In the test, the deformation (elongation) of the specimen is measured between two fixed points of the specimen as the applied load increases, and it is represented graphically as a function of the tension (applied load divided by the section of the specimen). In general, the stress-strain curve thus obtained presents four differentiated zones:

1. • Elastic deformations: The deformations are distributed along the specimen, they are small in magnitude and, if the applied load were removed, the specimen would recover its initial shape. The coefficient of proportionality between stress and deformation is called elasticity or Young's modulus and is characteristic of the material. Thus, all steels have the same modulus of elasticity although their resistances may be very different. The highest stress reached in this region is called the yield limit and is what marks the appearance of this phenomenon. There can be two zones of elastic deformation, the first straight line and the second curve, the limit of proportionality being the value of the tension that marks the transition between the two. Generally, this last value is of no practical interest and an elastic limit (conventional or practical) is then defined as the one for which a predetermined elongation occurs (0.2%, 0.1%, etc.). It is obtained by drawing a straight line parallel to the proportional section (straight) with an initial deformation equal to the conventional one.

2. • Creed or yield. It is the sudden deformation of the specimen without an increase in the applied load. The creep phenomenon occurs when impurities or alloying elements block the dislocations "Dislocation (crystalline defect)") of the crystalline lattice, preventing its sliding, a mechanism by which the material is plastically deformed. Once the yield limit is reached, the dislocations are released, producing deformation suddenly. The deformation in this case is also distributed uniformly throughout the specimen but concentrating in the areas in which the dislocations have been released (Lüders bands). Not all materials present this phenomenon, in which case the transition between elastic and plastic deformation of the material is not clearly appreciated.

3. • Plastic deformations: if the load applied in said area is removed, the specimen only partially recovers its shape, leaving it permanently deformed. The deformations in this region are more pronounced than in the elastic zone.

4. • Narrowing"). At a certain point in the test, the deformations are concentrated in the central part of the specimen, showing a marked reduction in the section of the specimen, at which point the deformations will continue to accumulate until the specimen breaks in that area. Narrowing is responsible for the decrease in the stress-strain curve; the stresses do not actually decrease until the breakage, what happens is that what is represented is the quotient of the applied force (increasing until the beginning). of the necking) between the initial section: when the necking occurs the section decreases (and therefore also the necessary force), a decrease in section that is not taken into account in the graphic representation. Brittle materials do not suffer significant necking or plastic deformations, the specimen breaking suddenly. Once the test is completed, the breaking load, ultimate load or tensile strength is determined: the maximum resisted by the specimen divided by its initial section, the elongation in (%) and the necking. in the area of the break.

Other characteristics that can be characterized by the tensile test are resilience "Resilience (engineering)") and tenacity, which are, respectively, the elastic and total energies absorbed and which are represented by the area under the stress-strain curve up to the elastic limit in the first case and until reaching failure in the second.

The specimens used in the tensile test have a circular or rectangular cross section. The central part must be machined so that its section is constant. If the material is fragile, the surface will need to be polished.

The initial length () of the test piece is marked on the calibrated part. The length of the calibrated part must be between and if the specimens are cylindrical. If the test pieces are rectangular or square, the length will be between and .

At the ends of the specimen the section increases to facilitate its attachment to the jaws "Clamp (mechanism)") of the traction machine. These areas are called heads. To avoid areas where stresses are concentrated, the section of the specimen varies from the calibrated part to the head in a smooth and gradual way.

For tests with specimens of different dimensions to be comparable, it must remain constant.

• - Proportionality limit (): Stress beyond which the deformations are no longer proportional to the stresses.

• - Elasticity limit ( and ): Stress beyond which the deformations are no longer reversible. Its value is very close to the limit of proportionality. It is difficult to measure since it is necessary to apply tension to the specimen and subsequently remove it to check whether or not it has recovered its initial length.

If the specimen recovers its initial length, the elastic limit will be higher than the applied stress, and the test must be continued with higher stresses. If the specimen shows permanent deformation, the stress will be greater than the elastic limit. Once deformed, the specimen is useless and must continue to be dimensioned below and above the elasticity limit using other specimens.

To solve these difficulties, two tensions are used:

• - Permanent deformation limit (): Stress that causes a permanent deformation equal to a certain percentage of the initial length. Generally the percentage is 0.2%, indicated by . To determine this tension, the specimen is subjected to increasing loads that are maintained for 10 seconds and are subsequently eliminated, measuring the permanent deformation. The value is obtained by interpolation.

