Izod impact tests Mechanical testing

In Section 6.8, a detailed analysis of the most frequently used impact tests (i.e., Charpy and Izod impact tests) is used to characterize fracture toughness. Temperature, strain rate, crack tip curvature, specimen thickness, annealing, aging, irradiation, and environmental effects are discussed as test variables using the Iramework of fracture mechanics. 

Zhou and co-workers [27] studied the effect of surface treatment of calcium carbonate with sulfonated PEEK on the mechanical properties of the polymer. Tests used included tensile tests, flexural tests, notched Izod impact tests, TGA, DSC and SEM. The modulus and yield stress of the composites increased with CaCOs particle loading. This increase was attributed to the bonding between the particles and the PEEK matrix, was proved by the SEM of the tensile fracture surface of the composites. The treated fillers were found to give a better combination of properties, which indicated that the sulfonated PEEK played a constructive role in the calcium carbonate/PEEK composites. 

Multiphase polymers are commonly toughened plastics which contain a soft, elastomeric or rubbery component in a hard glassy matrix or in a thermoplastic matrix. An example of the typical brittle fracture morphology of an unmodified thermoplastic is shown by SEM of nylon (Fig. 5.45A). Addition of an elastomeric phase modifies the brittle fracture behavior of the matrix, as shown in a fracture surface of a modified nylon (Fig. 5.45B). The modification depends on the composition and deformation mechanism of the material [204, 215], but normally it increases the fracture toughness and strength from that of the unmodified matrix resin. Impact strength, as measured for instance by an Izod impact testing apparatus, is affected by the dispersed phase... 

Dynamic Mechanical Analysis determines the elastic modulus (storage modulus), viscous modulus (loss modulus) and damping coefficient (Tan 5) as a function of temperature. The test specimens dimension was 3 mm X 13 mm x 20 mm and was the same for those used in the Izod impact test but without a notch. The test specimens were clamped between the movable and stationary fixtures, and then enclosed in the thermal chamber. The frequency, amplitude, and a temperature range of25-220°C were set-up for the material. The analyzer applied torsional oscillation to the test sample while slowly moving through the specified temperature range of 25-220°C. 

FIGURE 10.2 Mechanical failure tests (a) tensile test on dumbbell specimen (b) tensile test on ring specimen (c) notched crescent and trousers tear specimens (d) Izod impact test machine (Data from HaUinan, A. J., Jr., J. Qual. Tech., 25, 85, 1993) (e) motor-driven brittleness temperature tester. (Data from Book of Standards, ASTM, Baltimore, MD, 1958, 286,356.)... 

ANALYSIS OF THE CHARPY AND IZOD IMPACT TESTS USING FRACTURE MECHANICS... 

In recent years impact testing of plastics has been rationalised to a certain extent by the use of fracture mechanics. The most successful results have been achieved by assuming that LEFM assumptions (bulk linear elastic behaviour and presence of sharp notch) apply during the Izod and Charpy testing of a plastic. 

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]. 

Impact Testing (Nonins t rumen ted). Because the Izod impact is a failure test, some scatter of data is expected. Reasons for this scatter include the presence of weak domains, mechanical anisotropy, and any variability in test conditions. Extreme care was taken to maintain constant test conditions. To increase the reliability of the results, 10 test pieces of each sample were tested and the average was calculated. 

This action eliminates the need for a costly mechanical roughening process that most other materials require. The depositing of a metal surface on plastic parts can increase environmental resistance of the part, also its mechanical properties and appearance. As an example a plated ABS part (total thickness of plate 0.015 in.) exhibited a 16% increase in tensile strength, a 100% increase in tensile modulus, a 200% increase in flexural modulus, a 30% increase in Izod impact strength, and a 12% increase in deflection temperature. Tests on outdoor aged samples showed complete retention of physical properties after six months. 

Since several different wear characteristics were noted for the materials tested (e.g.y charring, flow, and brittle behavior), it can be inferred that there is no unique mechanism associated with impact wear of polymer thin films. Further, because of this aspect and the probability that the same mechanisms do not occur under impact testing conditions (Charpy and Izod), it is reasonable to infer that there is little correlation between impact wear resistance and impact strength. This latter point may be illustrated by considering polycarbonate. Even though it has the highest impact strength of any unfilled polymer (4), it exhibits the poorest wear behavior in this study. 

However, the kind of technique used to mold these blends seems to be important in determining their mechanical properties. In fact, mechanical tests carried on injection molded samples [37] show, with respect to compression molded samples, a significant enhancement of the energy to break for all samples (Tables 20.2 and 20.3). Moreover the addition of 10wt% of SEBS to an 80 20 wt% sPS/HDPE blend involves in the injection molded samples an increase in both the energy at break and the Izod impact strength, whereas in the thermo-compressed samples no improvement is observed. Differences between compression and injection molded samples are widely acknowledged [38] and... 

Mechanical Properties. The mechanical properties of the selected blends studied, including the results of tensile, Izod impact, and falling-weight impact tests, are summarized in Table I. Generally, lower-than-expected toughening efficiency (especially for Izod impact) and data scattering were obtained because it is hard to maintain consistent moisture content of the specimens (especially for blends in which PA is the major component). The presence of the compatibilizer in all the blends resulted in consistent and substantial improvement in properties (Nos. 2, 3, and 4 vs No. 1, and No. 20 vs... 

Mechanical tests were carried out in a laboratory where the temperature was maintained at 25°C using a Universal Testing Machine, LR-50 K (LLOYD Instrument, England) at a crosshead speed of 50 mm/min and 98 mm as gauge length. Stress at break, strain at break, work of rupture, and initial modulus were determined as per ASTM standards. Izod notched impact test specimens were... 

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. 

Newman and Williams (1978) carried out sharp-notch Charpy tests for ABS at 193 < T(K) < 333 and showed that linear elastic fracture mechanics was applicable only up to 233 K. Above 273 K, the energy absorbed in impact was proportional to the fi"acture area and correlated well with the volume of the whitened zone. Mixed behavior occurred at the intermediate temperatures. More detailed study of the notched Izod impact behavior of ABS was carried out using instrumented... 

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