Example 6: Upgrading a Propulsion Shaft

Context:

An engineering consulting firm is collaborating with a European shipbuilder to design a new, larger class of vessel to be manufactured in the shipyards of Saint Nazaire, France. The legacy design uses a main propulsion shaft made of AISI 4340. Due to the increased size of the new vessel, the shaft must handle higher torque loads. Additionally, the project has strict sustainability targets; continuing to import heavy steel bars from the US (AISI standard) is flagged for high lead times, risk on tariffs and excessive transport-related carbon emissions.

Objective:

Find a material defined by EN Standards (European Norms) available in Bar form that offers higher Yield Strength, Tensile Strength, and Elongation than the original AISI 4340, while minimizing Carbon Footprint and keeping Price under control. The switch must support local French manufacturing to reduce the project's carbon footprint.

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1

Select Equivalent Mode

Search for AISI 4340 and select it as your reference material. This selection will pre-fill the criteria on the next steps to help you define your needs and will be pinned at the top of the results for easy comparison.

2

Form

Add a Form criteria for "Long products". This criterion should be set as mandatory to ensure all selected materials are available in bars. Assign it the lowest importance score of 0.1, so while it ensures compatibility with the product form, it minimally influences the overall material score.

3

Standard

Select EN standard to ensure selecting a material that could be found more easily in the European market.

4

Cost

Set this criteria to "Lower better" and delete the Min value to enable Optimizer to find materials potentially costing less than 4340 AISI. While the cost of a project is always crucial, the focus of our material selection should rather be the mechanical performance, for this reason keeping the importance to 1 will allow price to remain influential in final score.

5

High Yield Strength

Configure it as "Higher is better" with "High" importance (5) as this is the decisive criteria in our material selection. The Min and Max fields are prefilled with the range of 4340 AISI. In order to enable us finding a material with a higher yield, it is recommended to remove the upper boundary of the range (Max) and simply keep the Min in order not to be suggested under-performing materials.

6

Elongation at Break

Following the same logic as for Yield, configure it as "Higher is better" and remove the higher bound of the range. Ductility is a desirable property but it is largely less important than yield so a medium importance (1) should suffice to take it into account.

7

European Shipbuilding Regulations

The European Union has implemented stringent regulations on materials used in shipbuilding to promote sustainability and environmental protection. These regulations necessitate that materials are selected not only for their performance but also for their recyclability. Adding the No 1257/2013 -EMSA regulation to your selection will ensure that your material is compliant with these recyclability constrains. The criteria should be set as mandatory so that material respect it but it importance can be minimal (0.1) in order to keep the score solely on the performance of the materials.

8

Reduced Carbon Footprint

Reducing the carbon footprint of shipbuilding being one of the main criteria triggering the selection of a new material. Climate Change (GWP100) can be added a criteria with an aim for "Lower Better" in such a case it is as well advised to remove the Min boundary so that materials with lower footprint can be found. The importance of this criteria not over-passing the mechanical or cost constrains, it can be left with a standard importance of 1.

9

Apply

10

Compare your results

Create a Parallel Coordinate plot containing all the relevant properties to compare the top results with 4340 AISI reference material.

There are clearly better alternatives to this material in all properties, note 41Cr4 outperforms 4340 in all categories.