Thermomechanical Stability Research Articles

A thermomechanical analysis leading to a novel flank face design providing longer tool lives for tools used in the drilling of Inconel 718

Inconel 718 is a versatile material due to its excellent properties. However, machining and in particular drilling of Inconel 718 present great challenges for the tools. In order to increase process reliability and tool life, a novel modification for the applied drilling tools was developed. It consists of a flank face retraction behind the cutting edge which is created by grinding. While regular drilling tools feature a continuous flank face on the tool tip, the retraction provides a minimized frictional surface between the tool tip and the bore hole ground. Furthermore, computational fluid dynamics simulations have shown that the created vacuous volume behind the cutting edge becomes filled with cutting fluid during the drilling process. The described effects result in longer tool lives which could be shown in experimental investigations. This paper presents the conducted experiments in which both the occurring mechanical and thermal loads were examined in order to determine the radius-dependent thermomechanical loads along the cutting edge. The results have shown that an increase in either cutting speed or feed result in significantly higher temperatures at the cutting edge corners while temperatures at the inner diameter of the tool remained almost constant. At the same time, a rise in feed leads to notably higher mechanical loads along the whole cutting edge. In addition, reference tool life tests were conducted using standard tools and under variation of the cutting values. The resulting tool wear as well as the tool-workpiece contact zones were investigated in detail. The gathered findings were then used to develop a flank face modification whose sufficient thermomechanical stability was ensured by FEM simulations. Afterwards, the new tool design was applied to drilling tools and then validated in field tests. The results show that a considerably higher drilling distance as well as lower tool wear and thus a longer tool life could be achieved with the modified drills.

High temperature PEMs developed from the blends of Polybenzimidazole and poly(azomethine-ether)

Proton exchange membrane (PEM) has been developed from the polymer blend of polybenzimidazole (PBI) and poly(azomethine-ether) (PAME). The effects of the blend compositions on the properties such as thermo-mechanical stability, proton conductivity etc. of PEM were studied. The miscibility of the blend membranes was confirmed by characterizing the blend samples using varieties of spectroscopy and thermo dynamical techniques. FT-IR and SS-NMR studies revealed the presence of specific interactions between the two polymers. All blend membranes showed single glass transition temperature (Tg) attributing that the this blend system is a miscible blend. The thermogravimetric studies confirmed that the blend membranes were more stable than the pristine PBI below 300 °C temperatures and less stable above 300 °C. Morphology probed by transmission electron microscopy studies displayed morphological features which consisted of both thread like structure and particle like structures thus confirming the uniform mixing of polymers in the blends. Mechanical stabilities of the blend membranes were quite high compared to the pristine polymers as obtained from the dynamic mechanical analyzer (DMA) studies. The blend membranes showed higher proton conductivity compared to pristine PBI. The proton conductivity increased upon increasing the percentage of PAME in the blend membranes. All these results indicated that the blend membranes are promising candidates for the application in high temperature proton exchange membrane in fuel cell.

Thermomechanical nonlinear stability of pressure-loaded CNT-reinforced composite doubly curved panels resting on elastic foundations

AbstractNonlinear stability of nanocomposite spherical and cylindrical panels reinforced by carbon nanotubes (CNTs), resting on elastic foundations and subjected to uniform external pressure in thermal environments is investigated in this paper. CNTs are embedded into matrix phase through uniform distribution (UD) or functionally graded (FG) distribution, and effective properties of CNT-reinforced composite are estimated through an extended rule of mixture. Governing equations are based on classical shell theory taking geometrical nonlinearity, initial geometrical imperfection and panel-foundation interaction into consideration. Approximate solutions of deflection and stress functions are assumed to satisfy simply supported boundary conditions and Galerkin method is applied to obtain nonlinear load-deflection relation. Numerical examples show the effects of volume fraction and distribution type of CNTs, in-plane condition of edges, curvature of panel, thermal environments, elastic foundations and imperfection size on the nonlinear response and snap-through instability of the curved panels. The present study reveals that efficiency of CNT distribution type depends on curvature of panel and in-plane behavior of boundary edges, and bifurcation type buckling response of pressure-loaded panels may occur at elevated temperature.

