Sentence:  Essentially these birefringence studies show that at low rates of <WSD>shear</WSD> a tension is present at 45 ` to the direction of shear , and as the rate of shear increases , the direction of the maximum tension moves asymptotically toward the direction of shear . 
Meaning of the word marked with <WSD> tags:  (physics) a deformation of an object in which parallel planes remain parallel but are shifted in a direction parallel to themselves