Young's Modulus Decrease Research Articles

SIMULATION OF NONLINEAR MAGNETORHEOLOGICAL PARTICLE-FILLED ELASTOMERS

Polymer matrix filled with ferromagnetic particles is a class of smart materials whose mechanical properties can be changed under different magnetic field. They are usually referred to as magnetorheological elastomers (MREs). A finite element simulation was presented to describe the mechanical behavior of MREs with the nonlinearity of the particle magnetization being incorporated. By introducing the Maxwell stress tensor, a representative volume element (RVE) was proposed to calculate the Young's modulus and shear modulus of MREs due to the applied magnetic field. The influences of the applied magnetic field and the particle volume fractions in the shear modulus and Young's modulus were studied. Results show that the shear modulus increases with the magnitude of the applied magnetic field, while the Young's modulus decreases.

Nanoindentation of functionally graded hybrid polymer/metal thin films

Hybrid functionally graded coatings (2D-FGC) were deposited by magnetron co-sputtering from poly(tetrafluoroethylene) (PTFE) and AISI 316L stainless steel (316L) targets. The carbon and fluorine content varied from 7.3 to 23.7at.% and from 0 to 57at.%, respectively. The surface modification was developed to change the surface of 316L vascular stents in order to improve the biocompatibility of the outmost layer of the metallic biomaterial. In-depth XPS analysis revealed the presence of a graded chemical composition accompanied by the variation of the film structure. These results were complemented by those of transmission electron microscopy (TEM) analysis that highlighted the nanocomposite nature of the coatings.The nanomechanical characterization of 2D-FGC was performed by nanoindentation at several loads on the thin films deposited onto two different steel substrates: 316L and AISI M2. The study allowed establishing 0.7mN as the load that characterized the coatings without substrate influence. Both hardness and Young modulus decrease with the increase of fluorine content due to the evolution in chemical composition, chemical bonds and structure.

On the biodegradability, mechanical behavior, and cytocompatibility of amorphous Mg72Zn23Ca5 and crystalline Mg70Zn23Ca5Pd2 alloys as temporary implant materials

The evolution of microstructure and mechanical properties of almost fully amorphous Mg(72) Zn(23) Ca(5) and crystalline Mg(70) Zn(23) Ca(5) Pd(2) alloys during immersion in Hank's balanced salt solution (HBSS), as well as their cytocompatibility, are investigated in order to assess the feasibility of both materials as biodegradable implants. Though the crystalline Mg(70) Zn(23) Ca(5) Pd(2) sample shows lower wettability and more positive corrosion potential, this sample degrades much faster upon incubation in HBSS as a consequence of the formation of micro-galvanic couples between the nobler Pd-rich dendrites and the surrounding phases. After 22-h immersion, the concentration of Mg ions in the HBSS medium containing the Mg(70) Zn(23) Ca(5) Pd(2) sample is six times larger than for Mg(72) Zn(23) Ca(5) . Due to the Zn enrichment and the incipient porosity, the mechanical properties of the Mg(72) Zn(23) Ca(5) sample improve within the first stages of biodegradation (i.e., hardness increases while the Young's modulus decreases, thus rendering an enhanced wear resistance). Cytocompatibility studies reveal that neither Mg(72) Zn(23) Ca(5) nor Mg(70) Zn(23) Ca(5) Pd(2) are cytotoxic, although preosteoblast cell adhesion is to some extent precluded, particularly onto the surface of Mg(70) Zn(23) Ca(5) Pd(2) , because of the relatively high hydrophobicity. Because of their outstanding properties and their time-evolution, the use of the Pd-free alloy in temporary implants such as screws, stents, and sutures is envisioned.

English

The study of thermal, chemical and mechanical properties of pure nickel being an alternative automotive body material is presented in this paper. Current automotive components are mainly used steel as a body material. Due to the increasing demand of high performance and related issues interest moving towards other materials to replace the existing steel. The hardness value of both heat treated and non-heat treated pure nickel does not change after annealing. The hardness values are in the range of 118 to 123 HV. As the annealing temperature increases, the ultimate tensile strength, yield strength and young modulus decreases, which show the ductility increase. The highest ultimate tensile strength of pure nickel at 300oC annealed temperature is 758.78 MPa. X-ray diffraction (XRD) studies confirmed pure nickel of face centered cubic (FCC)with lattice constant measured as 0.3492 nm for unannealed sample, which is increased to 0.3512 for annealed samples. The corrosion rate of both annealed, and non-heat treated pure nickel is in the range of 0.0266 to 0.048 mm/year.

