M. Cengiz Altan

• Ph.D.
• Perkinson Chair Professor at University of Oklahoma

A novel method, Magnet Assisted Composite Manufacturing (MACM), which utilizes a magnetic compressive pressure, is proposed to improve laminate quality in wet lay-up/vacuum bag (WLVB) processes. This paper first describes the salient features of MACM/WLVB process, and then demonstrates the effectiveness of this process by investigating the void con...

Moisture absorption is known to detrimentally affect the mechanical integrity and durability of polymeric materials. Consequently, accurately characterizing the moisture diffusion into these materials is critical when predicting their service life behavior. The hindered diffusion model (HDM), that is, Langmuir-type absorption, has been widely used...

Adequate stress transfer between the inorganic reinforcement and surrounding polymeric matrix is essential for achieving enhanced structural integrity and extended lifetime performance of fiber-reinforced composites. The insertion of an elastomeric interlayer helps increase the stress-transfer capabilities across the fiber/matrix interface and cons...

A novel approach for characterisation of nanoclay dispersion in polymeric composites using electron microprobe analysis (EMPA) is presented. Dispersion analysis was performed on three sets of centre-gated discs fabricated by resin transfer moulding. The first set was neat epoxy polymer without reinforcement, whereas the second set comprised 17 vol....

Preparation of E-glass/waterborne epoxy prepregs containing natural nanoclay and properties of their composites are presented. Prepregs were prepared by wetting randomly oriented, chopped glass fiber preforms with aqueous dispersion of EpiRez 3522-W-60 resin, dicyandiamide, 2-methylimidazole and natural nanoclay (Cloisite® Na+). The nanoclay conten...

The use of hybrid reinforcement in polymer composites has been getting attention due to its potential for weight and cost reduction while achieving improved design flexibility for mechanical and thermal properties. In this study, an interply hybridization of epoxy laminates was performed using layers of solid and hollow glass fibers. The structural...

Material extrusion additive manufacturing of short carbon fiber epoxy composite ink should exhibit thixotropic behavior which enables the fabrication of complex as well as simple 3D structures with controlled and tailored fiber arrangement within the composite part. This study investigates a method to automatically segregate fibers from voids and e...

This study investigated the tribological performance of hybrid composites composed of scrap carbon fiber (CF), glass fabric (GF), and polyamide 6.6 (PA6.6) through an innovative approach for reusing scrap CFs in high‐value composite structures. The experimental setup included CF/GF/PA6.6 hybrid composite laminates with varying CF contents and surfa...

Highly flexible, deformable, and ultralightweight structures are required for advanced sensing applications, such as wearable electronics and soft robotics. This study demonstrates the three-dimensional (3D) printing of highly flexible, ultralightweight, and conductive polymer nanocomposites (CPNCs) with dual-scale porosity and piezoresistive sensi...

The conventional composite fabrication processes, such as hand lay-up, autoclave, vacuum-assisted resin transfer molding, and filament winding, hinder the prospect of future development and application due to expensive mold fabrication, limited part geometries, and lack of repeatability. An extrusion-based additive manufacturing technique, such as...

This study proposes an innovative processing approach for high-added value hybrid fiber-reinforced composite structures by reusing scrap carbon fiber (CF). Thermoplastic prepregs were produced via wet-laid method using chopped polyamide 6.6 fibers as matrix and short scrap CFs as the reinforcing phase. These prepregs were then hot stacked with wove...

An investigation is presented on direct-ink-writing (DIW) of carbon fiber epoxy composite with and without an electric field. Initial emphasis is focused on the importance of DIW and a common notion that DIW/3D printing aids in better alignment across a printed specimen. For this purpose, the DIW technique is utilized in printing a single filament...

The overmolding of short fiber reinforced polymer compounds onto continuous fiber reinforced composite substrates provides design flexibility and the ability to tailor stiffness, strength, and damage tolerance for structural applications. In this work, a novel molding approach that enhances the bonding strength by mechanical interlocking is present...

Floating vessel-type oil collecting devices based on sorbent materials present potential solutions to oil spill cleanup that require a massive amount of sorbent material and manual labor. Additionally, continuous oil extraction from these devices presents opportunities for highly energy-efficient oil skimmers that use gravity as the oil/water separ...

