Creep Mechanism, Quenching Process, Tempering, Hardness And Alloying In Materials

1. a)Is the creep mechanism Bulk Diffusion highly dependent with stress? Explain why help yourself with drawings.

b)Is the creep mechanism Bulk Diffusion highly dependent on grain size? Explain why help yourself with drawings.

c) Which mechanism of creep can be prevented using a single crystal part? Why?

d) Which mechanism of creep can be accentuated with alloying elements? Why? 

Bulk diffusion mechanism in creep

The creep mechanism Bulk Diffusion is weakly dependent upon the stress. As the creep is the tendency of a material to change its shape when it is subjected to a particular load in a prolonged period. (Frost, et.al 1982)

The method of accelerated cooling of a heated material is known as the quenching process. The heat treatment processed metal will be cooled by the exposure of quenching medium like water, gas, air, etc. Rapid cooling is achieved by the application of liquid quenching mediums. (Rahaman, M.S.A et.al 2007)

There are various commercially available types of quench mediums are:

• water
• vegetable oil
• animal oil
• gas
• cold water
• brine
• Caustic soda 

Due to the hardening process, martensitic material properties change and it will be brittle, lose its ductile and toughness. In order to improve these properties, the heat treatment process is carried out which is known as tempering process. The tempering is generally done after the hardening process. The tempering process is done by heating the material to be tempered below its martensitic temperature and then allowing to cool down itself in a slow and steady process.

The results of Martensitic transformation is theSME (shape memory effect). The process in which the deformed material returns to its initialshapewhen heat treatment is done is known as shape memory effect.There are some specific alloys known as shape memory Alloys which exhibit pure properties of shape memory effect (Pichkaleva, M., et.al 2017) .

The measurement of the capacity of the material to withstanding scratches and indentation is called the hardness of the material. Material with high hardness tends to exhibit very low ductility and machinability properties. The machining process of the hard material is challenging so the geometry or the dimensions of the hard material should be simple and easy to machine no complex curves shall be implemented in the design (Taufik, A., et.al 2018)

The alloying of the carbon in steel found to increase its hardness to a greater extent. The carbon decreases the ferrite and pearlite formation and increases the hardness of the material. The hardness of a material is directly proportional to the percentage of carbon content in it. There are many processes to improve the hardness such as Carburizing, nitriding, carbonitriding, flame hardening, induction hardening, etc.

Function	a) Suspension of Truck
Constraints	a) Fixed length b) Max displacement is given c) Stiffness is given
Objective	a) Mass reduction or minimization
Free variables	a) The width of the leaf spring b) The thickness of the leaf spring c) The required material selection

Objective: Mass reduction

Total mass,

Here,

L – Spring Length

b  -Spring breadth

t – Spring overall thickness

is the density of the material.

Length is fixed.

The breadth and the thickness are variable and can be changed.

Effects of stress and grain size on bulk diffusion mechanism

Constraints:

The Stiffness S is given as:

S = F/ δ

Here,

F is the force

δ  is the deflection.

The Maximum displacement δ_maxis given by the equation:

Where,

L is the length

E is the Young's modulus

T is the thickness

is the stress applied.

The above equation may be rewritten for thickness as:

t=

Now,

We have the deflection equation:

Here,

I am the moment of inertia

F is the force

L is the length

E is the Young’s modulus

Substitute the Value of  and the Value of L² in the Stiffness equation we get:

Now,

Calculate b from the above equation:

b = SL³ / (4Ebt³)

Substitute the Values of the t and b in the mass equation we will get:

The Spring Mass is minimized with index maximization

The fracture toughness constraints may be given as K_1c> 15 Mpa.m^0.5 which is given in order to safeguard against the accidental impact.

Now the listed material can be selected for the purpose by considering the performance index and the fracture toughness constrain.  

