Among numerous types of health-monitoring and damage-sensing sensors that can be integrated into composites, electrically conductive sensors offer a simple, cost-effective, and durable option for structural health monitoring in fiber reinforced composites. In this study, a novel approach is introduced to create electrical conductive networks in glass fiber reinforced composites. For this purpose, hollow micro-channels are generated using vaporization of sacrificial components (VaSCs) which are subsequently filled with CNT-epoxy conductive fillers to induce conductive pathways within the composite. The presence of vascular conductive pathways was not found to hinder the structural integrity of the composites. The use of such conductive pathways for in situ strain monitoring of composites was investigated. The strain sensitivity of the prepared conductive pathways in the composite were found more than twice that of conventional strain sensors, rendering such conductive pathways a promising alternative for in-situ strain monitoring of continuous fiber-reinforced composites.

The remarkable electrical and mechanical properties of carbon nanotubes (CNTs) render CNT-reinforced nanocomposites as potentially attractive materials for strain-sensing and monitoring purposes. The dispersion state of CNTs in polymeric matrix has a significant role on the physical and the mechanical properties of the resulting CNT reinforced nanocomposites. In this study, a series of experiments were designed to investigate the effect of dispersion process parameters and CNT concentration, as well as their interactions on electrical, mechanical and strain sensing properties of CNT/epoxy nanocomposites. Composite samples were produced under different CNT/resin dispersion conditions based on a design of experiments approach, and were characterized using tensile testing, conductivity measurements and micrography. Based on the results, two regression models were established to predict the electric conductivity and the tensile strength of the CNT/epoxy nanocomposites. The robustness and accuracy of the models were verified by implementing verification tests. It was found that the nanocomposites fabricated by dispersing of lower amount of CNT with high mixing speeds and long mixing times had improved sensory properties and were more suitable for strain sensing applications. The effect of post dispersion state on electrical conductivity was also investigated by curing nanocomposites into a magnetic field. A straight forward 2D percolation-based model was used to predict the electrical conductivity and piezoresistivity of the magnetized nanocomposites. Both Experimental and numerical results showed that the electric conductivity could be increased significantly with post dispersing of CNTs using magnetization.

Composite sandwich structures are fabricated by placing partially-cured thermoset prepreg sheets and an adhesive layer on either side of a honeycomb core enclosed by a vacuum bag in an autoclave and co-cured under a pressure and temperature ramp. It is imperative that the adhesive layer forms a good bond between the core and the prepreg face sheets. One of the complications is the bubbles/voids could form due to outgassing and grow in and around the bond-line during the manufacturing process. In this work, a model of bubble growth is incorporated in a simulation that provides the distribution and size of voids within the adhesive layer as a function of the process, material, and geometric parameters. This understanding should prove useful in reducing or eliminating voids from the bond line during processing of such sandwich structures.

Process-induced total spring-in of corner-shaped composite parts manufactured via autoclave-forming technique using unidirectional prepreg is studied both numerically and experimentally. In the numerical study, a three-dimensional finite element model which takes into account the cure shrinkage of the resin, anisotropic material properties of the composite part and the tool-part interaction is developed. The outcome of the numerical model is verified experimentally. For this purpose, U-shaped composite parts are manufactured via autoclave-forming technique. Process-induced total spring-in, due to the combined effect of material anisotropy and tool-part interaction, at different sections of the U-shaped parts are measured with use of the combination of the three-dimensional optical scanning technique and the generative shape design. Total spring-in determined by the numerical model is found to be in good agreement with the average total spring-in measured experimentally. The effect of tool-part interaction mechanism on the total spring-in is studied separately to ascertain its effect on the total spring-in behavior clearly. It is shown that with the proper modeling of the tool-part interaction, numerically determined total spring-in approaches the experimentally determined total spring-in.