This paper presents the synthesis, characterization, and multiscale modeling of hybrid composites with enhanced interfacial properties consisting of aligned zinc oxide (ZnO) nanowires and continuous carbon fibers. The atomic layer deposition method was employed to uniformly synthesize nanoscale ZnO seeds on carbon fibers. Vertically aligned ZnO nan...

Porous conductive polymer nanocomposites (CPNCs) have attracted significant attention for developing flexible piezoresistive sensors. In this work, a novel approach is developed by combining direct ink writing (DIW) and solvent evaporation induced phase separation method to synthesize porous CPNC with strain sensing capabilities. CPNC is prepared b...

This paper reports a fast and straightforward method for controlling the pore size distribution and mechanical properties of porous polydimethylsiloxane (PDMS) structures. The solvent evaporation-induced phase separation is implemented for the fabrication of absorbent PDMS sheets. The ternary polymer solution containing PDMS, water (nonsolvent), an...

This paper reports the synthesis and characterization of the hierarchical porous structure of polydimethylsiloxane (PDMS) sheets. A two-step phase separation synthesis protocol is designed based on a ternary solution of PDMS that contains both a nonsolvent and solvent. Tetrahydrofuran (THF) and Toluene with various mixing ratios are utilized as a s...

Porous piezoresistive sensors offer promising flexible sensing functionality, such as human joint motion detection and gesture identification. Herein, a facile fabrication method is developed using a microwave-based rapid porogen removal technique for the manufacturing of porous nanocomposite sponges consisting of polydimethylsiloxane (PDMS) and we...

This article reports the fabrication and characterization of porous polydimethylsiloxane (PDMS) structures developed by the solvent evaporation‐induced phase separation technique. Ternary systems containing water/tetrahydrofuran (THF)/PDMS with various concentrations are produced to form a stable solution. The porous PDMS structures are formed by r...

In recent years, highly flexible nanocomposite sensors have been developed for the detection of a variety of human body movements. To precisely detect the bending motions of human joints, the sensors must be able to conform well with the human skin and produce signals that effectively describe the amount of deformation applied to the material durin...

Carbon nanotubes (CNTs) have the unique ability to absorb microwave radiation and efficiently transfer the energy into substantial heat. When adequately dispersed in a thermoset polymer, such as polydimethylsiloxane (PDMS), the nanocomposite can be fully cured in seconds in a microwave oven rather than in hours in a convection oven. In this paper,...

This paper presents the fabrication and characterization of porous polydimethylsiloxane (PDMS) plates. The framework for obtaining porous PDMS is based on the solvent evaporation induced phase separation technique. A mixture of PDMS, water, and tetrahydrofuran (THF) with different concentrations is prepared. The three phases are stirred to reach a...

Accurate monitoring of human motion holds enormous promise for broad applications, such as athlete training, rehabilitation, health monitoring, and gaming. Wearable sensors are required to have intimate contact with the skin, wide sensing range, high sensitivity, and outstanding durability. In this paper, we report ultrastretchable and wearable str...

The controlled orientation of short fibers on the surface of structural laminates while obtaining good dispersion and uniform spatial distribution is highly desirable. In this paper, a new magnetic field assisted fabrication method is proposed to align nickel coated carbon (NiC) fibers on the surface of ternary NiC/glass/epoxy laminates. Excellent...

Thermosetting polymer composites are often exposed to wet and humid environments, leading to a considerable reduction in their thermo-mechanical properties. Hence, accurate description of the moisture absorption dynamics, including anomalous effects such as molecular bonding and interfacial storage of moisture, is particularly important. In this st...

Moisture absorption of composites with nanoscale carbon additives such as carbon nanotubes, carbon nanofibers, graphite nanoplatelets, and carbon black is investigated using thermogravimetric data and a non-Fickian hindered diffusion (Langmuir-type) model. The moisture absorption parameters are determined using this model for six different types of...

In this paper, polydimethylsiloxane (PDMS) and multi-walled carbon nanotube (MWCNT) nanocomposites with piezoresistive sensing function were fabricated using microwave irradiation. The effects of precuring time on the mechanical and electrical properties of nanocomposites were investigated. The increased viscosity and possible nanofiller re-agglome...

