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Metals are the most resistant to corrosion among all classes of materials.
Metals are the most resistant to corrosion among all classes of materials.
False
Ceramics and glasses retain their strength at high temperatures.
Ceramics and glasses retain their strength at high temperatures.
True
Elastomers are classified as a type of composite material.
Elastomers are classified as a type of composite material.
False
All members of the same class of engineering materials have similar properties.
All members of the same class of engineering materials have similar properties.
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High strength metals do not show ductility at all.
High strength metals do not show ductility at all.
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Ceramics are known for their ability to deform easily under stress.
Ceramics are known for their ability to deform easily under stress.
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Polymers, elastomers, and composites are all classified under one category of engineering materials.
Polymers, elastomers, and composites are all classified under one category of engineering materials.
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Metals can be processed by methods such as rolling, forging, and extrusion.
Metals can be processed by methods such as rolling, forging, and extrusion.
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Plastic deformation can occur in brittle materials allowing stress accommodation.
Plastic deformation can occur in brittle materials allowing stress accommodation.
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Polymers can develop a permanent set under load at room temperature.
Polymers can develop a permanent set under load at room temperature.
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Ceramics display a narrow scatter in strength, making them easy to design with.
Ceramics display a narrow scatter in strength, making them easy to design with.
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At temperatures above 200°C, polymers retain their strength.
At temperatures above 200°C, polymers retain their strength.
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Composites combine properties of different materials while mitigating their drawbacks.
Composites combine properties of different materials while mitigating their drawbacks.
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The performance of polymer matrix composites is outstanding at high temperatures.
The performance of polymer matrix composites is outstanding at high temperatures.
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Polymers are corrosion resistant and have a high friction coefficient.
Polymers are corrosion resistant and have a high friction coefficient.
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Ceramics are easier to design with than ductile materials.
Ceramics are easier to design with than ductile materials.
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Young’s modulus, E, describes shear loading.
Young’s modulus, E, describes shear loading.
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Poisson’s ratio, n, is a dimensionless quantity that represents the ratio of lateral strain to axial strain.
Poisson’s ratio, n, is a dimensionless quantity that represents the ratio of lateral strain to axial strain.
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For metals, the yield strength is taken as the 0.2% offset tensile strength.
For metals, the yield strength is taken as the 0.2% offset tensile strength.
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Composites containing fibers are stronger in compression than in tension.
Composites containing fibers are stronger in compression than in tension.
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Bulk modulus, K, describes the effect of shear loading on materials.
Bulk modulus, K, describes the effect of shear loading on materials.
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The slope of the stress-strain curve can provide values for both Young’s modulus and shear modulus.
The slope of the stress-strain curve can provide values for both Young’s modulus and shear modulus.
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Polymers exhibit greater strength in tension compared to compression.
Polymers exhibit greater strength in tension compared to compression.
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The fracture strength for ceramics in tension is typically greater than the crushing strength in compression.
The fracture strength for ceramics in tension is typically greater than the crushing strength in compression.
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The elastic moduli are represented by the symbol E and measured in GPa.
The elastic moduli are represented by the symbol E and measured in GPa.
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The Archard wear constant is classified under thermal properties.
The Archard wear constant is classified under thermal properties.
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Corrosion rates in the material properties are expressed in units of m2/s.
Corrosion rates in the material properties are expressed in units of m2/s.
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The yield function for metals uses the Tresca criterion for multiaxial loading.
The yield function for metals uses the Tresca criterion for multiaxial loading.
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The thermal conductivity of materials is measured in K/m.
The thermal conductivity of materials is measured in K/m.
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Fracture toughness is a property that indicates a material's ability to resist crack propagation.
Fracture toughness is a property that indicates a material's ability to resist crack propagation.
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In polymers, the yield function does not consider the effects of pressure.
In polymers, the yield function does not consider the effects of pressure.
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The thermal shock resistance is denoted by the symbol Tm.
The thermal shock resistance is denoted by the symbol Tm.
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Specific heat is indicated by the symbol Cp and measured in J/kg K.
Specific heat is indicated by the symbol Cp and measured in J/kg K.
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The unit of density is Mg/m3.
The unit of density is Mg/m3.
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The modulus of rupture (MOR) is the maximum surface stress in a bent beam at the instant of failure in units of MN/m2.
The modulus of rupture (MOR) is the maximum surface stress in a bent beam at the instant of failure in units of MN/m2.
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For brittle solids, the ultimate tensile strength su differs from the tensile failure stress.
For brittle solids, the ultimate tensile strength su differs from the tensile failure stress.
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The hardness of a material is related to its strength and is measured in units of MPa.
The hardness of a material is related to its strength and is measured in units of MPa.
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Ductile polymers have a lower ultimate tensile strength than brittle solids.
Ductile polymers have a lower ultimate tensile strength than brittle solids.
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Hardness is defined as the indent force divided by the projected volume of the indent.
Hardness is defined as the indent force divided by the projected volume of the indent.
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Large hardness indicates better wear properties and resistance to plastic deformation.
Large hardness indicates better wear properties and resistance to plastic deformation.
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Load transfer in composites can lead to a lower ultimate tensile strength compared to metals.
Load transfer in composites can lead to a lower ultimate tensile strength compared to metals.
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The hardness test involves pressing a pointed diamond or hardened steel ball into the surface of a material.
The hardness test involves pressing a pointed diamond or hardened steel ball into the surface of a material.
