In situ TiB 2 /Al-4.5Cu composites with different TiB 2 particle amounts were fabricated by the salt-metal reaction technique. The effects of in situ TiB 2 on the microstructure and mechanical properties of Al-4.5Cu alloy were studied in this paper. The results showed that in situ TiB 2 particles had significant effect on refining grain size and improving mechanical properties of as-cast Al-4.5Cu alloy. With the amounts of TiB 2 particles increasing, the yield strength and ultimate tensile strength were improved, while the elongation reduced. The strengthening mechanisms of the in situ particle-reinforcing Al matrix composites were discussed, and the yield strength was predicted accurately by accounting for the three strengthening mechanisms and particle distribution.

W-Cu alloy and 1Cr18Ni9 steel were brazed with NiCrSiBFeTi and NiMnSiCuZr filler metals in a vacuum furnace. The main microstructure of the NiCrSiBFeTi brazing seam region was a Ni-based solid solution of W, Cu, Cr, and Fe dissolved in the Ni phase and intermetallic compounds CrB and TiCr 2 . The main microstructure of the NiMnSiCuZr brazing seam region was a Ni-based solid solution of Cu, Cr, and Fe dissolved in the Ni phase Fe-based solid solution of Ni, Cu, and Cr dissolved in the Fe phase and intermetallic compounds Mn 5 Si 3 , Ni 3 Si, and Ni 7 Zr 2 . The elements Ni, Si, and Ti contained in the NiCrSiBFeTi filler metal and the elements Ni, Mn, and Si contained in the NiMnSiCuZr filler metal were more easily diffused into the interface of W-Cu alloy compared with that of 1Cr18Ni9 steel. The shear strength values of NiCrSiBFeTi joint and NiMnSiCuZr joint were approximately 285 and 249 MPa, respectively, and fracture of the two joints occurred at the interface near the W-Cu alloy side. The fracture morphology of the former was identified as cleavage brittle fracture, and the latter was identified as intergranular brittle fracture.

The demand for high-performance and cost-effective composite materials is gaining attention in today’s competitive world. In this work, an attempt has been made to prepare low-cost reinforced aluminum metal matrix composite by reinforcing 10% and 20% weight fractions of wet grinder stone dust (WSD) particles, an industrial waste produced during stone dressing operation in the wet grinder manufacturing industry. As drilling is one of the major machining operations carried out in industries, the prepared composite materials are subjected to drilling studies using carbide, TiN-coated carbide, and HSS drills of 5 mm diameter under dry conditions. The major concern with the machining of composites is the extreme tool wear. Tool wear is a very important and challenging task for manufacturing engineers because it has adverse affects on the product quality and increases the production cost. Hence, there is a need to identify the factors that have most significant influence on the tool wear. In this work, the Taguchi-based design of experiments and analysis of variance were used to determine the optimal cutting parameters and to analyze their effects on thrust force, torque, and tool wear. Multivariable linear regression analysis was also employed to determine the correlations between the factors and the response, namely, thrust force, torque, and tool wear. Finally, a confirmation test was conducted to validate the Taguchi optimization method. From the experimental results, feed rate was identified as the dominant factor influencing the thrust force and spindle speed was identified as the significant factor influencing the torque. Thrust force, torque, and tool wear were found to increase with the increase in the reinforcement content irrespective of the drill used for the investigation.

Natural fiber reinforced thermoplastic composites using flax and polypropylene were prepared using compression molding process. Needle punched nonwovens were used as preforms for preparing the composites. Three variables namely fiber weight proportion, areal weight of the mat, and needling density were chosen for the study. Modified Taguchi L18 experimental design with dummy variable was chosen for the study and the effect of the above variables on tensile, flexural, and impact properties of the composites were studied. By altering the fiber weight proportion and areal weight of the mat, tensile and flexural properties improved. An increase in 34% of tensile strength and 40% of flexural strength has been observed. Impact properties of the composites were significantly altered by modifying the process variables. Increasing the needling density led to a decrease in overall mechanical properties of the composites.

New generation non-crimp fabric (NCF) offers an attractive thin and lightweight building block alternative in the design of composite materials and structures. Pre-assembly of multiple plies of parallel fibers, each laying in a different orientation would not require crimping of the fibers and would enable one-axis lay-up that can substantially reduce the labor, scrap, and manufacturing costs. A state-of-the-art tow-spreading technique enables ply thickness to be reduced to as low as one-third of the typical commercial high quality pre-preg ply thickness. The thin-ply NCF stacks result in well-dispersed plies of different fiber orientations and creates the so-called homogenized laminates without ply clustering. As an option, bi-angle thin-ply NCF offers two different fiber orientations with one being off-axis, e.g. at ϕ °, along with an on-axis 0° forming (0/ ϕ ) assembly. This allows to design in anisotropic properties within the NCF building block. An overview of several aspects of the thin-ply bi-angle NCF composites is provided to address associated benefits and opportunities in the lightweight structural composites design process.

