Effect of processing on fracture toughness and fatigue crack propagation in unplasticized polyvinyl chloride (uPVC)

The effect of processing on the fracture toughness and fatigue crack propagation rates in unplasticized PVC pipes, both along and perpendicular to the extrusion direction, is evaluated in this paper. The methylene chloride test is used to distinguish between well processed and poorly processed pipes. Well processed pipes have higher fracture toughness under monotonic loading test conditions. However, under impact conditions processing has no significant effects on notched Charpy fracture toughness. For the well processed pipes, there is no directional effect on the fatigue crack propagation rates. For the poorly processed pipes, fatigue crack growth is faster in the extrusion direction, but slight improvement in the processing level removes this difference. Generally, fatigue in the longitudinal direction is independent of the level of processing, but in the transverse (extrusion) direction it is quite sensitive to variations in processing.     

Nitrocarburizing of low-carbon unalloyed steel

Low-carbon unalloyed steel has been investigated after nitriding accomplished by either the salt-bath method (Tenifer) or the gas method (Nitroc). The resulting changes in the mechanical properties are reported in this paper, while changes in positron annihilation parameters are reported in Part 2. The mechanical properties show that the increase in both the lower yield stress and the ultimate stress is influenced greatly by the cooling rate after nitriding. A rapid cooling rate resulted in an increase of ～200 MPa while an increase of only 55 Mpa was observed for a slow cooling rate. These increases proved independent of prior straining in the range 0 to 20%, showing that the nitrogen uptake is not significantly influenced by internal defects. Annealing of rapidly cooled nitrided specimens resulted in a maximum of both the lower yield stress and the ultimate yield stress around 100° C. A transition from brittle to ductile fracture around this temperature was also observed. A large recovery of elongation to fracture was obtained after annealing at 140° C, which was not accompanied by any significant decrease in the lower yield stress. Dilatometer measurements indicated two precipitation stages, one around room temperature and another around 100° C.     

Involvement of residues 296-299 in the enzymatic activity of tissue-type plasminogen activator

The tetra-alanine substitution variant KHRR 296–299 AAAAof tissue-type plasminogen activator (t-PA) was previously shownto have enhanced fibrin specificity and enhanced activity inthe presence of fibrin compared with the wild-type form of themolecule. The structural requirements for these alterationsin enzymatic activity were investigated by constructing severalamino acid substitution variants at each of the positions from296 to 299 and evaluating their activities under a variety ofconditions. Effects on plasminogen activator activity were commonamong the point mutants at positions 296–299; nearly allhad a phenotype similar to the KHRR 296–299 AAAA variant.The greatest effects on enzymatic function were found with multiplesubstitution variants, but some single charge reversals andproline substitutions had substantial effects. The enhancedfibrin specificity of KHRR 296–299 AAAA t-PA results inless fibrinogenolysis than seen with wild-type t-PA. Approximatelyfour times greater concentration of KHRR 296–299 AAAAcompared with wild-type t-PA was required to consume 50% ofthe fibrinogen in human plasma.     

Mycotoxicosis in chicks produced by toxins from Phomopsis sp. or Diaporthe phaseolorum var. sojae

The possibility of producing toxic effects in day-old chicks with mycotoxins from Phomopsis sp. or Diaporthe phaseolorum var. sojae isolates was studied. Evidence was found that Phomopsis sp., but not Diaporthe, produces hepatic necrosis with high mortality in chicks. Enzymatically, the hepatotoxin produced by Phomopsis sp. caused an increase in the level of liver glucose-6-P dehydrogenase. Mycotoxicosis caused by Phomopsis sp. was compared with lupinosis.