Mechanical properties of metals

Mechanical properties of metals

Following mechanical properties is important.

1. Elasticity-

The term elasticity may be defined as the property of a metal by virtue of which it is able to retain its original shape after the removal of the load.In nature no material is perfectly elastic, over the entire range of stress, up to rupture.

2. Plasticity

The term plasticity may be defined as the property of a metal by the virtue of which a permanent deformation (without fracture) take place, whenever it is subjected to the action of external forces.The plasticity of metal depends upon its nature and environmental condition.

3. Ductility-

The term ductility may be defined as the property of metal by virtue of which it can be drawn into wires or elongated before rupture takes place. it depends upon grain size of the metal crystal.

4. Percentage elongation-

The term percentage elongation is the maximum increase in the length expressed as percentage of original length. So percentage elongation.

= Increase in length x 100/Original length

Similarly the term percentage reduction of cross sectional area is the maximum decrese in cross sectional area. So mathematically

= Decrease in cross sectional area x100/ Original cross sectional area

Note:- Common metal have ductility in the decreasing order

1. Gold 2. Platinum 3. Silver 4. Iron 5. Copper 6. Aluminium 7. Nickel 8. Zinc 9. Tin 10. Lead

5. Brittleness -

It is the property of metal by virtue of which it will fracture without any appreciable deformation.

6. Hardness-

It is the property of metal by the virtue of which it is able to resist abrasion, indentation, scratching by harder bodies.

Note- Increasing trend of hardness on the original Moh's scale are.

1. Talc 2. Gypsum 3.Calcite 4.Fluorite 5.Apatite 6.Orthoclase 7.Quartz 8.Topaz 9. Corundum 10. Diamond

7. Toughness-

The term toughness may be defined as the property of a metal by virtue of which it can absorb maximum energy before fracture takes place. Tenacity and hardness of metal are the measure of toughness.

8. Stiffness-

Stiffness may be defined as the property of a metal by virtue of which it resist deformation. Modulus of elasticity is a measure of stiffness of metal.

9. Resilience-

The term resilience may be defined as the property of a metal by the virtue of which it stores energy and resist shocks and impact.The resilience of a metal is measured by the amount of energy that can be stored, per unit volume, after it is stressed up to the elastic limit.

10. Creep-

The term creep is the property of a metal by virtue of which it deforms continuously under steady load. Creep occurs in steel at higher temperature.

Creep is a fascinating and important phenomenon in materials science and engineering, particularly in the study of materials' mechanical behavior. It refers to the time-dependent and permanent deformation that occurs in a material when it is subjected to a constant load or stress at elevated temperatures. Unlike other mechanical behaviors, such as elastic deformation (instantaneous and reversible) or plastic deformation (time-dependent but non-permanent), creep involves a gradual and progressive deformation over time.

The understanding of creep is crucial when designing and using materials in applications where high temperatures and prolonged stresses are involved, such as in the aerospace, power generation, and manufacturing industries. Creep behavior is commonly encountered in materials like metals, alloys, ceramics, and even certain types of polymers.

Several factors influence the rate and extent of creep in a material. The most significant parameters include temperature, stress level, and time of exposure. As the temperature increases, so does the creep rate, making high-temperature applications more susceptible to this type of deformation. Similarly, higher stress levels accelerate creep, leading to a reduced lifetime for the material under such conditions.

One fundamental concept in creep is the notion of "creep curves." These curves depict the relationship between strain rate and time under constant load and temperature. A typical creep curve consists of three distinct stages: primary, secondary, and tertiary creep. In the primary stage, the strain rate is high but gradually decreases over time. The secondary stage exhibits a relatively constant strain rate, while the tertiary stage shows a rapidly accelerating strain rate until failure.

Engineers and scientists employ various models and equations to predict and quantify the creep behavior of materials accurately. One of the earliest and most well-known models is the power-law creep equation, which relates the creep rate to temperature, stress, and a material-dependent constant.

Overall, the study of creep is indispensable for ensuring the reliability and safety of materials used in demanding environments. By comprehending this unique deformation mechanism, researchers and engineers can design materials capable of withstanding prolonged exposure to high temperatures and stresses, leading to enhanced performance and longevity of critical components in numerous industries.

