High speed impact tests

Two types of mechanical tests have been used the low rate of deformation tensile, compressive or bending tests and the high speed impact tests. Immiscibility of polymers is reflected in both. For example, in tensile tests the maximum strain at break (or the maximum elongation), and the yield stress (or the maximum strength) can be... 

A high-speed impact test system with an electron thermal (ET) gun is illustrated in Fig. 1. First, a substrate with coating film is mounted on a specimen holder. The specimen is to be mounted mechanically in line with the ET gun and the solenoid coils. Then, a spherical magnet of samarium-cobalt (Sm2Con, density 8.4g/cm, hardness 5.4 GPa, Young s modulus 151 GPa, strength 118 MPa) is mounted in a plastic sabot as a simulated foreign object. 

Figure 1. An overall view of the high speed impact testing system.

The rate at which the impact occurs also affects the impact strength of a viscoelastic material. Often, it is very difficult to achieve very high rates of impact with conventional laboratory testing. In certain applications (military and aerospace) high-speed impact tests have been developed. In order to attain the high speeds required chemical explosives or electromagnetic energy are employed [59]. 

E. High-Speed Impact Tests (ASTM D3763, ISO 6603-2)... 

Most versatile high-speed impact testing machinery is capable of testing everything from the thin film which may require as low an impact rate as 30in./min to the plastic automotive bumper which may require an impact rate up to 30,000in./min. The specimen or product can be tested under a controlled environment of tempera-... 

Examination of oven-aged samples has demonstrated that substantial degradation is limited to the outer surface (34), ie, the oxidation process is diffusion limited. Consistent with this conclusion is the observation that oxidation rates are dependent on sample thickness (32). Impact property measurements by high speed puncture tests have shown that the critical thickness of the degraded layer at which surface fracture changes from ductile to brittle is about 0.2 mm. Removal of the degraded layer restores ductiHty (34). Effects of embrittled surface thickness on impact have been studied using ABS coated with styrene—acrylonitrile copolymer (35). 

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. 

Polymer blends must provide a variety of performance parameters. Usually it is a set of performance criteria that determines if the material can be used or not For specific apphcatimi more weight can be given to one or another material property. The most important properties of polymer blends are mechanical. Two types of tests have been used the low rate of deformation (tensile, compressive, or bending) and the high-speed impact Inuniscibility affects primarily the maximum elongation at break and the yield stress. 

Fig. 7. Hydraulic high speed impact tester, (a) Specimen enclosed in environmental chamber (b) hydraulic drive unit at the end of the rails for component testing. Courtesy of Instron Corp., Canton, Mass.

High-speed penetration tests were conducted by subjecting samples to shock cylindrical punching at speeds of 125, 600 and 800 m/s [13]. At the moment of impact, the temperature distribution over the punch pattern on the backside of the samples was recorded using an infrared camera. 

Impact Toughness property of a material indicating its ability to absorb energy of a high-speed impact by plastic deformation rather than crack or fracture. See also Impact Property Tests. 

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