RU2438114C2 - Procedure and device for determination of hardness and polymer materials elasticity modulus - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: impact is made against tested objects with rigid indenter with specified kinematic energy. There are obtained dependencies of current contact force from depth of indention. There is determined a specimen with the least contact force, and there is chosen a value of contact force equal to 1/3 of maximal value of force at impact. There are determined values of residual depth of a dent formed after completion of an impact and values of depth of indenter depression at active and passive stages of an impact corresponding to a chosen value of contact force. Hardness is determined by ratio of value of contact force to difference of depths at active and passive stages of an impact. Modulus of elasticity is assessed by ratio of contact force to difference of residual depth of dent and depth of impression at a passive stage of an impact. The device consists of a case, of a main rotary lever on the end of which there is secured the indenter with a built-in main permanent magnet, and of a coil of inductivity enveloping the main permanent magnet. The coil is attached to the case, interacts with field of the main permanent magnet and is connected with a computing unit and indication unit. An additional rotary lever with an additional permanent magnet is located in plane of rotation of the main rotary lever. The additional permanent magnet is magnetised opposite to the main permanent magnet. An arrester of rotation angle attached to the case is positioned over the main rotary lever.

EFFECT: procedure and device for more accurate hardness and elasticity modulus of polymer.

2 dwg

Description

Technical field

The invention relates to the field of testing equipment, namely, to determine the physicomechanical characteristics of solid polymers, in particular fluoroplastic, and can be used to directly control products without destroying them. State of the art

A known method for determining the hardness of metal products (UK patent No. 1485218, MKI G01N 3/52, "Method for determining materials for hardness and device for its implementation"). The method consists in striking with a rigid indenter on the test object, measuring the speed of the rebound and the speed of falling, in relation to which they judge the hardness of the material. However, this method cannot be applied to determine the hardness of plastics or solid polymers due to the strong dependence of the measurement results on the modulus of elasticity of the polymers, the value of which is not a constant value, such as for steel, but strongly depends on the technological conditions of manufacture.

The closest method to the claimed invention is a method for determining the hardness and elastic modulus by using a continuous indentation diagram during the impact in the form of a dependence of the contact force on the indentation depth, determining on the diagram the maximum values of force and penetration depth, and the hardness is determined from the ratio, and the angle of inclination the unloading curve determines the modulus of elasticity (Rudnitsky V.A., Dyakovich V.V. "Assessment of the modulus of elasticity of metallic materials by dynamic indentation method "Factory laboratory (diagnostic materials), 1995 №11, s.59-61). The disadvantage of this method is the low accuracy of determination of hardness in the control of polymers due to the strong influence of elastic deformation on the result of measuring hardness. In addition, the accuracy of determining the elastic modulus is reduced due to the uncertainty in the registration of the initial portion of the unloading curve.

The device for determining hardness according to UK patent No. 1485218 contains an indenter with a built-in permanent magnet, which accelerates due to the action of a compressed spring in the guide sleeve. The device is equipped with an inductor connected to the processing unit and the display unit. The disadvantage of this device is the low accuracy of the measurement due to the inevitable deviation of the indenter from the direction specified by the guide sleeve, and touching the walls of the sleeve during its free movement, especially when testing inclined products.

The prototype of the invention is a device (AS USSR No. 1138696, MKI G01N 3/48 "Device for determining the hardness of materials", publ. 1985, bull. No. 5), contains an indenter with a built-in permanent magnet mounted on the end of the pivot arm , an inductor attached to the housing, covering a permanent magnet and electrically connected to the processing and display units. The disadvantage of this device is the inability to control products located arbitrarily in space, since acceleration is carried out under the influence of gravity.

Another disadvantage of the prototype is the rather complicated design of the drive designed to lift the indenter (includes a spring motor, gear reducer and lever system).

Disclosure of invention

The present invention is the creation of a method and device that allows you to more accurately assess the hardness of the polymer as a function of only plastic deformation, and the elastic modulus of the polymer as a function of only elastic deformation.

This problem is solved due to the fact that in the method for determining hardness and elastic modulus, a blow is applied by a rigid indenter with a given kinetic energy to the test objects to be controlled, the dependences of the current contact force P on the indentation depth α are obtained, and the dependences P (α) are determined sample with the lowest contact force selected value of a contact force equal to 1/3 of the maximum force at impact P _in = 1 / 3P _max, for an arbitrary sample from the dependence of P (α) is determined by the depth values of the residual echatka α _ost formed after the closure pin, and the depth of indentation values of the active and passive α ₁ α ₂ pin stages corresponding to the selected value of the contact force P _in, and the hardness values are judged with respect to the difference P _in depths (α ₁ -α ₂ ), and the elastic modulus is judged by the ratio of the contact force P _in to the difference between the residual imprint depth and the indentation depth at the passive stage of the impact (α _ost -α ₂ ).

