Toughness projectile testing

The advantage of projectile testing is that the test can be developed to mimic the actual end-use conditions and materials can be evaluated in that context The disadvantage is that the equipment, and the actual tests, are not standardized, and it may not be possible to correlate the results of these tests with other types of toughness tests (Figure 5.14). 

The shrouds and exhaust chutes were made from tough materials like polycarbonate, ABS, occasionally even polypropylene. The key was projectile testing, specifically small objects weighing grams or ounces that were projected at fairly high speed. The performance requirements might vary, minor deformation allowed, no structural failure allowed, etc. While projectile testing can be a slow and tedious process, it can provide valuable information on performance in real-world applications. 

While some might think that the purpose of this demonstration was to prove the toughness of thermoplastics from GE Plastics, I prefer to think of it a subtle reminder of importance of projectile testing when evaluating the use of thermoplastics in an application subject to high velocity impacts. 

The measurement of mechanical properties is a major part of the domain of characterisation. The tensile test is the key procedure, and this in turn is linked with the various tests to measure fracture toughness... crudely speaking, the capacity to withstand the weakening effects of defects. Elaborate test procedures have been developed to examine resistance to high-speed impact of projectiles, a property of civil (birdstrike on aircraft) as well as military importance. Another kind of lest is needed to measure the elastic moduli in different directions of an anisotropic crystal this is, for instance, vital for the proper exploitation of quartz crystal slices in quartz watches. 

Fracture energy In addition to the peak load, the fracture energy is also very commonly measured in impact tests. Most commonly, this is taken as the area either under the complete load vs. deflection curve, or under this curve out to some particular deflection. Unfortunately, as indicated earlier, the fracture energy (or toughness) determined in this way depends strongly upon the mass and velocity of the impact hammer (or projectile), and upon the relative masses of the specimen and the impact hammer. It is thus essentially impossible at the present time to compare different tests. 

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