Reference Material
This post is a place holder for reference material
Engineering Materials Database
[
{
"Question": ["What does a tensile test measure?", "How is a tensile test performed?"],
"Answer": "A tensile test measures the strength and ductility of a material. The test specimen is usually a flat or round bar. The two ends of the test specimen are clampedduring the test. The specimen is then stretched slowly until it breaks. Results are expressed by stress-strain diagrams. A stress-strain diagram is a plot of measured stress versus measured strain. The measured stress is on the y axis. The measured strain is on the x axis. The measured stress is the measured applied force divided by the original area. The units of stress are force divided by area. In SI units, this is newtons divided by square meters. This unit has a special name. The special name is pascals. The measured strain is the deformed length divided by the original length. The strain is dimensionless."
},
{
"Question": ["What is tensile strength?"],
"Answer": "Tensile strength is the maximum stress measured during a tensile stress. It is the peak of the stress-strain curve. It is also referred to as ultimate tensile strength. This is abbreviated as UTS. :::3|Stress_strain_ductile.jpg|UQ Lectures::\n\nTensile strength or UTS is the peak of the stress-strain curve shown in the above image."
},
{
"Question": ["What is yield strength?"],
"Answer": "Yield strength is the sress level at which the material starts permament deformation. In a tensile test, yield strength is the measured stress level at which the test sample starts stretching rapidly with little or no increase in force. Below the yield strength, the material will return to its original length when the load is removed. The deformation below the yield limit is called elastic deformation. The deformation above the yield limit is called plastic deformation. The yield strength is the point on the stress-strain curve where the curve deviates from a straight line. The yield strength is easier to identify for carbon steels. For non-ferrous metals there is no pronounced yield point. The yield strength for non-ferrous metals is determined by the offset method. The offset method uses a line drawn parallel to the linear portion of the stress-strain curve. The parallel line is drawn at an offset of 0.2% strain. The intersection of the parallel line and the stress-strain curve is the yield strength. This method is also used for titanium and certain high-strength steels."
},
{
"Question": ["What is the proportional limit?"],
"Answer": "The proportional limit is another name for the yield point."
},
{
"Question": ["What is Hooke's Law?"],
"Answer": "Hooke's Law defines the relation between the measured stress and the strain in the linear portion of the stress-strain curve. I states that stress($\\sigma$) is proportional to strain($\\epsilon$), expressed as $\\sigma=\\epsilon E$. The symbol E represents the modulus of elasticity. The modulus of elasticity is a material property. It is a measure of the stiffness of the material. The modulus of elasticity is also called Young's Modulus. The units of Young's Modulus are the same as the units of stress. In SI units, this is pascals. The modulus of elasticity does not vary much with the alloying elements or the heat treatment. The modulus of elasticity for steels is about 200 GPa. The modulus of elasticity for aluminium is about 70 GPa. The modulus of elasticity for titanium is about 110 GPa."
},
{
"Question": ["What is the modulus of elasticity?"],
"Answer": "The modulus of elasticity (E), also called Young's Modulus, is the proportionality constant in Hooke's Law. The units of Young's Modulus are the same as the units of stress. In SI units, this is pascals. The modulus of elasticity does not vary much with the alloying elements or the heat treatment. The modulus of elasticity for steels is about 200 GPa. The modulus of elasticity for aluminium is about 70 GPa. The modulus of elasticity for titanium is about 110 GPa."
},
{
"Question": ["What is ductility?"],
"Answer": "Ductility is the measure of deformation before ultimate fracture. A more ductile material streches more during a tensile test before it breaks. The opposite of ductility is brittleness."
},
{
"Question": ["How is ductility typically measured?"],
"Answer": "Ductility is usually measured by the tensile test. Ductility is the percent elongation of the test specimen at fracture."
},
{
"Question": ["How is percent elongation calculated?"],
"Answer": "Percent elongation = [(Lf - Lo)/Lo] \u00d7 100%. In this equation, Lf is the final length at fracture. Lo is the original length measured before the test starts."
},
{
"Question": ["When is a material considered ductile versus brittle?"],
"Answer": "A material is considered ductile if its percent elongation is greater than 5%. A material is considered brittle if its percent elongation is less than 5%."
