FE Other Disciplines Practice Question Solution included after investigation
CASE E-100 · FE

The Stronger Material That Made the Heavier Tie Rod

Material A had the higher yield strength, but its density penalty was much larger. After sizing both rods to the same factor of safety, Material B produced the lighter design.

▶ INTERACTIVE CASE FILE • 5–10 MIN • CLICK TO INVESTIGATE

Inspect, commit, prove, fix, and sign off.

Case E-100 engineering failure visual
HOW THIS WORKS

Think like
a real engineer.

Follow the investigation process used in the field — in five guided steps.

1

Inspect

Review the problem, diagram, and evidence.

2

Commit

Choose your hypothesis.

3

Prove

Run calculations and test your idea.

4

Fix

Select and validate a safe correction.

5

Sign Off

See the full debrief and key takeaways.

Case Brief

SAME PRINCIPLES. HIGHER STANDARDS.
PROBLEM STATEMENT

A 1.0 m tie rod must carry 60 kN in tension with factor of safety 2 against yielding. Material A has yield strength 300 MPa and density 7800 kg/m³. Material B has yield strength 240 MPa and density 2700 kg/m³. Neglect connection mass. Determine the minimum required area and mass for each material and select the lighter design.

Materials Other Disciplines Design Verification Root Cause Analysis Safe Correction
E-100
INVESTIGATION WORKSPACE WORK THROUGH THE CASE — YOUR CHOICES MATTER.
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DEBRIEF (LOCKED)

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Find the root cause, confirm the fix, and see how this connects to the exam.

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CASE CLOSED · ENGINEERING VERDICT

What actually failed — and what should change.

What failed

Highest yield strength was treated as the only selection criterion.

What was missed

Density strongly affects member mass.

Corrected model

Size by allowable stress, then compare rho A L or use strength-to-density as a screening metric.

QUICK ANSWER

With FS=2, Material A needs 400 mm² and has mass 3.12 kg. Material B needs 500 mm² but has mass only 1.35 kg, so B is the lighter strength-compliant choice.

ENGINEERING TAKEAWAY

For a tension member sized by allowable stress, mass is proportional to rho/sigma_allow, so strength and density must be considered together.

CASE QUESTIONS

Questions this case should settle.

What screening metric helps minimize mass in a strength-limited tie rod?

For common geometry and safety factor, maximize yield strength divided by density.

NEXT FE PRACTICE QUESTION

The Wire That Had 0.17 Ohm, Not 170

Materials · 5–10 min

Continue Practice →
WHAT YOU’LL LEARN

Real failures. Lasting skills.

Each case is designed to build the judgment, analysis, and confidence you need for engineering exams — and beyond.

  • Apply core engineering concepts to real-world problems
  • Practice structured troubleshooting and analysis
  • Strengthen exam-ready thinking through realistic scenarios
COMMON QUESTIONS
Do I need prior knowledge to use these cases?

Basic subject familiarity helps, but every case is designed to teach through the investigation itself.

How long does a case take?

Most cases are designed for a focused 5–10 minute investigation.

Are the cases aligned with engineering exams?

Each case is mapped to a verified exam, subject, topic, and misconception before publication.

What happens after I complete a case?

The sealed debrief unlocks with the root cause, corrected reasoning, fix, and takeaway.