Lecture 30: Part -1: Wrap up shape

selection Part 2: Introduction to

process selection

Jayant Jain Assistant Professor,

Department of Applied Mechanics, IIT Delhi, Hauz Khas, 110016

Presentation Schedule

Monday morning group Wednesday, 22/04/2015, 8:00-8:20

Monday afternoon group Wednesday, 22/04/2015, 8:20-8:40

Tuesday morning group Wednesday, 22/04/2015, 8:40-9:00

Tuesday afternoon group Friday, 24/04/2015, 8:00-8:20

Wednesday morning group Friday, 24/04/2015, 8:20-8:40

Wednesday afternoon group Friday, 24/04/2015, 8:40-9:00

Thursday morning group Tuesday, 28/04/2015, 8:00-8:20

Thursday afternoon group Tuesday, 28/04/2015, 8:20-8:40

Friday morning group Tuesday, 28/04/2015, 8:40-9:00

Note: All the discussions, questions and key concepts will be the part of your final exam

Recap

Shape factors (SF), significance of SF, derived SFs for common loading conditions Microscopic shape factors, derived SFs for common shapes Combined Macro and microscopic shape factors Graphical approach of solving problem: 4 Q approach, limitations were also highlighted Calculated Materials Indices that includes shape, this can be used for any material selection problem that involves shape as a variable

The indices can be used to allow comparison and selection of best material-shape combinations: will seek maximum of Material indices The co-selection of Material and Shape can be carried by two ways: 1. Calculations

2. Graphical

Material-Shape co-selection

Your task would be is to select best material from the choices given below in the table for a stiff beam of minimum mass. Note that you have to propose your choice for both when shape is variable and when it is not.

Problem: By calculations

Fixed shape Shape as a variable

Solve the same problem by graphical approach: How to utilise shape factors in graphical selection

The structured material behaves like a new material with a modulus and a density, moving it from a position below the broken selection line to one above.

Introduction of shape has moved material below the line to above the line

A similar procedure can be adopted for other cases e.g. Failure in bending

The material with strength and density, when shaped, behaves in bending like a new material of strength and density

Introduction to process selection

What is a process? A process is a method of shaping, joining and finishing a material Examples of various processes 1) Sand casting 2) Injection molding 3) Fusion welding 4) Electro polishing

There can be hundreds other...............

Processes

It is important to choose the right process-route at an early stage in the design before the cost-penalty of making changes becomes large.

What could be the factors on which the choice of a process for a given component depends? 1) Material 2) Shape 3) Size, required precision, quantity.......

Each process is characterized by a set of attributes Process selection means finding the best match between process attributes and design requirements

Processes

Process attributes

Material-Process-Shape Interaction

Included process now Processing selection depends on material and shape. The process attributes can be used as criteria for selection

Materials properties and shape limit the choice of process How does a choice of material affects the process selection? Example: Ductile materials vs. Brittle materials How does a shape affects the process selection? Example: Slender shape vs. Hollow shapes How does the processing affects the materials properties Example: Rolling, forging of metals

Material properties, shape and processes

Process-property Interaction

Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon

Soft, stretchy rubber becomes hard and brittle when vulcanized

Annealing a metal increases its ductility Glass becomes bullet-proof through a

specific heat treatment Electroplating improves corrosion

resistance

Processing has dual functions

It is imp to understand the relationship between process and property

Strengthening mechanisms and the consequent drop in

ductility, here shown for copper alloys. The mechanisms are

frequently combined. The greater the strength, the

lower the ductility.

Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby

Effect of processing on properties

Thermal conductivity and strength for aluminum

alloys.

Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby

The best choice of material for a cable is one with high

strength and low resistivity, but

strengthening mechanisms increase resistivity.

Copper cables

The changes in fracture toughness and yield strength for a plain

carbon steel on heat treatment. Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby