About: Toughness is a(n) research topic. Over the lifetime, 29719 publication(s) have been published within this topic receiving 495055 citation(s). The topic is also known as: tensile toughness & toughness (physical properties).
26 Sep 1997-Science
Abstract: The Young's modulus, strength, and toughness of nanostructures are important to proposed applications ranging from nanocomposites to probe microscopy, yet there is little direct knowledge of these key mechanical properties. Atomic force microscopy was used to determine the mechanical properties of individual, structurally isolated silicon carbide (SiC) nanorods (NRs) and multiwall carbon nanotubes (MWNTs) that were pinned at one end to molybdenum disulfide surfaces. The bending force was measured versus displacement along the unpinned lengths. The MWNTs were about two times as stiff as the SiC NRs. Continued bending of the SiC NRs ultimately led to fracture, whereas the MWNTs exhibited an interesting elastic buckling process. The strengths of the SiC NRs were substantially greater than those found previously for larger SiC structures, and they approach theoretical values. Because of buckling, the ultimate strengths of the stiffer MWNTs were less than those of the SiC NRs, although the MWNTs represent a uniquely tough, energy-absorbing material.
01 Sep 1981-Journal of the American Ceramic Society
Abstract: The application of indentation techniques to the evaluation of fracture toughness is examined critically, in two parts. In this first part, attention is focused on an approach which involves direct measurement of Vickers-produced radial cracks as a function of indentation load. A theoretical basis for the method is first established, in terms of elastic/plastic indentation fracture mechanics. It is thereby asserted that the key to the radial crack response lies in the residual component of the contact field. This residual term has important implications concerning the crack evolution, including the possibility of post indentation slow growth under environment-sensitive conditions. Fractographic observations of cracks in selected “reference” materials are used to determine the magnitude of this effect and to investigate other potential complications associated with departures from ideal indentation fracture behavior. The data from these observations provide a convenient calibration of the Indentation toughness equations for general application to other well-behaved ceramics. The technique is uniquely simple in procedure and economic in its use of material.
01 Jan 1991-Advances in Applied Mechanics
Abstract: Publisher Summary This chapter describes the mixed mode cracking in layered materials. There is ample experimental evidence that cracks in brittle, isotropic, homogeneous materials propagate such that pure mode I conditions are maintained at the crack tip. An unloaded crack subsequently subject to a combination of modes I and II will initiate growth by kinking in such a direction that the advancing tip is in mode I. The chapter also elaborates some of the basic results on the characterization of crack tip fields and on the specification of interface toughness. The competition between crack advance within the interface and kinking out of the interface depends on the relative toughness of the interface to that of the adjoining material. The interface stress intensity factors play precisely the same role as their counterparts in elastic fracture mechanics for homogeneous, isotropic solids. When an interface between a bimaterial system is actually a very thin layer of a third phase, the details of the cracking morphology in the thin interface layer can also play a role in determining the mixed mode toughness. The elasticity solutions for cracks in multilayers are also elaborated.
15 Feb 2001-Nature
TL;DR: A structural polymeric material with the ability to autonomically heal cracks is reported, which incorporates a microencapsulated healing agent that is released upon crack intrusion and polymerization of the healing agent is triggered by contact with an embedded catalyst, bonding the crack faces.
Abstract: Structural polymers are susceptible to damage in the form of cracks, which form deep within the structure where detection is difficult and repair is almost impossible. Cracking leads to mechanical degradation of fibre-reinforced polymer composites; in microelectronic polymeric components it can also lead to electrical failure. Microcracking induced by thermal and mechanical fatigue is also a long-standing problem in polymer adhesives. Regardless of the application, once cracks have formed within polymeric materials, the integrity of the structure is significantly compromised. Experiments exploring the concept of self-repair have been previously reported, but the only successful crack-healing methods that have been reported so far require some form of manual intervention. Here we report a structural polymeric material with the ability to autonomically heal cracks. The material incorporates a microencapsulated healing agent that is released upon crack intrusion. Polymerization of the healing agent is then triggered by contact with an embedded catalyst, bonding the crack faces. Our fracture experiments yield as much as 75% recovery in toughness, and we expect that our approach will be applicable to other brittle materials systems (including ceramics and glasses).
01 Nov 2000-Wear
Abstract: Although hardness has long been regarded as a primary material property which defines wear resistance, there is strong evidence to suggest that the elastic modulus can also have an important influence on wear behaviour. In particular, the elastic strain to failure, which is related to the ratio of hardness (H) and elastic modulus (E), has been shown by a number of authors to be a more suitable parameter for predicting wear resistance than is hardness alone. There is presently considerable interest in the development of nanostructured and nanolayered coatings, due to the fact that materials with extreme mechanical properties (which are difficult to synthesise by other methods) can be created, particularly when using plasma-assisted vacuum processing techniques. Until now, scientific research has been directed mainly towards the achievement of ultra-high hardness, with associated high elastic modulus, the latter of which, conventional fracture mechanics theory would suggest, is also desirable for wear improvement (by preventing crack propagation). In this study, we discuss the concept of nanocomposite coatings with high hardness and low elastic modulus, which can exhibit improved toughness, and are therefore better suited for optimising the wear resistance of ‘real’ industrial substrate materials (i.e. steels and light alloys, with similarly low moduli). Recent advances in the development of ceramic–ceramic, ceramic–amorphous and ceramic–metal nanocomposite coatings are summarised and discussed in terms of their relevance to practical applications. We also discuss the significance of elastic strain to failure (which is related to H/E) and fracture toughness in determining tribological behaviour and introduce the topic of metallic nanocomposite coatings which, although not necessarily exhibiting extreme hardness, may provide superior wear resistance when deposited on the types of substrate material which industry needs to use.