Effect of moisture on the mechanical properties of CFRP–wood composite: An experimental and atomistic investigation

Adhesive bonding of fiber-reinforced polymers (FRP) to wood has been proven as a general way to achieve reinforcement and rehabilitation for wood structures. Although a significant mechanical enhancement can be acquired by using such approach, there exists a big concern about the long-term performance of the FRP–wood composite, especially under the effect of moisture. In this paper, both experimental and atomistic approaches are adopted for investigating the moisture effect on the entire FRP–wood composite system. Macroscopic mechanical tests show that its mechanical properties and its fracture behaviors notably change at different levels of ambient humidity. From an atomistic perspective, molecular dynamics (MD) simulations reveal that water molecules significantly reduce the adhesion energy between wood and epoxy. Results from experimental and numerical studies imply that the strength of the FRP–wood interface critically determines the mechanical performance of the entire system. The water molecules absorbed at the interface are crucial to the durability of multi-layer systems and a general mechanism governing the failure modes of such systems is found.     

Effect of the POSS–Polyimide nanostructure on its mechanical and electrical properties

Nanocomposite films consisted of Polyhedral Oligomeric Silsesquioxane (POSS) filler in a Polyimide (PI) matrix were prepared. The effect of the nanocomposites’ structure on its mechanical and electrical properties was evaluated with respect to survival in the low Earth orbit (LEO) environment. The POSS–PI structure consists of POSS nano-aggregates formed in the bulk and on the surface. The aggregates’ size and distribution are POSS content-dependant. The fracture mechanism during hypervelocity impact at extreme temperature conditions was studied. The hypervelocity impacts of the POSS–PI films result in a brittle fracture, compared to ductile fracture in the case of PI, and in formation of radial cracks. A model based on formation and coalescence of voids around the aggregates, when load is applied, is suggested to explain the effect of the POSS content on the POSS–PI fracture mechanism. The size and density of the POSS aggregates also affect the nanocomposite’s volume electrical resistivity. An inverse dependence exists between the POSS aggregates’ surface density and the nanocomposites’ volume electrical resistivity.     

Effect of particle size distribution on the mechanical and electrical properties of reverse-offset printed Sn–Ag–Cu solder bumps

A reduction of the particle size used in solder pastes was shown to affect the electrical and mechanical properties of finely printed solder bumps. Sn–3.0Ag–0.5Cu solder nanoparticles were synthesized using a radio frequency thermal plasma system, and solder pastes were formulated for reverse-offset printing of solder bump arrays with a size of 30 µm. As the nanoparticle ratio in the paste increased, the degree of supercooling, ΔT, increased with a separation of the exothermic peaks for the solidification of β-Sn and the precipitation of intermetallic compounds (IMCs). The networks of finely precipitated IMCs formed at the boundaries of large β-Sn increased the shear strength to 73 MPa. However, insufficient flux deteriorated the electrical and mechanical properties because it delayed the solidification of primary β-Sn as well as the melting of the solder. As a result, the Sn–3.0Ag–0.5Cu solder paste containing a nanoparticle ratio of 25% exhibited an optimum printability for reverse-offset printing of solder bumps, and the resulting bumps had an electrical conductance of 0.4 mΩ and a shear strength of 73 MPa.     

Effect of MWCNT alignment on mechanical and self-monitoring properties of extruded PET–MWCNT nanocomposites

Self-monitoring aligned MWCNT loaded PET composites, with different CNT content, were prepared via twin-screw extrusion starting from a PET/MWCNT masterbatch, and fully characterized. All electrically conductive samples showed self-monitoring ability, i.e. a variation in electrical resistance as a function of stress. Moreover, the insertion of MWCNTs resulted in mechanical reinforcement with respect to neat PET. It was found that both self-monitoring behavior and mechanical performance are directly related to MWCNT content and to the direction of applied stress with respect to CNT orientation. In particular, too high MWCNT content decreased sensitivity at low strain, whereas a minimum MWCNT content was required to insure ohmic conductivity.     

The relationship between the electrical and mechanical properties of polymer–nanotube nanocomposites and their microstructure

A range of polymer–nanotube nanocomposites were produced using different processing routes. Both polymer-grafted and as-grown nanotubes were used and latex and polystyrene matrices investigated. The microstructures of the nanocomposites were studied, mainly by electron microscopy, in terms of the dispersion state of the nanotubes and the polymer–nanotube interface. The mechanical and electrical properties of the composites were also measured. The relationship between the microstructures observed and the resulting physical properties are discussed. It is found that composites with apparently similar microstructures can exhibit similar mechanical properties but very different electrical behaviours. Moreover, the nanocomposites produced using polymer-grafted nanotubes exhibit a clear improvement of the stress at large deformation. Thus, from our results, it appears that the mechanical and electrical properties do not necessarily depend on the same microstructural parameters. However it is still a challenge to simultaneously improve both physical properties.     

