CN110967296A

CN110967296A - A method for testing the interfacial shear strength of connecting rod composites

Info

Publication number: CN110967296A
Application number: CN201911351126.2A
Authority: CN
Inventors: 王荣国; 徐忠海; 赫晓东; 蔡朝灿; 白玉娇; 刘文博; 苗琳琳; 邹肖灿; 董旭伦
Original assignee: Zhaoqing Haite Composite Technology Research Institute
Current assignee: Zhaoqing Haite Composite Technology Research Institute
Priority date: 2019-12-24
Filing date: 2019-12-24
Publication date: 2020-04-07

Abstract

The invention relates to a method for testing the interface shear strength of connecting rod composite materials, which solves the problem of difficulty in testing the interface shear strength of existing composite materials, and belongs to the design field of aircraft structures. The composite material includes a resin matrix and carbon fibers. The present invention includes: S1, making the composite material into a sample; S2, connecting the sample with a micro-loading unit, and the upper and lower cutters are as close to the carbon fiber as possible but not in contact with it, under the action of micro-loading, The tool does not move, the carbon fiber moves slowly along the direction of force and contacts with the resin ball. With the gradual increase of the loading value, the resin ball is debonded and slipped along the carbon fiber under the action of the tool, and the sensor will record the resin drop. The maximum force F _max that produces debonding; S3, substitute the value measured by S2 into

The interfacial shear strength IFSS is obtained by calculation, d represents the diameter of the carbon fiber monofilament, and l represents the length of the carbon fiber embedded in the resin ball.

Description

Method for testing interface shear strength of connecting rod composite material

Technical Field

The invention relates to a composite material connecting rod, in particular to a method for testing the interface shear strength of a connecting rod composite material, and belongs to the field of design of airplane structures.

Background

The development of the airplane mainly aims at low cost and high carrying capacity, and the problem of weight reduction of the structure is firstly solved to achieve the aim, and the lower connecting rod of the hanging box section is an important force transmission part of the hanging box section and is used for connecting the bottom of the hanging box section and the lower wing surface of the wing to transmit the thrust of an engine. The traditional airplanes, including B737, B777 and C919 airplanes, are made of metal materials, but with the progress of composite material technology, compared with the traditional steel connecting rod structure, if the hanging connecting rod is made of metal and composite materials, the weight can be reduced by 50% -60%, and potential economic benefits are huge. Therefore, the development of the composite material connecting rod is one of the key technologies for achieving the weight reduction purpose of the airplane.

The composite material integrates the respective advantages of the reinforcing material and the matrix, and has excellent performance. But this is based on the fact that both can transfer loads by means of interfacial shear. Therefore, the mechanical properties of the composite material are controlled to a large extent by the interface conditions. A large number of researches show that the interface strength between the carbon fiber and the resin matrix has obvious influence on the mechanical property of the carbon fiber reinforced resin matrix composite. Various micromechanical testing techniques are used by many scholars to measure the shear strength between the matrix and the carbon fibers in the composite. The critical fiber length method requires that the strength of the filament at the critical length of the fiber must be known, however, the strength value is difficult to determine by experiment and can only be estimated by interpolation. The monofilament pull-out test requires that the length variation of the fibers embedded in the matrix must be sufficiently small, which makes the preparation of the sample difficult.

Disclosure of Invention

Aiming at the problem that the interface shear strength of the existing composite material is difficult to test, the invention provides an easily-realized interface shear strength test method for the connecting rod composite material.

The invention discloses a method for testing the interface shear strength of a connecting rod composite material, wherein the composite material comprises a resin matrix and carbon fibers, and the method comprises the following steps:

s1, preparing the composite material into a sample;

s2, connecting the sample with a micro-loading unit, enabling the upper cutter and the lower cutter to be close to the carbon fiber as much as possible but not to be in contact with the carbon fiber, enabling the cutters to be fixed under the action of micro-loading, enabling the carbon fiber to slowly move along the stress direction and to be in contact with the resin ball, enabling the resin ball to be debonded and slide along the carbon fiber under the action of the cutters along with the gradual increase of the loading value, and enabling the sensor to record the maximum debonding force F generated by the resin drop_max；

S3, substituting the measured value of S2

The interfacial shear strength IFSS is obtained by calculation, d represents the monofilament diameter of the carbon fiber, and l represents the embedding length of the carbon fiber in the resin sphere.

