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Manufacturing Process > Week 1. > Flashcards

Week 1. Flashcards

1
Q

What is the definition of force?

A

The product of mass and acceleration.

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2
Q

What is a direct force?

A

A force that is normal to the surface it is applied.

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3
Q

What are the two types of direct force?

A

Tensile or compressive.

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4
Q

What is shear force?

A

A force that tends to tear the member into two and makes the layers of the particles of a body slide over each other.

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5
Q

What is the definition of engineering stress?

A

Engineering Stress = Force (F) / Original Cross-sectional Area (A)

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6
Q

What are the two types of stress?

A

Direct or Shear

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7
Q

What are the two types of direct stress?

A

Compressive or tensile

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8
Q

How is engineering strain defined?

A

Engineering strain is the increase in length per unit original length.

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9
Q

What is the formula for calculating engineering strain?

A

Strain = (change in length) / (original length).

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10
Q

What are the two types of engineering strain?

A

Tensile and Compressive.

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11
Q

What does Hooke’s Law state?

A

Stress is proportional to strain.

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12
Q

How is stress related to strain in Hooke’s Law?

A

Stress = E * Strain, where E is the Young’s Modulus of Elasticity.

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13
Q

What is the constant of proportionality in Hooke’s Law called?

A

Young’s Modulus of Elasticity (E).

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14
Q

What are the three types of static stresses to which materials can be subjected?

A
  1. Tensile - tend to stretch the material
  2. Compressive - tend to squeeze it
  3. Shear - tend to cause adjacent portions of material to slide against each other
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15
Q

What is a stress-strain curve?

A

It is the basic relationship that describes mechanical properties for all three types of stresses.

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16
Q

What is the tensile test commonly used for studying?

A

Stress-strain relationship, especially in metals.

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17
Q

What happens to the material during a tensile test?

A

It is elongated and its diameter is reduced.

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18
Q

What does ASTM stand for?

A

American Society for Testing and Materials.

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19
Q

What does ASTM specify the preparation of?

A

Test specimen.

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20
Q

What is the purpose of a tensile test?

A

To determine the mechanical properties of materials.

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21
Q

What is shown in Figure 3.1 of the document?

A

A typical test specimen for a tensile test.

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22
Q

What is the typical progress of a tensile test?

A

1) Beginning of test, no load

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23
Q

What happens if pieces are put back together after fracture in a tensile test?

A

The final length can be measured.

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24
Q

What does a compression test apply to a cylindrical specimen?

A

A load that squeezes the ends between two platens.

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25
Q

How is the compression force applied to the test piece?

A

Between two platens.

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26
Q

What is the resulting change in height during a compression test?

A

It decreases.

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27
Q

How is engineering stress in tension defined?

A

As force divided by original area.

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28
Q

What does the symbol ‘F’ represent in the equation for engineering stress?

A

Applied force.

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29
Q

What does the symbol ‘Ao’ represent in the equation for engineering stress?

A

Original area of the test specimen.

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30
Q

What happens to the height of the specimen during compression?

A

It is reduced.

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31
Q

How does the cross-sectional area change during compression?

A

It is increased.

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32
Q

What does the symbol A_o represent in the equation for engineering stress in compression?

A

Original area of the specimen.

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33
Q

How is engineering strain defined in tension?

A

e = (L - L0) / L0

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34
Q

How is engineering strain defined in compression?

A

As the reduction in height, resulting in a negative value of strain.

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35
Q

What is the value of engineering strain in compression?

A

Negative (the negative sign is usually ignored when expressing compression strain).

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36
Q

How is the shape of the plastic region different in a compression test compared to a tensile test?

A

The cross-section increases in a compression test.

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37
Q

Is the calculated value of engineering stress higher in a compression test or a tensile test?

A

Higher in a compression test.

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38
Q

What type of test is represented by the engineering stress-strain curve in Figure 3.8?

A

Compression test.

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39
Q

What does the elastic region of the stress-strain curve indicate?

A

It is the region prior to yielding of the material.

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40
Q

What does the plastic region of the stress-strain curve indicate?

A

It is the region after yielding of the material.

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41
Q

What is the Elastic Region in Stress-Strain Curve?

