Aluminium Alloys - Jarrett D

During our last meeting we decided that an aluminium alloy could be used to create the legs of the crane. So I have done some research and found that there are two main categories of alloys, Wrought and cast. We will be using a cast alloy as it is stronger. However, as there are thousands of variations of cast aluminium alloys, I thought it best to find out the upper and lower strength limits of most cast aluminium alloys rather than to find these values for a specific alloy.

Facts on aluminium alloys
Tensile strength = 320-550 mpa
Yield strength = 250-450 Mpa
Density = 2626-2790 kg/m3
Young’s modulus = 70-74 Gpa

Advantages
· Aluminium alloys have a high strength to weight ratio so using them would make the crane easier to carry.
· Has a low fatigue limits which isn’t a problem as it fits the criteria of our crane perfectly.
· Excellent corrosion resistance

Disadvantages
· Has a lower tensile strength than steel so if a metal pipe (ie. The tripod legs) is to built out of an aluminium alloy. The diameter of the pipe would have to be larger then a pipe made out of steel to be able to deal with the same amount of stress.
· Cost is higher then that of steel.

Sources:
R.E. Sanders, Technology Innovation in aluminium Products, The Journal of The Minerals, 53(2):21–25, 2001.
Metals reference book(5th edn, Butterworths 1976)

Research on materials for the main frame of the crane - Jarrett D

I have found three materials that have the ideal properties to cope with the stresses and strains of a cranes function. the first of which is :

Carbon steel
Carbon steels are steels which contain only carbon as its main alloying ingredient. The amount of carbon ranges from 0.05% to 2% of the steels total wieght. This is a very important factor as generally the more carbon within the steel, the higher its stregnth (tensile and yield) and hardeness, the lower its ductility and harder it becomes to weld. For this reason we should consider using a medium steel containing around 0.5% to 0.6% carbon as this amount balances ductility with stregnth. some facts on general mediums steels are below:

medium steel facts
density = 7850 kg/m^3
tensile stregnth = 520 Mpa
yield stregnth = 350 Mpa
young's modulus = 208 Gpa

Advantages
Carbon steel can be used on parts of the crane where the stresses aren't particularly high (such as the crank arm or perhaps one of the tripod legs) and could even be used to create some of the rivets. doing this would save alot of money on cost.
Disadvantages
Although carbon steel is fairly strong, as far as steel goes it is relatively weak. its low tensile strength means that creating an entire crane out of the stuff would make the end product very heavy. Also as the steel includes no other alloyiong ingredients so its corrosion resistance isnt the best either, which means it may have to be painted to protect it.

T1 (AKA A514)/ High speed steel
High speed steels are steels that contain other alloying elements apart from carbon. they typically contain between 0.05% to 0.025% carbon along with other elements depending on the properties the material is required to have. Carbon steels that are required to be highly weather resistant will include elements such as nickel, silicon and phosphurus. Carbon steels reqiuered to be strong will include elements such as copper, titanium anad vanadium. However one high speed steel in particular is ABSOLUTLY ESSENTIAL to the construction of cranes, which is known as T1.

properties of T1
density = 7800 kg/M^3
tensile stregnth = 700 - 895 Mpa
yield stregnth = 620 - 690 Mpa
young's modulus = 205 Gpa

Advantages

• T1 has a high tensile stregnth therefore less material would have to be used as aposed to carbon steel, which would save weight. because of this fact T1 should be used on high stress components such as the boom, rivets and steel wire
• very good corrosion resistance when compared with carbon steels
• easliy welded and fairly ductile

Disadvantages

• Generally costs more than carbon steel

Titanium Alloys (grade 5)
Titanium alloys are split into 39 grades the most commonly used grade being grade 5, generally the higher the grade the better the alloy. Typically titanium alloys are used because of there extremely high strength to weight ratio however, they are also very hard which makes them great for creating cogs and gears with.

Grade 5 properties
Density = 4500kg/m^3
Tensile strength = 1000 Mpa
Yield strength = 880 Mpa
Young’s Modulus = 110 Gpa

Advantages

• 
  As the titanium alloys have a low density and high tensile and yield strength using this material would save a lot of weight.
• 
  High hardness which makes it ideal for moving parts where metal on metal friction occurs (pulley).
• 
  Alloys tend to include elements such as silicon, phosphorus etc which make the very corrosion resistant

Disadvantages
· Poor shear strength means this material cannot be used to make the rivets or screws
· Very expensive

sources:
metals references book 5th edn Butterworths, 1976
A.M. Howatson, P.G. Lund and J.D. Todd, "Engineering Tables and Data" p41
http://www.matbase.com/material/ferrous-metals/low-temperature-steel/a514-a/properties
http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MTP641http://www.efunda.com/materials/alloys/carbon_steels/show_carbon.cfm?ID=AISI_1040&prop=uts&Page_Title=Carbon%20Steel%20AISI%2010xx