},
{
"Question": ["What is the recommended percent elongation for machine members subject to repeated loads or shock impacts?"],
"Answer": "For machine members subject to repeated loads or shock impacts, it is recommended to use a material with a percent elongation of 12% or higher."
},
{
"Question": ["What is another indication of ductility besides percent elongation?"],
"Answer": "Percent reduction in area is another indication of ductility. Percent reduction in area is also found by the tensile test. It is [(Ao - Af)/Ao] \u00d7 100%. In this equation, Ao is the cross-sectional area before the test starts. Af is the reduced cross-sectional area of the fractured specimen. Af is measured by the tester after the test is completed."
},
{
"Question": ["How is yield strength in shear estimated?"],
"Answer": "Yield strength in shear is difficult to measure. Yield strength in shear is often estimated as half of the yield strength in tension. The yield strength in shear is also referred to as the shear yield strength."
},
{
"Question": ["How is ultimate strength in shear estimated?"],
"Answer": "Ultimate strength in shear is difficult to measure. Ultimate strength in shear is often estimated as 75% of the ultimate tensile strength."
},
{
"Question": ["What is Poisson's ratio?"],
"Answer": "During a tensile test, the specimen is stretched in the direction of the applied force. During a tensile test, the specimen contracts in the direction perpendicular to the direction of the applied force. Poisson's ratio (v) is the ratio of the contraction strain to the stretch strain. The contraction strain is measured as the shortened width divided by original width of the test specimen. The stretch strain is measured as the length of the test specimen divided by the original length of the test specimen. Poisson's ratio is a dimensionless number. Poisson's ratio is usually between 0.25 and 0.35 for most metals."
},
{
"Question": ["What is the modulus of elasticity in shear?"],
"Answer": "The modulus of elasticity in shear (G) is the ratio of shearing stress to shearing strain.It represents a material's stiffness under shear loading."
},
{
"Question": ["How is the modulus of elasticity in shear related to Young's modulus?"],
"Answer": "G = E/(2(1 + v)), where E is Young's modulus and v is Poisson's ratio."
},
{
"Question": ["What is hardness?"],
"Answer": "Hardness is the resistance of a material to indentation by a penetrator. In steel, it indicates both wear resistance and strength."
},
{
"Question": ["What are the most frequently used hardness testers for machine elements?"],
"Answer": "The Brinell hardness tester is a common hardness testing machine. Rockwell hardness tester is also a common hardness testing machine. They differ in terms of the penetrator used and the method of measuring the indentation. The Brinell hardness tester uses a hard steel ball as the penetrator. The Rockwell hardness tester uses a diamond penetrator."
},
{
"Question": ["What is the relationship between Brinell Hardness (HB) and tensile strength for steels?"],
"Answer": "For steels, especially highly hardenable alloy steels, 0.50(HB) = approximate tensile strength (ksi). The strength is in ksi. The hardness is in HB. This relationship is not valid for low carbon steels."
},
{
"Question": ["What are the two main types of Rockwell hardness tests?"],
"Answer": "Rockwell B (HRB), which uses a hardened steel ball as the indentor, and Rockwell C (HRC), which uses a diamond penetrator of sphero-conical shape."
},
{
"Question": ["Which Rockwell test is used for softer materials and what is its range?"],
"Answer": "Rockwell test HRB is used for softer materials. Rockwell HRB values range from 60 to 100."
},
{
"Question": ["Which Rockwell test is used for harder metals and what is its range?"],
"Answer": "Rockwell test HRC is used for harder metals. Rockwell HRC values range from 20 to 65."
},
{
"Question": ["What is Vickers hardness?"],
"Answer": "The Vickers hardness test is similar to the Brinell test but uses a square-based diamond pyramid as the penetrator."
},
{
"Question": ["What is wear and how can it be controlled?"],
"Answer": "Wear occurs when two components slide against each other. It can be controlled by material selection, surface finish, controlling contact pressure, lubrication, operating temperature, and prevention of contamination."
