New Insights into the Mechanical Behavior of Thin-Film Composite Polymeric Membranes.

Limited predictions of thin-film composite (TFC) membranes' behavior and functional life exist due to the lack of accurate data on their mechanical behavior under different operational conditions. A comprehensive investigation of the mechanical behavior of TFC membranes addressing deformation and failure, temperature and strain rate sensitivity, and anisotropy is presented. Tensile tests were conducted on commercial membranes as well as on individual membrane layers prepared in our laboratories. The results reveal the overall mechanical strength of the membrane is provided by the polyester layer (bottom layer), while the rupture stress for the middle and top layers is at least 10 times smaller than that of the polyester layer. High anisotropic behavior was observed and is attributed to the nonwoven structure of the polyester layer. Rupture stress in the transverse (90°) direction was one-third of the rupture stress in the casting direction. Limited temperature and strain rate dependence was observed in the temperature range that exists during operation. Scanning electron microscopy images of the fractured surfaces were also analyzed and correlated with the mechanical behavior. The presented results provide new insights into the mechanical behavior of thin-film composite membranes and can be used to inform novel membrane designs and fabrication techniques.

Printability for additive manufacturing with machine learning: Hybrid intelligent Gaussian process surrogate-based neural network model for Co-Cr alloy.

AM has revolutionized the manufacturing industry, involving several operating parameters that may affect the properties of the final manufactured part. In AM, LPBF has proved its reliability in producing dense components; however, process development for every material necessitates extensive testing. Even the tiniest change can negate all the data for the same material. It is vital to have a P-P correlation that can train itself following a change in powder or machine to achieve defects-free parts and optimal properties. These goals cannot be met alone by multi-physics. One of the ways to address this issue is to apply ML, but it requires a huge data set for training and testing purposes. A framework has been developed for Co-Cr S-S curves to resolve this issue. Twenty-two experimental S-S curves have been generated to produce YS, TS, and EL data points. In combination with DNN, these data points have been applied to the validated and tested GPS-surrogate model to develop a smart processing window to achieve desired YS, TS, and EL. LP, LSS, HD, and PLT have been selected during the whole framework as inputs, while YS, TS, and EL have been classified as outputs. The output of the smart window was verified experimentally. It is found that the highest YS (1110.91 MPa) is attained using LP = 180 W, LSS = 600 mm/s and HD = 70 µm, while least YS (645.05 MPa) is identified using LP = 160 W, LSS = 900 mm/s and HD = 70 µm. For TS, the maximum (165.91 MPa) and minimum (689.73 MPa) values have been achieved using LP = 180 W, LSS = 900 mm/s and HD = 70 µm, and LP = 180 W, LSS = 1000 mm/s and HD = 70 µm, respectively. In the case of EL, LP = 180 W, LSS = 700 mm/s and HD = 70 µm, and LP = 180 W, LSS = 600 mm/s and HD = 70 µm, resulted 23.04% and 0.789% EL, respectively. Using CC, LP and HD did not significantly affect the TS, YS, and EL, while a negative relationship has been found for LSS with TS, YS, and EL. The smart processing window showed that the YS and TS could be achieved at low-high LP and low LSS at the cost of EL. This study provides a technique for framework development in the case of P-P relation based on the provided inputs and the corresponding outputs, leading toward process smartification.

A Review on the Modeling of the Elastic Modulus and Yield Stress of Polymers and Polymer Nanocomposites: Effect of Temperature, Loading Rate and Porosity.

Porous polymer-based nanocomposites have been used for various applications due to their advantages, including multi-functionalities, easy and known manufacturability, and low cost. Understanding of their mechanical properties has become essential to expand the nanocomposites' applications and efficiency, including service-life, resistance to different loads, and reliability. In this review paper, the focus is on the modeling of the mechanical properties of porous polymer-based nanocomposites, including the effects of loading rates, operational temperatures, and the material's porosity. First, modeling of the elastic modulus and yield stress for glassy polymers and polymer reinforced by nanofillers are addressed. Then, modeling of porosity effects on these properties for polymers are reviewed, especially via the use of the well-known power-law approach linking porosity to elastic modulus and/or stress. Studies related to extending the mechanical modeling to account for porosity effects on the elastic modulus and yield stress of polymers and polymer-nanocomposites are discussed. Finally, a brief review of the implementation of this modeling into 3D computational methods to predict the large elastic-viscoplastic deformation response of glassy polymers is presented. In addition to the modeling part, the experimental techniques to measure the elastic modulus and the yield stress are discussed, and applications of polymers and polymer composites as membranes for water treatment and scaffolds for bone tissue engineering are addressed. Some modeling results and validation from different studies are presented as well.

Towards the Development of Novel Hybrid Composite Steel Pipes: Electrochemical Evaluation of Fiber-Reinforced Polymer Layered Steel against Corrosion.

Corrosion remains one of the major and most costly challenges faced by the steel industry. Various fiber-reinforced polymer coating systems have been proposed to protect metallic piping distribution networks against corrosion. Despite increasing interest among scientific and industrial communities, there is only limited predictive capability for selecting the optimum composite system for a given corrosive condition. In this study, we present a comprehensive evaluation of the electrochemical behavior of two different fiber-reinforced polymer composite systems against the corrosion of carbon steel pipes under a wide range of acidic and corrosive solutions. The composites were made of glass and Kevlar fibers with an epoxy resin matrix and were subjected to corrosive solutions of 0.5 M NaCl, 0.5 M HCl, and 0.5 M H2SO4. The kinetics of the corrosion reactions were evaluated using potentiodynamic polarization (PDP) tests. In addition, electrochemical impedance spectroscopy (EIS) tests were carried out at open circuit potentials (OCPs). It was demonstrated that the glass fiber-reinforced polymer coating system offered the best protection against corrosion, with a high stability against deterioration when compared with epoxy and Kevlar fiber-reinforced polymer coating systems. Scanning electron microscopy images revealed cracks and deteriorated embedded fibers due to acid attack, sustained/assisted by the diffusion of the corrosion species.

