Changes In Mechanical Performance Research Articles

Microstructural evolution and mechanical properties of brazed IN718 ultrathin-walled capillary structure using different particulate reinforced filler alloy

The development of hypersonic precooled combined cycle engine provides a reliable power system for the future intercontinental navigation and reusable space orbital transportation. The compact heat exchanger precooler is the key component of the cooling cycle system, which provides efficient heat management for the hypersonic engine. This investigation mainly focused on the manufacturing process of precooler, and the typical structure of the precooler, ultrathin-walled capillary structure, was facilitated by the vacuum brazing using the particle reinforced composite filler alloy. The effects of different types and contents of the reinforced particle on the spreading behaviour, microstructural evolution, mechanical performance changes were investigated in detail. During the cooling process, the nucleation and growth of the γ-Ni solid solution on the surface of the reinforced particles was the main reason for the microstructure homogenization. Compared to the Ni particles, the more obvious mechanical properties improvement could be achieved by using IN718 particles reinforced composite filler alloy. The tensile strength and elongation of the brazed ultrathin-walled structure present 9.36% and 47.27% higher than that using initial filler alloy. Moreover, the micro-hardness distribution result revealed that the reinforced particles reduced the overall micro-hardness of the brazed region, dispersed the eutectic structure and increased the hardness dispersion, which would reduce the stress concentration tendency and improve the structural properties.

Long-Term Failure Mechanisms of Thermal Barrier Coatings in Heavy-Duty Gas Turbines

Thermal barrier coatings serve as thermal insulation and antioxidants on the surfaces of hot components. Different from the frequent thermal cycles of aero-engines, a heavy-duty gas turbine experiences few thermal cycles and continuously operates with high-temperature gas over 8000 h. Correspondingly, their failure mechanisms are different. The long-term failure mechanisms of the thermal barrier coatings in heavy-duty gas turbines are much more important. In this work, two long-term failure mechanisms are reviewed, i.e., oxidation and diffusion. It is illustrated that the growth of a uniform mixed oxide layer and element diffusion in thermal barrier coatings are responsible for the changes in mechanical performance and failures. Moreover, the oxidation of bond coat and the interdiffusion of alloy elements can affect the distribution of elements in thermal barrier coatings and then change the phase component. In addition, according to the results, it is suggested that suppressing the growth rate of uniform mixed oxide and oxygen diffusion can further prolong the service life of thermal barrier coatings.

Computational Study to Identify the Effects of the KCNJ2 E299V Mutation in Cardiac Pumping Capacity.

The KCNJ2 gene mutations induce short QT syndrome (SQT3) by directly increasing the IK1 current. There have been many studies on the electrophysiological effects of mutations such as the KCNJ2 D172N that cause the SQT3. However, the KCNJ2 E299V mutation is distinguished from other representative gene mutations that can induce the short QT syndrome (SQT3) in that it increased IK1 current by impairing the inward rectification of K+ channels. The studies of the electromechanical effects on myocardial cells and mechanisms of E299V mutations are limited. Therefore, we investigated the electrophysiological changes and the concomitant mechanical responses according to the expression levels of the KCNJ2 E299V mutation during sinus rhythm and ventricular fibrillation. We performed excitation-contraction coupling simulations using a human ventricular model with both electrophysiological and mechanical properties. In order to observe the electromechanical changes due to the expression of KCNJ2 E299V mutation, the simulations were performed under normal condition (WT), heterogeneous mutation condition (WT/E299V), and pure mutation condition (E299V). First, a single-cell simulation was performed in three types of ventricular cells (endocardial cell, midmyocardial cell, and epicardial cell) to confirm the electrophysiological changes and arrhythmogenesis caused by the KCNJ2 E299V mutation. In three-dimensional sinus rhythm simulations, we compared electrical changes and the corresponding changes in mechanical performance caused by the expression level of E299V mutation. Then, we observed the electromechanical properties of the E299V mutation during ventricular fibrillation using the three-dimensional reentry simulation. The KCNJ2 E299V mutation accelerated the opening of the IK1 channel and increased IK1 current, resulting in a decrease in action potential duration. Accordingly, the QT interval was reduced by 48% and 60% compared to the WT condition, for the WT/E299V and E299V conditions, respectively. During sustained reentry, the wavelength was reduced due to the KCNJ2 E299V mutation. Furthermore, there was almost no ventricular contraction in both WT/E299V and E299V conditions. We concluded that in both sinus rhythm and fibrillation, the KCNJ2 E299V mutation results in very low contractility regardless of the expression level of mutation and increases the risk of cardiac arrest and cardiac death.

