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fracture toughness

Rajesh Kumar, Avinash Parashar
Molecular dynamics-based simulations were performed in conjunction with reactive force-field potential parameters to investigate the effect of crack-edge passivation via hydrogenation on the fracture properties of h-BN nanosheets. In semi-hydrogenated (H is attached to either B or N) and fully hydrogenated (H is attached to both B and N) crack-edge atoms, three hybridisation states-sp(2), sp(3) and sp(2) + sp(3)-were considered in the simulations. Significant improvement in the fracture toughness of h-BN nanosheets was predicted with semi- and fully hydrogenated crack-edge atoms...
March 20, 2017: Nanotechnology
Natalie Birk-Braun, Kamran Yunus, Eric J Rees, Wilhelm Schabel, Alexander F Routh
The fracture toughness of colloidal films is measured by characterizing cracks which form during directional drying. Images from a confocal microscope are processed to measure the crack width as a function of distance from the crack tip. Applying theory for thin elastic films the fracture toughness is extracted. It is found that the fracture toughness scales with the particle size to the -0.8 power and that the critical energy release rate scales with the particle size to the -1.3 power. In addition, the fracture toughness is found to increase at lower evaporation rates, but the film thickness does not have a significant effect...
February 2017: Physical Review. E
Huasong Qin, Yu Sun, Jefferson Zhe Liu, Mengjie Li, Yilun Liu
In this work, we perform molecular dynamics (MD) simulations to study the effect of rippling on the Poisson's ratio of graphene. Due to the atomic scale thickness of graphene, out-of-plane ripples are generated in free standing graphene with topological defects (e.g. heptagons and pentagons) to release the in-plane deformation energy. Through MD simulations, we have found that the Poisson's ratio of rippled graphene decreases upon increasing its aspect ratio η (amplitude over wavelength). For the rippled graphene sheet η = 0...
March 10, 2017: Nanoscale
Jonathan Reeve
In this review, I consider the varied mechanisms in cortical bone that help preserve its integrity and how they deteriorate with aging. Aging affects cortical bone in two ways: extrinsically through its effects on the individual that modify its mechanical loading experience and 'milieu interieur'; and intrinsically through the prolonged cycle of remodelling and renewal extending to an estimated 20 years in the proximal femur. Healthy femoral cortex incorporates multiple mechanisms that help prevent fracture...
2017: BoneKEy Reports
Jiajun Lin, Sun Hwi Bang, Mohammad H Malakooti, Henry A Sodano
The development of nanoscale reinforcements that can be used to improve the mechanical properties of a polymer remains a challenge due to the long-standing difficulties with exfoliation and dispersion of existing materials. The dissimilar chemical nature of common nanofillers (e.g., carbon nanotubes, graphene) and polymeric matrix materials is the main reason for imperfect filler dispersion and, consequently, low mechanical performance of their composites relative to theoretical predictions. Here, aramid nanofibers that are intrinsically dispersible in many polymers are prepared from commercial aramid fibers (Kevlar) and isolated through a simple, scalable, and low-cost controlled dissolution method...
March 15, 2017: ACS Applied Materials & Interfaces
O Kirichek, J D Timms, J F Kelleher, R B E Down, C D Offer, S Kabra, S Y Zhang
Internal stresses in materials have a considerable effect on material properties including strength, fracture toughness, and fatigue resistance. The ENGIN-X beamline is an engineering science facility at ISIS optimized for the measurement of strain and stress using the atomic lattice planes as a strain gauge. Nowadays, the rapidly rising interest in the mechanical properties of engineering materials at low temperatures has been stimulated by the dynamic development of the cryogenic industry and the advanced applications of the superconductor technology...
February 2017: Review of Scientific Instruments
Nicolas Rauner, Monika Meuris, Mirjana Zoric, Joerg C Tiller
The cartilage and skin of animals, which are made up of more than fifty per cent water, are rather stiff (having elastic moduli of up to 100 megapascals) as well as tough and hard to break (with fracture energies of up to 9,000 joules per square metre). Such features make these biological materials mechanically superior to existing synthetic hydrogels. Lately, progress has been made in synthesizing tough hydrogels, with double-network hydrogels achieving the toughness of skin and inorganic-organic composites showing even better performance...