The primary interest in numerous research problems in both polymer composites and Machine Learning (ML) is to develop predictive models for one or more variables of interest using relevant independent variables, or inputs. However, these two fields have often adopted different approaches, where modeling of composite behavior is often based on physi...

This paper proposes a simple and accurate technique to quantify both fiber and void volume fractions of natural fiber composites. This technique involves the separate pyrolysis of natural fibers, polymer resin, and natural fiber/polymer composite in a pure nitrogen atmosphere. The remained fractional residuals of these materials are used for the de...

Flexible and sensitive strain sensors can be utilized as wearable sensors and electronic devices in a wide range of applications, such as personal health monitoring, sports performance, and electronic skin. This paper presents the fabrication of a highly flexible and sensitive strain sensor by 3D printing an electrically conductive polydimethylsilo...

Fabrication of multifunctional materials via incorporation of the third component into structural composite laminates is of great interest, especially for manipulating surface properties. However, achieving a uniform, well‐dispersed surface microstructure in ternary composites is quite challenging by using the traditional fabrication processes. In...

The three-dimensional nano-morphology of poly(methyl methacrylate; PMMA) microcapsules filled with carbon nanotubes (CNTs) and epoxy resin were investigated by various microscopy methods, including a novel, laser scanning confocal microscopy (LSCM) method. Initially, PMMA microcapsules containing various amounts of CNTs were synthesized by a solven...

This paper presents highly flexible strain sensors fabricated by extrusion-based 3D printing of electrically conductive nanocomposites consisting of multi-walled carbon nanotube (MWNT)/polydimethylsiloxane (PDMS). The effects of printing parameters and nanocomposite formulation on the piezoresistive behavior of the 3D-printed sensors are investigat...

In recent years, a number of studies have used carbon nanotubes (CNTs) to enhance the thermomechanical properties of polymer-based composites. The improvement of properties, in most cases, is dependent on the uniform and complete dispersion of CNTs throughout the composite parts. The challenges in breaking up nanotube agglomerates and achieving ade...

This article presents three-dimensional printed and highly sensitive polydimethylsiloxane/multi-walled carbon nanotube sensors for compressive strain and pressure measurements. An electrically conductive polydimethylsiloxane/multi-walled carbon nanotube nanocomposite is developed to three-dimensional print compression sensors in a freestanding and...

Applying external pressure on the vacuum bag in heated-Vacuum Assisted Resin Transfer Molding (heated-VARTM) is a new approach for manufacturing high quality composite laminates with minimal voids. The present study focuses on the effects of external pressure and resin flushing on the microstructural features of the laminates, including spatial var...

This paper presents the additive manufacturing of electrically conductive polydimethylsiloxane (PDMS) nanocomposites for in-situ strain sensing applications. A straight line of pristine PDMS was first 3D printed on a thin PDMS substrate using an in-house modified 3D printer. Carbon nanotubes (CNTs) were uniformly sprayed on top of uncured PDMS line...

Polymers and polymeric composites have been well known to absorb and retain moisture in wet and humid environment, resulting in severe degradation of optical, electrical and thermo-mechanical properties. To describe the degree of property loss, moisture absorption by polymers and polymer composites have been often investigated using diffusion-based...

Short carbon fibers have excellent mechanical properties and high electrical conductivity which make them a suitable reinforcement for polymer composites. It is well-known that the mechanical and electrical properties of polymeric composites can be tailored by controlling the orientation of these fibers. There are different methods to produce compo...

During manufacturing of high-quality composite laminates, an elevated pressure is often applied over the laminate to increase the fiber content, reduce process-induced defects, and achieve enhanced interlaminar consolidation. In processes involving a vacuum bag, such as wet lay-up and vacuum assisted resin transfer molding, the consolidation pressu...

With growing environmental awareness, natural fibers have recently received significant interest as reinforcement in polymer composites. Among natural fibers, silk can potentially be a natural alternative to glass fibers, as it possesses comparable specific mechanical properties. In order to investigate the processability and properties of silk rei...

The compaction pressure on the fibrous preform is one of the most critical parameters in vacuum assisted resin transfer molding (VARTM), which significantly affects the preform permeability, mold filling time, and final thickness of the fabricated composite. In this study, the compaction pressure on the vacuum bag was controlled during and after th...

