MPa In Compression Research Articles

Double-cross-linking strategy for preparing flexible, robust, and multifunctional polyimide aerogel

Polymer-based aerogels have many uses because they possess excellent mechanical properties, such as high moduli and remarkable fatigue resistances. Freeze drying is an appealing aerogel preparation method because it is simple, green and inexpensive. However, polymer-based aerogels prepared by freeze drying always exhibit inferior mechanical properties compared to those prepared by classic supercritical drying, even if the raw material is polyimide. Herein, we report a novel double-cross-linking strategy to obtain a freeze-dried and robust polyimide/reduce graphene oxide/cobalt (PI/rGO/Co) aerogel with an interdigitated cellular architecture. The double-cross-linking strategy was attributed to hydrogen bonds derived from the graphene oxide (GO sheets) and coordination interactions from the Co ions. The interdigitated cellular architecture is the critical factor for achieving aerogels with low densities, flexibilities, high moduli (0.506 MPa compression modulus, 43% improvement of tensile modulus), and high fatigue resistances (1000 cycles). The as-prepared aerogel could be modified to achieve hydrophobicity with a 146.1° water contact angle. It was also difficult to be ignited and it exhibited excellent heat stability and low thermal conductivities (0.040 W·m−1·K−1 at 25 °C; 0.046 W·m−1·K−1 at 100 °C).

Concrete with Reused Concrete Sand

This paper examines the impacts of substitution of reused concrete sand (RCS) with sands, on the new and hardened physiognomies of concrete. the property of RCS blended concrete was examined and likened with ordinary concrete of 40 MPa compression strength. the physiognomies of RCS concrete vary from ordinary concrete arranged with characteristic sand, as an outcome of the quality of connected mortar, old cement glue, and more fines. the outcomes demonstrate that the RCS concrete demonstrations tantamount workability in contrast with ordinary concrete. the mechanical physiognomies (compressive, flexure, split tensile and elastic modulus) of concrete developed with RCS was lower in compression to ordinary concrete however worthy up to 60percentage RCS in the blend. The drying shrinkage strain of 100percentage RCC mixed concrete at twenty-eight days was watched twice in compression to controlled concrete and it demonstrated more abrasion value in that comparison and furthermore concrete developed with 100 percent RCS indicated 41percentage and 11.3percentage lower in sorption value at ahead of schedule and later age organize individually in that examination.

The effect of vanadium on microstructure and mechanical properties of Fe-based high-strength alloys

In this paper, the microstructure and mechanical properties of FeCrMoVC high-speed steels fabricated using a rapid solidification technique were investigated. It was found that the alloy with free V content exhibited ultra-high fracture strength of 4900 MPa and large compression strain of 31.8%, but a lower yield strength of 1100 MPa. In contrast, with V content to 4 at%, the yield strength increased significantly to 3200 MPa. Micro-structure analysis revealed that the V addition plays an important role in promoting the formation of skeleton-like carbide (V6C5 phase), which can hinder the rapid propagation of shear bands, resulting in a good mechanical property. This special hard and finely ramified carbide network throughout the overall specimen can be regarded as a specific structure signal for the excellent mechanical properties of FeCrMoVC alloys. This result of the alloy with good mechanical property is expected to be used in industry as a high strength tool steel.

A facile hydrothermal method-fabricated robust and ultralight weight cellulose nanocrystal-based hydro/aerogels for metal ion removal.

Heavy metal ion contamination, in particular that associated with Pb2+, Cd2+, and Cu2+, poses a considerable threat to aquatic environments and human health. To obtain a highly efficient adsorbent, in this work, a facile hydrothermal method was applied to prepare acrylic acid grafted onto cellulose nanocrystal (AA-g-CNC) hydro/aerogel as an adsorbent for Pb2+, Cd2+, and Cu2+ removal. The obtained AA-g-CNC hydrogels withstood up to 0.821 MPa of compression and showed good reciprocating performance when the deformation reached 40%. The as-formed AA-g-CNC aerogels had highly porous honeycomb structure, with many functional groups and a high zeta potential, all of which are essential features for an effective adsorbent. The maximum Pb2+, Cd2+, and Cu2+ removal capacities of AA-g-CNC aerogels reached 1026, 898.8, and 872.4 mg/g respectively. Their adsorption followed the Freundlich isotherm model and fitted well with pseudo-second-order kinetic models. The adsorption mechanism mainly attributed to electrostatic chelation between metal ions with sulfonate and carboxylate groups.