Less is More: Improved Thermal Stability and Plasmonic Response in Au Films via the Use of SubNanometer Ti Adhesion Layers.

The use of a metallic adhesion layer is known to increase the thermo-mechanical stability of Au thin films against solid-state dewetting, but in turn results in damping of the plasmonic response, reducing their utility in applications such as heat-assisted magnetic recording (HAMR). In this work, 50 nm Au films with Ti adhesion layers ranging in thickness from 0 to 5 nm were fabricated, and their thermal stability, electrical resistivity, and plasmonic response were measured. Subnanometer adhesion layers are demonstrated to significantly increase the stability of the thin films against dewetting at elevated temperatures (>200 °C), compared to more commonly used adhesion layer thicknesses that are in the range of 2-5 nm. For adhesion layers thicker than 1 nm, the diffusion of excess Ti through Au grain boundaries and subsequent oxidation was determined to result in degradation of the film. This mechanism was confirmed using transmission electron microscopy and X-ray photoelectron spectroscopy on annealed 0.5 and 5 nm adhesion layer samples. The superiority of subnanometer adhesion layers was further demonstrated through measurements of the surface-plasmon polariton resonance; those with thinner adhesion layers possessed both a stronger and spectrally sharper resonance. These results have relevance beyond HAMR to all Ti/Au systems operating at elevated temperatures.

Multiblock copolymers of sulfonated PSU/PPSU Poly(ether sulfone)s as solid electrolytes for proton exchange membrane fuel cells

Sulfonated multiblock copolymers composed of Polysulfone (PSU) and Polyphenylsulfone (PPSU) poly(ether sulfone) segments (SPSU/SPPSU) are synthesized for the first time by polycondensation in a “one-pot two-step synthesis” of commercial monomers, followed by sulfonation reaction with trimethylsilyl chlorosulfonate (TMSCS). Both segments are responsible for proton conductivity, although the PSU block has greater affinity to be sulfonated. Even though no microphase separation is detected, the resulting ionomers exhibit good mechanical properties due to the non-sulfonated blocks remaining and to the high molecular weights of the ionomers. The chemical structure is confirmed by 1H-NMR, 19F-NMR and FTIR analysis. The degree of sulfonation (0.93–1.58) is determined from the IEC values and 1H-NMR spectra. In situ through-plane proton conductivity measured on the MEAs is 34.1 mS cm−1 at 70 °C. A maximum power density of 400 mW cm−2, a current density of 1100 mA cm−2 and outstanding thermo-mechanical stability, these proton-conducting membranes can therefore be implemented in PEMFC.

Establishing a phthalocyanine-based crosslinking interphase enhances the interfacial performances of carbon fiber/epoxy composites at elevated temperatures

A novel phthalocyanine-based interphase with a higher crosslinking density and glass transition temperature (Tg) was designed to enhance the interfacial properties of the carbon fiber/epoxy composite at elevated temperatures. The crosslinking density and the Tg of the interphase were tailored by tetraaminophthalocyanine (TAPc) with abundant amine groups and rigid heteroaromatic structures coated on the surface of the carbon fibers. Characterizations of the fiber surface properties were performed before and after coating, including topography, surface chemistry and surface energy. A sharp improvement in the interfacial shear strength for TAPc-coated carbon fibers (CF-TAPc) of 127.3% was obtained compared to that of the commercial carbon fibers (CF-commercial) at 150 °C. The modulus of the carbon fiber composite at the interface was investigated by force-mode atomic force microscopy (AFM), which indicated that the interphase of the CF-TAPc was stiffer than that of CF-commercial at 180 °C. Following the experimental observations, the dynamic mechanical thermal properties were investigated to confirm the better thermomechanical stability of the CF-TAPc interphase. This strategy is based on multireactive sites and the stiff structures of TAPc that generate higher Tg and act as a buffer between the fiber and matrix to counteract the generation of stress in the interphase, resulting in increased interfacial shear strength at elevated temperatures.

Boron nitride: a promising material for proton exchange membranes for energy applications.

