RU2750491C1 - Method for creating test samples for carrying out strength studies in the system of monofilament - polymer matrix (drop - sting test) and a device for creating test samples - Google Patents

Abstract

FIELD: test samples creation.

SUBSTANCE: invention relates to a method for creating test samples for conducting strength studies in a monofilament-matrix system (cured thermo-plastic binder) for fibers of various sizes, including ultra-thin ones (fiber diameter less than 10 microns). The resulting test sample differs from samples of other adhesive micromechanical techniques in that during its creation, the area of ​​the monofilament-matrix interface is precisely controlled. Shallow immersion depths (several tens of micrometers) make it possible to reduce the fracture load of the adhesive system below the cohesive failure load of the monofilament.

EFFECT: obtaining a test sample for carrying out deformation and strength studies of the monofilament - matrix system, suitable for studying interfacial interactions in systems with ultrathin monofilaments (less than 10 microns).

2 cl, 8 dwg

Description

The invention relates to a method for creating test samples for conducting strength studies in a monofilament-matrix system (cured thermo-plastic binder) for fibers of various sizes, including ultra-thin ones (fiber diameter less than 10 microns).

In modern industry, fibrous polymer composite materials (PCM), based on thermo-plastic matrices, reinforced with fibers of various natures are widely used [Pedram Parandoush, Dong Lin A review on additive manufacturing of polymer-fiber composites // Composite Structures, 2017, V.182, pp .36-53; Kablov E.N. Composites: today and tomorrow // Metally Evrazii, 2015; Yao S.-S., Jin F.-L., Rhee K.Y., Hui D., Par S.-J. Recent advances in carbon-fiber-reinforced thermoplastic composites: A review // Composites Part B: Engineering, 2018, V.142, pp. 241-250]. The deformation and strength properties of reinforced composites are determined not only by the characteristics of the matrix and the fiber, but also by the properties at the fiber-matrix interface [Hughes J.D.H. The carbon fiber / epoxy interface - a review // Composites Science and Technology, 1991, V.41, pp.13-45]. It is known that the matrix evenly distributes the load between the fibers; therefore, the state of the boundary layer in the fiber-matrix system largely determines the degree of realization of the strength of the reinforcing filler in the composite. In this regard, for the development of modern fibrous composite materials with a complex of high physical and mechanical characteristics, it is necessary to have a reliable, reproducible technique that allows adhesion studies at the fiber-matrix interface in a wide range of component characteristics.

It is important that the methods of direct measurement of strength in a monofilament-matrix system simulating the unit cell of a fibrous PCM [Karzov I.M., Alentiev A.Yu., Bogdanova Yu.G., Kostiina Yu.V., Shapagin A.V. The influence of "fiber-matrix" interface energetic characteristics on the polymer composite strength // Moscow University Chemistry Bulletin, 2010, V.51, N.6, p.462], allow avoiding the imposition of structural, large-scale and other factors on the result, and obtain the true values of strength, taking into account only the physicochemical properties of the components of the system. The measurement of the adhesive strength by the micromechanical technique in such a cell corresponds to the maximum extent to the processes occurring in real polymer composite materials during fracture.

The main difficulty in the study of adhesion strength by micromechanical methods in the monofilament-matrix system is the preparation of test samples [Chand S. Review Carbon fibers for composites // J. of Materials Science, 2000, V. 35, pp. 1303-1313]. To date, the best strength properties are demonstrated by PCMs reinforced with carbon fibers (CF), the diameters of which vary from 5 to 10 microns. Ultrathin monofilaments are characterized by low absolute values of cohesive strength, which requires, when developing a micromechanical technique for determining strength, to reduce the contact surface in an adhesive monofilament-matrix pair to values that exclude cohesive destruction of the monofilament during its extraction.

