ME 6: Materials

Proof required

Link the public repo with 3.032 problem sets 3–4 (Fall 2007) and problem set 5 (Fall 2006) written up (a typeset PDF, LaTeX source or notebook), and show the self-check: which answers matched and how you fixed the ones that did not.

What gets checked

• Elastic constants carry units and sensible orders of magnitude.
• Anisotropic answers say which direction they apply to.
• Answers match the published solutions, and misses are reworked.

Common mistakes

• Answers copied from a solution with no working.
• Missing units, or a free-body diagram or sign convention left out.

Powstik Guide

A public write-up of 3.032 problem sets 3–4 (Fall 2007) and problem set 5 (Fall 2006), with the self-check shown.

Steps

1. Study the linked course material.
2. Solve the problems on your own first.
3. Check them against the self-check and rework the misses.
4. Typeset the write-up (LaTeX or a notebook) in a public repo.
5. Ask someone who knows the subject to check it.

README
ME 6: Materials, unit 1: Structure, elasticity and stiffness
Problems:
Self-check result (matched / reworked):
What I got wrong first and why:

What gets sent back

• No working shown.
• The self-check result is missing.

Resources

What a verifier looks for

• Elastic constants carry units and sensible orders of magnitude.
• Anisotropic answers say which direction they apply to.
• Answers match the published solutions, and misses are reworked.
• Is the engineering right, not just the final number?

You'll sign in first, then come straight back here.

Proof required

Link the public repo with 3.032 problem sets 5–6 (Fall 2007) and problem set 6 (Fall 2006) written up (a typeset PDF, LaTeX source or notebook), and show the self-check: which answers matched and how you fixed the ones that did not.

What gets checked

• Yield criteria are applied with stated stress states.
• Strengthening answers name the mechanism and its scaling.
• Answers match the published solutions, and misses are reworked.

Common mistakes

• Answers copied from a solution with no working.
• Missing units, or a free-body diagram or sign convention left out.

Powstik Guide

A public write-up of 3.032 problem sets 5–6 (Fall 2007) and problem set 6 (Fall 2006), with the self-check shown.

Steps

1. Study the linked course material.
2. Solve the problems on your own first.
3. Check them against the self-check and rework the misses.
4. Typeset the write-up (LaTeX or a notebook) in a public repo.
5. Ask someone who knows the subject to check it.

README
ME 6: Materials, unit 2: Plasticity, dislocations and strengthening
Problems:
Self-check result (matched / reworked):
What I got wrong first and why:

What gets sent back

• No working shown.
• The self-check result is missing.

Resources

What a verifier looks for

• Yield criteria are applied with stated stress states.
• Strengthening answers name the mechanism and its scaling.
• Answers match the published solutions, and misses are reworked.
• Is the engineering right, not just the final number?

You'll sign in first, then come straight back here.

Proof required

Link the public repo with 3.032 problem set 7 (Fall 2007) and problem set 7 (Fall 2006) written up (a typeset PDF, LaTeX source or notebook), and show the self-check: which answers matched and how you fixed the ones that did not.

What gets checked

• Fracture answers use the stress-intensity factor with the crack geometry stated.
• Creep answers name the mechanism and find its activation energy from the Arrhenius relation.
• Answers match the published solutions, and misses are reworked.

Common mistakes

• Answers copied from a solution with no working.
• Missing units, or a free-body diagram or sign convention left out.

Powstik Guide

A public write-up of 3.032 problem set 7 (Fall 2007) and problem set 7 (Fall 2006), with the self-check shown.

Steps

1. Study the linked course material.
2. Solve the problems on your own first.
3. Check them against the self-check and rework the misses.
4. Typeset the write-up (LaTeX or a notebook) in a public repo.
5. Ask someone who knows the subject to check it.

README
ME 6: Materials, unit 3: Fracture, fatigue and creep
Problems:
Self-check result (matched / reworked):
What I got wrong first and why:

What gets sent back

• No working shown.
• The self-check result is missing.

Resources

What a verifier looks for

• Fracture answers use the stress-intensity factor with the crack geometry stated.
• Creep answers name the mechanism and find its activation energy from the Arrhenius relation.
• Answers match the published solutions, and misses are reworked.
• Is the engineering right, not just the final number?

You'll sign in first, then come straight back here.

Proof required

Link the public repo with the raw data (or links to it), photos of the set-up, the analysis notebook and the predicted-vs-measured table with uncertainties (under 18 without an adult: a simulation of the same set-up, compared with published values), and a README that says how to rerun it and what limits the result.

What gets checked

• The raw counts for every clip are in the repo, with the wire diameter and each rod radius measured.
• The log–log plot and the fitted exponent with its uncertainty are shown and compared with published values.
• Scatter is reported (mean and spread per rod size) and its causes are discussed.

Common mistakes

• A result that nobody else can rerun from the repo.
• A table with no explanation of the gaps.

Powstik Guide

A measured low-cycle fatigue experiment: steel paperclips bent back and forth around rods of three diameters until they break, in a public repo.

Steps

1. Write down what you expect before you start.
2. Straighten the clips. Bend each one around a rod through 90° each way and count cycles to failure. One cycle is +90°, back through −90°, and back to straight. Use three rod sizes, such as a pen refill, a pencil and a marker, with at least five clips each. The rod sets the strain, not the angle: ε ≈ d/(2R + d), with d the wire diameter and R the rod radius. Plot strain amplitude against reversals to failure (2N) on log axes. The slope is the Coffin–Manson exponent; compare it with the usual −0.5 to −0.7. Explain the scatter with a statistic, not a guess. Hold the clip with pliers or a cloth: broken ends are sharp and the bend gets warm.
3. Fill the predicted-vs-measured (or hand-vs-simulated) table.
4. Explain every gap with a cause someone can check.
5. Write the README and ask someone who knows the subject to check it.

README
ME 6: Materials — Fatigue-test paperclips
What I expected:
How to rerun it:
Predicted vs measured:
Why they differ:
Safety: hand tools and eye protection only

What gets sent back

• No predicted-vs-measured table, or no uncertainties.
• Machine tools, welding, pressure vessels, combustion, or springs and flywheels storing dangerous energy without a trained supervisor.

Resources

What a verifier looks for

• The raw counts for every clip are in the repo, with the wire diameter and each rod radius measured.
• The log–log plot and the fitted exponent with its uncertainty are shown and compared with published values.
• Scatter is reported (mean and spread per rod size) and its causes are discussed.
• Check the engineering and the numbers, not just that it exists: do the units, the hand calculation and the table agree?
• Build photos show hand tools only and eye protection worn: no machine tools, welding, pressure vessels, combustion, or springs and flywheels storing dangerous energy (unless a trained supervisor and a proper workshop are shown).

You'll sign in first, then come straight back here.