Tensile impact test

Impact tests are, however, used to try to compare the impact strength of different materials. Of these tests four require specific mention. These are the Izod test, the Charpy test, the falling weight tests and the tensile impact test. 

Other impact tests widely used are the falling weight tests where a weight is allowed to fall onto a supported flat or domed surface and tensile impact tests in which a sample is subjected to a sudden shock in tension. Whilst the... 

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. 

Methods employed to determine the impact resistance of plastics include pendulum methods (Izod, Charpy, tensile impact, falling dart, Gardner, Dynatup, etc.) and instrumented techniques. In the case of the Izod test, what is measured is the energy required to break a test specimen transversely struck (the test can be done either with the specimen notched or unnotched). The tensile impact test has a bar loaded in tension and the striking force tends to elongate the bar (Chapter 5, Impact Strength). 

The materials and morphological parameters are usually studied as function of test temperature and test speed. The Izod method as function of temperature (9,10) is standard. Also studied is the Charpy impact behavior, both as a function of test temperature and test speed (12). With a notched tensile impact test, both test speed and test temperature can easily be varied (I, 2,13). 

Figure 2. Results of notched tensile impact tests versus displacement for the PA-6-EPR blend (24 vol%, 0.3 pm), for different piston speeds (13).

Figure 6. Results of notched tensile impact tests versus temperature for PA-polybutadiene at lOr3 m/s for different rubber concentrations. Key M, 0 vol% , 15 vol% and A, 30 vol% (2).

Ligament Thickness. The ductile-to-brittle transition as measured in notched Izod, notched Charpy, and notched tensile impact tests is discontinuous and is dependent on both rubber concentration and particle size. These two parameters can be combined into a new morphological parameter that governs the ductile-to-brittle transition. The ligament thickness (interparticular distance), which is a function of rubber concentration and particle size,... 

Correlation of results from one test to another for a given material becomes difficult because of different stress states of the specimen and the associated strain rates in different tests. In the tensile-impact test, the stress state is uniaxial and it measures the tensile property at a high strain rate. In Izod and Charpy tests, the presence of notch gives a triaxial state of stress. The falling-... 

Figure 8. Stress whitening of composite 39-b formed by tensile stress in the tensile impact test.

Both the previous two methods require the test piece to be sufficiently rigid for buckling of the specimen under test to be negligible. For thinner section materials and for those exhibiting a high elongation before fracture, the tensile impact test may be the only viable... 

Figure 11-19. Schematic representation of different types of flexural tests. I, Flexural test with sample supported at two points II, flexural text, sample clamped at one point III, pendulum impact test to determine the flexural impact strength IV, flexural impact test V, tensile impact test.

ITIT instrumented notched tensile-impact test... 

The following Figures 5.8-5.10 contain further results of instrumented tensile-impact tests with the aim of determining the fracture resistance of elastomeric materials. In Figure 5.8, /d values of SBR/BR blends reinforced with various fillers and various filler contents are summarized. 

The method of instrumented notched tensile-impact testing is preferably used for elastomeric materials which cannot be tested under other impact-like loading conditions. However, also for thermoplastics, especially thermoplastic films, also the characterization of the fracture behaviour under impact loading can be necessary. Therefore, the following Tables show a summary of available data of fracture mecha-nics tests under impact-like loading conditions for thermoplastics and elastomers. 

Dijkstra, K., Laak, J., and Caymans, R. J. 1994. Nylon-6/rubber blends 6. Notched tensile impact testing of nylon-6/(ethylene- propylene rubber) blends. Polymer 35 315-322. 

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