Plastic deformation of metals and alloys

This chapter focuses on relationships between plastic deformation structures and mechanical properties in metals and alloys deforming by dislocation glide. We start by summarizing plastic deformation processes, then look at the fundamental mechanisms of plastic deformation and explore how deformation structures evolve. We then turn to experimental techniques for characterization which have allowed deformation microstructures to be quantified in terms of common structural parameters. The microstructural evolution has been described over many length scales and analyzed theoretically based on general principles. The deformation microstructures are related to work hardening stages. Finally we identify correlations between a wide range of microstructural features and mechanical properties, particularly flow stress, and use experimental observations to illustrate their inter-relationships.

Size effects in the conical indentation of an elasto-plastic solid

The size effect in conical indentation of an elasto-plastic solid is predicted via the Fleck and Willis formulation of strain gradient plasticity (Fleck, N.A. and Willis, J.R., 2009, A mathematical basis for strain gradient plasticity theory. Part II: tensorial plastic multiplier, J. Mech. Phys. Solids, 57, 1045-1057). The rate-dependent formulation is implemented numerically and the full-field indentation problem is analyzed via finite element calculations, for both ideally plastic behavior and dissipative hardening. The isotropic strain-gradient theory involves three material length scales, and the relative significance of these length scales upon the degree of size effect is assessed. Indentation maps are generated to summarize the sensitivity of indentation hardness to indent size, indenter geometry and material properties (such as yield strain and strain hardening index). The finite element model is also used to evaluate the pertinence of the Johnson cavity expansion model and of the Nix-Gao model, which have been extensively used to predict size effects in indentation hardness. © 2012 Elsevier Ltd.

The development of a scanning strategy for the manufacture of porous biomaterials by selective laser melting.

Porous structures are used in orthopaedics to promote biological fixation between metal implant and host bone. In order to achieve rapid and high volumes of bone ingrowth the structures must be manufactured from a biocompatible material and possess high interconnected porosities, pore sizes between 100 and 700 microm and mechanical strengths that withstand the anticipated biomechanical loads. The challenge is to develop a manufacturing process that can cost effectively produce structures that meet these requirements. The research presented in this paper describes the development of a 'beam overlap' technique for manufacturing porous structures in commercially pure titanium using the Selective Laser Melting (SLM) rapid manufacturing technique. A candidate bone ingrowth structure (71% porosity, 440 microm mean pore diameter and 70 MPa compression strength) was produced and used to manufacture a final shape orthopaedic component. These results suggest that SLM beam overlap is a promising technique for manufacturing final shape functional bone ingrowth materials.

Closely correlating lower and upper bound plastic analysis of real slabs

An engineer assessing the load-carrying capacity of an existing reinforced concrete slab is likely to use elastic analysis to check the load at which the structure might be expected to fail in flexure or in shear. In practice, many reinforced concrete slabs are highly ductile in flexure, so an elastic analysis greatly underestimates the loads at which they fail in this mode. The use of conservative elastic analysis has led engineers to incorrectly condemn many slabs and therefore to specify unnecessary and wasteful flexural strengthening or replacement. The lower bound theorem is based on the same principles as the upper bound theorem used in yield line analysis, but any solution that rigorously satisfies the lower bound theorem is guaranteed to be a safe underestimate of the collapse load. Jackson presented a rigorous lower bound method that obtains very accurate results for complex real slabs.

Plastic limit solution for the response of plate anchors under combined translational and torsional undrained loading

Plate anchors are increasingly being used to moor large floating offshore structures in deep and ultradeep water. These facilities impart substantial vertical uplift loading to plate anchors. However, extreme operating conditions such as hurricane loading often result in partial system failures, with significant change in the orientation of the remaining intact mooring lines. The purpose of this study is to investigate the undrained pure translational (parallel to plate) and torsional bearing capacity of anchor plates idealized as square and rectangular shaped plates. Moreover, the interaction response of plate anchors under combined translational and torsional loading is studied using a modified plastic limit analysis (PLA) approach. The previous PLA formulation which did not account for shear-normal force interaction on the vertical end faces of the plate provides an exact solution to the idealized problem of an infinitely thin plate but only an approximate solution to the problem of a plate of finite thickness. This is also confirmed by the three-dimensional finite element (FE) results, since the PLA values exceed FE results as the thickness of the plate increases. By incorporating the shear-normal interaction relationship in the modified solution, the torsional bearing capacity factors, as well as the plate interaction responses are enhanced as they show satisfactory agreement with the FE results. The interaction relationship is then obtained for square and rectangular plates of different aspect ratios and thicknesses. The new interaction relationships could also be used as an associated plastic failure locus for combined shear and torsional loading to predict plastic displacements and rotations in translational and torsional loading modes as well. Copyright © 2011 by the International Society of Offshore and Polar Engineers (ISOPE).

3 Gbit/s LED-based step index plastic optical fiber link using multilevel pulse amplitude modulation

Multilevel PAM is investigated for a LED-based SI-POF link. Using PAM-8, transmission at a record 3 Gbit/s is demonstrated for a maximum length of 25 m step index POF with offline post-receiver processing. © 2013 OSA.

FEC-free 50 m 1.5 Gb/s plastic optical fibre link using CAP modulation for home networks

LED-based carrierless amplitude and phase modulation is investigated for a multi-gigabit plastic optical fibre link. An FPGA-based 1.5 Gbit/s error free transmission over 50 m standard SI-POF using CAP64 is achieved, providing 2.9 dB power margin without forward error correction. © 2012 OSA.

The role of damping in steel pan manufacture

Results are presented of systematic studies of vibration damping in steel of a type, and processed by a route, rel-evant to Caribbean steel pans. Damping is likely to be a significant factor in the variation of sound quality be-tween different pans. The main stages in pan manufac-ture are simulated in a controlled manner using sheet steel, cold-rolled to a prescribed level of thickness reduc-tion then annealed at a chosen temperature in a laboratory furnace. Small test strips were cut from the resulting material, and tested in free-free beam bending to deduce the Young’s modulus and its associated loss factor. It is shown that the steel type, the degree of cold working and the annealing temperature all have a significant influence on damping. Furthermore, for each individual specimen damping is found to decrease with rising frequency, ap-proximately following a power law. Comparison with samples cut from a real pan show that there are further influences from the pan’s geometrical details.