Izod method

There are two principle methods for measuring impact and notched impact strength, which in practice differ only in the way in which the test bar is held. In the Charpy method the test piece is suspended at both ends and is struck in the center by a weighted pendulum. In the Izod method the test piece is clamped at one end only and is struck at the free end by the pendulum. 

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). 

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... 

The impact resistance by the Izod method shows similar behavior for the resins under study. The same can be said for the deflexion temperature under flexural load except for the unmodified lignan resin composition (Fig. 11],... 

A plot of An over BD0 should give, therefore, a straight line with slope R = Gc-Testing nine different brittle and ductile polymers (from PS to PE) by the Charpy and the Izod methods, Plati and Williams [64] were able to arrive at fairly unique values of Gc (cf. Table 9.2). They point out, however, that in order to obtain linear BD0 plots they had to consider an effective crack length consisting of the initial crack length and the size of a suitably chosen plastic zone. 

Charlie CHARMm Charpy Izod impact Charpy method Charpy test CHARTEK59 Charybdotoxin Chaser mill Chatecholates... 

Whilst Izod tests are, perhaps surprisingly, generally reproducible it has been found impossible to scale up the results and thus predict the energy required to break a bar of large cross-section from results obtained with a bar of smaller cross-section. This has led to some uncertainty in the method of quoting results and the following approaches are used ... 

Because of the diversity of the sources for this book the Izod data frequently referred to are expressed in a variety of units according to the test method used and no attempt has been made to convert the data to the use of a common unit. 

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 popular Izod impact tester can use different size specimens depending on the type of plastic and their method of fabrication. The specimen is usually 1/8 in. x l/2 in. x 2 in. other sizes are also used. Specimens can be notched or unnotched. A notch is cut in a specified manner on the narrow face of the specimen. The sample is clamped in the base of a pendulum testing machine so that it is cantilevered upward with the notch facing the direction of impact. The pendulum is released, and the force expended in breaking the sample is calculated from the height the pendulum reaches on the follow-through. The speed of the pendulum at impact is controlled. 

Nylon-6-clay nanocomposites were also prepared by melt intercalation process [49]. Mechanical and thermal testing revealed that the properties of Nylon-6-clay nanocomposites are superior to Nylon. The tensile strength, flexural strength, and notched Izod impact strength are similar for both melt intercalation and in sim polymerization methods. However, the heat distortion temperature is low (112°C) for melt intercalated Nylon-6-nanocomposite, compared to 152°C for nanocomposite prepared via in situ polymerization [33]. 

The Charpy test and the Izodtest are both pendulum-type impact tests. The difference between these two tests is essentially the orientation of the sample. In the Charpy test, or simple-beam method, the sample is supported at both ends, but is not held down, as shown on the left in Figure 15.30. In the Izod test, or cantilever beam method, the sample is supported on one end in a vice, as shown on the right in Figure 15.30. In both tests the sample is at the bottom of the pendulum arc and the amount of energy absorbed by the sample is measured. 

The test method may specify either a notched sample or an unnotched sample. If a notched specimen is specified, the dimensions of the notch are also given. Figure 15.31 is an example of these dimensions for a metal sample. In the Charpy test the notched sample is struck from behind the notch. In the Izod test the notch is facing the hammer. The notch, called a stress raiser, concentrates the stresses applied by the impact load. It makes the material brittle and increases the elastic limit in the notch area. Without the notch, many materials will bend without fracture, and the capacity to absorb energy will not be accurately determined. 

IZOD impact test—method for determining the behavior of materials subjected to shock loading. Specimen supported as a cantilever beam is strack by a weight at the end of a pendulum. Impact strength is determined from the amount of energy required to fracture the specimen. The specimen may be notched or unnotched. 

Impact Test. Impact testing is of importance because adhesives, like most polymeric materials, are sensitive to high rates of application of force. The resistance of an adhesive to impact can be determined by ASTM D 950. This test is analogous to the Izod impact test method used for impact studies on materials. 

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