Balance Of Toughness Research Articles

SANS-characterized influence of degree of rolling reduction on the microstructure of Ti-containing cold-work tool steel

The influence of rolling reduction on the microstructural variations in Ti-containing tool steel was investigated. The microstructures, including the prior-austenite grain structure and primary/secondary carbides, were characterized using optical and electron microscopy; the carbides were quantitatively analyzed by small-angle neutron scattering data collected from macro-samples. In parallel with refining the primary carbides, increases in the degree of rolling reduction significantly changes the precipitation kinetics of the secondary MC and M23C6 (M = metallic element) carbides, and thus their mechanical properties, especially the hardness to toughness balance throughout the aging. The improvement of this balance is attributed to the refinement of the prior-austenite grain structure, as well as the retardation of M23C6 precipitation. The reaction kinetics of the precipitation reactions were analyzed by the reduced heat of reaction observed in a calorimetry experiment.

Effect of cooling rate on microstructure, inclusions and mechanical properties of weld metal in simulated local dry underwater welding

Quenched and tempered E550 steel was joined using flux-cored arc welding. The effect of cooling rate on microstructure, inclusions and mechanical properties of the weld metal was investigated by optical microscope, scanning electron microscope, transmission electron microscope and mechanical testing. Results show that weld metal microstructures consist of proeutectoid ferrite, ferrite side plate and acicular ferrite. As the cooling rate increased, the volume fraction of proeutectoid ferrite and ferrite side plate decreased, acicular ferrite increased accompanied with refined grain. Furthermore, inclusions of Ti, Mn oxide with diameter below 2.0μm were found in the weld metal and rapid cooling rate causes distinct Mn-depleted zone between inclusions and matrix. Excellent balance of high strength and toughness is obtained as more acicular ferrite in weld metal with rapid cooling rate. This can attribute to the increased of acicular ferrite with its refined grain and high density dislocation. These findings suggest that the rapid cooling rate can improve the impact toughness and tensile strength of weld metal in local dry underwater welding.

Influence of processing parameters on the impact strength of biocomposites: A statistical approach

Injection molded biocomposites from a new biodegradable polymer blend based matrix system and miscanthus natural fibers were successfully fabricated and characterized. The blend matrix, a 40:60wt% blend of poly(butylene adipate-co-terephthalate), PBAT and poly(butylene succinate), PBS was chosen based on their required engineering properties for the targeted biocomposite uses. A big scientific challenge of biocomposites is in improving impact strength within the desired tensile and flexural properties. The stiffness–toughness balance is one of the biggest scientific hurdles in natural fiber composites. Thus, the key aspect of the present study was in investigating an in-depth statistical approach on influence of melt processing parameters on the impact strength of the biocomposite. A full factorial experimental design was used to predict the statistically significant variables on the impact strength of the PBS/PBAT/miscanthus biocomposites. Among the selected processing parameters, fiber length has a most significant effect on the impact strength of the biocomposites.

Junction configuration-induced mechanisms govern elastic and inelastic deformations in hybrid carbon nanomaterials

Although various hybrid 3D carbon-based architectures are reported by covalently connecting low dimensional carbon allotropes, the effect of junction configuration on deformation and mechanical properties of the hybrid carbon architectures remain elusive. Here, we focus on Pillared Graphene Nanostructure (PGN) as a model system with symmetric and asymmetric junctions to explore its diverse elastic and inelastic properties via first-principles and molecular dynamics simulations. By introducing heptagonal and octagonal rings in the junctions, our findings demonstrate that in contrast to the stacked of graphene sheets, which exhibit weak out-of-plane properties, both junction types impart a cooperative two-regime deformation mechanism that provides a number of superior characteristics in PGN, including 3D balance of strength and toughness as well as an outstanding ∼42% out-of-plane ductility preceding the failure. Furthermore, asymmetric junctions impose wrinkles in the PGN sheets, which add extra in-plane flexibility and shear compliance, result in a nearly zero/negative in-plane Poisson's ratio in PGN, and cause the octagonal rings to act as hotspot for initiating of fracture. Our results provide the first atomistic “lens” on fundamental understanding of junction-induced deformation mechanisms in pillared graphene and can potentially provide a new phase space to better control and design mechano-mutable hybrid carbon nanostructures.

Binary Synergy Strengthening and Toughening of Bio-Inspired Nacre-like Graphene Oxide/Sodium Alginate Composite Paper.

