Fracture fibrous

Features The root is obtainable in longitudinally split pieces or in transverse slices. Ringed, brownish-grey externally, hard and whitish inside fibrous fracture. Berries purplish-black, nearly globular, ten carpels, each containing one lens-shaped seed. 

Ceramic matrix composites require a fiber interface coating to prevent fiber-matrix bonding and to produce crack deflection and fibrous fracture in the composite. Work at the... 

S. Gonczy, R. Leung, J. Sikonia, NearNet Shape Formability, Fibrous Fracture, and Low Dielectric Properties in Glass Matrix Composites Reinforced with Continuous Fibers , DARPA Workshop on Ceramic Matrix Composites, Alexandria, VA, August 1, 1991. 

R Y. Leung, S. T. Gonczy, G. T. Stanford, C. E. Southern, D. M. Lipkin, Near-Net Shape Formability and Fibrous Fracture in Glass Matrix Composites Reinforced with Continuous Ceramic Fibers, NASA Conference Publication 3097, Proceedings ofthe 14th Conference on Metal Matrix, Carbon, and Ceramic Matrix... 

R. D. Yasukawa, D. G. Polensky, R. Y. Leung, S. T. Gonczy, J. G. Sikonia, Blackglas Ceramic Matrix Composites with Dielectric Properties and Fibrous Fracture, Presentation at 2d Aimual Ceramic Composites and Structures Meeting, USAF, West Palm Beach, FL, Oct. 20-22, 1992. 

The N720/A fracture surfaces obtained at 1000 and 1100 °C exhibit regions of uncoordinated brushy failure as well as areas of nearly planar fracture. The fracture surfaces produced at 1000 °C are dominated by regions of fibrous fracture. At 1100 C, uncorrelated fiber fracture is prevalent in air, and coordinated fiber failure is predominant in steam. The fracture surface appearance can be correlated with failure time. Predominantly planar fracture surface corresponds to a short life, while fibrous fracture indicates longer life. Stress corrosion of the N720 fibers is likely the mechanism behind poor creep resistance of the N720/A composite in steam. 

Lateral expansion is the amount of growth experienced by the specimen at the notch. The percent shear, or percent of fibrous fracture, is determined by comparing the samples to fracture appearance charts in ASTM A 370. 

Extra energy is then absorbed in fracturing the fibres and in fibre PULLOUT (q.v.) from the matrix. A fibrous fracture surface (q.v.) results, rather than the smooth continuous surface which would result from brittle fracture (q.v.) of both components were the fibre-matrix bond strength high. Most continuous fibre reinforcement is unidirectional, and... 

Particle failure induces microcracks in the material. They deform to form ellipsoidal cavities. In between the particles, the matrix is only single-phase and thus has an increased ductility. The cavities thus grow by slipping of the matrix (see sections 6.2.3 and 6.2.5) on planes of maximum shear stress (e.g., in a uniaxial stress state at 45° to the loading direction). The matrix between the cavities is drawn to thin tips or ridges. The finally formed fracture surface is characterised by a large number of dimples formed in this way. The size of the dimples is in the range of a few micrometres. Sometimes, this kind of fracture is called fibrous fracture. 

Two approaches have been taken to produce metal-matrix composites (qv) incorporation of fibers into a matrix by mechanical means and in situ preparation of a two-phase fibrous or lamellar material by controlled solidification or heat treatment. The principles of strengthening for alloys prepared by the former technique are well estabUshed (24), primarily because yielding and even fracture of these materials occurs while the reinforcing phase is elastically deformed. Under these conditions both strength and modulus increase linearly with volume fraction of reinforcement. However, the deformation of in situ, ie, eutectic, eutectoid, peritectic, or peritectoid, composites usually involves some plastic deformation of the reinforcing phase, and this presents many complexities in analysis and prediction of properties. 

Table 13 is a representative Hst of nickel and cobalt-base eutectics for which mechanical properties data are available. In most eutectics the matrix phase is ductile and the reinforcement is britde or semibritde, but this is not invariably so. The strongest of the aHoys Hsted in Table 13 exhibit ultimate tensile strengths of 1300—1550 MPa. Appreciable ductiHty can be attained in many fibrous eutectics even when the fibers themselves are quite britde. However, some lamellar eutectics, notably y/y —5, reveal Htde plastic deformation prior to fracture. 

Some common flake-shaped LCMs consist of shredded cellophane and paper, mica (qv), rice hulls, cottonseed hulls, or laminated plastic. These materials He flat across the opening to be sealed or are wedged into an opening such as a fracture. Some are sufficiently strong to withstand considerable differential pressure, whereas others are weak and the seal may be broken easily. Weaker flake materials typically are used near the surface or in combination with fibrous or granular additives. 

Many fibrous composites are made of strong, brittle fibres in a more ductile polymeric matrix. Then the stress-strain curve looks like the heavy line in Fig. 25.2. The figure largely explains itself. The stress-strain curve is linear, with slope E (eqn. 25.1) until the matrix yields. From there on, most of the extra load is carried by the fibres which continue to stretch elastically until they fracture. When they do, the stress drops to the yield strength of the matrix (though not as sharply as the figure shows because the fibres do not all break at once). When the matrix fractures, the composite fails completely. 

Acute coronary syndromes most often result from a physical disruption of the fibrous cap, either frank cap fracture or superficial endothelial erosion, allowing the blood to make contact with the thrombogenic material in the lipid core or the subendothelial region of the intima. This contact initiates the formation of a thrombus, which can lead to a sudden and dramatic blockade of blood flow through the affected artery. If the thrombus is nonocclusive or transient, it may either be clinically silent or manifest as symptoms characteristic of unstable angina. Importantly, if collateral vessels have previously formed, for example, due to chronic ischemia produced by multi vessel disease, even total occlusion of one coronary artery may not lead to an acute myocardial infarction. 

Fig. 10. Scanning electron micrograph of a fracture surface parallel to the direction of extrusion of an extrudate of a 45 55 PS-HDPE blend with a viscosity ratio p 1. Fibrous PS is shown at different stages of breakup the diameter of the largest fiber is about 1 pm (Meijer el til., 1988).

Kelly A. (1970). Interface effects and the work of fracture of a fibrous composites. Proc. Roy. Soc. Land. A 319, 95-116. 

Mandell 3.F., Darwish, A.Y. and McGarry F.3. (1981). Fracture testing of injection-molded glass and carbon fiber-reinforced thermoplastics. In Testing Methods and Design Allowable for Fibrous Composites, ASTM STP 734 (C.C. Chamis ed.), ASTM, Philadelphia, PA, pp. 73 90. 

Piggotl M.R. (1970). Theoretical estimation of fracture toughness of fibrous composites. J. Mater. Sci. 5, 669-675. 

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