Extrapolation of Mechanical Strengthening Effect in Nanoclay/Epoxy Nanocomposites to Elevated Temperature Environments

The economical nanoclay/polymer nanocomposite with laudable thermal and barrier properties motivates scientists for its potential exploration in widespread engineering applications. The present investigation has been focused on the mechanical durability study of these nanocomposites at above ambient temperature environment. In-situ flexural testing was performed on epoxy based nanocomposites with 0, 0.5, 1 and 3 wt% nanoclay content at various temperatures (30, 50, 70 and 90 °C). Addition of only 0.5 wt% nanoclay in epoxy resulted in 17 and 26% improvement in flexural strength and modulus respectively (which is maximum among all the materials), when tested at room temperature, due to highest degree of exfoliation of nanoclay as confirmed from XRD analysis. At higher testing temperatures, all the materials exhibited a decreasing trend in their mechanical properties and a positive reinforcement effect was evident even up to the close vicinity of glass transition temperature. These findings were further verified by dynamic mechanical thermal analysis in a wide range of temperature varying continuously from 40 to 200 °C. The degree of dispersion and possible deformation and failure mechanisms were identified by scanning electron microscope.     

Surface Characteristics of Rare Earth Treated Carbon Fibers and Interfacial Properties of Composites

Effect of rare earth treatment on surface physicochemical properties of carbon fibers and interfacial properties of carbon fiber/epoxy composites was investigated, and the interfacial adhesion mechanism of treated carbon fiber/epoxy composite was analyzed. It was found that rare earth treatment led to an increase of fiber surface roughness, improvement of oxygeaa-containing groups, and introduction of rare earth element on the carbon fiber surface. As a result, coordination linkages between fibers and rare earth, and between rare earth and resin matrix were formed separately, thereby the interlaminar shear strength （ILSS） of composites increased, which indicated the improvement of the interfacial adhesion between fibers and matrix resin resulting from the increase of carboxyl and carbonyl.     

Effect of Aging Environment on Degradation of Glass-Reinforced Epoxy

The effects of immersing coupons of glass-reinforced epoxy in four different liquid media at two separate temperatures were investigated in this study which is aimed at examining the durability of fiber-reinforced plastics currently being used in the construction industry. A commercially available epoxy resin was reinforced with 47% by weight of an epoxy-compatible, E-glass woven fabric. Composite samples were soaked for up to 5 months in distilled water, a saturated salt solution (30g/100 cc NaCl), a 5-molar NaOH solution, and a 1-molar hydrochloric acid solution. Aging was conducted at room temperature and at 60°C. Samples were harvested periodically and their tensile and fracture properties determined. The fracture surfaces were also examined using scanning electron microscopy. Results show that commercial epoxy resins used in glass fiber-reinforced polymers are fairly durable. It was found that all the solutions marginally degraded the mechanical properties of the neat resin, especially at the higher temperature; this was mainly the result of polymer hydrolysis. The strength of the composites, however, was reduced by more than 70% by the acid at room temperature and by the alkali at the elevated temperature. Water immersion was less damaging than either acid or alkali soaking, and immersion in brine had the least effect on mechanical properties. As evidenced by SEM micrographs, the worst cases of damage involved attack on the glass fibers in acid at 60°C compared to room temperature. Therefore, reinforcing glass fibers have to be protected from attack by liquid media to improve the durability of composites.     

Effect of Notch Root Radius on the Apparent Fracture Toughness in CNT and Carbon Fiber Reinforced, Epoxy-Matrix Hybrid Composite

Significantly improved fracture resistance (in terms of fracture toughness) can be imparted to monolithic materials by adopting composite design methodology based on fiber and nano particulate reinforcement technology. The present work describes the fracture behaviour of one such reinforced material; in this case, carbon fiber (C_f)- and carbon nanotube (CNT)- reinforced epoxy composite. The C_f and CNT reinforced, epoxy-matrix hybrid composite in longitudinal and transverse orientations with varied finite notch root radii (in the range of 120–750 μm) are subjected to mode-I (tensile) fracture. The fracture toughness/resistance (K_Q) of the material is then evaluated and analyzed by investigating the influence of varying notch root radii in longitudinal and transverse orientations. Such an analysis has revealed that the present unidirectional epoxy hybrid composite exhibits a critical notch root radius of 270 μm in longitudinal and 390 μm in transverse orientation.     

