Low-temperature impact test

Low-temperature impact tests cooled samples are subjected to a conventional impact test. Generally, the temperatures most often used are -20°C, -30°C or -40°C. 

ISO 4646. 1989. Fabrics coated with rubber or plastics Low temperature impact test. 

A special pneumatic multiposition low-temperature impact testing machine was developed to allow investigation of impact strength with samples inside the coolant bath, containing liquid helium. The impact test machine is shown in Fig. 6. It enables investigation of the temperature dependence of fracture, crack propagation, and maximum and proportionality limit loading. 

Fig. 6. Schematic view of the unit for low-temperature impact tests. Legend (1) outer cryostat shell, (2) internal cryostat shell, (3) nitrogen vessel, (4) screen, (5) siphon, (6) circular anvil, (7) crushed sample trap, (8) vacuum transfer, (9) dynamometer with strain gauges, (10) packing, (11) actuating power pneumatic cylinder, (12) hammer, (13) cutter, (14) piston, (15) upper test section, (16) lower test section, (17) rod, (18) cutter movement sensor shutter (19) cutter movement sensor, (20) lock crown, (21) lock, (22) support, and (23) control pneumatic cylinder.

Rotomolded tanks were treated to irradiation levels of 120, 200 and 280 kilogray and the test results were compared against an un-irradiated control sample. Two test methods, environmental stress crack resistance (ESCR) and low temperature impact were used to determine differences between the samples. Low temperature impact testing was performed at -40 C. ESCR testing used both a 10% and 100% Igepal solution and the comparison used only the 280 kGy sample. This test was performed for a maximum of 1000 hours. The results of these tests are shown in figures 3 and 4. 

Impact Testing Materials conforming to ASTM specifications listed in the code may generally be used at temperatures down to the lowest temperature listed for that material in the stress table without additional testing. When welding or other operations are performed on these materi s, additional low-temperature toughness tests may be reqiiired. The code requirements are listed in Table 10-57. 

Requirements for Low Temperature Toughness Tests for Metals. .. Tabular Values for Minimum Temperatures Without Impact Testing... 

Figure 15-4. Low temperature brittleness test broken lines show position of striker and test piece (assumed unbroken) after impact...

Liquid chlorine is generally stored in vessels made from non-alloyed carbon steel or cast steel. Fine grain steel, stress-relieved and subjected to Charpy impact tests for low temperature impact resistance [29], is used. Erosion of the protective layer on steel... 

Most of the properties given in Table 14.1 are relatively standard physical property measurements with standard methods referenced. The notched Izod ductile-brittle transition temperatiure is an approximate method to estimate the midpoint temperatiure at which notched Izod behavior shifts from fully ductile to fully brittle. It may be very sensitive to a variety of differences among samples. It is used here only for iUus-trative purposes to show the low-temperature impact capabihty hmits as measured by this notched Izod test. Each user should determine the relevance of this small-scale laboratory impact test on small laboratory-molded parts to full-scale molded parts at end-use conditions for a given application. 

The low temperature impact strength of the material used in the ROPS shall be verified by suitable material tests or material certification (see paragraph (f)(2)(iv) of this section). 

Since all specimens exhibited ductile fracture it was possible to compare used and unused polymers. It was noted that, although the materials had been in service for ten years before recycling, the low-temperature impact properties had not deteriorated. As before, it is difficult to compare the values determined for injection-moulded test specimens with those exhibited by the original tank material and those specified by the quality order since the test specimens were only 3 mm thick, compared with the average thickness of a tank, which is between 5 and 8 mm. 

The most common test for impact resistance of plastics is the Izod pendulum method, ASTM D256, often used with rigid PVC. In this method, either the mass of the weight or the extent of arc can be used to specify failure. It is differentiated into notched and un-notched Izod the former, notably more severe, uses a sample with a cut notch of specific dimensions. With suitable instrumentation, Izod measurements can be extended to determination of low-temperature impact resistance. 

As mentioned in Section 2.5, the trend to higher modulus substrates will also reduce the painted part impact performance. Coating systems showing ductile failure when tested with a 790 MPa TPO can exhibit brittle failure when tested with a 1500 MPa TPO (Table 3). The current trend is to increase the coating flexibility to compensate for the more brittle substrate and still maintain acceptable low-temperature impact performance. Of course, other painted part properties (e.g., environmental etch, out-of-oven finessability) will likely be compromised with this change. 

Low Temperature Brittleness. Brittleness temperature is the temperature at which polyethylene becomes sufficiently brittle to break when subjected to a sudden blow. Because some polyethylene end products are used under particularly cold climates, they must be made of a polymer that has good impact resistance at low temperatures namely, polymers with high viscosity, lower density, and narrow molecular weight distribution. ASTM D746 is used for this test. 

Low-temperature service is defined as being below—29°C (—20°F), and impact testing of many materials is required. The code is restrictive in the type or welding permitted. 

This test is of some use in judging the relative merits of various materials for low-temperature flexing or impact. However, it is specifically relevant only for materials and conditions specified in the test, and the values cannot be directly applied to other shapes and conditions. 

Materials With Limited Service. The desirability of specifying some degree of production impact testing, in addition to the weld procedure qualification tests, when using materials with limited low-temperature service experience below the minimum temperature stated in Table IX-2. 

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