Material Properties, Testing & Selection Criteria
Material Properties
A) Sensory Properties
Material selection often depends on their effect on our senses. Natural materials (cotton, silk, linen, etc.) are generally more pleasant to the touch than synthetics. Other sensory factors include smell, shape, luster, texture, and color.
B) Optical Properties
Opaque materials block light, transparent materials allow light to pass through, and translucent materials allow light but distort vision.
C) Thermal Properties
These describe a material’s behavior when exposed to heat.
D) Magnetic Properties
These relate to a ferrous metal’s ability to be attracted by a magnet.
E) Chemical Properties
A key chemical property is resistance to oxidation and corrosion.
F) Mechanical Properties
- Elasticity: Ability to regain original shape after deformation.
- Plasticity: Ability to retain a new shape after deformation.
- Ductility: Ability to be stretched into wires.
- Malleability: Ability to be formed into sheets without breaking.
- Hardness: Resistance to scratching or indentation.
- Brittleness: Tendency to shatter upon impact (opposite of toughness).
- Toughness: Resistance to fracture under slow stress.
- Fatigue: Deformation under varying loads.
- Machinability: Ease of being cut or shaped.
- Hardenability: Ability to increase hardness, brittleness, and resistance in some cast metals.
- Castability: Ability to fill a mold.
- Resilience: Resistance to sudden shocks or impacts.
Physical Stress on Materials
Force applied to an object causes deformation. The type of deformation depends on the stress type, direction, and point of application.
- Tension: Force perpendicular to the surface, tending to elongate the object.
- Compression: Force perpendicular to the surface, tending to shorten the object.
- Flexion (Bending): Force parallel to the surface, tending to bend the object.
- Torsion: Force parallel to the surface, tending to twist the object.
- Shear: Force parallel to the surface, tending to cut through the object.
- Buckling: Similar to compression, but in long, slender objects.
Material Testing
To determine a material’s suitability for specific stresses, various tests are performed.
- Tensile Test: A specimen is slowly stretched until fracture, analyzing elongation.
- Fatigue Test: A specimen is rapidly rotated until failure, determining fatigue limit.
- Hardness Test: A diamond or steel ball is pressed into the material to measure hardness (Brinell, Rockwell scales).
- Impact Test (Charpy): A pendulum strikes a specimen to measure energy absorbed upon fracture.
Material Selection Criteria
Effective material selection requires knowledge of material properties, potential stresses, and part design.
A) Material Properties
Engineers and designers need comprehensive knowledge of material properties and product purpose.
B) Stress Types
Product design must consider the types of stress encountered during use.
C) Part Design
The same material can perform differently under stress depending on its shape and force direction.
Sustainable Material Use
Unsustainable practices lead to premature material depletion and environmental damage.
A) Premature Material Depletion
- Renewable Materials: Sustainable with responsible use (e.g., wood, paper, cotton).
- Non-Renewable Materials: Finite resources (e.g., copper, aluminum, iron).
B) Solutions
- New Designs: Optimized designs minimize material usage.
- Recycling: Reclaiming materials from end-of-life products.
- Reuse: Reusing products or components.
Industrial Waste
A) Waste Types
- Inert Waste: Poses no environmental risk (e.g., rubble, textiles).
- Toxic/Hazardous Waste: Flammable, corrosive, or toxic (solid, liquid, or gas).
B) Waste Management
- Reduction: Minimizing waste generation through new technologies.
- Treatment: Physical, chemical, or biological waste processing.
- Incineration: Burning waste to reduce volume and generate energy.
- Landfill: Disposing of waste in designated areas.