iMechanica - impact - Comments

Nanoindentation for measuring hardness of nanograined materials

Henry Tan — Thu, 03 Jan 2008 07:02:13 -0500

Link: Indentation of polymer-matrix composites

For measuring hardness of nanograined materials, nanoindentation is used.

In nanoindentation small loads and tip sizes are used, so the indentation area may only be a few square micrometres or even nanometres. This presents problems in determining the hardness, as the contact area is not easily found. Atomic force microscopy or scanning electron microscopy techniques may be utilized to image the indentation, but can be quite cumbersome. Instead, an indenter with a geometry known to high precision (usually a Berkovich tip, which has a three-sided pyramid geometry) is employed. During the course of the instrumented indentation process, a record of the depth of penetration is made, and then the area of the indent is determined using the known geometry of the indentation tip. While indenting various parameters, such as load and depth of penetration, can be measured. A record of these values can be plotted on a graph to create a load-displacement curve. These curves can be used to extract mechanical properties of the material.

Rolls-Royce project

Henry Tan — Thu, 13 Dec 2007 08:00:44 -0500

Waqas,

Can you put some of your results on this web, with pictures and physical explanations?

Henry.

Industrial Placement

Waqas Ahmad — Wed, 21 Nov 2007 19:17:42 -0500

Industrial Placement

‘Optimising Superplastic Forming Die Shape and Platens for Next Generation Aero Engine Production’

Background

The design of hot forming dies was optimised in the 1980s for the engine types at the time, the knowledge bank has remained constant ever since. The current high by-pass ratio engines are larger and therefore require larger hot forming dies. The increase in size of dies and presses along with the increase in mass of material and thermal efficiency means the cooling time has increased significantly.

The dies are regularly changed for routine maintenance, this includes die surface cleaning or re-cut. However, the current cooling rates are approximately 37°C per hour, this takes 3 to 4 days and consequently has an adverse impact on productivity. The actual die model has been simplified to fit into the scope of the project. The die is manufactured from cronite (HR4), a nickle based alloy. This project is of interest to Rolls-Royce, as the research done will be used by the company to conduct their own investigations on the hot forming process and improve the entire manufacturing process for fan blades.

Aims and Objectives

The project has aim of the project is:

1. To reduce the thermal cycling time during die change over/maintenance through optimised die and platen design.

These aims have been broken down into the following objectives

1. Model current die and platen thermal stress during thermal cycling,

2. Model current die and platen stress during forming,

3. Consider ways of redesigning die to speeding up the cooling press,

4. Define minimum working surface thickness before distortion occurs in normal surface,

5. Develop designs to optimise die shape and to achieve maximum cooling rates

Current Progress

The material used in the die is specially made for Rolls-Royce, as the material must perform at a temperature of 900°C and pressure in the region of 30bars this and the fact that Cronite has a high nickel content makes the material far too expensive therefore, it was beyond the scope of this project to conduct actual experiments on the material. Finite element analysis has been recognised as the best method of analysing the problem.

The finite element package Ansys was chosen to model the current die and platen stresses so far the progress has been reasonable. Several designs have been analysed and the best design will be taken to the next stage and studied in greater detail. The designs will be analysed structurally to determine the effect of the design change on the cooling time and to make sure the die can withstand the working conditions.

Thanks for your interest

Ashkan Vaziri — Tue, 10 Oct 2006 10:06:30 -0400

Thanks for your interest in this mini-symposium. The topic you mentioned is definitely of interest. Please check iMechanica for updates for 9thUNCCM, including the deadline for abstract submission.

Wheel Impact in Insulated Rail Joints

Manicka Dhanasekar — Mon, 09 Oct 2006 19:10:21 -0400

I wonder if FE modelling of wheel impact in insulated rail joints would be of interest to your mini-symposium?