My Saved Article|CONCLUSIONS
on the experimental program presented in this report, the following
conclusions were made:
Control (Hg-free) Specimens
- Differences in the performance of
Al-alloy 5083-0 were observed when mechanically tested in inert
environments (i.e. air, water, oil) and when exposed to Hg in the
presence of either air, water or oil. The material was subject to Hg
attack and liquid metal embrittlement (LME). This behavior was
manifested by embrittlement and reductions in the strength of the
material when tested in the form of either stressed 1T compact tension
(CT) specimens and pressurized pipe specimens.
- Maximum susceptibility to Hg attack was noted under
conditions of (a) prolonged load cycling of the pressurized pipe
specimen which produced the low failure pressures relative to similarly
cycled control (Hg-free) specimens, and (b) when surface wetting agent
was used to promote surface contact of the Al-alloy and Hg which
produced increased Hg attack, LME and strength loss.
- Acoustic Emission (AE) monitoring of both
CT specimens and pipe specimens was successful in observing
characteristic emission from most specimens. These emissions can be
characterized as indicated below:
Hg Contaminated Specimens
was observed to occur during periods of load or pressure increase.
emissions ware of highest amplitude during the onset of yielding and
- AE decreased rapidly during hold periods of
constant maximum load and were not observable during periods of partial
or total unloading or during hold periods following these unloading
- The Kaiser effect was exhibited indicating an
re-initiation of AE only after the maximum load or pressure from a
previous cycle was reached or exceeded.
- MONPAC severity
analysis of control specimens indicated maximum intensity in the
location of final fracture during pressure/load cycles corresponding to
yielding of the material.
- The AE
characteristics were more complex than those observed for the control
- Most specimens exposed to Hg exhibited an increase
in low amplitude AE over comparable control specimens.
- The low
amplitude AE was most prevalent during the initiation of the tests
during periods of low loads in the CT specimens or low pressure (<500
psi) in the pipe specimens. The AE was somewhat random but also
increased during hold periods following partial or total unloading of
- Higher amplitude AE appear to occur during hold
periods at maximum load in a particular loading cycle. By comparison,
this behavior was very limited and attenuated rapidly in the control
- The AE response was difficult to evaluate in terms
of Kaiser or Felicity effects. The AE described for Hg contaminated
specimens in Items b and c above resulted in emissions occurring at
loads and/or pressures less than the previous maximum. However, the
response could not be determined to be categorized as either Kaiser or
- MONPAC severity analysis for Hg-contaminated
specimens were difficult to interpret. However, maximum intensity index
occurred in the location of final fracture during load/pressure
corresponding to yielding of the material. However, significant
intensity ratings were obtained even at very low pressures (0 - 500 psi)
in pipe specimens.
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Effect of Metallurgical
and Environmental Variables Upon Acoustic-Emission Energy per Unit Area
of Crack Advance during Fracture of Three Steels
Nominal Chemical Composition and Tensile
Properties of Al-Alloy 5083-0
* = Minimum Values
+ = Maximum Values
Figure 1: Influence of electrochemical and mechanical factors in SCC
Figure 2: Embrittlement and non-embrittlement couple involving solid/liquid metals
Figure 3: Crack growth rates of Al-alloy 5083-0 in Hg at 75 F
Figure 4: Acoustic Emission (AE) aources in metals related to corrosion or
Figure 5: AE response during tensile strain of copper
Figure 6: Relationship between AE and crack growth rate (velocity) in Al-alloy during SCC.
Figure 7: Compact Tension (CT) fracture mechanics specimen
Figure 8: Aluminum pipe specimen with butt weld and internal backing ring
Figure 9: Schemctic of compact tension specimen test frame and AE monitoring
Figure 10: Setup for pipe tests with AE monitoring
Figure 11: Precracked Compact Tension and pipe specimens in contact with Hg