Materials CH 6
Which of the following materials has the highest Young's modulus? a. Ceramic b. Metal c. Composite d. Polymer
Ceramic
Only one test currently exists for determining hardness. True False
False
When a metallic-glass compression sample is deformed at a constant displacement rate, the load will remain constant. a. True b. False
False
Identify the correct method used to find the yield strength in a typical stress-strain curve. a. Find the offset strain at 0.2, draw a line parallel to the linear portion of the engineering stress-strain curve, and then read the intersection stress value b. Find the offset strain at 0.2, draw a line perpendicular to the strain axis of the engineering stress-strain curve, and then read the intersection stress value c. Find the offset strain at 0.002, draw a line perpendicular to the strain axis of the engineering stress-strain curve, and then read the intersection stress value d. Find the offset strain at 0.002, draw a line parallel to the linear portion of the engineering stress-strain curve, and then read the intersection stress value
Find the offset strain at 0.002, draw a line parallel to the linear portion of the engineering stress-strain curve, and then read the intersection stress value
In many ductile materials, deformation does not remain uniform. At some point, one region deforms more than others and a large local decrease in the cross-sectional area occurs. This phenomenon is known as ______________. a. retrenching b. narrowing c. necking d. local reducing
Necking
If the relationship between the applied shear stress and the shear strain rate is linear, we refer to that material as__________. If the relationship between shear stress and shear strain rate is nonlinear, these materials are __________. a. Nichian, Newtonian b. Newtonian, Nichian c. non-Newtonian, Newtonian d. Newtonian, non-Newtonian
Newtonian, non-Newtonian
____________ occurs when a stress is removed and the material does not go back to its original shape. a. Plastic deformation b. Permanent deformation c. Unchangeable deformation d. Constant deformation
Plastic deformation
The equation for determining engineering stress is __________ and the equation for engineering strain is __________. a. e=Δl/lo, S=F/Ao b. S=F/Ao, e=Δl/lo c. e=Δl/Ao, S=F/Ao d. S=F/Ao, e=Δl/Ao
S=F/Ao, e=Δl/lo
For a typical metal specimen in the stress-strain test, which stress represents the maximum applied force the specimen can take? a. Breaking strength b. Lower yield strength c. Upper yield strength d. Tensile strength
Tensile strength
Which of the following mechanisms can be used to explain why the Titanic experienced steel hull failure? a. The applied strength exceeded the tensile strength of the steel b. The applied strength exceeded the yield strength of the steel c. The crack size exceeded the fracture toughness it could handle d. The steel was at a temperature lower than the ductile to brittle transition temperature
The steel was at a temperature lower than the ductile to brittle transition temperature
Which of the following statements is correct? a. There is no maximum in the true stress-true strain curve b. High temperatures are defined irrespective of a material's melting temperature c. The normal tensile test is commonly used for brittle materials d. Hardness does not correlate well with wear resistance
There is no maximum in the true stress-true strain curve
Ceramics normally have poor toughness, even if they display high strength, because they have virtually no ductility. These materials show both poor tensile toughness and poor impact toughness. a. True b. False
True
For load-bearing applications, engineered materials are selected by matching their mechanical properties to the component's design specifications and service conditions. True False
True
Nanoindentation techniques are important for deforming free-standing micro and nanoscale structures. a. True b. False
True
The critical stress needed to initiate plastic deformation is the elastic limit of the material. True False
True
The two most common measures of ductility are percent elongation and percent reduction. a. True b. False
True
In metals, the yield strength decreases rapidly at higher temperatures due to a decreased _____________ density and an increase in ______________. a. relocation, grain size b. relocation, dislocation c. grain size, dislocation d. dislocation, grain size
dislocation, grain size
The ability of a material to withstand an impact blow is often referred to as the __________ of the material. a. impact toughness b. impact reliability c. impact energy d. impact test
impact toughness
Material dislocations must be introduced into the crystal structure of a material in order to induce a nonuniform shape change. Such dislocations are called geometrically ___________________. a. necessary relocations b. installed dislocations c. necessary dislocations d. required dislocations
necessary dislocations
The equation for true stress is expressed as ________ while the equation for true strain is expressed as _________. After necking begins, the equation ___________ must be used to determine true strain. a. σ= F/A, ε = ln(l/lo), ε = ln(Ao/A) b. ε = ln(Ao/A), σ= F/A, ε = ln(l/lo) c. ε = ln(l/lo), σ= F/A, ε = ln(Ao/A) d. ε = ln(l/lo), ε = ln(Ao/A), σ= F/A
σ= F/A, ε = ln(l/lo), ε = ln(Ao/A)