Interpolation is a common practice when you have several pairs of data (x, y) and you want to determine the ordinate y, which corresponds to a certain abscissa (x).

Linear interpolation considers that the ordinate varies linearly between every two pairs of points. If you have the pair of data (1,2), (3,4) and (4,5), and you want to know the ordinate that corresponds to x = 2.5, you take the first two pairs of points and consider the line that passes through them. The ordinate sought (y = 3.5) will be the one that corresponds to x.

• - Limit of loss of proportionality (): Voltage that causes a non-proportional elongation equal to a certain percentage of the initial length. Generally the percentage is 0.2%, indicated by . To obtain this value, it is necessary to consider the intersection between the traction curve and the line parallel to the proportional area of ​​the curve that cuts the x-axis by the set percentage.

• - Young's Modulus (E): Relationship between stress and deformation in the zone of proportional behavior.

• - Tensile strength (): Maximum tension that the specimen supports during the test.

• - Break resistance (): Tension supported by the specimen at the moment of breakage. As long as the specimen does not suffer "necking", its value is close to that of the tensile strength. Once the tensile strength is exceeded, the specimen is considered broken.

• - Elongation at break (A): Greater plastic elongation achieved by the specimen. It is measured as a percentage.

being the length of the specimen after the test.

• - Breakage necking (Z): Decrease in section that occurs after breakage. It is measured as a percentage.

being the smallest section of the test tube.

If the specimens are rectangular, the calculation of the breaking stresses, the section is expressed by:.

being a' and b' the dimensions.

• - Deformation work: Area under the force-elongation curve, which is calculated by and represents the work that is necessary to develop to break the specimen and the capacity of the material to absorb work. Particularly in the automotive industry, it is of utmost importance to know the behavior of the parts of a vehicle in the event of a collision.

As the test progresses, the section of the specimen gradually decreases, and the stress it supports is:

S being the section of the specimen at each instant, which reaches its minimum value in the necking zone, and the true tension.

As the test progresses, the length of the specimen gradually increases, and the deformation must be measured with respect to the length it presents at each moment. The deformation will be given by:.

L being the length of the specimen at each moment of the test, the true deformation and the engineering deformation.

In many metals the true stress and strain are linked by the Hollomon relation"):, where and are characteristic constants of the material.

Many metals, such as low carbon steels, do not present a gradual transition between the elastic and plastic behavior zones. Once the limit of the elastic zone has been exceeded, there is a zone of yielding or yielding, in which the specimen experiences plastic deformation under a fluctuating stress. The existence of creep is due to the presence of nitrogen impurities.

In these cases two tensions are defined:

• - Upper yield strength (): Stress measured at the first maximum.

• - Lower yield limit (): Lowest stress supported by the specimen.

When an element of a structure is designed, it is necessary to know all the forces that are exerted on it, to calculate its section in such a way that it is within the zone of proportionality between its deformation and tension. This ensures that the deformation suffered by the material is reversible and proportional to the stress supported.

You really cannot accurately assess the forces to which a piece will be subjected. In these cases, action is taken by increasing the forces to which the piece may be subjected and/or reducing the resistance of the material.

In the first case, the forces acting on the element are multiplied by a safety coefficient greater than unity. In the second case, a tension indicative of the resistance of the material is divided by another safety coefficient greater than unity.

The machines used in the tensile test consist of a load-producing device and another device that measures recorded loads and displacements. The machine must meet the following characteristics:.

• - The application of the traction force takes place in the direction of the axis of the specimen.

• - It must be possible to regulate the speed of load application. The download process must be carried out progressively.

The load-producing device can be mechanical or pneumatic, with a moving head and another fixed head.

The load and displacement measuring device operates electronically, regulating the speed of load application and generating printed diagrams of the traction curve.

Tensile tests generally must meet the requirements given the standards with which it is carried out, which define the shape and dimensions of the specimen, the speed of the test, the calibration and precision of the equipment, the environmental conditions and the information that must be presented in the test report. For metallic materials, the standards implemented are EN ISO 6892-1 and ASTM E8/8M.

• - Compression test.

• - Universal machine.

• - Stress test (material) "Stress test (material)").

• - stress-strain-diagram.

• - The content of this article incorporates material from an entry of the Free Universal Encyclopedia, published in Spanish under the Creative Commons Share-Alike 3.0 license.