},
{
"Question": ["What are the different types of wear?"],
"Answer": "Thwere are five common types of wear: Erosive wear, abrasive wear, adhesive wear, fretting wear, and surface fatigue. Erosive wear is removal of particles from a surface. Erosive wear is caused by impact of solids or liquids. Abrasive wear is mechanical tearing of particles from one material by the action of the mating material. Adhesive wear is caused by one material adhering to the mating material. Fretting wear is caused by cyclical relative motion of two tightly joined parts under high surface pressure. Surface fatigue is progressive damage caused by high contact stresses between mating components."
},
{
"Question": ["What is machinability?"],
"Answer": "Machinability relates to the ease with which a material can be machined. A good surface finish is one measure of machinability. Achieving this surface finish with reasonable tool life is another measure of machinability. Machinability is usually reported in comparative terms."
},
{
"Question": ["What is toughness?"],
"Answer": "Toughness is the ability of a material to absorb energy without failure. Parts subjected to suddenly applied loads, shock, or impact need a high level of toughness."
},
{
"Question": ["What are two popular methods for determining toughness?"],
"Answer": "The Izod and Charpy methods are two popular methods for determining toughness."
},
{
"Question": ["What is the drop-weight tester used for?"],
"Answer": "The drop-weight tester is another impact testing method used for some plastics, composites, and completed products."
},
{
"Question": ["What is fatigue strength?"],
"Answer": "Fatigue strength is the alternating stress level the material can resist under repeated load applications. The repetitions are referred to as cycles. The number of cycles mey reach several thousands or millions before the material fractures. Such fracture is called fatigue failure. Fatigue strength is also called endurance strength."
},
{
"Question": ["What is creep?"],
"Answer": "Creep is the progressive elongation of materials over time. Creep occurs when a part is subjected to a high contoinuous static load. It becomes more important at elevated temperatures. It should be considered for metals if the operating at temperature is above 30% of the melting temperature. The temperature is expressed in an absolute scale. For example,the melting pooint of steel is about 1800 degrees K."
},
{
"Question": ["What is the SAE/AISI designation system for steel?"],
"Answer": "The SAE/AISI designation uses a four-digit number. The first two digits refer to alloying. The last two digits indicate the amount of carbon. Divide by 100 to get carbon content as percentage)."
},
{
"Question": ["How much carbon is in low carbon steels"],
"Answer": "Low carbon steels have less 0.30% carbon content. The last two digits of SAE designation for low carbon steels is less than 30."
},
{
"Question": ["How much carbon is in medium carbon steels"],
"Answer": "The carbon content in medium carbon steels varies from 0.30% to 0.50%. The last two digits of SAE designation for medium carbon steels is a number between 30 and 50."
},
{
"Question": ["How much carbon is in high carbon steels"],
"Answer": "The carbon content in high carbon steels varies from 0.50% to 0.95%. The last two digits of SAE designation for high carbon steels is a number between 50 and 95."
},
{
"Question": ["What is the engineering definition of strain?"],
"Answer": "Materials deform under load. The length of a bar increases under tension. The bar gets shorter under coimpression. Strain is the ratio of the change in length to the original length. Strain is a dimensionless number.The strain is positive for tension and negative for compression."
},
{
"Question": ["What is the engineering definition of stress?"],
"Answer": "Stress is the ratio of the applied load to the original cross-sectional area. Stress is a measure of the intensity of the internal forces in a material. Stress is expressed in pascals (N/m^2)."
},
{
"Question": ["What is the difference between true stress and engineering stress?"],
"Answer": "True stress is the instantaneous load divided by the instantaneous area. Engineering stress is the load divided by the original area."
},
{
"Question": ["What is cold working"],
"Answer": "Cold working is the process of plastically deforming a material at room temperature. Cold working increases the strength and hardness of the material. Cold working is also called strain hardening. Cold working occurs when steel bars or plates are manufactured using cold rolling, cold drawing, and cold extrusion. Cold working is done below the recrystallization temperature."
},
{
"Question": ["What is hot working"],
"Answer": "Hot working is the process of plastically deforming a material at elevated temperatures. Hot working is done above the recrystallization temperature. Hot working is also called hot forming. Hot working occurs when steel bars or plates are manufactured using forging, hot rolling, hot extrusion, and hot pressing."
},
{
"Question": ["What are the common heat treatment operations for steels?"],
"Answer": "The common heat treatment operations for steels are annealing, normalising, quenching and tempering."
