Fracture tests of uncharged and hydrogen-charged single edge bend specimens of additively manufactured 304 stainless steels are simulated with the cohesive zone modeling (CZM) approach. Two-dimensional plane strain finite element analyses without cohesive elements are conducted to identify the values of cohesive energy. Similar analyses using CZM with the trapezoidal traction-separation laws are then conducted. The best-fit cohesive parameters reflect the values of cohesive strength for the uncharged specimens are higher than those for the hydrogen-charged ones whereas the value of cohesive energy for the uncharged specimens can be either slightly lower or higher than that for the hydrogen-charged ones.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Kelvin probe force microscopy for high-resolution imaging of hydrogen in steel alloys [Poster]

Kelvin probe force microscopy (KPFM) was used to image and co-locate the presence of hydrogen in stainless steel (SS) with microstructure. Various SS samples were investigated, including forged, welded, LENS® fabricated, and pinch welded materials. KPFM images the local work function of a surface as a function of spatial position using atomic force microscopy. KPFM is capable of delivering high spatial (~10 nm) and potential (~5mV) resolution maps characterizing the microstrucure and the locally varying work function of surfaces. Hydrogen segregated at the surface of SS increases the local work function by either reducing tensile strain or by reducing the chemical potential of surface species. In a process known as hydrogen embrittlement, hydrogen segregates to and becomes trapped at extended defects (e.g. dislocations, boundaries, pores) which leads to the initiation of cracking and can result in structural failure. Hydrogen storage necessitates a proper understanding of the mechanisms of hydrogen embrittlement in SS. Developing advanced characterization techniques for hydrogen embrittlement is critical to identify long term solutions for materials exposed to hydrogen. Current techniques of observing hydrogen embrittlement involve mechanical testing, and optical microscopy with low resolution. Advance microstructural imaging techniques capable of resolving features down to the nanometer scale are needed. KPFM provides high resolution imaging for the characterization and development of SS components for hydrogen storage.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2017

SNL/SRNL Joint Project on degradation of mechanical properties in structural metals and welds for GTS reservoirs

The objective of this project is to measure the hydrogen-affected fracture properties of structural welded metals exposed to hydrogen isotopes. The main goal of FY16 was to evaluate low-temperature effects on fracture properties of stainless steel welds pre-charged with hydrogen. Forged stainless steels consisting of 316L, 304L, and 21-6-9 welded with 308L filler metal were pre-charged and tested at 223 K at select displacement rates to evaluate fracture behavior over the lower STS temperature range. Reductions in fracture thresholds were observed for all stainless steel welds when samples were precharged with hydrogen; however, temperature effects were not observed in the 304L and 21-6-9 welds. Only 316L exhibited enhanced degradation at 223 K. In addition to fracture testing, tensile specimens were extracted from the weld region and tested at 296 K and 223 K in the hydrogen pre-charged condition. A slight increase in yield strength was measured in the pre-charged condition at 296K and 223 K for the three different welds. A reduction in total elongation of 3-11% was observed at 296 K, whereas reductions in total elongation from 50-64% were observed at 223 K. Microhardness and ferrite numbers were measured in the weld regions to try to elucidate the factors affecting fracture. Lastly, in collaboration with Savannah River National Laboratory (SRNL), weld and heat-affected zone bend specimens extracted from forged 304L and 21-6-9 stainless steel were supplied to SRNL and are in the final stages of sample preparation for subsequent tritium exposure, aging, and fracture testing. The collection of testing completed and planned between Sandia and SRNL contributes to the development of a comprehensive database of properties for materials as a function of hydrogen-isotope concentrations.

36 MATERIALS SCIENCE↗

NASA NTRS2003

The Single Nucleotide Polymorphism Consortium

I want to discuss both the Single Nucleotide Polymorphism (SNP) Consortium and the Human Genome Project. I am afraid most of my presentation will be thin on law and possibly too high on rhetoric. Having been engaged in a personal and direct way with these issues as a trained scientist, I find it quite difficult to be always as objective as I ought to be.

Morgan, Michael↗

NASA NTRS1993

Flight data for the Cryogenic Heat Pipe (CRYOHP) Experiment

This paper presents the flight test results and data correlation for the Cryogenic Heat Pipe Flight Experiment (CRYOHP). CRYOHP is a Hitchhiker Canister experiment that was flown aboard the shuttle Discovery (STS-53) in December of 1992. Two different axially grooved oxygen heat pipes were tested to determine their startup behavior and transport capability in micro-gravity. Three startup cycles were conducted with each heat pipe and transport data was obtained over the range of 60 K to 140 K. Startup in flight was repeatable but slower than observed in ground tests. The transport data shows good agreement with the theoretical model. The CRYOHP test bed, which incorporates five Stifling cycle refrigerators to provide the cryo-cooling, performed as predicted and offers a good micro-gravity test bed for cryogenic thermal devices.

Brennan, Patrick J.↗

NASA NTRS1992

Performance of the Cryogenic Heat Pipe Experiment

The Cryogenic Heat Pipe (CRYOHP) Experiment has been designed to test two cryogenic heat pipes independently in a micro-gravity environment. The CRYOHP experiment is manifested for flight aboard the shuttle (STS-53) which is scheduled for launch in November, 1992. This paper presents the design of this experiment and the thermal vacuum verification test results. A correlation of the test data and the planned mission operations are also provided.

Brennan, Patrick J.↗