Balance Of Toughness Research Articles

High strength and fracture toughness balance on the extruded Mg–Ca–Zn alloy

The mechanical properties were investigated by Mg–0.3 at.% Ca–1.8 at.% Zn alloy, which was produced by hot extrusion, having an average grain size of about 1 μm and spherical precipitates in the matrix. The extruded alloy showed a good balance of the yield strength ( σ ys = 291 MPa) and plane-strain fracture toughness ( K IC = 28.3 MPa m 1/2), obtained by the stretched zone analysis, which were higher than those of conventional wrought magnesium alloys. The microstructure control of both the grain refinement and the dispersion of precipitates in the matrix was a possible method for improvement of the mechanical properties in magnesium alloys.

The structure and physical properties of polypropylene and thermoplastic olefin nanocomposites containing nanosilica

The morphology and physical properties of thermoplastic olefin blend (TPO) based nanocomposites containing nanosilica are reported. Addition of maleated PP resulted in improved filler dispersion within the PP matrix, where the filler resided exclusively. This separated morphology resulted in selective reinforcement of the PP matrix without compromising ductility, as demonstrated by mechanical property characterization. The tensile moduli, impact and flexural properties of TPO/nanosilica composites showed improvements at low loadings of nanosilica, indicating a good balance of stiffness and toughness. The addition of nanosilica into the TPOs decreased the size of the dispersed elastomer phase, which was a factor in the observed improvements of impact strength. Silane-modified nanosilica dispersed more efficiently in the polymer matrix, giving rise to improved impact properties of the TPO composites, compared to the unmodified filler.

MICROSTRUCTURE AND MECHANICAL PROPERTY DEVELOPMENT IN THE SIMULATED HEAT AFFECTED ZONE OF V TREATED HSLA STEELS

The simulated heat affected zone (HAZ) of the high strength low alloy (HSLA) steels containing 0%, 0.047%, 0.097% and 0.151% vanadium, respectively, were studied with Gleeble-2000 thermomechanical simulator to determine the influence of vanadium addition on the mechanical properties of the HAZ. The HAZ simulation involved reheating the samples to 1350°C, and then cooling to ambient temperature at a cooling rate of 5°C/s ranging from 800 to 500°C(Δt 8/5 =60s). The mechanical properties including tensile strength and −20°C impact toughness were conducted. The microstructures of the base steel and the simulated HAZs were investigated using optical microscope, scanning electron microscope (SEM) and transmission electron microscope (TEM). Based on the systematic examination, the present work confirmed that about 0.05% vanadium addition to low carbon low alloy steels resulted in expected balance of strength and toughness of the HAZ. And more than 0.10% levels addition led to detrimental toughness of the HAZ. SEM study showed that the simulated 0.097% and 0.151%V HAZs consisted of more coarse ferrite plates with greater and more M-A constituents along austenite grain and ferrite plate boundaries. The impact fracture surfaces of the simulated 0.097% and 0.151% V HAZs showed typically brittle mode with predominant cleavages. The size of the facet in the fracture surface increased with increasing vanadium level from 0.097% to 0.151%. As a result, the simulated 0.151%V HAZ has the lowest impact toughness of the four specimens.

The Effect of Polyethylene-Octene Elastomer on the Morphological and Mechanical Properties of Polyamide 6/Polypropylene Nanocomposites

Rubber-toughened nanocomposites (RTNC) consisting of ternary blends of polyamide 6 (PA6), polypropylene (PP) and polyethylene-octene elastomer (POE) containing 4 wt% of organophilic modified montmorillonite were produced by melt compounding followed by injection moulding. The blend composition was kept constant (PA6/PP=70/30 parts by weight) while the POE content was varied between 5 and 20 wt%. Maleated PP (PP-g-MA) was used as compatibilizer. The morphology of the RTNC was studied by scanning electron microscopy and X-ray diffraction (XRD). The mechanical properties of RTNC were studied through tensile, flexural, Izod impact and fracture toughness properties. While the tensile and flexural properties were found to decrease with the increasing concentration of POE, the toughness was significantly enhanced as compared to the neat PA6/PP blends. In general, the blends containing 10-15 wt% of POE had the best balance of stiffness, strength and toughness. The addition of 30 wt% of PP in the PA6 matrix improved the compatibility between PA6 and the rubber phase. XRD established that the organoclay was well dispersed (exfoliated) and preferentially embedded in the PA6 phase.

