ELASTIC-MODULUS AND STRENGTH OF FIBROUS MATERIAL

As a rule, the large increase of elastic modulus with increasing draw ratio obtainable in highly‐drawn or extruded semicrystalline polymers is not reflected in a similarly large increase of strength. This is closely connected with the wellknown fact that with increasing plastic deformation one obtains fibrous material with decreasing strain to break. The axial elastic modulus is mainly caused by the taut tie molecules which bridge the amorphous layers between consecutive crystal blocks and thus provide an efficient axial force transmission through the sample. The defects at the ends of microfibrils interrupt this transmission because they contain few if any taut tie molecules connecting the end of microfibril with adjacent fibrillar elements. As a consequence of the small number of such ends, they only marginally reduce the elastic modulus. But as the mechanically weakest areas of the fibrous material, they drastically depress the strength. They fail as soon as the strain concentration upon them reaches their strain to break. The growth and coalescence of resulting microcracks finally lead to bulk fracture as the growing crack reaches critical dimensions. Copyright © 1979 Society of Plastics Engineers, Inc.