Steam oxidation and mechanical performance of a ferritic–martensitic steel with slurry aluminide coating

AbstractA key route to advancing power plant efficiency is to enhance current steam operating parameters, namely, increase in steam temperature and pressure from the current levels of 540°C and 180 bar to the proposed 700°C (EU) and 300 bar. Conventional ferritic–martensitic steels, while having good mechanical properties and fatigue resistance, do not possess the high‐temperature corrosion resistance for long‐term use, with a temperature limit of ~620°C. Adding aluminide coatings to the surfaces of the steels can improve the oxidation resistance of this class of material through the growth of an Al2O3 scale. One of the major concerns in using coating is the potential deleterious effects on the mechanical properties of the substrate, either through the precipitation of brittle phases or through cracks in the coating. This study compares the microstructural features of slurry aluminide coatings applied to Grade 91 and the change in mechanical performance. The tensile, thermomechanical fatigue and creep test results showed that while the coated samples entered the tertiary creep zone earlier than the uncoated ones, cracking of the coating remained confined to the surface of the specimen. Nanoindentation mapping showed a hardness increase in the coating and within the aluminium diffusion zone, which is related to the exposure time.

Synergistic effect of zeolite 4A on thermal, mechanical and flame retardant properties of intumescent flame retardant HDPE composites

The combination of synergistic agent with intumescent flame retardant (IFR) systems provides a promising way to prepare high performance IFR composites. In this study, the effects of the synthetic zeolite 4 A in combination with the IFR system consisting of ammonium polyphosphate (APP) and tris (2-hydroxyethyl) isocynurate (THEIC) on thermal degradation, mechanical properties, flame retardancy and char formation of high-density polyethylene composites were investigated by limiting oxygen index (LOI) measurement, cone calorimetry, scanning electron microscopy and laser Raman spectroscopy. The LOI value of HD/FR/Z-0.5 composite with an optimum content of 0.5 wt. % zeolite 4 A and 25 wt. % of total flame retardant reaches 26.3 %. A low loading of zeolite 4 A can improve the bench-scale combustion performance as determined by cone calorimetry, and promote the formation of more compact char residue with a highly graphitic structure. However, a low loading of zeolite in combination with the IFR system consisting of APP and THEIC produces no significant changes in mechanical performance.

Mechanical performance of wood under artificial and natural weathering treatments

Natural and artificial weathering treatments were studied to determine the change of wood properties as a function of exposure time. This paper aimed to provide general information about the mechanical performance of wood under natural and artificial weathering treatments and define a relationship between them. The eight strength classes of ABNT NBR 7190 (1997) were considered, in addition to a paired sampling approach. The modulus of elasticity and conventional strength value in static bending, strength in compression parallel to the grain, hardness perpendicular to the grain, and the elastic limit in the static bending test were investigated. Linear regression models for mechanical performances under artificial and natural aging treatments of the exposure time were made and tested using an analysis of variance. According to the results, 360 days of natural weathering provoked a change in mechanical performance of 15.72% that included a decrease in strength and modulus of elasticity and an increase in elastic limit. Twelve hours of the artificial weathering treatment provided the effect of 6.22 days of natural weathering exposure.

Heat-treated blue agave fiber composites

To meet consumer demand for low carbon-footprint transportation, automakers have been replacing high-density fillers with low-density natural fibers in polymeric composites. Torrefaction can improve natural fiber composite thermal performance, but leads to significant fiber mass loss. This study sought to balance the benefits and limitations of torrefaction by investigating the effects of low-temperature fiber heat treatment on the performance of 20 wt % agave-polypropylene composites. Heat treatment increased the thermal stability of agave fibers, but resulted in no observable change to composite thermal properties or crystallization kinetics. Additionally, treatment resulted in a reduction in rheological properties, but less than a 10% change in mechanical performance of agave composites.