A

The relationship between stress and strain is linear.

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42
Q

What happens to the material when stress is removed in the Elastic Region?

A

The material returns to its original length.

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43
Q

What is Hooke’s Law?

A

σe = Ee, where E is the modulus of elasticity.

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44
Q

What does the modulus of elasticity (E) measure?

A

The inherent stiffness of a material.

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45
Q

How does the value of modulus of elasticity (E) differ for different materials?

A

Its value differs for different materials.

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46
Q

What is the Yield Point in a stress-strain curve?

A

The point at which the material begins to yield and the linear relationship changes slope at the upper end of the linear region.

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47
Q

How is the Yield Point identified?

A

By the change in slope at the upper end of the linear region.

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48
Q

What is another name for the Yield Point?

A

Yield strength, yield stress, and elastic limit.

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49
Q

What happens at the Yield Point in terms of strain?

A

0.2% permanent set of strain or 0.002 strain offset, meaning the material won’t return to its original length.

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50
Q

How is the Young’s Modulus value calculated at the Yield Point?

A

By subtracting 0.002 from the strain value of the yield point to get the strain which corresponds to the Young’s Modulus value.

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51
Q

What is the modulus of elasticity of the material?

A

Change in stress / Change in strain

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52
Q

How is tensile strength determined?

A

By dividing the maximum load by the original cross-sectional area of the specimen.

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53
Q

What is the percent elongation if fracture occurs at a gage length of 7.4 cm?

A

((7.4 - 5) / 5) * 100%

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54
Q

How is the percent reduction in area determined if the specimen necked to an area of 1.56 cm^2?

A

((3.125 - 1.56) / 3.125) * 100%

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55
Q

What does AR stand for and how to calculate it?

A

AR = (Ao - Af) / Af

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56
Q

What does the yield point mark in the stress-strain curve?

A

The beginning of plastic deformation.

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57
Q

What law is no longer guided beyond the yield point in the stress-strain relationship?

A

Hooke’s Law.

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58
Q

What happens to the elongation rate beyond the yield point?

A

It proceeds at a much faster rate than before.

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59
Q

How does the slope of the stress-strain curve change beyond the yield point?

A

It changes dramatically.

60
Q

What happens to the cross-sectional area during elongation in a tensile test?

A

It undergoes a uniform reduction.

61
Q

What is the engineering stress at the point where the applied load reaches a maximum?

A

Tensile strength or ultimate tensile strength.

62
Q

How is the ultimate tensile strength (TS) defined?

A

TS = F max / A

63
Q

What is ductility in the context of a tensile test?

A

The ability of a material to plastically strain without fracture.

64
Q

How is elongation (EL) calculated in a tensile test?

A

EL = (L - Lo) / Lo, where L is the specimen length at fracture and Lo is the original specimen length.

65
Q

How is true stress calculated?

A

True stress is obtained by dividing the instantaneous area into the applied load.

66
Q

What does true strain provide a more realistic assessment of?

A

Instantaneous elongation per unit length.

67
Q

What type of stress-strain values were used to plot the previous curves?

A

True stress and strain values.

68
Q

What department at Stellenbosch University is associated with this information?

A

Industrial Engineering Department.

69
Q

What happens to true stress in the plastic region until necking?

A

It increases continuously.

70
Q

Why was the significance of strain hardening lost in the engineering stress - strain curve?

A

Because stress was based on an incorrect area value.

71
Q

What does it mean when a metal is becoming stronger as strain increases?

A

It exhibits strain hardening.

72
Q

What happens to the plastic region of the true stress-strain curve when plotted on a log-log scale?

A

It becomes linear.

73
Q

What is the relationship between true stress and true strain in the plastic region?

A

It is a straight line in a log-log plot.

74
Q

What does the symbol ‘K’ represent in the flow curve equation?

A

Strength coefficient.

75
Q

What does the symbol ‘n’ represent in the flow curve equation?

A

Strain hardening exponent.

76
Q

What is the formula for the flow curve equation in a tensile test?

A

σ = Kε^n

77
Q

What does ‘K’ represent in the flow curve equation?

A

The strength coefficient.

