5456-H116 Plate ST Cracking
5456-H116 Plate ST Cracking
(OP)
5456 H116 - 2" plate is fabricated in to a hinge that is part of a welded structure. The system has operated in the marine environment for 15 years. There has been several cases this cracking issue. There is machinery close to the structure that vibrates at 21 and 84 Hz.
The hinges are cracking (multiple) in the Short Transverse (ST) plane. The cracks are perpendicular to primary load axis and are propagating on planes parallel to the rolled surfaces of the material which implies environmentally enhanced cracking due to ST loads. Fracture surface appears to exhibit a combination of crystallographic chemical attack, fatigue, and ductile mechanical overload. ASTM-G67 Mass Loss is low (<15mg/cm2) indicating the material is not sensitized.
Fractography photos are attached
Does anyone have information on 5456 ST fatigue or recommendations of how to procede with analysis the cracks? Would tensile testing in the ST direction provide useful data for modeling the structure?
The hinges are cracking (multiple) in the Short Transverse (ST) plane. The cracks are perpendicular to primary load axis and are propagating on planes parallel to the rolled surfaces of the material which implies environmentally enhanced cracking due to ST loads. Fracture surface appears to exhibit a combination of crystallographic chemical attack, fatigue, and ductile mechanical overload. ASTM-G67 Mass Loss is low (<15mg/cm2) indicating the material is not sensitized.
Fractography photos are attached
Does anyone have information on 5456 ST fatigue or recommendations of how to procede with analysis the cracks? Would tensile testing in the ST direction provide useful data for modeling the structure?





RE: 5456-H116 Plate ST Cracking
Nice pictures regarding the fracture surfaces. However,has there been a proper failure analysis performed by a competent metallurgical lab? If not, this is your first step in determining a root cause.
RE: 5456-H116 Plate ST Cracking
They said, "Fracture surface appears to exhibit a combination of crystallographic chemical attack, fatigue, and ductile mechanical overload" and the plate is non-Isotropic.
Since the loading in the plane of the cracking is low (the hinge should be free to rotate) I am trying to understand where to go next in the metallurgical analysis and FEA model. Looking at the 5456 in saltwater 10**8 cycles the allowable is ~3 ksi. Should I have them do the tensile testing in the ST direction?
RE: 5456-H116 Plate ST Cracking
I suspect sensitization occurred along the grain boundaries, and an ASTM G67 test would prove it. Sensitization of the magnesium-rich phase would also render a preferred path for fatigue crack propagation even under low stress conditions.
RE: 5456-H116 Plate ST Cracking
A tiny bit of corrosion, not enough to detect in G67, and then enough fatigue to open a slight crack, then a little more corrosion.....
I would look at the the non-homogeneous properties, especially the ST.
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Plymouth Tube
RE: 5456-H116 Plate ST Cracking
RE: 5456-H116 Plate ST Cracking
I am not sure of what use tensile testing will provide in your analysis. If the hinge failed after 15 years under low stress or strain amplitude service conditions, and it appears to be environmental-assisted cracking (which is a catch-all phrase for SCC or fatigue or corrosion fatigue), you can either change the material to a more corrosion resistant grade of Al, or modify the hinge geometry to avoid any resonance vibration.
RE: 5456-H116 Plate ST Cracking
RE: 5456-H116 Plate ST Cracking
RE: 5456-H116 Plate ST Cracking
A sketch of the part and the loading vectors would be helpful.