Diane J. Mynors

Hyperbolic Sine Representation of a Constitutive Equation for Superplastic Forming Grade Inconel 718

The superplasticity of Inconel 718 has been reported, but there has been little development of the required constitutive relations. This paper describes the work undertaken to develop hyperbolic sine relations for superplastic forming grade Inconel 718 to represent the relationships between flow stress, strain rate and temperature over a wide range of deformation conditions. The model includes the hardening due to grain growth and the softening due to the evolution of cavitations. Introduction The superplasticity and constitutive models of titanium and aluminium alloys have been studied extensively [1-6]. A number of the constitutive models developed have included the evolution of microstructure during superplastic deformation [3-6]. Zhou et al [3], Cheong et al [4] and Lin et al [5] have developed constitutive models with grain growth hardening for the Ti-6Al-4V alloy. Hhaleel et al [6] have developed a constitutive model, which includes the effect of strain hardening, strain rate sensitivity, dynamic and static recovery, nucleation and the growth of voids for the aluminium alloy AA5083. Although the superplasticity of Inconel 718 has been reported [7-11], there appears to have been limited development of its constitutive model. Kashyap et al [7] evaluated the activation energy for superplastic forming grade Inconel 718. They assumed that the stress-strain data beyond a certain strain level represented a steady state condition. However, other researchers found that the strain hardening and flow softening could not be neglected for superplastic forming grade Inconel 718 [9-10]. Indicating that it is necessary to develop a constitutive model for superplstic forming grade Inconel 718, which considers strain hardening and flow softening. This paper describes the work undertaken to develop hyperbolic sine relations for superplastic forming grade Inconel 718 to represent the relationships between flow stress, strain rate and temperature under a wide range of deformation conditions. The model includes the hardening due to grain growth and the softening due to the evolution of cavitations. Stress Strain Data The stress strain data used in the work described here were measured under two temperature and three strain rate conditions. The test samples were cut from superplastic grade Inconel 718 sheet * * The authors would like to thank the partners involved in the MMFSC (Manufacturing and Modelling of Fabricated Structural Components) project and the European Commission for funding the work. Contract number G4RD-CT-2000-00217. www.mmfsc.net. Materials Science Forum Online: 2004-02-15 ISSN: 1662-9752, Vols. 447-448, pp 171-176 doi:10.4028/www.scientific.net/MSF.447-448.171

Design and Simulation of a Femoral Component Peg in Total Knee Replacement

Aseptic loosening of the femoral component is one cause of failure in total knee replacement (TKR). Inadequate bone stock in the distal femur after TKR, due to the stress shielding, was often found in revision of the femoral component. The pegs in the femoral component are used as an aid to the correct placement of the component but they also help to transfer the load to the diaphyseal part of the bone and improve stability. This paper investigates the influence of femoral component peg design on stress distribution and bone remodelling in the distal femur after TKR. Eight different peg designs were investigated and reported in this paper. The bone remodelling parameters in the distal femur are presented, compared and analysed. Results show that a slender peg is advantageous in TKR.

Simulating the UltraSTEELTM Surface Dimpling Process

The UltraSTEELTM process, developed by Hadley Industries Plc (Hadleys), is a novel surface dimpling process used on steel strip prior to cold roll forming. This dimpling process increases the strength of the final rolled products and enhances other product properties such as fire test performance and screw retention. Reported in this paper are the results of finite element analysis conducted to simulate the application of the spatially distributed dimple pattern to the metal sheet prior to the cold roll forming process. The model contains a representation of the two rotating rolls that plastically deform, imparting the spatially distributed dimple pattern on the sheet as it moves between them. The simulation results are compared with industrially processed UltraSTEELTM steel sheet. Consideration is given to the plastic region developed in the dimples and the effect of rolling action on the regions. The dimensional change of the metal sheet is also discussed.

Deflection Analysis of Sleeve Jointed Purlin Systems with Non-Linear Rotational Stiffness

Sleeved purlin systems are usually used in roof constructions. A non-linear relationship between the bolt hole extension and the load transferred to the bolt was derived with experimental testing and numerical simulation. Consequently, the non-linear rotational stiffness of sleeved joints was derived based on the configuration of sleeves in this paper. The procedure for calculating the deflection of purlin systems with non-linear rotational stiffness at the joints is presented. The analysis and calculation of the deflection is demonstrated through a case study.