78
Q

What does ‘n’ represent in the flow curve equation?

A

The strain-hardening exponent.

79
Q

How is the strength coefficient (K) calculated in the flow curve equation?

A

K = σ/ε^n

80
Q

How is the strain-hardening exponent (n) calculated in the flow curve equation?

A

n = ln(σ2/σ1) / ln(ε2/ε1)

81
Q

What are the differences between engineering stress-strain curves in tension and compression?

A

Although differences exist, the true stress-strain relationships are nearly identical.

82
Q

How are flow curve values from tensile test data applied to compression operations?

A

The flow curve values (K and n) from tensile test data can be applied to compression operations.

83
Q

What phenomenon should be ignored when using tensile K and n data for compression?

A

Necking, which is peculiar to straining induced by tensile stresses.

84
Q

What are the categories of Stress-Strain Relationship?

A
  1. Perfectly elastic, 2. Elastic and perfectly plastic, 3. Elastic and strain hardening.
85
Q

What defines the behavior completely?

A

Modulus of elasticity (E).

86
Q

What happens to materials defined by modulus of elasticity (E) when stressed?

A

They fracture rather than yielding to plastic flow.

87
Q

What type of materials are considered brittle?

A

Ceramics, many cast irons, and thermosetting polymers.

88
Q

What are the three categories of stress - strain relationship?

A

Perfectly elastic, perfectly plastic, and strain hardening.

89
Q

What is the symbol used to represent stiffness?

A

E.

90
Q

What happens to a material once it reaches the yield point?

A

It deforms plastically at the same stress level.

91
Q

What are the values of K and n in the flow curve when a material behaves elastically and perfectly plastically?

A

K = Y, n = 0.

92
Q

When do metals behave like elastic and perfectly plastic materials?

A

When heated to sufficiently high temperatures (above recrystallization).

93
Q

What does Hooke’s Law describe in the elastic region?

A

The relationship between stress and strain.

94
Q

What does a flow curve with K > Y and n > 0 indicate?

A

Most ductile metals behaving this way when cold worked.

95
Q

In which category of stress-strain relationship does elastic and strain hardening fall?

A

Elastic and Strain Hardening.

96
Q

What type of materials are often tested by a bending test?

A

Hard brittle materials (e.g., ceramics).

97
Q

What is another name for the bending test?

A

Flexure test.

98
Q

How is the specimen positioned in a bending test?

A

Between two supports, with a load applied at its center.

99
Q

What happens to brittle materials before fracture?

A

They deform elastically until fracture.

100
Q

How does failure occur in brittle materials?

A

Failure occurs because tensile strength of outer fibers of specimen are exceeded.

101
Q

What is the common failure type with ceramics and metals at low temperatures?

A

Cleavage, in which separation rather than slip occurs along certain crystallographic planes.

102
Q

What is Transverse Rupture Strength (TRS) derived from?

A

The bending test.

103
Q

How is Transverse Rupture Strength (TRS) calculated?

A

TRS = F / (b * t)

104
Q

What does ‘F’ represent in the TRS formula?

A

Applied load at fracture.

105
Q

What does ‘L’ represent in the TRS formula?

A

Length of specimen between supports.

106
Q

How is shear stress defined?

A

Shear stress is defined as F/A, where F = applied force and A = area over which deflection occurs.

107
Q

How is shear strain defined?

A

Shear strain is defined as δ/b, where δ = deflection element and b = distance over which deflection occurs.

108
Q

What is the relationship for shear elastic stress-strain in the elastic region?

A

G = shear modulus, where G = 0.4E for most materials.

109
Q

What is the relationship between shear plastic stress and strain?

A

Similar to the flow curve.

110
Q

How can shear strength be estimated from tensile strength?

A

Shear strength ≈ 0.7 * Tensile Strength.

111
Q

What type of stress-strain curve is the engineering stress-strain curve for shear similar to?

A

True stress-strain curve.

112
Q

What is the formula for calculating the factor of safety?

A

Factor of safety = Yield stress / Working stress.

113
Q

How is working stress defined?

A

The stress a component is subjected to during its day-to-day usage.

114
Q

What is the purpose of incorporating a factor of safety in a component’s design?