Preparation and Characterization of Polycarbonate/Poly(propylene)/Attapulgite Ternary Nanocomposites with the Morphology of Encapsulation

AbstractSummary: Ternary nanocomposites based on polycarbonate (PC), poly(propylene) (PP), and attapulgite (AT) were prepared via the method of two‐step melt blending, by which the AT was blended with PP prior to compound with PC. Structure and properties of the ternary PC/PP/AT nanocomposites were investigated. The degradation of PC triggered by AT during direct blending process can be inhibited effectively by using two‐step melt blending. It was found that the morphology of encapsulation structure like sandbag was formed in PC matrix, where PP encapsulated AT fibrillar single crystals. DSC experiments showed that in PC/PP/AT ternary nanocomposites, AT had a strong heterophase nucleation effect on PP, resulting in the enhancement of crystallization degree and the crystallization temperature of PP. DMA and mechanical property results showed that the ternary nanocomposites exhibited good balanced toughness and stiffness.TEM photograph of PC/PP/AT ternary nanocomposite.magnified imageTEM photograph of PC/PP/AT ternary nanocomposite.

Prediction of structural stabilities of transition-metal disilicide alloys by the density functional theory

Transition metal silicide based refractory composite alloys have great potential for applications as the next generation of turbine airfoil materials, due to their significantly higher operating temperatures than advanced Ni-based superalloys. In order to achieve the most of refractory silicide based materials, multi-component alloying has been considered to be the most useful route for developing alloys of a good balance of creep resistance, fracture toughness, oxidation resistance, and room-temperature ductility. In this work, structural stabilities of disilicides of the group IVB to VIB transition metal elements are studied using the ab initio density functional theory, shedding light on alloying/bonding behaviour at the electronic level. The results are also useful for developing full thermodynamic databases using the CALPHAD approach, where lattice stabilities of counter-phases are critical for accurate thermodynamic descriptions of multi-component systems.

Analyses of eutectoid phase transformations in Nb-silicide in situ composites.

Nb-silicide in situ composites have great potential for high-temperature turbine applications. Nb-silicide composites consist of a ductile Nb-based solid solution together with high-strength silicides, such as Nb5Si3 and Nb3Si. With the appropriate addition of alloying elements, such as Ti, Hf, Cr, and Al, it is possible to achieve a promising balance of room-temperature fracture toughness, high-temperature creep performance, and oxidation resistance. In Nb-silicide composites generated from metal-rich binary Nb-Si alloys, Nb3Si is unstable and experiences eutectoid decomposition to Nb and Nb5Si3. At high Ti concentrations, Nb3Si is stabilized to room temperature, and the eutectoid decomposition is suppressed. However, the effect of both Ti and Hf additions in quaternary alloys has not been investigated previously. The present article describes the discovery of a low-temperature eutectoid phase transformation during which (Nb)3Si decomposes into (Nb) and (Nb)5Si3, where the (Nb)5Si3 possesses the hP16 crystal structure, as opposed to the tI32 crystal structure observed in binary Nb5Si3. The Ti and Hf concentrations were adjusted over the ranges of 21 to 33 (at.%) and 7.5 to 33 (at.%) to understand the effect of bulk composition on the phases present and the eutectoid phase transformation.