External Corrosion Behavior of Steel/GFRP Composite Pipes in Harsh Conditions.

In this study, we report on the corrosion behavior of hybrid steel/glass fiber-reinforced polymer (GFRP) composite pipes under harsh corrosive conditions for prolonged durations. Specimens were immersed in highly concentrated solutions of hydrochloric acid, sodium chloride, and sulfuric acid for durations up to one year. Detailed qualitative analysis using scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and energy-dispersive X-ray spectroscopy (EDX) is presented. It is shown that the hybrid pipes have excellent corrosion resistance with a corrosion rate of less than 1% of the corrosion rate for conventional steel pipes. That low corrosion rate can be attributed to the formation of pores in the GFRP layer due to increased absorption and saturation moisture in the material with increased soaking time. This can be reduced or even prevented through a more controlled process for fabricating the protective layers. These promising results call for more utilization of GFRP protective layers in novel design concepts to control corrosion.

Engineering the Surface and Mechanical Properties of Water Desalination Membranes Using Ultralong Carbon Nanotubes.

In this work, novel polysulphone (PS) porous membranes for water desalination, incorporated with commercial and produced carbon nanotubes (CNT), were fabricated and analyzed. It was demonstrated that changing the main characteristics of CNT (e.g., loading in the dope solutions, aspect ratio, and functionality) significantly affected the membrane properties and performance including porosity, water flux, and mechanical and surface properties. The water flux of the fabricated membranes increased considerably (up to 20 times) along with the increase in CNT loading. Conversely, yield stress and Young's modulus of the membranes dropped with the increase in the CNT loading mainly due to porosity increase. It was shown that the elongation at fracture for PS/0.25 wt. % CNT membrane was much higher than for pristine PS membrane due to enhanced compatibility of commercial CNTs with PS matrix. More pronounced effect on membrane's mechanical properties was observed due to compatibility of CNTs with PS matrix when compared to other factors (i.e., changes in the CNT aspect ratio). The water contact angle for PS membranes incorporated with commercial CNT sharply decreased from 73° to 53° (membrane hydrophilization) for membranes with 0.1 and 1.0 wt. % of CNTs, while for the same loading of produced CNTs the water contact angles for the membrane samples increased from 66° to 72°. The obtained results show that complex interplay of various factors such as: loading of CNT in the dope solutions, aspect ratio, and functionality of CNT. These features can be used to engineer membranes with desired properties and performance.

Inorganic Membranes: Preparation and Application for Water Treatment and Desalination.

Inorganic membrane science and technology is an attractive field of membrane separation technology, which has been dominated by polymer membranes. Recently, the inorganic membrane has been undergoing rapid development and innovation. Inorganic membranes have the advantage of resisting harsh chemical cleaning, high temperature and wear resistance, high chemical stability, long lifetime, and autoclavable. All of these outstanding properties made inorganic membranes good candidates to be used for water treatment and desalination applications. This paper is a state of the art review on the synthesis, development, and application of different inorganic membranes for water and wastewater treatment. The inorganic membranes reviewed in this paper include liquid membranes, dynamic membranes, various ceramic membranes, carbon based membranes, silica membranes, and zeolite membranes. A brief description of the different synthesis routes for the development of inorganic membranes for application in water industry is given and each synthesis rout is critically reviewed and compared. Thereafter, the recent studies on different application of inorganic membrane and their properties for water treatment and desalination in literature are critically summarized. It was reported that inorganic membranes despite their high synthesis cost, showed very promising results with high flux, full salt rejection, and very low or no fouling.

Enhancement of osteoblast gene expression by mechanically compatible porous Si-rich nanocomposite.

Synthesis of a porous bioactive ceramic implant for load bearing applications is a challenging task in maxillofacial and orthopedic surgeries. A novel bioactive resorbable silica-calcium phosphate nanocomposite (SCPC) has recently been introduced as a potential bone graft. In the present study, we employed SCPC to develop a resorbable porous scaffold and analyzed the effects of composition and porosity on the mechanical properties. The ranges of compressive strength and modulus of elasticity of SCPC containing 32-56% porosity were 1.5-50 MPa and 0.14-2.1 GPa, respectively, which matched the corresponding values for trabecular bone. The compressive strength of dense SCPC was dependent on the Si content and acquired values (93-285 MPa) comparable to that of cortical bone. The superior mechanical properties of SCPC are attributed to the intricate interactions at the boundaries of the nanograins and to the homogenous distribution of hierarchical pore-structure throughout the material volume. X-ray computed tomography and mercury porosimetry analyses revealed high interconnectivity of the pores in the size range 3 nm to 650 microm. Quantitative real-time PCR analyses showed that neonatal rat calvarial osteoblasts attached to Si-rich SCPC expressed 5- and 26-fold higher osteocalcin mRNA levels compared to cells attached to ProOsteon hydroxyapatite disks and tissue culture polystyrene plates respectively, after four days in culture. Results of the present study strongly suggest that porous, bioactive resorbable SCPCs can serve as tissue engineering scaffolds for cell delivery to treat load-bearing bone defects in orthopedic and maxillofacial surgeries.