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Mild steel has a fatigue ratio that is defined as the ratio of the fatigue limit to the yield strength.
Mild steel has a fatigue ratio that is defined as the ratio of the fatigue limit to the yield strength.
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Fatigue failure occurs even if the maximum stress is less than the fatigue limit.
Fatigue failure occurs even if the maximum stress is less than the fatigue limit.
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The fatigue limit for some materials can be zero.
The fatigue limit for some materials can be zero.
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Cyclic stress is not a significant factor in engineering failures, accounting for about 30% of them.
Cyclic stress is not a significant factor in engineering failures, accounting for about 30% of them.
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The parameters S, sm, and frequency are crucial for evaluating fatigue in materials.
The parameters S, sm, and frequency are crucial for evaluating fatigue in materials.
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The safe region for fatigue is indicated when stress amplitude is greater than the fatigue limit.
The safe region for fatigue is indicated when stress amplitude is greater than the fatigue limit.
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Fatigue occurs due to stress variations over time.
Fatigue occurs due to stress variations over time.
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Stress amplitude (S) is the average of the maximum and minimum stresses experienced during a cycle.
Stress amplitude (S) is the average of the maximum and minimum stresses experienced during a cycle.
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Study Notes
Engineering Material Selection - CH 560
- This course, CH 560, covers engineering material selection.
- Engineering materials fall into six broad classes: Metals, Polymers, Elastomers, Ceramics, Glasses, Composites.
- Members of each class share similar properties, processing routes, and applications.
- Composites are combinations of two or more of the above classes.
Metals
- Metals have relatively high moduli.
- Ductility allows for shaping through processes like rolling, forging, and extrusion.
- Even high-strength metals exhibit some ductility (e.g., spring steel 2%) and typically fracture in a ductile manner.
- Metals are prone to fatigue.
- Metals are the least resistant to corrosion among all material classes.
Ceramics and Glasses
- Ceramics and glasses have high moduli (stiffness).
- They are brittle.
- They are hard and abrasion resistant (used in bearings/cutting tools).
- They maintain strength at high temperatures.
- They are corrosion resistant but have low tolerance for stress concentrations (e.g., holes, cracks).
- They have low tolerance for high contact stresses.
Polymers and Elastomers
- Polymers and elastomers have low moduli (50 times less than metals).
- Polymers can be strong.
- Polymers can exhibit large elastic deflections.
- Polymers creep even at room temperature, potentially developing a permanent set over time.
- Polymer properties depend significantly on temperature.
- At 20°C: tough and flexible
- At 4°C: brittle
- At 100°C: can creep rapidly
- Strength is poor above 200°C.
- Polymers are easy to shape, allowing for complex part creation in a single step.
- Polymers have good strength-to-weight ratios.
- Polymers are corrosion resistant.
- Polymers have low coefficients of friction.
- Polymers are widely used and are becoming increasingly prevalent.
Composites
- Composites combine the attractive properties of other material classes while minimizing their drawbacks.
- Composites are frequently used, often incorporating polymer matrix components reinforced with fibres like glass, carbon, or Kevlar.
- At room temperature, composites can perform outstandingly.
- Above 250°C, polymer matrix composites soften.
- Composites are expensive, making their component joining difficult.
- Engineered components incorporate composites where performance enhancements outweigh increased costs.
Material Properties - Definitions
- Density: Weight per unit volume (measured by weighing in air and fluid). Units: Mg/m³.
-
Elastic Modulus: Derived from the elastic part of the stress-strain curve. Units: GPa or GN/m².
- Young's Modulus (E) describes tension/compression.
- Shear Modulus (G) describes shear loading.
- Bulk Modulus (K) describes hydrostatic pressure effects.
- Poisson's ratio (v) is the negative ratio of lateral strain to axial strain.
-
Strength:
- Metals: Often the 0.2% offset yield strength.
- Polymers: Stress (σy) at which the stress-strain curve becomes non-linear (typically at 1%). Polymers are stronger in compression (~20%) than tension.
- Ceramics and Glasses: Strength is heavily dependent on loading mode. Tensile strength is the fracture strength, while compressive strength is the crushing strength (typically much higher).
- Composites: Often taken as the 0.5% offset linear elastic behavior. They are usually weaker in compression (~30% less) than tension.
- Hardness: Measured by pressing an indenter into a material. Hardness (H) is force divided by the projected area of the indent; roughly proportional to 3σy. Higher hardness resists plastic deformation and cracking in compression.
Other material properties
- Toughness (Gc): Resistance to crack propagation. Units: kJ/m².
- Fracture Toughness (Kc): Determined by loading a specimen with an existing crack of length 2c. Units: MPam1/2 or MN/m3/2.
- Loss Coefficient (η): Measures energy dissipation in a stress-strain cycle. Dimensionless.
- Fatigue: Failure under cyclic loading. The Fatigue limit (Sfat) is a critical stress amplitude below which fatigue failure is prevented.
-
Creep: Deformation under constant stress over time.
Three phases:
- Primary: Creep rate decreases with time.
- Secondary: Creep rate is constant.
- Tertiary: Creep rate increases with time, leading to acceleration.
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Description
This quiz covers the main concepts from Engineering Material Selection in CH 560, focusing on the properties, processing routes, and applications of various materials. Explore the differences among metals, ceramics, glasses, and composites, and understand their significance in engineering applications.