11. Endurance-

The term endurance may be defined as the property of a metal by virtue of which it can withstand varying stress. The maximum value of stress, That can be applied for an indefinite times without causing its failure, is known as endurance limit.

12. Strength-

The term sterength may be defined as the property of metal by virtue of which it can withstand or support an external force or load without rupture.

13 Elastic strength-

Elastic strength, also known as yield strength or elastic limit, is a fundamental mechanical property of materials, especially metals and alloys. It refers to the maximum stress a material can withstand without undergoing permanent deformation or plastic deformation while still returning to its original shape after the stress is removed.

When a material is subjected to an external force or load, it undergoes elastic deformation, meaning it temporarily changes shape but retains its original structure and dimensions once the load is removed. The elastic strength is the point at which the material transitions from elastic deformation to plastic deformation.

In engineering and material science, the elastic strength is a crucial parameter as it defines the safe working limit of a material in many applications. Engineers use the elastic strength to ensure that the materials used in the design of structures or components can withstand the expected loads without experiencing permanent damage or failure.

The elastic strength is typically represented by a stress-strain curve, which illustrates the relationship between the applied stress and the resulting strain in the material. At low stress levels, the material exhibits a linear elastic response, following Hooke's law. However, as the stress increases, the strain may become non-linear, indicating the onset of plastic deformation.

It is important to note that exceeding the elastic strength of a material can lead to permanent deformation or even fracture. Therefore, engineers must carefully consider the elastic strength of materials when designing structures to ensure their safety and reliability under various loading conditions.

In summary, elastic strength is a critical mechanical property that defines the limit of elastic deformation in a material. Understanding this property allows engineers to design structures and components that can withstand loads without undergoing permanent damage, ensuring the integrity and safety of the engineered systems.

14. Plastic strength-

Plastic strength, also known as yield strength, is a fundamental mechanical property of materials, especially in the field of engineering and material science. It represents the maximum stress a material can withstand without undergoing permanent deformation or plastic deformation. In other words, it is the point at which the material transitions from elastic deformation (where it can return to its original shape after the applied load is removed) to plastic deformation (where it undergoes permanent deformation even after the load is removed).

When a material is subjected to external forces or loads, the atoms and molecules within the material start to move, leading to the distortion of its crystal structure. In the elastic region, the deformation is reversible, and the material behaves like a spring, obeying Hooke's law. However, as the applied stress increases, the material eventually reaches its yield point.

At the yield point, the material's ability to return to its original shape diminishes, and it starts to deform permanently. This plastic deformation occurs due to the movement of dislocations within the material's crystal lattice. The presence of defects and imperfections in the atomic arrangement facilitates the dislocation movement, and it becomes increasingly easier for the material to deform plastically.

Plastic strength is a critical parameter in the design and analysis of structures and components, as it helps engineers determine the safety margins and structural integrity of materials under various loading conditions. By understanding the plastic strength of a material, engineers can ensure that the applied loads remain within the elastic region, avoiding failure and ensuring the longevity of the structures.

The plastic strength of materials can vary significantly depending on their composition, manufacturing processes, and temperature conditions. Some materials exhibit high plastic strength, making them suitable for load-bearing applications, while others may have lower plastic strength but possess other desirable properties for different purposes.

In summary, plastic strength is a crucial mechanical property that influences the behavior and performance of materials in real-world applications. Engineers and researchers continue to study and develop materials with enhanced plastic strength to meet the ever-evolving demands of modern technology and construction.

15. Tensile strength-

Maximum tensile load/Original cross sectional area

Unit- N/mm2 or MN/mm2

16. Compressive Strength-

Maximum compressive load/Original cross sectional area

Unit- N/mm2 or MN/mm2

17. Shear strength-

Maximum tangential load/Original cross sectional area

Unit- N/mm2 or MN/mm2

18. Torsional Strength-

Maximum twisting load/Original cross sectional area

Unit- N/mm2 or MN/mm2

19 Malleability-

The term malleability may be defined as the property of a metal by virtue of which it can be deformed into thin sheet by rolling or hammering without rupture.

