The Effect of Elastic Strain and Small Plastic Deformation on Tensile Strength of a Lean Al–Mg–Si Alloy

Al–Mg–Si alloys are usually formed into their final shape by rolling or extrusion. After extrusion, the aluminium profiles are usually straightened, causing the material to be subjected to a small plastic deformation. This study demonstrates the positive effect on strength that can be obtained from such small deformation levels or from only elastically straining the material. Elastic straining of a lean Al–Mg–Si alloy, when performed immediately after solution heat treatment, enhances the material yield strength after artificial ageing to T6. Transmission electron microscopy shows that this effect can be attributed to a higher number density and finer dispersion of the age-hardening precipitate needles. Furthermore, introducing a small plastic deformation of 1% after solution heat treatment results in a comparable strength increase to elastically straining the material. In this case, however, the strength increase is due to the increased dislocation density, which compensates for a lower density of precipitate needles. Finally, by combining plastic deformation with a succeeding elastic strain, we demonstrate how elastic strain can cause an on-set of dislocation cell formation in this material.

The Dang Van Criterion for Fatigue Design

The present work intends to evaluate, using simple, exemplary cases, the importance of a full elasto-plastic analysis in fatigue design. A strain cycling situation (-ε to ε) was modelled with ABAQUS considering two situations: firstly a linear σ vs. ε relationship was assumed, and secondly, the real cyclic σ vs. ε curve was used to model each cycle, which includes a small plastic deformation. The case of change of cross section in a steel shaft subjected to constant torsion and cyclic bending was analysed through finite element modelling using ABAQUS.

A New Calculating Model of Rolling Pressure during Temper Rolling Process

A set of new mathematical models have been developed to calculate the temper rolling force of 2050 strip temper rolling mill. Based on the fact of small plastic deformation and elastic deformation occurring on the entry and exit of the deformation zone, new stress boundary conditions are described. The inhomogeneous distribution of internal stress in thickness direction is taken into account in the models, instead of uniform internal stress and assumption of plane strain traditionally. The new mathematical models have been applied into the temper rolling of 2050 hot rolling mills with good results. Comparison of calculated values and testing values for nine typical products has been given. The result shows that the calculated value of rolling force of temper mill is accurate.

The Grain Size and Porosity Dependent Constitutive Modeling for Nanocrystalline Ceramics with Small Plastic Deformation

In order to understand the grain size and porosity dependent mechanical behavior of porous, multi-phase nanocrystalline ceramics, each phase is treated as a mixture of grain interior and grain boundary, and pores are taken as a single phase. In conjunction with the secant-modulus approach and iso-strain assumption, Budiansky’s self-consistent method is extended to build a constitutive model for nanocrystalline ceramics with small plastic deformation. Based on the developed model, the predicted yield strength (σ0.2) values of porous, multi-phase nanocrystalline ceramics with different grain size and porosity are compared with experimental data in the literature, the comparison shows that the predictions are in good agreement with the published data. This suggests that the developed model is capable of describing the grain size and porosity dependent mechanical behaviors of nanocrystalline ceramics with small plastic deformation.