Hybrid epoxy‐based thermosets based on polyhedral oligosilsesquioxane: Cure behavior and toughening mechanisms

AbstractPolyhedral oligosilsesquioxane (POSS)‐reinforced thermosets based on octaglycidyl epoxy polyhedral oligosilsesquioxane cured with 4,4′‐diaminodiphenyl sulfone (DDS) were prepared and studied for their cure, thermomechanical, and microstructural characteristics. Particular attention was paid to nanometer‐scale deformation processes responsible for toughening, as revealed by transmission electron microscopy (TEM) in conjunction with the thermal properties. A cure analysis investigated with calorimetry and rheometry showed a significant dependence of the cure mechanism and kinetics on the DDS content, but all hybrid thermosets reacted completely below 300 °C into rigid solids. A dynamic mechanical analysis of this hybrid resin system showed that increasing the DDS concentration used during cure increased the dynamic storage modulus in the glassy (temperature < glass‐transition temperature) and rubbery (temperature > glass‐transition temperature) states, simply through an increase in the crosslink density. The phase structures revealed by TEM with selective POSS staining were drastically affected by the DDS concentration and manifested as altered nanomechanical deformation structures. It was qualitatively found that the main toughening mechanism in the studied POSS‐reinforced thermosets was void formation at the nanometer scale, possibly templated by limited POSS aggregation. As the crosslinking density increased with the DDS concentration, microshear yielding between voids prevailed, providing a balance of stiffness, strength, and toughness. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3299–3313, 2003

Pragmatic multiscale modelling of bone as a natural hybrid nanocomposite

A multiscale modelling strategy is proposed to predict the mechanical properties of polymer-inorganic hybrid nanocomposites. In particular, high volume fractions of oriented mineral plates in a ductile polymer matrix offer the potential of an attractive balance of stiffness and toughness. Bone is used here as a natural example of such a material, since it has a hierarchy of structures at all scales of dimension, and is an excellent subject for multiscale materials modelling. The key step in the model is to predict the individual properties of the component materials by a self-consistent mean-field method from their molecular structure. This allows the synergistic interaction of mineral and polymer at the large number of interfaces in a nanocomposite to be modelled as an energy sharing process, whose main effect is upon the polymer modulus. The interface-modified mechanical properties are then used in composite models at higher scales to predict the nonlinear stress–strain curve to failure as a function of the main variables of mineral volume fraction (MVF) and particle aspect ratio.

A review of very-high-temperature Nb-silicide-based composites

The temperatures of airfoil surfaces in advanced turbine engines are approaching the limits of nickel-based superalloys. Innovations in refractory metal-intermetallic composites (RMICs) are being pursued, with particular emphasis on systems based on Nb-Si and Mo-Si-B alloys. These systems have the potential for service at surface temperatures >1350 °C. The present article will review the most recent progress in the development of Nb-silicide-based in-situ composites for very-high-temperature applications. Nb-silicide-based composites contain high-strength silicides that are toughened by a ductile Nb-based solid solution. Simple composites are based on binary Nb-Si alloys; more complex systems are alloyed with Ti, Hf, Cr, and Al. In higher-order silicide-based systems, alloying elements have been added to stabilize intermetallics, such as Laves phases, for additional oxidation resistance. Alloying schemes have been developed to achieve an excellent balance of room-temperature toughness, high-temperature creep performance, and oxidation resistance. Recent progress in the development of composite processing-structure-property relationships in Nb-silicide-based in-situ composites will be described, with emphasis on rupture resistance and oxidation performance. The Nb-silicide composite properties will be compared with those of advanced Ni-based superalloys.

Ultrahigh-Temperature Nb-Silicide-Based Composites

AbstractThis article reviews the most recent progress in the development of Nb-silicide-based in situ composites for potential applications in turbine engines with service temperatures of up to 1350°C. These composites contain high-strength Nb silicides that are toughened by a ductile Nb solid solution. Preliminary composites were derived from binary Nb-Si alloys, while more recent systems are complex and are alloyed with Ti, Hf, W, B, Ge, Cr, and Al. Alloying schemes have been developed to achieve an excellent balance of room-temperature toughness, fatigue-crack-growth behavior, high-temperature creep performance, and oxidation resistance over a broad range of temperatures. Nb-silicide-based composites are described with emphasis on processing, microstructure, and performance. Nb silicide composites have been produced using a range of processing routes, including induction skull melting, investment casting, hot extrusion, and powder metallurgy methods. Nb silicide composite properties are also compared with those of Ni-based superalloys.