Unique interfacial reaction and so-induced change in mechanical performance of Sn–3.0Ag–0.5Cu/Cu solder joints formed during undercooled and eutectic liquid soldering processes

A novel technique is proposed to prepare Sn–3.0Ag–0.5Cu/Cu joints at three different processing temperatures, which are called undercooled liquid (UL, 213.0 °C), eutectic liquid (EL, 217.0 °C) and normal liquid (NL, 231.0 °C) soldering temperatures correspondingly, and each of them is lower than, equal to and higher than Sn–3.0Ag–0.5Cu solder’s melting point (217.0 °C), respectively. The interfacial reaction, intermetallic compound growth and mechanical performance of Sn–3.0Ag–0.5Cu/Cu joints formed during UL, EL and NL soldering processes were investigated systematically. Results show that for Sn–3.0Ag–0.5Cu solder as the undercooled liquid melt or eutectic liquid melt or normal liquid melt in the formation of joints, the thickness of interfacial intermetallic compound (IMC) layer in the joints increases with prolonging dwelling time. For three different liquid soldering processes, the change tendency of the interfacial IMC layer thickness is distinct. For joints formed at UL and EL temperatures, the excessive growth of primary Cu6Sn5 and interfacial IMC (mainly Cu6Sn5) can be suppressed during isothermally dwelling in the liquid state for more than 5 min. Ball shear test results show that solder joints formed at UL and EL temperatures have lower value of the maximum shear force (MSF) than those formed during the NL soldering process. For UL and EL types of joints, the fracture occurs either by shear slide fracture totally along the shear tool tip movement plane (i.e., in-plane shear slide fracture) or by shear slide fracture initially along the shear tool tip movement plane and afterwards shear deformation fracture in the solder matrix under the plane (i.e., out-of-plane shear slide and deformation mixed-mode fracture), while the fracture takes place in NL joints only by in-plane shear slide fracture mode.

Fabrication of a thick three-dimensional scaffold with an open cellular-like structure using airbrushing and thermal cross-linking of molded short nanofibers

Nanoscale fibers mimicking the extracellular matrix of natural tissue can be produced by conventional electrospinning, but this approach results in two-dimensional thin dense fibrous mats which can hinder effective cell infiltration. The aim of the present study was to design a thick, three-dimensional (3D) cylindrical scaffold with an open pore structure assembled from short polycaprolactone (PCL) fibers using a facile airbrushing approach. In addition, magnesium particles were incorporated into the PCL solution to both enhance the mechanical properties of the scaffold and stimulate cellular activity following cell seeding. Separated short composite airbrushed fibers were assembled into a 3D cylindrical structure by cold-press molding and thermal cross-linking. The microstructure, chemical composition, porosity and thermal properties were subsequently investigated, along with changes in mechanical performance following immersion in PBS for 60 d. The results showed that the assembled 3D fibrous 10 mm thick cylindrical matrix had an interconnected fibrous network structure with 31.5%–60% porosity. Encapsulation of the Mg particles into the 3D assembled fibrous scaffold enhanced the mechanical properties of the plain PCL scaffolds. The results also demonstrated controlled release of Mg ions into the PBS media for up to 60 d, as evaluated by changes in Mg ion concentration and pH of the media. In addition, the 3D fibrous assembled matrix was shown to support human osteoblast-like cell adhesion, proliferation and penetration. The results suggest that this novel fabrication method of biodegradable thick 3D scaffolds with an open pore structure is promising for the production of a new generation of 3D scaffolds for tissue regeneration applications.