Elastic properties of SWCNTs with curved morphology: Density functional tight binding based treatment

The self-consistent charge density functional based tight-binding method is used to calculate the effect of curvature on the structure, average energy of atoms and Young's modulus of armchair single-wall carbon nanotubes (SWCNTs) under axial strains. We found that as the amount of curvature increases, the average energy of atoms and the Young's modulus decrease and the equilibrium CC distance increases for (7,7) SWCNTs. However, we also found that the average energy of atoms and Young's modulus of (5,5) SWCNTs are weakly affected by increasing the amount of curvature. Our results also show that the average energy of atoms and Young's modulus of smaller diameter armchair nanotubes are smaller than that of the larger diameter ones.

Mechanical Characterization of Co/Cu Multilayered Nanowires

The mechanical deformation properties of (110) Co/Cu multilayered nanowires were studied by Molecular Dynamics under uniaxial tensile and compressive stresses. The potential of the immiscible CoCu system was modeled by a second-moment tight-binding approximation. Stress-strain curves at different conditions were obtained and the elastic modulus and yield stress were analyzed. Both magnitudes are approximately independent of the strain rate, except at high values. They decrease linearly with increasing temperature. Below a volume-to-surface-area ratio, their values drastically increase and diverge from the bulk values. If the thickness of the Cu sublayers increases, the Young's modulus and yield stress decrease, although in a different way. The elastic modulus decreases linearly and the yield stress falls steeply whenever Cu is present in the nanowire, since the lattice distortion takes place firstly and fundamentally in Cu sublayers. The change in the axial stress at the interface is little significant on average and rather localized. Unlike, the transverse stress has a non-uniform distribution along the Cu sublayer, especially at the yield point. The Young's modulus and yield stress are larger in tension than in compression. Under tensile stress, nanowires slip via partial dislocation nucleation and propagation. Unlike, compressive deformation of nanowires takes place via both partial and full dislocations.

Mechanical properties of graphene oxides

The mechanical properties, including the Young's modulus and intrinsic strength, of graphene oxides are investigated by first-principles computations. Structural models of both ordered and amorphous graphene oxides are considered and compared. For the ordered graphene oxides, the Young's modulus is found to vary from 380 to 470 GPa as the coverage of oxygen groups changes, respectively. The corresponding variations in the Young's modulus of the amorphous graphene oxides with comparable coverage are smaller at 290-430 GPa. Similarly, the ordered graphene oxides also possess higher intrinsic strength compared with the amorphous ones. As coverage increases, both the Young's modulus and intrinsic strength decrease monotonically due to the breaking of the sp(2) carbon network and lowering of the energetic stability for the ordered and amorphous graphene oxides. In addition, the band gap of the graphene oxide becomes narrower under uniaxial tensile strain, providing an efficient way to tune the electronic properties of graphene oxide-based materials.

A molecular dynamics study on the impact of defects and functionalization on the Young modulus of boron–nitride nanotubes

Abstract In this article, we examine the Young modulus of ( 6 , m ) boron–nitride nanotubes with vacancy and functionalization defects. We employ molecular dynamics simulations using the Parrinello–Rahman approach. To this end, all systems are modeled with a reactive many-body bond order Tersoff potential with parameters due to Matsunaga et al. [K. Matsunaga, Y. Iwamoto, Molecular dynamics study of atomic structure and diffusion behavior in amorphous silicon nitride containing boron, Journal of American Ceramics Society 84(10) (2001) 2213–2219], which is able to accurately describe covalent bonding. We apply external stress to periodically repeated tubes in vacuum and derive stress–strain curves for various tensile loads at standard temperature and pressure. In addition to the Young modulus, we study visualized stress-per-atom snapshots of the simulation runs. Our results show that the decrease in Young modulus with increasing defect concentration is independent of the chirality of the tube for vacancy defects. Also, we observe that functionalization does not weaken the tube. There is even indication of a relative strengthening for armchair types.