The wages of spin [engineering management

This article outlines how company spins-outs and engineering consultancy have been a lucrative business for the Generics Group, but asks whether it is becoming a tough balancing act?

Soaps and detergents: a tough balancing act for chemical suppliers

Soaps and detergents: a tough balancing act for chemical suppliers

HDPE/LLDPE reactor blends with bimodal microstructures—part I: mechanical properties

Reactor blends of polyethylene/poly(ethylene- co-1-octene) resins with bimodal molecular weight and bimodal short chain branching distributions were synthesized in a two-step polymerization process. The compositions of these blends range from low molecular weight (LMW) homopolymer to high molecular weight (HMW) copolymer and, vice versa, HMW homopolymer to LMW copolymer. The physical properties of the blends were found to be consistent with the nature of the individual components. For the tensile properties, the stiffness decreases with increasing the fraction of the copolymer, regardless of the molecular weight of the homopolymer fraction. For these blends with bimodal microstructures, it was confirmed that the degree of crystallinity governs the stiffness of the polymer. However, the energy dampening properties of the polymers benefit from the presence of the copolymer. A balance of stiffness and toughness can be obtained by altering the composition of the blends. For some blends, the presence of HMW homopolymer can dominate the tensile properties, showing little variation in the stiffness with increased addition of copolymer. It was also demonstrated that the testing conditions and thermal treatment of the polymer greatly influence the resulting elastic and energy dampening properties. Depending on the desired application, annealing these polymers (especially very low density copolymers) not only increases the crystallinity and stiffness, but also changes the frequency response of the dynamic mechanical properties.

The effect of elastomeric nano-particles on the mechanical properties and crystallization behavior of polypropylene

Generally, toughness of polypropylene (PP) is an issue which has been investigated for many years to search for improvements. A traditional approach is to blend with rubber particles to enhance the toughness of PP yet modulus of PP decreases accordingly. Recently, we have achieved a good balance of toughness and stiffness of PP via blending PP with a small amount of elastomeric nano-particles (ENP). Based on our measurements, mechanical properties of the blends studied both the toughness of PP at room temperature and at −20 °C show substantial increase. On the other hand, the stiffness of the PP blends retains or even possesses a slight enhancement. One of the reasons for this improvement is due to the fact that the ENP is not only a toughening modifier but also a nucleation agent for the PP. The nucleation density of the blends increases, while the crystallization kinetics of the blends becomes faster compared with the pure PP samples.

The effect of morphology of ternary‐phase polypropylene/glass bead/ethylene‐propylene rubber composites on the toughness and brittle‐ductile transition

AbstractCorrelation between the morphology and the impact toughness was studied for ternary‐phase polypropylene (PP)/glass bead (GB)/ethylene‐propylene rubber (EPR) composites containing 5–40 vol % of rigid filler at a fixed volume fraction ratio EPR/GB equal to 0.33. The three following types of phase morphology were obtained: (1) separate dispersion of phases and weak GB–PP adhesion; (2) separate dispersion of phases and high GB–PP adhesion; and (3) encapsulation of GB particles by elastomer shell. Maleated PP or EPR was used for the preparation of second and third types of composites, respectively. Binary composites with either rigid or rubbery phases were prepared as model systems. Young's modulus values of composites containing GB encapsulated by a soft interlayer stay close to neat PP modulus and are located in the bounds corresponding to ternary systems with phase‐separate distribution and rubber‐modified PP. Notched impact strength was measured by Izod and three‐point bending tests. Systems with the phase‐separate distribution both with weak and with high adhesion exhibit quasi‐brittle fracture. The encapsulation of GB particles by elastomer results in significant improvement of the toughness. An increase in core‐shell inclusion fraction leads to intense matrix yielding within a specimen bulk and brittle–ductile transition similar to the rubber‐toughened PP. A criterion of brittle–ductile transition was proposed on the basis of load‐time curve analysis, which is an accumulation of critical plastic deformation on a crack initiation stage. The stress of start of local failure microprocesses at the inclusion–matrix boundary was found to play the dominating role in energy‐dissipating mechanisms. The lowering of the stress at which a local matrix yielding starts at elastomer shell–PP interface compared to the stress of GB debonding is a main source of intensive energy adsorption at the initiation stage in the system with encapsulated GB. The optimal stiffness–toughness balance can be obtained by coating the rigid particles with an elastomer shell. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1911–1928, 2002

