RU2698105C1 - Method of determining tearing resistance of a tear-off element of a polymer article - Google Patents

Abstract

FIELD: test technology.

SUBSTANCE: invention relates to a method for determining tearing resistance of a tear-off element of a polymer article, comprising using a polymer article, making, in the polymer article sample, two through holes having parallel axes, forming a constant-thickness tear zone located between the closest through-hole walls, the tear-off element is passed through the through-holes in the sample of the polymer article to form tear-off element branches, the tear-off element branches are placed so that they do not touch the walls of the through-holes and their edges, from which branches of the tear-off element extend, the tear-off element is moved relative to the sample until the tear-off element completion through the tear-off area, the force applied to the tear-off element is measured during its movement and calculating the tear resistance of the tear-off element of the polymer article as the ratio of the force applied to the tear-off element as it moves towards the thickness of the tear zone.

EFFECT: high accuracy of determining tear resistance of a polymer article.

14 cl, 7 dwg, 2 ex

Description

Technical field

The invention relates to a method for determining the strength properties of articles made of polymers, namely, determining the tear resistance of a tearing element.

State of the art

Tear resistance is a commonly used indicator in the study of rubber properties. To determine it, the installations and methods developed are described in GOST 262-93 (ISO 34-79) “Interstate Standard. Rubber. Determination of tear resistance (bifurcated, angular and sickle-shaped specimens). ” To characterize the strength properties of polymers having a higher stiffness than rubber, for example, pipe grades of polyethylene, it is also proposed to use the indicator of tear resistance by a tearing element.

The methodology and testing machine for determining the tear resistance by a tearing element are described in STO73011750-009-2012 “Plastics. "Method for determining the resistance to tearing by a reinforcing element at various temperatures on bifurcated samples." The tests are carried out on a universal machine for testing tensile materials - a device having two clamps: one clamp for attaching the specimen, and a second clamp for attaching the tearing element, which provides continuous measurement of the force applied to the tearing element when moving the beam on which the sample is located, fixed in the clamp. The force applied to the tearing element is measured during the tearing of the sample by the tearing element, passed through the hole made in the sample, when the sample is fixed in the first clamp in the direction from the second clamp, and the tear resistance N is calculated.

However, for the implementation of the method requires specially made samples with controlled sizes, which requires special equipment and time-consuming.

In the work of the authors V.G. Kolbaia et al. (Published in the journal "Plastics" No. 11-12, 2014, pp. 48-50), which is the closest analogue of the claimed technical solution, it is proposed to use the above method according to STO73011750-009-2012 to determine the resistance tearing a polymer product, according to which a sample of a polymer product is used, two through holes having parallel axes are made in the polymer product sample, and a tearing zone of constant thickness located between the adjacent walls of the through holes is formed, a gap tearing the tearing element through the through holes in the sample of the polymer product with the formation of branches of the tearing element, moving the tearing element relative to the sample until completion of the tearing element through the tearing zone, measure the force applied to the tearing element when moving it, and calculate the tearing resistance of the tearing element of the product sample from polymer as the ratio of the force applied to the tearing element during its movement, to the thickness of the tear zone.

However, the disadvantage of this method is the low accuracy of the measurement, because during the test, the branches of the tearing element can touch the walls of the holes in the sample and / or the edges at the exit of the branches of the tearing element from the sample, which introduces a significant systematic error in the determined value of the force applied to the tearing element and, thus, distorts the measurement results.

Summary of the invention.

The technical problem solved by the claimed method for determining the tear resistance of a tearing element of a polymer product is to eliminate the indicated drawback of the analogue, and the technical result achieved is to increase the accuracy of determining the tear resistance of a tearing element of a polymer product sample.

In the claimed method for determining the resistance to tearing by a tearing element of a polymer product, the technical result is achieved due to the fact that a sample of the polymer product is used, two through holes with parallel axes are made in the sample, a tear zone of constant thickness is located located between the walls of the through holes, pass the tearing element through the through holes in the sample of the polymer product with the formation of branches of the tearing element, arrange the branches of the tearing element in such a way that they do not touch the walls of the through holes and their edges, from which the branches of the tearing element come out, move the tearing element relative to the sample until the passage of the tearing element through the tearing zone is completed, measure the force applied to the tearing element when moving it, calculate the tearing resistance of the tearing element of the product from the polymer as the ratio of the force applied to the tearing element during its movement, to the thickness of the tear zone.

