Falling-weight impact

In the falling-weight impact test a circular disc of material (typically 6 cm diameter and 2 mm thickness, freely supported on an annulus of 4 cm diameter) is impacted by a metal dart with a hemispherical tip (t3q5ically of radius 1 cm). The tests are carried out either under conditions where the impact energy is far in excess of that required to break the specimen or at low levels of impact energy so that damage tolerance and the possible initiation of a crack can be observed. 

Moore and his colleagues have described the application of such tests to polymers and to polymer composites [117-119]. It is emphasized that for any reasonable attempt at interpretation the following must be carried out  

Measurement of the force time curve so that the input energy to maximum force can be determined, as well as the total impact energy. 

Photography of the tension surface during the impact event. 

For fibre composites Moore and colleagues showed that the peak on the foree time curve corresponds well with the energy required to initiate a crack. It was shown also that for both composites and polymers the total fracture energy corresponded quite well with that detemined from notched Charpy tests. 

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Falling Weight (Impact) Test. Ten tests with 0.05 to 0.1 Og samples, using an apparatus having an anvil 1.27cm(0.5") in diameter, should show that the explosive is less sensitive than Picric Acid (PA)... 

Figure 8.13 Dependence of two estimates on the impact strength on the amount of PDMS in PDMS-modified Si02 glasses.144 The impact strengths were obtained from (O) the Charpy pendulum impact test (A) the falling-weight impact test.

Mechanical Properties. The mechanical properties of the selected blends studied, including the results of tensile, Izod impact, and falling-weight impact tests, are summarized in Table I. Generally, lower-than-expected toughening efficiency (especially for Izod impact) and data scattering were obtained because it is hard to maintain consistent moisture content of the specimens (especially for blends in which PA is the major component). The presence of the compatibilizer in all the blends resulted in consistent and substantial improvement in properties (Nos. 2, 3, and 4 vs No. 1, and No. 20 vs... 

Figure 11.32 Falling weight impact load-time traces of the ct-PP and (3-PP SEN specimens. (From Reference 64 with permission from Elsevier.)...

The simplest way to approach detection of brittleness point is quickly to bend the material while holding it at the low temperature, and a considerable number of tests of this type have been devised and some standardized. The degree of strain is often not precisely defined, and these tests tend to be operator-dependent, so that reproducibility can be poor. A more satisfactory approach is to impact a test piece at low temperatures. Adaptations of falling weight impact tests are tests are commonly used for rigid plastics, but for flexible materials a procedure in which a strip test piece held as a simple cantilever and impacted by a striker is very widely standardized. 

A new part to ISO 179 is under preparation that will cover the instrumentation of the Charpy pendulum so that force-time (and by integration, force-dcflection) curves can be obtained. This allows for a fuller characterization of the impact behavior of the plastic than can be derived from only the energy to break of the typical test. There has been an instrumented version of the falling weight impact test (see later in this section) for several years and the same principles apply to both. 

Figure 3.1 Effect of photooxidation on falling weight impact resistance ofPVC ( ) and ABS (10%) modified PVC (O, A) duplicate results (Reproduced with permission from G. Scott, in Development in Polymer Stabilisation -1, ed. G. Scott, Applied Science Publications, 1979, p. 310)...

Figure 10.28 Falling weight impact failure energy vs. temperature for Victrex PEEK resins.

Fig. 8.41 Video images during the falling weight impact test for neat PA above) and PA/EGMA alloy below)...

C. Santulli, M. Janssen and G. Jeronimidis, Partial replacement of E-glass fibers with flax fibers in composites and effect on falling weight impact performance. /. Mater. Sci. 40, 3581-3585 (2005). 

Milliken HPN-600ei is used to improve aesthetics, Gardner (falling weight) impact resistance, flexural modulus, and top-load strength of thermoformed PP parts (e.g., cups and lids). ... 

Instrumented falling weight impact test were conducted on a home build machine. Details of which have already been given elsewhere (6). Test panels were circular clamped between metal plates with a circular opening of 80 mm. The mass of the falling weight was 0.9 kg. A hemispherical dart with a diameter of 10 mm was used in all cases. 

Figure 7. Effect of hybridization on visible damage after falling weight impacts of 10 Joule.

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