Brittle material

These lab tests were done to gain a specific data base for such a brittle material compared to the normal steels used for the manufacturing of pressure equipments. In any case the application of AE was only possible due to the rapid development of the data processing and the new state-of-the-art equipment where this technique is built in.(3)... 

It is very important, from one hand, to accept a hypothesis about the material fracture properties before physical model building because general view of TF is going to change depending on mechanical model (brittle, elasto-plastic, visco-elasto-plastic, ete.) of the material. From the other hand, it is necessary to keep in mind that the material response to loads or actions is different depending on the accepted mechanical model because rheological properties of the material determine type of response in time. The most remarkable difference can be observed between brittle materials and materials with explicit plastic properties. 

Figure 3. Brittle material AE responses as count velocity N and logarithm spectrum log (S) characteristics of the process...

Figure 6. Location of poles and zeros for visco-elasto-plastic material (left) and brittle material (right) under loading close to fiacture.

These are relatively infusible, brittle materials that are insoluble in most solvents. 

Raw Materials. PVC is inherently a hard and brittle material and very sensitive to heat it thus must be modified with a variety of plasticizers, stabilizers, and other processing aids to form heat-stable flexible or semiflexible products or with lesser amounts of these processing aids for the manufacture of rigid products (see Vinyl polymers, vinyl chloride polymers). Plasticizer levels used to produce the desired softness and flexibihty in a finished product vary between 25 parts per hundred (pph) parts of PVC for flooring products to about 80—100 pph for apparel products (245). Numerous plasticizers (qv) are commercially available for PVC, although dioctyl phthalate (DOP) is by far the most widely used in industrial appHcations due to its excellent properties and low cost. For example, phosphates provide improved flame resistance, adipate esters enhance low temperature flexibihty, polymeric plasticizers such as glycol adipates and azelates improve the migration resistance, and phthalate esters provide compatibiUty and flexibihty (245). 

The use of the single parameter, K, to define the stress field at the crack tip is justified for brittle materials, but its extension to ductile materials is based on the assumption that although some plasticity may occur at the tip the surrounding linear elastic stress field is the controlling parameter. 

Although PS is normally considered a rather brittle material, biaxial orientation imparts some extremely desirable properties, particularly in regard to an increase in elongation. Thus, the 1.5—2% of elongation normally associated with unoriented PS can become as high as 10%, depending on the exact conditions of preparation (267,268). 

Glassy, or vitreous, carbon is a black, shiny, dense, brittle material with a vitreous or glasslike appearance (10,11). It is produced by the controUed pyrolysis of thermosetting resins phenol—formaldehyde and polyurethanes are among the most common precursors. Unlike conventional artificial graphites, glassy carbon has no filler material. The Hquid resin itself becomes the binder. 

V. D. Frnchette, Failure Analysis of Brittle Materials, Advances in Ceramics, Vol. 28, The American Ceramic Society, Inc., Westervike, Ohio, 1990. 

The fundamental goal in the production and appHcation of composite materials is to achieve a performance from the composite that is not available from the separate constituents or from other materials. The concept of improved performance is broad and includes increased strength or reinforcement of one material by the addition of another material. This is the well-known purpose in the alloying of metals and in the incorporation of chopped straw into clay for bricks by the ancient Egyptians and plant fibers into pottery by the Incas and Mayans. These ancient productions of composite materials consisted of reinforcing britde materials with fibrous substances. In both cases the mechanics of the reinforcement was such as to reduce and control the production of cracks in the brittle material during fabrication or drying (2). 

The modem interest in composite materials can be traced to the development of BakeHte, or phenoHc resin, in 1906. BakeHte was a hard, brittle material that had few if any mechanical appHcations on its own. However, the addition of a filler— the eadiest appHcations used short cellulose fibers (2)—yielded BakeHte mol ding compounds that were strong and tough and found eady appHcations in mass-produced automobile components. The wood dour additive improved BakeHte s processibiHty and physical, chemical, and electrical properties, as weU as reducing its cost (3,4). 

