Youssef K. Hamidi

• PhD
• Faculty Member at University of Houston - Clear Lake

Aerospace industry is intensely shifting towards the usage of composite materials, as the new Airbus and Boeing aircrafts, among others, comprise increasing percentages of these materials. Beyond their higher specific mechanical properties, fiber reinforced polymer composites are non-magnetic, and thus do not interfere with the magnetic compass of...

Polyether-ether-ketone (PEEK) is one of the high-performance polymers and has versatile applications in different industries. It has higher mechanical strength compared to other high-temperature polymers, and achieving this mechanical strength using additive manufacturing is not straightforward. Additive manufacturing of PEEK requires great attenti...

In this study, a relatively new and low-cost commodity-type 3D printing filament material, acrylonitrile styrene acrylate (ASA), was used as a feedstock to a commercially available, desktop fused filament fabrication 3D printer. The aim was to correlate the mechanical properties of the 3D printed specimen to the raster orientation and extrusion tem...

COVID-19 has created shortages of personal protective equipment. In resource-constrained situations, limited cycles of disinfection and extended use of gloves is recommended by the U.S. Centers for Disease Control and Prevention to conserve supplies. However, these guidelines are based on limited evidence. In this study, serial cycles of hand hygie...

Many healthcare professionals have been forced, under acute shortages, to extend medical exam gloves beyond their intended single use. Despite limited available literature, the CDC proposed a set of guidelines for repeated exam gloves use, indicating a maximum number of treatments for three widely available disinfectants. This study examines how th...

The human cost of the COVID-19 pandemic has taken a great toll, and led, around the globe, to a shortage in personal protective equipment (PPE) such as medical exam gloves. To face this shortage and keep themselves and patients safe, many front-line healthcare providers have been overextending the life of PPE. Though not ideal, one pragmatic soluti...

Abstrac Since the mass outbreak of COVID-19 globally, the unique challenges of the pandemic have demanded the global economy, governments , and scientific community adapt in unprecedented ways. Despite pre-existing federal stockpiles of personal protective equipment (PPE) in countries such as the United States, rising shortages and resource constra...

Background: The COVID-19 pandemic has created global shortages of personal protective equipment (PPE) such as medical exam gloves, forcing healthcare workers to either forgo or reuse PPE to keep themselves and patients safe from infection. In severely resource-constrained situations, limited cycles of disinfection and extended use of gloves is reco...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

In recent years, fiber-reinforced composites integrated key technological areas such as aerospace, defense and automotive industries [1-5]. The attractiveness of these man-made materials is mainly due to their lower costs and lower weight to strength ratios when compared to conventional materials. Another attractive feature that certain manufacturi...

Although known for their ease of production and high specific properties, fiber reinforced polymer composites are highly susceptible to environmental conditions such as moisture absorption. While the adverse effects of moisture on composite parts are well documented, effects of repeated loading on moisture absorption of composites are not fully kno...

Effect of fiber volume fraction on occurrence, morphology, and spatial distribution of microvoids in resin transfer molded E-glass/epoxy composites is investigated. Three disk-shaped center-gated composite parts containing 8, 12, and 16 layers of randomly-oriented, E-glass fiber perform are molded, yielding 13.5, 20.5 and 27.5% fiber volume fractio...

Dispersion of nanoclay clusters during resin transfer molding of nanoclay/glass/epoxy disks is investigated. In addition to a center-gated disk containing only 14% glass fibers, three nanocomposite disks are fabricated with the addition of 2, 5 or 10 wt% Cloisite® 25A nanoclay. The spatial distribution of nanoclay clusters along the radial axis of...

The state of nanoclay dispersion in a molded epoxy disk and its effects on the thermo-mechanical properties of the resulting nanocomposite are analyzed. A commercially available nanoclay, Cloisite® 25A, is mechanically mixed at 2 wt% with EPON 815C epoxy resin. The epoxy/clay compound is then mixed with EPI-CURE 3282 curing agent by a custom made m...

Effects of nanoclay content on morphology and spatial distribution of voids in resin transfer molded nanoclay/E-glass/epoxy composite disks are investigated. Closite®25A nanoclay loads of 2, 5, and 10wt% are mixed by sonication with a low-viscosity epoxy resin prior to filling the mold cavity containing 13.6% E-glass preform by volume. A disk witho...

Recent progress in the field of nanotechnology has increased the curiosity in new polymers reinforced with nanosized particles. These new polymers, called nanocomposites, are reported to exhibit strikingly improved mechanical, thermal, optical and physico-chemical properties, when compared to the pristine polymers or conventional (microscale) compo...