Vacuum-assisted resin transfer molding (VARTM) has several inherent shortcomings such as long mold filling times, low fiber volume fraction, and high void content in fabricated laminates. These problems in VARTM mainly arise from the limited compaction of the laminate and low resin pressure. Pressurized infusion (PI) molding introduced in this pape...

This study presents a novel method to fabricate high-quality, large composite parts which can be used in a wet lay-up/vacuum bag (WLVB) process. The new method utilizes a commercial lifting magnet, which is commonly used for transporting ferrous plates, to apply a magnetic consolidation pressure on the WLVB composite lay-up. The pressure is applied...

In recently developed magnet assisted composite manufacturing (MACM) processes, a magnetic consolidation pressure is applied on composite laminates by a set of permanent magnets during fabrication. This magnetic pressure was shown to provide considerable benefits such as increased fiber volume fraction, improved mechanical properties, and reduced v...

Carbon fibers are widely used as reinforcement in polymer-matrix composites due to their excellent mechanical properties combined with their lightweight. Coating of short carbon fibers with nickel not only preserves the desired specific mechanical properties of both the fiber and the resulting composite but also improves their electrical conductivi...

Voids are the most common process-induced defects in composite laminates fabricated by vacuum assisted resin transfer molding (VARTM). Reduction or total elimination of these defects is essential for the improved performance and long-term durability of the structural composites. This study introduces a novel method that reduces the void content in...

This paper presents the additive manufacturing of a stretchable and electrically conductive polydimethylsiloxane (PDMS) nanocomposite for strain sensing. A long, thin PDMS strip in a zig‐zag pattern of five parallel lines is 3D printed on elastomer substrate using an in‐house modified 3D printer. Multi‐walled carbon nanotubes (MWCNTs) are uniformly...

This paper introduces a comprehensive, data-driven method to predict the properties of composite materials, such as thermo-mechanical properties, moisture saturation level, durability, or other such important behavior. The approach is based on applying data mining techniques to the collective knowledge in the materials field. In this article, first...

Application of natural fibers in polymer composites has been gaining popularity in several industries pursuing environmentally friendly products. Among the natural fibers with proven potential applications, silk fibers have recently received considerable attention from researchers. Silk fibers provide higher mechanical properties compared to other...

This work demonstrates a protocol to improve the quality of composite laminates fabricated by wet lay-up vacuum bag processes using the recently developed magnet assisted composite manufacturing (MACM) technique. In this technique, permanent magnets are utilized to apply a sufficiently high consolidation pressure during the curing stage. To enhance...

The video component of this article can be found at https://www.jove.com/video/57254/

Resin transfer molding (RTM) is an attractive, versatile and cost-effective alternative to autoclave processing for manufacturing geometrically complex, structural polymer matrix composites (PMC). However, process induced defects such as microvoids or unwetted, dry spots often limit wider usage of RTM parts in high performance, mission critical app...

Microcapsules of poly(methyl methacrylate) [PMMA] containing epoxy and multi-walled carbon nanotubes were formed by solution evaporation in an aqueous emulsion. Thin PMMA shells precipitated at the resin/water interface as the solvent was removed, thus encapsulating the dispersion of epoxy and nanotubes. Dichloromethane (DCM) was selected as the co...

This paper demonstrates the feasibility of using high-power, permanent magnets in developing high consolidation pressure during a variety of fabrication methods for composite laminates. First, the salient features of this new manufacturing method, expected enhancement of the mechanical properties, and possible improvements in part quality are discu...

This paper presents the application of a new technique, Magnet Assisted Composite Manufacturing (MACM), to enhance the quality of composite laminates fabricated by wet lay-up/vacuum bag (WLVB) and vacuum assisted resin transfer molding (VARTM). Towards this goal, a set of high-power, Neodymium permanent magnets, which are placed on a magnetic tool...

Liquid Composite Molding (LCM) processes are cost efficient manufacturing alternatives to traditional autoclave technology for producing near-net shape structural composite parts. However, process induced defects often limit wider usage of LCM in structural applications. Thorough knowledge of these defects, as well as their formation mechanisms and...

A novel fabrication method, Magnet Assisted Composite Manufacturing (MACM), is developed to produce high-quality composite laminates out of an autoclave. This technique involves the placement of high-temperature Neodymium permanent magnets on a vacuum bag to generate sufficiently high consolidation pressure during cure, thus eliminating the necessi...