In the test, the deformation (elongation) of the specimen is measured between two fixed points of the specimen as the applied load increases, and it is represented graphically as a function of the tension (applied load divided by the section of the specimen). In general, the stress-strain curve thus obtained presents four differentiated zones:

1. • Elastic deformations: The deformations are distributed along the specimen, they are small in magnitude and, if the applied load were removed, the specimen would recover its initial shape. The coefficient of proportionality between stress and deformation is called elasticity or Young's modulus and is characteristic of the material. Thus, all steels have the same modulus of elasticity although their resistances may be very different. The highest stress reached in this region is called the yield limit and is what marks the appearance of this phenomenon. There can be two zones of elastic deformation, the first straight line and the second curve, the limit of proportionality being the value of the tension that marks the transition between the two. Generally, this last value is of no practical interest and an elastic limit (conventional or practical) is then defined as the one for which a predetermined elongation occurs (0.2%, 0.1%, etc.). It is obtained by drawing a straight line parallel to the proportional section (straight) with an initial deformation equal to the conventional one.

2. • Creed or yield. It is the sudden deformation of the specimen without an increase in the applied load. The creep phenomenon occurs when impurities or alloying elements block the dislocations "Dislocation (crystalline defect)") of the crystalline lattice, preventing its sliding, a mechanism by which the material is plastically deformed. Once the yield limit is reached, the dislocations are released, producing deformation suddenly. The deformation in this case is also distributed uniformly throughout the specimen but concentrating in the areas in which the dislocations have been released (Lüders bands). Not all materials present this phenomenon, in which case the transition between elastic and plastic deformation of the material is not clearly appreciated.

3. • Plastic deformations: if the load applied in said area is removed, the specimen only partially recovers its shape, leaving it permanently deformed. The deformations in this region are more pronounced than in the elastic zone.

4. • Narrowing"). At a certain point in the test, the deformations are concentrated in the central part of the specimen, showing a marked reduction in the section of the specimen, at which point the deformations will continue to accumulate until the specimen breaks in that area. Narrowing is responsible for the decrease in the stress-strain curve; the stresses do not actually decrease until the breakage, what happens is that what is represented is the quotient of the applied force (increasing until the beginning). of the necking) between the initial section: when the necking occurs the section decreases (and therefore also the necessary force), a decrease in section that is not taken into account in the graphic representation. Brittle materials do not suffer significant necking or plastic deformations, the specimen breaking suddenly. Once the test is completed, the breaking load, ultimate load or tensile strength is determined: the maximum resisted by the specimen divided by its initial section, the elongation in (%) and the necking. in the area of the break.

Other characteristics that can be characterized by the tensile test are resilience "Resilience (engineering)") and tenacity, which are, respectively, the elastic and total energies absorbed and which are represented by the area under the stress-strain curve up to the elastic limit in the first case and until reaching failure in the second.

The specimens used in the tensile test have a circular or rectangular cross section. The central part must be machined so that its section is constant. If the material is fragile, the surface will need to be polished.

The initial length () of the test piece is marked on the calibrated part. The length of the calibrated part must be between and if the specimens are cylindrical. If the test pieces are rectangular or square, the length will be between and .

At the ends of the specimen the section increases to facilitate its attachment to the jaws "Clamp (mechanism)") of the traction machine. These areas are called heads. To avoid areas where stresses are concentrated, the section of the specimen varies from the calibrated part to the head in a smooth and gradual way.

For tests with specimens of different dimensions to be comparable, it must remain constant.

• - Proportionality limit (): Stress beyond which the deformations are no longer proportional to the stresses.

• - Elasticity limit ( and ): Stress beyond which the deformations are no longer reversible. Its value is very close to the limit of proportionality. It is difficult to measure since it is necessary to apply tension to the specimen and subsequently remove it to check whether or not it has recovered its initial length.

If the specimen recovers its initial length, the elastic limit will be higher than the applied stress, and the test must be continued with higher stresses. If the specimen shows permanent deformation, the stress will be greater than the elastic limit. Once deformed, the specimen is useless and must continue to be dimensioned below and above the elasticity limit using other specimens.

To solve these difficulties, two tensions are used:

• - Permanent deformation limit (): Stress that causes a permanent deformation equal to a certain percentage of the initial length. Generally the percentage is 0.2%, indicated by . To determine this tension, the specimen is subjected to increasing loads that are maintained for 10 seconds and are subsequently eliminated, measuring the permanent deformation. The value is obtained by interpolation.

