On the Cover of this Issue: Cyclic Strain Heterogeneity and Damage Formation in Rolled Magnesium by N. Shafaghi,E. Kapan,and C.C. Aydıner

Experimental Mechanics -     

Comments on “Vibration suppression for high-speed railway bridges using tuned mass dampers” [J.F. Wang,C.C. Lin,B.L. Chen, 2003. Int. J. Solids Struct. 40(2) 465–491]

In this comment, the discusser makes some remarks on the paper “Vibration suppression for high-speed railway bridges using tuned mass dampers” by Wang, J.F., Lin, C.C., Chen, B.L., published in the International Journal of Solids and Structures, 2003, Vol. 40, No. 2, pp. 465–491. First, the formulation of H(t, t_k) on p. 470 is questionable. Second, for a moving suspension mass model, the interaction force between moving mass and bridge is incorrectly given. Third, for a moving mass model for the train and without the installation of PTMD (passive tuned mass damper), the equation of motion of the bridge is incorrect. Lastly, for the train load model, which consists of one-half of a train car, one bogie, two wheel sets, spring and dashpot between bogie and half of a train car, and spring and dashpot between bogie and each wheel set, the authors did not put forward the formulation of interaction force between wheel set and bridge, but the discusser does.     

Texture development and plastic anisotropy of B.C.C. strain hardening sheet metals

A Taylor-like polycrystal model is adopted here to investigate the plastic behavior of body centered cubic (b.c.c.) sheet metals under plane-strain compression and the subsequent in-plane biaxial stretching conditions. The <111> pencil glide system is chosen for the slip mechanism for b.c.c. sheet metals. The {110} <111> and {112} <111> slip systems are also considered. Plane-strain compression is used to simulate the cold rolling processes of a low-carbon steel sheet. Based on the polycrystal model, pole figures for the sheet metal after plane-strain compression are obtained and compared with the corresponding experimental results. Also, the simulated plane-strain stress—strain relations are compared with the corresponding experimental results. For the sheet metal subjected to the subsequent in-plane biaxial stretching and shear, plastic potential surfaces are determined at a given small amount of plastic work. With the assumption of the equivalence of the plastic potential and the yield function with normality flow, the yield surfaces based on the simulations for the sheet metal are compared with those based on several phenomenological planar anisotropic yield criteria. The effects of the slip system and the magnitude of plastic work on the shape and size of the yield surfaces are shown. The plastic anisotropy of the sheet metal is investigated in terms of the uniaxial yield stresses in different planar orientations and the corresponding values of the anisotropy parameter R, defined as the ratio of the width plastic strain rate to the through-thickness plastic strain rate under in-plane uniaxial tensile loading. The uniaxial yield stresses and the values of R at different planar orientations from the polycrystal model can be fitted well by a yield function recently proposed by Barlat et al. (1997b).     

On uniqueness of multiple-slip solutions in constrained and unconstrained F.C.C. Crystal deformation problems

A modification of the simple theory of rotation-dependent anisotropy is applied to the analysis of f.c.c. crystals, in both constrained and unconstrained multiple-slip orientations, with the object of resolving the question of uniqueness of solution. Specifically, tensile loading in each of 4-, 6- and 8-fold symmetry and [110] loading in channel die compression for each of [ 10] and [00 ] lateral constraint are investigated. It is established that the modified simple theory, augmented by the postulate of minimum plastic work, uniquely predicts equal multiple-slip and lattice stability (relative to the force axis or axes) in all cases.