Impact behavior Strength

Comparison of mechanical and processing properties with morphology shows that the formation of a network structure is the desired morphology for high impact strength, low viscosity and low shrinkage as indicated in Figure 6 for the impact behavior.12... 

An important corollary to impact behavior of reinforced thermoplastics is shown in Figure 6. Two different ABS resins are used for this illustration relating to low temperature impact strength retention. The unreinforced ABS will retain from 20-30% of its room temperature impact strength in going to — 20°F. The graphs for both the low and high... 

As obvious from Fig. 3a, the flowability of the resins has a strong influence on their impact behavior at room temperature assessed by their Charpy double edge-notched impact strengths (ISO 179/lfA). As expected, for both non-nucleated and -nucleated series, a higher molecular weight favors the resistance to crack propagation due to the high density of inter- and in-... 

We can predict the impact behavior, namely impact strength and fracture mode, over a wide range of temperatures independent of specimen size by using standard specimens. 

Blends of PC/PET/TPU with EVAc-GMA and optionally MBS or ABS, have good flexural modulus, strength, weld line strength, solvent resistance, and impact behavior [Laughner, 1994]. PC blends with a polycaprolactone-polyurethane resin, TPU Pellethane , and either MBS or MBA showed similar behavior [Henton et al., 1993]. 

Geometry of a toughened plastic specimen also influences the impact strength and its mode of failure. The specimen s length, width and thickness may affect the fracture behavior. Whether the specimen is notched or not, as well as the dimensions of the notch may also influence the impact behavior [Kinloch and Young,... 

Commercial impact modified PPE/PA blends exhibit notched Izod impact strengths ranging from 175 to 500 J/m at room temperature. They also differ in their ductile brittle transition temperature and low temperature impact behavior. The type of nylon used (PA-6 or PA-66 or copolymer type), its end group concentrations and molecular weight, and more importantly, the nature of the rubber modifier used (compatible... 

The ranking of the materials with regard to impact strength is seen to be influenced by the test temperature. Thus, at room temperature (approximately 20°C) polypropylene is superior to acetal at subzero temperatures (e.g., — 20°C) polypropylene does not perform as well as acetal. This comparison pertains to impact behavior measured with a sharp (0.25-mm) notch. Note that notch sharpness can influence the impact strength variation with temperature quite significantly. Figure 3.39 shows that when a blunt (2-mm) notch is used, there is indeed very little difference between acetal and polypropylene at 20°C, whereas at — 20°C acetal is much superior to polypropylene. 

This temperature is defined as the value at which the impact strength of the material with a sharp notch (1/4-mm tip radius) is 10 kj/m (4.7 ft-lbf/in ). When quoted, it provides an indication of the temperature above which there should be no problem of brittle failure. However, it does not mean that a material should never be used below its Tb (1/4), because this temperature, by definition, refers only to the impact behavior with a sharp notch. When the material is unnotched or has a blunt notch, it may stiU have satisfactory impact behavior well below Tb (1/4). 

Other environmental factors besides temperature may also affect impact behavior. For example, if the material is in the vicinity of a fluid which attacks it, then the crack-initiation energies may be reduced, resulting in lower impact strength. Some materials, particularly nylon, are significantly affected by water, as illustrated in Figure 3.40. The absorption of water produces a spectacular improvement in the impact behavior of nylon. 

Finally, creative combinations of low-cost fillers in various forms allow reduced resin content without reducing desired properties. Blends of small and large particles of the same filler material, or blends of plate-like filler particles and coarse filler, help limit the filler s most extreme, unwanted effects on stiffness, strength, or impact behavior. For example, platy talc, mica, or kaolin day in a PO provides stiffness enhancement, which complements the strength properties provided by fiber-shaped wollastonite or the more forgiving impact properties of spherical caldum carbonate partides [7-6]. 

The impact behavior of PP is affected by CNTs. Seo et al. [32] found that the notched Izod impact strength of PP was improved by about 20% upon the addition of lwt% of... 

The residual strength and impact behavior of the fiber/matrix on carbon fiber reinforced metal laminates has been studied [130,131]. 

More important for practical applications is the impact behavior of the composite. The correlation of unnotched impact strength with fiber elrmgatimi is depicted in Fig. 18.16. A correlation coefficient as high as 0.97 is found, which is the best value in this series. A slightly lower correlation (coefficient 0.82) is found for single fiber elongation and notched Charpy impact strength. 

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. 

In addition, it is foimd that moisture increases the intensity of the relaxation and reduces its activation energy, as well as decreases the peak height of the Y relaxation with little change in activation energy. The decrease in y intensity has been referred to as an antiplasticization effect, since it is associated with an increase in modulus and decrease in impact strength. This is discussed further below in reference to impact behavior. The increase in intensity has been associated with the motion of water molecules H-bonded with carbonyl and amide groups about the H-bond axis (84,90). 

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