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fracture toughness

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 (Ca2+, Zn2+, Al3+, and Ce3+) 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/m3)...
February 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...
January 16, 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
Albin Thomas, Krishna C R Kolan, Ming C Leu, Gregory E Hilmas
Although implants made with bioactive glass have shown promising results for bone repair, their application in repairing load-bearing long bone is limited due to their poor mechanical properties in comparison to human bone. This work investigates the freeform extrusion fabrication of bioactive silicate 13-93 glass scaffolds reinforced with titanium (Ti) fibers. A composite paste prepared with 13-93 glass and Ti fibers (~16µm in diameter and lengths varying from ~200µm to ~2 mm) was extruded through a nozzle to fabricate scaffolds (0-90° filament orientation pattern) on a heated plate...
December 31, 2016: Journal of the Mechanical Behavior of Biomedical Materials
C J Hernandez, M C H van der Meulen
Increases in fracture risk beyond what are expected from bone mineral density (BMD) are often attributed to poor "bone quality" such as impaired bone tissue strength. Recent studies, however, have highlighted the importance of tissue material properties other than strength, such as fracture toughness. Here we review the concepts behind failure properties other than strength and the physical mechanisms through which they cause mechanical failure: strength describes failure from a single overload; fracture toughness describes failure from a modest load combined with a pre-existing flaw or damage; and fatigue strength describes failure from thousands to millions of cycles of small loads...
January 9, 2017: Journal of Bone and Mineral Research: the Official Journal of the American Society for Bone and Mineral Research
Peter Hess
A consistent set of 2D elastic and fracture properties of hexagonal boron nitride (h-BN) monolayers (boronitrene) and molybdenum disulfide (MoS2) nanosheets is derived. Reported literature values for Young's moduli and fracture strengths, based on experiments and DFT calculations, were used to estimate the line or edge energy with a local 2D bond-breaking model. Consistent information was obtained for intrinsic fracture properties. The basic mechanical properties of boronitrene are roughly 25% lower than the corresponding graphene values...
January 9, 2017: Nanotechnology
Kyudae Shim, Mohamed Abdellatif, Eunsoo Choi, Dongkyun Kim
The safety and effectiveness of antimicrobial ZnO films must be established for general applications. In this study, the antimicrobial activity, skin irritation, elution behavior, and mechanical properties of nanostructured ZnO films on stainless steel were evaluated. ZnO nanoparticle (NP) and ZnO nanowall (NW) structures were prepared with different surface roughnesses, wettability, and concentrations using an RF magnetron sputtering system. The thicknesses of ZnO NP and ZnO NW were approximately 300 and 620 nm, respectively, and ZnO NW had two diffraction directions of [0002] and [01-10] based on high-resolution transmission electron microscopy...
January 7, 2017: Applied Microbiology and Biotechnology
Huafeng Tian, Jiaan Yan, A Varada Rajulu, Aimin Xiang, Xiaogang Luo
In this work, starch/polyvinyl alcohol (PVA) blend films with different compositions were prepared by melt processing. The effect of the composition and relative humidity (RH) on the structure and properties of the resulting blends were investigated. OH groups on starch and PVA formed hydrogen bonding interactions, which could improve the compatibility of the two components. With the increase of starch, the degree of crystallinity of PVA component decreased. The fracture surface of the blend films exhibited rough surface, suggesting the tough fracture...
December 26, 2016: International Journal of Biological Macromolecules
Ning Zhang, Philippe Carrez, Rouzbeh Shahsavari
Nanoscale defects such as dislocations have a profound impact on the physics of crystalline materials. Understanding and characterizing the motion of screw dislocation and its corresponding effects on the mechanical properties of complex low-symmetry materials has long been a challenge. Herein, we focus on triclinic tobermorite, as a model system and a crystalline analogue of layered hydrated cement, and report for the first time how the motion of screw dislocation can influence the strengthening-toughening relationship, imparting brittle-to-ductile transitions...
January 18, 2017: ACS Applied Materials & Interfaces
Carmine Maletta, Emanuele Sgambitterra, Fabrizio Niccoli
Temperature dependent fracture properties of NiTi-based Shape Memory Alloys (SMAs), within the pseudoelastic regime, were analyzed. In particular, the effective Stress Intensity Factor (SIF) was estimated, at different values of the testing temperature, by a fitting of the William's expansion series, based on Digital Image Correlation (DIC) measurements. It was found that temperature plays an important role on SIF and on critical fast fracture conditions. As a consequence, Linear Elastic Fracture Mechanics (LEFM) approaches are not suitable to predict fracture properties of SMAs, as they do not consider the effects of temperature...
December 2016: Scientific Reports
Siegward D Heintze, Nicoleta Ilie, Reinhard Hickel, Alessandra Reis, Alessandro Loguercio, Valentin Rousson
OBJECTIVE: To evaluate a range of mechanical parameters of composite resins and compare the data to the frequency of fractures and wear in clinical studies. METHODS: Based on a search of PubMed and SCOPUS, clinical studies on posterior composite restorations were investigated with regard to bias by two independent reviewers using Cochrane Collaboration's tool for assessing risk of bias in randomized trials. The target variables were chipping and/or fracture, loss of anatomical form (wear) and a combination of both (summary clinical index)...
December 16, 2016: Dental Materials: Official Publication of the Academy of Dental Materials
Amirhossein Kazemi, Majid Abdellahi, Armina Khajeh-Sharafabadi, Amirsalar Khandan, Neriman Ozada
In this study, diopside bioceramic was synthesized using a mechanical milling process and subsequent heat treatment. The simplicity of experiments and also the high energy available in ball milling lead to rapid synthesis of the products in comparison with other synthesis methods. Magnesium oxide (MgO), silicon dioxide (SiO2) and eggshell (as the calcium source) powders were weighted in stoichiometric conditions and milled to initial activation of the surface of the powder's mixture. Then a sintering process was conducted to complete formation of diopside nanopowder and also evaluates its thermal stability...
February 1, 2017: Materials Science & Engineering. C, Materials for Biological Applications
Seung-Hei Oh, Jung-Hong Ha, Sang Won Kwak, Shin Wook Ahn, WooCheol Lee, Hyeon-Cheol Kim
INTRODUCTION: This study evaluated the effect of torsional preloading on the torsional resistance of nickel-titanium (NiTi) endodontic instruments. METHODS: WaveOne Primary (Dentsply Maillefer, Ballaigues, Switzerland) and ProTaper Universal F2 (Dentsply Maillefer) files were used. The ultimate torsional strength until fracture was determined for each instrument. In the phase 1 experiment, the ProTaper and WaveOne files were loaded to have a maximum load from 2...
January 2017: Journal of Endodontics
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