The uniaxial tensile test is often used to determine the mechanical properties of beryllium copper . This test provides data for component design. The tensile test data can also be used for material acceptance and control process operations. Such as: stamping, bending, rolling, machining, drawing and cutting. Test itself is relatively simple, but the use of beryllium copper and explanations of test data, requires a full understanding of the processes and procedures of the intrinsic behavior of the test of alloy.
Tensile test According to the shape and equipment of the sample, there are a series of accessories for testing, fixtures and stress and strain measuring devices. The determination and confirmation of the tensile properties of all the supplied beryllium copper by Jintian Company are based on Test procedure described in ASTM E-8 (Standard Test Method for Tensile Test Metallic Materials), which allows for a wide range of test conditions, equipment and sample shape selection.
The test speed of beryllium copper at a strain rate of 0.005 to 0.2 is moderate in sensitivity to the rate of change. Inspection is usually performed at a constant speed or strain rate. Although the sample may rise in sections after reaching the yield stress, the test time is minimized for high elongation alloys.
For the inspection of beryllium copper strips, the most commonly used test piece with a narrow cross-section in the middle section (dog bone shape) is also available for straight-sided test pieces. The axis of the test specimen is along the longitudinal direction of the strip, ie the rolling direction. Any method that can produce a smooth, corner-free stress sample can be used. The edges of the specimen can be gently thrown with a diamond cloth to remove the burrs, which can affect the premature failure of the specimen or inaccurate test results. When Jintian Company inspected the strip products, the sample size was 12.5m.m and the gauge length was 50m.m.
For large or large beryllium copper products, the tensile test bars are machined to a standard cross section of 9 m.m in diameter, 35 m.m in length or 12.7 mm in diameter by 50.8 mm in length. As a strip sample, ASTM E-8 requires that the gauge length be at least 4 times the standard diameter, and the surface finish of the tensile test strip is at a maximum speed of 1.5 μm.rm.s, and the depth of the knife is at least 0.08 mm. Minimize the stress on the surface of the bar.
From the positional extension test, the engineering stress should be bent, as shown in Figure 1, the stress is on the vertical axis, and the test load is divided by the cross-sectional area of ​​the sample. The stress is expressed in pounds per inch 2 (psl or 1b/in2), and the kilobits per hour (KSI) or in meters are: Newtons/mm 2 (N/mm 2 ) or megabars (MPa). One megabar is set to 1N/mm 2 . Unusual metric stress is expressed in kg/mm 2 (kg/m.m2 or kg.f/mm 2 ). [next]
Table 1. List of conversions for stress units: | |
Psi×1000=ksi | Mpa×0.012=Kg/mm 2 |
Ksi×6.895=N/mm 2 | Mpa×0.145=ksi |
Ksi×6.895=Mpa | N/mm2×0.145=ksi |
Ksi×0.703=kg/mm 2 | Kg/m.m2×1.422=ksi |
Mpa×1=N/mm 2 | Kg/m.m2×9.807=Mpa |
Strain, located on the horizontal axis of the stress-cored line, is the elongation of the test specimen divided by the length of the standard section. Since the strain is in English/English or mm/mm, the strain is expressed without dimensions. Dimensions or percentages, sometimes provided by gauge length strain units. For example, "11% in 2 inches" analyzes the stress enthalpy curve, which can determine the yield strength, tensile strength, elastic (Yang's) modulus, uniform strain and total strain, determination of section yield, for round test Samples are required and are performed after the specimen has been inspected.
The initial part of the stress-strain curve stress-strain curve (Figure 1) is linear, and the value of the slope (stress divided by strain) is the elastic modulus of the material. The elastic modulus is also known as the Young's modulus. Measuring the resistance of a material to small deformations is also a measure of material properties. The larger the modulus of elasticity, the smaller the strain result under given stress conditions. Metal elastic modulus is conventionally measured in millions of psi (msi), thousand ksi, and metric units in gigapascals (Gpa). [next]
Another measure of rigidity is the shear modulus, which is sometimes used in design as a representation of the stiffness of the view. At this time, the strain of the test sample exceeded the elastic limit, as shown in FIG.
The calculation of the shear modulus requires an accurate stress-strain curve and a specific strain value. The shear modulus is not a simple material property, and the set factor (strain variable) affects the value of the shear modulus. The shear modulus is always lower than the elastic modulus. [next]
The initial linear portion of the stress-strain curve is elastic. There is no permanent displacement of the specimen when the load is removed. Exceeding the deformation of the elastic region and entering the plastic deformation region is always the result of some permanent displacement or strain. When the load is removed, the elastic deformation is restored.
