RU2320974C2 - Device for measuring hardness - Google Patents

Abstract

FIELD: testing materials.

SUBSTANCE: device comprises housing, dynamometer, pusher, plug, tip with a ball indenter, race, measuring beam, measuring rod, and strain gages that record the loading and depth of indentation of the ball. The depth of indentation is measured with respect to the surface of the specimen through a unmovable race provided with the measuring beam and measuring rod passing through the opening made in the tip and pressed to the top point of the ball indenter.

EFFECT: enhanced precision.

8 dwg

Description

The invention relates to the field of testing materials for mechanical strength and can be used to assess the mechanical properties of materials without making samples of standard sizes.

MEI-T10A and PITM-DV02 devices were chosen as analogues.

The MEI-T10A device is intended for automatic recording of hardness diagrams in elastic and plastic regions according to the results of measuring the depth of a hole. Markovets M.P. Determination of the mechanical properties of metals by hardness. - Engineering, 1979, pp. 162-166. Figure 1 shows the kinematic diagram of this device: 1 - table, 2 - leg, 3 - power lever, 4 - spring, 5 - ball, 6 - movable dial indicator, 7 - pusher, 8 - rocker, 9 - cargo screw, 10 - bracket, 11 - stop, 12 - test sample, 13 - spring, 14 - bearings, 15 - frame, 16 - movable depth gauge rod, 17 - depth gauge, 18 - clamps, 19 - hinge.

The device measures the penetration depth of the indenter (5) in relation to the reference (at the same time as the base) surface of the sample (12). To do this, he uses a bracket (10), pivotally mounted on a table (1). In the upper part of the bracket (10), a photoelectric sensor (17) is fixed with a movable frame (15) that controls the movement of the lateral points of the ball indenter (5) in the vertical direction, in the lower part of the bracket there is a stop (11), which is fixed relative to it during measuring

Depth of penetration is measured using a photoelectric sensor (17) made of an opticator, in which a disk is mounted instead of an arrow. Holes have been made in the disk along the periphery. When the disk is rotated, the photoelectric pulse sensor detects pulses in proportion to the angle of rotation. Figure 2 shows the part of the device responsible for measuring the depth of penetration of the ball indenter (5) into the sample (12). The dimensional chain is made up of the following links: A ₁ - distance from the place of fixing the ball to the table, A ₂ - height of the test sample, A ₃ - distance from mounting the ball to its lower point, x1 - penetration depth, which can be calculated by the formula:

x ₁ = A ₁ -A ₂ -A ₃ .

In this measurement error will be folded parts of the sizes of deviations, Δx ₁ = ΔA _{1 2} + ΔA + ΔA ₃ occurring during the load changes from zero to maximum values. The construction under consideration gives a minimum error in measuring the indenter penetration depth. The change in the gap between the sample (12) and the table (1) under load is compensated by the rotation of the bracket (10) relative to the hinge (19).

The disadvantages of the device include the fact that the measured indentation depth includes the amount of elastic deformation of compression of the sample over the thickness, and this value depends on the height of the samples and is a systematic error in determining the penetration depth from the surface into which the indentation is performed. The disadvantages include the fact that the device is designed to test samples of small sizes, which can be placed in a very limited space on the table (1) of the device between the power lever (3), the bracket (10) and the leg (2).

The device PITM-DV02 (figure 3) is intended for non-destructive rapid determination of the characteristics of hardness, strength and ductility of materials from continuous diagrams of elastoplastic indentation ("Factory Laboratory. Diagnostics of materials" No. 1, 2003, pp. 41-45). The operation of the device is based on real-time recording of the process of local elastoplastic deformation of the material in the form of diagrams in the coordinates “load-displacement”, “load-time” and “displacement-time” with continuous indentation.

The device consists of the following elements: a base (20), two columns (21), a traverse (22) with a power cylinder (28), on the pusher (27) of which a measuring head (23) is mounted, resting with its probe (25) on the traverse ( 22). A ball indenter (26) is fixed at the end of the pusher.

The dimensional chain of measurement consists of the following links: A ₄ - the distance from the beam to the base, A ₅ - the distance from the shoulder of the pusher to the beam, A ₆ - the distance from the shoulder of the pusher to the top of the ball, A ₇ - the diameter of the ball indenter, A ₈ - height sample. The indenter indentation depth is calculated by the formula:

x ₂ = A ₄ -A ₅ -A ₆ -A ₇ -A ₈ .

