A comparative study of thermal and hydraulic autofrettage

Thermal autofrettage is a potential process to generate beneficial compressive residual stresses at and around the inner wall of a thickwalled cylinder for increasing its pressure carrying capacity. Due to its simplicity and inexpensive arrangement, it can compete with the conventional hydraulic autofrettage process. In this work, a comparative study of the thermal autofrettage and the hydraulic autofrettage is carried out. As the thermal autofrettage does not require hydraulic power pack, the process is more economical than the hydraulic autofrettage. The thermal autofrettage process is also studied for the thick-walled cylindrical vessels subjected to high thermal gradient with or without pressure and is compared with the hydraulic autofrettage. Comparison shows that for cylinders subjected to high thermal gradient without pressure, the thermal autofrettage is superior to the hydraulic autofrettage.     

Parameter optimization of friction stir welding of cryorolled AA2219 alloy using artificial neural network modeling with genetic algorithm

In this paper, parameter optimization of FSW of cryorolled AA2219 alloy was carried out to obtain defect free weld joint with maximum weld strength. To achieve this, artificial neural network (ANN) was used to model the relationship between the input parameters and the mechanical and corrosion properties (output) of the weld joints. The optimal FSW parameters were determined by genetic algorithm (GA). The feasible solution of the GA was tool rotational speed of 1005 rpm, tool travel speed of 20 mm/min and tool tilt angle of 3°. The feasible parameter was used to weld and check the ability of the parameter to produce better weld joint than the L₉ orthogonal array parameters. The weld, subjected to the confirmation test, was investigated by means of metallurgical, mechanical, and corrosion testing. This process reduces the costs associated with trial runs to obtain optimal parameters and also the production cost of the cryorolled (CR) plate which is high.     

The Effect of Spray-Freeze Drying of Montmorillonite on the Morphology,Dispersion, and Crystallization in Polypropylene Nanocomposites

The spray-freeze drying (SFD) technique was applied to sonicated aqueous suspensions of spray-dried montmorillonite clay (MMT) to produce highly porous agglomerates (SFD-MMT). Both MMT (used as a reference) and SFD-MMT were subsequently incorporated in polypropylene (PP) via melt compounding to produce 2 wt % nanocomposites with and without maleic anhydride grafted polypropylene (PP-g-MA). Polypropylene nanocomposites containing SFD-MMT exhibited thinner silicate flake layers compared to large agglomerates in PP/MMT nanocomposites. SFD-MMT particles became even more finer in the presence of PP-g-MA (i.e., in PP/PP-g-MA /SFD-MMT) where it hindered PP crystallization instead of serving as nucleation sites for the PP crystallization during rapid cooling. SFD-MMT improved the thermal stability of PP/PP-g-MA by 30°C compared to only 5–8°C for MMT/nanocomposites. MMT acts as a heterogeneous nucleating agent in the nucleation-controlled PP nanocomposites, but the hindrance effect was observed for the PP/PP-g-MA with SFD-MMT. PP/PP-g-MA/SFD-MMT exhibited twice the edge surface energy as compared to PP/PP-g-MA/MMT. The incorporation of both types of MMT raised the tensile moduli of PP and PP/PP-g-MA, with no improvement in their tensile strength and a decrease in the elongation at break. The PP/PP-g-MA/SFD-MMT showed brittle failure. POLYM. ENG. SCI., 60:168–179, 2020. © 2019 Society of Plastics Engineers     

Nondegradative additive manufacturing of medical grade copolyesters of high molecular weight and with varied elastic response

Although additive manufacturing through melt extrusion has become increasingly popular as a route to design scaffolds with complex geometries the technique if often limited by the reduction in molecular weight and the viscoelastic response when degradable aliphatic polyesters of high molecular weight are used. Here we use a melt extruder and fused filament fabrication printer to produce a reliable nondegradative route for scaffold fabrication of medical grade copolymers of L-lactide, poly(ε-caprolactone-co-L-lactide), and poly(L-lactide-co-trimethylene carbonate). We show that degradation is avoided using filament extrusion and fused filament fabrication if the process parameters are deliberately chosen based upon the rheological behavior, mechanical properties, and polymer composition. Structural, mechanical, and thermal properties were assessed throughout the process to obtain comprehension of the relationship between the rheological properties and the behavior of the medical grade copolymers in the extruder and printer. Scaffolds with a controlled architecture were achieved using high-molecular-weight polyesters exhibiting a large range in the elastic response causing negligible degradation of the polymers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48550.     

Synthesis,Characterization and Catalytic Activities of Palladium(II) Nitroaryl Complexes

Two palladium(II) nitroaryl complexes trans-[bromo(p-nitrophenyl)bis(triphenylphosphine)palladium(II)] 1 and trans-[bromo(2,4-dinitrophenyl)bis(triphenylphosphine)palladium(II)] 2 have been synthesized. The complexes were characterized by FTIR and NMR (¹H, ¹³C and ³¹P) spectroscopy and elemental analysis. The molecular structure of complex 2, as confirmed by X-ray crystallography, reveals that the Pd atom and its neighboring groups (two PPh₃, Br and phenylene group) lie in a slightly distorted square plane. In the UV–Vis spectra of the complexes 1 and 2, the palladium to aryl charge transfer bands were observed. The emission peaks from the singlet excited states (S₁ → S₀) were observed in the photoluminescence spectra of the complexes. The thermal stability of the complexes has been studied by thermal gravimetric analysis (TGA). TGA data showed that both complexes are thermally stable up to 200 °C, and complex 1 is more stable than 2. The catalytic efficiency of the new palladium(II) complexes was studied as demonstrated using the Sonogashira coupling reactions with good yields. The experimental results suggest that the Sonogashira coupling reactions can be performed at moderate temperature (50 °C) using these new palladium(II) complexes as catalysts.     

