Impact testing notched

In Charpy impact testing, notches are normally made to initiate the crack near the proximity of the notch. The agglomerates may also act as stress raiser in nanocomposites if the mixing process is ineffective. The... 

Figure 1.29 Izod and Charpy impact test notch details.

Charpy impact ASTM D6110 (also. Research Report D20-1034) Similar to Izod impact test. Notched specimen is supported on two ends and struck by a pendulum in the middle, a three-point-bend setting. 

FIGURE 10.5 Impact testing (notched Izod). Original and final heights hi and/ij of hammer... 

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). 

In recent years impact testing of plastics has been rationalised to a certain extent by the use of fracture mechanics. The most successful results have been achieved by assuming that LEFM assumptions (bulk linear elastic behaviour and presence of sharp notch) apply during the Izod and Charpy testing of a plastic. 

For the purposes of performing an impact test on a material it is proposed to use an elastic stress concentration factor of 3.5. If the notch tip radius is to be 0.25 mm estimate a suitable notch depth. 

Methods employed to determine the impact resistance of plastics include pendulum methods (Izod, Charpy, tensile impact, falling dart, Gardner, Dynatup, etc.) and instrumented techniques. In the case of the Izod test, what is measured is the energy required to break a test specimen transversely struck (the test can be done either with the specimen notched or unnotched). The tensile impact test has a bar loaded in tension and the striking force tends to elongate the bar (Chapter 5, Impact Strength). 

The impact test, with its usual notch, indicates the energy required to break notched specimens under standard conditions. It is calculated as foot-pounds per inch (J/m) of notch and is usually calculated on the basis of 1 in. wide specimen, although the specimen may be thinner in the lateral direction. 

The Izod impact test may indicate the need to avoid inside sharp corners on parts made of such materials. For example, nylon and acetal-type plastics, which in molded products are among the toughest materials, are notch-sensitive and register relatively low values on the notched Izod impact test. 

V-notch impact tests, such as the Charpy test, are used to test the susceptibility of materials to brittle failure see Wells (1968) and BS 131. 

Impact tests are not required when the maximum obtainable Charpy specimen has a width along the notch of less than 2.5 mm (0.098 in.). Under these conditions, the design minimum temperature shall not be less than the lower of -48°C (-55°0 or the minimum temperature for the material in Table IX-1 A. 

Impact tests are not required when the maximum obtainable Charpy specimen has a width along the notch of less than 2.5 mm (0.098 in.). 

The Izod and Charpy impact tests are mostly used. A defined pendulum strikes the specimen sample, notched or un-notched, clamped with a defined device. The absorbed energy is calculated and expressed ... 

All pressure retaining steels applied at a specified minimum design metal temperature (2.11.4.5) below -30°C (-20°F) require a Charpy V-notch impact test of the base metal and the weld joint unless they are exempt in accordance with the requirements of paragraph UHA-51 in Section Vlll, Division 1 of the ASME Code. Impact test results shall meet the requirements of paragraph UG-84 of the Code. 

There are two principle methods for measuring impact and notched impact strength, which in practice differ only in the way in which the test bar is held. In the Charpy method the test piece is suspended at both ends and is struck in the center by a weighted pendulum. In the Izod method the test piece is clamped at one end only and is struck at the free end by the pendulum. 

Figure 5.79 Izod (notched) impact test. Reprinted, by permission, from F. Rodrignez, Principles of Polymer Systems, 2nd ed., p. 235. Copyright 1982 by Hemisphere Pnblishing Corporation.

Polyolefins. Ultra-High-Molecular-Weight Polyethylene.TIus is easily made by conventional low-pressure coordination polymerization. Hercules Hi-fax 1900 has a molecular weight of 2.5-5.0 million. Its outstanding properties are low coefficient of friction (0.11) abrasion-resistance superior to nylon, polyurethane, and steel unbreakable in the Izod notched impact test and high resistance to most inorganic and many organic chemicals. 

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