Boron nitride (BN) is an exciting material and has drawn the attention of researchers for the last decade due to its surprising properties, including large surface area, thermomechanical stability, and high chemical resistance. Functionalization of BN is a new area of interest to build up novel properties and applications of BN. BN and functionalized BN are promising membrane materials and show enormous advantages ascribed to their simple synthesis, high surface area, mechanical and thermal stability, and distinctive mechanical properties. BN-based proton exchange membranes show improvement in their physicochemical, electrochemical, thermal, mechanical, and barrier properties. Only a few research studies have been carried out on BN-based highly stable proton exchange membranes (PEMs) for various electrochemical applications. In this review, we discuss the recent advances in the functionalization of BN by different methods. The synthesis of different proton exchange membranes has also been discussed in this article. In addition, the potential applications of hybrid proton exchange membranes have also been mentioned.

First-Principles Study on Thermodynamic Stability of UO 2 with He Gas Incorporation via Alpha-Decay

Using first principles calculations we investigated the thermomechanical stability of spent nuclear fuels (SNF), especially how mechanical properties of UO2, such as, bulk, shear and Young’s moduli and Poisson’s ratio vary through alpha-decay of U into Th with generation of He gas. Our results indicate that substitution of U by Th through alpha decay (U1-xThxO2) does not significantly affect the stability of the grain in a fuel matrix. In addition, we studied the transport properties of He in and boundaries of the U1-xThxO2 grain. Helium preferentially resides at the grain boundaries through diffusion. Our study can contribute to substantial reduction of environmentally risk and enhancement of our sustainability by safe control of radioactive materials.

Viscosity and fragility of confined polymer nanocomposites: a tale of two interfaces.

Viscosity and fragility are key parameters determining the processability and thermo-mechanical stability of glassy polymers and polymer nanocomposites (PNCs). In confined polymers, these parameters are largely dominated by the long relaxation times of the polymers adsorbed at the substrate-polymer interface. On the other hand, for polymer nanocomposites, the interface layer (IL) between the nanoparticles and the surrounding matrix chains often control not only the morphology and dispersion but also various parameters like viscosity and glass transition temperature. Confined PNCs, hence, present a unique opportunity to study the interplay of these two independent interfacial effects. Here, we report the results of X-ray scattering based dynamics measurements of PNC thin films, with a two IL width, unraveling the subtle interplay of these two interfaces on the measured viscosity and fragility. Coupled with coarse-grained molecular dynamics (MD) simulations, our experimental results demonstrate that the viscosity of the PNC films increases with both the IL width and the thickness of the polymer layer adsorbed at the substrate interface. However, while both pristine PS and PNCs with a higher IL width become stronger glasses, as estimated by their fragility, the PNC with a lower IL width shows an increase in fragility with increasing confinement. Our results suggest a novel method to control thermo-mechanical properties and stability of PNC coatings by independently controlling the two interfacial effects in athermal glassy PNCs.

Energy Efficiency of Briquettes Derived from Three Agricultural Waste’s Charcoal Using Two Organic Binders

Waste management could contribute significantly to reducing environmental degradation. Studies showed that briquetting provides with or without binder helps to manage wastes as energy fuels. However, the properties of many binders are not investigated extensively. This work investigated the effect of two organic binders’ low rate on energy efficiency of Briquettes produced from charcoals of Tender Coconut Husks (TCH), Palm Kernel Shells (PKS) and Corn Cobs (CC). Bombax Costatum calyx (B) and Cissus Repens barks (C) were used separately as binders to elaborate briquettes. The briquettes were compared based on their energy efficiency parameters with wood charcoal as control. Energy efficiency parameters such as water boiling time (WBT), mass of biomass used (MB), burning rate (BR), temperature rise rate (TR) and maximum temperature in the furnace (Tmax) were measured from each biomass charcoal briquette and wood charcoal combustion. Water boiling test was applied to determine briquettes thermal properties. The results of WBT, BR, TR and Tmax were respectively within the ranges 3.4 - 12.3 min, 2.90 - 7.71 g/min, 4.63°C/s - 16.10°C/s and 623°C - 900°C. Corn Cobs charcoal briquettes with Bombax binder took the shortest time to boil water and also presented a high temperature rise rate and the highest maximum temperature. The lowest burning rates were obtained for Tender coconut husks charcoal briquettes with Cissus binder. They showed good material conservation for bombax bound briquettes. The results of our investigations showed that binders content increasing enhanced the thermomechanical stability and affected negatively the energy efficiency parameters of the studied briquettes.