Measurement of Epoxy Resin Tension, Compression, and Shear Stress–Strain Curves over a Wide Range of Strain Rates Using Small Test Specimens

The next generation aircraft engines are designed to be lighter and stronger than engines currently in use by using carbon fiber composites. In order to certify these engines, ballistic impact tests and computational analyses must be completed, which will simulate a “blade out” event in a catastrophic engine failure In order to computationally simulate the engine failure, properties of the carbon fiber and resin matrix must be known. When conducting computer simulations using a micromechanics approach, experimental tensile, compressive, and shear data are needed for constitutive modeling of the resin matrix material. The material properties of an Epon E862 epoxy resin will be investigated because it is a commercial 176°C (350°F) cure resin currently being used in these aircraft engines. These properties will be measured using optical measurement techniques. The epoxy specimens will be tested in tension, compression and torsional loadings under various strain rates ranging from 10?5?to?10?1?s?1 and temperatures ranging from room temperature to 80°C. To test the specimens at high temperatures, a specialized clear temperature chamber was used. The results show that the test procedure developed can accurately and quickly categorize the material response characteristics of an epoxy resin. In addition, the results display clear strain rate and temperature dependencies in the material response.     

Evaluation of Fracture Energy of Composite-Concrete Bonded Interfaces Using Three-Point Bend Tests

In this paper, a conventional test method using a notched three-point bending beam (3PBB) specimen is adapted to characterize Mode I fracture of composite-concrete bonded interfaces, and the interface fracture energy is evaluated based on a fictitious crack model. Two types of fiber fabrics—E-glass and carbon—are used, and a common epoxy resin is applied to bond the composite fabri?s to concrete. Mode I fracture tests of the 3PBB specimens for carbon fiber reinforced polymer (CFRP)- and glass fiber reinforced polymer (GFRP)-concrete bonded interfaces are performed to determine the applied load and load point displacement relationship from which the interface fracture energy is computed. The effects of loading rates, types of fiber fabrics, and curing time on the fracture energy of FRP-concrete bonded interfaces are studied and discussed. It is expected that the proposed experimental method can be used effectively to obtain fracture data for performing delamination studies under various environmental exposures and service loading.     

Acoustic Emission Characterization of Damage in Hybrid Fiber-Reinforced Polymer Rods

The development and testing of a pseudoductile hybrid fiber-reinforced polymer rod consisting of glass and carbon fibers is described. Two different hybrid forms were considered for the development of the hybrid rods, including (1) random dispersion of the glass and carbon fibers; and (2) a core-shell design with a glass fiber core protected by the carbon fiber shells. The mechanical properties of the hybrids were evaluated through uniaxial tension tests. The hybrid rods developed by way of the core-shell approach exhibited pseudoductile properties that included a yield point of 1,153 MPa and an ultimate strength of 1,191 MPa, with a strain of 3.5% at ultimate. The experimental program also included damage assessment by way of a single-channel fiber optic acoustic emission (AE) sensor. The acoustic emission technique was employed for real-time determination of the progressive damage due to rupture of fibers. Moreover, the spectral energies of the frequency spectrum from the AE signals were employed for assessment of the state of damage in the rods. The spectral energies distinguish between the carbon and glass fiber ruptures. This differentiation of signals provides information about the condition and the state of health of the hybrid rod.     

Microstructure,Mechanical Properties,and Abrasive Wear Behaviour of Si‐Mn‐Cr‐B Cast Steel as a Function of Carbon Concentration

The microstructures, mechanical properties and abrasive wear behaviour of five kinds of Si‐Mn‐Cr‐B cast steels were studied. The steels investigated contained X wt.% C with X= 0.15, 0.25, 0.35, 0.45, 0.55, 2.5 wt.% Si, 2.5 wt.% Mn, 0.5 wt.% Cr, 0.004 wt.%B . The results showed that the A_c1temperatures increased and A_c3 and M_s temperatures decreased with increasing carbon concentration. From the continuous cooling transformation (CCT) curves, it was discovered that the incubation period of pearlitic transformation was prolonged and the transformation curves of pearlite and bainite were separated significantly with rising carbon concentration. At lower carbon concentration, the normalized structure of Si‐Mn‐Cr‐B cast steel consisted mainly of granular bainite and M‐A islands. The normalized microstructures of the cast steel changed from granular bainite gradually to needle‐like bainite, upper bainite, and lower bainite with rising carbon concentration. The tensile strength and hardness of Si‐Mn‐Cr‐B cast steel increased and impact and fracture toughness decreased with increasing carbon content. The wear testing results showed that the wear resistance of Si‐Mn‐Cr‐B cast steel improved with higher carbon content but was obviously unchanged beyond the carbon concentration of 0.45%. The best balance of properties of Si‐Mn‐Cr‐B cast steel is obtained at the carbon concentration range of 0.35 ‐ 0.45%C.     