Mechanical characterization of Hyposand: A new material of sand solidified by sodium thiosulphate salt

A new material, named Hyposand, is proposed. Its fabrication by means of sand and sodium thiosulfate pentahydrate salt is presented, and the results of some characterization tests are discussed. Three families of samples were produced using different types of sands. The samples were tested to identify their mechanical properties and to understand how these properties are affected by the microstructure, the mixing proportions and the temperature of salt when mixing. Furthermore, information on the effects of exposure to humidity was sought. For these purposes, the following experimental campaigns were run and are presented here: (i) sieve tests and X-ray tomography analyzes, (ii) compression tests, and (iii) flexural tests. The results indicated an average strength of 25 MPa in compression and 8 MPa in flexion, with values depending on the above mentioned conditions. Although more research is needed to know the new material in detail, Hyposand seems to develop satisfactory strengths, promising technical accessibility, and minimal consumption of resources.

Moderate activation of Wnt/β-catenin signaling promotes the survival of rat nucleus pulposus cells via regulating apoptosis, autophagy, and senescence.

This study aimed to investigate the specific role of Wnt/β-catenin signaling in compression-induced apoptosis, autophagy, and senescence in rat nucleus pulposus (NP) cells. Initially, the cells underwent various periods of exposure to 1.0 MPa compression. Wnt/β-catenin signaling associated molecules were assessed in detail, and then 0, 24 and 48 hours exposure periods were selected. The cells were then divided into control, Wnt/β-catenin inhibitor (IWP-2), Wnt/β-catenin activator (LiCl), and β-catenin overexpression groups. After 0, 24, and 48 hours of compression, apoptosis, autophagy, and senescence were evaluated by Western blot analysis and real-time polymerase chain reaction and were visually observed by Hoechst33258, monodansylcadaverine, and SA-β-gal stainings, respectively. Additionally, the regulatory effect of Wnt/β-catenin signaling on cell morphology, viability, cell cycle, death ratio, and ultrastructure was detected to thoroughly evaluate the survival capacity of NP cells. The results established that compression elicited a time-dependent activation of Wnt/β-catenin signaling. The IWP-2 treatment decreased cell survival rate, which corresponded to downregulation of autophagy as well as increases in apoptosis and senescence. LiCl treatment enabled more efficient of cell survival accompanied by increased autophagy and downregulated apoptosis and senescence; however, in contrast to LiCl, overexpression of β-catenin aggravated compression-induced NP cells death. In conclusion, moderate activation of Wnt/β-catenin signaling enables more efficient of NP cells survival via downregulation of apoptosis, senescence, and upregulation of autophagy, and overactivation of Wnt/β-catenin signaling achieved the opposite effect. Treatment strategies that aim to regulate Wnt/β-catenin signaling might be a novel target for improving compression-induced NP cells death and potential treatment of intervertebral disc degeneration.

Stress Controllability in Thermal and Electrical Conductivity of 3D Elastic Graphene‐Crosslinked Carbon Nanotube Sponge/Polyimide Nanocomposite

AbstractStress controllability in thermal and electrical conductivity is important for flexible piezoresistive devices. Due to the strength‐elasticity trade‐off, comprehensive investigation of stress‐controllable conduction in elastic high‐modulus polymers is challenging. Here presented is a 3D elastic graphene‐crosslinked carbon nanotube sponge/polyimide (Gw‐CNT/PI) nanocomposite. Graphene welding at the junction enables both phonon and electron transfer as well as avoids interfacial slippage during cyclic compression. The uniform Gw‐CNT/PI comprising a high‐modulus PI deposited on a porous templated network combines stress‐controllable thermal/electrical conductivity and cyclic elastic deformation. The uniform composites show different variation trends controlled by the porosity due to different phonon and electron conduction mechanisms. A relatively high k (3.24 W m−1 K−1, 1620% higher than PI) and suitable compressibility (16.5% under 1 MPa compression) enables the application of the composite in flexible elastic thermal interface conductors, which is further analyzed by finite element simulations. The interconnected network favors a high stress‐sensitive electrical conductivity (sensitivity, 973% at 9.6% strain). Thus, the Gw‐CNT/PI composite can be an important candidate material for piezoresistive sensors upon porosity optimization based on stress‐controllable thermal or electrical conductivity. The results provide insights toward controlling the stress‐induced thermal/electrical conductivities of 3D interconnected templated composite networks for piezoresistive conductors or sensors.

