Propagation of crack

The onus for the organisation of any inspection programme beyond that required by Class rests with the owner or operator of the ship. Under certain circumstances, for example, when the propagation of cracks could lead to pollution through the loss of cargo, an owner of an oil tanker operating in US coasted waters may spend a considerable amount of money on preventative inspections. 

Priedman A., Lin Y. (1996) Propagation of cracks in elastic media. Arch. Rat. Mech. Anal. 136, 235-290. 

Critical stress intensity factor Klc and critical strain energy release rate G1C quantify the stability of a polymer against the initiation and propagation of cracks. Stress intensity factor and energy release rate G, are not independent but they are related [76] by means of the appropriate modulus E. ... 

In fiber-reinforced composites the deformation of the matrix is then used to transfer stresses by means of shear tractions at the fiber-matrix interface, to the embedded high-strength fibers. On the other hand, fibers retard the propagation of cracks and thus produce a material of high strength. 

Fracture toughness is the resistance to propagation of cracks through a material and is usually quantified by the stress intensity factor, K, defined as... 

It is inherently difficult to measure the strength of a material since this is strongly influenced by the microstructure of the material, i.e., the distribution of flaws which strongly influence the propagation of cracks. This concept is illustrated in Fig. 31, where the elastic stress distribution in an ideally elastic, brittle material is seen to become infinite as the crack tip is approached. The key properties which characterize the strength of a material are ... 

As discussed above, because materials often fail by the propagation of cracks, particularly brittle ones, it is difficult to measure the true yield stress, oy, of a material. Instead one measures a fracture stress, Op which is related to the size of the process zone and actual crack length by ... 

Concrete is an inherently brittle material with low tensile strength and strain capacities. Its brittle characteristics lead to easy nucleation and propagation of cracks, thus restricting its range of applications. To address this deficiency, fibers of different materials such as asbestos, glass, metal, and synthetics " are used as additives, with the following results"" ... 

Sato N., Kurauchi T., Sato S. and Kamigaito O. (1983). SEM observation of the initiation and propagation of cracks in a short fibre reinforced thermoplastic composite under stress. J. Mater. Sci. Lett. 2, 188-190. 

Structural applications of composite materials require not only acceptable static mechanical properites but the ability to withstand the generation and propagation of cracks without premature failre. For example, impact resistance, fracture toughness and fatigue resistance are desireable composite properties. Fiber-matrix structure at the interphase can affect the values attainable for these properties. 

LGMs of the AT/alumina and AT/ZTA displayed some very interesting properties which include excellent machinability, low thermal expansion coefficient, improved thermal shock resistance, low hardness (about 5 GPa), low Young s modulus (E) (250 GPa) and excellent flaw tolerance [Pratapa, 1997 Pratapa Low, 1998 Skala, 2000 Manurung, 2001], These materials appeared to display a large degree of near-surface quasi-plasticity under the Hertzian or the Vickers indenter which effectively inhibits the formation and propagation of cracks. The ductile behaviour of these materials was... 

Moreover, in the stabilization phase of the intumescent structure, the change in the viscosity of the charred material under stress may explain the loss of the protective character of the intumescent shield. Indeed, if the shield becomes too hard, the creation and the propagation of cracks leading to a rapid degradation of the material occurs.33... 

Finally, we note that voids, cracks, and gaps can absorb thermal expansion and provide sites at which fracture may be initiated or means by which the propagation of cracks may be interrupted. 

In principle any isotropic material can be reinforced the combination of the materials has to meet the requirement that the reinforcing material has to be stiffer, stronger or tougher than the matrix furthermore there has to be a very good adhesion between the components. In a composite the reinforcement has to carry the stresses to which the composite material is subjected the matrix has to distribute the stresses. By means of a good distribution of the reinforcement the latter blocks the propagation of cracks, which mostly start at the outer surface, and would lead to rupture of the whole object if no blockade were present. By optimum reinforcement the strength of a matrix material can be improved to the tenfold, albeit in one direction. 

A widely accepted theory for lamination presented by Long [29] and reformulated by Ritter and Sucker [30] attributes capping to the residual die wall pressure. This pressure is said to cause internal shear stresses in the tablet causing the propagation of cracks, which results in lamination or capping. The propagation of cracks can be prevented by plastic relaxation of shear stresses. Therefore, materials having sufficient plasticity may not be susceptible to lamination. Some properties of the powder mixture, such as moisture content, type and amount of the binder, and... 

The word brittle to most people implies poor impact resistance. As we will see, it s a bit more complicated than this and in general brittle materials have poor resistance to the propagation of cracks. 

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