Due to the location of the branches of the tearing element in such a way that the branches of the tearing element do not touch the walls of the through holes and their edges from which the branches of the tearing element come out, the systematic measurement error inherent in the known method is eliminated and the accuracy of determining the resistance to tearing by the tearing element of a polymer product is improved .

To implement the method, two elements can be used, one of which is intended for fixing a sample of a product made of polymer, and the other for fixing a tearing element, while at least one element for fixing is made with the possibility of movement relative to the other. The movement of the branches of the tearing element is carried out by moving one element relative to another. Such fastening elements can be clamps for securing the sample and clamps for securing the branches of the tearing element.

In order to avoid the branches of the tearing element touching the walls of the through holes, displacement limiters of the branches of the tearing element are used, which are provided with the element for securing the branches of the tearing element. These stops prevent the branches from moving to the walls and edges of the through holes of the polymer product sample from the side where the branches of the tearing element come from and touch these walls and edges.

As such limiters, holes made in the element for fixing the branches of the tearing element can be used.

It is possible to use a metal wire as a tearing element. In one embodiment of the method, a smooth metal wire is used, in another, twisted.

As a sample of a polymer product, the product itself can be used.

In another embodiment of the method, cut

part of the product.

When implementing the method, an element can be used to secure the branches of the tearing element, configured to control the distance between the holes made in this element. It is also possible to use the element for securing the branches of the tearing element with an unregulated distance between the holes made in this element.

In the particular case of the implementation of the method, an element is used to fix the branches of the tearing element, made with the possibility of smoothly adjusting the distance between the holes made in this element. In another, particular case of the method, an element is used to secure the branches of the tearing element, made with the possibility of stepwise regulation of the distance between the holes made in this element.

To implement the method, a tensile testing machine can be used, having the first and second clamps, the first of which is used to fix the sample, and the second to fix the branches of the tearing element, made with the possibility of moving at least one clamp relative to another.

A brief description of the drawings.

In FIG. 1 shows a diagram of a method.

In FIG. 2 shows one embodiment of a method using elements for securing a sample of a polymer product and branches of a tearing element.

In FIG. 3 shows the location of the holes in the element for securing the branches of the tearing element.

In FIG. 4 is a diagram illustrating the calculation of the distance between the branches of the tearing element.

In FIG. 5 shows an embodiment of a method with a continuously adjustable distance between the branches of the tearing element.

In FIG. 6 shows an embodiment of a method with a stepwise adjustable distance between the branches of the tearing element.

FIG. 7 shows a graphical dependence of the force applied to the tearing element, depending on its movement relative to the sample of the product from the polymer.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, to implement the method, a sample 1 of a polymer product is used, in the sample 1 of a polymer product two through holes 2 with parallel axes 3 are made. Between the walls of the through holes adjacent to each other, a tear zone 4 of constant thickness A is located. The tearing element 5 is passed through through holes 2 in the sample 1 of the polymer product with the formation of branches 6 and 7 of the tearing element. The branches of the tearing element 6 and 7 are positioned so that they do not touch the walls of the through holes and those edges of the through holes from which the branches of the tearing element come out. The tearing member 5 is moved relative to the sample 1 in the direction of application of the force F shown in FIG. 1 by arrows, until the tearing element passes through the tearing zone 4. Using a force meter (not shown in the drawing), the force F applied to the tearing element during its movement is measured, and the tear resistance of the tearing element of the polymer product is calculated as the ratio of the force F applied to tearing element when moving it, to the thickness A of the tear zone 4.

In FIG. 2 shows an embodiment of a method in which the elements 8 and 9 are used, intended for fastening to them a sample 1 of a polymer product and a tearing element 5, respectively. At least one of the elements 8 and 9 has the ability to move relative to the other. The branches of the tearing element 6 and 7 are fixed to the element 9 with the help of fasteners 10 and 11.