A crucial requirement for most engineering materials is the excellent balance of strength and toughness. By mimicking the hybrid hierarchical structure in nacre, a kind of nacre-like paper based on binary hybrid graphene oxide (GO)/sodium alginate (SA) building blocks has been successfully fabricated. Systematic evaluation for the mechanical property in different (dry/wet) environment/after thermal annealing shows a perfect combination of high strength and toughness. Both of the parameters are nearly many-times higher than those of similar materials because of the synergistic strengthening/toughening enhancement from the binary GO/SA hybrids. The successful fabrication route offers an excellent approach to design advanced strong integrated nacre-like composite materials, which can be applied in tissue engineering, protection, aerospace, and permeable membranes for separation and delivery.

Effects of combined plasma chromizing and shot peening on the fatigue properties of a Ti6Al4V alloy

A plasma chromizing treatment was conducted on Ti6Al4V samples by employing the recently developed double glow plasma surface alloying technology. The Cr-alloyed layer consisted of four sub-layers, namely the Cr deposition, Cr2Ti, CrTi4, and Cr-Ti solid-solution layers. The local hardness and moduli were determined via nanoindentation. In addition, the fatigue properties of the samples were evaluated by using a rotating-bending fatigue machine under a given load. The results showed that the hardness or elastic moduli of the adjacent sub-layers differed significantly and the fatigue properties of the Ti6Al4V alloy deteriorated with the plasma chromizing treatment. This deterioration stemmed mainly from cracks initiated at the interfaces between the sub-layers and the microstructural changes of the substrate; these changes were induced by the high temperature used in the plasma chromizing process. However, the fatigue life of the plasma-chromized samples was increased by a shot peening post-treatment. The fatigue life of the samples resulting from this combination of treatments was slightly higher than that of the single-shot-peened Ti6Al4V substrate. In fact, the sample retaining only the Cr-Ti solid-solution layer (that is, the first three sub-layers were removed), when shot-peened, exhibited the highest fatigue life among all the tested samples; this was attributed to that sample having the highest residual compressive stress, the significant work hardening, and the good hardness to toughness balance.

Isotactic polypropylene (PP) modified by ABS and CaCO3 nanoparticles: effect of composition and compatibilization on the phase morphology, mechanical properties and fracture behavior

Attempt was made to improve the properties of isotactic polypropylene (iPP) by simultaneous incorporation of ABS and CaCO3 nanoparticles. The goal was to achieve a balanced toughness and stiffness by the development of ternary PP/ABS/CaCO3 nanocomposite. The effects of compatibilization and composition on the phase morphology, mechanical properties and deformation behavior under impact loadings were systematically studied. The phase structure and mechanical properties of binary PP/ABS and PP/CaCO3 systems was also investigated in detail to clarify the contribution of individual ABS and CaCO3 components in the macroscopic response of ternary hybrid. It was found that the ABS could effectively toughen the PP matrix by the suitable compatibilization. Moreover, the CaCO3 nanoparticles alone serve as stiffener and toughener in the material. Accordingly, the impact toughness of ternary PP/ABS/CaCO3 nanocomposites was larger than those of compatibilized PP/ABS blend and PP/CaCO3 system and, therefore, much higher than that of unmodified iPP. The mechanical properties and toughening mechanisms of different binary and ternary samples were rationalized by fractographic analysis. In the case of Izod impact-fractured samples, the characteristics of fractured surfaces were closely examined at the crack initiation and propagation stages of the impact fracture process.

Simultaneously toughening and reinforcing poly(lactic acid)/thermoplastic polyurethane blend via enhancing interfacial adhesion by hydrophobic silica nanoparticles

This work focuses on satisfactorily toughening and reinforcing poly(lactic acid)/thermoplastic polyurethane (PLA/TPU) blend with low TPU content (10 wt%) using appropriate amounts of hydrophobic silica nanoparticles (SiO2) via simple melt mixing. Both thermodynamic prediction and transmission electron microscopy micrographs demonstrate that most SiO2 nanoparticles distribute at interfaces between the PLA and TPU phases. This improves interfacial adhesion between the phases, which is attributed to good bonding strength between the PLA and SiO2 via hydrophobic interaction and formation of hydrogen bonds between the TPU and SiO2. The PLA/TPU (90/10) ternary blend nanocomposite with 2 wt% SiO2 exhibits obviously high impact strength (about 5.0 and 12.6 times that of the corresponding blend and PLA, respectively) and higher tensile strength than the blend and even the PLA. Crazing is the main reason for improved impact toughnesses of the blend nanocomposites. This work provides a simple and effective strategy to endow PLA/elastomer blends with optimum strength–toughness balance by adding appropriate amounts of nanoparticles.