The previously developed methods for direct determination of strength have a number of disadvantages associated with the methods of creating test samples. In the micromechanical technique of "three fibers" [Gorbatkina Yu.A., Ivanova-Mumzhieva V.G. Adhesion of modified epoxides to fibers // Moscow, TORUS PRESS, 2018, 216p .; Gorbatkina Yu.A. Adhesive Strength of Fiber-Polymer System // Ellis Horwood, New York, London, 1992] the area of contact between the monofilament and the matrix cannot be adjusted, since it is determined by the diameter of the auxiliary glass fibers. The technique for which the preparation of test samples is carried out in this way cannot be used when examining monofilaments with diameters less than 10 μm. Micromechanical technique of microbond [Day R.J., Caucih Rodrigez J.V. // Investigation of the micromechanics of the microbond test // Composites Science and Technology. 1998. V. 58, Iss. 6, pp. 907-914; Wu Q., Zhao R., Zhu J, Wang F. //. Interfacial improvement of carbon fiber reinforced epoxy composites by tuning the content of curing agent in sizing agent // Applied Surface Science. 2020. V. 504. p. 12] cannot be used to measure the adhesion strength in the carbon monofilament-matrix system, since the diameter of the carbon monofilaments determines the small droplet size of the cured binder (matrix), which makes it impossible to use test equipment. SFFT fragmentation test [Feih S., Wonsyld K., Minzari D. Wesermann P., Lolholt H. Testing Procedure for the Single Fiber Fragmentation Test // Roskilde: Risø National Laboratory, 2004 Report no .: Risø-R-1483 ( EN)] provides reliable results for virtually any fiber thickness. However, its use significantly limits the complexity of preliminary calibration procedures and processing of experimentally obtained data, and the method of creating test samples significantly affects the accuracy and reproducibility of the results. One of the most popular, along with the microbond technique, is the pull-out test in both modifications (clamping from above and fixing with a knife) [Sørensen BF, Lolholt H. Fiber pull-out test and single fiber fragmentation test - analysis and modeling // IOP Conference Series: Materials Science and Engineering, Volume 139, 37th Risø International Symposium on Materials Science 5-8 September 2016, Risø, Denmark; Di Francia S., Ward T.C., Claus R.O. The single-fiber pull-out test. 1: Review and interpretation // Composites Part A: Applied Science and Manufacturing, 1996, V.27, Iss.8, pp.597-612.], But its capabilities do not allow determining the strength of adhesive systems with ultra-thin carbon monofilaments, due to with the absence of conditions for controlling the surface area of the adhesive contact.

Thus, to date, for monofilaments with sizes less than 10 microns, there are no methods for measuring the strength in the monofilament-thermosetting matrix system. This is due to the absence in the existing methods of creating test samples of the possibility of achieving between the components of the system of the contact area of a given size, ensuring the separation of the components without cohesive destruction of the monofilament.

The present invention includes a method for creating test specimens for performing monofilament-matrix strength studies for thermo-plastic cured binders and fibers of virtually any size. The name of the patented method for creating test samples - Drop-Sting test was determined by the team of authors.

The developed method of creating test samples for conducting micromechanical studies Drop-Sting test allows with sufficient accuracy to reproduce the processes of structure formation in composite materials, and is devoid of most of the disadvantages inherent in the existing methods. The indisputable advantage of this method is to conduct research on monofilament in a hardened binder. This makes it possible to obtain the true values of the strength characteristics in the monofilament-matrix system, which is an elementary cell of the PCM, excluding the features associated with the impregnation of the threads and, as a consequence, with the processing of the results obtained.

The technical result of the claimed invention is to obtain a test sample for carrying out deformation and strength studies of the monofilament-matrix system, suitable for studying interfacial interactions in systems with ultra-thin monofilaments (less than 10 microns).

The resulting test sample differs from samples of other adhesive micromechanical techniques in that the area of the monofilament-matrix interface is precisely controlled during its creation. Shallow immersion depths (several tens of micrometers) make it possible to reduce the fracture load of the adhesive system below the cohesive failure load of the monofilament.

The technical result is achieved by:

the monofilament is placed in a clamp, which allows it to be securely fixed vertically without mechanical damage, the free end of the monofilament has a length not less than the immersion depth in the binder;

a substrate made of copper (silver, aluminum) wire (diameter 100 ÷ 500 μm) is placed on a thermostatically controlled table vertically under the monofilament;

a drop of thermo-plastic binder is applied to the substrate (on the end of the wire);

the end of the monofilament and the top of the drop are aligned, positioning is carried out using a goniometric table with micromechanical screws along the oX, oY axes and using a precision stepping motor along the oZ axis, control is carried out by the operator through the video camera of a horizontal microscope;

immerse the monofilament in a drop of binder to a predetermined depth by precisely moving the substrate upward on a thermostatted table;

the adhesive system is heated to the curing temperature of the binder and held until the components of the system are fixed (to the point of gelation);

complete curing of the system is carried out in a thermostatted cabinet to increase the speed of creating test samples;

the test piece is glued into the holder for deformation and strength tests.

