Izod test 404 Subject

An alternative to the Izod test is the Charpy test in which a sample supported, but not gripped, at each end is subject to an impact in the centre. According to the test a notch may be present in the centre of the sample on the face opposite to that subjected to impact. In spite of the differences between the tests there is a surprisingly good correlation between Izod and Charpy test results as shown by Figure 9.5 based on tests on several thermoplastics. ... 

Impact is a catastrophic event that has become very important for plastics. While measurements of impact performance have always been made in the past, new applications in the automotive, electronic, and consumer appli-cance industries have placed considerable importance on the quantification of this behavior. Historically, the Izod test has been used routinely to characterize impact. A notched rectangular bar is clamped in a vise and broken by a sharp impact from a hammer attached to a moving pendulum. The test has been widely criticized for being unsuitable for plastics, but it remains the most common test for impact and failure characterization. The Charpy test, widely used in Europe, has seen better acceptance by the scientific community. Here the test specimen, similarly notched, is held in a flexural mode while it is subjected to the impact. 

What is important to realise is that a polymer may be tough when exposed to tensile load but brittle when assessed by an Izod-type test where a notched sample is subjected to a bending load. Table 9.3 attempts to summarise the behaviour of typical polymers to different stresses. 

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. 

LDPE has a lower coefficient of expansion (10 X 10 cm/cm C) and a lower heat deflection temperature (40 C) than hope, lope does not break when subjected to the Izod impact test. The of lope is about 120 C. 

For polymer sheets, the notched Izod impact strength is often reported (ASTM D256). In this test, as well as the Charpy impact test in the same ASTM standard, the polymer sample is subjected to an impact from a falling hammer, and the... 

Often associated with the Gardner (ball or falling dart) test, with a known weight falling at a known distance and hitting a part, thereby subjecting it to an instantaneous high load. ASTM impact tests for material properties are the Izod, Charpy, and tensile impact tests. The test can also be a pendulum type. 

Standardized notched impact tests such as the Izod and Charpy tests (ASTM, ISO, DIN) are the most commonly used to characterize the impact strength of plastic materials. It is very difficult to use measured data from tests using idealized laboratory specimens to predict impact behavior of end-use polymeric material. The apparent lack of good correlation between measured impact fracture energy and end-use impact resistance is due to the extreme complexity of microscopic fracture processes. In particular, the influence of specimen geometry is sometimes poorly matched with the type of failure mechanism of defects present in the actual molded part subjected to end-use impact forces. 

Glass-filled polypropylene has been the subject of several studies involving tensile testing and the measurement of notched Izod impact strength. Gupta and coworkers... 

In common with most polymeric materials, adhesives and sealants are sensitive to the rate of applied force. There are several different types of impact test for adhesives. The most common test (similar in application to the Izod impact test for plastic materials) has been withdrawn without replacement however, the test was not widely used in a production situation due to the difficulty in achieving reproducible results. A more informative test for impact is the cleavage test in which the test specimen is subject to an impact force through a wedge (refer to Table 24). This can be initiated by a pendulum impact machine with an impact energy range of 50-300 J and an impact speed of 3-5.5 m/s. 

The biggest advantage of the falling-weight impact test over the pendulum impact test or high-rate tension test is its ability to duplicate the multidirectional impact stresses that a part would be subjected to in actual service. The other obvious advantage is the flexibility to use specimens of different sizes and shapes, including an actual part. Unlike the Izod impact test, which measures the notch... 

---