In order to maintain the location of the branches 6 and 7 of the tearing element 5, in which they do not touch the walls of the through holes 2 and the edges of the through holes, from which the branches of the tearing element 5 come out, their position can be fixed either by fasteners 10 and 11, or fasteners 10 and 11 and displacement limiters of the branches of the tearing element mounted on the element 9 for securing the branches of the tearing element. If the design of the limiters allows you to fix the branches of the tearing element, then the position of the branches can be fixed by the limiters.

As the limiters, holes 12 made in said element 9, shown in FIG. 3. In FIG. 3 shows the holes 12, the axes of which are perpendicular to the surface of the element 9 and the holes 12, which are made in the positioning part 13, which can be provided with the element 9. In the latter case, the axis of the holes 12 extend parallel to the surface of the element 9. In the specified element 9, holes 12 can be made and with perpendicular and parallel axes at the same time. The branches 6 and 7 of the tearing element 5 are passed either through a pair of holes 12, the axes of which are perpendicular to the surface of the element 9, or through a pair of holes 12, the axes of which extend parallel to the surface of the element 9. The holes 12 do not allow the branches to deviate from the set position and touch the walls of the through holes 2 and their edges at the exit of the branches of the tearing element.

The element 9 for securing the branches of the tearing element may be provided with a positioning part 13 in the event that the implementation of the stops directly in the element 9 is difficult.

In FIG. 1 and 2 it is shown that the branches 6 and 7 of the tearing element 5 do not touch the walls of the through holes 2 and their edges, from which the branches of the tearing element come out.

The branches can be arranged in the indicated way by controlling their position visually or by calculating the distance between the axes of the branches of the tearing element, depending on the diameter and depth of the through holes 2 in the sample of the polymer product, the thickness of the tear zone A, and other parameters.

An example of calculating this distance indicated by “B” is illustrated in FIG. 4, which shows a sample 1 of a polymer product in which two through holes 2 are made, having parallel axes 3 and a tear zone 4. A tear zone 15 passes through the tear zone 4 and the axis of symmetry of the tear zone 15 passes. Relative to this axis, the walls of the holes 2 adjacent to each other are located symmetrically . The force F applied to the tearing element 5 when moving relative to the sample 1 of the polymer product, acts along the branches of the tearing element. The position of the branches of the tearing element is limited by the holes 12a and 12b, which include the branches 6 and 7, respectively. The distance "B" determines the location of these holes relative to the axis 15.

The initial data for the calculation:

A is the thickness of the tear zone,

D is the diameter of the through hole 2 in the sample, while if the through holes have a different diameter, then the diameter of the smaller hole is selected,

d is the diameter of the tearing element,

L is the depth of the through holes 2 made in the sample of the product of polymer 1. If the holes have different depths, then choose the largest.

b is the distance between the exit point 14 of the branch 7 of the tearing element from the sample 1 to the entry point to the limiter, in this example, to the point of entry of this branch of the tearing element into the hole 12b, measured along the symmetry axis of the tearing zone 15 before the movement of the tearing element 5 relative to the sample 1 polymer products.

So that the branches 6 and 7 of the tearing element 5 do not touch the walls of the through holes 2 and their edges, from which the branches of the tearing element 5 come out, the axis of the branches of the tearing element 5 should be located at a distance "B" selected from the condition:

A + d <B≤A + (2D-d) (L + b) / L, where:

B is the distance between the axes of the branches of the tearing element;

A is the thickness of the tear zone;

D is the diameter of the through hole 2 in the sample, while if the through holes have a different diameter, then the diameter of the smaller hole is selected;

d is the diameter of the tearing element;

L is the depth of the through holes 2 made in the sample 1 of the polymer product. If the holes have different depths, then choose the largest;

b is the distance between the exit point 14 of the branch 7 of the tearing element to the entry point of this branch of the tearing element into the hole 12b, measured along the axis 15 before the movement of the tearing element relative to the sample of the polymer product begins to move.

Depending on the calculated distance "B", the location of the holes 12 is determined directly in the element 9 or in the positioning part 13. The diameter of the holes 12 is chosen to be minimal, ensuring the branches of the tearing element to pass through these holes. The distance between the centers of the holes is chosen no more than B-d.

Similarly, the distance between the fasteners 10 and 11 and their location on the element 9 or in the positioning part 13 can be calculated.