The material yield limit is defined as the stress required to produce a given permanent deformation of the specimen. In order not to be obscured, the yield strength should be defined by its amount of strain or permanent displacement, for example: 0.01%, 0.2% or 0.5%. The 0.2% yield strength (also known as 0.2% displacement yield) is the most frequently measured yield strength, which is 0.2% when the dependent variable is omitted. Before the computerization of the tensile testing equipment, the yield strength is determined by drawing, and on the right side of the origin of the stress-strain curve, a certain amount of strain is displaced, and a line is drawn parallel to the elastic deformation line. The intersection of the drawn line and the stress-strain curve is the yield strength. The determination of the yield strength is affected by the accuracy of the line drawn, whether it is through the drawing or computer to complete the turning point of the elastic and plastic regions (0% yield strength) called the elastic limit.
For many non-ferrous metals, the transition between elastic and plastic behavior is very moderate. Its elastic limit or the yield strength of any small displacement, without high sensitivity instrument, is very difficult to accurately measure. With the latest equipment, the computer-controlled determination of the elastic modulus and the elastic limit is severely affected by the inaccurate measurement of the slope of the elastic zone. Accurate determination of the slope may fail due to bending compensation of the testing machine or setting of early plastic deformation of the specimen. Accurate elastic limit test, which measures the yield strength of 0.0001% displacement. (A slight strain or a dependent variable of 1 microsecond per gauge).
Due to measurement difficulties, the elastic limit of beryllium copper and the low yield (less than 0.2%) yield strength are not routinely reported and are available from Jintian's Customer Technical Services Department.
When the stress-strain curve is further moved into the plastic zone, the stress used to complete the extension of the sample continues to rise, reaching a maximum, which is called tensile strength or tensile strength at break. When the tensile test reaches this point, the tensile specimen is uniformly elongated along the gauge length (its cross-sectional contraction). When the maximum strength or tensile strength is reached, the tensile test piece becomes unstable in size and the deformation is uneven and very localized - the test piece begins to neck, and the points of maximum stress and maximum strain do not coincide with each other.
The strain or elongation measured from the tensile test provides a characterization of the plasticity or formability of the alloy. The total strain is the most frequently reported data, as shown in Figure 1, which is the strain recorded until the end of the test until the sample is broken. The total strain includes elastic strain, uniform strain, and uneven strain during necking of the specimen after the material has passed the tensile stress. The value of uniform strain in component design work is much more important than the total strain value because it measures only the amount of "available" deformation, the maximum allowable design stress at the point of breaking the tensile stress point. [next]
On the other hand, for the material properties of the metal to be processed, such as machining, stamping or staking, the molding process which causes the metal to break, the total deformation amount is more meaningful than the uniform deformation amount.
Interpretation of test data Each batch of beryllium copper products that Jintian Company lends to it will confirm the tensile properties of the following standards; breaking tensile strength, yield strength of 0.2% displacement, and elongation. These measured values ​​indicate the characteristic properties of the alloy for most applications. The component quality of some applications may be affected by the approximate elastic properties (low displacement yield strength). For this reason, the standard tensile test is not sensitive, when the alloy sample gives (shows) qualified pull Extensible test certificates have different performance when used and may require sensitive tensile tests or additional material properties to identify the problem.
In addition, when the conditions of use are very close to the actual test conditions, the tensile test data will accurately reflect the performance of the material. This situation is very rare, because in most environments, the stress state is more complex than the uniaxial tensile test. Much more.
When tensile test data may be used to express the properties of a material in compression, bending or plane strain, then more information is needed to more accurately represent the performance of the material under non-stretch conditions.
The hardness test is used to indicate the strength of the material, but it does not measure the strength of the alloy. It cannot be used to replace the tensile test value. The hardness test determines the relatively small volume of metal, which may be affected by the uneven microstructure. The tensile test, due to the size of the test piece, is less sensitive to tissue changes.
For deep or hot processed products, the tensile properties are not isotropic. The relationship between non-axial tensile properties and longitudinal properties depends on the properties of the material, modulus, strength, elongation, alloy, microstructure, and degree of deformation. For cold-worked strips, the transverse elastic modulus is slightly higher than the longitudinal direction, while the elongation is slightly lower than the longitudinal direction.
For all products of beryllium copper, the performance range of the tensile test is provided in the "Bronze Guide" published by Jintian Company.
Tensile properties are usually measured at room temperature unless otherwise specified. At room temperature, from -70 to 150 ° C, the tensile properties of beryllium copper are not sensitive to temperature. Jintian Company provides tensile data for beryllium copper at high and low temperatures.
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