Impact tests, types

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. 

Although the Izod and Charpy tests are widely used for plastics, other types of test are also popular. These include tensile impact tests and flexural plate (falling weight) tests. The latter is particularly useful in situations where the effects of flow anisotropy are being assessed. In addition, arbitrary end-product tests are widely used to provide reassurance that unforseen factors have not emerged to reduce the impact performance of the product. 

Tensile and flexural properties were studied with an Instron 4204 testing machine. Tensile tests were performed on the drawn strands at a test speed of 3 mm/ min, while three-point-bending tests (ISO 178) at a speed of 5 mm/min were applied to the injection molded specimens. Charpy impact strength was measured of the unnotched samples with a Zwick 5102 pendulum-type testing machine using a span of 70 mm. The specimens (4 X 10 X 112 mm) used for three-point-bending tests were also used for the impact tests. It should be noted that neither the tensile tests for the strands nor the impact tests were standard tests. The samples were conditioned for 88 h at 23°C (50% r.h,) before testing. 

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. 

There are other types of impact tests for shock loading where energy is required to cause complete failure is reported. Each has their specific behaviors that can be related to specific product performance requirements. Tests include ball burst, ball or falling dart using different weights and heights, bag drop, bullet-type instantaneous impact, Charpy, dart drop, Mullen burst, tear resistance, and tub (2). 

Figure 8.7 Schematic Illustration of a pendulum type impact testing device...

The Charpy test and the Izodtest are both pendulum-type impact tests. The difference between these two tests is essentially the orientation of the sample. In the Charpy test, or simple-beam method, the sample is supported at both ends, but is not held down, as shown on the left in Figure 15.30. In the Izod test, or cantilever beam method, the sample is supported on one end in a vice, as shown on the right in Figure 15.30. In both tests the sample is at the bottom of the pendulum arc and the amount of energy absorbed by the sample is measured. 

More recently, explosives have been tested for impact sensitivity by an impact machine in which 40 mg of explosive on sandpaper are placed between an anvil and a steel cylinder. A 2.5 kg weight is dropped from different heights and the sound produced serves to indicate a go or no go . The result from 25 drops is calculated to give a height at which the probability of explosion is 50%. Results from a compilation104 are presented in Table 12 and show that the relative values of TNT and picric acid are reversed from the previous table. TNT is relatively more sensitive on the Type 12 impact machine than in the FI impact test. TATB is so insensitive that it fails to explode at the maximum drop height of the machine. 

Brittle fracture is probably the most insidious type of pressure-vessel failure. Without brittle fracture, a pressure vessel could be pressurized approximately to its ultimate strength before failure. With brittle behavior some vessels have failed well below their design pressures (which are about 25 percent of the theoretical bursting pressures). In order to reduce the possibility of brittle behavior. Division 2 and Sec. Ill require impact tests. 

Rates of Strain , 3rdONRSympDeton(1960), Vol 2, pp 420-35 (Included is description of Type 1 and Type 2 Impact Tests, which are also described in Ref 67)... 

Type 1-Type 2 tests. Whereas the Susan Test is a quick and reliable way of obtaining a comparative assessment of an explosive s behavior under impact, the Type 1-Type 2 experiments provide a way of elaborating on that behavior but at the cost of a considerably larger number of experiments than that required for the Susan Test... 

Detonation, Type 1- and Type 2-Impact Tests in. See Ref 67 under DETONATION (AND EXPLOSION), EXPERIMENTAL PROCEDURES, Section 4... 

Impact Machines and Impact Tests. One frequently hears the remark that there are as many types of impact machines as there are explosives test laboratories. This is somewhat misleading. In reality, all laboratories use essentially similar equipment but test procedures, and test data analyses differ. Basically an impact machine is an apparatus that drops a steel weight from a pre-determined height onto a plunger or striker resting on top of the test sample which is placed on a steel anvil... 

The literature reports several types of impact testing apparatus also known as fall hammer apparatus , for the determination of impact sensitivity of explosives. 

ERL impact apparatus, type 12 This test was developed by the US Army Armament Research, Development and Engineering Center and is optional for use. The machine (Bruceton Machine) Type 12 consists of a striker pin (made of hardened tool steel, ground and polished) with surface in contact... 

Proposed as an exptl expl by E.E. Gilbert G.P. Sollott of USA ARRADCOM, Dover, NJ. First prepd by permanganate oxidation of the corresponding tetraaminoadamantane. Calcns indicate an expl output greater than TNT TNA has a five-second expin temp of 400°. Impact test data show no go from 150 to 240cm in the ERL Type 12 tooling app (TNT explds at 65 5cm)... 

Many impact tests measure the energy required to break a standard sample under certain specified conditions. The most widely used tests are the lzod test (pendulum-type instrument with notched sample, which is struck on the free end), the Charpy test (pendulum-type instrument with sample supported at the two ends and struck in the middle), the falling-weight test (standard ball dropped from known height), and the high-speed stress-strain test. 

Same exceptions from Impact tests as Division 1. except that types 316 and 316L are not in the first category exempt from testing down to -425aF (-254° C). 

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