Common metal have malleability in the decreasing order.

1. Gold 2. Silver 3.Aluminium 4. Copper 5.Tin 6. Platinum 7.Lead 8. Zinc 9.Iron 10.Nickel

20. Machinability-

Machinability of metal refers to the ease with which a metal material can be cut, drilled, shaped, or otherwise processed using various machining techniques. It is an essential property to consider when selecting a metal for a specific application that involves machining processes. Several factors influence the machinability of a metal:

1. Composition:

The chemical composition of the metal plays a significant role in its machinability. Metals with a uniform and consistent composition generally exhibit better machinability.

2. Microstructure:

The microstructure of the metal, including grain size and distribution, can affect how easily it can be machined. Metals with fine and uniform grain structures tend to be more machinable.

3. Hardness:

Hardness is a critical factor influencing machinability. Softer metals are usually easier to machine, while harder metals can cause excessive tool wear and slower cutting speeds.

4. Heat Treatment:

The heat treatment history of the metal can impact its machinability. Some heat treatments may increase hardness and reduce machinability, while others might improve it.

5. Cutting Tool Material:

The selection of appropriate cutting tools, such as high-speed steel (HSS) or carbide, can significantly affect the machining process's efficiency and the quality of the machined surface.

6. Cutting Parameters:

Machining parameters like cutting speed, feed rate, and depth of cut should be optimized to suit the specific metal's machinability characteristics.

7. Workpiece Stability:

The stability of the workpiece during machining affects the quality and accuracy of the machining process. Adequate fixturing is essential to prevent vibration and chatter.

8. Coolant and Lubrication:

Proper coolant and lubrication help dissipate heat, reduce friction, and prevent tool wear, contributing to better machinability.

9. Work Hardening:

Some metals are prone to work hardening during machining, leading to increased cutting forces and tool wear.

10. Chip Formation:

The formation and evacuation of chips during machining impact the machining process's smoothness and efficiency.

Common machinability rating systems, such as the SAE (Society of Automotive Engineers) scale or AISI (American Iron and Steel Institute) scale, are used to compare the machinability of different metals. These scales provide valuable information for machinists and manufacturers to choose the most suitable material for their machining operations and to determine the best machining practices for a particular metal.

21. Formability or workability-

Term formability may be defined as the property of a metal which indicates the ease with which it can be formed into different shapes and sizes.

Factors affecting formability/

1. Crystal structure

2. Grain size

3. Hot and cold working

4. Alloying element present in the parent metal.

Formability, also known as workability, is a critical property in materials science and engineering, particularly in the context of metalworking and manufacturing processes. It refers to the ease with which a material can be shaped, formed, or deformed without experiencing failure or fracture. The formability of a material is a fundamental consideration in various industries, including automotive, aerospace, construction, and consumer goods.

Several factors influence the formability of a material, including its mechanical properties, microstructure, temperature, strain rate, and lubrication. Ductility, which is the ability of a material to undergo plastic deformation without rupture, is one of the key mechanical properties that directly impacts formability. Materials with high ductility are generally more formable as they can sustain large plastic deformations without failure.

Processes that rely on formability include rolling, forging, stamping, deep drawing, and extrusion. For example, in sheet metal forming, such as car body panels, the formability of the metal sheets determines their ability to be shaped into complex geometries without cracking or wrinkling. Understanding and optimizing the formability of materials are essential for achieving cost-effective and efficient manufacturing processes.

Formability testing is commonly performed to assess the behavior of materials under specific forming conditions. This involves subjecting test specimens to controlled deformation, allowing engineers to evaluate their ability to withstand shaping without defects. The data obtained from such tests aid in material selection and process design, ensuring that the chosen material is suitable for the intended application and forming method.

In conclusion, formability or workability is a crucial property that directly impacts the manufacturability of materials. By comprehending and tailoring the formability characteristics, engineers and manufacturers can produce high-quality products with intricate shapes and designs while minimizing waste and optimizing production efficiency.

Stress strain curve