The device for creating a test sample allows you to lower the monofilament to a certain depth in a thermo-plastic binder and fix the monofilament-matrix system by curing the binder at a given temperature. The formation of an adhesive bond occurs with microscopic control on a developed original precision device and includes:

clip for fastening monofilament, providing a secure fit;

a system for precision positioning of the monofilament relative to the matrix along the oX and oY axes, consisting of a goniometric table with micromechanical adjustment screws along the oX and oY axes;

a positioning control system along the oZ axis, which includes a stepper motor with a gearbox, for immersing the monofilament in the matrix to a predetermined depth;

thermostatically controlled table for maintaining the temperature in the range from 20 to 220 ° С;

horizontal optical microscope equipped with a video camera for positioning control;

a computer for processing video images from a microscope.

The essence of the claimed invention is further illustrated by a detailed description and illustrations, which depict the following:

Fig. 1. Photograph of the device for creating test samples according to the Drop-Sting test method and auxiliary equipment, where:

A - device for creating test samples;

B - horizontal optical microscope with a video camera;

B - computer monitor with an image of a test sample;

Г - device control unit (temperature and immersion depth);

FIG. 2. Photo images of the views: in front, on the side and on the thermostatted stage of the device for creating test samples according to the Drop-Sting test method, where:

1 - clamp;

2 - substrate;

3 - thermostatically controlled table;

4 - thermo-plastic binder;

5 - goniometric table;

6 - micromechanical screw along the oX axis;

7 - micromechanical screw along the oY axis;

8 - precision stepper motor along the oZ axis;

9 - horizontal optical microscope;

FIG. 3. Image of a test sample obtained through the objective of a horizontal microscope, where:

2 - substrate;

4 - thermo-plastic binder;

10 - monofilament;

FIG. 4. Test piece in holder, where:

2 - substrate;

4 - thermo-plastic binder;

10 - monofilament;

11 - holder

FIG. 5. Burning through the test specimen holder before carrying out deformation and strength studies, where:

11 - holder;

12 - clamps of physical and mechanical equipment;

13 - electrode;

FIG. 6. An example of an adhesion pattern obtained by breaking a test sample created by the Drop-Sting test method;

FIG. 7. SEM image of a monofilament extracted from the matrix with the marked geometric parameters of the surface in contact with the matrix, where:

10 - monofilament;

14 - meniscus of the hardened binder;

l - length

d - diameter

FIG. 8. Optical image of the destroyed test specimen after deformation and strength tests, where:

2 - substrate;

4 - thermo-plastic binder;

10 - monofilament;

14 - meniscus of the hardened binder;

15 - hollow channel after removing the monofilament from the matrix.

The competitive advantage of the method for creating test samples Drop-Sting test is the absence of requirements for the minimum fiber thickness and its cohesive strength, since the developed method is fundamentally different from those described earlier in that a special device for creating test samples of PCM unit cells allows you to adjust the immersion depth of the monofilament in a binder with its subsequent fixation during curing. Thus, by varying the contact surface of the monofilament in the matrix, the condition is reached when the strength of the monofilament-matrix adhesive system is lower than the cohesive strength of the monofilament. Compliance with this condition when applying a tensile load to the test specimen excludes cohesive destruction of the monofilament. The threshold depth of fixation of the monofilament in the matrix is determined empirically, proceeding from the condition that the absolute value of the strength of the adhesive joint should be lower than the previously experimentally determined value of the strength of the monofilament.

The deformation and strength tests of test specimens according to the Drop-Sting test method are carried out on physical and mechanical equipment, which should ensure the application of a tensile load to the test specimens at a speed in the range of 0.1 ÷ 10 mm / min and registration of the load with high accuracy in the range of 0 ÷ 1 N.

