Crack propagation impact resistance testing

Testing of Plastics - Instrumented Charpy impact test Procedure for determining the crack resistance behaviour using the instrumented impact test Part I Determination of characteristic fracture mechanics parameters for resistance against unstable crack propagation Part II Determination of characteristic fracture mechanics parameters for resistance against stable crack propagation... 

A high level of uimotched impact resistance is seen in Fig. 18.12 both at room temperature and at — 18°C virtually independently from the fiber concentration. Unreinforced PP is soft enough to slide through the sample holder and not to break at all. Both crack initiation and propagation is tested in this experiment in contrast to the notched experiment in Fig. 18.13, where crack propagation plays the major role. Here, the impact resistance increases approximately linearly with the fiber content. 

Some of the more common mechanical properties are provided in Table 10.1 from IAEA (2009). Relative to various measures of toughness, some tests use a blunt notch, while others use a sharp crack to determine material resistance to crack initiation, crack propagation or both, and are conducted under either quasi-static (slow) loading or dynamic (fast) loading conditions. Of all these tests, the Charpy V-notch (CVN) impact test is the most commonly used. In addition to those mechanical properties, there are common reference fracture toughness indices used for RPV steels and many of those are also shown in IAEA (2009). These indices are important because they are used in various ways to normalize fracture toughness of RPV steels. 

The glass mat at the core of the STX sheet was shown to impart some very unusual impact properties to the material. The testing performed in the laboratory (Gardner drop test) and the field results from production components have shown that, in contrast to glass reinforced plastics, the failure mode is elastic rather than brittle. The resultant damage is a hole with little or no crack propagation around the impact area whereas the other reinforced materials will shatter under similar conditions. The STX failure mode applies not only at room temperature, but is equally valid at -40°F. STX impact resistance increases with the thickness of the material, i.e., V4 in. thick plate will resist much higher impact loads than Vs in. thick plate. 

Two quantities can be measured to describe a material s resistance to crack propagation fracture toughness, IQ, and strain energy release rate, G. Different stress states can be applied, with the most common being the opening mode (Mode I). Materials can also be tested in inplane shear (Mode n) and in torsional shear (Mode III). Testing in these modes typically involves strain rates much lower than those associated with impact teste such as the Charpy and Izod methods. Other methods... 

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