Stress and fatigue analysis of SVI-tested camshaft lobes

Nondestructive evaluation techniques were employed to fully characterize three 2.3L camshafts tested in an engine simulator for an equivalent of 100,000 miles. Optical microscopy, acoustic microscopy (SAM), and profilometry were used to characterize wear and fatigue, crack depth, and surface roughness, respectively. Results show cracking to occur mainly in the opening ramp of the most abusively ground cam lobes. No clear evidence was found for subsurface cracking at depths as great as 200 μm from the lobe's surface. Profilometry results show no evidence of any major tribological effect due to the sliding friction of the follower. Fractography studies show a difference between fracture surfaces among the cracks examined; straight cracks exhibit features resembling fatigue propagation, while fracture surfaces from pitted cracks show a more brittle behavior. Small grinding cracks (approximately 300 μm in length) were found in the opening ramps of the most abusively ground lobes prior to testing. Knoop and Nanoindenter microhardness indicate a near-surface rehardening for the most abusively ground lobe (confirmed by metallography), and temper burn for the remaining lobes. X-ray residual stress results made in the opening ramp of the tested lobes show evidence of residual stress relaxation. X-ray line width data as a function of depth does not correlate with residual stress.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Materials Science and Engineering

Department dc:contributor.department

Materials Science and Engineering

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

1996

Author dc:creator

• Escobar, Jose Alejandro

Chair dc:contributor.committeechair

• Hendricks, Robert Wayne

Committee members dc:contributor.committeemember

• Landgraf, Ronald W.
• Kampe, Stephen L.
• Reynolds, William T. Jr.

• fracture surfaces
• fatigue engine testing
• rolling contact stress
• fatigue life prediction
• grinding residual stress
• camshaft lobes
• thermal damage

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Dc Identifier Other

etd-38431826109623300

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/36656