Effects of amphiphilic monomers and their hydrophilic spacers on polyacrylamide hydrogels.

Hydrogels based on physical interactions have been extensively studied due to their special network structure and excellent mechanical properties. In this paper, a series of hydrogels based on hydrophobic interactions were prepared via the free-radical copolymerization of acrylamide and polymerizable amphiphilic monomers dodecanol polyoxyethylene (n) acrylates (AEO-n-AC, n = 3, 7, 9, 15, 23) by a simple and facile method. The prepared single-network hydrogels cross-linked by the self-assemble AEO-n-AC micelles acting as cross-linkers exhibited great tensile strength of 0.45 MPa and excellent compression strength of 4.5 MPa. Transmission electron microscopy tests reflected that the morphologies of the self-associated micelles were determined by the hydrophilic segment of the amphiphilic monomers, which further affected the mechanical properties of the hydrogel. Amphiphilic monomer with appropriate length of hydrophilic spacers could significantly enhance the tensile strength of the hydrogel. Meanwhile, amphiphilic monomers with long hydrophilic segment were advantageous for the compression properties of the hydrogel. Furthermore, the hydrogels exhibited excellent micro self-repair ability during the cycling tensile and loading-unloading test even at the strain and compression were 400%, 0.95, respectively. This discover of hydrophilic spacer effect is of great significance for the design of physical interaction-based hydrogels with high strength and compression properties.

High-dry dewatering of sludge based on different pretreatment conditions

Reducing the moisture content (Mc) of sludge contributes greatly to subsequent treatment and disposal. An ultrahigh-pressure (UHP) and thin-cake-press (TCP) dewatering device was designed to achieve high-dry sludge using technique involving the addition of little or no cationic polyacrylamide (CPAM). The relationships between the Mc of the cake and compression pressure, dewatering time, sludge quality and category, pressurization mode, pretreatment methods and the thickness of the cake were studied.The compression pressure, dewatering time, sludge quality and category, thickness of the cake and pretreatment methods substantially influence the Mc of the cake, while the pressurized mode has almost no influence on the Mc of the cake. The time of pressure drop (TOPD) reflects, to a certain extent, the dewatering performance of sludge. The Mc of municipal sludge can reach to 45% or 39.47% with 60 or 90 min of dewatering time, respectively, and 12 MPa compression pressure, achieving a cake thickness of 3.2 mm and 3.1 mm, respectively. Sludge with high organic matter content is more difficult to dehydrate, and the dewatering performance of municipal sludge is considerably worse than that of river sludge and electroplating sludge. Pretreatment methods can change the dewatering performance of sludge. Microwave and freeze-thaw pretreatments are favorable for dewatering performance, while ultrasound and magnetic field pretreatment are disadvantageous for dewatering. After microwave pretreatment, the Mc of municipal sludge can reach a minimum value of 28%. Mc has a positive correlation with the thickness of the cake; the thinner the sludge cake is, the lower the moisture content is. Thus, the thin-cake-press and microwave pretreatments are effective methods for high-dry dewatering. Sludge has good compression characteristics, and the compression ratios (Cr) of municipal activated sludge and river sludge are 79% and 59%, respectively.

Biomimetic Bottlebrush Polymer Coatings for Fabrication of Ultralow Fouling Surfaces.

Demand for long-lasting antifouling surfaces has steered the development of accessible, novel, biocompatible and environmentally friendly materials. Inspired by lubricin (LUB), a component of mammalian synovial fluid with excellent antifouling properties, three block polymers offering stability, efficacy, and ease of use were designed. The bottlebrush-structured polymers adsorbed strongly on silica surfaces in less than 10 minutes by a simple drop casting or online exposure method and were extremely stable in high-salinity solutions and across a wide pH range. Antifouling properties against proteins and bacteria were evaluated with different techniques and ultralow fouling properties demonstrated. With serum albumin and lysozyme adsorption <0.2 ng cm-2 , the polymers were 50 and 25 times more effective than LUB and known ultralow fouling coatings. The antifouling properties were also tested under MPa compression pressures by direct force measurements using surface forces apparatus. The findings suggest that these polymers are among the most robust and efficient antifouling agents currently known.

