Low notch sensitivity

Polyarylate It is a form of aromatic polyester (amorphous) exhibiting an excellent balance of properties such as stiffness, UV resistance, combustion resistance, high heat-distortion temperature, low notch sensitivity, and good electrical insulating values. It is used for solar glazing, safety equipment, electrical hardware, transportation components and in the construction industry. 

Notch sensitivity n. The extent to which a material s tendency to fracture under load, particularly an impact load, is increased by the presence of a surface in homogeneity such as a notch or sharp inside corner, a sudden change in section thickness, a crack, or a scratch. Low notch sensitivity is usually associated with ductility, while brittle materials exhibit higher notch sensitivity. Most engineers and physical testers consider the notched Izod and Charpy impact tests to be as much measures of notch sensitivity as they are of pure impact strength. 

FIGURE 2.15 Influence of temperature on Izod impact strength of various polymers of low and high melt indexes. GMT 61 is a low-melt-index and low-notch-sensitivity polypropylene copolymer. KMT 61 is a high-melt-index and low-notch-sensitivity polypropylene polymer. HDPE 65045 is a high-melt-index and high-notch-sensitivity high-density polyethylene. 

Arguably, the most remarkable property of polycarbonate Is its very low notch sensitivity in thin sections. As thickness goes up, the notched Izod impact goes down, PBT/PCO blends exploit this behavior effectively, ameliorating the notch sensitivity which is a drawback of plain PBT. These blends also Improve other mechanical properties over those of the base polymer, especially stiffness and heat deflection temperature. Of course, there Is no "free lunch" here either, but the price is modest - Increased creep with PCO content, associated with an apparent drop in the glass transition temperature [24]. 

All polymers have some degree of notch sensitivity. The polycarbonates are outstanding in having very low notch sensitivity. The notch sensitivity of polysulfones can be eliminated by proper part design, that is by using generous radii or fillets to prevent stress concentration. 

The use of PC—ABS blends has grown significantly in the early 1990s. These blends exhibit excellent properties, particularly low temperature ductihty, reduced notch sensitivity, and ease of melt fabrication. The blend morphology (229), ABS composition, thermal history (215), PC content and molecular weight (300), processing conditions, etc, all affect the mechanical behavior of PC—ABS blends. These blends have been most frequently used in automotive and other engineering appHcations. 

Low notch toughness high notch sensitivity rapid, running failures below DBT. 

Polycarbonates with superior notched impact strength, made by reacting bisphenol A, bis-phenol S and phosgene, were introduced in 1980 (Merlon T). These copolymers have a better impact strength at low temperatures than conventional polycarbonate, with little or no sacrifice in transparency. These co-carbonate polymers are also less notch sensitive and, unlike for the standard bis-phenol A polymer, the notched impact strength is almost independent of specimen thickness. Impact resistance increases with increase in the bis-phenol S component in the polymer feed. Whilst tensile and flexural properties are similar to those of the bis-phenol A polycarbonate, the polyco-carbonates have a slightly lower deflection temperature under load of about 126°C at 1.81 MPa loading. 

Block copolymers of polycarbonates and silicone polymers have also been commercially marketed (e.g. Makrolons KU 1-1198 and KU 1-1207). These block copolymers show a marked increase in toughness at low temperatures coupled with reduced notch sensitivity. (They show little improvement in toughness at normal ambient temperatures.)... 

Notch sensitivity Effect of low temperature Maximum transition temperature ( O... 

The Izod impact test may indicate the need to avoid inside sharp corners on parts made of such materials. For example, nylon and acetal-type plastics, which in molded products are among the toughest materials, are notch-sensitive and register relatively low values on the notched Izod impact test. 

The mechanical properties are good with medium to low elongations at break and more limited strains at yield. Moduli and hardnesses are in a high range but notched impact strengths are in a medium range. Polyetherimide displays notch sensitivity and stress concentrators must be avoided when designing. 

Low carbon steels can be notch sensitive and susceptible to brittle fracture at ambient or low temperatures. Therefore, only fully killed, normalized steels made to fine grain practice are acceptable. The use of steel made to a coarse austenitic grain size practice (such as ASTM A515) is prohibited. 

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