MECH180 Strengths of Materials Lab #6

Test of a Bolted Joint

OBJECTIVE:

Determine the optimum size bolt for connecting two plates to produce the strongest possible joint.

PROCEDURE:

1. Measure samples and calculate the predicted capacity of each join. See discussion on calculations.

2. Place the samples in the flat grips of the testing machine. If samples tend to slip, rough up the gripping surfaces of the plates with a chisel.

3. Apply the tensile load slowly and record the maximum load capacity and mode of failure of each joint and a solid bar.

4. If jaws stick, do not strike them or the handles with a hammer.

Note: for Bolt ratings see appendix

DISCUSSION:

There are three possible types of failure:

1. The bolt may shear.

2. The plate may fail in tension at its weakest point.

3. The plate (or bolt) may fail in bearing (a piece may tear out of the plate).


DISCUSSIONS:

The maximum load capacity for each type of failure can be calculated since S=P/A or load P=A*S where S is the maximum unit stress for the material and type of loading.

The joint will fail when the weakest case above is reached. Therefore, the predicted load at failure will be the smallest load of the three cases.

The joint efficiency is defined as the (percent) ratio of the actual load carrying capacity of the joint as compared to the load carrying capacity of a solid (continuous) plate.

INITIAL DATA:

Assembly / Nominal
Bolt
Diameter / Actual Bolt Dia.
Root/Shank / Plate Width / Plate
Thickness / Diameter
of hole / Edge
Distance
Joint 1 / 1/2
Joint 2 / 5/8
Solid Bar / XXXXX / XXXXX / XXXXX / XXXXX

PREDICTED RESULTS:

Joint / A
Maximum
Tensile
Load of
Plate at Hole / B
Maximum
Shear Load
of Root/Shank / C
Maximum
Shear
Tear Out
Load / Mode of
Failure of Joint
(A, B or C) / Maximum
Load / Maximum load of solid plate / Predicted joint
efficiency
#1
#2

ACTUAL DATA & RESULTS:

Joint / Maximum
Load of Joints / Description
of fracture / Maximum Load of Solid Plate / Actual Joint Efficiency
#1
#2

QUESTIONS & CONCLUSIONS:

1. Did each joint fail as predicted? If not, explain why.

2. How accurate were your predicted joint efficiencies? Give the % Diff. for each.

3. State two reasons that could justify % Diff. (from question 2) in this experiment.

4. Based on your initial data, was edge split a possible mode of failure? Why?

5. Would using higher-grade bolts affect the results for either joint #1 or joint #2? Explain

6. Using the same grade bolts, would you recommend either a 9/16 diameter or 11/16-diameter bolt to increase the joint efficiency for either joints #1 or #2? Why?

7. If you could purchase any size bolt for the same price, what would you use as the optimum size bolt?

Appendix A Bolt Data

Test of Bolted Joints.docx Page 4 of 4