Experiment 2: Torsion Test
Investigation of shear stress, shear strain, and modulus of rigidity.
Objectives
- To determine the Modulus of Rigidity (Shear Modulus), G of different materials.
- To determine the Shear Yield Stress, τy and Ultimate Shear Stress, τu.
- To observe and analyze the fracture pattern of ductile and brittle materials under torsion.
- To understand the relationship between Applied Torque (T) and Angle of Twist (θ).
Real World Application [Image of drive shaft in car transmission]
Torsion testing is critical for designing drive shafts, axles, twist drills, and screws. Any component that transmits rotational power is subject to torsional loading. Understanding how a material behaves under twist ensures safety in automotive and aerospace transmissions.
Safety Precautions
- Ensure the specimen is securely tightened in the chucks before applying load.
- Do not exceed the maximum capacity of the torsion testing machine.
- Wear safety goggles; brittle materials may shatter explosively upon fracture.
- Keep hands away from the rotating chucks during operation.
Theory of Torsion
For a solid circular shaft subjected to a twisting moment (Torque, T), the stress distribution is defined by the Elastic Torsion Formula:
Where:
- T = Applied Torque (N·m)
- J = Polar Moment of Inertia (m4)
- τ = Shear Stress at radius R (MPa)
- R = Radius of shaft (m)
- G = Modulus of Rigidity (GPa)
- θ = Angle of twist (radians)
- L = Length of shaft (m)
Key Equations:
1. Polar Moment of Inertia (J):
For a solid shaft of diameter D:
2. Max Shear Stress (τmax):
Maximum stress occurs at the surface:
Fracture Modes
Ductile Material (e.g., Mild Steel)
Fails in Shear. The fracture surface is flat and perpendicular to the axis of the shaft (transverse plane).
Brittle Material (e.g., Cast Iron)
Fails in Tension. Maximum tensile stress occurs at 45°. The fracture forms a characteristic 45° helical/spiral shape.
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1. Select Specimen
2. Run Test
Press & HOLD to apply torque. Release exactly at the limit!
Test Results
Waiting for test run...
Mission Target
Select a material...
Experimental Procedure
1. Specimen Details
Polar Moment of Inertia (J)
-
mm⁴
2. Recorded Data
| Torque (Nm) | Angle (°deg) |
|---|
3. Results
Modulus of Rigidity (G)
-
GPa
Max Shear Stress
-
MPa
Slope (T / θ)
-
Nm/rad
MEQ491 Laboratory Report Rubric
Use this rubric to self-audit your torsion test report before submission. Scroll horizontally on smaller screens to view all performance bands. Note that Item 4 and Item 5 carry double weight (×2).
| Item | Score 5 (Excellent 9-10) | Score 4 (Good 7-8) | Score 3 (Satisfactory 5-6) | Score 2 (Poor 3-4) | Score 1 (Very Poor 0-2) |
|---|---|---|---|---|---|
| 1. Appearance & Organisation | All sections sequence perfectly; diagrams/pages intact; layout clean with clear headings; only minor spelling or grammar slips neatly corrected; front cover fully completed with tape/ring binding and custom typed cover; submitted as a single PDF when required. | Sections ordered with generally good formatting; pages tidy, no tears; occasional spelling or grammar issues; one front-page detail missing (not title/name); tape or ring bound though minor formatting lapses. | All sections present but formatting rough; some torn pages; organisation uneven yet readable; multiple language errors with strike-through corrections; two non-title/name details missing; stapled without full binding or cover branding. | Sections out of order with messy formatting; inserts damaged; frequent language errors and white-out; more than two details missing including title or names; poorly stapled with minimal organisation. | Meets most "Poor" conditions or report absent. |
| 2. Objectives & Theory | All objectives rephrased clearly in original language; detailed paragraph linking torsion theory to prior knowledge or related coursework; integrates relevant external sources beyond the manual. | Objectives identified though phrasing could be sharper; prior knowledge paragraph present; mainly paraphrases the manual with some new wording. | Objectives partially identified and loosely stated; heavy reliance on manual text with limited original phrasing; some prior knowledge mentioned. | Objectives unclear or missing; minimal relevant prior knowledge offered; theory largely copied verbatim. | Meets most "Poor" conditions or content absent. |
| 3. Apparatus & Procedures | Complete equipment list with labelled torsion apparatus diagrams; numbered step-by-step procedure in own words; safety points highlighted and safety report submitted with photo evidence. | Vital items listed with minor omissions; procedure mostly paraphrased with diagrams where appropriate; safety report attached but photo evidence missing. | Partial equipment list with key items missing; steps unclear, unnumbered, or copied directly; diagrams absent. | Equipment largely missing; procedure confusing or unusable; no supporting diagrams. | Meets most "Poor" conditions or content absent. |
| 4. Results, Calculations & Graphs (×2) | Accurate, well-organised torque-angle data showing trends clearly; all figures/tables numbered, labelled, and captioned; units consistent; full calculation walkthroughs including G, τmax, and J with sample workings. | Correct data but trends less obvious; figures/tables largely labelled with units; only minor calculation gaps or missing examples. | Some data missing or disorganised; figures/tables incomplete or inconsistently labelled; several calculations absent or incorrect. | Most data missing or unreliable; figures poorly constructed without labels; calculations largely absent or incorrect. | Meets most "Poor" conditions or content absent. |
| 5. Discussion (×2) | Addresses every question accurately; explains trends, compares data, and links outcomes to torsion theory and objectives; analyses errors, their impact, and mitigation strategies. | Misses one question but remaining answers clear; minor gaps in trend interpretation; notes errors and effects. | Misses two questions or answers inconsistently; partial understanding of data-story link; errors mentioned without depth. | Misses multiple questions; little or incorrect interpretation; no meaningful error discussion. | Meets most "Poor" conditions or content absent. |
| 6. Conclusions | Summarises key torsion data supporting conclusions; states whether objectives were achieved with validity commentary; addresses experimental errors and proposes improvements. | Missing one "Excellent" element. | Missing two "Excellent" elements. | Missing three or more "Excellent" elements. | No conclusion provided. |
| 7. References | More than nine sources across journals, books, and reputable online media; >=30% published within the last five years; formatted exactly as specified in the lab manual. | Six to eight sources from varied media; manual formatting observed. | Three to five sources drawn from at least two media types; formatting partially compliant. | One or two sources cited; formatting requirements ignored. | No references supplied. |
Attendance Rule:
Absent students receive 0% for the report. Students who conduct the experiment but fail to submit a report earn a maximum of 10%.
Test Your Knowledge
Select the correct answer for each question.