Although vacuum-assisted transfer molding (VARTM) is preferred for manufacturing medium to large composite parts due to its simple tooling and low cost, part quality dictated by dimensional tolerances, void content and mechanical properties is usually low due to inherent limitations of the process. In this study, the conventional VARTM process was...

The importance of using the exact solution of the hindered diffusion model is demonstrated on experimental data from a nanoclay/epoxy composite.

Susceptibility of polymeric composites to moisture has been well known for several decades. Most high performance epoxy or bismaleimide (BMI) resins and their fiber-reinforced composites may absorb up to 5 wt% moisture which could lead to 10-30% reduction in various mechanical properties, including flexural strength, stiffness, impact resistance, a...

Cognitive Empathy, often referred to as perspective taking, refers to the ability to identify and understand details about another’s experience so that one can understand why people may think and feel the way that they do. In recent years the need for designers to develop Cognitive Empathy skills has been recognized and has given rise to human-cent...

Fiber-reinforced polymer composites may offer numerous attractive features such as low cost, high specific performance, and ease of production. However, there are concerns about the overall durability of these materials, especially for sustained performance under severe and changing environmental conditions. There also is a general lack of data on...

Bismaleimide (BMI) resin with Quartz (AQ581) fiber reinforcement is desirable for systems requiring a high glass transition temperature, low dielectric properties, and high laminate mechanical properties. These properties make quartz/BMI an ideal composite material for complex aerospace structures, and are currently being used in various aircraft e...

Bismaleimide (BMI) resin with Quartz (AQ581) fiber reinforcement is a high-temperature composite material that is frequently used in aerospace structures, such as engine cowlings and radomes. Variations in laminate fabrication conditions, such as prepreg conditioning and applied cure pressure, can have a significant effect on microstructural featur...

Use of composite materials in complex and robust systems, such as aircraft fuselage and load-bearing structures, is becoming more prevalent as analysis and manufacturing techniques improve. Bismaleimide (BMI) resin with Quartz (AQ581) fiber reinforcement is one such composite material used in products requiring a high glass transition temperature a...

Water within thermal insulation can significantly affect the fluid and gas flow properties through the pipelines by altering the thermal properties of the insulation material. This paper reports on moisture absorption and thermal conductivity of some common pipeline insulation materials such as calcium silicate, cellular glass, mineral wool, perlit...

Moisture content of composite prepregs are known to significantly affect the process-induced laminate microstructure and formation of microvoids during cure. In this study, the moisture absorption of eight-ply quartz (AQ 581)/Bismaleimide (BMI) composite laminates is investigated. Four different types of composite laminates are fabricated using eig...

Bismaleimide (BMI) resin with quartz (AQ581) fiber reinforcement is a composite material frequently used in aerospace applications, such as engine cowlings and radomes. Various composite components used in aircrafts are exposed to different types of hydraulic fluids, which may lead to anomalous absorption behavior over the service life of the compo...

Susceptibility of polymeric composites to moisture absorption has been well known for several decades. It has been common practice to use a one-dimensional Fickian model to characterize and predict the diffusion of moisture into polymeric composite laminates. However, in several high-performance and mission critical applications more sophisticated...

Degradation of properties of composite materials due to exposure to humid environment has been well-known for several decades. In most cases, degree of degradation is correlated to the amount of the absorbed moisture. Although the rate and amount of moisture absorption is most often modeled by one-dimensional Fickian model [1,2], polymeric composit...

It is known that fiber-reinforced thermosetting composites are susceptible to absorbing moisture and other liquid contaminants. Irreversible damage, such as resin plasticization, laminate swelling, and fiber-matrix debonding, can be caused by small amounts of liquid penetrants absorption. Quartz fiber (AQ581) reinforced Bismaleimide (BMI) is a high...

Void formation as a result of prepreg moisture content and processing pressure during cure was experimentally investigated in thermosetting composite laminates. This was achieved by determining the void contents of eight-ply laminates fabricated from TenCate® BT250/7781 E-glass/epoxy prepreg at processing pressures of 1.7 atm, 3.0 atm, 4.4 atm, and...