Physico-chemical properties of whey protein isolate films containing oregano oil and their antimicrobial action against spoilage flora of fresh beef

Antimicrobial films were prepared by incorporating different levels of oregano oil (0.5%, 1.0%, and 1.5% w/w in the film forming solution) into sorbitol-plasticized whey protein isolate (WPI) films. The moisture uptake behavior and the water vapor permeability (WVP) were not affected by the addition of oregano oil at any of the concentrations used. A reduction of the glass transition temperature (∼10–20 °C), as determined by dynamic mechanical thermal analysis (DMTA), was caused by addition of oil into the protein matrix. A decrease of Young modulus ( E) and maximum tensile strength ( σ max) accompanied with an increase in elongation at break (%EB) was observed with increasing oil concentration up to a level of 1.0% (w/w). Wrapping of beef cuts with the antimicrobial films resulted in smaller changes in total color difference (Δ Ε) and saturation difference (Δ chroma) during refrigeration (5 °C, 12 days). The maximum specific growth rate ( μ max) of total flora (total viable count, TVC) and pseudomonads were significantly reduced ( P < 0.05) by a factor of two with the use of antimicrobial films (1.5% w/w oil in the film forming solution), while the growth of lactic acid bacteria was completely inhibited. These results pointed to the effectiveness of oregano oil containing whey protein films to increase the shelf life of fresh beef.

Thermal (In)Stability of Type I Collagen Fibrils

We measured the Young's modulus at temperatures ranging from 20 to 100 degrees C for a collagen fibril that is taken from a rat's tendon. The hydration change under heating and the damping decrement were measured as well. At physiological temperatures 25 to 45 degrees C, the Young's modulus decreases, which can be interpreted as an instability of the collagen. For temperatures between 45 and 80 degrees C, the Young's modulus first stabilizes and then increases when the temperature is increased. The hydrated water content and the damping decrement have strong maximums in the interval 70 to 80 degrees C indicating complex intermolecular structural changes in the fibril. All these effects disappear after heat-denaturation of the sample at 120 degrees C. Our main achievement is a five-stage mechanism by which the instability of a single collagen at physiological temperatures is compensated by the interaction between collagen molecules.

Nanohardness examination of cesium tungstophosphate glasses

Abstract The cesium tungstophosphate glasses x CsPO 3 (1 − x )WO 3 ( x = 0.20–0.90) were examined by means of nanoindentation. A linear decrease of the Young's modulus and drastic decrease of hardness were observed for the glasses with x > 0.35. The hardness and the Young's modulus were found to be in a range of 5.1–0.8 and 49.0–23.5 GPa, respectively.

Simulations of the mechanical properties of crystalline, nanocrystalline, and amorphous SiC and Si

Molecular-dynamics simulations of crystalline (c), nanocrystalline (nc), and amorphous (a) silicon carbides and silicon were carried out to investigate their vibrational and mechanical properties. The atomic configurations, vibrational spectra, and stress-strain curves were calculated at room temperature. In the case of the nanocrystalline structures, these characteristics were analyzed as functions of grain size. Young's and bulk modul and yield and flow stresses were determined from uniaxial deformation of samples under periodic boundary constraints and from experiments on rod extension. For silicon carbides, Young's modulus and flow stress decrease in the sequence ``c-nc-a,'' and with decreasing grain size, which is attributed to a weakening of the Si--C bonds in the amorphous matrix. The enhancement of the strength properties of the homopolar nc--Si structures is attributed to their deformation anisotropy. The calculated vibrational spectra and Young's moduli are in rather good agreement with the corresponding experimental characteristics.

