Specimens, notched Izod

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). 

This test has possible advantages over the notched Izod test. The notch sensitivity factor is eliminated, and energy is not used in pushing aside the broken portion of the specimen. The test results are recorded in ft-lb/in.2 (kJ/m2). This allows for minor variations in dimensions of the minimum in cross-section area. 

The strong sub-rg relaxation in PCT also contributes to increased toughness of this polymer in the amorphous state. When measured on amorphous specimens, the notched Izod impact strength of PCT is greater than 1000 J/m, while that of PET is less than 100 J/m [22],... 

Figure 17. Notched Izod impact strength of PVC-VC/PE graft copolymer alloys and proportion of unbroken specimens hammer 10 ft-lb...

In the notched Izod impact test, with the exception of some rubber modified plastics, the fracture surface of a specimen that has failed ductilely exhibits significant inward collapsing on the sides of the impact bar near the notch, indicating that a large amount of plastic flow has... 

Figure 1. Typical appearances of failed notched Izod impact specimens...

Ductile and Brittle Failure in Notched Izod Specimens of BPA Carbonate Polymers... 

Impact Failure. Standard notched Izod impact measurements have been made over wide temperature ranges on specimens cut from compression molded %-inch thick sheets of BPA polycarbonate and two BPA carbonate-silicone block polymers (Figure 4) (see Table I for compositions and properties). In the homopolymer a ductile-brittle transition occurs at 0° to —15°C, as reported previously (4, 5). Introduction of 15 and 25% silicone lowers the transition to —45° and —110°C (block polymers A and B). As indicated in Table I, this increase in toughness at low temperature is accompanied by the reduction of modulus and yield stress. 

Instron Three-Point Bending Failure. Three-point bending tests have also been conducted on notched Izod specimens at crosshead rates of 0.02-20 inches/min (Figure 5). Plots of work to break obtained from the areas under the Instron force-displacement traces show abrupt ductile-brittle transitions these are displaced to lower temperatures as the test rate is decreased. However the temperature interval between ductile-brittle transitions of the two materials remains about the same. The force-displacement trace for each specimen shows a yield point with a ductile failure but a sharp termination when the sample breaks in a brittle fashion. 

Figure 4. Temperature dependence of impact energy for Vs inch thick notched Izod specimens cut from compression molded sheets of BPA polycarbonate and two of its block polymers. A 15% silicone, B 25% silicone. Silicone DPn = 20.

Block polymer B differs substantially in its failure characteristics from BP A polycarbonate. For the block polymer a mixed failure mode predominates in three-point bend tests of notched specimens from —100°-90°C. In the mixed mode craze breakdown and plane strain fracture occur first inside the specimen subsequently shear failure occurs in the surface regions of the specimen. Shear lips (11) are formed as a result. Shear lips are also found on the notched Izod impact fracture surfaces of block polymer B, implying that the same mixed mode of failure occurs under high speed loading conditions. 

New grades of SMMA are being developed that have shown tremendous potential for blends in SBC. These new grades result in very high impact in the blends with higher loadings of SMMA. Notched Izod impact values of almost 5 ft-lb/in have been reported for injection molded test specimens containing 50 % SMMA [22]. 

PS blends with EPDM were compatibilized by addition of either SB (polystyrene/polybutadiene di-block copolymer) or SEP (polystyrene/ethylene propylene di-block copolymer) and were blended in a corotating twin-screw extruder T = 200°C (Table 11.9). The strands were quenched and pelletized. Some of the pellets were injection-molded (200°C) into 4 mm-thick specimens and irradiated to 50 kGy (3-MeV electron accelerator). Another part of the pellets was similarly irradiated and then injection-molded. The samples for notched Izod impact testing (ASTM D256) were annealed for 24 h at 80°C, or were left at RT for 3 weeks, before testing [van Gisbergen et al., 1990,1991b]. 

A cracked specimen of transparent PVC is being tensile tested. Is it realistic to expect to see the craze at the crack tip with the naked eye The Kic value is 2.0 MN m and the craze stress (Jq = 60 MPa. Discuss whether the notched Izod impact strengths of 3.2 mm thick plastic sheet are of any value for design purposes. 

Notched Izod impact strength aiN is calculated from the absorbed energy W, related to the smallest initial cross-section area of the specimen at notch base ... 

Injection molded specimens were prepared according to ASTMD4101 methods. The specimens were tested for flexural modulus (MPa), tensile yield strength (MPa), tensile elongation at break (%), notched Izod impact (J/m), and HDT (°C). 

ASTM D-3763) (20). The notched Izod test is familiar to most workers in the plastics field. A standard notch is cut in a rectangular specimen. The specimen is broken by a dropping pendulum. The impact strength of the material is computed from loss of momentum of the pendulum. 

Izod impact strength 3.2-mm specimen, notched, J/m D252 22 41... 

Freitag and Reinking reported on the property profile of Bayer s commercial polyarylate [31], They observed that polyarylate was less sensitive to specimen thickness than polycarbonate in the notched izod impact test. They stated that polyarylate is quite similar to polycarbonate in hydrolytic degradation by alkalis, dilute acids, and hot water. The injection moldability... 

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