Mechanical and Thermal Properties of Hemp Fiber-Unsaturated Polyester Composites Toughened by Butyl Methacrylate

Hemp fiber-reinforced unsaturated polyester (UPE) composites were prepared by hand lay-up compression molding. The UPE resins were modified with butyl methacrylate (BMA) to improve the flexibility and toughness of the hemp-UPE composites. The results indicate that the toughness of the composites significantly increased as BMA usage increased. Compared to the unmodified UPE composites, the composites obtained from BMA-modified UPE resins had 27.4, 63.0, and 36.6% greater elongation at break, flexural strain, and impact strength, respectively. The optimum BMA usage to achieve an adequate balance of stiffness and toughness is 20 to 30%. Dynamic mechanical analysis (DMA) indicated that incorporation of BMA significantly decreased the storage modulus and glass transition temperature of the composites and increased its damping parameter due to the introduction of flexible segments into the UPE resins. Thermogravimetric analysis showed that the thermal stability of the composites decreased slightly following the incorporation of BMA. Scanning electron microscopy images of the impact-fractured surfaces of the composites revealed that BMA incorporation improved interfacial adhesion between hemp fibers and UPE matrices and that the main mechanism for the increase in the toughness of the composites was the added ductility of the matrices.

Universal composition-structure-property maps for natural and biomimetic platelet-matrix composites and stacked heterostructures.

Many natural and biomimetic platelet-matrix composites--such as nacre, silk, and clay-polymer-exhibit a remarkable balance of strength, toughness and/or stiffness, which call for a universal measure to quantify this outstanding feature given the structure and material characteristics of the constituents. Analogously, there is an urgent need to quantify the mechanics of emerging electronic and photonic systems such as stacked heterostructures. Here we report the development of a unified framework to construct universal composition-structure-property diagrams that decode the interplay between various geometries and inherent material features in both platelet-matrix composites and stacked heterostructures. We study the effects of elastic and elastic-perfectly plastic matrices, overlap offset ratio and the competing mechanisms of platelet versus matrix failures. Validated by several 3D-printed specimens and a wide range of natural and synthetic materials across scales, the proposed universally valid diagrams have important implications for science-based engineering of numerous platelet-matrix composites and stacked heterostructures.

Influence of Ti addition on the microstructure and mechanical properties of a 5% Cr–Mo–V steel

A systematic study to determine the effect of Ti addition on the microstructure and mechanical properties of a 5% Cr–Mo–V tool steel has been made in terms of optical and electron microscopy, as well as X-ray diffraction, thermal analysis, and small angle neutron scattering. With the characterization of the as-quenched structure, the microstructural variation as a function of aging time was investigated. The Ti addition effectively refines the prior austenite grain structure as expected. More importantly, it can change the precipitation behavior of secondary carbides formed upon aging. As this change is attributed to the resisted Cr diffusion into cementite, the resultant precipitation of M23C6 carbides was restricted. Hence this leads to a significant improvement of the hardness to toughness balance, which is coupled with grain refinement. This variation in precipitation behavior was considered to have a thermodynamic aspect, especially the driving force for nucleation of equilibrium carbides involved in the present alloy system.

Effect of difunctional acids on the physicochemical, thermal, and mechanical properties of polyester polyol‐based polyurethane coatings

