Question

(Materials Testing Results)

Q: The 30% rubber group reported a strain at yield of 0.38 and a strain at break of 0.3. Please explain this change.

Answer 1

If a material is taken beyond the yield point (it is deformed plastically) and the stress is then released, the material ends up with a permanent strain. The amount of elastic strain that it will take before reaching the yield point is called elastic strain recovery. But as the rubber tries to regain its original length. But, as it has already crossed the yield point it is in the plastic deformation zone. Yielding started at 0.38. But after fracture the rubber will have both ends of fracture to regain some of its original length. The length compromised by rubber after fracture is greater than the yielding limit by 0.08. So, the final length after fracture is less than yield. And also, there a stress being applied at yield limit, but there won't be any stresses acting after fracture. This gives rubber to recover the length.