Another problem is solved due to the fact that in the device for determining hardness and modulus of elasticity, which includes a housing, a main rotary lever, at the end of which an indenter is mounted with a mounted main permanent magnet, an inductor covering the main permanent magnet attached to the body and interacting with the field of the main permanent magnet connected to the computing unit and the display unit, while in the plane of rotation of the main rotary lever is an additional rotary lever with additional with a permanent magnet magnetized opposite to the main permanent magnet, a limiter of the angle of rotation attached to the housing is placed above the main rotary lever.

The technical result consists in providing the ability to measure with high accuracy the properties of objects that are variously oriented in space, namely, the determination of hardness and elastic modulus.

Brief Description of the Drawings

Figure 1 presents a diagram of a device for determining hardness and elastic modulus.

Figure 2 shows the dependence of the contact force P on the indentation depth α.

Figure 1 presents a diagram of a device for determining hardness and elastic modulus, including an indenter 1, with a mounted permanent permanent magnet 2, mounted on the free end of the main rotary lever 3, the maximum angle of rotation of which is limited by the limiter 4. Inductive coil 5, covering the main permanent magnet 2, is fixedly mounted on the housing 6 of the device and connected to the computing unit 7 and the indicating unit 8, the additional pivoting arm 9 contains an additional permanent magnet 10, the field which is directed opposite to the main permanent magnet 2. The test polymer material is indicated at 11.

Figure 2 shows the dependence of the contact force P on the indentation depth α. The active stage of impact OA represents the stage of loading, and AB represents the stage of unloading or the passive stage of impact. The selected value of the contact force P _in correspond to the value of the indentation depth α ₁ at the active stage of the impact and α ₂ at the passive stage of the impact; α _ost means the residual deformation or indentation depth immediately after the end of the impact.

Device operation

The proposed method is illustrated by the operation of the device. Click on the free end of the additional pivot arm 9 (Fig. 1), while raising the additional permanent magnet 10. The field of the additional permanent magnet 10 interacts with the field of the main permanent magnet 2 and rotates the main pivot lever 3, while raising the indenter 1 until it touches stop 4. Continuing pressing the additional pivot arm 9, the additional permanent magnet 10 passes the neutral position, after which the main permanent magnet 2 falls into the zone of strong repulsion from the additional 10 permanent magnet downward. Under the action of this force, the indicator 1 accelerates and strikes the test sample 11. During the movement of the indicator 1 with a permanent magnet 2 in the inductive coil 5, a signal is proportional to the speed of the indicator. After calibrating the signal and performing the operations of differentiation and integration in the computing unit 7, the signal is processed, as a result of which 4 we obtain the dependence of the contact force P on the penetration depth α. Selected value of the contact force P _in what make measurements on objects to be monitored, determining a sample with the lowest value of the maximum contact force P _max and find P _in = 1/3 P _max (in our case, P _in = 20H) and now on the dependence of P (α) for an arbitrary sample, we find the values α ₁ = 54 μm, and α ₂ = 111 μm (Fig. 2), in addition, from the dependence P (α) we determine the residual deformation α _oct = 77 μm.

Now, using the values of P, α ₁ , α ₂ and α _ost, we determine the hardness by the formula

where D is the diameter of the spherical tip of the indenter, in our case D = 1 mm, and the elastic modulus is determined by the formula

µ - Poisson's ratio (for solid polymers µ = 0,4)

Industrial application

The proposed method and device allows with high accuracy to determine the hardness and elastic modulus, rebuilding from their mutual influence, in products made of solid polymer materials, randomly oriented in space.

Claims (2)

1. A method for determining the hardness and elastic modulus, according to which a hard indenter with a given kinetic energy is applied to the test objects to be controlled, the dependences of the current contact force P on the indentation depth α are obtained, characterized in that the sample P is determined from the dependence P (α) the smallest contact force, choose the value of the contact force equal to 1/3 of the maximum value of the force at impact Р _в = 1 / 3Р _max , for an arbitrary sample, according to the dependence Р (α) determine the values of the residual baking depth weft α _rest formed after the end of the impact, and the indentation indentation depth at the active α ₁ and passive α ₂ impact stages corresponding to the selected value of the contact force P _in , and hardness is judged by the ratio of the value of P _in to the difference in depth (α ₂ -α ₁ ), and the elastic modulus is judged by the ratio of the contact force P _in to the difference between the residual imprint depth and the indentation depth at the passive stage of the impact (α _ost -α ₂ ). 2. A device for determining hardness and elastic modulus, including a housing, a main rotary lever, at the end of which an indenter is mounted with a mounted main permanent magnet, an inductor covering the main permanent magnet attached to the body and interacting with the field of the main permanent magnet connected to the computing unit and an indication unit, characterized in that in the plane of rotation of the main pivot arm there is an additional pivot arm with an additional permanent magnet Thus, magnetized opposite to the main permanent magnet, a limiter of the angle of rotation attached to the housing is placed above the main rotary lever.

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