Interpolation is a common practice when you have several pairs of data (x, y) and you want to determine the ordinate y, which corresponds to a certain abscissa (x).

Linear interpolation considers that the ordinate varies linearly between every two pairs of points. If you have the pair of data (1,2), (3,4) and (4,5), and you want to know the ordinate that corresponds to x = 2.5, you take the first two pairs of points and consider the line that passes through them. The ordinate sought (y = 3.5) will be the one that corresponds to x.

• - Limit of loss of proportionality (): Voltage that causes a non-proportional elongation equal to a certain percentage of the initial length. Generally the percentage is 0.2%, indicated by . To obtain this value, it is necessary to consider the intersection between the traction curve and the line parallel to the proportional area of ​​the curve that cuts the x-axis by the set percentage.

• - Young's Modulus (E): Relationship between stress and deformation in the zone of proportional behavior.

• - Tensile strength (): Maximum tension that the specimen supports during the test.

• - Break resistance (): Tension supported by the specimen at the moment of breakage. As long as the specimen does not suffer "necking", its value is close to that of the tensile strength. Once the tensile strength is exceeded, the specimen is considered broken.

• - Elongation at break (A): Greater plastic elongation achieved by the specimen. It is measured as a percentage.

being the length of the specimen after the test.

• - Breakage necking (Z): Decrease in section that occurs after breakage. It is measured as a percentage.

being the smallest section of the test tube.

If the specimens are rectangular, the calculation of the breaking stresses, the section is expressed by:.

being a' and b' the dimensions.

• - Deformation work: Area under the force-elongation curve, which is calculated by and represents the work that is necessary to develop to break the specimen and the capacity of the material to absorb work. Particularly in the automotive industry, it is of utmost importance to know the behavior of the parts of a vehicle in the event of a collision.

As the test progresses, the section of the specimen gradually decreases, and the stress it supports is:

S being the section of the specimen at each instant, which reaches its minimum value in the necking zone, and the true tension.

As the test progresses, the length of the specimen gradually increases, and the deformation must be measured with respect to the length it presents at each moment. The deformation will be given by:.

L being the length of the specimen at each moment of the test, the true deformation and the engineering deformation.

In many metals the true stress and strain are linked by the Hollomon relation"):, where and are characteristic constants of the material.

Many metals, such as low carbon steels, do not present a gradual transition between the elastic and plastic behavior zones. Once the limit of the elastic zone has been exceeded, there is a zone of yielding or yielding, in which the specimen experiences plastic deformation under a fluctuating stress. The existence of creep is due to the presence of nitrogen impurities.

In these cases two tensions are defined:

• - Upper yield strength (): Stress measured at the first maximum.

• - Lower yield limit (): Lowest stress supported by the specimen.

When an element of a structure is designed, it is necessary to know all the forces that are exerted on it, to calculate its section in such a way that it is within the zone of proportionality between its deformation and tension. This ensures that the deformation suffered by the material is reversible and proportional to the stress supported.

You really cannot accurately assess the forces to which a piece will be subjected. In these cases, action is taken by increasing the forces to which the piece may be subjected and/or reducing the resistance of the material.

In the first case, the forces acting on the element are multiplied by a safety coefficient greater than unity. In the second case, a tension indicative of the resistance of the material is divided by another safety coefficient greater than unity.

The machines used in the tensile test consist of a load-producing device and another device that measures recorded loads and displacements. The machine must meet the following characteristics:.

• - The application of the traction force takes place in the direction of the axis of the specimen.

• - It must be possible to regulate the speed of load application. The download process must be carried out progressively.

The load-producing device can be mechanical or pneumatic, with a moving head and another fixed head.

The load and displacement measuring device operates electronically, regulating the speed of load application and generating printed diagrams of the traction curve.

Tensile tests generally must meet the requirements given the standards with which it is carried out, which define the shape and dimensions of the specimen, the speed of the test, the calibration and precision of the equipment, the environmental conditions and the information that must be presented in the test report. For metallic materials, the standards implemented are EN ISO 6892-1 and ASTM E8/8M.

• - Compression test.

• - Universal machine.

• - Stress test (material) "Stress test (material)").

• - stress-strain-diagram.

• - The content of this article incorporates material from an entry of the Free Universal Encyclopedia, published in Spanish under the Creative Commons Share-Alike 3.0 license.