Toughness Izod test

Most HIPS fail in the uniaxial loading of a cantilever impact (Izod) test only if the test specimens have been notched beforehand. In the notched impact test, the stress direction in injection molded specimens is the same as the preferred orientation direction. This increases the measured impact toughness and the flexural impact test and, therefore, serves primarily for comparing the toughness of different products. 

The quality known as toughness describes the way a material reacts under sudden impacts. It is defined as the work required to deform one cubic inch of metal until it fractures. Toughness is measured by the Charpy test or the Izod test. 

Elastic-plastic fiacture mechanics has been extensively used in studies on plastics, but to data mainly tty research laboratories. The plastics industry continues to rely on impact testing, and in particular the notched Izod test, as the principal method for assessing toughness. One of the most important contributions of fracture mechanics to potymer engineering has been to provide a theoretical basis for understanding these impact test data. 

The chip impact test is carried out in a similar way to the Izod test but without a notch. The test specimen is usually 25.4 mm long, 12.7 mm wide, and 1.65 mm thick. The tests are carried out using ASTM D4508 [79]. Because the test involves an un-notched sample, it reflects material toughness rather than the notch sensitivity measured for the Izod and Charpy tests. 

The superior performance of 25% glass-reinforced PVC, 30% glass-reinforced polystyrene in unnotched Izod impact strength, and tensile-impact values (Table 3-1), when compared to work-to-break values at various loading speeds (Figs. 3-5 and 3-9), demonstrate the weakness of the notched Izod test for comparing the toughness of these materials. 

Test and service data with PVC both rate low in notched Izod impact tests and performs well in normal service applications that involve impact loading. Another example is with some grades of rubber-modified high impact PSs that show up well in the Izod test fail on impact under field test conditions. These results have led to continual reexamination of the tests used to determine the toughness of plastics. 

Izod test plane strain plane strain fracture toughness stress raiser thermal fatigue transgranular fracture... 

While instrumented impact testing can be quite simple (as in the instrumented Izod test described earlier), the real value of instrumented testing lies in the ability to isolate and control the various test parameters and to precisely record the output data. When applied properly, instrumented testing can provide valuable data on almost aspect of material toughness. The primary disadvantage of instrumented testing is that the equipment can be quite complex (and expensive). 

Ultimate strength Yielding Toughness Weibull distribution Stress concentration Trousers tear Simple shear test Energy to cause rupture Impact tester Izod test Charpy test... 

The effect of PPE-MM-A on the fracture toughness (Kic) of epoxy is shown in Figure 8. The fracture toughness increases with PPE-MM-A levels, confirming the increased toughness seen in the Izod test. 

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. 

Table 7-17 Example of a simplified readout for TPs toughness or fracture behavior Izod impact test results...

The flaw spectrum approach may be capable also of correlating failure data obtained under conditions which appear to give different material behavior. For example, tensile, Izod, and dart drop impact tests all give different impact energies or toughness measures. In part, this may be explained by the simple idea that a different fraction of flaws is active in each test. Equal biaxial loading (as in dart drop) and uniaxial tension (as in tensile impact) give rise to different flaw activities thus it is to be expected that the number of crazes produced in each test will be different. 

Numerous studies have been made of the mechanical properties of fibrous composites these include recently published papers on impact properties by Izod (1,2, 3,4) and Charpy (5,6) and drop weight (7) tests. We reported the Charpy impact fracture behavior of various glass-polyester composites regarding the effects of temperature (8,9,10), specimen size (8), and fiber orientation (10). This paper describes the effects of the tough-brittle transition in the impact behavior of glass-polyester composites which occurs with a variation of temperature and specimen size. 

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