Nanoclay reinforced composites have gained significant research interest since the early 1990’s due to the possibility of achieving improved mechanical and thermal properties [1]. The utility of nanoclay with thermoplastics have been studied extensively and its effects on various properties are characterized [2,3]. However, the expected improvement...

Nanoclay has been gaining acceptance as a nano-meter scale reinforcement for polymers during the last two decades [1]. It has proven to be successful for reinforcing thermoplastics [2], however, its utilization in thermosetting resins has been problematic. To improve dispersion of nanoclay into thermosetting resins, a number of companies developed...

Effects of applying a packing pressure on void content, void morphology, and void spatial distribution were investigated for resin transfer molding (RTM) E-glass/epoxy composites. Packing pressures of zero and 570 kPa were respectively applied to center-gated composites containing 17.5% randomly oriented, E-glass fiber preform. Radial samples of th...

Detailed analyses of shape, size, and spatial variations of void morphology are presented for a disk-shaped, resin transfer molded (RTM), E-glass/epoxy composite. The disk is molded at constant injection rate and contains 17.5% E-glass random fiber mats. Voids throughout the composite are evaluated by microscopic image analysis of through-the-thick...

Composite materials often suffer from process-induced defects such as voids that lower their overall performance and thus limit their wider application. Void formation mechanisms and detrimental effects of voids on mechanical properties of composite parts have been studied extensively. In contrast, limited void reduction strategies are available fo...

Thermo-mechanical properties of polymers can be significantly altered by the addition of nano-scale particulates such as carbon nanotubes and nanofibers. Among the nano-scale particulates, inclusion of nanoclay is proven to improve thermal and mechanical properties of polymers significantly even at small volume fraction levels. In addition, nanocla...

Inclusion of nanoclay in various polymer systems is being studied as a viable improvement method for thermo-mechanical properties for more than a decade. It has also been shown that addition of nanoclay into polymers significantly enhances thermal durability of the part. It is possible that the addition of nanoclay to conventional fiber-reinforced...

Polymer composites are mixtures of a polymer, which is the major or continuous phase, and a filler, which can be either metal, ceramic, or even another polymer. Both thermosetting and thermoplastic resins can be used as the polymer phase; the former has the advantage of low viscosity while the latter has the advantage of the possibility of recyclin...

Models based on one-dimensional solution of Fickian diffusion equation are commonly used to characterize diffusion coefficients of polymers. These methods are known to have errors due to edge effects, which are believed to be compensated by correction factors. In order to better understand these errors and performance of various correction factors,...

Spreading behavior and advancing contact angle of a low viscosity epoxy resin on three commercially available nanoclays — Cloisite® Na+ , Cloisite® 15A and Cloisite® 25A — at 52°C is investigated. In addition, effect of temperature on spreading dynamics of epoxy on Cloisite® Na+ is analyzed at 33, 52 and 77°C. For wetting experiments, nanoclay powd...

Effects of mixing temperature on the quality of dispersion of nanoclay in an epoxy resin are investigated. Cloisite ® 25A nanoclay is mixed at 5wt.% loading with EPON 815C epoxy resin at 30, 50 and 75°C by the aid of a sonicator. The resin/nanoclay compound is then mixed with Epicure 3282 curing agent and molded into center-gated disk shaped parts...

Resin transfer molded (RTM) composites usually suffer from the formation of flow-induced defects such as voids. Detrimental effects of voids on performance of molded parts have been studied extensively. Yet, knowledge of effective void removal strategies, along with detailed morphological void distribution within molded composites is very limited....

Performance of composite materials usually suffers from process-induced defects such as dry spots and microscopic voids. While effects of void content in molded composites have been studied extensively, knowledge of void morphology and spatial distribution of voids in composites manufactured by resin transfer molding (RTM) remains limited. In this...

The common methods used to determine the diffusion coefficients of polymer composites are based on the solution of Fickian diffusion equation in one-dimensional rectangular domain. However, these diffusivities usually involve errors primarily due to finite sample dimensions and anisotropy introduced by fiber reinforcements. In this study, the solut...

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....

A novel approach for characterization of nanoclay dispersion in polymeric composites using electron microprobe analysis (EMPA) is presented. Dispersion analysis is performed on three sets of center-gated disks f abricated by resin transfer molding. The first set is neat epoxy polymer without reinforcement, where as the second set comprises 17vol.%...

