Fatigue transparent

Polycarbonates are used in optics, transparent technical parts, aesthetic applications and protection devices for their transparency, mechanical properties, impact resistance, rigidity, good creep behaviour, fatigue resistance, insulating properties, dimensional stability, low moisture uptake, broad range of service temperatures (-100°C up to -i-135°C),food contact and sterilization possibilities for suitable grades. 

Good mechanical and electrical properties rigidity fair creep behaviour fatigue resistance low moisture absorption broad range of continuous use temperatures -60°C up to 130°C UHF transparency. 

Good thermo-mechanical, chemical and electrical properties rigidity gamma irradiation resistance UHF transparency good creep resistance and fatigue behaviour low moisture uptake low shrinkage heat behaviour fire resistance low coefficient of thermal expansion. 

For non-transparent specimens, as shown by Bucknall and Stevens useful information relative to the deformation mode can be obtained by recording hysteresis loops as a function of cycles. Figure 6 shows hysteresis loops obtained at 0.2 Hz at various N values for PS tested at a stress amplitude of 24.1 MPa and Fig. 7 for HIPS tested at 17.2 MPa. For PS, with Nf = 1,451 cycles, there is no detectable change in loop area at this stress amplitude up to the final cycle. This illustrates the highly localized nature of the fatigue-induced damage zone in PS and indicates that, for this polymer, hysteresis loop observations are not an effective method for detecting craze... 

Ccmipared to many thermoplastics, PVDF has excellent resistance to creep and fatigue. Yet in thin sections such as films, filament and tubing PVDF components are flexible and transparent. The dynamic mechanical spectrum of KYHAR PVDF in Figure 3 shows that its dynamic modulus of elasticity (E ) is high and decays only gradually as the temperature is increasing. 

These materials have higher stiffness than PAEK between Tg of the PAEK and Tg of the sulfone or etherimide. The performance of the PAEK can be improved by adding reinforcing fibres but there remain some applications in which this performance window is critical. Since they are amorphous they undergo less shrinkage on cooling and this leads to better dimensional tolerance and stability. They are also relatively transparent. However, amorphous resins tend to have much lower chemical resistance, inferior fatigue performance and will lose useful properties immediately above Tg. These limitations of amorphous resins mean that it is usually obvious when a PAEK is required. 

PC Better transparency Higher toughness and modulus Higher continuous use temperature Higher cost and density Notch sensitive Lower fatigue resistance... 

A typical material selection involves many properties which are not easily quantifiable in numerical terms (such as weathering, warpage, surface finish, ease of machining, etc.) or which may have very obscure units (such as transparency, fatigue, wear. 

Crystallinity is an important consideration in injection molding because of the impact of a part s crystalline eontent on its properties and appearance. Most polymers are semicrystalline, meaning that there is a relatively large volume increase as the polymer melts and becomes entirely amorphous. After a part has been molded, the rate at which it is cooled (the speed of cooling the part) will determine the extent of its recrystallization. For example, flex fatigue life and transparency increase when crystallinity decreases. Mechanical strength and various moduli increase at higher crystallinity. 

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