A

To avoid premature failure of the component.

115
Q

What is hardness in materials?

A

Resistance to permanent indentation.

116
Q

What does good hardness in a material indicate?

A

Resistance to scratching and wear.

117
Q

Why must most tooling used in manufacturing be hard?

A

For scratch and wear resistance.

118
Q

Why are hardness tests commonly used for assessing material properties?

A

Because they are quick and convenient.

119
Q

Why are a variety of testing methods appropriate for hardness tests?

A

Due to differences in hardness among different materials.

120
Q

What are the most well-known hardness tests?

A

Brinell and Rockwell.

121
Q

Apart from Brinell and Rockwell, what are some other hardness test methods?

A

Vickers, Knoop, Scleroscope, and durometer.

122
Q

What is the load used in Brinell hardness testing?

A

500, 1500, or 3000 kg.

123
Q

What type of specimen surface is a hard ball pressed into in Brinell hardness testing?

A

Specimen surface of metals and nonmetals of low to medium hardness.

124
Q

What is the name of the hardness testing method where a hard ball is pressed into the specimen surface?

A

Brinell hardness testing.

125
Q

What is the formula for calculating Brinell Hardness Number (BHN)?

A

HB = F / (π * D * (D - sqrt(D^2 - d^2))),
where HB is the Brinell Hardness Number,
F is the indentation load in kg,
D is the diameter of the ball in mm,
d is the diameter of the indentation in mm.

126
Q

What is the Rockwell Hardness Test?

A

A widely used test where a cone-shaped indenter is pressed into a specimen using a minor load of 10 kg followed by a major load of 150 kg.

127
Q

What is the purpose of the minor load in the Rockwell Hardness Test?

A

To seat the indenter in the material.

128
Q

What happens when the major load is applied in the Rockwell Hardness Test?

A

It causes the indenter to penetrate beyond its initial position.

129
Q

How is the Rockwell hardness reading determined?

A

By converting the additional penetration distance (d) into a reading using the testing machine.

130
Q

What is hot hardness?

A

The ability of a material to retain hardness at elevated temperatures.

131
Q

What does hot hardness measure?

A

The ability of a material to maintain its hardness at elevated temperatures.

132
Q

Why is hot hardness important in manufacturing processes?

A

It ensures that materials maintain their hardness at high temperatures.

133
Q

What is recrystallization in metals?

A

The formation of new grains that are free of strain when a metal is heated to a sufficiently high temperature and deformed.

134
Q

What happens to the strain hardening of metals when heated to a sufficiently high temperature?

A

Strain hardening does not occur, and the metal behaves as a perfectly plastic material with n = 0.

135
Q

How do most metals behave at room temperature according to the flow curve?

A

Most metals strain harden at room temperature (n > 0).

136
Q

What is recrystallization in metals?

A

Formation of new strain-free grains.

137
Q

How is the recrystallization temperature of a metal related to its melting point?

A

About one-half of its melting point (0.5 Tm) on an absolute temperature scale.

138
Q

How is the recrystallization temperature specified?

A

As the temperature at which new grains are formed in about one hour.

139
Q

What is recrystallization in the context of manufacturing?

A

Heating a metal to its recrystallization temperature prior to deformation.

140
Q

What are the advantages of heating a metal to its recrystallization temperature before deformation?

A

Allows a greater amount of straining and requires lower forces and power for the process.

141
Q

What is the term for forming metals at temperatures above the recrystallization temperature?

A

Hot working.

142
Q

What do mechanical properties determine in a material?

A

A material’s behavior when subjected to mechanical stresses.

143
Q

What are some examples of mechanical properties?

A

Elastic modulus, ductility, hardness, and various measures of strength.

144
Q

What is the dilemma related to mechanical properties in design and manufacturing?

A

Desirable mechanical properties for high strength usually make manufacturing more difficult.

145
Q

What should the manufacturing engineer appreciate in relation to the design viewpoint?

A

The desirable mechanical properties for high strength.

146
Q

What should the designer be aware of in relation to the manufacturing viewpoint?

A

The impact of desirable mechanical properties on manufacturing difficulty.

Manufacturing Process (11 decks)

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