CFS Joint Design & Load Calculations 3

Question 1

The 'separation load' (Ps) in a preloaded bolted joint is the external tensile load at which:

Accepted Answer

The joint faces begin to separate (clamp load = 0)

Answer

Separation occurs when the external load reduces the compressive stress between joint members to zero, eliminating clamping force.

Question 2

Using the Shigley joint diagram approach, what percentage of an external tensile load is carried by the bolt in a well-designed preloaded joint?

Accepted Answer

A small fraction determined by Kb/(Kb+Km)

Answer

The bolt takes only the fraction Kb/(Kb+Km) of the external load because the compliant clamped material absorbs most of it.

Question 3

Which thread form has a 60° flank angle and is the most common in US industrial fastener applications?

Accepted Answer

Unified National (UN/UNC/UNF)

Answer

The Unified National thread with its 60° flank angle is the dominant fastener thread form in the United States for clamping applications.

Question 4

In a bolted joint subjected to fatigue loading, which design change most effectively reduces the alternating stress in the bolt?

Accepted Answer

Decreasing bolt stiffness (longer grip, reduced shank diameter)

Answer

A more compliant bolt takes a smaller fraction of the alternating external load, reducing the amplitude of cyclic stress and improving fatigue life.

Question 5

What does the 'k factor' (nut factor) represent in the torque-tension equation T = k × F × d?

Accepted Answer

An empirical coefficient combining all frictional and geometric effects

Answer

The nut factor k ≈ 0.1–0.2 for typical lubricated bolts is an empirical constant that lumps thread friction, under-head friction, and geometry into a single multiplier.

(CFS) Certified Fastener Specialist Practice Test

(CFS) Certified Fastener Specialist Practice Test

CFS Joint Design & Load Calculations 3