KovXcs and FErTtIAM [1] and Kov 93 and NAGY [2] derived an equation for the total equivalent mean shear strain ~ of a wire plastically twisted about its axis at constant tensile load. In this equation ~ consists of a torsional shear strain ND/L and the shear strain component equivalent to the associated tensile strain dL/L o, as follows:where N is the number of turns of twist, D is the diameter of the wire, L o and L ate the initial and instantaneous lengths of the wire, ~ and/~ are constants. KovAcs and FELTHAM [1] took the numerical values of ~ and fl to be 1/3 and 2.24, respectively, but they indicated that these values were underestimated because the mean torsional strain was evaluated on the assumption that the wire was purely elastic: they pointed out that GAYDON'S [3] assumption of ideal plasticity would be more appropriate. Recent work [4,5] has indicated that the values of ~ and fl are 2~/3 and 3, respectively. Eq. (1) can be written in the form:,JLILo = --(~I~)mblL + Ylt~ of C = --(~/~)e + y/~,where C = AL~Lo and O = ND/L.

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Technically pure aluminium-4.5 wtyo magnesium alloy samples are subjected to bidirectional twisting under various applied loads and a t different temperatures. The associated tensile strain is measured up to fracture of the test samples. It is realized that the investigated alloy exhibits superplastic behaviour under appropriate conditions of deformation. This behaviour is attributed to the relieve of internal stresses and recovery of the damage caused by the initial strain. A loss in superplasticity is found a t temperatures higher than 200 "C. Intergranular cracks are believed to be responsible for the observed decrease in ductility. Furthermore, a remarkable decrease in ductility values occurs when the investigated alloy is deformed in the temperature range 400 to 600 "C. This may result from the rapid onset of grain growth under these conditions.Unter verschiedener LuBerer Belastung und bei verschiedenen Temperaturen werden technisch reine Aluminium4,5 Crew% Magnesium-Legierungsproben einer doppeltgerichteten Verdrehung unterzogen. Die damit verknupften Dehnungen werden bis zum Bruch der Testproben gemessen. Es wird gefunden, dalj die untersuchte Legierung unter geeigneten Deformationsbedingungen superplastisches Verhalten zeigt. Dieses Verhalten wird der Entlastung innerer Spannungen und der Ausheilung von Storungen durch innere Verzerrungen zugeschrieben. Bei Temperaturen hoher als 200 "C wird ein Verlust der Superplastizitiit gefunden. E s wird angenommen, dalj intergranulare Spalten fur den beobachteten Abfall der Duktibilitat verantwortlich sind. Dariiberhinaus tritt ein merklicher Duktilitatsabfall auf, wenn die nntersuchte Legierung im Temperaturbereich von 400 bis 600 "C deformiert wird. Dies kann von dem plotzlichen Einsatz von Kornwachstum bei diesen Bedingungen herruhren.

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Cyclic torsion (twisting in a forward clockwise direction followed by twisting in the reverse direction) of high purity AI wires under the simultaneous application of a small tensile load (P) was found to increase the torsional ductility considerably. The number of twists in each direction (N) varied between 5 and 50 and P ranged between 0.1 and 0.78 kg mm -2 . The average shear strain (~) increased considerably as N and/or P decreased. Specimens with a fine grain size showed higher ductility than those with a coarse grain size. By suitable combination of N, P and grain size, ~ exceeding 3000%, indicating superplastic behaviour, was obtained. The accompanying electrical resistivity changes were small and did not exceed 1%. The results are discussed in terms of recovery mechanisms and possible dislocation interactions occurring during this complex mode of deformation.

The effect of extraneous deformation on the c r e e p curves has been extensively investigated. It s e e m s that extraneous deformation, under certain conditions, results in a decrease in the c r e e p rates, which is due, in general, to the increase in the induced internal s t r e s s e s /1 to 5 , ' .The aim of the present work, in which the literature s e e m s lacking, is to compare the effect of the type of pre-torsional deformation given at room temperature on the tensile c r e e p rate. The torsional deformation is c a r r i e d out either unidirectionally or bidirectionally.The material used is an aluminium dilute alloy containing 0.25 wt% silicon and 0.26 wt% zinc, in the form of wire samples (1 mm in diameter and of length 100 mm) .The effect of pre-torsional deformation on the tensile c r e e p rate is investigated at 300 OC and under an applied tensile s t r e s s of 3 kp/mm2. The examined alloy samples are subjected to tensile c r e e p tests under three different conditions: a) samples annealed at 350 OC for 3 h, b) one s e t of the annealed samples are subjected (while in place) to unidirectional type of torsion and given five twists (N = +5) before the c r e e p test, c) another set of the annealed samples are subjected to bidirectional type of torsion before the c r e e p test. The samples are given five turns of twist in the forward clockwise direction followed by an equal number of twists in the anti-clockwise direction (N = -+5).in Fig. 1 . It can be seen that the c r e e p strain a t any instance of time of predeformed samples is relatively low compared with those of annealed samples.The results of observations of the c r e e p strain-time relation are illustrated 1) Dokki, Cairo, Egypt.