Embrittlement of amorphous Fe40Ni38Mo4B18 alloy by electrolytic hydrogen

The effects of hydrogen on the tensile properties and fracture processes at room temperature were investigated. Specimens were tested at various strain rates in air or under different cathodic charging-current densities. The slopes of the stress-strain curves were essentially identical for all the specimens, except that the fracture points varied under different test conditions. Macroscopically, hydrogen only affected the elastic deformation behavior, but microscopically, the embrittlement was caused by the heterogeneous nucleation of localized plastic deformation. The degree of hydrogen embrittlement increased as the charging current increased or as the strain rate decreased. With the same charging current and time, longer dynamic charging resulted in more severe embrittlement. Before fracture took place, the strength of the alloy could be completely restored if hydrogen had been removed. Hydrogen diffusivity and solubility were used to draw the time-dependent hydrogen concentration profiles for the specimens under different charging conditions. The difference in the mechanical properties was correlated with the hydrogen concentration within the specimen. Formerly Graduate Student, Department of Materials Science and Engineering, National Tsing Hua University.     

Cracking of amorphous Fe40Ni38Mo4B18 induced by static charging with hydrogen

Cracking in amorphous ribbon of Fe₄₀Ni₃₈Mo₄B₁₈ without external loading could be induced by cathodic charging with hydrogen in 0.1 N H₂SO₄ + 5 mg/L NaAsO₂. However, before cracking was initiated, the effect of hydrogen on the mechanical properties could be eliminated if hydrogen had been removed. A series of static charging experiments was carried out to study the cracking characteristics in this alloy. The diffusivity and concentration of hydrogen were obtained from both permeation and cathodic charging /thermal evolution experiments. The cause of cracking by static charging could be attributed to the build up of an internal hydrogen pressure around heterogeneous sites. The critical pressures for crack initiation were calculated based on the diffusivity and concentration data. Formerly Graduate Student, Department of Materials Science and Engineering, National Tsing Hua University     

Optimizing the mixture blending for castable aluminized plastic-bonded explosives

Castable aluminized plastic-bonded explosive (PBX) is a multiple components blending. To find an optimum mixture blending (formulation) for PBX to meet several required specifications is formidable. This is due to the fact that there are unlimited candidate formulations from which an appropriate one could be chosen. In general, trial and error type of engineering judgement is still the primary approach to reach the desired goal. This paper, however, employs a statistical approach named Mixture Experiments as well as an optimization routine called Eureka to find the optimum formulation, which meets five required specifications. Finally, two confirmation runs are performed. The results justify that the theroretical solution derived from the systematic statistical approach is indeed applicable.     

Technical Improvements for SEC Studies

An on-line system to measure hoop-strain of strain evaluation cylinders (SECs) has been developed. The experimental results compared with the data measured by intermicrometer are acceptable. A modified mathematical equation to calculate thermal expansion coefficient of propellant is proposed and gives excellent agreement in comparing with the data measured by thermomechanical analysis (TMA).