},
{
"Question": ["What is annealing?"],
"Answer": "Annealing is a heat treatment process. Annealing involves heating the material and then cooling it slowly. The purpose of annealing is to reduce hardness, improve ductility, and relieve internal stresses."
},
{
"Question": ["What is normalising?"],
"Answer": "Normalising is similar to annealing. Normalising is a heat treatment process. Normalising involves heating the material and then cooling it in air. Normalising temperature is higher than annealing temperature. The purpose of normalising is to refine the grain structure and improve mechanical properties."
},
{
"Question": ["What is quenching?"],
"Answer": "Quenching is a heat treatment process. Quenching involves heating the material and then rapidly cooling it in water or oil. The purpose of quenching is to increase hardness and strength."
},
{
"Question": ["What is tempering?"],
"Answer": "Tempering is a heat treatment process. Tempering follows quenching. Tmpering involves heating the quenched material and then cooling it slowly. The purpose of tempering is to reduce brittleness and improve toughness."
},
{
"Question": ["What is austenite?"],
"Answer": "Austenite is a high-temperature phase of iron and steel that is non-magnetic. At room temperature, austenite is not stable in carbon steels. In stainless steels, austenite is made stable by addition of the alloying elements. Heat treatment takes steel first to sustenite. The final form depends on the cooling rate and the carbon content."
},
{
"Question": ["What is through hardening?"],
"Answer": "Through hardening is a heat treatment process. Through hardening involves heating the material to austenite and then quenching it. The purpose of through hardening is to increase hardness and strength throughout the entire material."
},
{
"Question": ["What is martensite?"],
"Answer": "Martensite is a hard, brittle phase formed by rapid cooling of austenite."
},
{
"Question": ["What is case hardening?"],
"Answer": "Case hardening is a heat treatment process. Case hardening involves heating the surface of the material to austenite and then quenching it. The purpose of case hardening is to increase hardness and strength at the surface of the material while maintaining a softer core."
}
]
Continuous Text (uploaded as a file separately)
A tensile test measures the strength and ductility of a material. The test specimen is usually a flat or round bar. The two ends of the test specimen are clampedduring the test. The specimen is then stretched slowly until it breaks. Results are expressed by stress-strain diagrams. A stress-strain diagram is a plot of measured stress versus measured strain. The measured stress is on the y axis. The measured strain is on the x axis. The measured stress is the measured applied force divided by the original area. The units of stress are force divided by area. In SI units, this is newtons divided by square meters. This unit has a special name. The special name is pascals. The measured strain is the deformed length divided by the original length. The strain is dimensionless.
Tensile strength is the maximum stress measured during a tensile stress. It is the peak of the stress-strain curve. It is also referred to as ultimate tensile strength. This is abbreviated as UTS. :::3:Stress_strain_ductile.jpg::Tensile strength or UTS is the peak of the stress-strain curve shown in the above image.
Yield strength is the sress level at which the material starts permament deformation. In a tensile test, yield strength is the measured stress level at which the test sample starts stretching rapidly with little or no increase in force. Below the yield strength, the material will return to its original length when the load is removed. The deformation below the yield limit is called elastic deformation. The deformation above the yield limit is called plastic deformation. The yield strength is the point on the stress-strain curve where the curve deviates from a straight line. The yield strength is easier to identify for carbon steels. For non-ferrous metals there is no pronounced yield point. The yield strength for non-ferrous metals is determined by the offset method. The offset method uses a line drawn parallel to the linear portion of the stress-strain curve. The parallel line is drawn at an offset of 0.2% strain. The intersection of the parallel line and the stress-strain curve is the yield strength. This method is also used for titanium and certain high-strength steels.
The proportional limit is another name for the yield point.
Hooke's Law defines the relation between the measured stress and the strain in the linear portion of the stress-strain curve. I states that stress($\sigma$) is proportional to strain($\epsilon$), expressed as $\sigma=\epsilon E$. The symbol E represents the modulus of elasticity. The modulus of elasticity is a material property. It is a measure of the stiffness of the material. The modulus of elasticity is also called Young's Modulus. The units of Young's Modulus are the same as the units of stress. In SI units, this is pascals. The modulus of elasticity does not vary much with the alloying elements or the heat treatment. The modulus of elasticity for steels is about 200 GPa. The modulus of elasticity for aluminium is about 70 GPa. The modulus of elasticity for titanium is about 110 GPa.