Sub-structures of aircraft structures mainly consist of stiffened shells such as fuselage frames, ribs and multi-cell box beams. Conventionally, these stiffened shells are manufactured through a process wherein shells and stiffeners are fabricated separately and then are integrated either through mechanical fastening and adhesive bonding. Co-curing is an integral molding technique that can greatly reduce the part count and the final assembly costs for composite materials. This article presents a simulation of integral manufacturing of a three-cell composite box beam by vacuum assisted resin infusion process. To validate the model, the characterization tests of both resin and reinforcement materials were carried out. Porosity and permeability testing of the reinforcement materials were conducted. Moreover, the effect of stacking sequence and vacuum level on the preform porosity were investigated. Additionally, the resin viscosity measurements were performed and the influence of temperature and curing on resin viscosity were examined. Having obtained the characterization data, vacuum infusion model was validated using RTMWorx software and then simulation of a three-cell composite box beam was conducted.

Mass-production of microfluidic devices is important for biomedical applications in which disposable devices are widely used. Injection molding is a well-known process for the production of devices on a mass scale at low-cost. In this study, the injection molding process is adapted for the fabrication of a microfluidic device with a single microchannel. To increase the product quality, high-precision mechanical machining is utilized for the manufacturing of the mold of the microfluidic device. A conventional injection molding machine is implemented in the process. Injection molding was performed at different mold temperatures. The warpage of the injected pieces was characterized by measuring the part deformation. The effect of the mold temperature on the quality of the final device was assessed in terms of the part deformation and bonding quality. From the experimental results, one-to-one correspondence between the warpage and the bonding quality of the molded pieces was observed. It was found that as the warpage of the pieces decreases, the bonding quality increases. A maximum point for the breaking pressure of the bonding and the minimum point for the warpage were found at the same mold temperature. This mold temperature was named as the optimum temperature for the designed microfluidic device. It was observed that the produced microfluidic devices at the mold temperature of 45 °C were able to withstand pressures up to 74 bar.

An approach is introduced for determining accurate two-dimensional equivalent laminated models of sandwich laminates with honeycomb core and composite facesheets by optimization involving modal behavior. The approach relies on minimizing the objective function which is defined as the sum of the square of the differences between the natural frequencies of the honeycomb sandwich laminate estimated by the finite element analysis of the 3D detailed model with the actual honeycomb core geometry and by the 2D equivalent laminated model with the honeycomb core replaced by the equivalent 2D orthotropic material model. Equivalent elastic constants of the 2D orthotropic model of the honeycomb core are defined as the design variables of the optimization problem, and a finite element solver and genetic algorithm-based optimizer are coupled to perform the optimization task. Results show that with the optimization-based approach, very accurate 2D equivalent models of honeycomb sandwich laminates are obtained compared to equivalent models obtained by replacing the honeycomb core with elastic constants of the 2D orthotropic material model obtained utilizing analytical models available in the literature.

Selective laser sintering was used for producing uniformly porous and graded porous polyamide structures. The porous structures were infiltrated with epoxy to produce composites. The porous and composite specimens were physically and mechanically characterized. Within the capabilities of the selective laser sintering machine and the materials used, porosities in the range 5–29% could be obtained in a controlled, repeatable manner. The ultimate tensile strength of the produced uniformly porous polyamide structures ranged from 20 MPa (for 29% porosity) to 44 MPa (for 5% porosity). The graded porous structures exhibited continuously changing porosity grades. As the number of grade increments rose, the grade profile fit closely with the design grade profile. The grades need to be constructed at porosities 9% or more for clear grade variation. Five percent porosity remained in all epoxy-polyamide composites after infiltration of the polyamide preforms with epoxy resin. Improvement in strength with epoxy infiltration was observed for preform porosities above 9%. The composite strength varied from 37 MPa to 44 MPa with respect to epoxy resin volume fraction. The maximum strength of the composites was found to be the same as the strength of the sintered polyamide powder (44 MPa).

A particle–resin suspension impregnation model is used for analyzing the mold filling process in compression resin transfer molding (CRTM) of particle-filled, continuous fiber composites. The model is based on Darcy flow coupled with particle filtration and is applicable to two-dimensional impregnation through isotropic/anisotropic fiber preforms. Comparisons with simple analytical solutions and experimental results from the literature were made to validate the numerical solution. Simulations showed that CRTM was advantageous over resin transfer molding (RTM) for smaller non-homogeneity in composite microstructure, when particle filtration was high. Limits on certain process parameters were observed beyond which molding pressures in CRTM became comparable with those in RTM. The preform anisotropy was effective in the particle distribution profile. The choice of inlet gate configuration in CRTM was found influential in the particle distribution homogeneity and molding pressures. The developed modeling tool can be extended to analyze any composite liquid molding process involving particle fillers.

