LINES OF NO FINITE LONGITUDINAL STRAIN
The plot of 1+e1 orÍl1(against 1+e2 or Íl2. When e1 and e2 are both zero, the aterial will remain undeformed. If bothe e1 and e2 negative but equal, there is only volume loss but no distortion. If both e1 and e2 positive and equal, there is volume gain but no distortion. If bothe e1 and e2 are negative but not equal, the material is decreased in volume as well as distorted the example being cross folds or dome and basin structures formed by constrictional deformation. If both e1 and e2 positive but unequal, it implies the volume increase as well as distortion, the geological situation being boudinage which may be irregular or chocolate tablet type with breaking in two subperpendicular directions. If e1 is positive and e2 negative, there is no change in volume (as far as this plot is concerned ) and the folds may develop whose limbs are boudinaged by +ve e1 and the folding itself is suggestive of -ve e2. Or, folds may develop breakage or extension joints perpendicular to their hinges. What structures form will depend on whether e1 lies parallel to fold hinges or perpendicular to their hinges but within the axial planes of folds. The circle smaller in diameter shows e1=e2 both -ve. The circle larger in diameter shows e1=e2 both positive. Where ellipse lies outside the circle is the field of extension in all directions leading to overall irregular or chocolate boudinage. Where ellipse lies inside the circle is the field of prolate deformation with development of domes and basins. Where circle cuts the ellipse is the field of both folding and boudinage but no area change.
If e1=0 and e2<0 then then the point falls on 1+e1=unity line, implying there is only folding and no boudinage. If e2=0 and e1>1 then it implies that there is no folding but only boudinage.
LINES OF NFLS, PROJECTIONS FOR ELLIPSOIDS