The modulus of elasticity (E), also called Young's Modulus, is the proportionality constant in Hooke's Law. The units of Young's Modulus are the same as the units of stress. In SI units, this is pascals. The modulus of elasticity does not vary much with the alloying elements or the heat treatment. The modulus of elasticity for steels is about 200 GPa. The modulus of elasticity for aluminium is about 70 GPa. The modulus of elasticity for titanium is about 110 GPa.
Ductility is the measure of deformation before ultimate fracture. A more ductile material streches more during a tensile test before it breaks. The opposite of ductility is brittleness.
Ductility is usually measured by the tensile test. Ductility is the percent elongation of the test specimen at fracture.
Percent elongation = [(Lf - Lo)/Lo] × 100%. In this equation, Lf is the final length at fracture. Lo is the original length measured before the test starts.
A material is considered ductile if its percent elongation is greater than 5%. A material is considered brittle if its percent elongation is less than 5%.
For machine members subject to repeated loads or shock impacts, it is recommended to use a material with a percent elongation of 12% or higher.
Percent reduction in area is another indication of ductility. Percent reduction in area is also found by the tensile test. It is [(Ao - Af)/Ao] × 100%. In this equation, Ao is the cross-sectional area before the test starts. Af is the reduced cross-sectional area of the fractured specimen. Af is measured by the tester after the test is completed.
Yield strength in shear is difficult to measure. Yield strength in shear is often estimated as half of the yield strength in tension. The yield strength in shear is also referred to as the shear yield strength.
Ultimate strength in shear is difficult to measure. Ultimate strength in shear is often estimated as 75% of the ultimate tensile strength.
During a tensile test, the specimen is stretched in the direction of the applied force. During a tensile test, the specimen contracts in the direction perpendicular to the direction of the applied force. Poisson's ratio (v) is the ratio of the contraction strain to the stretch strain. The contraction strain is measured as the shortened width divided by original width of the test specimen. The stretch strain is measured as the length of the test specimen divided by the original length of the test specimen. Poisson's ratio is a dimensionless number. Poisson's ratio is usually between 0.25 and 0.35 for most metals.
The modulus of elasticity in shear (G) is the ratio of shearing stress to shearing strain.It represents a material's stiffness under shear loading.
G = E/(2(1 + v)), where E is Young's modulus and v is Poisson's ratio.
Hardness is the resistance of a material to indentation by a penetrator. In steel, it indicates both wear resistance and strength.
The Brinell hardness tester is a common hardness testing machine. Rockwell hardness tester is also a common hardness testing machine. They differ in terms of the penetrator used and the method of measuring the indentation. The Brinell hardness tester uses a hard steel ball as the penetrator. The Rockwell hardness tester uses a diamond penetrator.
For steels, especially highly hardenable alloy steels, 0.50(HB) = approximate tensile strength (ksi). The strength is in ksi. The hardness is in HB. This relationship is not valid for low carbon steels.
Rockwell B (HRB), which uses a hardened steel ball as the indentor, and Rockwell C (HRC), which uses a diamond penetrator of sphero-conical shape.
Rockwell test HRB is used for softer materials. Rockwell HRB values range from 60 to 100.
Rockwell test HRC is used for harder metals. Rockwell HRC values range from 20 to 65.
The Vickers hardness test is similar to the Brinell test but uses a square-based diamond pyramid as the penetrator.
Wear occurs when two components slide against each other. It can be controlled by material selection, surface finish, controlling contact pressure, lubrication, operating temperature, and prevention of contamination.
Thwere are five common types of wear: Erosive wear, abrasive wear, adhesive wear, fretting wear, and surface fatigue. Erosive wear is removal of particles from a surface. Erosive wear is caused by impact of solids or liquids. Abrasive wear is mechanical tearing of particles from one material by the action of the mating material. Adhesive wear is caused by one material adhering to the mating material. Fretting wear is caused by cyclical relative motion of two tightly joined parts under high surface pressure. Surface fatigue is progressive damage caused by high contact stresses between mating components.
