# Material selection case study

__Material Selection Case Study for a Convertible Car Sing Folding Roof:__

#### Material Case Study:

The map defines the usage of the merchandise that would be produced. A constituent has two or more maps that need to be satisfied. In this instance the chief map of the stuff to be certain should be able to defy daze tonss should be able to defy the fluctuations in the temperature and the stuff should be waterproof. The aim of the constituent should advert what belongings of the stuff should be minimised or maximised. In this instance the monetary value should be minimised, the weight or denseness should besides be minimised and fracture stamina should be maximised.

The restraint that the stuff should run into agencies what are all the belongingss that should non be negotiated while planing the merchandise. In this casing the size of the roof panel like length, comprehensiveness and thickness has to be equal to the desired value of the client. Temperature is besides a restraint where the coveted stuff should hold as big runing point as possible. Tensile strength is another restriction where the stuff to be selected should possess high raggedness and strength.

So the Function, Objectives and Constraints of the stuff to be selected for the folding roof panel of a exchangeable auto are set. Then material indices are used depending on the map and the restraints.

The stuff index for a level panel which besides undergoes flexing is given by:

E1/3/? – ( 1 )

Where E denotes the immature ‘s modulus of the stuff and ? denotes the denseness of the stuff.

This home base is merely applicable for a level home base which is under flexing.

Now by utilizing the CES 2007 Design Selector a graph has to be plotted by taking denseness ( ? ) on the X-axis and immature ‘s modulus on the Y-axis.

The stuffs near the line are to be considered for the choice for the roof of coupe exchangeable autos.

Here is a five suited stuffs are given below.

- GFRP epoxy matrix ( isotropic )
- CFRP epoxy matrix ( isotropic )
- Rigid polymer froth ( HD )
- Flexible polymer froth
- Rigid Polymer froth ( LD )

#### STEEL AS A REFERENCE MATERIAL:

By utilizing CES work on Ashby the choice chart with a steel point ( 1,1 ) on the choice graph as shown below to place the stuffs utilizing this techniques that perform comparatively good or ill compared.

#### Dehghan-Manshadi Method of Digital Logic:

The digital logic of deghan manshdi is used to place or choose the outstanding stuff. Short listing is based on public presentation index of the stuffs. The stuffs which I short listed are as follows:

- GFRP, epoxy matrix ( isotropic )
- CFRP, epoxy matrix ( isotropic )
- Rigid Polymer Foam ( HD )
- Flexible Polymer Foam ( MD )
- Rigid Polymer Foam ( LD )

Deghan Manshadi method of Digital Logic is based on the belongingss of the stuffs which are to be satisfied the necessary considerations of weight, stiffness, immature ‘s modulus, thermic conduction and strength.

As we are to see the roof panel on a coupe exchangeable auto these maps and aims demands to be critically taken into consideration to cipher the public presentation indices of the stuff.

Therefore using Deghan Manshadi method of choice of stuffs to the five stuffs which I have short listed is. Harmonizing to digital logic method ; Entire figure of possible determinations ( N ) = n ( n-1 ) /2.

Where, n signifies the figure or ends into consideration.

The comparative accent coefficient ( ? ) is found out from this tabular array. The more the comparative accent for a belongings the more it needs to be sought after and the more it is given importance. The grading factor ( Y ) needs to be found out utilizing the undermentioned equations:

Y1= a1ln ( b1 X + c1 ) ( 2 )

Y2= a2ln ( b2/X + c2 ) ( 3 )

Where Y stands for scaly factor of the stuff and X stands for the numerical value of belongings and a1, b1, c1, a2, b2, c1, c2 are the invariables.

Eq. ( 2 ) is applicable merely for those belongingss which have higher desired value whereas, Equation. ( 3 ) is applicable for belongingss which concerns a lower value.

The invariables a1, b1, c1, a2, b2, c2 are interrelated by equations which are given by ;

- a1 = -100/ ( ln ( XC/ ( Xmax-XC ) ( 4 )
- b1 = ( Xmax-2XC ) / ( XC ( Xmax-XC ) ) ( 5 )
- c1 = XC/ ( Xmax-XC ) ( 6 )
- a2 = -100/ ( ln ( Xmin/ ( Xmin-XC ) ( 7 )
- b2 = -X2c +2XminXc/ ( Xmin – Ninety ) ( 8 )
- c2 = -Xmin/ ( Xmin-XC ) ( 9 )

Epoxy stuff is the most suited of all the five stuffs which are taken into consideration and stiff polymer froth ( LD ) , is the least coveted stuff.

The stuffs that are selected in the normal CES mode are:

- CFRP, epoxy matrix ( isotropic )
- GFRP, epoxy matrix ( isotropic )
- Rigid Polymer Foam ( HD )
- Rigid Polymer Foam ( MD )
- Rigid Polymer Foam ( LD )

The normal CES process gives merely the stuffs that are suited for the applications. This is done by first finding the virtue indices and plotting the graph with required incline. The stuffs which are found in the CES can non be ranked easy. This can be done by proper experience in the choice process. Another method that can be used for material choice is Digital Logical ( DL ) method which is besides known as Dehghan-Manshadi Method of Digital Logic which is explained in inquiry 2, above.

#### Trade Off and Value Function

The five stuffs that were selected for turn uping roof in exchangeable auto utilizing the normal CES process are as follows ;

- CFRP, epoxy matrix ( isotropic )
- GFRP, epoxy matrix ( isotropic )
- Rigid Polymer Foam ( HD )
- Flexible Polymer Foam ( MD )
- Rigid Polymer Foam ( LD )

The equations to happen out the public presentation indices ( P ) of the stuffs that are considered are

P1= E1/3/? , P2= ?f1/2 / ? P1= E1/3/? , P2= ?f1/2 / ?

Two or more aims may be present sometime ; a rare solution exists that can optimise all the belongingss at one time. Any betterment in one belongings is the loss of another belongings. So we need to compromise when the aims to be desired are beliing in existent life determination devising. This contradiction rises because of different pick of stuffs used.

The chief aim in taking a suited stuff is to optimise the figure of prosodies public presentations in the merchandise which could be used.

Multi nonsubjective optimisation is used for this intent ; by plotting the public presentation indices on matching two axes the suited stuffs are selected. Then a trade off surface is plotted. The stuff which falls on the trade off surface are selected for that the coveted aim.

A composite nonsubjective map or value map is formatted which is given by

V= ?1 P1 + ?2 P2 + ?3 P3… + ?iPi…

Where, P1 and P2 are the public presentation indices for the stuffs ?1, ?2 are the exchange invariables which are defined by

?1 = ( ? V/ ?P1 ) p2, … pi

?1 = ( ? V/ ? P2 ) p1, … pi

This measures a alteration in value for a unit alteration in the public presentation metric when all other are held changeless.