Laboratory Report On Material Selection In Engineering

This Laboratory focuses on the process in which manufacture, and design engineers must go through to select the right material of a product. Material selection is in every part of day to day life from a toothbrush to a phone. All products go under a research process to determine the best possible material for a product, this process also has to take in other variables such as cost, manufacturability as to how easy are hard the material is to work with, how much stress it can under go, is it bio-degradable and many more possible design parameters which will all be determined by the products use. The reason as to why this material selection process is so important in business terms is due to the competitive market with companies being able to make better and more affordable products. In a manufacturing industry it comes down to how reliable a material is if the wrong material is selected the part is more likely to fail and cause set backs in productions or potential hazards. The main importance is the safety factor such as construction buildings or aviation if the material is selected without being able to take the required stress it can cause a building to collapse or a plane to crash as quoted from Alan Carr “there isn’t enough surgeons in the world to save the amount of people an engineer can put at risk”.

Cambridge engineering selector (CES)

The Cambridge Engineering Selector or CES for short was developed by Mike Ashby in the University of Cambridge it is a unique programme which houses a large database of materials and the values of each of these materials from its Young’s modulus to its cost. This selector allows engineers to select and construct the appropriate materials for there required needs rather than having to spends day or weeks to compare all the properties of materials and researching them instead the engineer can look for specific parameters such as a high density/temperature resistance material. The CES programme will give all the available materials on a chart that suit the parameters and from here the engineer can ether select a suitable material or narrow the search down further by using a (x, y) slope on a graph to determine a set value of the material.

Case Study 1

Study brief: must try to determine which materials would be best suited to the construction of an oar, based on an adequate selection or the objectives and the constraints. Clearly it is desirable to reduce the mass of the oar, so that the rower does not have to expend too much energy in overcoming inertia (objective). At the same time, the oar must exhibit a high stiffness while we also need to keep the costs low (constraints).

The first step is to determine the parameters of the oar and how it is used:

• Must be lightweight
• High Youngs Modulus
• Corrosion resistant
• Durable due to its use in rivers (rocks, strong currents)
• Machinable due to its design being aerodynamic to glide through water.

Using these parameters and applying them in the CES programme by accessing the charts and selecting an X and Y axis of the most important parameters like density and Young’s modulus. The CES programme outputs a bubble chart of all materials in the database. Now using the slope function on CES to determine the most appropriate material that has a high Young’s Modulus and low density which leaves 6 available options:

• Foam
• Soft wood
• Bamboo
• Carbon fibre
• Silicon Carbide
• Bannon Carbide.

To further reduce the options to get a more precise material selection a second graphing process was added in which I focused on its machinability and recyclable properties as being environmentally friendly plays a large role in today’s market place and the design of the oar place a large part in the consumers performance in rowing.

The CES programme further reduced my search into a bar chart graph: The new graph allows me to choose a material from my previous graph showing all the 6 materials within my original parameters, from here I can entre specific values as to the exact Young’s Modulus that is need. By judging the two charts I can see that carbon fibre is in the mid-range of both charts so that it has a high Young’s modulus/low density ratio and its reasonable machinable/recyclable. Therefore, without needing much research I have a material that will suit the needs of the oar and by double-clicking the chart I can see its exactValues to fully understand the material I have selected for this case study on the oar.

To further constrain the material for the oar I can factor in cost which would leave me to select a different material. Carbon fibre comes at a high cost where as bamboo is both light [image: ]weight, stiff and low cost, allowing for a more affordable product that is easy to machine and good for the environment but not as stiff as carbon fibre which is the compromise.

Case Study 2

Design Brief: Using CES to select the appropriate material for a crankshaft in a V6 engine Having decided on the constraints, derive a bubble chart, or charts, to describe the material in terms of the most important material properties. From the chart, select the most suitable materials to meet the design specification.

Constraints:

• Output a high amount of torque.
• Work under high speeds for long periods of time.
• Be wear resistance to corrosion.
• Resistance to high temperatures.
• Stiff as the alignment of the pistons will vary causing engine failure.
• Handle a high amount of stress and strain.

These are only the basics of manufacturing specification if a crankshaft material.

