Notch-resistant

Elements made of composite materials with a soft, notch-resistant material and an outer layer with higher wear resistance. 

Metal powder composite materials fulfil many of these requirements. A tough, notch-resistant core material is able to transmit the high torques reliably, while the outer... 

ASTM E23-93, "Notched Bar Impact Testing of MetaUic Materials," Annual Book of ASTM Standards, ASTM Puhhcations, Philadelphia, 1993. ASTM D256-92, "Impact Resistance of Plastics and Electrical Materials," Annual Book of ASTM Standards, ASTM Puhhcations, Philadelphia, 1993. A. N. Atiuri and T. Nishioka, Int. / fract. 27, 245 (1985). 

Carbon content is usually about 0.15% but may be higher in bolting steels and hot-work die steels. Molybdenum content is usually between 0.5 and 1.5% it increases creep—mpture strength and prevents temper embrittlement at the higher chromium contents. In the modified steels, siUcon is added to improve oxidation resistance, titanium and vanadium to stabilize the carbides to higher temperatures, and nickel to reduce notch sensitivity. Most of the chromium—molybdenum steels are used in the aimealed or in the normalized and tempered condition some of the modified grades have better properties in the quench and tempered condition. 

The second parameter, tear strength, describes the film resistance to tear propagation. It is measured with a special apparatus, the Ehnendorf Tear Tester (ASTM D1922), and defined as the weight of a loaded pendulum capable of tearing a notched piece of film. Two values are usually measured for each film sample. One determines tear propagation in the machine direction of the film, the other in the transverse direction. 

The glass-fibre nylons have a resistance to creep at least three times as great as unfilled polymers. In the case of impact strength the situation is complex since unfilled nylons tend to break showing tough fracture whereas the filled polymers break with a brittle fracture. On the other hand the glass-filled polymers are less notch sensitive and in some tests and service conditions the glass-filled nylons may prove the more satisfactory. 

Due to the polyether blocks, these polymers retain their flexibility down to about -40°C and only Grade 6333 breaks in an Izod test at this temperature (using specimens of thickness 3.2 mm). The materials generally show excellent resistance to crack growth from a notch during flexure some grades are reported... 

Polycarbonates with superior notched impact strength, made by reacting bisphenol A, bis-phenol S and phosgene, were introduced in 1980 (Merlon T). These copolymers have a better impact strength at low temperatures than conventional polycarbonate, with little or no sacrifice in transparency. These co-carbonate polymers are also less notch sensitive and, unlike for the standard bis-phenol A polymer, the notched impact strength is almost independent of specimen thickness. Impact resistance increases with increase in the bis-phenol S component in the polymer feed. Whilst tensile and flexural properties are similar to those of the bis-phenol A polycarbonate, the polyco-carbonates have a slightly lower deflection temperature under load of about 126°C at 1.81 MPa loading. 

The styrene-based terpolymers were originally used to the extent of some 2-9% in order to reduce the notch sensitivity of the polycarbonate and to improve the environmental stress cracking resistance. More recently emphasis has been on alloys with 10-50% of SAN or ABS. Alloys of polycarbonates with ASA have also become available (Luran SC-BASF)... 

Polycarbonates based on tetramethylbisphenol A are thermally stable and have a high Vicat softening point of 196°C. On the other hand they have lower impact and notched impact resistance than the normal polymer. Blends with styrene-based polymers were introduced in 1980, and compared with PC/ABS blends, are claimed to have improved hydrolytic resistance, lower density and higher heat deflection temperatures. Suggested applications are as dishes for microwave ovens and car headlamp reflectors. 

Several blends based on polysulphone materials have been marketed. Probably the most well known is Mindel, originally produced by Uniroyal, acquired by Union Carbide, but now marketed by Amoco. Whilst not exhibiting the heat resistance of the unblended homopolymer, Mindel materials, which are blends of polysulphone and ABS, are lower in cost, easier to process and have higher notched impact strengths. The Mindel A materials are unreinforced, the Mindel B grades contain glass fibre, and the Mindel M grades contain other mineral fillers. A related polysulphone/SAN blend has been marked as Ucardel. 

Kerb-tier, n. insect, -tierkunde,/. entomology, -zahigkeit, /. (Mstal.) notch toughness, impact resistance or strength (in notched-bar test). 

As pointed out earlier, even if the metal is under stress for an infinite number of cycles, it will not fail as long as the stress level is below its fatigue limit. However, if the metal is damaged or notched in any way, the fatigue resistance decreases, as shown in Figure 4-443. Note that the nonferrous metals have no... 

Endo, K., Komai, K. and Nakamuro, N., Estimation of corrosion fatigue strength from corrosion resistance and notch sensitivity of the materials . Bull. Jap. Soc. Mech. Eng., 13, 837-46 (1970)... 

A crack count of 30-80 cracks/mm is desirable to maintain good corrosion resistance. Crack counts of less than 30 cracks/mm should be avoided, since they can penetrate into the nickel layer as a result of mechanical stress, whilst large cracks may also have a notch effect. Measurements made on chromium deposits from baths which produce microcracked coatings indicate that the stress decreases with time from the appearance of the first cracks . It is more difficult to produce the required microcracked pattern on matt or semi-bright nickel than on fully bright deposits. The crack network does not form very well in low-current-density areas, so that the auxiliary anodes may be necessary. 

The concept of a ductile-to-brittle transition temperature in plastics is likewise well known in metals, notched metal products being more prone to brittle failure than unnotched specimens. Of course there are major differences, such as the short time moduli of many plastics compared with those in steel, that may be 30 x 106 psi (207 x 106 kPa). Although the ductile metals often undergo local necking during a tensile test, followed by failure in the neck, many ductile plastics exhibit the phenomenon called a propagating neck. Tliese different engineering characteristics also have important effects on certain aspects of impact resistance. 

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