CPE008_Engineering Economics ; Material Selections ; and Teamwork

Engineering Economics

• Economic factors always play important roles in engineering design decision making.

• Products that are too expensive cannot be sold at a price that consumers can afford and still be profitable to the company.

• Products must be designed to provide services not only to make our lives better but also to make profits for the manufacturer.

Electrical resistivity

• Measure of resistance of material to flow of electricity

• Plastics and ceramics typically have high resistivity

• Metal typically has low resistivity

• Silver and copper are one of the best conductors of electricity.

Density

• Defined as mass per unit volume

• Measure of how compact the material is for a given volume

• Average density of
  
  

  • aluminum alloys = 2700 kg/m³

  • steel = 7850 kg/m³

Modulus of elasticity (Young’s modulus)

• Measure of how easily a material will stretch when pulled

• Measure of how well material will shorten when pushed

• The larger the modulus of elasticity, the larger the force required to stretch or shorten a piece of material.

• Modulus of elasticity for
  
  

  • aluminum alloy = 70 to 90 GPa

  • steel = 190 to 210 GPa

Modulus of rigidity (shear modulus)

• Measure how easily a material can be twisted or sheared.

• Value of shear modulus shows the resistance of a given material to shear deformation.

  • Shear modulus for

    • aluminum alloys = 26 to 36 GPa

    • steel = 75 to 80 GPa

Tensile strength

• Determined by measuring the maximum tensile load a material specimen in the shape of a rectangular bar or cylinder can carry without failure.

• Tensile strength or ultimate strength is expressed as the maximum tensile force per unit cross-sectional area of the specimen.

Compressive strength

• Is determined by measuring the maximum compressive load a material specimen in the
  shape of a rectangular bar, cylinder, or cube can carry without failure

• Is expressed in force per unit cross-sectional area of specimen.

• In concrete ranges between 10 to 70 MPa.

Modulus of resilience

• Mechanical property that shows how effective the material is in absorbing mechanical energy without going through any permanent damage.

Modulus of toughness

• Mechanical property that indicates the ability of the material to handle overloading before it fractures.

Strength-to-weight ratio

• Ratio of strength of the material to its specific weight

• Either tensile strength value or yield strength value can be used to determine the ratio.

Thermal expansion

• Shows the change in the length of a material that would occur if the temperature of the material were changed.

• Important material property to consider when designing products and structures that are expected to experience a relatively large temperature swing during their service lives.

Thermal conductivity

• Shows how good a material is in transferring thermal energy (heat) from a high temperature region to a low temperature region within the material.

Heat capacity

• Represents the amount of thermal energy required to raise the temperature of 1 kg mass of material by 1^oC, or 1 lb-mass of material by 1^oF

• Materials with large heat capacity values are good at storing thermal energy.

Viscosity

• Fluid property that measures how easily a given fluid can flow

• The higher the viscosity value is, the more resistance the fluid will offer to flow

• For example, less energy is needed to transport water in a pipe than to transport motor oil or glycerin.

Vapor pressure

• Under the same conditions, fluids with low vapor-pressure values will not evaporate as quickly as those with high values of vapor pressure

• For example, water has a higher vapor pressure value than glycerin.

Bulk modulus of compressibility

• Measures how compressible a fluid is.

• Represents how easily can one reduce the volume of fluid when the fluid pressure is increased.

• For example, it would take 2.24x10⁹ N/m² of pressure to reduce 1 m³ of water to 0.99 m³ a change of 1%.

Design team

• a group of individuals with complementary expertise, problem solving skills, and talent
  who are working together to solve a problem or achieve a common goal.

• Employers are looking for individuals who not only have a good grasp of engineering fundamentals but who can also work well with others in a team environment.