ABSTRACTPolyester polyol (PP)‐based polyurethanes (PUs) consisting of two difunctional acids [1,4‐cyclohexanedicarboxylic acid (CHDA) and 1,6‐adipic acid (AA)] and also two diols [1,4‐cyclohexanedimethanol (CHDM) and 1,6‐hexanediol (HDO)] were synthesized by a two‐step procedure with a variable feed ratio of CHDA to AA but fixed ratio of CHDM and HDO. The prepared PPs and/or PUs were characterized by Fourier transform infrared spectroscopy, X‐ray diffraction spectroscopy, and atomic force microscopy. The effects of difunctional acids on the thermal, mechanical, and dynamic mechanical thermal properties of PPs or PU films were investigated by thermogravimetry analysis, differential thermogravimetry and dynamic mechanical thermal analysis. The results show that PP exhibits a lowest viscosity with the mole fraction of CHDA and AA at 3 : 7 whereas it delivers a lowest melting point with the mole fraction at 9 : 1. After PPs being cross‐linked by isocyanate trimers, the impact resistance, shear strength and glass transition temperature increase the mixed‐acid formulations with increasing the content of CHDA. In detail, the resultant PU almost simultaneously exhibits the best mechanical and thermal properties when the mole fraction of CHDA and AA is kept constant at 9 : 1, thus giving rise to a high glass transition temperature of 56.4°C and a onset decomposition temperature of 350°C, and also delivering a balanced toughness and hardness with an impact resistance of 100 J/g and storage modulus as high as 109 Pa. This path for synthesis of PP‐based PU provides a design tool for high performance polymer coatings. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41246.

Synergistic Behavior of Tubes, Junctions, and Sheets Imparts Mechano-Mutable Functionality in 3D Porous Boron Nitride Nanostructures.

One-dimensional (1D) boron nitride nanotube (BNNT) and 2D hexagonal BN (h-BN) are attractive for demonstrating fundamental physics and promising applications in nano-/microscale devices. However, there is a high anisotropy associated with these BN allotropes as their excellent properties are either along the tube axis or in-plane directions, posing an obstacle in their widespread use in technological and industrial applications. Herein, we report a series of 3D BN prototypes, namely, pillared boron nitride (PBN), by fusing single-wall BNNT and monolayer h-BN aimed at filling this gap. We use density functional theory and molecular dynamics simulations to probe the diverse mechano-mutable properties of PBN prototypes. Our results demonstrate that the synergistic effect of the tubes, junctions, and sheets imparts cooperative deformation mechanisms, which overcome the intrinsic limitations of the PBN constituents and provide a number of superior characteristics including 3D balance of strength and toughness, emergence of negative Poisson’s ratio, and elimination of strain softening along the armchair orientation. These features, combined with the ultrahigh surface area and lightweight structure, render PBN as a 3D multifunctional template for applications in graphene-based nanoelectronics, optoelectronics, gas storage, and functional composites with fascinating in-plane and out-of-plane tailorable properties.

Anomalous impact strength for layered double hydroxide‐palmitate/poly(ε‐caprolactone) nanocomposites

ABSTRACTInherent physical properties and commercial availability makes poly(ε‐caprolactone) (PCL) very attractive as a potential substitute material for nondegradable polymers for commodity applications. However, a balance of toughness and stiffness is needed in order to transfer this potential into reality, particularly for short‐term packaging applications. In this context, layered double hydroxide modified with palmitic acid (LDH‐palmitate), was used as a nanoadditive to enhance the mechanical properties of PCL. Composites from PCL were prepared by melt‐blending with LDH‐palmitate loadings in the 1−10 wt % range. Scanning electron microscopy, transmission electron microscopy, and X‐ray diffraction were used to study the structure and morphology of the composites. The results showed homogeneous dispersion of clay particles in composites, but the degree of stacking of clay platelets was related to the LDH‐palmitate loadings. Charpy impact test measurements revealed an anomalous toughness improvement in the case of composite containing 5 wt % LDH‐palmitate, attributed to a combination of microcavitation and changes in crystallite sizes in the composite. The addition of LDH‐palmitate improved the water vapor barrier permeation of neat PCL film. In summary, LDH‐palmitate was shown to have potential as a nanoadditive to obtain tougher LDH‐PCL composite with improved barrier property. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41109.

Enhancement of toughness by grain boundary control in magnesium binary alloys

The mechanical properties, i.e., strength and toughness, were investigated on five fine-grained Mg–0.3at% X (X=Al, Ca, Sn, Y and Zn) alloys by two different processes: extrusion and caliber rolling. The extruded and caliber rolled alloys had the same texture distribution, but different grain boundary structures. The caliber rolled alloys, which had high fraction of low-angle grain boundaries, showed higher toughness and larger void size as compared to those of the extruded alloys, regardless of the alloying elements. The low-angle grain boundaries played a role in suppression of micro-void nucleation site. Thus, the control of grain boundaries is an effective method to enhance the mechanical properties in magnesium alloys, especially toughness. Importantly, the addition of aluminum or zinc elements in the caliber rolled alloys was the most effective in improving the strength and toughness balance among the well-known binary alloying elements.

Reprocessable silane-crosslinked polyethylene: property and utilization as toughness enhancer for high-density polyethylene

Silane-crosslinked polyethylene (Si-XLPE) has been increasingly used as a replacement of polyvinyl chloride for use as residence water pipes and hydronic heating systems. Unfortunately, good management of Si-XLPE wastes originated in the manufacturing processes or from already used products is limited. This article presents a melt-recycling (remelting and remolding) of waste Si-XLPE and its use to produce the high-density polyethylene (HDPE) composition of improved thermal endurance, along with attractive balance of stiffness and toughness. Experiments were carried out with a series of Si-XLPE of different gel fraction and crosslink structure, either loose or tight, aiming at understanding the factors which dictate the reprocessability and properties of crosslinked waste. Tensile and impact properties, crystallization, and heat stability of the HDPE and waste blends were investigated. It is found that waste Si-XLPE materials of loosely network structure can be remelting and remolding as thermoplastic PE. Interestingly, the results showed that crosslink gel in the wastes could be as high as 70 %. Both tensile modulus and impact strength of the HDPE systematically increased with increasing loading and content of gel in the crosslinked materials. The addition of 50 % crosslinked waste led to a rise of heat distortion temperature of HDPE by 20 °C, without evitable change in the melting and crystallization temperatures.

Effect of Triclosan on Self‐Assembly of Alkyl Ammonium Surfactants Adsorbed within Montmorillonite Galleries in Silicone Elastomer Composites

SummaryPoly(propylene) homopolymer/fly ash (50% wt) composites have been prepared from two samples of fly ash that differ in terms of the geographic source of coal feedstock, which left one of the samples with a higher group I and II metal content. A screening study indicated that Lubrizol Solplus® C800 (an unsaturated carboxylic acid dimer coupling agent), initiated with dicumyl peroxide, conferred the best strength–toughness balance to the composites. In some cases, however this was related to detachment of the interfacial region due to possible extraction of PP‐C800 adduct‐group I and II ion reaction products. Interfacial adhesion was arguably too high in the case of the fly ash sample bearing a lower level of group I and II ions. These deductions were also supported by DSC data.

Poly(propylene)/Fly Ash Composites: Effect of Coupling Agents on Mechanical Properties and Matrix Crystallinity

SummaryPoly(propylene) homopolymer/fly ash (50%wt) composites have been prepared from two samples of fly ash. One of the samples has a greater soluble group I and II metal content. A screening study indicated that Lubrizol Solplus® C800 (an unsaturated carboxylic acid coupling agent), initiated with dicumyl peroxide (DCP), conferred the best strength–toughness balance to composites produced by small scale batch mixing followed by compression moulding, i.e. long residence time in the melt. In the latter case, however the good mechanical properties were related to detachment of the interfacial region due to possible extraction of PP‐C800 adduct‐group I and II ion reaction products. Interfacial adhesion was arguably too high in the case of the fly ash sample bearing a lower level of group I and II ions. These deductions were also supported by DSC data. However, higher shear ‐ low residence time processing, i.e. by twin screw extrusion and injection moulding, led to better mechanical properties being obtained from C800‐DCP modification when the fly ash contained a reduced level of soluble group I and II ions.

Synergistic Toughening of Bioinspired Poly(vinyl alcohol)–Clay–Nanofibrillar Cellulose Artificial Nacre

Inspired by the layered aragonite platelet/nanofibrillar chitin/protein ternary structure and integration of extraordinary strength and toughness of natural nacre, artificial nacre based on clay platelet/nanofibrillar cellulose/poly(vinyl alcohol) is constructed through an evaporation-induced self-assembly technique. The synergistic toughening effect from clay platelets and nanofibrillar cellulose is successfully demonstrated. The artificial nacre achieves an excellent balance of strength and toughness and a fatigue-resistant property, superior to natural nacre and other conventional layered clay/polymer binary composites.

High-temperature metal matrix composites

This paper presents an overview of studies of creep-one of the most important characteristics of high-temperature materials. A structural model of creep and methods of accelerated creep tests are considered, and the effect of structural parameters on the creep resistance is studied. The problem of fracture toughness of metal matrix composites is analyzed. The possibility of designing composites with the necessary balance of high-temperature strength, fracture toughness, and oxidation resistance (heat resistance), in particular, composites operated at temperatures of 1400–1600°C is demonstrated by the example of a molybdenum oxide composite.