In this study, the effect of coir fiber reinforcement on the mechanical properties of vulcanized natural rubber composite has been studied. An attempt has been made to predict the effect on tensile strength, maximum load, and elongation at break (%) of coir fiber-reinforced vulcanized natural rubber composites under cold, heat, and water aging tests. The natural rubber was vulcanized at 150°C. The fibers were soaked in a 5% solution of NaOH for 48 h at room temperature. At different temperatures, cold, heat, and water aging resistance tests were conducted to understand the behavior of the composite under different environment. The properties recorded after aging tests were compared with initial properties to investigate the effect of fiber reinforcement. The results revealed that the samples containing coir fiber showed better performance after each aging test. The specimens showed the highest properties in case of water aging resistance.

In this work, the effects of processing parameters including temperature, time, and pressure on the properties of amorphous polyvinyl chloride (PVC)/fiberglass thermoplastic composite laminates were evaluated. The film stacking and hot pressing procedure was used to produce the composite laminates, and samples with [0/90] 10 layup and thickness of 3 mm were produced. Flexural strength and modulus of the samples were measured using three-point bending test (according to ASTM D790 standard test method), and microscopic images were used to evaluate the failure mechanisms and impregnation quality. The effects of the parameters on the strength were studied using analysis of variance (ANOVA), and it was found that processing temperature has the maximum effect on the products strength and increase of the temperature up to 230°C increases the flexural strength while more increase of temperature results in the matrix degradation and strength reduction. Also, processing time improves the wetting and impregnation quality; however, more increase of the processing time results in the matrix degradation and excessive reduction of the strength.

The aims of the present study were to develop a dental composite filled with silanized nanoalumina and then to investigate the effect of nanoalumina filler on the two-body and three-body wear behavior under distilled water and food slurry medium, respectively. The dental composites were fabricated by adding silane treated nanoalumina filler particle in the weight percentage of (0–3 wt.%) to the matrix of BisGMA, TEGDMA, CQ and EDMAB. Two-body and three-body wear tests were performed in dental wear simulator machine with varying parameters such as normal load, chewing speed and chamber temperature in such a way as to simulate mastication process. Taguchi’s orthogonal array (L 16 ) design, steady state condition and ANOVA were applied to evaluate the optimum parameter for minimum wear and effect of each parameter on the wear performance of dental composites. The finding of the result indicated that mean volumetric wear rate of dental composite in distilled water (i.e. two-body abrasion) was 33.23% more than that of the same composite in food slurry condition (i.e. three-body abrasion).

This research work has been aimed at understanding the effects of different fiber orientations and different stacking sequences of composite laminates on their damage during drilling of CFRP/Al stack. Finite element code Abaqus/CAE has been used for the implementation and analysis of the numerical model. Surface-based cohesive behavior available in Abaqus/CAE contact pairs has been used to simulate delamination behavior in the adhesive interfaces. In order to use the Hashin damage criterion (for intra-laminar damage) available in the finite element code, continuum shell elements have been used for laminates. Three stacking sequences each with 24 layers including [0°] 24 , [0°/90°] 12s , and [−45°/90° 4 /45° 2 /−45°] 3s have been considered for this study. The display group manager available in Abaqus/CAE visualization module enabled the individual access of the damage in each layer. Two layers both at drill entry and at CFRP/Al interface were used to study peel-up and push-down delamination, respectively. Sequence [0°] 24 was found to have the largest damaged in both entry and interfaces, while sequence [−45°/90° 4 /45° 2 /−45°] 3s was found to show better resistance to delamination damage.

The polyacrylic acid/tungsten oxide (PAA/WO 3 ) composite films with good electrochromic properties have been prepared by a layer-by-layer method. The porous PAA layers were used as a template for the deposition of WO 3 , and finally, the composite film showed a network structure with high porosity. The electrochromic performance of the PAA/WO 3 composite film was investigated by means of cyclic voltammogram (CV), chronoamperometry (CA), and transmittance measurements. The PAA/WO 3 film also exhibited a remarkable electrochromism ability with the reversible color change from transparent colorless to dark blue and the transmittance change from 83% to 24% at 620 nm. This research provided a cost-effective approach for the preparation of PAA/WO 3 composite films with controllable microstructure and good electrochromic property.

This research work investigated the effect of fiber loading and alkali treatment on hair fiber (HF)-reinforced high-density polyethylene (HDPE) composites in terms of mechanical properties and water absorption behavior. The mechanical stability of the composite material was studied by Universal Testing Machine. The alkali treatment of HF-reinforced HDPE composites was responsible for the investigation of the mechanical and water absorption properties. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) analysis were also done for the study of the reinforced polymer composites. The results of the SEM analysis were very helpful for the study of the morphology of the fiber-matrix interface for better/optimum mechanical properties.