An experimental study is performed to characterize the effect of the thickness of random preforms on injection pressure and mechanical properties of resin transfer molded (RTM) parts. Center-gated, disk-shaped parts are molded using two different chopped-strand glass fiber preforms. Both preforms have random microstructure but different planar dens...

Liquid composite molding (LCM) processes such as resin transfer molding (RTM) have been successfully used to manufacture high performance fiber-reinforced composites at a low cost. However, these composites usually suffer from dry spots and voids formed during molding that decrease their load-bearing capability. Void formation mechanisms and detrim...

High-speed processing is essential to achieve lower production cost in the fabrication of fiber-reinforced composites with the current liquid molding practices. A major consequence of increasing the resin injection velocity is the formation of defects such as voids and dry regions that decrease the load-bearing capability of the composite. Void for...

Performance of composite materials usually suffers from process-induced defects such as dry spots or microscopic voids. While effects of void content in molded composites have been studied extensively, knowledge of void morphology and spatial distribution of voids in composites manufactured by resin transfer molding (RTM) remains limited. In this s...

The state of nanoclay dispersion in a molded epoxy disk and its effects on the thermo-mechanical properties of the resulting nanocomposite are analyzed. A commercially available nanoclay, Cloisite® 25A, is mechanically mixed at 2wt.% with EPON 815C epoxy resin. The epoxy/clay compound is then mixed with EPI-CURE 3282 curing agent by a custom made m...

Significant spatial variation in void content and morphology might exist for resin transfer molded E-glass/epoxy composites. These variations seem to correlate well with the local velocity of the fluid front during filling. The slower moving fluid front traps less and more circular voids, whereas the voids might be sheared into more elliptical and...

Composites are being increasingly used in various applications because of their light weight and high performance. One of the common disadvantages of composite materials is the formation of defects during manufacturing such as voids and dry spots that adversely affect mechanical and physical properties. Although void formation mechanisms and analyt...

Hydrophilicity of polymers makes them prone to moisture absorption that leads to degradation of mechanical properties. Kinetics of moisture ingress needs to be fully characterized to perform reliable designs with polymeric materials. The rate of diffusion is the essential parameter in determining the time scale of the moisture uptake in polymeric m...

Transient water sorption studies were carried out at constant temperature (45 °C) to assess the hydrolytic stability and wet-adhesion properties of glass fiber/epoxy composites having different sizings. Lower effective diffusivity values correlated with improved overall mechanical performance in relation to the control (unsized) samples, and reveal...

The common methods used to determine the diffusion coefficients of polymer composites are based on the solution of Fickian diffusion equation in one-dimensional (1D) rectangular domain. However, these diffusivities usually involve errors primarily due to finite sample dimensions and anisotropy introduced by fiber reinforcements. In this study, the...

Fiber reinforced polymer composites are highly susceptible to environmental conditions despite their favorable properties. Among various environmental factors, moisture absorption is known to have significant adverse effects on such materials. This work investigates the effects of accelerated moisture absorption on the mechanical properties of resi...

Fiber reinforced polymer composites are highly susceptible to environmental conditions despite their favorable properties. Among various environmental factors, moisture absorption is known to have significant adverse effects on such materials. This work investigates the effects of accelerated moisture absorption on the mechanical properties of resi...

Desorption characteristics and mechanical property retention of previously moisture conditioned glass-epoxy composites are studied. Resin transfer molding is used to fabricate disk shaped parts reinforced with randomly oriented chopped glass fiber preforms. Neat polymer as well as composite parts reinforced with different number of preform layers a...

Mold fill velocities of 0.067 cm3/s and 2.66 cm3/s were used to impregnate glass fiber preforms with different architectures and sizing types in two force-controlled resin transfer molding (RTM) fixtures. The fabrication of disk-shaped parts at high molding speed and high post-cure fill pressure was proven successful in reducing the amount of flow-...

Fiber reinforced polymer composites are preferred in many structural applications for their ease of production and high specific strengths. Although fatigue loading is commonly encountered in structural applications, behavior of composites under cyclic loading is less understood compared to fatigue behavior of more conventional metals and their all...

The type and volume fraction of fibrous preform used in resin transfer molding has significant influence on the properties of the molded composite parts. In this study, effect of preform architecture and fiber volume fraction on the mechanical properties of resin transfer molded composites is experimentally investigated. A molding setup is construc...

Organosilane coupling agents are widely used in the composites industry to improve the wetting of inorganic reinforcements by low surface energy resins. An increased wettability is often a harbinger of better mechanical properties in a structural composite. Silane coatings effectively increase the spreading of liquid matrixes over glass reinforceme...