Experimental Studies of the Behaviour at High Strain Rates of Unfilled and Filled Polypropylenes

Thermo mechanical behaviour of unfilled and filled polypropylenes are studied in tension from 10-4 to 102 s-1. Complementary low velocity compression and shear tests are also performed. A high-speed video camera (up to 2500 frames/s) combined with image analysis, image correlation and an infra red pyrometer allow measuring 3D-strain fields and temperature during tests. Thus, data can be processed without restrictive assumptions. Beside usual (for polymers) temperature and strain rate sensitivities it is found that plastic deformation in these materials does not obey incompressibility assumption. Voiding damage is evidenced in the polymer matrix by SEM observations that result in volume change and significant decrease in Young modulus for both materials. Moreover, an increase in the temperature of more than 10 °C is observed and is likely to modify the behaviour of each material at high strain rates. Shear and compression measurements demonstrate that yield criteria and constitutive equation depend on loading. It is concluded that apparent yield stress in semi-crystalline polypropylene can be a result of a combination of “non strain rate sensitive” “non-cohesive mechanisms” and “strain rate sensitive” “cohesive mechanisms”. Experimental characterisation on polymers should then be revisited as most of the usual assumptions are invalid and non monotonic tests should be generalized.

Filler-Induced Structural Order and Mechanical Properties of Polystyrene-Silica Nanocomposites

This study is concerned with the relationship between wide angle X-ray scattering (WAXS) analysis and physical properties of amorphous polystyrene (PS)-silica (SiO2) composites. Nanoporous SiO2 for the fillers was prepared by the hydrothermal reaction and the structures of the composites were examined by WAXS. In their WAXS patterns, two characteristic peaks, inner peak and outer peak, were observed at q ≈ 7 nm−1 and 15 nm−1 corresponding to the intermolecular structure of PS chains and the intramolecular order of benzene rings, respectively. The ratio (Iin⁄Iout=P) in intensity of the inner peak (Iin) to outer peak (Iout) affords the structural parameter to well characterize the intermolecular and intramolecular structures of PS molecules and the P values are observed to change widely from 0.183 to 1.16 depending on the material compositions. The elongation at the break point increases monotonously with increasing P, whereas the yield strength and the Young's modulus decrease with P for P=0.497 or below but remain almost constant for larger P values. The elongation of 4.5% for (PS+MPS) / SiO2 is enormously larger than those for PS and the other composites, in contrast to a slight decrease of the other two properties relative to those for PS. It is also revealed that a strong interaction works between the COO or COOH groups of maleic anhydride modified polystyrene (MPS) and the OH groups of SiO2, which makes the PS polymer molecules to stack regularly on SiO2 nanofillers, leading to control the physical properties of the composites.

Design of Mechanically Robust High-Tg Polymers: Mechanical Properties of Glassy Poly(ester carbonate)s with Cyclohexylene Rings in the Backbone

The incorporation of trans cyclohexylene (C-ring) groups into the main chain glassy polymers has been found to increase chain motion. With the increase in trans C-ring content, Young's modulus and yield stress both decrease. A linear correlation among Young's modulus, yield stress, and the inverse of the coefficient of thermal expansion has been found in this work. With the increase in trans C-ring content, post-yield stress drop (PYSD) decreases, the tendency to necking in tensile test decreases, and the activation volume increases. The results are consistent with the idea that thermal expansion, Young's modulus, and yield stress are predominantly controlled by intermolecular forces. Necking and PYSD are related not only to chain stiffness but also closely to polymer chain motion. On the basis of the results, the hypothesis that the incorporation of trans C-ring enhances local segmental motions, which effectively modulates interchain interactions, is proposed.

Design of Mechanically Robust High-Tg Polymers: Physical Properties of Glassy Poly(ester carbonate)s with Cyclohexylene Rings in the Backbone

The incorporation of trans cyclohexylene (C-ring) groups into the main chain glassy polymers has been found to increase chain motion. With the increase in trans C-ring content, Young's modulus and yield stress both decrease. A linear correlation among Young's modulus, yield stress, and the inverse of the coefficient of thermal expansion has been found in this work. With the increase in trans C-ring content, post-yield stress drop (PYSD) decreases, the tendency to necking in tensile test decreases, and the activation volume increases. The results are consistent with the idea that thermal expansion, Young's modulus, and yield stress are predominantly controlled by intermolecular forces. Necking and PYSD are related not only to chain stiffness but also closely to polymer chain motion. On the basis of the results, the hypothesis that the incorporation of trans C-ring enhances local segmental motions, which effectively modulates interchain interactions, is proposed.

