THE INFLUENCE OF STRESS HISTORY ON THE PLASTIC POTENTIAL

Abstract

THE EXPERIMENTAL PROGRAMME CONSISTED OF TESTS CARRIED OUT ON POWDERED SLATE DUST (REGARDED AS SILTY CLAY) AT CONSTANT STRESS RATIO WHERE THE VALUE OF THE STRESS RATIO WAS CHANGED TO A NEW VALUE DURING THE TEST, THE STRESSES THEN BEING FURTHER INCREASED. THE DIRECTION OF THE STRAIN INCREMENT VECTOR WAS INVESTIGATED. DEVIATIONS OF THE STRESS PATH FROM A CONSTANT STRESS RATIO (INVOLVING ROTATIONS OF THE STRESS INCREMENT VECTOR AND POSSIBLE ROTATIONS OF THE STRAIN INCREMENT VECTOR) ARE NOT COVERED. IT IS SHOWN THAT STRESS HISTORY HAS A CONSIDERABLE EFFECT ON THE DIRECTION OF THE STRAIN INCREMENT VECTOR AND THIS EFFECT IS VERY PERSISTENT EVEN WITH A SUBSTANTIAL RISE IN THE STRESS LEVEL. A COMPARISON OF THE PLASTIC POTENTIAL FOR THREE STRESS HISTORIES SHOW THAT THEY APPEAR TO EXHIBIT 'KINEMATIC' BEHAVIOUR. TWO POSSIBLE METHODS OF INTERPRETING THE RESULTS, WHICH MAY BE USED TO PREDICT STRESS-STRAIN BEHAVIOUR ARE PRESENTED. THE FIRST METHOD SUGGESTS THAT THE PLASTIC POTENTIAL IS ELLIPTICAL, AND SYMMETRICAL ABOUT AN AXIS THAT LIES BETWEEN THE STRESS SPACE DIAGONAL AND THE ORIGINAL STRESS PATH. THE SECOND METHOD SUGGESTS THAT THERE IS A SIMPLE RELATION BETWEEN THE DIRECTION OF THE NEW STRESS PATH AND THE DIRECTION OF THE STRAIN INCREMENT VECTOR.