Loss of Toughness

Additionally, the instrumented impact showed that even though the acrylic is called impact-modified, it is only so relative to unmodified acrylic. Interestingly, its impact properties start off at about where unprotected PECT copolymer ends up after 3 months of exposure when it has severely embrittled. 

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Bromine compounds are often used as flame retardant additives but 15-20ptsphr may be required. This is not only expensive but such large levels lead to a serious loss of toughness. Of the bromine compounds, octabromo-diphenyl ether has been particularly widely used. However, recent concern about the possibility of toxic decomposition products and the difficulty of finding alternative flame retarders for ABS has led to the loss of ABS in some markets where fire retardance is important. Some of this market has been taken up by ABS/PVC and ASA/PVC blends and some by systems based on ABS or ASA (see Section 16.9) with polycarbonates. Better levels of toughness may be achieved by the use of ABS/PVC blends but the presence of the PVC lowers the processing stability. 

The mechanical properties of wood are hardly affected by acetylation. There is no embrittlement since there is no three-dimensional resin network the hydroxyls are replaced by acetyl groups. There is no loss of toughness, and the wood is very resistant to attack by fungi, termites and marine organisms. 

Finally, hydrogen in relatively small amounts can lead to cracking, especially as the strength increases. If the presence of hydrogen cannot be adequately lowered by the ladle treatment, combinations of low carbon and silicon, inclusion shape control, and more than 0.25% copper can be helpful in minimizing loss of toughness. 

Reactive blending of PPE/SBS with dioctylamine CRNI To improve resistance to loss of toughness upon thermal cycling Richards Pickett, 1995... 

The influence of physical aging on the comparative and intrinsic toughness of PEEK and PPS carbon-fiber composites was determined by Ma et al. [1992]. Both types exhibited a loss of toughness with increase in aging time and temperature. The PEEK composites tended to retain more impact toughness but after aging were less ductile than the PPS composites. 

It must be added that some situations which favour the loss of toughness with passing time are not easily measured during operation. For example, even if the maximum Ni content in base metal and welds is specified to less than 1 per cent, it cannot be avoided that the Ni percentage in the vessel material adjacent to the stainless steel liner reaches values up to 4-5 per cent. 

The differences in toughness between the as-fired YAG and N-phase samples are consistent with the predicted differences in the thermal expansion mismatch strains at the whisker/matrix interfaces in the composites. The subsequent loss of toughness after heat treatment may be due to the formation of. strong interfacial bonds after the long-term thermal exposure. Additional analysis is currently underway to identify the specific mechanisms which control the composite properties. 

Forming. Ti-6Al-6V-2Sn is readily formable in the annealed condition. For sheet or plate, it is generally used in the annealed condition, although the alloy is capable of heat treatment to higher strength levels with some loss of toughness. When Ti-6Al-6V-2Sn sheet and plate are hot formed at... 

Finely distributed carbon black in a concentration of 1.5 to 2 wt.% provides by far the best UV protection. However, at this load, a slight loss of toughness may occur and thermal-oxidative resistance is reduced. That is why a lower concentration, e.g., 0.5 wt.% is used in many cases. 

This macroscopically detected loss of toughness is explained by the reduction of all deformation zones in the total volume. It is caused by the change that occurs in polycarbonate subsequent to annealing below its glass transition temperature ductile deformation zones (shear bands, homogeneous deformation zones) are replaced by strongly localized deformation zones and fibrillated crazes [768]. 

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