This paper presents the preliminary results of an experimental study undertaken to investigate the particle distribution in particle-filled, continuous fiber-reinforced composites produced via two liquid molding methods: Resin Transfer Molding (RTM) and Compression Resin Transfer Molding (CRTM). Composite specimens are produced and characterized to compare composite microstructures (particle filler distributions) obtained in each method, as well as to study the effect of a processing parameter (injection speed) in RTM. For 20 % by vol particle concentration in injected resin and fiber volume fractions around 20 %, RTM process is found to yield little variation in particle distribution, resulting in nearly homogenous composite parts. CRTM process yields a clear non-homogeneity of particle volume fraction distribution in the composite, indicating presence of particle filtration. Due to experimental difficulties, the effect of injection speed on particle distribution for RTM process could not be assessed. Further experimental work is planned to assess repeatability of production. The experimental analysis will be expanded to study the effect of various processing parameters on the resulting particle distribution for the two liquid molding methods.

PurposeThe purpose of this paper is to propose and evaluate a novel tool for the assessment and selection of rapid prototyping (RP)/manufacturing (RM) systems as alternative processes for low‐volume production in the machinery and equipment design sector. By analysing previous RP/RM selectors, this research addresses the necessary factors that a knowledge‐based engineering (KBE) system must include for the analysis, comparison and ranking of candidate technologies.Design/methodology/approachThis research starts with the analysis of previous KBE solutions for RP/RM process selection, then a new KBE tool is proposed through the integration of artificial intelligence tools such as fuzzy logic, artificial neural networks (ANNs) and relational databases. Three case studies, provided by a Spanish machinery design centre, are used in order to measure the suitability of the proposed system for the assessment of real designs of special purpose mechanical parts.FindingsThe paper reports several improvements based on case studies which include a more suitable logic for process selection according to the designer's criteria and improvements in the overall parts cost estimation when compared to conventional parametric methods.Practical implicationsThe newly proposed KBE system has proven useful especially in cases where non‐experts or students need to select a RP/RM process according to an initial product design specification. The cost estimation module based on ANNs provides a practical tool which may be used by academics but also practitioners who wish to automate product costing calculations.Originality/valueUnlike previous solutions, the proposed system provides a straightforward means for RP/RM selection by an overall ranking of candidate processes, part cost estimation and materials selection. The main contribution is the modular design and logical planning, that overcomes the dilemma: material‐or‐process first.

Selective laser sintering (SLS) is a rapid prototyping technique which is used to manufacture plastic and metal models. The porosity of the final product obtained by SLS can be controlled by changing the energy density level used during the manufacturing process. The energy density level is itself dependent upon manufacturing parameters such as laser power, hatching distance and scanning speed. Through mechanical characterization techniques, it is possible to quantitatively relate the energy density levels to particular strength values. The present study is directed towards manufacturing functionally graded polyamide products by changing the energy density level in a predetermined manner. The mechanical properties of the functionally graded components are characterized by means of tensile testing. Both homogeneous and functionally graded specimens are produced and tested in order to examine the influence of the energy density level on the mechanical response and on the ultimate tensile and rupture strengths. Selective laser sintering is shown to possess the potential to produce functionally graded porous specimens with controlled variations in physical and mechanical properties.

In this study, uniform and graded porous polyamide structures are produced using selective laser sintering process by varying three processing parameters: hatching distance, laser power, and scanning speed. The PA 2200 polyamide powder is used to produce parts and the production is carried out in EOSINT P 380 laser sintering system. The effect of the three process parameters on porosity and mechanical properties are investigated on uniform porous structures using 2 3 factorial design. The produced samples are characterized in terms of apparent density, pore size distribution and microstructure. Tensile tests are carried out to assess the part mechanical properties with changing part porosities. Graded porous structures are then produced by varying the three process parameters during production, and characterized. It is concluded that a desired porosity grade within the limits of the machine capabilities can be induced in polyamide samples produced via SLS.