Structure and strength of Al,Cu-Al3Ni directionally solidified composites

A series of Al₃Ni fiber reinforced composites with a matrix composition varying from pure aluminum to Al-3.3 wt pct Cu were prepared by directional solidification of Al-Ni-Cu alloys. The solidification conditions were kept constant in all cases atG/R ≃ 10⁴ °C · s/mm² (G is the temperature gradient andR is the growth rate). The mechanical properties of the composites were studied in the as grown and in the heat treated conditions and the results were discussed in terms of the structure and composition. With the techniques used, it was possible to preserve the Al-Al₃Ni eutectic composite structure while strengthening the matrix by copper addition. The addition of 1 wt copper to the matrix caused a considerable increase in the mechanical strength, especially after heat treatment, without affecting the ductility. Strength values of the order of 530 MN/m² were reached in the heat treated composites which is higher than predicted by the rule of mixtures. This is attributed to the high work hardening capacity of the matrix especially in the presence of θ’ phase. Massive Al₃Ni rods and dendrites caused premature fracture and reduction in the strength of the composites containing 2 and 3 wt pct copper. Eliminating these defects by using higherG/R values can produce composites with exceptionally high strength.     

Structure and strength of Al, Cu-Al3Ni directionally solidified composites

A series of Al₃Ni fiber reinforced composites with a matrix composition varying from pure aluminum to Al-3.3 wt pct Cu were prepared by directional solidification of Al-Ni-Cu alloys. The solidification conditions were kept constant in all cases atG/R ≃ 10⁴ °C. s/mm² (G is the temperature gradient andR is the growth rate). The mechanical properties of the composites were studied in the as grown and in the heat treated conditions and the results were discussed in terms of the structure and composition. With the techniques used, it was possible to preserve the Al-Al₃Ni eutectic composite structure while strengthening the matrix by copper addition. The addition of 1 wt copper to the matrix caused a considerable increase in the mechanical strength, especially after heat treatment, without affecting the ductility. Strength values of the order of 530 MN/m² were reached in the heat treated composites which is higher than predicted by the rule of mixtures. This is attributed to the high work hardening capacity of the matrix especially in the presence of θ′ phase. Massive Al₃Ni rods and dendrites caused premature fracture and reduction in the strength of the composites containing 2 and 3 wt pct copper. Eliminating these defects by using higherG/R values can produce composites with exceptionally high strength.     

Study on preparation and properties of CeO2/epoxy resin composite coating on sintered NdFeB magnet

The CeO₂/epoxy resin composite coating was deposited on NdFeB substrate by cathode electrophoresis method for enhancing the anticorrosion and anti-wear performances. The morphologies and structures were characterized by a scanning electron microscope and an X-ray diffractometer. The micro hardness of the composite coating was evaluated by a microhardness tester. The corrosive behaviors of the coatings were studied by potentiodynamic polarization curve, electrochemical impedance spectroscopy and neutral salt spray tests. The concentration of CeO₂ nanoparticles (NPs) in the electrophoresis bath was optimized according to the coating structures and anticorrosion performances. The results show that CeO₂ NPs can enhance the microhardness of the composite coatings. Moreover, the nanoparticles disperse uniformly in the matrix when the concentration is lower than 30 g/L. The microhardness of CeO₂/epoxy resin (30 g/L) composite coating is about 63% higher than that of the blank epoxy resin coating. And the NSS time of the CeO₂/epoxy resin (30 g/L) composite coated sample can reach 1248 h. Meanwhile, the composite coatings possess no deteriorate influence on the magnetic properties of NdFeB substrates. The anticorrosion mechanisms of the composite coatings on the NdFeB substrate are deeply discussed.     

Comparison of the Wear Properties of Polymer Composites Having CNT With and Without Glass Fiber Reinforcement

The adoption of light weight and high performance polymer matrix composites are needed for industries related to aerospace, automotive, consumer goods, etc. Polymer fiber reinforced composite material have very good desirable mechanical and thermal properties like low density, higher specific stiffness with high specific strength and a controlled co-efficient of thermal expansion with dimensional stability. The addition of carbon nanoparticle in these composites improved mechanical as well as wear properties of the material, which leads to more applications of these composites in various fields. In the present investigation carbon nanotube addition along with the glass fiber reinforced composite material was used as work material. The sliding wear tests were carried out on pin on disc wear tester. The tribological performance was studied by varying the applied load. The wear surfaces were analyzed by using scanning electron microscope, X-ray diffraction and energy-dispersive X-ray spectroscopy which are presented in detail.     

