Gear 3 Flashcards
What are common forms of gear failure?
Bending fatigue, pitting, micropitting, scuffing.
What causes bending fatigue in gears?
Cyclic bending stress at the tooth root.
What is pitting in gears?
Surface damage from cyclic contact stress.
What is scuffing in gears?
Adhesive wear caused by poor lubrication and high-speed contact.
What are the two main gear stresses?
Bending stress at the root and contact stress on the face.
What is Lewis’ bending equation used for?
To estimate maximum bending stress assuming tooth as a cantilever.
What is the simplified formula for bending stress using geometry factor?
σb = Wt / (YmF)
What equation estimates contact stress?
Hertzian contact stress: σc = sqrt[(Wt / (F cosϕ)) × elastic and geometry factors]
What is the AGMA bending stress equation?
σ = Wt·Ko·Kv’·Ks·KH·KB / (m·F·YJ)
What is the AGMA contact stress equation?
σc = sqrt[(Wt·Ko·Kv’·Ks·KH·ZR·ZI) / (dp·F·Ze)]
What is Ze in AGMA contact stress?
Elastic coefficient based on materials’ Young’s modulus and Poisson’s ratio.
What is the AGMA allowable bending stress formula?
σall = σFP / (SF·YN·Yθ·YZ)
What is the AGMA allowable contact stress formula?
σC,all = σHP / (SH·ZN·ZW·Yθ·YZ)
What should be done if calculated stress > allowable stress?
Iterate design: adjust module, face width, or material.
What is YJ in gear design?
Geometry factor accounting for bending strength and stress concentration.
What is ZI in gear design?
Geometry factor for contact strength.
What does ZN account for in AGMA?
Life (cycle) factor for allowable contact stress.
What are key AGMA safety/reserve factors?
SF for bending, SH for contact (typically 1.5–2).
How is transmitted load calculated in gear analysis?
Wt = (60,000 × P) / (π·d·n)
True or False: Contact stress arises due to bending moment at gear root.
False