Mechanical properties of ethylene/1-hexene copolymers with tailored short chain branching distributions

Recently, we have investigated a metallocene catalyst system that can produce polyethylene and ethylene/α-olefin copolymers with tailored molecular weight and short chain branching distributions (SCBD). Ethylene/α-olefin copolymers produced with this system have narrow molecular weight distributions as expected from metallocene catalysts. However, these copolymers are quite unique in that their SCBDs are broad and sometimes bimodal, similar to Ziegler–Natta LLDPE. To examine the effect of these broad SCBDs on the polymer properties, a series of poly(ethylene- co-1-hexene) resins with very distinct, and in some cases bimodal crystalline distributions, were synthesized. The attractive feature of the resins in this study is that their molecular weight distributions are similar but each possesses a different SCBD, thus effectively minimizing the effect of molecular weight on the properties investigated. It was found that the tensile properties of a copolymer could be controlled by the ratio of the crystalline species present in the sample. In this study, a balance of stiffness and toughness was exhibited by a copolymer containing a large proportion of crystalline material and a small fraction of material of lower crystallinity.

Impact of new rolling and cooling technologies on thermomechanically processed steels

At the hot strip mill, two different important trends are being observed: the development of thinner hot strips for direct applications as a substitute for cold rolled and annealed sheets; and the production of strip of increased strength, for various applications, which requires an adequate balance of ductility, formability, weldability, fatigue resistance, toughness, and/or crash resistance. In these grades the absence of internal stresses is also often required. The development of new rolling and cooling technologies that allow the production at low cost of new grades with better reproducibility and consistency of the mechanical properties is reviewed.

Processability and mechanical properties of ternary composites PP/EPDM/GF

AbstractThe enhancement of the mechanical properties of neat PP is achieved by the addition of glass fibers and EPDM rubber. The Young's modulus and notched Charpy impact strength of the composites obtained are improved with respect to the original polymer, leading to a new composite material with a very good balance of toughness and rigidity properties. The tensile behavior of these multiphase systems is successfully compared with theoretical predictions using the Halpin‐Tsai/Nielsen theory for uniaxially short fiber composites, which considers the matrix as a blend with spherical particles and can predict the tensile modulus considering an average fiber orientation angle. An accurate morphological study performed by scanning electron microscopy (SEM) shows a very good dispersion of the rubbery phase into the neat matrix. No special affinity between the rubber and the fibers is reported. The good dispersion and the small particle diameter indicate the good processability of the ternary systems studied.

New Wholly-Aromatic Thermotropic Polyesters with Controlled Flexibility

ABSTRACTIn this work, we present the synthesis and characterization of a new series of wholly-aromatic copolyesters derived from the condensation of various weight fractions of 4,4'-(o- phenylenedioxy)dibenzoic acid (OPDB) and substituted terephthalic acid (BTA) with 2-phenylhydroquinone (PHQ). The Higashi method, involving tosyl chloride and pyridine as solvent, was employed to yield polymer with significant molecular weight. These polymers are intended to enable accessible clearing transition and to control the balance of stiffness and toughness in melt-spun fibers systematically. We report the synthetic details along with characterization of quiescent phase behavior and morphology.