As a tearing element, a metal wire can be used: twisted or smooth.

In FIG. 5 shows a side view of an embodiment of an element 9 for fixing a tearing element 5 with a continuously adjustable distance between holes 12 made in the positioning part 13, which is equipped with an element 9 for securing the branches of the tearing element 6 and 7. A dovetail groove 16 is made in the positioning part 13 tail ”for moving movable elements 17 with openings 12 for placement of branches 6 or 7 of tearing element 5 in them. Moreover, for placing branches 6 and 7 of tearing element 5 in positioning part 13 edge 18. Moving the movable elements 17 adjust the distance between the holes 12. The movable elements 17 are moved and fixed using, for example, nuts 19 with left and right threads.

In FIG. 6 shows a diagram of an embodiment of an element for fastening a tearing element 5 with a stepwise adjustable distance between the holes 12, where the holes 20 are fixed by means of the control pins 21 in the holes 22 of the positioning part 13 of the element 9 for fixing the tearing element.

In FIG. 7 shows a graphical record (i.e., the dependence) of the force F applied to the tearing element 5 when it is moving relative to the sample 1. This dependence determines the force F applied to the tearing element 5 when it is moving.

To determine the tear resistance N by the tearing element according to the claimed method, a sample 1 of a polymer product is used, in which through holes 2 are made with parallel axes 3 for passing through the tearing element 5. As a tearing element, a smooth or twisted metal wire is used. Such a tearing element holds a shape, which facilitates its positioning and increases the accuracy of determining the tear resistance of a polymer product.

As a device for implementing the method, for example, a machine for testing tensile materials is used, which is equipped with an element 8 for attaching a sample 1, an element 9 for attaching a tearing element 5 and a force meter (not shown in the drawings). The machine allows you to measure the force applied to the tearing element 5 when tearing the sample 1, when it moves relative to the sample 1.

Sample 1 is fixedly mounted on element 8, as shown in FIG. 2, the tearing element 5, which is a metal wire, is passed through the through holes 2 in the sample 1 of the polymer product, with the formation of branches 6 and 7 of the tearing element 5, the branches 6 and 7 are arranged so that they do not touch the walls and edges of the through holes 2, from which the branches of the tearing element 5 come out. Fix the branches 6 and 7 of the tearing element 5 on the element 9 and move the tearing element 5 relative to the sample 1 until the passage of the tearing element 5 through the tearing zone 4 is completed. the tearing element 5 is the force when it is moved, and the resistance to tearing by the tearing element of the sample of the polymer product is calculated as the ratio of the force applied to the tearing element 5 when it is moving to the thickness A of the tear zone 4.

Sample 1 of the polymer product, mounted in the element 8, under the action of the drive moves relative to the tearing element 5 in the downward direction from the stationary element 9.

As elements 8 and 9, clamps of a tensile testing machine may be used. The clamp designs may be any of the known that are capable of holding the sample and / or tearing element under conditions of applied force. One clamp can hold the sample, the other a tearing element. The design of the clamp can allow you to hold both a sample of a polymer product and a tearing element, depending on what needs to be fixed in it.

The tearing element 5 goes around the tearing zone 4, as shown in FIG. 2, the through holes 2 are made with axles 3 parallel to each other, which is necessary for accurate and reproducible determination of the tearing force and tear resistance of the tearing element.

The distance between the adjacent walls of the through holes 2 in the sample 1 of the polymer product, i.e. the thickness of the tear zone, as well as the size of the cross section of the holes in the plane perpendicular to their axis, must be selected taking into account the properties of the test polymer and the tearing element, namely, the ability of the tearing element not to be destroyed during the test. So, for polyethylene of various grades, tests of product samples made it possible to establish that the distance between the adjacent walls of the holes in the sample should preferably be 2-5 mm, and the diameter of the holes themselves should be at least 2 mm.

In one embodiment of the method, an element 9 is used to secure the tearing element 5 with an unregulated distance between the holes 12 in the positioning part 13 of the element 9 (Fig. 3).

In another embodiment of the method, an element 9 is used to secure the tearing element 5 with a continuously adjustable distance between the holes 12 in the positioning part 13 of the element 9 shown in FIG. five.