Applications and Engineering Analysis of Lotus Roots under External Water Pressure

Engineers can learn from nature for inspirations to create new designs. The internal structure of lotus roots with several oval holes was studied in this paper for engineering inspirations. The structural performance of lotus roots under outside water pressure was simulated and compared with various cross-sectional areas. The distribution of stresses in the cross-sectional area of lotus roots was analysed and presented. It was found that the maximum compressive stresses in the cross-sectional area of lotus roots were occurring at the long axis ends of the holes. This was very different from that of circular holes. Further analysis on the triaxiality factors revealed that the cross-sectional area of the lotus root resulted in large areas of high triaxiality factors. The resulting hydrostatic stress in the cross-sectional area of lotus root ranges from zero to 2.7 times the applied outside pressure. In contrast, the hydrostatic stress in a cylindrical cross-sectional area is a fixed value. The study showed that the lotus root and the orientation of the oval holes could be mimicked in the design of new structures, for example, underwater pipes and vessels.

Numerical and Experimental Studies on the Laser Melting of Steel Plate Surfaces

The direct impingement of laser on the surface of a platform occurs during additive layer manufacturing especially for the first layer of powder coating. As a result, thermal stresses develop due to high temperature gradients in a thin layer of the plate surface, which can result in undesired surface deformation of the steel platform used. This study investigates the residual stress profiles on a hot-rolled AISI 1015 steel plate produced by direct laser application. A three-dimensional finite element simulation model is developed which considers the laser heating process as a sequentially coupled thermal elasto-plastic problem. Experiments using optical laser scanning microscopy to obtain surface topography of the melted surface are also presented showing reasonable agreement with the simulation results. The influence of the plate thickness on the stress-depth distribution is presented.

Simulating the Mechanical and Structural Properties of UltraSTEELTM Dimpled Sheet

The novel surface dimpling UltraSTEELTM process developed by Hadley Industries increases the strength of the final rolled products and enhances other product properties such as the load carrying capacity. The dimpled UltraSTEELTM sheet is used in steel framing, ceilings and other structural components. The mechanical properties and structural behaviour of the dimpled sheet are different from plain sheet due to non-uniformly distributed plastic strain and geometry of the dimples.

Experimental and Numerical Analysis of Residual Stresses in Additive Layer Manufacturing by Laser Melting of Metal Powders

Determining the three-dimensional residual stress fields and the associated distortions using numerical simulations for multi-layered parts has proved to be a challenge in additive layer manufacturing. This paper presents an innovative three-dimensional thermal-elasto-plastic finite element model for predicting the deformation and residual stress fields in TiAl6V4 parts built on steel platforms. The developed model utilises temperature dependent material physical and mechanical properties as well as latent heat of melting. Experiments conducted using surface profilometry showed good agreement with the simulation results. The finite element model was used to investigate the overall effect of the melting powder on the platform deformation and residual stresses for multiple layers of deposited powder.

A Low Volume Production Process Capability Analysis

Statistical Process Control (SPC) and Process Capability Indices (PCI) are used extensively within manufacturing and service environments. This paper reports the results of a statistical quality improvement programme when applied to a low volume, high gauge frequency machining process. The resultant capability indices (Cp and Cpk) are calculated from acquired data both before and after process modification, and are discussed in relation to the specific process. Box Cox data transformations are utilised in order to centralise data and the applicability of the capability improvements are determined. Historically SPC and capability analysis are performed on high volume processes with data being gathered on a sample basis. This investigation applies the high volume theory to a low volume 100% data gathering process. The validity of capability analysis of this nature is discussed due to long cycle times and large gauge inspection frequency.

Acoustic performance of cold-formed steel buildings

This chapter introduces the requirements associated with acoustic performance in buildings and sound insulation properties of building partitions composed of cold-formed steel sections. Developments in experimental tests, analytical and numerical methods for determining acoustic performance of cold-formed steel buildings are presented. Design and construction methods for walls and floors using cold-formed steel sections to achieve desired acoustic performance are included. Recent research on cold-formed steel acoustic studs is highlighted. Typical acoustic performance values of building partitions using cold-formed steel sections are provided. Finally, acoustic design examples of a wall and a floor are described for reference.