The total measurement error x _{2 is the} sum of the deviations of the dimensions due to the deformation of the structural elements:

Δx ₂ = ΔA ₄ + ΔA ₅ + ΔA ₆ + ΔA ₇ + ΔA ₈

The values of A ₆ and A ₇ during the tests, when the load increases from zero to maximum values, change their sizes slightly, therefore, ΔA ₆ and ΔA ₇ do not make a large contribution to the total value of the measurement error. A ₈ is the height of the sample, changing under load, and therefore ΔA ₈ makes a significant contribution to the error in measuring the depth of indentation of the ball from the surface of the sample, A ₅ is the value measured by the sensor, so the error ΔA ₅ can be considered minimal. The maximum contribution to the formation of the error value is made by ΔA ₄ , since the size of A ₄ varies significantly due to deflections of the base and crosshead under load.

The disadvantages of the device include the fact that during the test the elements of the dimensional chain A ₄ , A ₅ , A ₆ , A ₇ , A ₈ can change their sizes according to the nonlinear law of the magnitude of the load (for contact pairs “sample-base” and “column -traverse "). This introduces a nonlinear error in the measurement results of the indenter penetration depth. In addition, the capabilities of the device are limited by the size of the space between the base and the traverse on the one hand and between the columns on the other.

The SSM-1000 instrument was chosen as a prototype. It is intended for measuring the mechanical properties of materials by the non-destructive method of indenter indentation with fastening with a magnetic bracket on the test sample (pipeline). A general view of the device is presented in figure 4. The device consists of a loading mechanism, a mounting bracket for a displacement sensor (35), a displacement sensor (34), a pusher for the loading mechanism (33), a cartridge (32), a magnetic bracket (31) and an indenter in the form of a cylindrical rod with a spherical surface at the end (30 ), and sample (29). Consider the part of the device that is responsible for measuring the depth of immersion of the indenter in the material (figure 5). To build the force – indentation depth diagram and determine such important material characteristics as the proportionality limit and yield strength, it is necessary to determine the indenter indentation depth at each moment of time with the maximum accuracy for the corresponding load:

X ₃ = (A ₁₃ + A ₁₂ + A ₁₁ ) - (A ₁₀ + A ₉ ),

where x ₃ - the indentation depth of the indenter,

And ₉ - the height of the reference prism with a magnetic device for fixing (is under load),

A ₁₀ is the distance from the mounting terminal of the displacement sensor to the upper surface of the reference magnetic prism (a change in this size is monitored by the displacement sensor (34),

A ₁₁ - the size of the part of the pusher of the loading device,

And ₁₂ is the size from the end of the pusher of the loading device (33) to the surface of the cartridge (30), which rests on the indenter (30),

And ₁₃ is the length of the indenter.

Assessment of measurement error is:

Δx ₃ = ΔA ₉ + ΔA ₁₀ + ΔA ₁₁ + ΔA ₁₂ + ΔA ₁₃ ,

where - ΔА ₉ , ΔА ₁₀ , ΔА ₁₁ ΔА ₁₂ , ΔА ₁₃ - dimensional deviations due to deformation of the corresponding structural parts in the process of testing the sample.

The disadvantages of the device include the extended dimensional chain of the device, some elements of which (A ₉ , A ₁₂ , A ₁₃ ) nonlinearly depend on the loads that occur when the indenter is pressed, because they include gaps between the sample and the magnetic bracket (A ₉ ), gaps in the conical shank of the cartridge and pusher (A ₁₂ ) and the gap between the cartridge and the indenter (A ₁₃ ). As a result, the accuracy of measuring the indenter indentation depth with respect to the surface of the test sample (pipeline) is significantly reduced.

Consider the device we offer: a measuring head to a Brinell hardness tester to record the load and the depth of indentation. Axonometric view of the measuring system is presented in Fig.6.

The essence of the invention is expressed in the fact that the selected scheme for measuring the depth of penetration of a ball indenter using a special part - a clip pressed to the sample, with a displacement sensor and a measuring rod fixed on it, resting directly on the ball indenter, allows to eliminate the measurement errors inherent in the prototype ( SSM-1000).

Analysis of the known technical solutions (analogues) in the studied area allows us to conclude that there are no signs in them that are similar to the existing distinctive signs in the claimed device, and to recognize the claimed solution as meeting the criterion of "significant differences".