Preferably, in S1, the preparing the composite material into a sample further includes:

s11, fixing the carbon fibers on a hollow iron frame, dotting prepared TED-85 glue solution on the carbon fibers by using a steel needle, and forming spindle-like micro-droplets on the carbon fibers by the resin under the balance action of surface tension of a gas-liquid interface;

s12, moving the carbon fibers into an oven, and curing resin;

s13, making a paper frame by using a hardboard, taking a cured carbon fiber, keeping the cured carbon fiber in a stretched state, fixing the carbon fiber on the hardboard by using a double-faced adhesive, fixing the carbon fiber again by using the adhesive, and cutting off the redundant part to obtain the finished sample.

The method has the advantages that the debonding method is adopted, the interface shear strength is calculated according to the maximum debonding force generated by the resin drops, the method is easy to realize, and the test result precision is high.

Drawings

FIG. 1 is a schematic representation of the measurements of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.

The invention is further described with reference to the following drawings and specific examples, which are not intended to be limiting.

The composite material of the present embodiment includes a resin matrix TDE-85 (epoxy resin) which is a pale yellow viscous liquid having an epoxy value of 0.85Eq/100g and a viscosity of 2.0Pa · s (25 ℃), and carbon fibers, and has a chemical structure shown below:

TDE-85 is a trifunctional high-performance alicyclic epoxy resin, and the molecule contains 1 alicyclic epoxy group and 2 glycidyl ester groups. Has higher shearing strength, lower shrinkage and excellent temperature resistance. Its curing is mainly composed of two reactions: the reaction of glycidyl ester group and the further crosslinking of alicyclic group, no small molecule exists in the reaction, and the modified aromatic amine curing agent and absolute ethyl alcohol are selected as diluents.

The fiber is the main load-bearing part of the composite material, and the performance of the composite material is mainly determined by the reinforcing fiber. The requirements for the reinforcing fiber material are:

a) high strength and modulus, low density;

b) the thermal stability is good, and the thermal expansion coefficients of the fiber and the matrix are relatively consistent or close;

c) the resin has good wettability;

d) has good winding manufacturability, uniform tightness of fiber bundles and the like.

The carbon fiber is a novel material with higher strength and lighter specific weight than steel, and the PAN-based carbon fiber has excellent mechanical property, so that the PAN-based carbon fiber is widely applied to the high and new technical field and the civil industry. Its main properties are as follows:

(l) Compared with metal materials, the specific gravity is small and is only 1.7-2.0g/cm³The light composite material is easy to be prepared, and the light weight of the product is easy to realize.

(2) The tensile strength is high, and is generally between 3.0 and 7.0 GPa. Because of its small specific gravity, high strength and thus high specific strength.

(3) The Young's modulus is high, and is generally between 200 GPa and 650 GPa. And thus the specific modulus (stiffness) is rather high.

(4) The elongation at break is between 1.5 and 2.2 percent, and the fabric is soft and can be woven, and has good processing performance.

(5) Fatigue resistance, high fatigue strength and long service life.

(6) The damping and energy absorbing performance is excellent, the vibration is not easy to start, the vibration can be quickly suppressed after the vibration starts, and the excellent vibration attenuation characteristic is presented.

(7) The graphite is friction-resistant and wear-resistant, and has excellent graphite self-lubricating property.

(8) Small coefficient of thermal expansion (0-1.1X 10)^-6K^-1) The product has stable size and strong adaptability to sudden changes of environmental conditions. The thermal expansion coefficient of the product can be reduced to the minimum degree through careful design and strict construction.

(9) High thermal conductivity (10-160 Wm)^-1K^-1) And the phenomena of heat accumulation and overheating can not occur.

(10) The heat resistance is excellent in an inert atmosphere without lowering the strength, which is not comparable to any material.