Innovative Target for Production of Technetium-99m by Biomedical Cyclotron.

Technetium-99m (99mTc) is the most used radionuclide worldwide in nuclear medicine for diagnostic imaging procedures. 99mTc is typically extracted from portable generators containing 99Mo, which is produced normally in nuclear reactors as a fission product of highly enriched Uranium material. Due to unexpected outages or planned and unplanned reactor shutdown, significant 99mTc shortages appeared as a problem since 2008 The alternative cyclotron-based approach through the 100Mo(p,2n)99mTc reaction is considered one of the most promising routes for direct 99mTc production in order to mitigate potential 99Mo shortages. The design and manufacturing of appropriate cyclotron targets for the production of significant amounts of a radiopharmaceutical for medical use is a technological challenge. In this work, a novel solid target preparation method was developed, including sputter deposition of a dense, adherent, and non-oxidized Mo target material onto a complex backing plate. The latter included either chemically resistant sapphire or synthetic diamond brazed in vacuum conditions to copper. The target thermo-mechanical stability tests were performed under 15.6 MeV proton energy and different beam intensities, up to the maximum provided by the available GE Healthcare (Chicago, IL, USA) PET trace medical cyclotron. The targets resisted proton beam currents up to 60 µA (corresponding to a heat power density of about 1 kW/cm2) without damage or Mo deposited layer delamination. The chemical stability of the proposed backing materials was proven by gamma-spectroscopy analysis of the solution obtained after the standard dissolution procedure of irradiated targets in H2O2.

Synthesis, Characterization and Application of Disodium Tetraborate Cross-Linked Polyvinyl Alcohol Membranes for Pervaporation Dehydration of Ethylene Glycol

Dehydration of ethylene glycol-water mixture was carried out in a laboratory pervaporation unit using a flat sheet membrane test cell. Polyvinyl alcohol-polyether sulfone (PVA-PES) composite membranes were synthesized and cross linked with two different concentrations, viz 0.2 and 0.5% of disodium tetraborate (borax). The derived membranes were extensively characterized for their morphology, intermolecular interactions, thermo-mechanical stability, and physicochemical properties using field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and water uptake studies. The membrane performance was evaluated in terms of pervaporation flux, separation factor, selectivity, permeability and solute diffusion coefficients of EG-water mixture at varying feed flow rate. Both in terms of flux and separation factor PVA-PES-0.2% borax composite membrane was found superior to PVA-PES-0.5% borax crosslinked and its uncrosslinked counterpart. Cross-linking the composite with borax produced a membrane with lower crystallinity and a smaller swelling degree, but having improved thermostability and mechanical properties.

In Situ Armoring: A Robust, High-Wettability, and Fire-Resistant Hybrid Separator for Advanced and Safe Batteries.

Development of nonflammable separators with excellent properties is in urgent need by next-generation advanced and safe energy storage devices. However, it has been extremely challenging to simultaneously achieve fire resistance, high mechanical strength, good thermomechanical stability, and low ion-transport resistance for polymeric separators. Herein, to address all these needs, we report an in situ formed silica@silica-imbedded polyimide (in situ SiO2@(PI/SiO2)) nanofabric as a new high-performance inorganic-organic hybrid separator. Different from conventional ceramics-modified separators, this in situ SiO2@(PI/SiO2) hybrid separator is realized for the first time via an inverse in situ hydrolysis process. Benefiting from the in situ formed silica nanoshell, the in situ SiO2@(PI/SiO2) hybrid separator shows the highest tensile strength of 42 MPa among all reported nanofiber-based separators, excellent wettability to the electrolyte, good thermomechanical stability at 300 °C, and fire resistance. The LiFePO4 half-cell assembled with this hybrid separator showed a high capacity of 139 mAh·g-1@5C, which is much higher than that of the battery with the pristine PI separator (126.2 mAh·g-1@5C) and Celgard-2400 separator (95.1 mAh·g-1@5C). More importantly, the battery showed excellent cycling stability with no capacity decay over 100 cycles at the high temperature of 120 °C. This study provides a novel method for the fabrication of high-performance and nonflammable polymeric-inorganic hybrid battery separators.