Material	Description
Titanium Alloy	Expensive Lighter
Carbon Fiber Reinforced Plastics	Lighter Expensive Strong
Rubbers	Lighter inexpensive

Given data:

Temperature, T₁ = 450K

Time t₁ = 30 secs

T₂ = 430K

 t₂ = 81.5s

Now,

We know that,

Time,     t₀ =

Q is heat transfer

C is the specific heat transfer

The relation between the injection timing can be taken as:

Finding Q  and C from the above equation:

Q = = 8.039 x 10⁴  J/ mol

C =  =  = 7.156 X 10⁷     _1/Sec

The overall time is given as:

_Overall= = 3.5Seconds

The time is calculated at 3.5 seconds

The thermosetting polymer isan irreversible plastic polymer which cannot be reverted back to its original state after curing. The thermosets exhibit the creep when the thermoset plastics are exposed to loads for an extended period of time even though they tend to have higher rigidity. Tensile creepis the most common type of creep that is observed in the thermosetting plastics. Thermoset creep mechanism is temperature dependent. It is also dependent upon the stress which is actedon the polymer.The creep mechanism occurs inthe thermoplastic is the bulk diffusion in that the type is mostly bending and the tensile creep. Both the thermoset and thermoplastics are showing creep but the thermoset material are stronger than that of the thermoplastics.

We can study the creep influence of the plastics by observing the structure of the thermo and thermoset plastics. The thermoplastic is chain linked and they have comparatively lower rigidity compared with the thermoset plastic as the thermoset plastic forms a cross-linked structure, so the creep in thermo plastics are higher than the creep in thermoset plastics.

Preventing creep mechanism with single crystal part

The viscoelastic equation is used to study the creep

The injection is modelled using the equation:

The viscoelastic equation is based on the diameter, temperature and time and the injection timing equation is related with the time and temperature only as we can see the first equation considers the geometrical constrains also.

The connecting rod is an integral part which is present inside the IC(Internal Combustion) engine. The conversion ofthe linear motion into oscillating motion is done by the Connecting rod. The connecting rod is connected to the piston at one end and it is connected to the crankshaft at the other end. There are two variable size hoses present in a connecting rod among them one is larger diameter another one is with a smaller diameter. The larger diameter one is connected to the crankshaft and the smaller dia is connected to the piston. The linear motion of the piston is converted into rotary motion of the crankshaft with the help of oscillating motion achieved in the connecting rod (Kou, S., et.al 2017)

The given constraints in the problem are the length is fixed, must be lighter in weight, Fatigue and buckling should be lowered.

The objectives are :

Withstand Force up to 20KN.

Lighter in weight.

Strong.

The variable over which we have the control is known as free variables they are not fixed. In this sytem the free variables are:

Material choice

Breadth

Width

The mass of the connecting rod is given as:

Mass, m = (M₁)+ (M₂)

M₁ Rectangle

M₂ Circle

 ) ρ in kgs

Here,

ρ- the density of the material

D diameter

b- breadth

W- width

t- thickness

The mathematical representation the variables which are responsible for the fatigue in the form in indices are known as performance index for the fatigut

The mass of connecting rod is calculated previously as:

 ) ρ  in kgs

W² t + 2(²) X ρ    

The buckling material index

The material index can be found as:

M = E/ρ

We have,

E = FL² /

Substituting on first eqn:

M = FL²ρ /

Application of two performance indices gives greater control over the product design and the quality. It also improves the performance of the product for a long time.

References: 

Frost, H.J. and Ashby, M.F., (1982). Deformation mechanism maps: the plasticity and creep of metals and ceramics. Pergamon press. 

Rahaman, M.S.A., Ismail, A.F. and Mustafa, A., (2007). A review of heat treatment on polyacrylonitrile fibre. Polymer degradation and Stability, 92(8), pp.1421-1432. 

Pichkaleva, M., Timofeeva, E., Tagil'tsev, A., Panchenko, E. and Chumlyakov, Y., (2017). The Effect of Heat Treatment on the Shape Memory Effect and Superelasticity in NiMnGa Single Crystals. In Key Engineering Materials (Vol. 743, pp. 91-94). Trans Tech Publications. 

Taufik, A., Suprapto, A. and Sonief, A.A.A., (2018), September. The effect of heat treatment quench-temper and radius bending against hardness hot rolled plate steel. In IOP Conference Series: Materials Science and Engineering (Vol. 420, No. 1, p. 012045). IOP Publishing. 

Kou, S., Gao, Y., Zhao, Y. and Lin, B., (2017). Stress analysis and optimization of Nd: YAG pulsed laser processing of notches for fracture splitting of a C70S6 connecting rod. Journal of Mechanical Science and Technology, 31(5), pp.2467-2476.