Biomimetic Bottlebrush Polymer Coatings for Fabrication of Ultralow Fouling Surfaces

AbstractDemand for long‐lasting antifouling surfaces has steered the development of accessible, novel, biocompatible and environmentally friendly materials. Inspired by lubricin (LUB), a component of mammalian synovial fluid with excellent antifouling properties, three block polymers offering stability, efficacy, and ease of use were designed. The bottlebrush‐structured polymers adsorbed strongly on silica surfaces in less than 10 minutes by a simple drop casting or online exposure method and were extremely stable in high‐salinity solutions and across a wide pH range. Antifouling properties against proteins and bacteria were evaluated with different techniques and ultralow fouling properties demonstrated. With serum albumin and lysozyme adsorption &lt;0.2 ng cm−2, the polymers were 50 and 25 times more effective than LUB and known ultralow fouling coatings. The antifouling properties were also tested under MPa compression pressures by direct force measurements using surface forces apparatus. The findings suggest that these polymers are among the most robust and efficient antifouling agents currently known.

Scientific and Theoretical Fundamentals of Alumina-silicate Binding Agent Design on the Basis of Technogenic Raw Materials Used to Produce Non-autoclaved Silicate Materials

These days the use of natural and technogenic raw materials is particularly relevant for the production of efficient construction composites, including the use of nature-like technologies. Successful development of efficient compositions of raw mixes using technogenic and natural raw materials of various genesis is only possible on the basis of in-depth and versatile study of physical, chemical and technological solidification. Thus, the use of nonconventional alumina-silicate raw materials during the production of construction composites provides for theoretical and experimental possibility of shifting from traditional raw materials to the production of composite materials on the basis of nonconventional natural and technogenic raw materials. The study resulted in scientific and theoretical fundamentals of alumina-silicate binding agent design on the basis of technogenic raw materials used to produce non-autoclaved silicate materials. It is suggested to use alumina-silicate rocks of incomplete stage of clay synthesis as an active component of non-autoclaved silicate materials, which structure differs with regard to their thermodynamically-unstable compounds, which, in turn, may result in the production of efficient energy-saving high-hollow silicate materials of a new generation with up to 32 MPa compression strength, F15-25 frost resistance and 1100-1200 kg/m3 average density.

Tension–Compression Asymmetry Improved by Cold Extrusion in Pure Magnesium

In this paper, cold extrusion was successfully used to fabricate the fine-grained pure Mg bar with average grain size of 2.5 μm. The microstructure, texture and mechanical properties were evaluated by electron backscattering diffraction and mechanical test. The results showed that the corresponding yield strengths for as-extruded fine-grained pure Mg were 130.8 MPa in tension and 125.6 MPa in compression, leading to a greatly improved yield asymmetry ratio. The improvement in tension–compression asymmetry is mainly due to grain refinement which favors the suppression of deformation twinning in compression and promotion of multi-deformation modes both in tension and compression at small strains.

Primary radiation damage of Fe-10%Cr models under uniaxial, biaxial, and hydrostatic pressure using MD simulation

Reduce activation ferritic/martensitic steels are candidate materials for future nuclear reactors due to their superior mechanical properties and reduced swelling under irradiation. In this research, single−crystal models of Fe-10%Cr have been built with [100][010][001] crystal orientations. The models stressed in both compression and tension by applying seven different pressures between −1000 MPa (tension) to +1000 MPa (compression) in uniaxial, biaxial, and hydrostatic cases. Displacement cascades have been initiated by imparting kinetic energy to an atom in the center of the simulation box. The produced point defects have been identified using the Wigner−Seitz cell method. In all cases, increasing the imparted energy increases the number of point defects. For models under uniaxial pressure, three different regions have been identified and each region has its own unique mechanism that controls the defect production process. For models under biaxial and hydrostatic pressure, the number of produced point defects increases with increasing the pressure in both tension and compression regions; in addition, the number of produced point defects with pressures shows an empirical power relationship. The Cr atoms prefer interstitial positions over creating vacancies in all cases.

