RU2470277C1 - Manufacturing method of strength test specimen of blade of air propeller model - Google Patents

Abstract

FIELD: test equipment.

SUBSTANCE: invention refers to strength tests, and namely to manufacture and design of blade specimens of air propeller model, which are intended for such tests. The method consists in manufacture of the tested component of the necessary length, on the ends of which there fixed are reinforcement components and fasteners. The tested component is cut from blade wing, and reinforcement components are made from the material similar to the blade material; for that purpose, the required number of layers is cut from dry cloth, saturated with high-strength synthetic resin and laid on surface of end section of the tested specimen, with the anti-adhesive layer applied to it in advance in the form of a thin polyethylene film or lubricant. Besides, order of laying, number of layers, their shape and orientation of base of fabric specimens of reinforcement components depends on design destructive load. Then, the specimen is put into a vacuum bag, closed by means of a sealant and air is pumped out of it; after the polymerisation process is completed, specimen with reinforcement components is removed from vacuum bag, reinforcement components and anti-adhesive layer are removed. Then, reinforcement components are subject to strengthening heat treatment; after that, process patches are bonded to the tested specimen external surface and fastening holes are made in the above patches, thus flattening the external surface of the tested specimen.

EFFECT: providing the possibility of improving the accuracy of determination of loads and graphic representation of the specimen destruction nature.

6 dwg

Description

The invention relates to the field of strength tests when creating a new generation of propellers.

As a rule, standard samples for testing the strength of the blades of propeller models have a flat or cylindrical shape with thinning in sections of the zone of the proposed destruction and reinforcement at the points of attachment to the grips of the explosive machine.

Since there are no analogues of the manufacturing methods and designs of samples from the blades of the aerodynamic models of propellers, a comparison was made with analogues of standard samples described in GOST 11262-80, GOST 25.601-80, and ASTM D 63 8 (Dastin S., LubinG ., Mungak J. and Slobodzinski A., “Mechanical Properties and Test Techniques for Reinforced Plastic Laminates, Technical Publication” No. 460, ASTM, 1970; Composite Materials Handbook, Book 2, edited by J. Lubin; trans. with the English.A.B.Geller and others, M., Engineering, 1988).

According to GOST 11262-80, GOST 25.601-80, samples are made of structural material in the form of a strip of rectangular cross section or in the form of a blade with reinforcing plates fixed at the ends without holes.

According to ASTM D 63 8 and AMS standards, samples are made in the form of plates with a section thinning in the gap zone, as well as with a smooth surface on which special reinforcing plates with mounting holes are fixed.

The disadvantages of standard samples are:

1. The processing of samples mechanically due to the cutting of part of the fibers with a cutting tool in the zone of the alleged destruction leads to an error in determining the strength of the sample.

2. The high accuracy of manufacturing smooth transitions for samples from flat plates near the gap zone can increase the cost of costs, as it will require the use of special machines and tools.

3. Since the manufacture of standard samples is carried out from flat plates with a thickness of 1 to 4 mm, and on real blades sections with a thickness of polymer composite materials from 0.5 mm to 20 mm may be encountered, it may be necessary to use the necessary correction factors in the calculations obtained experimentally, which will lead in general to lengthening the cycle of strength calculation.

4. In addition, standard samples are made of materials of the same type, and samples of real construction may include several types of materials (metals, polymers, wood, foams, etc.), interconnected in different ways (adhesive, press, carving), which as a whole complicates the calculation of ultimate fracture loads.

The closest is a method of manufacturing samples from structural materials included in the design of the blade according to ASTM D 63 8 and AMS, including the manufacture of a rectangular sample from polymer composite materials (PCM) with reinforcing pads at the ends of an eight-layer PCB. PCB linings have the orientation of the base fibers relative to the axis of symmetry of the sample 45 and 135 ° and are glued to the test sample on a glue of the type “Metalbond-329”. There are two holes in the clamps of the tensile testing machine for fixing the sample. Several samples are made separately from each material included in the blade structure.

The disadvantages of the prototype are:

- the need for mechanical manufacture of samples from technological allowances for the blade or using technological equipment other than the tools used in the manufacture of the blade, which leads to the cutting of part of the fibers and ultimately introduces an error in the calculation of the breaking load;

- the impossibility of accurately determining the nature of the destruction of a complex structure according to a simple shape sample, since in a real structure rectangular sections are practically absent;

- the impossibility of accurately determining the fracture load on a sample of one structural material, while in a real design several dissimilar materials of various thicknesses and sections are simultaneously used.

The objective of the invention is to develop a method of manufacturing samples of blades of propeller models for determining the actual load of destruction and a visual representation of the nature of the destruction in real sections of the structures of the blades, consisting of dissimilar materials.

The technical result consists in the ability to accurately determine the real load and a visual representation of the nature of the fracture in the samples, as well as to reduce the cycle of strength calculation and reduce the cost of strength tests of the blades of the propeller model.

The technical result is achieved by the fact that the method of manufacturing a sample of polymer composite materials for strength testing of the blades of the propeller model consists in manufacturing a test element of the required length, at the ends of which reinforce elements and fasteners are fixed, and the test element is cut from the blade feathers, and reinforce elements are made from a material similar to the material of the blade, for which the required number of layers of dry tissue are cut, which are impregnated with high-strength si with synthetic resin and lay them on the surface of the end portion of the test sample, previously applying a release layer in the form of a thin plastic film or lubricant, and the number of layers, the laying procedure and the position of the material when cutting reinforcing elements depends on the calculated breaking load, after which the sample is placed in vacuum bag, close with a sealant and pump air out of it, after completion of the polymerization process, a sample with reinforcing elements is removed from the vacuum bag, remove reinforcing elements and a release layer are then applied, then the reinforcing elements are subjected to hardening heat treatment, after which they are glued to the surface of the test specimen and the outer surface of the reinforcing element is smoothed using technological overlays in which mounting holes are made.