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of Vernonia galamensis oil

Matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) has been used to identify eight triacylglycerols (TAG) in Vernonia galamensis oil (VO). The TAG include trivernolin, divernoloylstearoylglycerol, divernoloyloleoylglycerol, vernoloyllinoleoylstearoylglycerol, vernoloyllinoleoyloleoylglycerol, and vernoloyldilinoleoylglycerol. Samples for the MALDI/TOF/MS analysis were prepared with alpha-cyano-4-hydroxycinnamic acid (matrix) in an acetonitrile/tetrahydrofuran solvent system. A mol ratio of matrix/VO (44:1) gave reproducible composite spectra, resulting in resolutions greater than 8,000 and signal-to-noise ratios of above 1000 for the most abundant molecular species. 1,3-Dioleoyl-2-stearoylglycerol and 1,2-dioleoyl-3-palmitoylglycerol were used as calibration standards.     

Effects of ZnO and MoS<Subscript>2</Subscript> Solid Lubricants on Mechanical and Tribological Properties of M50-Steel-Based Composites at High Temperatures: Experimental and Simulation Study

Prospective beneficial effects of mixtures of temperature-adaptive solid lubricants (ZnO–MoS₂) on mechanical and tribological properties of M50 alloy steel were investigated at temperatures from 25 to 800 °C. ZnO and MoS₂ were mixed with M50 (designated as M) to create composites MZ (M50 steel plus ZnO), MM (M50 steel plus MoS₂), and MZM (M50 steel plus both additives). Sliding friction and wear experiments were performed at different temperatures using a pin-on-disk at a sliding speed of 0.2 m s^?1 and a load of 12 N. Silicon nitride and M50 steel were used as the pin materials. In order to understand the friction and wear behavior of composites, analyses of their surfaces were done using XRD, EPMA, FESEM, EDS line/mapping, and XPS tests. A dynamic simulation model based on the finite element method was built to simulate the different stresses on the contact pairs. Results elucidated that MZM attained the least friction (0.17), compared to M (0.40), MZ (0.26), or MM (0.29) at 800 °C. The increase in surface roughness of MZM due to sliding was reduced by 37.3% compared to that of MZ (11.9%) or MM (22.7%). The good lubricating behaviors were referred to the synergetic effects of ZnO, MoS₂, and formed lubricating components on worn surfaces.     

Effects of Rheological Behavior of Viscoelastic Surfactants on Formation Damage in Carbonate Rocks

Viscoelastic surfactants (VES) are used in various oilfield applications such as matrix stimulation and enhanced oil recovery. The loss of surfactants during the propagation of VES could result in a significant reduction in the permeability of the rock (formation damage). The objective of the current work was to identify the effect of rheological behavior of the VES on the formation damage using core‐flooding experiments, nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM) analysis. A combination of core‐flooding, NMR, and SEM techniques was used to quantify and identify the location of formation damage in carbonate core samples. The viscosity and storage modulus strongly depend on the nature and concentration of salts. The viscosity increased by increasing the salt concentration up to a specific point (15 wt% CaCl₂) and then starts decreasing. The VES formulations that displayed the maximum and minimum viscosities were used to identify the impact of rheological behavior on formation damage. Core‐flooding experiments were performed to assess the formation damage due to high‐viscosity and low‐viscosity VES formulations. The reduction in the permeability of carbonate rocks reaches more than 90% of the initial permeability. It was found that low‐viscosity VES caused more damage compared with high‐viscosity VES when they were used at constant concentrations. NMR and core‐flooding results revealed that the damage took place both in pore body and pore throat. However, most of the surfactant was retained at the pore throat.     

Synthesis,characterization and demonstration of self-cleaning TiO2 coatings on glass and glazed ceramic tiles

An effort was made not only to demonstrate the performance of the self-cleaning coatings on building materials such as ceramic glazed tiles and glass windows, but also to understand the fundamental issues that are still alive in the field of self-cleaning surfaces based on photocatalysis. Nano TiO₂ transparent thin films were generated by dip, spray and flow coating method. The present results indicate that the inconsistent results in the self-cleaning studies may be due to the effect of aggregation of model pollutant (methylene blue) dye on TiO₂ surface. The effect of aliovalent metal ion (Ni²⁺, Fe³⁺, Nb⁵⁺) doping on phase formation, polymorphic transition, visible light absorbance and optical transparency of TiO₂ film were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV visible absorption spectroscopy. The improved visible light activity of doped TiO₂ thin film was correlated to the Ti(Ni/Fe)O₃ phase formation, UV and visible light absorbance, variation in the optical energy band gap and the probable light scattering associated with grain size.