Effect of γ-irradiation on the physical and mechanical properties of chitosan powder

In this study, locally produced chitosan powder was irradiated with pre-determined doses of γ-ray (Co-60) of 10 kGy, 25 kGy, 50 kGy and 100 kGy respectively. The properties of both chitosan powder and the chitosan film were examined and compared with unradiated chitosan. Physical characteristic of the irradiated powder and film was studied using stereo microscope. It was observed that the γ-ray induces a noticeable colour tone intensity change to the chitosan. Further investigation using Fourier Transformed Infrared Spectroscopy (FT-IR) analysis has confirmed that the chain scission reaction was occurred as a result of γ-ray exposure through the depolymerization mechanisms. Interestingly, the degree of deacetylation (DD) of chitosan measured using FT-IR showed a negligible effect due to the exposure of γ-ray radiation. Further investigation on the viscosity average molecular weight (M_v) showed a reduction of M_v from 577 kD of pure chitosan to 458 kD, 242 kD, 159 kD and 106 kD for 10 kGy, 25 kGy, 50 kGy and 100 kGy of γ-radiated chitosan respectively. In addition, the tensile strength and elongation at break showed a similar decreasing trend with increasing dosage of γ-ray.     

Effect of nanophase concentration on the properties of metal-containing silicon–carbon nanocomposites

We have studied the effect of tungsten, molybdenum, and hafnium concentrations on the electrical conductivity, nanohardness, and elastic modulus of metal-containing silicon–carbon nanocomposite films. The results demonstrate that the addition of these metals to the films leads to the formation of metal carbide particles a few nanometers in size. At metal contents from 5 to 35 at %, the conductivity of the films varies over four orders of magnitude (from 10^–1 to 10³ S/cm). The composition dependences of the mechanical properties of the nanocomposites depend on the nature of the metal. We have analyzed the mechanisms underlying the effect of the metals on these properties.     

Effect of aluminium on the microstructure and mechanical properties of as-cast magnesium–manganese alloys

In this paper, the effect of aluminium on microstructure and mechanical properties of as-cast magnesium–manganese alloy has been investigated by means of X-ray diffraction, optical microscopy and scanning electron microscopy. The results reveal that various Al–Mn intermetallic compounds form with an increase of Al content. As a result, microstructure of AM11 alloy has been effectively refined due to the formation of Al₈Mn₅ phase along the grain boundary, while Al addition is explained as the main reason on refining the microstructure of AM91 alloy due to its higher grain growth restriction factor value of ～4.32. The tensile yield strength (TYS) has been improved steadily from 27.4 to 122.9?MPa with increasing Al content, because of the combined effects of grain boundary strengthening, solid solution strengthening and precipitation hardening behaviours.     

Influences of film composition and annealing on the mechanical and electrical properties of W–Mo thin films

In this article, the mechanical and electrical characteristics of co-sputtered W–Mo thin films investigated for the application to microelectromechanical systems are described. W–Mo thin films with various compositions were deposited by co-sputtering onto a cover glass and silicon oxide (SiO _x ) film-coated Si wafer. The internal stress measured by Newton-ring method depended on film composition and Ar pressure, but were independent on annealing at 623 K. The hardness gradually decreased with an increase in Ar pressure, whereas the effective Young’s modulus stayed constant throughout Ar pressures ranging from 0.2 to 0.4 Pa. Both the mechanical properties showed no dependences of film composition and annealing. The resistivity was proportional to Ar pressure, but was not related to film composition. Annealing slightly affected the resistivity. Auger spectroscopy clarified that, by annealing, an oxide layer of approximately 10 nm thick was produced on the top surface, but film composition did not change. From the experimental results obtained, annealing at 623 K did not affect the mechanical and electrical properties of W–Mo films. This indicates that the co-sputtered film is very stable at temperatures ranging from RT to 623 K. By controlling Ar pressure, stress-free W–Mo films with superior mechanical characteristics and low resistivity can be produced regardless of film composition.     

An investigation on the precipitated phases and mechanical properties of cerium modified 2024 aluminum alloy

The effects of the addition of rare earth cerium on the cast microstructure and mechanical properties of 2024-T6 aluminum alloy were investigated in this work. The specimens for room-temperature tensile tests were prepared with a T6 heat treatment. Experimental results indicated that the cerium modified alloys showed refined grains, higher hardness, and strength values at room temperature. The hardness and the strength of the cerium modified alloys initially increased and then decreased as the cerium content increased. The maximum tensile strength was obtained at the 0.6 wt.% cerium modified 2024 aluminum alloy. This was improved from 464 MPa to 612 MPa. Simultaneous increases in the tensile strength and hardness were proposed to result from the refined α-aluminum dendrites, the formation of aluminum-rare earth intermetallic compounds at the grain boundaries and the grains, the more homogeneously distributed nano-scale S precipitates, and the smaller T diffusion phase.     