The present embodimentM55J series carbon fibers having a fiber density of 1.91g/cm manufactured by Toray of Japan were used³The tensile strength was 4.02GPa, the elastic modulus was 540GPa, and the elongation was 0.7%.

The surface of the carbon fiber has a plurality of concave-convex grooves and grooves with obvious depth, which is the characteristic of the wet spinning process. The increase of the concave-convex and the groove on the surface of the carbon fiber can increase the surface area of the carbon fiber on one hand, thereby increasing the surface energy of the fiber, being beneficial to forming stronger mechanical meshing action between the fiber and the matrix at the interface and being beneficial to improving the interlaminar shear strength of the composite material.

The cross section of the high-modulus carbon fiber is irregular and round, is flat and is concave in the middle, and the cashew nut-shaped cross section and other irregular cross sections such as cashew nut-shaped cross sections are beneficial to improving the specific surface area of the carbon fiber and improving the mechanical meshing effect at the interface of the composite material, so that the bending strength and the interlaminar shear strength of the composite material are improved. On the other hand, however, a circular cross-section has a smaller surface area under the same conditions, and the surface area is smaller as it approaches the circular shape. The smaller the surface area, the less the probability of surface microcracks and defects, which is beneficial to improving the strength of the fiber.

The method for testing the interface shear strength of the connecting rod composite material comprises the following steps:

s1, preparing the composite material into a sample;

s2, connecting the sample with a micro-loading unit, enabling the upper cutter and the lower cutter to be close to the carbon fiber as much as possible but not to be in contact with the carbon fiber, enabling the cutters to be fixed under the action of micro-loading, enabling the carbon fiber to slowly move along the stress direction and to be in contact with the resin ball, enabling the resin ball to be debonded and slide along the carbon fiber under the action of the cutters along with the gradual increase of the loading value, and recording the maximum debonding force F generated by the resin drop by the sensor_maxAs shown in fig. 1;

s3, substituting the measured value of S2

Calculating to obtain the interfacial shear strength IFSS, wherein d represents the monofilament diameter of the carbon fiber, and l represents the embedding length of the carbon fiber in the resin ball。

In this embodiment, the interface shear strength test is performed by using a device for evaluating the interface performance of a MODEL mode HM410 composite material manufactured by toyoho corporation, and the experiment is performed by preparing a sample of the composite material under a 120-fold microscope, and further includes:

s12, moving the carbon fibers into an oven, and curing resin;

The test times are not less than 20, linear fitting is carried out on the debonding force obtained by the test and the embedding length, so that the interface shear strength of the M55J body/TDE-85 composite material is 50.56MPa, and the resin and fiber interface are well combined.

Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that features described in different dependent claims and herein may be combined in ways different from those described in the original claims. It is also to be understood that features described in connection with individual embodiments may be used in other described embodiments.

Claims

1. A method for testing the interface shear strength of a connecting rod composite material, the composite material comprising a resin matrix and a carbon fiber, wherein the method comprises:

S1. Make the composite material into a sample;

S2. Connect the sample to a micro-loading unit. The upper and lower cutters are as close to the carbon fiber as possible without contacting it. Under the action of micro-loading, the cutter does not move, and the carbon fiber moves slowly along the direction of force and contacts with the resin ball. Gradually increase, under the action of the cutter, the resin ball will be debonded and slipped along the carbon fiber, and the sensor will record the maximum force F _max of the resin droplet to produce debonding;

S3. Substitute the value measured in S2 into

2. The method for testing the interface shear strength of connecting rod composite material according to claim 1, wherein in the S1, the composite material is made into a sample, further comprising:

S11. Fix the carbon fiber on a hollow iron frame, and use a steel needle to point the prepared TED-85 glue on the carbon fiber. The resin forms a spindle-like droplet on the carbon fiber under the balance of the surface tension of the gas-liquid interface. ;

S12. Move the carbon fiber into an oven to cure the resin;

S13. Use cardboard to make a paper frame, take a cured carbon fiber, keep it in a tight and straight state, first fix the carbon fiber on the cardboard with double-sided tape, then fix the carbon fiber with glue again, and cut off the excess part , the finished sample.