Calculation-experimental study of the phase composition of Al-Zn-Mg-(Cu)-Ni-Fe aluminum alloys

To optimize the compositions of new high-strength aluminum ATs7NZh and ATs6N0.5Zh alloys (economically alloyed nikalins), the thermodynamic optimization of the Al-Zn-Mg-Cu-Ni-Fe system is performed via the construction of polythermal sections and the calculation of the chemical composition and volume fraction of phases at characteristic temperatures. The concentrations of the matrix elements (Zn, Mg, Cu) that determine the high level of mechanical properties are shown to be 6–7 wt % Zn, 2–3 wt % Mg, and up to 0.3 wt % Cu. The concentrations of the eutectic-forming elements (Ni, Fe) that ensure the solidification of (Al) + Al₉FeNi eutectic are determined. This eutectic favors an increase in the manufacturing properties of the alloys during casting, metal forming, and welding along with a retained high level of the mechanical properties. In general, experimental results confirm the calculated data.     

Mechanical properties of NiAl-Y2O3-based powdered alloys produced by directional recrystallization

The mechanical properties of NiAl-Y₂O₃-based powdered composite alloys (0.5–7.5 vol %), including those with an NiAl intermetallic matrix alloyed with 0.5 wt % Fe and 0.1 wt % La have been studied. Structures with various aspect ratios (AR, the ratio of the grain length to the grain diameter) are formed using deformation and subsequent annealing. A combination of the optimum amount of strengthening phase (2.5 vol % Y₂O₃) and a quasi-single-crystalline structure with a sharp axial texture with the (100) main orientation and AR ≈ 20–40 provides the maximum short-term strength and life at temperatures up to 1400–1500°C. An NiAl-Y₂O₃ alloy (2.5 vol %) has the best strength properties among all known nickel superalloys at temperatures higher than 1200°C and can operate under moderate loads at temperatures higher than the working temperatures of nickel superalloys (by 100–400°C) and their melting points. Additional alloying with 10 wt % Co and 2 wt % Nb makes it possible to increase the ultimate tensile strength of an intermetallic NiAl matrix at 1100°C by a factor of 1.3–1.4.     

Creep and creep rate curves of a 10cr-30mn austenitic steel during carbide precipitation

The effect of carbide precipitation on creep and creep rate curves was investigated for 10Cr-30Mn austenitic steel containing 0.003 to 0.55 wt pct carbon. After solution annealing, the specimens were subjected to creep testing at 873 K for up to 30 Ms (8300 hours). In the low-carbon steels containing below 0.1 wt pct carbon, where carbide precipitation scarcely occurred, the decrease in creep rate with time in the transient creep region was described by log έ = A - (1/3) log t, where A is a constant depending on stress and carbon concentration. On the other hand, in the high-carbon steels containing above 0.2 wt pct carbon, where extensive precipitation of M₂₃C₆ occurred, the creep rate decreased significantly at long times above 3 to 5 ks (1 hour), deviating from the preceding equation for the low-carbon steels. The Johnson-Mehl equation with the time exponent n = 2/3 provided a reasonable approximation for the significant decrease in creep rate at long times. This resulted from a stress-induced precipitation of M₂₃C₆ on dislocation lines produced by creep deformation. The rate constant of the Johnson-Mehl equation depended on carbon concentration but not on stress levels examined.     

Fibridization Effect on the Mechanical Behavior of PA66/PTFE Blend Based Fibrous Composites

The use of natural fiber along with the glass fiber in polymer composites is one of the present material combinations for automotive industries. This article deals with the hybrid effect of 10 wt% short glass fibers (SGF) and 10 wt% short basalt fibers (SBF) on the mechanical behavior of 80 wt% PA66/20 wt% Teflon (PA66/PTFE) blend. These composite materials were prepared by melt mixing method, by using twin screw extruder followed by injection molding. The mechanical performance of the composite materials was tested as per ASTM method. The experimentally determined mechanical properties were tensile behavior, flexural behavior and impact behavior. Hardness and density of the blended composites were also studied. Experimental results revealed that the effect of hybrid short fibers on the blend greatly enhanced the mechanical behavior. Increase in tensile strength and flexural strength by 33% and 57% respectively and 6% reduction in elongation was exhibited by the blend due to the hybrid effect of fibers. The synergistic effect between the fibers and the matrix blend improved the mechanical behavior. The strain rate of the hybrid composites was deteriorated due to the hybrid effect. The enhancement of load carrying capacity by 17.35, 8.5 and 36% was exhibited by SGF, SBF and hybrid fiber filled PA66/PTFE blend composites respectively. The impact strength of the hybrid composites was reduced due to the brittle nature of the hybrid filled composites. Fiber fracture, fiber pull out and fiber misalignment were the certain mechanisms observed during mechanical performance. The fractured surfaces were analyzed through Scanning Electron Microscopy photographs.     