Effect of initial filament moisture content on the microstructure and mechanical performance of ULTEM® 9085 3D printed parts

This study investigates the moisture absorption characteristics of the ULTEM® 9085 filament and how the uptake concentration affects the quality of material extrusion manufactured 3-D parts. The filament was exposed to humidity conditions to achieve various moisture concentrations (0, 0.05, 0.1, 0.16, 0.4 and 0.8 wt.%) and corresponding printed parts were evaluated for mechanical performance using tensile test dogbones. The rate of transport was modeled by Fickian diffusion and diffusion coefficients were obtained for various exposure conditions. Moduli, strain to failure and ultimate strength were evaluated in the XY (flat horizontal) and ZX(vertical) direction relative to the build plate orientation. Image analyses of cross-sections as well as their corresponding fracture surfaces were evaluated for consolidation, porosity distribution and failure behavior. Mechanical test data showed a significant decrease in tensile strength (>60%) and failure strain (>50%) over the range of filament moisture levels investigated. A decrease in failure strain of 41% was observed with moisture levels as low as 0.16%. This degradation was especially sensitive in parts printed in the vertical direction, which resulted in an ultimate failure strain of only 1%. The changes in mechanical performance are believed to be due to a combination of entrapped volatiles resulting in increased porosity at higher moisture levels as well as moisture induced pseudo-crosslinking at lower concentrations. Optical micrographs showed that specimens with 0.16% moisture or greater were filled with observable porosity and increased surface roughness. The rheological behavior of extruded material indicated plasticization as evidenced by melt flow index measurements and changes in the flow characteristics of moisture-exposed extrudate. DMA data show a distinct decrease in Tg with increased moisture content, which is consistent with plasticization. The absorption characteristics at room temperature lab conditions indicate that the material will reach an unacceptable level within one hour of room-temperature exposure. This investigation emphasized the need for awareness of the moisture sensitivities of ULTEM® 9085 when manufacturing high-quality material extrusion processed structures.

A versatile and injectable poly(methyl methacrylate) cement functionalized with quaternized chitosan-glycerophosphate/nanosized hydroxyapatite hydrogels

Injectable polymethylmethacrylate (PMMA) bone cement is alluring because it allows a minimally invasive surgical approach, reducing both the cost of treatment and patient discomfort. However, several documented drawbacks have necessitated the design of a more versatile version with adorable properties for future application. In this study, to amend the bulk behavior of PMMA cement, we synthesized a modified version by combining PMMA with quaternized chitosan (N-(2-hydroxy)propyl-3-trimethylammonium chitosan chloride, HTCC)-based hydrogels loaded with nanosized hydroxyapatite (Nano-HA). Then, the physicochemical properties, antimicrobial properties, remineralization capacity and mechanical performance changes under imitated physiological conditions were tested for these cements using a type K thermocouple, scanning electron microscope (SEM), microcomputed tomography (μ-CT), calcium ion test kit and mechanical compression tests. The results demonstrated that the HTCC-GP thermosensitive hydrogel generated interconnected pores, lower the Tmax value, lengthened the working time, developed appropriate mechanical properties and imparted excellent antibacterial activity to the cement. The Nano-HA particles engendered improved biomineralization ability of the cements without adversely influencing the mechanical performance. Hence, these results indicated that the injectable and multifunctional cement resulting from the p-PMMA/HTCC-GP/Nano-HA combination grips rosy prospect for future applications in bone reconstruction.

Change of mechanical performance and characterization with replacement of Ca by Gd nanoparticles in Bi-2212 system and suppression of durable tetragonal phase by Gd

In this study, we concentrate on crucial evaluations of mechanical performances belonging to Bi2.1Sr2.0Ca1.1−xGdxCu2.0Oy superconducting ceramics with the partial replacement within the molar ratio change 0 ≤ x ≤ 0.30 of aliovalent Gd-sites on the Ca-sites in the system by means of microhardness measurements at different static compression test loads in the range of 0.245–2.940 N. The experimental measurement findings observed display that the mechanical performance tends to regress regularly with the enhancement of the Gd content level due to the increment in the local structural distortions, boundary weak connection between the grains and lattice disorders/strains/defects in the orientation of superconducting adjacent layers. Namely, the presence of Gd foreign impurities in the Bi-2212 crystal lattice leads to induce the crack-producing omnipresent flaws acting as the stress raisers and crack initiation sites. The long and short of it is that the Ca/Gd substitution in the adjacent layers damages seriously the mechanical strength (durability and stiffness), fracture and flexural strengths of the Bi-2212 material due to the increased operable slip systems so that the intergranular fracture becomes more dominant in the Bi-2212 matrix. In other words, the increment in Gd substitution level at the Ca site leads to accelerate the crack propagation and dislocation movement as a result of the decrement in Griffith critical crack length. Thus, the critical stress and durable tetragonal phase values degrade considerably in parallel to the enhancement of Gd content level, and the augmented cracks and dislocations with the existence of foreign impurities reach instantly to the critical propagation speed. The propagation of cracks and dislocation movements is hard to control along with the superconducting samples. At the same time, the Gd inclusions lead to change in mechanical characterization of the Bi-2212 ceramics. The pure sample presents Indentation Size Effect (ISE) behavior while the others exhibit Reverse Indentation Size Effect (RISE) feature, pointing out the increment of induced structural distortions and grain boundary couplings. Besides, the Vickers hardness experimental results are analyzed by the offered theoretical model of Hays–Kendall approach for the first time.

