A fastener bolt for the airframe of a glider has a cross-sectional area of 1.0 square cm and a length of 4.0 cm. The part must be able withstand a tensile force of 1.0 × 104 N, and as a factor of safety this tensile force can produce a stress of no more than 50 percent of the tensile yield stress in the bolt. For damage tolerance the bolt must have at least 10 percent strain to fracture. Because weight is critical for this glider design the maximum weight possible for this bolt is 8.0 g. The bolt is not subject to high or low temperatures. Of the materials covered in this chapter what would be the best material to select? Because this is an aircraft part it not necessary to choose the cheapest material, but excessive cost should be avoided.
What will be an ideal response?
Ceramics are eliminated from consideration because they should not be used in a design with any significant tensile forces. The weight requirement could limit the selection of the material. The maximum density (?) for the part is calculated from the maximum weight divided by the volume of the part.
There are is one magnesium alloy in two tempers that have this yield strength AZ80A-F and AZ80A-T6. The strain to failure for the AZ80A-T6 is only 5 percent and is therefore not sufficiently ductile. The alloy AZ80A-F has 11 percent strain to failure and satisfies all of the requirements. Of the polymers PEEK has a maximum tensile strength of 200 MPa. in Table 8.17, the yield strength would be less than the tensile strength. Therefore, PEEK is not suitable, and none of the polymers are suitable.
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A radiation source is to be built, as shown in the diagram, for an experimental study of radiation. The base of the hemisphere is to be covered by a circular plate having a centered hole of radius R/2. The underside of the plate is to be held at 555 K by heaters embedded in its surface. The heater surface is back. The hemispherical surface is well-insulated on the outside. Assume gray diffuse processes and uniform distribution of radiation. (a) Find the ratio of the radiant intensity at the opening to the intensity of emission at the surface of the heated plate. (b) Find the radiant energy loss through the opening in watts for R = 0.3 m. (c) Find the temperature of the hemispherical surface.
GIVEN
• A radiation source as shown above
• Radius of hole = R/2
• Temperature of underside of plate (T2) = 555 K
• Underside of plate is black
• Hemispherical surface is well insulated on the outside
FIND
(a) The ratio of the radiant intensity at the opening to the intensity at the surface of the heated plate (G1/ Eb2)
(b) The radiant energy loss through the opening (q1) in watts for R = 0.3 m
(c) The temperature of the hemispherical surface (T3)
ASSUMPTIONS
• Gray diffuse processes
• Uniform distribution of radiation
• Radiation entering A1 is negligible, i.e., A1 as a black body at 0 K Heat loss through insulation is negligible
PROPERTIES AND CONSTANTS
The Stephan-Boltzmann constant (?) = 5.67 × 10–8 W/(m2 K4)
How do we know how old the solar system is?
A) by measuring the rate of the expansion of the universe B) We estimate the age based on how fast the terrestrial planets cooled and solidified. C) by radiometric dating of meteorites D) by measuring how much mass the Sun has lost through fusion over time
At a particular instant, a proton moves Eastward in a uniform magnetic field that is directed straight downward. The magnetic force that acts on it is
A) to the South. B) zero. C) directed upward. D) Northward. E) Westward.
Metal lids on glass jars can often be loosened by running them under hot water. Why is this?
a. The hot water is a lubricant. b. The metal and glass expand due to the heating, and the glass being of smaller radius expands less than the metal. c. The metal has a higher coefficient of thermal expansion than glass so the metal expands more than the glass thus loosening the connection. d. This is just folklore.