Brittle part

Brittle parts Wet resin or overdried resin Molded-in stresses Poor part design Check drying instructions and conditions Increase melt temperature/reduce injection pressure Review part design Review design for notches and other stress concentrators... 

The shapes of crystals depend on the shapes and sizes of the acid spicules contained in them. Effervescence when an acid and an alkali come together is caused by the points of the acid, which are in violent motion, entering the pores of the alkali, which is composed of stiff and brittle parts. The add spicules, not having freedom of movement, split and break the parts of the alkali in attempting to escape. The effervescence with coral is less violent than with silver, since there is less resistance to be overcome. Neutrality results when all the points are broken off and all the pores are stopped. This skilful linking of dull facts with attractive theory must have endeared Lemery s book to students. 

As compatibilizers, dendritic poly(ester) resins are useful. This covers both dendrimers and hyperbranched polymers (51). Compatibilizers are needed, because conventional poly(arylene ether)/PA blends exhibit inadequate flow properties at the processing temperatures that are needed to minimize the thermal degradation of the resins. However, increasing the processing temperature beyond these temperatures in order to reduce viscosity of the blends results in brittle parts and surface imperfections in the final part. 

As discussed in Section 2.0 (Exploration), the earth s crust is part of a dynamic system and movements within the crust are accommodated partly by rock deformation. Like any other material, rocks may react to stress with an elastic, ductile or brittle response, as described in the stress-strain diagram in Figure 5.5. 

The tensile strength in the joint part shown Fig.ll has less than the maetrial strength. As for this, joint strength is thought to be a decrease more than the strength of Ti because of an increase in the intermetallic compound of TiC that a little brittle. 

Gobalt is a brittle, hard metal, resembling iron and nickel in appearance. It has a metallic permeability of about two thirds that of iron. Gobalt tends to exist as a mixture of two allotropes over a wide temperature range. The transformation is sluggish and accounts in part for the wide variation in reported data on physical properties of cobalt. 

The element is a gray-white metalloid. In its pure state, the element is crystalline and brittle, retaining its luster in air at room temperature. It is a very important semiconductor material. Zone-refining techniques have led to production of crystalline germanium for semiconductor use with an impurity of only one part in lOio. 

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). 

A mixture of PhenoHc MicrobaUoons and resin binder has a putty-like consistency. It can be molded to shape, troweUed onto surfaces, or pressed into a core. Curing gives a high strength, low density (0.144 g/cm ) foam free of voids and dense areas, and without a brittle skin. Syntactic foams are used in widely diverse appHcations, including boat flotation aids stmctural parts in aircraft, submarines, and missiles stmctural cores for waU panels and ablative heat shields for reentry vehicles and rocket test engines. 

Welding (qv) of titanium requires a protected atmosphere of iaert gas. Furthermore, parts and filler wire are cleaned with acetone (trichloroethylene is not recommended). The pieces to be welded are clamped, not tacked, unless tacks are shielded with iaert gas. A test sample should be welded. Coated electrodes are excluded and higher purity metal (lower oxygen content) is preferred as filler. Titanium caimot be fusion-welded to other metals because of formation of brittle intermetallic phases ia the weld 2oae. 

Quite often problems arise when instruments for normal seiwice are subjected to low temperature use. Since some metals become brittle at low temperatures, the instrument hteraUy falls apart. Elastomeric gaskets and seals contract faster with decreasing temperatures than the surrounding metal parts, and the seal often is lost. Even hermetically sealed instruments can develop pin holes or small cracks to permit ciyogenic liqmds to enter these cases with time. Warming the instrument causes the trapped hquid to vaporize, sometimes generating excessive gas pressure and failure of the case. 

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. 

Ceramics cannot be bolted or riveted the contact stresses would cause brittle failure. Instead, ceramic components are bonded to other ceramic or metal parts by techniques which avoid or minimise stress concentrations. 

Because polycarbonates are good light absorbers, ultraviolet degradation does not occur beyond a depth of 0.030-0.050 in (0.075-0.125 cm). Whilst this is often not serious with moulded and extruded parts, film may become extremely brittle. Improvements in the resistance of cast film may be made by addition of an ultraviolet absorber but common absorbers cannot be used in moulding compositions because they do not withstand the high processing temperatures. 

Amongst the important heat-resisting cross-linked polymers are the phenolic resins (chapter 23), the Friedel-Crafts resins (also Chapter 23), the polyphenylenes (Chapter 21) and certain polysulphides (also Chapter 21). One problem of these materials is that they tend to be brittle. This is overcome in part... 

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