Interactive Periodic Table
COMMENTS:
Interactive Periodic Table
LINK:
TOPIC:
Chemistry
POSTED:
Oct 2018
While installing this low carbon steel fastener to its specified clamp load, a crack formed internally and propagated to the periphery of the head. While the specimen shown here was only cracked, other samples experienced fracture where the top 1/2 or 2/3 of the head completely separated. Improper head forging caused the wire to buckle as indicated by the grain flow seen here. Grains in the origin of the crack were plate like (plates perpendicular to the axis of loading) resulting in poor axial strength between grains. Fasteners that fracture like this are usually limited to low carbon steels or non-heat treated steels and are a result of an issue called adiabatic shear banding.
Pearlite and ferrite in steel plate.
SEM secondary electron image of a low carbon resulfurized steel (AISI 12L14) which fractured in bending when loaded perpendicular to the rolling direction. Failure mode is ductile dimple rupture matrix; also seen here are stringer inclusions which provides local weakness. This weakness is why the dimple rupture surrounding the inclusions is much larger as opposed to regions where stringers are not observed.
Quench crack with a depth of 0.65 mm originated at the root of a thread. MnS stringers can be seen running parallel the axis of the wire in the drawing direction.
Severe decarburization on a fastener thread crest and flanks, Nital etch. ASTM F2328 is the governing specification for determining if a carburization and decarburization is within allowable limits of inch series fasteners.
This sample displayed complex fatigue loading with abrupt changes to loading conditions, i.e. (1) high cycle low load unidirectional bending to (2) high cycle low load reversed bending to (3) low cycle high load reversed bending and finally (4) sudden fast fracture.
SEM secondary electron image of a beautiful example of inharently brittle material that failed from impact loading.
Award for contributions to Material Advantage.
AISI 304 stainless steel fasteners were used in H₂SO₄ environment and suffered heavy general and pitting corrosion. The 304 stainless steel flat washer was paper thin by the time maintenance was performed on the joint.
AISI 4140/4142 alloy steel (tensile strength, min = 125 ksi) exposed to hydrogen cyanide. The fasteners were coated with a thick blue PTFE which has excellent resistance to HCN attack. Either mechanical damage, or, pinhole openings in the coating permitted the HCN to corrode and ultimately participate in stress corrosion cracking.
I was honored to receive the James A. Thomas Presidents Leadership Award from Ms. Katharine Morgan, ASTM President. There were excellent leaders at ASTM, both staff and fellow members, that propelled me to excel. My success was a reflection of their guidance.