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fracture toughness

Chuchai Anunmana, Wiroj Wansom
This study investigated the effect of cross-sectional areas on interfacial fracture toughness and bond strength of bilayered dental ceramics. Zirconia core ceramics were veneered and cut to produce specimens with three different cross-sectional areas. Additionally, monolithic specimens of glass veneer were also prepared. The specimens were tested in tension until fracture at the interface and reported as bond strength. Fracture surfaces were observed, and the apparent interfacial toughness was determined from critical crack size and failure stress...
April 18, 2017: Dental Materials Journal
Praneetha Pulyala, Akshay Singh, Marcela Ferreira Dias-Netipanyj, Sheron Compos Cogo, Luciane S Santos, Paulo Soares, Vasanth Gopal, V Suganthan, Geetha Manivasagam, Ketul C Popat
The goal of this work was to enhance the mechanical strength and fracture toughness of brittle hydroxyapatite (HAP) by reinforcing it with nanocomposites such as graphene oxide (GO), carbon nanotubes (CNT) and Titania. The goal was also to evaluate the cytotoxicity and the cellular adhesion/proliferation of these composites. The composites were characterized for their crystallinity, functionality, morphology and mechanical properties. Altering the composition by adding 1wt% GO and CNT significantly altered the wettability, hardness and roughness...
June 1, 2017: Materials Science & Engineering. C, Materials for Biological Applications
Shravan Suresh, Zi Ping Wu, Stephen F Bartolucci, Swastik Basu, Rahul Mukherjee, Tushar Gupta, Prateek Hundekar, Yunfeng Shi, Toh-Ming Lu, Nikhil Koratkar
Silicon (Si) shows promise as an anode material in lithium-ion batteries due to its very high specific capacity. However, Si is highly brittle, and in an effort to prevent Si from fracturing, the research community has migrated from the use of Si films to Si nanoparticle based electrodes. However, such a strategy significantly reduces volumetric energy density due to the porosity of Si nanoparticle electrodes. Here we show that contrary to conventional wisdom, Si films can be stabilized by two strategies: (a) anchoring the Si films to a carbon nanotube macrofilm (CNM) current collector and (b) draping the films with a graphene monolayer...
April 20, 2017: ACS Nano
F D Fischer, O Kolednik, J Predan, H Razi, P Fratzl
Twisted plywood architectures can be observed in many biological materials with high fracture toughness, such as in arthropod cuticles or in lamellar bone. Main purpose of this paper is to analyze the influence of the progressive rotation of the fiber direction on the spatial variation of the crack driving force and, thus, on the fracture toughness of plywood-like structures. The theory of fiber composites is used to describe the stiffness matrix of a twisted plywood structure in a specimen-fixed coordinate system...
April 7, 2017: Acta Biomaterialia
Paulo Francisco Cesar, Alvaro Della Bona, Susanne S Scherrer, Michael Tholey, Richard van Noort, Alessandro Vichi, Robert Kelly, Ulrich Lohbauer
OBJECTIVES: The objective is within the scope of the Academy of Dental Materials Guidance Project, which is to provide dental materials researchers with a critical analysis of fracture toughness (FT) tests such that the assessment of the FT of dental ceramics is conducted in a reliable, repeatable and reproducible way. METHODS: Fracture mechanics theory and FT methodologies were critically reviewed to introduce basic fracture principles and determine the main advantages and disadvantages of existing FT methods from the standpoint of the dental researcher...
April 6, 2017: Dental Materials: Official Publication of the Academy of Dental Materials
Lisa Mol, M Gomez-Heras, C Brassey, O Green, T Blenkinsop
Projectile damage to building stone is a widespread phenomenon. Sites damaged 100 years ago during the First World War still see daily use, while in a more contemporary setting numerous reports show the damage to buildings in Babylon, Mosul and Palmyra. While research has been carried out on the long-term effects of conflict such as fire damage, little is known about the protracted damage sustained through the impact of bullets, shrapnel and other metal projectiles outside of the field of engineering focused on ceramics and metals...
