Bolted Joints Flashcards
What is the difference between a bolt, screw, and stud?
Bolt: threaded fastener with nut. Screw: forms its own threads. Stud: headless, threads both ends.
What are the main joint types?
Non-permanent (e.g., bolts, screws), permanent (e.g., rivets, welds, adhesives).
Why pre-tension bolts?
To prevent joint separation under load and reduce fluctuating stress to improve fatigue life.
How is bolt preload calculated?
For non-permanent: Fi = 0.75Asσp; for permanent: Fi = 0.9Asσp.
How is proof strength related to yield strength?
σp ≈ 0.85σy.
How is torque to pre-load a bolt calculated?
T = K·Fi·d, where K ≈ 0.2.
How is bolt stiffness (Kb) calculated?
Kb = ASE / lt, or combined with Ad and ld using spring series formula.
How is clamped member stiffness (Kc) calculated?
Kc = 0.5774πEd / ln[…], based on cone compression model.
What is a hard joint?
Joint where Kc»_space; Kb, reducing bolt stress and improving fatigue life.
How is load distributed in a bolted joint?
Based on spring model: Pb = Kb/(Kb+Kc)·P, Pc = Kc/(Kb+Kc)·P.
What is the formula for reserve factor?
n0 = P0 / P ≥ 1.5–2, where P0 is max allowable load.
What does excessive external load cause?
Bolt joint separation (failure).
How does a bolt joint behave under cyclic loading?
Fluctuating bolt load is reduced, and steady load increased with pre-tension.
What are the benefits of necked bolts?
Reduces stiffness without loss of strength, helping achieve hard joints.
What is the goal in pre-tensioned joint design?
Ensure preload prevents separation and fluctuating loads are minimized.
How do you determine bolt grade properties?
Using BS 3692 or ISO 898 markings, e.g., 8.8: σUTS = 800 MPa, σy = 640 MPa.
What assumptions are made for stiffness modeling?
Bolt and component as two springs in parallel (same δ).
How does preload affect fatigue?
Preload reduces fluctuation in bolt stress, extending fatigue life.
Why is a hard joint preferred?
Components take most of the load; bolt is less stressed.
What is the main requirement in bolted joint design?
Avoid joint separation under max external load.
