Investigation on Rheological Properties and Storage Stability of Modified Asphalt Based on the Grafting Activation of Crumb Rubber

Acrylamide with a double bond and amide group can not only copolymerize with macromolecules of crumb rubber but also react with acidic groups in asphalt, so it was selected as a modifier to activate crumb rubber through chemical graft action. The purpose is to improve the compatibility between crumb rubber and asphalt and thus improve the rheological properties and storage stability of rubber asphalt. Infrared spectroscopy (IR) and scanning electron microscopy (SEM) were used to characterize the crumb rubbers and their modified asphalt. It was found that the crumb rubber of grafting acrylamide had better compatibility in asphalt due to its larger specific surface area and chemical reaction with asphalt. In addition, the high temperature rheological test, low temperature creep test, and polymer separation test were carried out to study the effect of grafted activated crumb rubber on the properties of modified asphalt. The results showed that compared with modified asphalt with common crumb rubber (CRMA), the rheological properties and storage stability of modified asphalt with grafting activated crumb rubber (A–G–R) were improved significantly. The results of microscopic and macroscopic tests show that the activated rubber particles have a larger contact area with asphalt due to a rougher surface and the chemical cross-linking between rubber particles and asphalt further strengthens their interaction. Therefore, there is a relatively stable blend system formed in modified asphalt, and its performance of modified asphalt has been improved.

Model of corrosion cracking of irradiated austenitic steels. Part 1. Analysis of damage mechanisms and formulation of the defining

Mechanisms having a potential effect on irradiation assisted stress corrosion cracking (IASCC) of austenitic steels in the LWR environment have been analyzed. Based on the analysis and generalization of reference and original data on IASCC, an IASCC initiation criterion has been formulated. Conditions for grainboundary microcrack propagation by IASCC mechanism have been formulated. The nature of low-temperature creep of irradiated austenitic steels has been considered, constitutive equations have been derived. Relying on the formulated criterion of grain-boundary microcrack nucleation and the derived creep equations, an IASCC initiation model has been developed. The model allows one to predict the dependence of the threshold stress σIASCC th on neutron dose and also to calculate the IASCC initiation time with stresses exceeding σIASCCth .

Investigation of In-service Creep Failures of Aircraft Ti-6Al-4V Bolts

Three Ti-6Al-4V bolts from mid-life jet aircraft failed during service operation. Each of the failed bolts were installed on a landing gear component. Metallurgical failure analysis indicated that the fracture mechanism is low temperature creep, possibly resulting from a sustained tension load over a long time. Visual inspection revealed ductile fracture morphology with no macroscopic deformation or corrosion. For all bolts fracture occurred close to the root at the first pitches of the thread. Scanning Electron Microscope (SEM) analysis revealed dimple morphologies with micro-void coalescence. Energy Dispersive X-Ray (EDX) analysis did not reveal any material deficiency that would have precipitated failure.