Connection between elastic and electrical properties of cortical bone

The paper focuses on the connection between elastic and electrical properties of cortical bone. Both these properties are governed by microstructure that consists of several pore systems filled with mechanically soft and electrically conductive tissue. Microstructural changes induced by aging, various diseases, microgravity conditions etc. lead to variation in both properties. The paper address the problem of evaluation of the changes in mechanical performance (decrease in Young׳s moduli) via monitoring electrical conductivity. The theoretical results are verified experimentally.

Processing and Characterization of PMMA Nanofiber Reinforced Epoxy Composites

Growing demand for high-performance materials is driving the development of composites with nano material reinforcement. The use of nano reinforcement can provide a distinct advantage due to high surface area of the material. There are still many challenges in achieving the full potential of nanocomposites. In this paper, we investigate the performance of epoxy nanocomposites reinforced with short polymethyl methacrylate (PMMA) nanofibers. PMMA nanofibers were chopped and mixed with the epoxy resin and then the mixture was poured into a mould. Samples were cut to an appropriate size after cure and mechanical testing was carried out. Tensile and flexural strength and modulus were evaluated for samples with various fiber volume fractions to determine changes in mechanical performance. Also Scanning Electron Microscopy was utilized to investigate fracture surface and fiber-matrix interface. Results indicated that mechanical performance dropped as volume fraction of fibers increased, namely poor fiber-matrix adhesion and presence of porosity resulted in deterioration in strength and modulus. Further research is required to develop fiber coating system to enhance performance of the nanocomposite by improving fiber-matrix adhesion and fiber wet-out.

Mechanical Properties of New and Recycled PIM Feedstocks

This paper deals with the mechanical properties of test specimens of commercially available PIM feedstocks based on a stainless steel powder. After injection molding, a part of the polymer binder has been removed in water. This process was followed by thermal removal of residual binder and sintering at 1360 °C in hydrogen atmosphere. For production of the mechanical test bars fresh and recycled feedstocks were employed. The aim is to determine the changes in mechanical performance resulting from injection molding processing stage, especially possible separation of feedstock components – the stainless steel powder and the polymer binder

Effect of Zr addition on the microstructure, phase transformation and mechanical property of Ni50Mn25Ga17Cu8 alloy

This study investigated the microstructure, phase transformation and mechanical property of Ni50Mn25Ga17Cu8−xZrx (x=0, 4 and 8) alloys. The microstructure of alloys changed from a single martensitic phase to a dual phase consisting of martensitic/austenitic matrix and second γ phase after substituting Cu with Zr and the volume fraction of second phase increased with increasing Zr content. The martensitic transformation temperature and transformation enthalpy were reduced after adding Zr, which was related to the introduction of second phase that changed the composition and reduced volume fraction participating in martensitic transformation of the alloy. The decrease of transformation hysteresis after introducing the second phase was thought to be caused by the martenstic structure change of the matrix from tetragonal to orthorhombic that reduced the lattice deformation of austenite→martensite transformation. The mechanical strength of the Cu8 alloy was increased firstly after substituting 4 at% Cu by Zr and then decreased after completely substituting Cu by Zr. The change of mechanical performance was related to the fracture character of the alloys. The intergranular fracture of matrix and second phase dominated in the Cu8 and Zr8 alloys, respectively, but the fracture of Cu4Zr4 alloy was determined by a mixture of intergranular fracture of second phase and transgranular fracture of matrix.