Experimental study on shear behavior of prestressed reactive powder concrete I-girders

As a new generation of concrete, RPC(Reactive Powder Concrete) has attracted great research attention for its ultra-high strength and high durability. In the present paper, experimental results from tests on eight prestressed RPC I-section girders failing in shear are reported herein. The beams with RPC of 120 MPa in compression were designed to assess the ability to carry shear stress in thin webbed prestressed beams with stirrups. The test variables were the level of prestressing, shear span-depth ratio (a/d) and stirrup ratio. Shear deformation, shear capacity and crack pattern were experimentally investigated in detail. With regard to the shear resistance of the test beams, the predictions from three standards (AFGC, JSCE and SIA) on the design of UHPC structures were compared with the experimental result suggesting that the experimental strength is almost always higher than predicted. RPC, as a new concrete, was different from normal concrete and fiber reinforced concrete. Further study should be needed to develop an analytical method and computation model for shear strength of RPC beams.

Effect of Solidification Cooling Rate on Microstructure and Mechanical Properties of an Extruded Mg-Zn-Y Alloy

The Effect of the solidification conditions and subsequent extrusion of a Mg-3.0Zn-0.5Y (at. %) alloy containing quasicrystalline icosahedral (i-) phase was studied. Solidification was carried out by three methods using a chill casting mold, a conventional steel mold and a water-cooled mold. Subsequently, castings were extruded in the temperature range of 235–270 ∘ C at an extrusion ratio of 25:1. The solidification molds showed different characteristics. The water-cooled mold was most effective in cooling through the walls, but least effective at the center of the mold. The conventional cast mold was the most effective in cooling at the mold center. All the castings had an interdendritic eutectic structure of the i-phase, and a supersaturation of the matrix in zinc. As a result, all the extrusions had similar grain size close to 1 μ m and very fine nano-size precipitation. Yield strengths in tension were in the range of 376 and 404 MPa, and from 300 to 330 MPa in compression. All elongations to fracture were about 13%. It is concluded that supersaturation of the matrix during solidification is the main factor, resulting in the dynamic precipitation of very fine precipitates and fine grain size during extrusion.

CsA attenuates compression-induced nucleus pulposus mesenchymal stem cells apoptosis via alleviating mitochondrial dysfunction and oxidative stress

AimsThis study aims to investigate the protective effects and potential mechanisms of cyclosporine A (CsA), which efficiently inhibits mitochondrial permeability transition pore (MPTP) opening, on compression-induced apoptosis of human nucleus pulposus mesenchymal stem cells (NP-MSCs). Materials and methodsHuman NP-MSCs were subjected to various periods of 1.0 MPa compression. Cell viability was evaluated using cell counting kit-8 (CCK-8) assay. The cellular ultrastructure and ATP level were analyzed via transmission electron microscopy (TEM) and ATP detection kit respectively. The apoptosis ratio was determined using Annexin V/PI dual staining and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assays. The levels of apoptosis-associated molecules (cleaved caspase-3, Bax and Bcl-2) were analyzed by western blot and qRT-PCR. Additionally, MPTP opening, mitochondrial membrane potential (MMP) and the levels of oxidative stress-related indicators (ROS), superoxide dismutase (SOD) and malondialdehyde (MDA) were monitored. Key findingsAnnexin V/PI dual staining and detection of apoptosis-associated molecules demonstrated that compression significantly up-regulated apoptosis level of NP-MSCs in a time-dependent manner. CsA greatly down-regulated compression-mediated NP-MSC apoptosis and the cell death ratio. Compression also notably exacerbated mitochondrial dysfunction, ATP depletion and oxidative stress in NP-MSCs, all of which were rescued by CsA. SignificanceOur results demonstrated that CsA efficiently inhibited compression-induced NP-MSCs apoptosis by alleviating mitochondrial dysfunction and oxidative stress. These findings provide new insights into intervertebral disc (IVD) degeneration (IVDD), and suggest CsA treatment as a potential strategy for delaying or even preventing IVDD.