Alleviating the Mechanical and Thermal Degradations of Highly Sulfonated Poly(Ether Ether Ketone) Blocks via Copolymerization with Hydrophobic Unit for Intermediate Humidity Fuel Cells.

In this contribution, sulfonated poly(ether ether ketone) (SPEEK) is inter-connected using a hydrophobic oligomer via poly-condensation reaction to produce SPEEK analogues as PEMs. Prior sulfonation is performed for SPEEK to avoid random sulfonation of multi-block copolymers that may destroy the mechanical toughness of polymer backbone. A greater local density of ionic moieties exist in SPEEK and good thermomechanical properties of hydrophobic unit offer an unique approach to promote the proton conductivity as well as thermomechanical stability of membrane, as verify from AC impedance and TGA. The morphological behavior and phase variation of membranes are explored using FE-SEM and AFM; the triblock (XYX) membranes exhibits a nano-phase separated morphology. Performance of PEFC integrated with blend and block copolymer membranes is determined at 60 °C under 60% RH. As a result, the triblock (XYX) membrane has a high power density than blend (2X1Y) membrane.

Enhancement of the Thermomechanical Properties of a Fly Ash- and Carbon Black-Filled Polyvinyl Chloride Composite by Using Epoxidized Soybean Oil as a Secondary Bioplasticizer

Plasticized polyvinyl chloride (PVC) was fabricated using epoxidized soybean oil (ESBO) as a secondary bioplasticizer with dioctyl phthalate (DOP). The PVC/MFA/CB composites were prepared by melt mixing of the plasticized PVC with modified fly ash (MFA), carbon black N330 (CB), and polychloroprene (CR) in a Haake Rheomix mixer using a rotation speed of 50 rpm at 175°C for 6 min and then compressed by Toyoseiki pressure machine under 15 MPa. The effect of ESBO content on morphology, melt viscosity, tensile properties, and flame retardancy of PVC/MFA/CB composites was investigated. The obtained results showed that the incorporation of ESBO has significantly enhanced the processing ability, Young’s modulus, tensile strength, and elongation at break of the PVC/MFA/CB composites. The torque of PVC/MFA/CB composites was increased to approximately 12% when 50 wt% of DOP was replaced by ESBO. When ESBO was 20 wt% in comparison with DOP weight, the elongation at break, tensile strength, and Young’s modulus of the composites were increased to 48%, 24%, and 4.5%, respectively. Correspondingly, thermogravimetric analysis results confirmed that ESBO had improved the thermostability of the PVC composites. The ESBO have potential as a secondary bioplasticizer replacement material for DOP owing to their better thermomechanical stability.

Highly Flexible Electrospun Hybrid (Polyurethane/Dextran/Pyocyanin) Membrane for Antibacterial Activity via Generation of Oxidative Stress.

A hybrid nanofibrous mat consisting of polyurethane, dextran, and 10 wt % of biopigment (i.e., pyocyanin) was facilely fabricated using a direct-conventional electrospinning method. The field emission scanning electron microscopy showed the bead-free fibers with a twisted morphology for the pyocyanin-loaded mat. The addition of pyocyanin enables the unprecedented approach to tailor the hydrophilicity of hybrid mat, as verified from the water contact measurement. Thermomechanical stabilities of electrospun mats were investigated in terms of thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. The bacterial inhibition test revealed that the antibacterial activity of electrospun mat containing pyocyanin was 98.54 and 90.2% toward Escherichia coli and Staphylococcus aureus, respectively. By the combined efforts of rapid release of pyocyanin and oxidative stress, the PU–dextran–pyocyanin (PUDP) electrospun mat significantly declined the viable cell number that disrupts the cell morphology. Hence, the proposed PUDP electrospun mat must meet the requirements of efficient antimicrobial material in various applications such as disinfectant wiping, food packaging, and textile industries.

