difference between stress and strain .briefly
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Stress
The term stress (s) is used to express the loading in terms of force applied to a certain cross-sectional area of an object. From the perspective of loading, stress is the applied force or system of forces that tends to deform a body. From the perspective of what is happening within a material, stress is the internal distribution of forces within a body that balance and react to the loads applied to it. The stress distribution may or may not be uniform, depending on the nature of the loading condition. For example, a bar loaded in pure tension will essentially have a uniform tensile stress distribution. However, a bar loaded in bending will have a stress distribution that changes with distance perpendicular to the normal axis.
Simplifying assumptions are often used to represent stress as a vector quantity for many engineering calculations and for material property determination. The word "vector" typically refers to a quantity that has a "magnitude" and a "direction". For example, the stress in an axially loaded bar is simply equal to the applied force divided by the bar's cross-sectional area.
It must be noted that the stresses in most 2-D or 3-D solids are actually more complex and need be defined more methodically. The internal force acting on a small area of a plane can be resolved into three components: one normal to the plane and two parallel to the plane. The normal force component divided by the area gives the normal stress (s), and parallel force components divided by the area give the shear stress (t). These stresses are average stresses as the area is finite, but when the area is allowed to approach zero, the stresses become stresses at a point. Since stresses are defined in relation to the plane that passes through the point under consideration, and the number of such planes is infinite, there appear an infinite set of stresses at a point. Fortunately, it can be proven that the stresses on any plane can be computed from the stresses on three orthogonal planes passing through the point. As each plane has three stresses, the stress tensor has nine stress components, which completely describe the state of stress at a point.
Strain
Strain is the response of a system to an applied stress. When a material is loaded with a force, it produces a stress, which then causes a material to deform. Engineering strain is defined as the amount of deformation in the direction of the applied force divided by the initial length of the material. This results in a unit less number, although it is often left, in the the less simplified form, such as inches per inch or meters per meter. For example, the strain in a bar that is being stretched in tension is the amount of elongation or change in length divided by its original length. As in the case of stress, the strain distribution may or may not be uniform in a complex structural element, depending on the nature of the loading condition.
If the stress is small, the material may only strain a small amount and the material will return to its original size after the stress is released. This is called elastic deformation, because like elastic it returns to its unstressed state. Elastic deformation only occurs in a material when stresses are lower than a critical stress called the yield strength. If a material is loaded beyond it elastic limit, the material will remain in a deformed condition after the load is removed. This is called plastic deformation.
Engineering and True Stress and Strain
The discussion above focused on engineering stress and strain, which use the fixed, undeformed cross-sectional area in the calculations. True stress and strain measures account for changes in cross-sectional area by using the instantaneous values for the area. The engineering stress-strain curve does not give a true indication of the deformation characteristics of a metal because it is based entirely on the original dimensions of the specimen, and these dimensions change continuously during the testing used to generate the data.
Strain is more fundamental than stress and that’s the reason strain is always plotted on the X- Axis.
20.7k Views · · Answer requested by
Stress is defined as the internal force or restoring force acting per unit area .
Actual meaning of stress is that whenever you apply some force let us say you are pulling a bar there is some resistance within the material due to its molecular properties that restoring force or the resisting force acting per unit area itself is stress.
However there are some special cases where there is a strain without any stress for example thermal strain .for example let us consider a bar which is fixed at only one end and it is heated there is change in the length of the bar which is a example of strain without any stress.
The term stress (s) is used to express the loading in terms of force applied to a certain cross-sectional area of an object. From the perspective of loading, stress is the applied force or system of forces that tends to deform a body. From the perspective of what is happening within a material, stress is the internal distribution of forces within a body that balance and react to the loads applied to it. The stress distribution may or may not be uniform, depending on the nature of the loading condition. For example, a bar loaded in pure tension will essentially have a uniform tensile stress distribution. However, a bar loaded in bending will have a stress distribution that changes with distance perpendicular to the normal axis.
Simplifying assumptions are often used to represent stress as a vector quantity for many engineering calculations and for material property determination. The word "vector" typically refers to a quantity that has a "magnitude" and a "direction". For example, the stress in an axially loaded bar is simply equal to the applied force divided by the bar's cross-sectional area.
It must be noted that the stresses in most 2-D or 3-D solids are actually more complex and need be defined more methodically. The internal force acting on a small area of a plane can be resolved into three components: one normal to the plane and two parallel to the plane. The normal force component divided by the area gives the normal stress (s), and parallel force components divided by the area give the shear stress (t). These stresses are average stresses as the area is finite, but when the area is allowed to approach zero, the stresses become stresses at a point. Since stresses are defined in relation to the plane that passes through the point under consideration, and the number of such planes is infinite, there appear an infinite set of stresses at a point. Fortunately, it can be proven that the stresses on any plane can be computed from the stresses on three orthogonal planes passing through the point. As each plane has three stresses, the stress tensor has nine stress components, which completely describe the state of stress at a point.
Strain
Strain is the response of a system to an applied stress. When a material is loaded with a force, it produces a stress, which then causes a material to deform. Engineering strain is defined as the amount of deformation in the direction of the applied force divided by the initial length of the material. This results in a unit less number, although it is often left, in the the less simplified form, such as inches per inch or meters per meter. For example, the strain in a bar that is being stretched in tension is the amount of elongation or change in length divided by its original length. As in the case of stress, the strain distribution may or may not be uniform in a complex structural element, depending on the nature of the loading condition.
If the stress is small, the material may only strain a small amount and the material will return to its original size after the stress is released. This is called elastic deformation, because like elastic it returns to its unstressed state. Elastic deformation only occurs in a material when stresses are lower than a critical stress called the yield strength. If a material is loaded beyond it elastic limit, the material will remain in a deformed condition after the load is removed. This is called plastic deformation.
Engineering and True Stress and Strain
The discussion above focused on engineering stress and strain, which use the fixed, undeformed cross-sectional area in the calculations. True stress and strain measures account for changes in cross-sectional area by using the instantaneous values for the area. The engineering stress-strain curve does not give a true indication of the deformation characteristics of a metal because it is based entirely on the original dimensions of the specimen, and these dimensions change continuously during the testing used to generate the data.
Strain is more fundamental than stress and that’s the reason strain is always plotted on the X- Axis.
20.7k Views · · Answer requested by
Stress is defined as the internal force or restoring force acting per unit area .
Actual meaning of stress is that whenever you apply some force let us say you are pulling a bar there is some resistance within the material due to its molecular properties that restoring force or the resisting force acting per unit area itself is stress.
However there are some special cases where there is a strain without any stress for example thermal strain .for example let us consider a bar which is fixed at only one end and it is heated there is change in the length of the bar which is a example of strain without any stress.
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Hey there!
Suppose we are applying a deforming force on an object. Then there is change in its shape or size. and we define elesticity as the tendency of an object to gain its original configuration either shape or size when the deforming force is removed.
While deformation of the body, the deforming force it applied and therefore by Newton's third law we can say that an equal restoring force also acts to retain the body in its original shape. So we define two things for this. i.e Stress and Strain.
We define Stress as the restoring forces per unit area of the body.
i.e Stress = Restoring force / Area = F / A
And, We define Strain as the ratio of the change in configuration to the original configuration of the body is called strain,.
i.e Strain = Δconfiguration / orginal configuration
I hope it helps You!
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