Figure 1 is a General view of the samples to determine the load of destruction in various sections of the blade.

Figure 2 - samples prepared for testing.

Figure 3 - contact molding of the reinforcing element at the end of the compartment.

Figure 4 is a sample of the regular part of the model of the blade before the test.

5 is a sample of the regular part of the model of the blade after the test.

6 is a sample of the butt part of the blade model after the test.

The manufacturing process of the blade 1 of the aerodynamic model of the propeller (Fig. 1), which, when tested, is installed on the screw device 2 in the wind tunnel, is necessarily accompanied by strength calculations, according to which a four-fold safety factor should be realized in the design of the blade. To confirm the strength calculations from each set of blades, one or two blades are cut in the transverse direction into small compartments - the test elements 3, from which special samples are made (Fig. 1). Subsequently, each sample is mounted on a tensile testing machine and accordingly destroyed.

Since the samples made from real compartments of the feather blades in the zone of the alleged destruction do not have distinct places with thinning sections that are typical for flat or round samples, then to ensure the destruction of the desired place, the ends of the tested elements are reinforced with additional reinforcing elements 4 (Fig. 2 ) with glue or bolts. The reinforcing elements 4 can be fixed at one end of the test sample or at two ends. The reinforcing elements are made in such a way as not to allow the specimen to collapse directly under the reinforcing element, but to transmit the breaking force to the open area — the test element. The manufacture of reinforcing elements is made from materials similar to the materials used in the design of the blades, which reduces the cost of the process of manufacturing samples. Thus, when reinforcing the ends of the compartment, destruction occurs in the area of the planned open area.

For mounting samples on the grips of a tensile testing machine, technological fastening elements 5 are added to the reinforcing elements, which are fixed with screws or bolts.

As the main technological process for the manufacture of reinforcing elements 4, contact vacuum molding is used (Fig. 3). The molding process begins with cutting the required number of layers of dry fabric (glass, carbon, organic). The number of layers, their shape and orientation of the base of the woven blanks relative to the axis of the blade depends on the estimated breaking load. Before laying, a release layer in the form of a thin plastic film or lubricant is applied to the surface of the test element. Each layer of tissue of the reinforcing elements is impregnated with a high-strength synthetic resin and in a certain order (the width of the glued sheets decreases along the thickness of the reinforcement) is laid on the surface of the end portion of the test sample by the applied release layer. After all layers of impregnated fabric with a total thickness of 5 to 12 mm are laid on the end sections of the test samples 3 cut from certain sections of the blade, the samples are placed in a vacuum bag 6. The vacuum bag is closed securely with a sealant, air is pumped out, creating air inside the necessary negative pressure. Due to atmospheric pressure, the layers of impregnated fabric under the bag are compacted during polymerization. After completion of the polymerization process, a sample with reinforcing elements is removed from the vacuum bag. Strengthening elements and a release layer are removed from the sample. Then, the reinforcing elements are subjected to hardening heat treatment, after which they are glued to the surface of the test sample with glue. The outer surface of the reinforcing element is leveled with the help of technological overlays in which mounting holes are made. On technological overlays are installed technological fastening links 5, which are connected with samples and reinforcing elements using a bolted connection.

Testing these compartments allows you to determine the real load, as well as the nature and sequence of real damage. The ability to install reinforcing elements on the surface of any curvature allows you to test the samples prepared by the above method in various types of tests: tensile, bending, torsion. This method was implemented when determining the strength of the butt and regular compartments of the blade of the aerodynamic model of the rotor of the helicopter.

Figure 4 shows a sample cut from the regular part of the blade model, prepared for testing to determine the load and the nature of the destruction. Figure 5 shows the destruction of the regular part of the blade model. The nature of the destruction (section A): rupture of the skin in the area of the tail section of the profile of the blade. Figure 6 shows the destruction of the butt portion of the blade model. The nature of the destruction: the crushing of the holes (section B) and the deformation of the skin (section C).

Thus, using only one sample, it is possible to determine the fracture load in a real structure; destruction rate of a real structure; the sequence of destruction of elements of a real structure While using standard samples would require 12 tests on 12 samples.

Thanks to the proposed method, both the test time and the complexity of manufacturing are reduced by ~ 2.5 times. And, consequently, the cost of strength testing of the blades of the propeller model is reduced.

Claims (1)

A method of manufacturing a sample of polymer composite materials for strength testing of a propeller model blade, which consists in manufacturing a test element of the required length, at the ends of which reinforcing elements and fastening parts are fixed, characterized in that the test element is cut from the feather of the blade and the reinforcement elements are made of material , similar to the material of the blade, for which the required number of layers of dry tissue is cut out, which are impregnated with high-strength synthetic resin and they are applied to the surface of the end portion of the test sample, having previously applied a release layer in the form of a thin polyethylene film or lubricant, the laying procedure, the number of layers, their shape and orientation of the base of the woven blanks of the reinforcing elements depends on the calculated breaking load, after which the sample is placed in vacuum bag, close with a sealant and pump air out of it, after completion of the polymerization process, a sample with reinforcing elements is removed from the vacuum bag, the element is removed s reinforcements and a release layer, then the reinforcing elements are subjected to hardening heat treatment, after which they are glued to the surface of the test specimen and the outer surface of the reinforcing element is smoothed using technological overlays in which fixing holes are made.

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