Tensile properties of directionally solidified Al-4 wt pct Cu alloys with columnar and equiaxed grains

The tensile properties of directionally solidified Al-4 wt pct Cu-0.15-0.2 wt pct Ti alloys with equiaxed grains were determined and compared with the properties of directionally solidified Al-4 wt pct Cu columnar structures. The tensile properties of the equiaxed structure were isotropic, but varied with the distance from the chill face. The mechanical properties of the equiaxed structure were generally between those of the longitudinal and transverse columnar structures. The 0.2 pct offset yield stress(σ _y, MPa) is represented as a function of the grain size,d (mm), the average concentration, C_o (wt pct), and the local concentration, C (wt pct), by σ_y = [(15.7 + 22.6 C_o) + (1.24 + 1.04 C_o)d ^-1/2] + [15.7 △C], where △C = C - C_o. The equiaxed structure exhibits inverse segregation similar to that in the columnar structure.     

Aluminum matrix composites: Fabrication and properties

Aluminum alloy matrix composites containing 1 to 30 wt pct of fibrous and particulate nonmetals varying in size from 0.06 μm to 840 μm were fabricated. The composites were cast into cylindrical molds for friction and wear tests, hot extrusion and tensile tests. The distribution of the nonmetals in the cast ingots was homogeneous. Friction and wear tests were done on a pin (52100 bearing steel) and dish type machine without lubrication. It was found that composites containing ∼10 wt pct or more of SiC, TiC, Si₃N₄, Al₂O₃, glass, solid waste slag, and silica sand wear less than the pure matrix alloy, but have slightly higher average coefficients of friction. Wear in composites containing soft particles, especially MgO and boron nitride was higher than the pure matrix alloy. The average coefficient of friction of all the composites was in the range of 0.35 to 0.58. Increasing the sliding velocity reduced this range to ∼ 0.4 to 0.45. The longitudinal tensile properties of the extruded composites (with the exception of loss of ductility in some cases) are comparable to that of the matrix alloys. Improvements in strength or ductility were noted. For example, addition of 15 wt pct of 3 μm size Al₂O₃ particles raised the yield and ultimate strength of the Al-4 pct Cu-0.75 pct Mg alloy matrix from 227 to 302 MPa, and 356 to 403 MPa, respectively. The corresponding percent elongation decreased from 25.8 to 12.5. The fact that the various composites can be readily cast and hot formed suggests a variety of engineering applications. AKIRA SATO, formerly Visiting Scientist at Massachusetts Institute of Technology, Cambridge.     

Composite biomaterials with chemical bonding between hydroxyapatite filler particles and PEG/PBT copolymer matrix

In an effort to make composites from hydroxyapatite and a PEG/PBT copolymer (Polyactive 70/30), chemical linkages were introduced between the filler particles and polymer matrix using hexamethylene diisocyanate as a coupling agent. Infrared spectra (IR) and thermal gravimetric analysis (TGA) confirmed the presence of Polyactive 70/30 on the surface of HA filler particles. The amount of chemically bound polymer was 4.7 wt.%, as determined by TGA. The mechanical properties of the composites, that is, tensile strength and Young's modulus, were improved significantly by the introduction of a chemical linkage between the filler particles and polymer matrix compared to control composites. This method provides an effective way to introduce chemical linkage between HA filler particles and a polymer matrix. By optimizing the grafting process, a further improvement of the mechanical properties in the composites can be expected.     

Oxygen and carbon sensing in Fe—O—C and Fe—O—C—Xn melts at elevated carbon contents

In the present study on solid electrolyte probes, the attempt was made to measure accurate and reproducible EMF values representing the extremely low oxygen activities in Fe—O—C melts at varying C contents. Various types of sensors were designed and successfully tested in laboratory experiments. Reliable oxygen activities were measured in Fe—O—C melts up to 4 wt. % C under pure CO gas, and f_o and f_c values were derived as a function of C content at 1 400 to 1 600°C. Further measurements were made in Fe—O—4 wt. % C—X_n melts at various contents of X_n (S_n = Si, Mn, Cr). Moreover, a solid oxide electrolyte probe with a CO gas channel to measure oxygen and carbon activities was developed and successfully tested in high-carbon iron melts.