The focus of this paper was to investigate the effects of microvoid content in quartz/BMI laminates on both short and long-term moisture absorption dynamics. The moisture absorption characteristics for the laminates were experimentally obtained by water immersion tests at 25°C of three-ply quartz/BMI samples that contain voids, ranging from 8.6% to...

The failure strength of polymeric composite materials is known to degrade as manufacturing defects such as microvoids are increased. The adverse effects of microvoids are typically assumed to increase with microvoid content and are often considered to be independent of fiber volume content. However, a survey of published experimental data indicates...

The effects of sizing on carbon fiber reinforced composites used in thermal management applications can be considerable due to the highly anisotropic nature of single carbon fiber thermal conductivity. Most commercially available carbon fiber is produced with sizing because it helps to optimize production speed, facilitates a cost-effective and qua...

Moisture absorption in polymers and polymeric composites is well known to lead to significant degradation in mechanical properties. Most epoxy based composites may absorb 2 to 5 wt.% moisture when they are subjected to humid environments. Moisture absorption in polymers has been often characterized with Fickian or various non-Fickian models to desc...

Moisture absorption in polymers and polymeric composites is well known to lead to significant degradation in mechanical properties. Most epoxy based composites may absorb 2 to 5 wt.% moisture when they are subjected to humid environments. Moisture absorption in polymers has been often characterized with Fickian or various non-Fickian models to desc...

Bladder Assisted Composite Manufacturing (BACM) is a recently developed out-of-autoclave process designed to fabricate geometrically complex, hollow composite parts. This paper assesses the ability of three new BACM process variations to fabricate parts with high fiber and low void contents. This was achieved by fabricating 4-ply cylinders from a c...

A recently developed moisture absorption model for thermosetting polymers that combines the non-Fickian, diffusion hindrance effects and three-dimensional anisotropy is introduced. The hindered diffusion model is shown to predict both short term Fickian and long term anomalous moisture absorption behavior often observed in thermosetting polymers an...

The three-dimensional anisotropic moisture absorption behavior of quartz-fiber-reinforced bismaleimide (BMI) laminates is investigated by collecting 21 months of experimental gravimetric data. Laminates of six, twelve, and forty plies and various planar aspect ratios are used to determine the three-dimensional anisotropic diffusion behavior when ex...

Carbon fiber-reinforced composites (CERCs) have been fabricated using a vacuum assisted resin transfer molding (VARTM) incorporating carbon nanofibers (CNFs). Incorporation of CNFs in the composite laminate was performed by both matrix-modification and fiber-modification routes. In the matrix-modification route, vapor grown carbon nanofibers (VGCNF...

The College of Engineering of the University of Oklahoma (OU) embarked on a journey to develop and maintain an I/UCRC (Industry/University Cooperative Research Center) for ten years under the guidance of the NSF (National Science Foundation) on the topic of Engineering Logistics and Distribution (CELDi). CELDi is a multi-university center of excell...

Effects of sizing and surface modification on flexural properties of carbon fiber reinforced epoxy composites have been investigated. Carbon fiber was desized using three types of treatments, namely heat, acetone, and acetone-acid. In addition, these fibers were coated with three different types of Polyhedral Oligomeric Silsesquioxane (POSS) molecu...

The nonlinear structural dynamics of a slender beam in flapping motion is examined both experimentally and computationally. In the experiments the periodic flapping motion is imposed on the clamped edge of the cantilever beam using a 4-bar crank-and-rocker mechanism. Aluminum beams with nominal dimensions of 150 mm×25 mm×0.4 mm are tested in air ov...

The use of high performance polymer composites has become more common during the last several decades. However, the high manufacturing cost of these materials currently limits their widespread use in various applications that require high production rate at a lower cost. One attractive manufacturing technique to fabricate low-cost, high performance...

A new, three-dimensional, anisotropic non-Fickian diffusion model is developed to characterize moisture absorption in polymeric composites. The new hindered diffusion model extends the classical Fickian theory to include the effects of the interaction of diffusing molecules with the chemical and physical structure of polymeric composites. The numer...

Polyester composite tiles (PCT) are synthesized from PET and fabricated by compression molding using micromarble clusters as filler. Identical PCTs are also fabricated by using commercially available polyester resin to compare properties. Three batches of marble clusters with different size distributions are used to assess the effect of filler part...