Critical contribution of RIPK1 mediated mitochondrial dysfunction and oxidative stress to compression-induced rat nucleus pulposus cells necroptosis and apoptosis.

The aim of this study was to investigate whether RIPK1 mediated mitochondrial dysfunction and oxidative stress contributed to compression-induced nucleus pulposus (NP) cells necroptosis and apoptosis, together with the interplay relationship between necroptosis and apoptosis in vitro. Rat NP cells underwent various periods of 1.0MPa compression. To determine whether compression affected mitochondrial function, we evaluated the mitochondrial membrane potential, mitochondrial permeability transition pore (mPTP), mitochondrial ultrastructure and ATP content. Oxidative stress-related indicators reactive oxygen species, superoxide dismutase and malondialdehyde were also assessed. To verify the relevance between oxidative stress and necroptosis together with apoptosis, RIPK1 inhibitor necrostatin-1(Nec-1), mPTP inhibitor cyclosporine A (CsA), antioxidants and small interfering RNA technology were utilized. The results established that compression elicited a time-dependent mitochondrial dysfunction and elevated oxidative stress. Nec-1 and CsA restored mitochondrial function and reduced oxidative stress, which corresponded to decreased necroptosis and apoptosis. CsA down-regulated mitochondrial cyclophilin D expression, but had little effects on RIPK1 expression and pRIPK1 activation. Additionally, we found that Nec-1 largely blocked apoptosis; whereas, the apoptosis inhibitor Z-VAD-FMK increased RIPK1 expression and pRIPK1 activation, and coordinated regulation of necroptosis and apoptosis enabled NP cells survival more efficiently. In contrast to Nec-1, SiRIPK1 exacerbated mitochondrial dysfunction and oxidative stress. In summary, RIPK1-mediated mitochondrial dysfunction and oxidative stress play a crucial role in NP cells necroptosis and apoptosis during compression injury. The synergistic regulation of necroptosis and apoptosis may exert more beneficial effects on NP cells survival, and ultimately delaying or even retarding intervertebral disc degeneration.

Physical and mechanical evaluation of artificial marble produced with dolomitic marble residue processed by diamond-plated bladed gang-saws

The production of artificial stone from the agglutination of the epoxy resin fine waste can be a viable alternative from technical, economic and ecological points of views. The residue derives from the dolomitic marble produced by diamond-plated bladed gang-saws and it is usually discarded. With this new application, there is value added to the residue, reducing the consequent environmental impact. The main objective of this research is to evaluate the physical and mechanical properties of an artificial marble produced through vacuum vibro-compression. With this purpose, stone plates were produced, using appropriate tools, characterized by a distribution of 85% of residual particle weight and 15% of epoxy system. The material was manufactured with the following conditions for 20 (twenty) minutes, compacting pressure of 0.5MPa and temperature of 90°C. Later on, the samples were characterized by density, water absorption, porosity, flexural strength, compressive strength and scanning electron microscopy. The result was an artificial marble produced applying vacuum vibro-compression with water absorption levels below 0.06%, flexural strength of 33.93MPa and uniaxial compression of 96.49MPa, thus indicating residual particles and epoxy resin grip at satisfactory levels.

Study of the effect of Kaolin in the mortar of cement matrices by confinement of ion exchange resins

Radioactive waste arising as a result of nuclear activities should be safely managed from its generation to final disposal in an appropriate conditioned form to reduce the risk of radiation exposure of technical personnel and of the public and to limit contamination of the environment. The immobilization of low and intermediate level radioactive wastes in cementitious matrices is the most commonly used technique to produce inexpensive waste matrix that complies with regulatory requirements in order to protect humans and the environment against nuisance caused by ionizing radiation. Cement based materials are used in radioactive waste management to produce stable waste forms. This matrix constitutes the first build engineering barrier in disposal facilities. In this work, the kaolin is used to enhance the mechanical performance of the matrix of confinement of ion exchange resins by gradually replacing the sand in mortar with kaolin clay. The Kaolin clay sample was a special pure product, sourced from a foreign country. The maximum quantity of resins that can be incorporated into the mortar formulation without the packages losing their strength is 13.915% which results in a better mechanical strength at 6.7686 MPA compression with kaolin.