Thermo-mechanical stability analysis of functionally graded shells

In this paper, the thermo-elastic nonlinear analysis of various Functionally Graded (FG) shells under different loading conditions is studied. A second-order isoparametric triangular shell element is presented for this purpose. The element is six-noded, and each node has all six independent degrees of freedom in space. It should be added, the first-order shear deformation theory is induced. Furthermore, Voigt’s model is adopted to define the FG material properties, which are considered to change gradually from one surface to another. The critical temperature is predicted. Both the pre-buckling and post-buckling equilibrium paths are traced. Since the linear eigenvalue analysis leads to wrong responses in the problems with strong nonlinearity, the suggested procedure is performed based on the FEM and more exact estimations are achieved using equilibrium path.

Enhanced Thermal Stability of Ultrathin Nanostructured Pt cathode by PdO: In Situ Nanodecoration for Low-Temperature Solid Oxide Fuel Cell

Due to its high surface area and catalytic activity, the nanostructure of platinum significantly enhances the electrochemical reactions of electrodes. However, the inherently poor thermomechanical stability of the nanostructure has been a critical issue. This study suggests a simple method of using a Pd layer deposited by sputtering to enhance the stability of the 20 nm thick nanoporous Pt. The microstructural analysis reveals that the Pd films are partially oxidized at operating temperature to nano-polycrystalline Pd formed around Pt particles and inhibiting the mobility of the Pt grains. By preserving the Pt nanostructure, the degradation rate of the Pt–Pd cathode structure is 10 times lower than that of the Pt cathode.

Features of Microstructure Formation in the Ni–Al–W System during SHS

New-generation superalloys based on Ni intermetallics possess high thermomechanical stability at high temperatures and are widely used in modern industry. The fabrication of such materials by self-propagating high-temperature synthesis (SHS) is advantageous over traditional metallurgical technologies due to the use of the chemical-reaction energy. The development of coatings and pads based on the NiAl intermetallic on the surface of tungsten articles during SHS is of great practical interest. In this work, experiments on the interaction of the W substrate and the Ni–Al-based melt are performed in the SHS mode. When the W substrate connects with the NiAl intermetallic during SHS, the gradient welded joint 200–400 μm in thickness having a complex structure occurs. The Ni and Al melt is formed during the SHS reaction, and surface layers of the W substrate diffuse into it. The crystallization of the dendrites of the tungsten-based phase (84‒86 at % W and 16–14 at % Ni) and dendrites of the pseudobinary NiAl-based eutectic (β phase), in which precipitates of W-containing phase smaller than 50 nm in size and needle Ni3Al inclusions (γ') are present, occurs during cooling in the near-surface layer. The W + Ni + Ni3Al (α + γ + γ') containing the solid solution particles based on Ni3Al intermetallics of about 100 nm in size is revealed in the transient layer. The modification of the W substrate is modified with the formation of globular precipitations of W (α phase) in it, which considerably increases the surface area.

Thermally stable current-collecting silver grid coated with ceramic-capping layer for low-temperature solid oxide fuel cells

In an effort to decrease the operating temperature of solid oxide fuel cells (SOFCs), nano-porous thin Pt layers have been used as a cathode material with catalytic activity. Because of porous and thin characteristic of the Pt cathode, however, a large cathode area results in a significant performance deterioration because of the increased sheet resistance of the Pt cathode. In this study, we developed a Ag-patterned grid as a current-collecting layer and a samaria-doped ceria (SDC) oxide-capping layer on the porous Pt cathode to decrease sheet resistance and enhance electrochemical performance. Enhanced electron transportation and thermo-stable behavior of fabricated fuel cells indicated three-fold enhanced peak power density and more than two-fold thermomechanical stability, as per scanning electron microscopy (SEM) and electrochemical analysis results.