MoO 3 nanobelts were prepared by a one-step hydrothermal method and then assembled with aluminum nanoparticles using polyvinylpyrrolidone as a binder. The physicochemical properties of the as-prepared samples were carefully characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, thermogravimetric analysis/differential scanning calorimetry, and drop weight impact test. The results showed that the T onset of Mo-Al-0, Mo-Al-1, Mo-Al-2, and Fe-Al-0 are 474.8°C, 484.2°C, 478.5°C, and 514.8°C, respectively, which are 66.0°C, 56.6°C, 62.3°C, and 26.0°C lower than that of pure Al-NPs (540.8°C). The total exothermic heat of self-assembled MoO 3 /Al during DSC test is about 2626.9 J/g, which is 229.6, 420.8, and 11.1 J/g higher than that of Al/commercial MoO 3 , Al/hydrothermal MoO 3 , and Al/referenced Fe 2 O 3 . Furthermore, the high exothermic self-assembled MoO 3 /Al thermite is totally insensitive to impact.

Lamb wave tomography can be used to evaluate structural integrity. The time-of-flight (TOF) data are usually recorded as input to the reconstruction algorithm. For composite materials, TOF estimation is complicated due to their anisotropy. To reduce the effects of anisotropy on image reconstruction, the TOF data of flawed plates are revised according to baseline data obtained from an unflawed plate. Tomographic images are reconstructed using the original and revised TOF data, respectively. Results show that images reconstructed using the revised TOF data have better visual quality and that TOF data revision can substantially reduce the artifacts resulting from anisotropy in defect detection of composite materials.

Aiming at the problem that a thin-walled plastic part easily produces warpage, an orthogonal experimental method was used for multiparameter coupling analysis, with mold structure parameters and injection molding process parameters considered synthetically. The plastic part deformation under different experiment schemes was comparatively studied, and the key factors affecting the plastic part warpage were analyzed. Then the injection molding process was optimized. The results showed that the important order of the influence factors for the plastic part warpage was packing pressure, packing time, cooling plan, mold temperature, and melt temperature. Among them, packing pressure was the most significant factor. The optimal injection molding process schemes reducing the plastic part warpage were melt temperature (260°C), mold temperature (60°C), packing pressure (150 MPa), packing time (2 s), and cooling plan 3. In this situation, the forming plate flatness was better.

Polyurethane-acrylate/SiO 2 composite (SPUA) emulsions were synthesized by in situ polymerization accompanying the sol-gel process, in which the hydrolysis reaction and polymerization of monomers could be accomplished at the same time. The particle morphology of the SPUA emulsions was observed by scanning electron microscopy and transmission electron microscopy. The particle diameter was measured on a laser particle size analyzer. The molecular structure of the copolymers was characterized by Fourier transform infrared spectrometer (FTIR). Furthermore, tensile testing machine, Shore durometer, and thermogravimetric analyzer were used to investigate the mechanical properties, hardness, and thermal properties. The results indicated that, by increasing the mass fraction of tetraethyl orthosilicate (TEOS), the mechanical properties of the films were improved remarkably. When the weight % of TEOS was 8% in the SPUA emulsion, the water absorption of obtained film was 2.1%, the tensile strength was 16.8 MPa, the shore hardness was 94, and the temperature for the maximal thermal mass-loss rate was 416°C.

The paper presents the synthesis and characterization of a carbon black-magnetite hybrid filler. The complex study on the structure of the filler has shown the magnetite phase to be distributed both over the surface (inter-aggregately) and inside (intra-aggregately) the carbon black particles, thus forming a true hybrid material. The results from the investigations on the mechanical and microwave properties of natural rubber-based composites filled with the new hybrid filler have been also reported. They have been compared to those of a composite comprising the physical mixture of carbon black and magnetite (at the same ratio as in the hybrid filler). The determined microwave characteristics of the composite comprising the hybrid filler obtained reveal the possibility for its use in manufacturing elastomer-based microwave absorbers.

We built a three-dimensional finite element (FE) model to investigate the impact response of fiber-metal laminates (FMLs). This FE model comprises two metal layers as facesheets and a carbon woven fabric-reinforced plastic laminate as inner core. Simulation was performed on ABAQUS/Explicit platform, and stiffness progressive degeneration criteria were implemented to evaluate damages in composites. The Johnson-Cook model was selected to calculate failures in metal, while surface-based cohesive behavior was adopted to simulate the delamination phenomenon. We studied the fiber stacking sequence, panel thickness, and incident angle effect on the impact behavior of FMLs. The critical penetration energy of the FMLs was determined, and the impact parameter history was discussed.