Chapter 7.3 Joints

Question 1

which adhesion techniques we don’t use?

Answer 1

adhesives and welding

Question 2

stress variation around holes shows that in the elastic range the stress at the edge of holes is …

Answer 2

… as much as three times the average stress

in the plastic range the load tends to distribute uniformly over the remaining material

Question 3

joint types in aerospace

Answer 3

1. shear (in-plane) joint
2. tension (out-of-plane) joint (we don’t like this one)

Question 4

joint’s failure mechanism

Answer 4

1. tension failure (net section)
2. tension cleavage failure
3. shear-out failure
4. bearing failure (preferred)
5. fastener shear-off
6. fastener pull-through (rare)

Question 5

joints and aerodynamics

Answer 5

longitudinal skin joints are single shear lap joint

transverse skin joints are buttstraps

Question 6

requirements for joints

Answer 6

1. fitting factor: additional factor of 1.15 should be applied to all portions of the fitting including the fastening and bearing on the joined member (cheap, common)
2. no fitting factor: for joints made under approved practices and based on comprehensive data (expensive, as it requires lots of testing)
3. efficiency of a joing must be greater of equal to that of the parent structure
4. (in aerospace) all joints must be supported
5. every fastener should be installed wet (in sealant) to be airtight, and the fasteners and joints’ fits should not be mixed

Question 7

all airframe structural joints are …

Answer 7

… supported joint designs

Question 8

fastener selection

Answer 8

1. permanent fastenerss (rivets): head rivets, blind countersunk rivets, lockbolts
2. removable fasteners (screw bolts): used only in areas where replacing/disassembly of a component is highly probable