Effect of BN grain size on microstructure and mechanical properties of the ZrB2–SiC–BN composites

ZrB₂–20 vol.%SiC composites containing 10 vol.% h-BN particles (ZSB) with average grain sizes ranging from 1 μm to 10 μm were hot-pressed. The fracture toughness of the ZSB composites was higher than reported results of monolithic ZrB₂ (2.3–3.5 MPa m^1/2) and SiC particle reinforced ZrB₂ composites (4.0–4.5 MPa m^1/2). The improvement in the fracture toughness of the ZSB composites was due to the high aspect ratio of h-BN and weaker interface bonding, which could enhance crack deflection and stress relaxation near the crack-tip. Compared with the flexural strength of the ZrB₂–SiC composites, the reduction in the flexural strength of the ZSB composites was attributed to the weaker interface bonding and the lower relative density. Furthermore, improvement in toughness and the reduction in the strength were valuable to improve the thermal shock resistance of the ZSB composites. The ΔT_c of ZSB5 material is 400 °C which is higher than ZrB₂–20%SiC and ZrB₂–15%SiC–5%AlN.     

Effect of processing parameters on the microstructure and mechanical properties of Al–steel composite foam

Al–steel composite foams comprise of steel hollow spheres embedded in an aluminum matrix and are processed using a gravity casting technique. The effect of processing parameters such as casting temperature and cooling rate on the microstructure and mechanical behavior was studied to establish structure–property relationships. Results show that the amount and composition of intermetallic phases present in the foam microstructure is directly related to casting temperature and cooling rate. Highest strength and energy absorption were obtained from Al–steel foams with fast solidification rates that minimize the growth of intermetallic phases.     

Effect of fine–grained structure on the mechanical properties of superalloys K3 and K4169

The fine–grained structures of superalloys K3 and K4169 were achieved by the addition of refiners. Test bars for the determination of mechanical properties were cast under the chosen conditions to study the tensile properties at room and intermediate temperatures, and the stress rupture properties at intermediate temperatures. Results show that for alloy K3, the yield and tensile strengths of the fine–grained samples are superior to those of the conventional ones at room and intermediate temperatures, but there is little difference in tensile plasticity. The stress rupture life of the fine–grained sample is much longer than that of the conventional at 750ºC, whereas it has no remarkable change at 800ºC. For alloy K4169, the yield and tensile strengths of fine–grained samples are still superior to those of the conventional ones at room temperature and 760ºC. In addition, the stress rupture life of the fine–grained sample is 1.1 times longer thanthat of the conventional one at 760ºC. However, the permanent plasticity almost remainsthe same. The fracture of the samples was examined by scanning electron microscopy (SEM) and the fracture mechanisms were investigated. © 2001 Published by Elsevier Science Ltd.     

Effect of processing routes on mechanical and thermal properties of copper–graphene composites

In this paper, copper–graphene composites were fabricated by using two different processing routes (ball milling (BM) and ultrasonication) followed by spark plasma sintering. Vickers hardness and anisotropic thermal conductivity of the composites were measured and observed that ultrasonicated fabricated composites gave better result compared with BM composite and even from pure copper. The hardness values obtained for ultrasonicated copper–graphene composite were 69?HV (57% higher) and thermal conductivity 387?W/m?K (13% higher) by using only 0.5?wt-% of graphene, while for pure copper the values were 44?HV and 341?W/m?K. The value of anisotropic thermal conductivity ultrasonicated composites was also 1.97 which is much higher than pure copper 0.94.     

Effect of ball milling on the physical and mechanical properties of the nanostructured Co–Cr–Mo powders

In the present study, Co-based machining chips (P1) and Co-based atomized alloy (P2) has been processed through planetary ball mill in order to obtain nanostructured materials and also to comprise some their physical and mechanical properties. The processed powders were investigated by X-ray diffraction technique in order to determine several microstructure parameters including phase fractions, the crystallite size and dislocation density. In addition, hardness and morphological changes of the powders were investigated by scanning electron microscopy and microhardness measurements. The results revealed that with increasing milling time, the FCC phase peaks gradually disappeared indicating the FCC to HCP phase transformation. The P1 powder has a lower value of the crystallite size and higher degree of dislocation density and microhardness than that of the P2 powder. The morphological and particle size investigation showed the role of initial HCP phase and chemical composition on the final processed powders. In addition results showed that in the first step of milling the crystallite size for two powders reach to a nanometer size and after 12 h of milling the crystallite size decreases to approximately 27 and 33 nm for P1 and P2 powders, respectively.     