March 1, 2017: Nature
Ke Chen, Jin Ding, Shuhao Zhang, Xuke Tang, Yonghai Yue, Lin Guo
Creating lightweight engineering materials combining high strength and great toughness remains a significant challenge. Despite possessing-enhanced strength and stiffness, bioinspired/polymeric materials usually suffer from clearly reduced extensibility and toughness when compared to corresponding bulk polymer materials. Herein, inspired by tiny amounts of various inorganic impurities for mechanical improvement in natural materials, we present a versatile and effective metal ion (M(n+))-based synergic cross-linking (MSC) strategy incorporating eight types of metal ions into material bulks that can drastically enhance the tensile strength (∼24...
March 1, 2017: ACS Nano
Brendyn Miller, Lyudmila Spevak, Lyudmila Lukashova, Behzad Javaheri, Andrew A Pitsillides, Adele Boskey, George Bou-Gharios, Alessandra Carriero
Tissue inhibitor of metalloproteinases-3 (TIMP-3) maintains a healthy extracellular matrix by regulating matrix metalloproteinases (MMP), disintegrin-metalloproteinases (ADAM), and disintegrin-metalloproteinases with ThromboSpondin-like motifs (ADAMTS) activity. Currently, there is a need for a comprehensive understanding of the effects of TIMP-3 on the bone quality and integrity. In this study, we examined the mechanical, morphological, and compositional properties of TIMP-3 knock out (Timp-3 (-/-)) mouse bone...
February 24, 2017: Calcified Tissue International
I Danilenko, G Lasko, I Brykhanova, V Burkhovetski, L Ahkhozov
The present study is devoted to the problem of enhancing fracture toughness of ZrO2 ceramic materials through the formation of composite structure by addition of Al2O3 and NiO particles. In this paper, we analyzed the general and distinguished features of microstructure of both composite materials and its effect on fracture toughness of materials. In this paper, we used the XRD, SEM, and EDS methods for determination of granulometric, phase, and chemical composition of sintered materials. The peculiarities of dependence of fracture toughness values from dopant concentration and changing the Y(3+) amount in zirconia grains allow us to assume that at least two mechanisms can affect the fracture toughness of ZrO2 ceramics...
December 2017: Nanoscale Research Letters
Jun Yang, Feng Xu, Chun-Rui Han
Utilization of reversible interactions as sacrificial bonds in biopolymers is critical for the integral synthesis of mechanically superior biological materials. In this work, cellulose nanofibrils (CNFs) reinforced covalent polyacrylamide (PAAm) composite hydrogels are immersed into multivalent cation (Ca(2+), Zn(2+), Al(3+), and Ce(3+)) aqueous solution to form ionic association among CNFs, leading to the ionic-covalent cross-linked hydrogels. The cations promote the formation of porous networks of nanofibrils by screening the repulsive negative charges on CNF surface and dominate the mechanical properties and self-recovery efficiency of the hydrogels, resulting in mechanically reinforced ionic hydrogels with stiff (Young's modulus 257 kPa) and tough properties (fracture toughness 386 kJ/m(3))...
March 13, 2017: Biomacromolecules
Christopher S Kovacs
During lactation, mammals resorb mineral from the maternal skeleton to provide calcium to milk. Rodents lose 25-35% of skeletal ash weight, ash calcium content, and bone mineral content by DXA, and have compromised material properties of bone, as assessed by crushing vertebrae and 3-pt bend tests of femora or tibiae. The strength, stiffness, and toughness of vertebrae, femora, and tibiae are reduced by as much as 60%. The effects of lactation are not uniform throughout the skeleton, but instead resorption is much more marked in the trabecular-rich spine than in the appendicular skeleton or whole body...
February 8, 2017: Journal of Bone and Mineral Research: the Official Journal of the American Society for Bone and Mineral Research
Jing Li, Xue-Hui Zhang, Ben-Cang Cui, Yuan-Hua Lin, Xu-Liang Deng, Ming Li, Ce-Wen Nan
OBJECTIVE: The aim of this study was to evaluate the microstructure and mechanical behavior of polymer-infiltrated zirconia ceramics as a function of pre-sintering temperature (1000-1150°C). METHODS: Polymer-infiltrated zirconia ceramics were prepared by combining the porous zirconia networks and polymer through infiltration and polymerization. XRD was employed to determine phase structure. The microstructure and fracture mechanism were observed by SEM. Flexural strength and fracture toughness were measured by three-point bending method and single-edge-notched beam method, respectively...
January 31, 2017: Journal of Dentistry
Jinlong Zhang, Xiaoqing Bu, Bin Ma, Hongfei Jiao, Xinbin Cheng, Zhanshan Wang
The thermomechanical property of the hafnium/silica antireflection (AR) coatings on lithium triborate (LBO) crystal was investigated by simulation and experiment. From the analysis of the stress and fracture toughness, it was found that the crack originated due to the high tensile stress in hafnium coating. Then we proposed the approaches of decreasing the deposition temperature and substituting the hafnium layers with alumina to improve the mechanical stability of AR coatings on LBO crystals, and cracks were effectively suppressed...