In another embodiment of the method, an element 9 is used to secure the tearing element 5 with a stepwise adjustable distance between the holes 12 in the positioning part 13 of the element 9, as shown in FIG. 6.

In cases where the tear resistance of samples of polymer products, the wall thickness of which remains constant, is determined on a large series of test samples (for example, control of manufactured finished products at the enterprise), an element with an unregulated distance between the holes in the positioning part is used.

The possibility of stepwise and smooth adjustment of the distance between the holes 12 in the positioning part 13 increases the accuracy of determining the tear resistance, as it allows you to adjust the position of the branches 6 and 7 of the tearing element 5 if necessary.

Next, the branches of the tearing element 5 are arranged so that they do not touch the walls of the through holes and their edges, from which the branches of the tearing element come out, fix the branches 6 and 7 of the tearing element 5 on the element 9, and the tearing element is moved with the application of force F relative to the sample 1 along the symmetry axis of the tear zone 15 until the passage of the tearing element through the tearing zone is completed, the force F applied to the tearing element is measured during its movement, and the tear resistance of the tearing element Leah of a polymer as a ratio of force applied to the rending element during its movement to the thickness of the tear band.

The inventive method for determining the resistance to tear by a tearing element on products made of polymers is illustrated by the following examples.

Example 1

A sample is used in the form of a polymer product, the upper and lower surfaces of which are parallel, make two through holes with axes parallel to each other, form a tear zone of constant thickness located between the walls of the through holes closest to each other. The thickness of the tear zone is measured. The sample of the polymer product is fixed in the first clamp, which acts as an element for fixing the sample. The tearing element is passed through the through holes in the sample of the polymer product to form the branches of the tearing element. The branches of the tearing element are placed under visual control in such a way that they do not touch the walls of the through holes and those edges of them from which the branches of the tearing element come out. The position of the branches of the tearing element relative to the through holes of the sample is fixed, they are fixed on the second clamp, which performs the function of the element designed to fix the tearing element. The clamp is moved, on which the tearing element is fixed relative to the sample until the tearing element passes through the tearing zone, the force applied to the tearing element is measured during its movement, the tear resistance is calculated by the tearing element of the polymer product as the ratio of the force applied to the tearing element during its movement , to the thickness of the tear zone.

Example 2

A sample is used in the form of a fragment of a pipe made of polyethylene 100 (pipe diameter 160 mm, SDR 11), having an arbitrary shape (Fig. 4), in which two through holes with parallel axes are made, with a hole diameter of 2.5 mm and 2, 7 mm and a constant thickness of the tear zone 5 mm.

To determine the tear resistance by a tearing element, a tensile testing machine with a force meter is used that meets the requirements of GOST 28840-90 “Machines for testing materials for tensile, compression and bending. General technical requirements. "

A tearing element with a diameter of 0.5 mm was used. The tensile testing machine has clamps, which are used as elements for securing:

the first clamp for fixing the sample of the polymer pipe, and the second clamp for fixing the tearing element. The second clamp is equipped with a stepwise adjustable positioning part. Fix the sample in the first clamp and pass the tearing element through the through holes in the sample of the polymer product, bypassing the tear zone, and form the branches of the tearing element. The depth of the through holes is determined and the largest L = 14.5 mm is chosen. Before the movement of the tearing element relative to the sample of the polymer product is started, the distance b between the exit point 14 of the branch of the tearing element to the entry point of this branch of the tearing element into the hole of the positioning part of the second clamp is measured along the symmetry axis. This distance is b = 83 mm.

Calculate the distance "B" between the axes of the branches of the tearing element in the positioning part of the second clamp according to the formula:

A + d <B≤A + (2D-d) (L + b) / L, where

A - tear zone thickness - 5 mm

D - hole diameter of the sample - 2.5 mm

d is the diameter of the tearing element -0.5 mm,

L is the distance between the upper and lower surfaces of the product, fixed in the first clamp - 14.5 mm,

b - the distance between the lower edge of the positioning part of the second clamp and the upper surface of the product fixed in the first clamp is 83 mm.

As a result of the calculation, it is determined that the distance "B" between the axes of the branches of the tearing element in the positioning part of the second clamp should not exceed 35.2 mm.

