An-Najah Staff

The research study the end of the fibre after tensile tension fracture in the longitudinal direction, the micrograph reveals the tendency of Kevlar 49 to fibrillate. The loop test was performed to study the occurrence of cracks or Kinks in compression.The research also study the effect of compression was observed after performing the “elastic loop” test. The micrograph reveals deformation kinks without crack of the surface of the untreated fibres. Here the loop was stressed beyond its elastic limit, at which many buckles have appeared on the compression side of the loop, these buckles represent plastic deformation. This shows the fibres to be permanently kinked and the deformation is very large. For very large loop stress the permanent nature of the deformation is apparent from observing the buckles themselves.The micrograph reveals  deformation kinks and some separation of surface layer of the untreated fibre. The micrograph reveals also fibrillation after cracking the surface of the fibre and also a presence of internal cracks, crack propagation can readily occur parallel to the fibre longitudinal axis because this only requires rupture of H bonds.
The micrograph  reveals a light knot tied in Kevlar 49 fibre annealed annealed at (150°C). No tensile fracture occurs but there is an extensive  buckling on the inside  surface of the loop. The deformation kinks clearly appeared on the surface of the fibre, the degree of bulcking is very large after stressing the fibres. Fibrillation and separation of surface layers appear.The micrograph  reveals also irregular deformation kinks on the stained surface of the fibre heated at (400°C), for very large loop stresses the permanent nature of the deformation is apparent from observing the buckles themselves.  The micrograph  reveals also more separation of surface layer of Kevlar 49 fibre heated at (400°C), this is caused by the rupture of more H bond at high annealing temperatures.