Research

Crankshaft of a V6 engine varies as different motor companies use all sorts of injection systems and turbocharged engines which all change the amount of force that is being applied to the piston head at any given time. By finding out the maximum force that can be applied during the combustion process will determine one design parameter or by choosing a material and designing the engine to work within the materials limits is another way to select it. In most cases the force acting on the piston is ranging from 160N – 200N idling, its the revolutions and temperature that has the most damaging effect on the crankshaft. As the speed increases the temperature increases, without proper cooling or pressure regulating sensors the crankshaft comes under a high amount of shear stress and the temperature increase can cause the material to soften which then fails or causes the pistons to go out of alignment.

CES

With the researched I have gathered I can now input my first chart on CES, these parameters will be based on the strength to weight ratio which is used in most car manufacturing companies as high strength low weight allows for best possible performance. Before I input any parameters, I can filter down my material selection by only looking for metals as the obvious choice.

From this point I used the same method as before with the slope to only select the materials within at range above the line. To further narrow the selection process, I inputted another constraint which was a ratio of the melting point to the price of manufacturing. In most cases cost plays a key factor in material selection as titanium came up as the most suitable product the cost in manufacturing the material was far too high.

A further bubble chart was displayed in which I applied a line with a slope of high melting point low cost this left me with only 3 choices hardened aluminium, mild steel and high carbon steel. I constrained the 2nd chart looking only for materials that have a melting point above 1000 degrees leaving me with just mild and high carbon steel. The CES programme is a highly useful tool in selecting and constructing materials with the large database and simple graphing method materials for any project can be easily selected with only the basic amount of researched needed. Upon searching for materials used for crankshaft the most common was high carbon steel and mild steel was also used in some engines proving just how precise the CES programme can be.

Stress analysis

To further use this information from CES a stress analysis was done on inventor pro to see the difference in the two metals and determine the most ideal material. Stress analysis allows an engineer to see what happens to a material as it under goes stress from an applied force depending on what the product is used for. This is highly cost effective as no money is spent on manufacturing the part and testing it under applied load and is also useful in getting more information on the exact type of material needed.

High Carbon Steel

Starting with high carbon steel on inventor and creating a mesh effect that brakes the crankshaft into sections for a more in-depth analysis of the force acting upon each section. Focusing on the piston alignment by creating a load force acting on a horizontal plane compared to rotational force. By fixing the flywheel plate connector and applying force on the opposite end of the crankshaft to see the most result a large amount of force was needed. The force applied was 40, 000lb with the maximum effect on carbon steel 367. 3ksi as seen in this image the max effect occurs where the force is applied but little to no effect is occurring at the point on fixture. In realistic terms the force will be applied at each piston arm connection point on the shaft but this force does not happen uniformly as each position on the crankshaft is on a different cycle. What this means is when piston one is on its first stroke cycle piston 2 is on its 2nd stroke cycle and piston 3 is almost complete cycle 3 and piston 4 has done a full cycle. This process will vary depending on engine manufacturing specifications but at no point is there a uniform load acting on all 6 pistons at the same time.

Mild Steel

The same stress analysis was done for mild steel with a 40000lb load acting on the crank shaft at a fixed point. The difference of force on the mild steel compared to high carbon steel. Where high carbon steel is 367. 3 and mild steel is 367. 8ksi. Although the difference is only minor these small differences in material can change the performance of the engine. When taking the temperature and pressures that will be surrounding the crankshaft mild steel will have a higher failure rate and with out this stress analysis to confirm this a manufacturing company could select the wrong material for a crank shaft even though it will work the chances of it failing due to the materials stiffness is higher than carbon steel this information is only possible due to the stress test as it will be difficult and costly to test the 2 different crankshafts.

Conclusion

From just a few hours of using CES I could grasp just how important it is as todays engineers must keep up with a highly competitive market with companies making safe affordable products using the right resources. CES helps to eliminate a lot of research time along with cost as its large database of materials allows for the use of more defined constraints combined with using inventor pro to test just how effect the material is from the stress analysis. Which can be seen in the image of rotation force acting upon a high carbon steel crankshaft which has a force of 40000lb acting on it. The force applied is much higher than the actual force that will be applied which will confirm that high carbon steel is a highly effective material. There is a lot of potential to gain from using the CES programme and inventor pro, such as creating different ways to make the oar by using bamboo for the light weight and stiff material then determine its stress point where it has potential to fail and adding carbon fibre to the failure point to both increase products strength and keep cost to a minimum.