Aris Phillips

The effect of loading path on the yield surface at elevated temperatures

Abstract The results of an experimental study of yield surfaces of pure aluminum at elevated temperatures from 70 to 305°F are presented. Several prestressing paths in σ-τ space are used. On the basis of these results a new law of hardening is formulated. In addition it is shown that the yield surfaces do not pass through the prestress points and that even at a relatively small prestress the yield surfaces do not enclose the origin.

YIELD SURFACES AND LOADING SURFACES - EXPERIMENTS AND RECOMMENDATIONS

Abstract The concepts of yield surface and loading surface at room temperature and elevated temperature are discussed and experimental results on pure aluminum in support of these concepts are presented. Recommendations for future experimental research are presented.

A Theory of viscoplasticity

Abstract An alternative to the currently used Perzynas theory of viscoplasticity for small strains is presented. The plastic strain rate vector is normal to the quasistatic yield surface which in turn may not include the origin. Consequently, new loading/unloading criteria are introduced.

Fundamental experiments in plasticity and creep of aluminum—Extension of previous results☆

Abstract Paper presents combined stress experiments in plasticity and creep of aluminum 1100-0. The purpose of these experiments was to determine the motion of the yield surface in tension-torsion space for three complicated prestressing paths, to investigate the validity of the normality hypothesis, to investigate the development of creep strains after prestressing, and finally to investigate the validity of the constant volume hypothesis. It is shown that the law of hardening proposed by the author previously [3,5,6] is valid, except possibly when the prestress path intersects the yield surface at a small angle. It is also shown that the normality hypothesis is valid. After prestressing the creep strain vector has in the beginning the same direction as the plastic strain vector but later its direction may change. Finally it is shown that at the level of permanent strains less than 1% the plastic strains follow the constant volume hypothesis but the creep strains do so only when they begin to appear.

Yield surfaces and loading surfaces of aluminum and brass: An experimental investigation at room and elevated temperatures

Abstract This paper presents the results of an experimental investigation with two specimes of commercially pure aluminum and one specimen of free cutting brass. These three experiments under deadweight loading involved the determination of yield surfaces at room and elevated temperatures and the comparison of these yield surfaces with their associated loading surfaces. The prestressings were performed at room and at elevated temperatures; they were three-dimensional and two-dimensional and they included portions directed towards the origin and away from the origin.

An investigation of yield surfaces based on dislocation mechanics—I: Basic theory☆

Abstract With the help of dislocation theory a new hardening law and a yield criterion are introduced and the initial and subsequent yield surfaces for both single crystals and polycrystalline aggregates are studied.

An investigation of yield surfaces based on dislocation mechanics—II: Application

Abstract The yield criterion and hardening law proposed in Part I are used to calculate the first and second subsequent yield surfaces of aluminium. The obtained yield surfaces exhibit the following features: They shrink in the direction of prestressing, they show a rounded vertex near the prestress point, they become inflated on the side of prestress and deflated on the opposite side, and finally they may exclude the origin.

The stress fields of continuous distribution of dislocations and of their movement in a polycrystalline aggregate

Abstract The elastic fields due to the simultaneous influence of body force, surface force, and the continuous distribution of dislocations are derived. The derivation due to the last part is primarily based on the geometry of dislocations distribution. The obtained results are extended to the elastic-plastic deformation through the concept of dislocations movement. The resultant expressions show that the term associated with the plastic distortional gradient — C ijkl β p lkj and the term associated with the plastic strain C ijkl β p ik n j are equivalent to the body force and the surface force respectively. This result agrees with Lin’s “equivalent body force” and “equivalent surface force” obtained in phenomenological plasticity.

On the kinematics of continuous distribution of dislocations in plasticity

Abstract The theory of continuous distribution of dislocations is applied to the phenomenological plane plasticity. It is shown that Henckys laws are equivalent to each other and that Geiringers relations can be used to determine the patterns of dislocation distribution. The deformation curvature caused by the presence and motion of dislocations and by the lattice deformation is also discussed.