Using the control pins 21, holes 22 are fixed, made on the positioning part 13 of the second clamp, with the corresponding holes 20. In this case, two holes 22 are located at the same distance from the axis of symmetry of the tear zone and the distance between the holes is set to not more than 35.2 mm, but not less than 5.5 mm.

The branches of the tearing element are passed through the selected holes in the second clamp. The branches of the tearing element are pulled, providing contact of the tearing element with the tearing zone, and they are fixed on the second clamp. The branches of the tearing element do not touch the walls of the through holes and their edges, from which the branches of the tearing element come out. The drive of the test machine is driven, and a sample of the polymer product is moved. In this case, the material of the sample is torn apart by the tearing element in the tearing zone as a result of moving the tearing element relative to the sample until the passage of the tearing element through the tearing zone is completed. In the process of tearing, the force meter measures the force F applied to the tearing element 5 during tearing of sample 1, and provides the measurement results in the form of a graphical record "force-displacement". A graphical record (i.e., dependence) of the force applied to the tearing element as it moves relative to the sample is shown in FIG. 7. This dependence determines the force applied to the tearing element during its movement.

The tear resistance of a tearing element of a polymer product is calculated as the ratio of the force applied to the tearing element when moving it to the thickness of the tear zone H = F / A. If necessary, carry out statistical processing of the obtained values of the force applied to the tearing element with the determination of the average value.

The above examples do not exhaust all possible variants of the method. As limiters for the branches of the tearing element, not only holes can be used, but also hinges, hooks, staples, rods and other elements mounted on the element for securing the tearing element, for example, on the second clamp of a tensile testing machine.

The inventive method for determining the tear resistance eliminates the systematic error in determining the specified indicator when using various embodiments of the limiters of the second clamp.

Claims (14)

1. A method for determining the tear resistance of a tearing element of a polymer product, which consists in using a sample of a polymer product, performing two through holes in the sample of a polymer product having parallel axes to form a tear zone of constant thickness located between the walls adjacent to each other through holes, pass the tearing element through the through holes in the sample of the polymer product with the formation of branches of the tearing element, arrange the branches of the tearing element in such a way Because they do not touch the walls of the through holes and their edges, from which the branches of the tearing element come out, move the tearing element relative to the sample until the passage of the tearing element through the tearing zone is completed, measure the force applied to the tearing element when it is moving and calculate the tearing resistance of the tearing element of the product from polymer as the ratio of the force applied to the tearing element during its movement, to the thickness of the tear zone. 2. The method according to p. 1, characterized in that two elements are used, one of which is intended for fixing a sample of a polymer product, and the other for fixing a tearing element, at least one element for fixing is made with the possibility of movement relative to another. 3. The method according to p. 2, characterized in that use the displacement limiters of the branches of the tearing element, which is equipped with an element for securing the branches of the tearing element. 4. The method according to p. 3, characterized in that the holes made in the element for fixing the branches of the tearing element are used as limiters for the displacement of the branches of the tearing element. 5. The method according to p. 1, characterized in that as a tearing element using a metal wire. 6. The method according to p. 5, characterized in that they use a smooth metal wire. 7. The method according to p. 5, characterized in that they use twisted metal wire. 8. The method according to p. 1, characterized in that the product itself is used as a sample of a polymer product. 9. The method according to p. 1, characterized in that as a sample use the part cut from the product. 10. The method according to p. 4, characterized in that they use the element to secure the branches of the tearing element, made with the possibility of adjusting the distance between the holes made in this element. 11. The method according to p. 4, characterized in that the element is used to secure the branches of the tearing element with an unregulated distance between the holes made in this element. 12. The method according to p. 10, characterized in that they use the element for securing the branches of the tearing element, made with the possibility of smooth adjustment of the distance between the holes made in this element. 13. The method according to p. 10, characterized in that they use the element for securing the branches of the tearing element, made with the possibility of stepwise regulation of the distance between the holes made in this element. 14. The method according to p. 1, characterized in that they use a tensile testing machine having first and second clamps, the first of which is used to fix the sample, and the second to fix the branches of the tearing element, made with the possibility of movement, at least , one clamp relative to another.

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