Freshman Engineering Clinic II, Section 2

Lab 2: Leonardo Da Vinci’s Tensile Tests (part 1 of metals in tension)

February 17, 2009

LEONARDO DA VINCI'S TENSILE TESTS (the following text taken from “LEONARDO DA VINCI'S TENSILESTRENGTH TESTS: IMPLICATIONSFOR THE DISCOVERYOF ENGINEERING MECHANICS” by JAY R. LUND, and JOSEPH P. BYRNECivil. Eng. and Env. Syst., Vol. 00, pp. 1 ± 8)

In his notebooks (CA, 82v-b) Leonardo Da Vinci describes an experiment for studying the tensile strength of wire, entitled, ``Testing the strength of iron wires of various lengths''. In the experiment, a wire of a given thickness and length was used to suspend a basket. The basket was filled slowly with sand, fed from an adjacently suspended hopper (Fig. 1). When the wire suspending the basket breaks, a spring closes the hopper opening, and the basket falls a short distance into a hole, so as not to upset the basket. The sand in the basket was then weighed to establish the tensile strength of the wire (Leonardo Da Vinci, 1972; Parsons, 1939).

Parsons' partial translation of Leonardo Da Vinci's text follows (1939): ``The object of this test is to find the load an iron wire can carry. Attach an iron wire 2 braccia long to something which will

firmly support it, then attach a basket or similar container to the wire and feed into the basket some fine sand through a small hole placed at the end of the hopper. A spring is fixed so that it will close the hole as soon as the wire breaks. The basket is not upset while falling, since it falls through a very short distance. The weight of sand and the location of the fracture of the wire are to be recorded. The test is repeated several times to check the results. Then a wire of 1/2 the previous length is tested and the additional weight it carries is recorded; then a wire of 1/4 length is tested and so forth, noting the ultimate strength and the location of the fracture''.

Purpose:

To perform an experiment similar to those of Da Vinci and determine the ultimate tensile strength of copper and steel wire and the influence of wire length on strength.

Materials:

  • 25 lb. Sand and additional weights
  • Weight buckets
  • Scoop
  • No.30 gauge (0.01 in.) steel wire
  • No.22 gauge (0.0253 in.) copper wire
  • No. 18 gauge (0.0403 in.) copper wire
  • Loading apparatus
  • Measuring tape
  • Duct Tape
  • C-Clamps
  • Wrench
  • Micrometer

Test Procedure:

  1. Measure 15, 30, and 60-inch lengths of each the copper and steel wire (1 braccia is approximately the length of the arm).
  2. Use the micrometer to measure the wire diameter at multiple locations.
  3. Take a 4-inch length of duct tape and tightly wrap around each end of each wire leaving the unwrapped portions of the wire with lengths of 15, 30, and 60 inches.
  4. Clamp each of the duct tape ends of one of the wire lengths as tightly as possible using a wrench if necessary.
  5. Suspend the wire in the test stand letting one end hang freely.
  6. Hang the bucket off the hanging clamp.
  7. Place weights in the bottom of the bucket and then slowly add sand to bucket until the wire breaks noting the location of the fracture and recording the weight of the bucket, sand, and freely hanging clamp. Note any other observations such as elongation of the wire.
  8. At least three samples of each length must be tested for each material.
  9. All groups will share the lab data resulting in 12 data points for each material of each length.

Report:

A written lab report is required at the start of class on Monday, February 23rd. The report is to be a team effort following the lab report guidelines and should be submitted with peer evaluation forms. Peer evaluations may also be emailed to Dr. Cleary.

At a minimum the report should address the following:

  1. The results section should show tabular or graphic presentation of the experimental results.
  2. Identify the experimental variables and indicate which of these had a discernable influence on the strength of the wires.
  3. Referring to the data, develop a theory for the strength of wires; the data from the copper wire tests may be helpful in this. Compare your theory to published strength data for copper and steel.
  4. Da Vinci concluded that the strength of a wire was reduced as length is increased. Did the experiments verify this? If not, suggest reasons Da Vinci could have found this trend.
  5. Stretch of the wires was not measured in this experiment although it may have been observed. Suggest a way it could be measured without use of electronic equipment.
  6. Feel free to address additional questions your group feels are important based on the experimental results.

References

Leonardo Da Vinci (1972) I Libri Di Meccanica, reconstructed from the original notes by

Arturo Uccelli, Kraus Reprint, Nendeln, Liechtenstein.

Parsons, William B. (1939) Engineers and Engineering in the Renaissance, MIT Press,

Cambridge, MA, 661 pp.