The method for creating a test sample is as follows.

the monofilament is placed in a clamp, which allows it to be securely fixed vertically without mechanical damage, the free end of the monofilament has a length not less than the immersion depth in the binder;

a substrate (2) made of copper (silver, aluminum) wire (diameter 100 ÷ 500 μm) is placed on a thermostatically controlled table (3) vertically under the monofilament;

a drop of thermo-plastic binder (4) is applied to the substrate (on the end of the wire);

align the end of the monofilament and the top of the drop, positioning is carried out using a goniometric table (5) with micromechanical screws along the oX, oY axes (6, 7) and using a precision stepping motor along the oZ axis (8), control is carried out by the operator through the video camera of a horizontal microscope ( nine);

immerse the monofilament (10) into a drop of binder to a predetermined depth, by precisely moving the substrate upwards on a thermostatted table;

the adhesive system is heated to the curing temperature of the binder and held until the components of the system are fixed (to the point of gelation);

complete curing of the system is carried out in a thermostatted cabinet to increase the speed of creating test samples;

the test specimen is glued into the holder (11) for carrying out deformation-strength tests.

The holder with the test sample is placed in the clamps of the physical and mechanical equipment (12) and, before loading, the side surfaces of the holder are burned with an ohmically heated electrode (13), which excludes mechanical damage to the test sample (Fig. 5). The application of a tensile load as a result of the movement of the clamp (12) at a given test speed leads to the extraction of the monofilament from the matrix. As a result of deformation-strength tests of the monofilament-matrix system, an adhesion pattern is recorded (Fig. 6). It is recommended to check the depth of immersion of the monofilament in the matrix and assess the nature of the destruction of the system by analyzing the extracted monofilaments in a scanning electron microscope (Fig. 7) or an optical microscope (Fig. 8) with a magnification that provides sufficient resolution for analysis. Analysis of micrographs (Fig. 7) makes it possible to determine the diameter (d) of the monofilament and its immersion depth (l) in the binder from the fragments on the monofilament of the material (14) of the matrix (meniscus). From these data, we calculate the surface area (S) of the monofilament at the interface with the matrix using the formula

S = πdl + π (d / 2) ² .

The obtained deformation-strength dependences (Fig. 6) make it possible to calculate the strength of the monofilament-matrix system as the maximum stress at fracture (σ _P ) of the test specimen according to the formula

σ _P = F _P / S,

and to differentiate the process of destruction, highlighting local peaks on the adhesionogram, which is important when carrying out both applied and fundamental work - to study the mechanism of destruction of elementary cells of PCM monofilament-matrix.

Thus, in the laboratory of structural and morphological studies of the Institute of Physical Chemistry and Electrochemistry named after V.I. A.N. Frumkin Russian Academy of Sciences developed a micromechanical method Drop-Sting test for creating test samples to determine the strength of the unit cell of PCM monofilament-matrix for thermo-plastic binders and for monofilaments with sizes from hundreds to units of micrometers. The method, in addition to its application for assessing the quality of adhesive contact by direct measurement, is useful in fundamental studies of wetting, adhesive characteristics and the mechanism of destruction in monofilament-matrix systems. To implement the method, an original device for creating test samples of a monofilament-matrix has been developed.

Claims (3)

1. A method of creating test samples for carrying out strength studies in the system monofilament - polymer matrix (Drop-Sting test), in which the monofilament is placed in a clamp, which allows it to be securely fixed vertically without mechanical damage, the free end of the monofilament has a length not less than the immersion depth in the binder ; the wire support is placed vertically under the monofilament on a thermostatted table; a drop of thermo-plastic binder is applied to the substrate (on the end of the wire); the end of the monofilament and the top of the drop are aligned, positioning is carried out using a goniometric table with micromechanical screws along the oX, oY axes and using a precision stepping motor along the oZ axis, control is carried out by the operator through the video camera of a horizontal microscope; immerse the monofilament in a drop of binder to a predetermined depth by precisely moving the substrate upward on a thermostatted table; the adhesive system is heated to the curing temperature of the binder and held until the components of the system are fixed (to the point of gelation); complete curing of the system is carried out in a thermostatically controlled cabinet to increase the speed of creating test samples; the test piece is glued into the holder for deformation and strength tests. 2. The method according to claim 1, characterized in that the wire is copper, or silver, or aluminum. 3. The method according to PP. 1 and 2, characterized in that the wire is used with a diameter of 100 to 500 μm.

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