February 2017: Royal Society Open Science
Megha Sahu, Lakshmi Narashimhan, Om Prakash, Ashok M Raichur
In the present study, noncovalently functionalized tungsten disulfide (WS2) nanosheets were used as a toughening agent for epoxy nanocomposites. WS2 was modified with branched polyethyleneimine (PEI) to increase the degree of interaction of nanosheets with the epoxy matrix and prevent restacking and agglomeration of the sheets in the epoxy matrix. The functionalization of WS2 sheets was confirmed through Fourier transform infrared spectroscopy and thermogravimetric analysis. The exfoliation of the bulk WS2 was confirmed through X-ray diffraction and various microscopic techniques...
April 13, 2017: ACS Applied Materials & Interfaces
Amrita Kataruka, Kavya Mendu, Orieka Okeoghene, Jasmine Puthuvelil, Ange-Therese Akono
Bone is a composite material with five distinct structural levels: collagen molecules, mineralized collagen fibrils, lamellae, osteon and whole bone. However, most fracture testing methods have been limited to the macroscopic scale and there is a need for advanced characterization methods to assess toughness at the osteon level and below. The goal of this investigation is to present a novel framework to measure the fracture properties of bone at the microscopic scale using scratch testing. A rigorous experimental protocol is articulated and applied to examine cortical bone specimens from porcine femurs...
June 2017: Bone Reports
Marion Grzelka, Joshua B Bostwick, Karen E Daniels
A droplet of surfactant spreading on an ultrasoft (E ≲ 100 Pa) gel substrate will produce capillary fractures at the gel surface; these fractures originate at the contact-line and propagate outwards in a starburst pattern. There is an inherent variability in both the number of fractures formed and the time delay before fractures form. In the regime where single fractures form, we observe a Weibull-like distribution of delay times, consistent with a thermally-activated process. The shape parameter is close to 1 for softer gels (a Poisson process), and larger for stiffer gels (indicative of aging)...
April 19, 2017: Soft Matter
Rémy Gauthier, Hélène Follet, Max Langer, Sylvain Meille, Jérôme Chevalier, Frédéric Rongiéras, Françoise Peyrin, David Mitton
Bone fracture is a major health issue worldwide and consequently there have been extensive investigations into the fracture behavior of human cortical bone. However, the fracture properties of human cortical bone under fall-like loading conditions remains poorly documented. Further, most published research has been performed on femoral diaphyseal bone, whereas it is known that the femoral neck and the radius are the most vulnerable sites to fracture. Hence, the aim of this study is to provide information on human cortical bone fracture behavior by comparing different anatomical sites including the radius and the femoral neck acquired from 32 elderly subjects (50 - 98 y...
March 22, 2017: Journal of the Mechanical Behavior of Biomedical Materials
Bumjoon Choi, Taehee Kim, Eue Soo Ahn, Sang Woo Lee, Kilho Eom
Prion fibrils, which are a hallmark for neurodegenerative diseases, have recently been found to exhibit the structural diversity that governs disease pathology. Despite our recent finding concerning the role of the disease-specific structure of prion fibrils in determining their elastic properties, the mechanical deformation mechanisms and fracture properties of prion fibrils depending on their structures have not been fully characterized. In this work, we have studied the tensile deformation mechanisms of prion and non-prion amyloid fibrils by using steered molecular dynamics simulations...
December 2017: Nanoscale Research Letters
Andrew J Conith, Michael J Imburgia, Alfred J Crosby, Elizabeth R Dumont
The Mesozoic marked a time of experimentation in the tooth morphology of early mammals. One particular experiment involved the movement of three points, or cusps, on the surface of a molar tooth from a line into a triangle. This transition is exemplified by two extinct insectivorous mammals, Morganucodon (cusps in a line) and Kuehneotherium (cusps in a triangle). Here we test whether this difference in cusp arrangement, alongside cusp heights and angles between cusps, is associated with differences in the ability of the teeth to fracture proxy-insect prey...
November 2016: Journal of the Royal Society, Interface
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...
April 21, 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 29, 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 28, 2017: ACS Nano
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