Study of Electrode Surface Characteristics under Short Single Pulse in Micro Ed-Milling

Laminated removal micro ED-Milling is a non-contact special processing technology, through electrode discharge removal in materials. Therefore, shape, size and overlapping degree of the discharge crater determine the surface roughness and surface morphology. Using the principle of electrode wears, through the experiment of Micro-EDM milling shallow groove under short single pulse, getting morphology of a single pulse discharge machining surface. And from the crater of morphological features analyses the different cause of formation, and contrasts in different electric parameters, the different of the electrode surface. For further analysis of the surface physical and mechanical performance changes to lay the foundation, and provides a way for the electrode material removal mechanism research and the calculation of the Single pulse discharge energy.

Carbon nanofiber type and content dependence of the physical properties of carbon nanofiber reinforced polypropylene composites

The variation of the physical properties of four different carbon nanofibers (CNFs), based-polymer nanocomposites incorporated in the same polypropylene (PP) matrix by twin-screw extrusion process was investigated. Nanocomposites fabricated with CNFs with highly graphitic outer layer revealed electrical isolation-to-conducting behaviors as function of CNF's content. Nanocomposites fabricated with CNFs with an outer layer consisting on a disordered pyrolitically stripped layer, in contrast, revealed better mechanical performance and enhanced thermal stability. Further, CNF's incorporation into the polymer increased the thermal stability and the degree of crystallinity of the polymer, independently on the filler content and type. In addition, dispersion of the CNFs' clusters in PP was analyzed by transmitted light optical microscopy, and grayscale analysis (GSA). The results showed a correlation between the filler concentration and the variance, a parameter which measures quantitatively the dispersion, for all composites. This method indicated a value of 1.4 vol% above which large clusters of CNFs cannot be dispersed effectively and as a consequence only slight changes in mechanical performance are observed. Finally, this study establishes that for tailoring the physical properties of CNF based-polymer nanocomposites, both adequate CNFs structure and content have to be chosen. POLYM. ENG. SCI., 54:117–128, 2014. © 2013 Society of Plastics Engineers

Nanostructured biolayers in food packaging

The interest in the development of biodegradable and renewable materials for food packaging applications has boosted research into new strategies to improve their barrier performance. This viewpoint compiles innovative strategies to achieve enhanced barrier properties by using “biolayering” technologies, based on nanolayers and nanostructured layers made of biopolymers, which are able to retain transparency and enhance barrier properties without significant changes in mechanical performance. This overview provides a description and original perspective related to the use of monolayer biocoatings, multi-layered biostructures, layer-by-layer nanobioassemblies, and of a methodology based on electrospun nanostructured biocoatings and biointerlayers to constitute novel functional biopackaging structures.

Coupled strain rate and temperature effects on the tensile behavior of strain-hardening cement-based composites (SHCC) with PVA fibers

This paper reports the experimental findings on the tensile behavior of Strain-hardening cement-based composites (SHCC) subjected to elevated temperatures and different strain rates and to combinations of these parameters. Uniaxial tension tests with in-situ temperature control were performed at 22°C, 60°C, 100°C and 150°C. In addition, the effect of loading rate was investigated using the strain rates of 10−5s−1, 3×10−4s−1 and 10−2s−1 at all four temperatures considered. It was shown that tensile strength decreases both with an increase in temperature and with a decrease in the strain rate. The strain capacity increases with decreasing strain rate at temperatures of 22°C and 60°C, but for the temperature of 100°C this material property increases when the strain rate increases. At 150°C the investigated SHCC loses its ductility and no noticeable strain rate effect can be observed. Furthermore, the residual properties of SHCC were evaluated using uniaxial tensile tests at room temperature on the specimens which were previously heated to 60°C, 100°C or 150°C. The residual tests showed that the strength, strain capacity, and work-to-fracture decrease with increasing pre-treatment temperature. However, in comparison with the results of the in-situ tests with elevated in-situ temperatures, the residual tests on SHCC yielded higher tensile strength and lower ductility. These results and possible mechanisms leading to changes in mechanical performance are discussed on the basis of the observed crack patterns on the specimens' surfaces as well as the microscopic investigations of the condition of fibers on fracture surfaces.