The measuring head consists of a housing (43), a dynamometer (45) with resistance strain gauges (48), a pusher (46), which is installed on the Brinell device instead of the standard indenter, a centering ball (49) to transfer the load from the pusher to the dynamometer strictly along the axis of the device , plugs (44), tip (39), ball indenter (38). A measuring rod (40) is mounted in the axial hole of the tip (39), abutting against a ball indenter (38). A clip (42) is mounted on the housing along a sliding fit. A displacement sensor in the form of a measuring beam with glued resistance strain gauges is fixed in the groove of the holder with a screw. A recess is made at the end of the measuring beam to fix the position of the pointed end of the measuring rod. To access the measuring beam to the measuring rod, oval cutouts are made in the housing. The load is transferred from the Brinell device through the pusher (46), the centering ball (49), the dynamometer (45), the housing (43), the plug (44) and the tip (39) to the ball indenter (38), which is embedded in the test sample (37 )

The vertical displacement of the ball indenter (38) relative to the surface area of the sample (37) located at some distance from the injection site is measured through a clip (42) tightly pressed to the sample (37), a measuring rod (40), by means of resistance strain gauges (47) glued to the measuring beam (41).

The device operates as follows. The pusher (46) is installed in the Brinell hardness tester (Fig. 8, item 50) instead of the standard tip and fixed with screws. A sample (37) is placed on the object table of the device (51), and the measuring head (52) is brought to the pusher (46) using the set screw (52) and the holder (42) with the sample (37) is pressed to the table (51) using clamping devices (not shown in FIG. 8). Then, the loading device of the Brinell device is turned on and the indenter penetration process is recorded using a two-coordinate potentiometer with recording of the load-indentation depth diagram. During loading, the cage remains stationary relative to the upper surface of the sample (37). A ball indenter (38) is immersed in the sample, followed by a measuring rod (40). The movement of the upper end of the rod is recorded by a measuring beam (41), the fixed end of which is fixed relative to the upper surface of the sample (37), since it is fixed on a stationary holder (42). 7 shows the lower part of the device, which is directly involved in measuring the indentation depth of the indenter.

The depth of the indentation of the ball is determined from the dimensional chain (Fig.7):

x ₄ = (A ₁₄ + A ₁₅ ) - (A ₁₆ + A ₁₇ ),

where x ₄ is the depth of indentation of the ball,

A ₁₄ - the size of the ball, changing under load indentation,

A ₁₅ - the size of the measuring rod under load only from a curved measuring beam (~ 10-20 N),

A ₁₆ - size, the change of which is monitored by a measuring beam with glued resistance strain gauges,

A ₁₇ - the height of the cage, abutting the test piece and under constant load, necessary to close the contact and not changing during the test sample (~ 30-40 N).

Assessment of measurement error will be:

Δx ₄ = ΔA ₁₄ + ΔA ₁₅ + ΔA ₁₆ + ΔA ₁₇ ,

where values A ₁₅ and A _17, obviously, vary slightly due ΔA ₁₅ ≈ΔA≈0 constant loads acting on these elements. The measurement error will consist only of ΔА ₁₄ (change in the size of the ball under the influence of the indentation load) and ΔА ₁₆ (measurement errors of displacement using the measuring beam).

The technical result is to reduce the error in measuring the depth of indentation of the indenter relative to the surface of the sample.

The installation of the measuring head in the Brinell hardness tester slightly reduces the working space for the placement of the test samples or parts, but it remains sufficient for testing even large-sized parts due to the large stroke of the set table screw and free access from three sides.

To determine the mechanical properties according to the diagram “load - indenter indentation depth”, one can use the dependences described in the literature [1], [2] and [3].

Information sources

1. Markovets M.P. Determination of the mechanical properties of metals by hardness. - Engineering, 1979, pp. 162-166.

2. Factory laboratory. Diagnostics of materials. No. 1, 2003, pp. 41-45.

3. www.atc-ssm.com/PDF/IPC04-0357.pdf.

Claims (1)

Measuring head, which includes a housing, a dynamometer, a pusher, a plug, a tip with a ball indenter, a holder, a measuring beam, a measuring rod and strain gauges that record the loading force and the depth of indentation of the ball, characterized in that to reduce the dimensional chain and reduce the measurement error the depth of penetration of the ball indenter, it is made relative to the surface of the sample through a stationary holder with a measuring beam fixed to it, a measuring rod passing in the hole The growth of the tip and pressed to the upper point of the ball indenter.

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