Polycarbonate fatigue

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. 

Property Summary Nylons are recommended for general-purpose gears and other mechanical components. Acetals for maximum fatigue life, for highly accurate parts, or exposure to extremely humid conditions. Phenolic-fabric laminates for low-cost, thin stamped gears or parts. Polycarbonates for intermittent, very high impacts (not recommended for applications involving repeated cyclical stress). TFE-filled acetals for heavy-duty applications. 

A significant improvement in the administration of a lipid-containing emulsion was achieved with a special additive to PC. As shown in Fig. 22b, the improved behavior of the new polycarbonate PC2 proved in practice to be verifiable by fracture mechanical fatigue crack growth experiments. In the presence of the fat emulsion the more lipid-resistant PC2 shows a higher fatigue threshold value AK as well as an improvement by a factor of two in AKcf in comparison to PCI used so far. 

Fig. 1. A short fatigue crack in polycarbonate showing the development of its first epsilon CTPZ ...

When polymers slide on machined metal surfaces, it is quite possible that steady-state wear Involves a combination of abrasive, fatigue, and adhesive wear mechanisms. To study fatigue wear, it would be desirable to minimize the contributions of the abrasive and adhesive wear modes. In this paper, the following polymers polycarbonate, polyvinyl chloride, ultra-high molecular weight polyethylene, siloxane modified epoxies, and polylmldes are tested in experiments in which the fatigue wear mode is predominant. 

Addition of a small amount of core-shell toughening particles of 0.3 pm diameter to a polycarbonate/copolyester blend reduced the fatigue crack propagation rate by a factor >20 and gave rise to significantly more plastic deformation during fitacture [134]. 

Fig. 4.77 Fatigue curves of polycarbonate using regular specimens, specimens with three mm hole as stress concentrator and dynamic weldline under alternating load conditions cjctai [O60ss].

Fatigue strength in alternating range of unreinforced and reinforced polycarbonate [12Els]. 

F igure 1.30. Relationship of fatigue crack growth rate per cycle in several polymers as a function of range of stress intensity factor AK, which is a measure of the range in stress concentrated at the crack tip during cyclic deformation (Hertzberg et ai, 1973). PVF, polyfvinylidene fluoride) PMMA, poly(methyl methacrylate) PC, polycarbonate PS, polystyrene. 

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