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 Fatigue & Failure Theories 48 Flashcards |
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What is the progressive structural damage from cyclic loading called? |
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Fatigue |
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True or False: Most mechanical failures in service are due to fatigue. |
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True |
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Calculate mean stress when σmax = 80 ksi and σmin = 20 ksi. |
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50 ksi |
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Which approach is best for high-cycle fatigue analysis? |
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B) Stress-life |
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The S-N curve plots stress amplitude versus _____. |
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Number of cycles to failure |
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What is the typical endurance limit ratio for steel? |
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0.5 × ultimate tensile strength |
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True or False: Aluminum alloys have a distinct endurance limit. |
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False. They have fatigue strength at specific cycles. |
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Which factor accounts for surface roughness in endurance limit calculation? |
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B) ka |
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What happens to notch sensitivity when q = 0? |
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Material is insensitive to notches, Kf = 1 |
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Calculate Kf when Kt = 2.5 and q = 0.8. |
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2.2 |
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Which mean stress theory is most conservative? |
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B) Soderberg |
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In fatigue analysis, stress concentration affects only _____ stress component. |
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Alternating |
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What does Miner's rule predict when D ≥ 1.0? |
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Fatigue failure occurs |
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True or False: Low-cycle fatigue involves primarily elastic deformation. |
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False. It involves significant plastic deformation. |
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Which theory is most accurate for ductile materials under static loading? |
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C) von Mises |
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Calculate von Mises stress when σ₁ = 60, σ₂ = 30, σ₃ = 0 MPa. |
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52.9 MPa |
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What does the maximum shear stress theory predict for ductile failure? |
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Failure when τmax = Sy/2n |
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True or False: Brittle materials should be analyzed using maximum normal stress theory. |
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True |
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In fracture mechanics, what does Y represent in K = Yσ√πa? |
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Geometry factor |
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When does crack propagation occur according to fracture mechanics? |
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C) K ≥ KIc |
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What is the load factor kc for torsional loading? |
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0.59 |
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True or False: Temperature factor kd equals 1.0 below 450°C. |
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True |
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Calculate reliability factor ke for 99% reliability requirement. |
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0.814 |
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Paris law describes the rate of _____ under cyclic loading. |
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Fatigue crack growth |
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