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A fibre investigation can compare a defined breaking load under controlled conditions. Keep fibre source and preparation, gauge length between supports, moisture state, loading procedure and attachment method comparable. A failure at a damaged clamp is not necessarily representative of failure in the fibre material.
Video by Professor SNAB. Use the demonstration alongside this lesson’s specification reference and written explanations.
Viewing focus: Control fibre preparation and loading conditions
After watching, attempt these questions before opening the answers. You can also use the written lesson below.
After watching 1: What is required to convert breaking force to tensile stress?
The appropriate original cross-sectional area. Stress normalises force by area.
After watching 2: Why control gauge length and attachment?
They can affect the observed failure behaviour. A comparison needs consistent mechanical conditions.
What you'll be able to do
A fibre investigation can compare a defined breaking load under controlled conditions. Keep fibre source and preparation, gauge length between supports, moisture state, loading procedure and attachment method comparable. A failure at a damaged clamp is not necessarily representative of failure in the fibre material.
Use the approved apparatus, eye protection and handling arrangements for falling masses or snapped fibres. Add or apply load by the specified controlled method rather than using sudden shocks. Record the actual measured dimensions and the location of failure, with a predefined rule for dealing with an invalid clamp-slip result.
A hanging mass gives force F = mg when the stated static-load model applies. Tensile stress is force divided by the original cross-sectional area. Breaking force alone depends on how much material is present, so a thicker fibre can withstand a larger force while having a lower failure stress.
For an assumed circular fibre, area = πr². Convert dimensions consistently: 1 mm² = 10⁻⁶ m². Real fibres or bundles may not be circular or uniform, and including several fibres changes the area interpretation. State the geometrical assumption and measurement uncertainty rather than reporting excessive precision from an uncertain diameter.
Repeat with appropriately independent fibres and compare distributions, not only the largest successful load. Plant source, extraction damage, knots, water content and biological variation can affect results. A force increment limits how precisely the breaking threshold is known.
Relate the measured mechanical behaviour to the supporting structure of fibres, including thick walls where appropriate, without inferring exact wall composition from a force result alone. A controlled comparison can support material selection, but processing, length, durability and other properties also affect practical use. Report whether the result is a load, force or area-normalised stress.
Attempt these problems on paper before opening the worked reasoning. Explain your steps as well as giving a final answer.
Common mistakes to avoid
Key takeaways
Question 1: Fibre A breaks at 0.50 N over 0.10 mm²; fibre B at 0.80 N over 0.20 mm². Compare stresses.
A has the higher estimated breaking stress despite B’s higher breaking force.
Check the assessed scope and practical or mathematical requirements.
An external explanation or interactive activity to use alongside the lesson. It may include extension material.
Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.
Test yourself
Answer a few questions, then review anything you missed.
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.