Material selection Flashcards
What are six categories of materials
Metals Plastics Ceramics Elastomers Composites Glasses
What are the 3 main steps in any material selection method
Analysis of material requirements
Screening of candidate materials
Selection of candidate material
What should be considered when analysing material requirements
Mandatory and additional material properties for the end product
Material properties required for the manufacturing process
Relative importance of each
What is determined using the screening of candidate materials process
Materials can be eliminated on a go/no go basis
What are the most common methods of material selection
Use of selection chart
Selection on cost
Subjective Selection
Weighted properties method
Why is selection on cost such a bad method for material selection
Neglects the fact that no two materials have the same properties
What is a good method for fixing selection based on cost
Use material indices such as cost per unit stiffness
What different costs will effect the overall cost of a product
Cost of materials
Cost of production
Cost of operating or maintenance
Cost of disposal
What is the material utilisation factor
A ratio of the weight of finished product and the weight of material used to make product
What is cost of production dependant on
Utilisation factor How easy it is to form or machine How long it takes to produce Cost of machinery Cost of specialist one off tools Cost of surface treatments
What factors effect the time to produce the material
Set up time
Operator handling time
Machining time
Dow/ lost time
What will effect the cost per unit production of different materials for the same production method
Weldability
Formability
Melting temperature
Aspect Ratio
What are chart election methods often used for in industry
To screen all potential materials on a go/no go basis to eliminate groups of materials early in design
Are material selection charts often used to make the final material selection in industry
No
What are the limitations of selection charts
Not suitable for complex shapes Lots of opportunity for mistakes in constraints etc
What are the some positives of selection charts
New engineering are not limited by minimum experience
New materials are considered
What are some qualities of the subjective method of material selection
Minimum calculation
Lots of engineering judgment
In terms of scaling of properties what is a disadvantage of the subjective method
Does not allow comparison to the degree of which one material is better than the other, just better, worse or even
What is another problem with the subjective methods with respect to weighting
All material properties are weighted the same
Describe how the weighted properties method can be used to take into account thickness
When Scaling properties the material properties can be multiplied by or divided by the relative thickness
What material properties are effected by thickness
Specific heat Stiffness Strength Cost Thermal conductivity
What is the digital logic method
A way of determining a more accurate ( But still subjective) way of calculating the weighting factors
What factors should be considered when deciding what materials properties to use in a selection method
Functional requirements Processability requirements Cost Reliability Resistance to service conditions Disposal requirements
What are rigid material requirements
Ones which are a simple yes or no decision such as must be transparent