February 1, 2017: Applied Optics
Eric N Hahn, Vincent R Sherman, Andrei Pissarenko, Samuel D Rohrbach, Daniel J Fernandes, Marc A Meyers
Avian eggshells may break easily when impacted at a localized point; however, they exhibit impressive resistance when subjected to a well-distributed compressive load. For example, a common demonstration of material strength is firmly squeezing a chicken egg along its major axis between one's hands without breaking it. This research provides insight into the underlying mechanics by evaluating both macroscopic and microstructural features. Eggs of different size, varying from quail (30 mm) to ostrich (150 mm), are investigated...
January 2017: Journal of the Royal Society, Interface
Jiliang Hou, Xiuyan Ren, Shuang Guan, Lijie Duan, Guang Hui Gao, Yu Kuai, Huixuan Zhang
In this study, a novel strategy was designed to prepare rapidly recoverable, anti-fatigue, super-tough double-network hydrogels by introducing macromolecular microspheres (MMs) as cross-linking centers for hydrophobic associations. MMs were prepared via emulsion polymerization using butyl acrylate (BA) as a main component and dicyclopentyl acrylate (DCPA) as a cross-linker. Then, a double-network (DN) hydrogel was prepared using gelatin as the first network and a copolymer of acrylamide and hexadecyl methacrylate stabilized by MMs as the second network...
January 23, 2017: Soft Matter
Jung-Hong Ha, Sang Won Kwak, Sung Kyo Kim, Asgeir Sigurdsson, Hyeon-Cheol Kim
INTRODUCTION: The purpose of this study was to evaluate differences in torsional resistance using up-regulated speed of rotational spindle. METHODS: Three NiTi rotary instrument systems were selected in this study: K3XF (SybronEndo, Glendora, CA), BLX (B&L Biotech, Ansan, Korea), and OneShape (MicroMega, Besançon, France). The tip size and taper for all files were #25 and 0.06. Experimental groups (n = 10/group) were assigned to 2-, 60-, 350-, and 600-rpm groups by the rotational speed of spindle...
March 2017: Journal of Endodontics
Aleksandra Ostafinska, Ivan Fortelný, Jiří Hodan, Sabina Krejčíková, Martina Nevoralová, Jana Kredatusová, Zdeněk Kruliš, Jiří Kotek, Miroslav Šlouf
Blends of two biodegradable polymers, poly(lactic acid) (PLA) and poly(ϵ-caprolactone) (PCL), with strong synergistic improvement in mechanical performance were prepared by melt-mixing using the optimized composition (80/20) and the optimized preparation procedure (a melt-mixing followed by a compression molding) according to our previous study. Three different PLA polymers were employed, whose viscosity decreased in the following order: PLC ≈ PLA1 > PLA2 > PLA3. The blends with the highest viscosity matrix (PLA1/PCL) exhibited the smallest PCL particles (d∼0...
January 10, 2017: Journal of the Mechanical Behavior of Biomedical Materials
Marianthi Topouzi, Eleana Kontonasaki, Dimitrios Bikiaris, Lambrini Papadopoulou, Konstantinos M Paraskevopoulos, Petros Koidis
PURPOSE: Fractures in long span provisional/interim restorations are a common complication. Adequate fracture toughness is necessary to resist occlusal forces and crack propagation, so these restorations should be constructed with materials of improved mechanical properties. The aim of this study was to investigate the possible reinforcement of neat silica nanoparticles and trietoxyvinylsilane-modified silica nanoparticles in a PMMA resin for fixed interim restorations. MATERIALS AND METHODS: Composite PMMA-Silica nanoparticles powders were mixed with PMMA liquid and compact bar shaped specimens were fabricated according to the British standard BS EN ISO 127337:2005...
January 9, 2017: Journal of the Mechanical Behavior of Biomedical Materials
B Karimi, B Ramezanzadeh
The reinforcement effect of graphene oxide nanosheets on the mechanical properties of an epoxy coating has been extensively studied. However, the effect of graphene oxide quantum dot (GOQD) as a new unique carbon based nanomaterial (with lateral dimension of 5-6nm and thickness of one carbon atom) on the mechanical properties of epoxy coating has not been reported and compared with GO yet. So this study aims at fabrication of a high-performance polymer composite with unique mechanical properties using GOQD nanosheets...
January 5, 2017: Journal of Colloid and Interface Science
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