Bu makalede, recine transfer kaliplama yontemi sirasinda recinenin elyaf icindeki akisinin benzetimi icin gelistirilen, Darcy kanunu temelli matematiksel model ve sayisal cozum yontemi sunulmustur. Gelistirilen model, karmasik sekilli kaliplar icin 2-boyutlu, esyonlu/esyonsuz recine akisini izotermal olarak modellemektedir. Dolum suresi, kalip ici basinc dagilimi, akis cephesinin ilerlemesi gibi kalip ve uretim tasarimi icin onemli veriler elde edilebilmektedir. 1 boyutlu akis konfigurasyonu icin sayisal ve analitik cozumler karsilastirilmis, cesitli surec degiskenlerinin uretime etkisi incelenmistir. Karmasik sekilli kalip ici 2boyutlu dolum analizi yapilmis, sayisal sonuclar onceki bildirislerdeki deneysel sonuclarla karsilastirilmistir. Gelistirilen modelin, karmasik sekilli ve esyonsuz elyaf preform ici recine akisinin benzetiminde tatmin edici dogrulukta sonuclar verdigi gozlenmistir.

An accumulation-detachment filtration model is incorporated into a two-dimensional flow solution technique, using Darcy's law, to model the impregnation/resin transfer molding (I/RTM) of particle filled preceramic polymers into fiber preforms.

For reliable particle filtration analysis during impregnation molding of particle-filled preceramic polymer (PCP) based continuous fiber ceramic composites, the properties of the injected particle-PCP suspensions must be known (predictable) and the suspension quality reproducible. In this study, a methodology for optimal preparation (homogeneous suspension with low agglomeration) of sterically stabilized α-phase SiC particle — Blackglas™ polymer (AlliedSignal, Inc.) suspensions is presented. The quality of the prepared suspensions is inspected rheologically and visually (through SEM). For determination of particle concentration in suspension samples, an electrostatic spraying set-up has been constructed to produce particle-PCP suspension aerosols that are directed to an aerodynamic particle sizer (APS). Through APS, particle size distribution and concentration in prepared suspensions are obtained. Although the measured values agree qualitatively with expected results, there are quantitative discrepancies due to particle loss during handling and measuring. Further investigation and quantification of particle loss mechanisms are required for reliable measurements with APS. An experimental analysis of particle filtration during impregnation based on the proposed methodology is also planned in the future in which the results will be coupled to previously developed process models for designing optimal processing conditions.

Development of preceramic polymers has enabled the use of traditional polymer processing techniques, such as resin transfer molding (RTM) for the processing of ceramic-ceramic composites where continuous-fiber ceramic preforms are impregnated using PCP's and then pyrolized to convert the matrix into ceramic. One of the issues in this process is the void formation due to densification of the PCP's and the mass loss during pyrolysis. An effective way of reducing voids and shrinkage is to use suspensions of filler particles for the matrix material. The filler particle distribution during the infiltration of fiber preforms with particle-filled preceramic polymers has a crucial effect on the degree of cure and the properties of the finished product. The filler particles are also expected to reduce microcracking during the service of the ceramic composite. This paper constitutes the first phase of a comprehensive study to investigate the mechanics of particle filtration during the impregnation process and to establish the correlations between various processing parameters. A two-dimensional numerical filtration model is developed to predict the volume fraction distribution of the filler particles during the impregnation process. The non-linear relations between the filler particle distributions, the flow properties and the mold geometry are also investigated.

The study of particle filtration in resin transfer molding of liquid preceramic polymer (PCP) based ceramic composites with filler particles is the topic of our current research, in order to prevent particle filtering during impregnation and to achieve a uniform particle distribution within the composite. This study targets an experimental analysis of filtration that will be coupled to previously developed filtration models. For reliable filtration data, the properties of the particle-PCP suspension must be known (predictable) and the suspension quality reproducible. This paper presents the initial stage of the experimental work, which consists of standardization of particle-polymer suspension preparation and its characterization. A methodology for optimal (homogeneous suspension with low agglomeration) steric stabilization of polymer / SiC particle suspensions is presented. The results Blackglas™1 preceramic of the characterization of the suspensions through visual inspection (SEM) and rheological measurements are reported. With the achievement of well-dispersed, low viscosity suspensions with reproducible properties, our current work is in the adaptation of electrostatic spraying and laser particle counting technology for the detection of particle size distribution and concentration to be used in subsequent filtration experiments.