E. R. EuUer, Jr., E. P. Butler, and W. C. Carter, in NATO Advanced Kesearch Workshop on Toughening Mechanisms in Quasi-Brittle Materials, Kluwer Academic PubUshers, Dordrecht, The Netherlands, 1990. 

Push -on joints (Fig. 10-137) require diametral control of the end of the pipe. They are used for brittle materials. Pipe, fittings, and valves are furnished with the bells cast on one or more ends. Considerable force is required to push the spigot through the O ring this is reduced by the extension on the O ring, which causes the friction of the pipe to elongate the cross sec tion of the main portion of the O ring. 

Y = coefficient naving value in Table 10-50 for ductile ferrous materials, 0.4 for ductile nonferrous materials, and zero for brittle materials such as cast iron t,n = minimum required thickness, in, to which manufacturing tolerance must be added when specifying pipe thickness on purchase orders. [Most ASTM specifications to which mill pipe is normally obtained permit minimum wall to be 12V percent less than nominal. ASTM A155 for fusion-welded pipe permits minimum wall 0.25 mm (0.01 in) less than nominal plate thickness.] Pipe with t equal to or greater than D/6 or P/SE greater than 0.385 reqmres special consideration. 

The alloy niobium titanium (NbTi) and the intermetaUic compound of niobium and tin (Nb.3 Sn) are the most technologically advanced LTS materials presently available. Even though NbTi has a lower critical field and critical current density, it is often selected because its metallurgical properties favor convenient wire fabrication. In contrast, Nb.3Sn is a veiy brittle material and requires wire fabrication under very well-defined temperature conditions. 

Hydraulic piston-type compactors for collection vehicles, on-site compactors, and transfer-station compactors roll crushers used to fracture brittle materials and to crush tin and aluminum cans and other ductile materials... 

Metallic Versus Ceramic/Brittle Materials Recovery... 

While the structure/property behavior of numerous shock-recovered metals and alloys has received considerable attention in the literature to date, the response of ceramics, cermets, and other brittle solids (including geological materials) to shock loading remains poorly understood [9], The majority of shock-recovery studies on brittle materials have concentrated on examining... 

Figure 6.11. Schematic drawing of a shock-recovery assembly for brittle materials.

The importance of inherent flaws as sites of weakness for the nucleation of internal fracture seems almost intuitive. There is no need to dwell on theories of the strength of solids to recognize that material tensile strengths are orders of magnitude below theoretical limits. The Griffith theory of fracture in brittle material (Griflfith, 1920) is now a well-accepted part of linear-elastic fracture mechanics, and these concepts are readily extended to other material response laws. 

The parameters for the model were originally evaluated for oil shale, a material for which substantial fracture stress and fragment size data depending on strain rate were available (see Fig. 8.11). In the case of a less well-characterized brittle material, the parameters may be inferred from the shear-wave velocity and a dynamic fracture or spall stress at a known strain rate. In particular, is approximately one-third the shear-wave velocity, m has been shown to be about 6 for various brittle materials (Grady and Lipkin, 1980), and k can then be determined from a known dynamic fracture stress using an analytic solution of (8.65), (8.66) and (8.68) in one dimension for constant strain rate. 

Although much as been done, much work remains. Improved material models for anisotropic materials, brittle materials, and chemically reacting materials challenge the numerical methods to provide greater accuracy and challenge the computer manufacturers to provide more memory and speed. Phenomena with different time and length scales need to be coupled so shock waves, structural motions, electromagnetic, and thermal effects can be analyzed in a consistent manner. Smarter codes must be developed to adapt the mesh and solution techniques to optimize the accuracy without human intervention. 

Table 4.1 Factors of safety for ductile and brittle materials and various loading conditions (values shown in brackets from 1905, without brackets from 1965) (,S = ultimate tensile strength,, Sy = yield strength)...

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