Machinability relates to the ease with which a material can be machined. A good surface finish is one measure of machinability. Achieving this surface finish with reasonable tool life is another measure of machinability. Machinability is usually reported in comparative terms.
Toughness is the ability of a material to absorb energy without failure. Parts subjected to suddenly applied loads, shock, or impact need a high level of toughness.
The Izod and Charpy methods are two popular methods for determining toughness.
The drop-weight tester is another impact testing method used for some plastics, composites, and completed products.
Fatigue strength is the alternating stress level the material can resist under repeated load applications. The repetitions are referred to as cycles. The number of cycles mey reach several thousands or millions before the material fractures. Such fracture is called fatigue failure. Fatigue strength is also called endurance strength.
Creep is the progressive elongation of materials over time. Creep occurs when a part is subjected to a high contoinuous static load. It becomes more important at elevated temperatures. It should be considered for metals if the operating at temperature is above 30% of the melting temperature. The temperature is expressed in an absolute scale. For example,the melting pooint of steel is about 1800 degrees K.
The SAE/AISI designation uses a four-digit number. The first two digits refer to alloying. The last two digits indicate the amount of carbon. Divide by 100 to get carbon content as percentage).
Low carbon steels have less 0.30% carbon content. The last two digits of SAE designation for low carbon steels is less than 30.
The carbon content in medium carbon steels varies from 0.30% to 0.50%. The last two digits of SAE designation for medium carbon steels is a number between 30 and 50.
The carbon content in high carbon steels varies from 0.50% to 0.95%. The last two digits of SAE designation for high carbon steels is a number between 50 and 95.
Materials deform under load. The length of a bar increases under tension. The bar gets shorter under coimpression. Strain is the ratio of the change in length to the original length. Strain is a dimensionless number.The strain is positive for tension and negative for compression.
Stress is the ratio of the applied load to the original cross-sectional area. Stress is a measure of the intensity of the internal forces in a material. Stress is expressed in pascals (N/m^2).
True stress is the instantaneous load divided by the instantaneous area. Engineering stress is the load divided by the original area.
Cold working is the process of plastically deforming a material at room temperature. Cold working increases the strength and hardness of the material. Cold working is also called strain hardening. Cold working occurs when steel bars or plates are manufactured using cold rolling, cold drawing, and cold extrusion. Cold working is done below the recrystallization temperature.
Hot working is the process of plastically deforming a material at elevated temperatures. Hot working is done above the recrystallization temperature. Hot working is also called hot forming. Hot working occurs when steel bars or plates are manufactured using forging, hot rolling, hot extrusion, and hot pressing.
The common heat treatment operations for steels are annealing, normalising, quenching and tempering.
Annealing is a heat treatment process. Annealing involves heating the material and then cooling it slowly. The purpose of annealing is to reduce hardness, improve ductility, and relieve internal stresses.
Normalising is similar to annealing. Normalising is a heat treatment process. Normalising involves heating the material and then cooling it in air. Normalising temperature is higher than annealing temperature. The purpose of normalising is to refine the grain structure and improve mechanical properties.
Quenching is a heat treatment process. Quenching involves heating the material and then rapidly cooling it in water or oil. The purpose of quenching is to increase hardness and strength.
Tempering is a heat treatment process. Tempering follows quenching. Tmpering involves heating the quenched material and then cooling it slowly. The purpose of tempering is to reduce brittleness and improve toughness.
Austenite is a high-temperature phase of iron and steel that is non-magnetic. At room temperature, austenite is not stable in carbon steels. In stainless steels, austenite is made stable by addition of the alloying elements. Heat treatment takes steel first to sustenite. The final form depends on the cooling rate and the carbon content.
Through hardening is a heat treatment process. Through hardening involves heating the material to austenite and then quenching it. The purpose of through hardening is to increase hardness and strength throughout the entire material.
Martensite is a hard, brittle phase formed by rapid cooling of austenite.
Case hardening is a heat treatment process. Case hardening involves heating the surface of the material to austenite and then quenching it. The purpose of case hardening is to increase hardness and strength at the surface of the material while maintaining a softer core.