Fabrication and mechanical properties of silicon carbide–silicon nitride nanocomposites

A powder mixture of ultrafine –SiC–35 wt% –Si₃N₄ containing 6 wt% Al₂O₃ and 4 wt% Y₂O₃ as sintering additives were liquid–phase sintered at 1800°C for 30 min by hot–pressing. The hot–pressed composites were subsequently annealed at 1920°C under nitrogen–gas–pressure to enhance grain growth. The average grain–size of the sintered bodies were ranged from 96 to 251 nm for SiC and from 202 to 407 nm for Si₃N₄, which were much finer than those of ordinary sintered SiC–Si₃N₄ composites. Both strength and fracture toughness of fine–grained SiC–Si₃N₄ composites increased with increasing grain size. Such results suggested that a small amount of grain growth in the fine–grained region (250 nm for SiC and 400 nm for Si₃N₄) was beneficial for mechanical properties of the composites. The room–temperature flexural strength and fracture toughness of the 8–h annealed composites were 698 MPa and 4.7 MPa · m^1/2, respectively.     

Effect of nitrile-functionalization and thermal cross-linking on the dielectric and mechanical properties of PEN/CNTs–CN composites

In this study, a novel series of composite films consisting of nitrile-functionalized carbon nanotubes (CNTs–CN) and poly(arylene ether nitriles) (PEN) were successfully fabricated by the tape-casting method. The –CN groups in PEN chains and the phthalonitrile groups on CNTs–CN formed the thermally stable triazine rings by thermal cross-linking reaction in the presence of diamino diphenyl sulfone, which was characterized by Fourier transform infrared spectroscopy. The result indicated that the chemical cross-linking reaction occurred accompanied by the emergence of a new absorption peak at 1,361 cm^?1. Besides, the effect of cross-linking on the morphology, thermal stability, mechanical and dielectric properties of the PEN/CNTs–CN was investigated. The SEM images showed that the phase interface between surface modified CNTs and PEN matrix was indistinct, and the surface modified CNTs presented a better dispersion behavior in PEN matrix. The mechanical properties of the processed films were improved substantially compared with the unprocessed films. Furthermore, the glass-transition temperature (T _g ) of composite films processed at 320 °C for 4 h (about 245 °C) was higher than that of composite films before thermal treatment (about 205 °C). The 5 % weight loss temperature of the composite films (processed at 320 °C for 4 h) increased by about 110 °C compared with the composite films (unprocessed). More importantly, by thermal cross-linking, the dielectric constant (ε) of composite films with 8 wt% CNTs–CN loading was increased from 31.8 to 33.9, and dielectric loss (tan δ) was decreased from 0.90 to 0.61 at 1 kHz.     

Thermal and mechanical properties of hemp fabric-reinforced nanoclay–cement nanocomposites

The influence of nanoclay on thermal and mechanical properties of hemp fabric-reinforced cement composite is presented in this paper. Results indicate that these properties are improved as a result of nanoclay addition. An optimum replacement of ordinary Portland cement with 1 wt% nanoclay is observed through improved thermal stability, reduced porosity and water absorption as well as increased density, flexural strength, fracture toughness and impact strength of hemp fabric-reinforced nanocomposite. The microstructural analyses indicate that the nanoclay behaves not only as a filler to improve the microstructure but also as an activator to promote the pozzolanic reaction and thus improve the adhesion between hemp fabric and nanomatrix.     

Effect of atmosphere on the electrical properties of TiO2–SnO2 varistor systems

This work illustrates the advancement of research on TiO₂-based electroceramics. In this work will be presented that the addition of different dopants, as well as thermal treatments at oxidizing and inert atmosphere, influences of the densification, the mean grain size and the electrical properties of the TiO₂-based varistor ceramics. Dopants like Ta₂O₅, Nb₂O₅, and Cr₂O₃ have an especial role in the barrier formation at the grain boundary in the TiO₂ varistors, increasing the nonlinear coefficient and decreasing the breakdown electric field. The influence of Cr_Ti is to increase the O and O₂ adsorption at the grain boundary interface and to promote a decrease in the conductivity by donating electrons to O₂ adsorbed at the grain boundary. In this paper, TiO₂ and (Sn,Ti)O₂-based studies of polycrystalline ceramics, which show a non-linear I–V electrical response typical of low voltage varistor systems are also presented. All these systems are potentially promising for varistor applications.