On the mechanosorptive effect in porous ceramics Part II Effect of heating on alumina

Gibbsite containing alumina samples have been heated up to 1200°C in air. The decomposition of gibbsite and/or the departure of hydroxyls are found to influence the mechanical behaviour of porous alumina in the presence of water to a large extent. Powdered products of gibbsite decomposition first lead to a decrease in the Young's modulus. Sintering then occurs, dominated by the hydroxyl content, to reestablish the initial values. Two mechanical models are presented. In the first one, cohesion of granular solids results from the density of H-bonds inside the solids. In the second one, surface energy effects across grain boundaries dominate the mechanical behaviour. Application to various granular solids is discussed.

Characterization of interfacial and mechanical properties of green composites with soy protein isolate and ramie fiber

Environment-friendly fiber-reinforced composites were fabricated using ramie fibers and soy protein isolate (SPI) and were characterized for their interfacial and mechanical properties. Ramie fibers were characterized for their tensile properties and the parameters for the Weibull distribution were estimated. Effect of glycerol content on the tensile properties of SPI was studied. Interfacial shear strength (IFSS) was determined using the microbond technique. Based on the IFSS results and fiber strength distribution, three different fiber lengths and fiber weight contents (FWC) were chosen to fabricate short fiber-reinforced composites. The results indicate that the fracture stress increases with increase in fiber length and fiber weight content. Glycerol was found to increase the fracture strain and reduce the resin fracture stress and modulus as a result of plasticization. For 10% (w/w) of 5 mm long fibers, no significant reinforcement effect was observed. In fact the short fibers acted as flaws and led to reduction in the tensile properties. On further increasing the fiber length and FWC, a significant increase in the Young's modulus and fracture stress and decrease in fracture strain was observed as the fibers started to control the tensile properties of the composites. The experimental data were compared to the theoretical predictions made using Zweben's model. The experimental results are lower than the predicted values for a variety of reasons. However, the two values get closer with increasing fiber length and FWC.

Internal friction and anelastic properties of vanadium and V–Ti–Cr alloys

Using an acoustic technique of composite oscillator, the effect of preliminary deformation on the amplitude dependence (amplitude range from 10 −6 to 3 × 10 −4) of ultrasound damping and the Young's modulus (resonance frequencies) for V and V–(4–10)Ti–(4–10)Cr alloys has been studied. The alloys differed in composition, manufacture technology and also irradiation type (protons, neutrons), environments and fluence were varied. Neutron irradiation (fast reactor, BR-10) of the samples was carried out in argon (irradiation temperature T I=410°C) and liquid lithium ( T I=480°C) environments. It has been found that, for anelastic deformations of the order of 10 −8–10 −6, irradiation may result in most cases in noticeable anelastic softening of alloys characterized by a Young's modulus decrease. The softening of the V–4Ti–4Cr alloy irradiated in Ar appeared to be the most significant. The experimental results of acoustic studies might be explained by changing the mobile dislocation point defect interaction, perhaps additionally influenced by existing internal stresses.

Dynamic fracture of a functionally gradient material having discrete property variation

A functionally gradient material (FGM) with discrete property variation is prepared, and the dynamic fracture in this material is studied using the technique of photoelasticity combined with high-speed photography. Transparent sheets required for the study are made by casting a polyester resin mixed with varying amounts of plasticizer. The mechanical (quasi-static and dynamic) and optical properties of the material are evaluated as a function of the plasticizer content. Results of material characterization show that the fracture toughness increases with increasing plasticizer content, whereas the Young's modulus decreases. The material fringe constant and the dynamic modulus are observed to be relatively insensitive to plasticizer content. The FGM is then prepared by casting together thin strips having different plasticizer content. The dynamic crack propagation phenomenon is studied for four different property variations along the crack propagation direction, and the effects of these property variations on crack speed, crack jump distance and dynamic stress intensity factor are investigated. Results of this investigation show that increasing the toughness in the direction of crack growth reduces the crack jump distance as compared to on increasing-decreasing toughness variation for the same initial energy.