CN110487643A - A kind of micron order fiber cutting strength test method - Google Patents

Abstract

The invention discloses a kind of micron order fiber cutting strength test methods, it is characterised in that comprises the steps of: the pedestal spacing range that (1) finite element analysis determines that fiber is under shearing condition；(2) pedestal for fixing fiber to be measured is pre-processed；(3) size of pedestal intermediate space is measured；(4) fixed fiber to be measured；(5) probe loads the central compression of fiber to be measured, and measures the shearing force F needed for cutting fiber_s；(6) the shear strength T of fiber to be measured is calculated according to formula.The present invention can test the shear strength of accurate micron order fiber, and then can analyze the failure criteria of fiber under complex stress condition.

Description

A method for testing the shear strength of micron-scale fibers

technical field

The invention relates to a fiber testing method, in particular to a micron-scale fiber shear strength testing method.

Background technique

Continuous fiber-reinforced composite materials have strong mechanical properties along the fiber axial direction (longitudinal direction), but poor strength perpendicular to the fiber direction (transverse direction), which becomes one of the safety hazards when composite materials are used in complex environments , so it is necessary to measure the shear stress of the fiber. It is also difficult to measure the shear strength of micron-scale fibers with different diameters according to traditional methods.

Contents of the invention

Purpose of the invention: In order to overcome the deficiencies in the prior art, the purpose of the invention is to provide a micron-scale fiber shear strength test method capable of analyzing the failure criteria of fibers under complex stress states.

Technical solution: A method for testing the shear strength of micron-scale fibers according to the present invention comprises the following steps:

(1) Gradually change the distance between the bases until the shear stress of the cross-section of the fiber to be tested suddenly increases. At this time, the base distance of the fiber to be tested is in a shear state, and the finite element analysis is performed on the base of the fiber to be tested in a shear state. spacing, the base is made of a material with a high modulus of elasticity and does not react with acids, preferably a tungsten sheet;

(2) Pre-treat the base used to fix the fiber to be tested. The plane on which the fiber to be tested is pasted must be parallel, the two planes for shearing must be vertical, and the surface roughness of the plane is less than 1/2 of the radius of the fiber to be tested. 10%, the diameter of the fiber to be tested is 1-900μm;

(3) Measure the size of the gap in the middle of the base, the gap in the middle of the base is less than or equal to 5 times the radius of the fiber to be measured, measure the size of the gap with an optical microscope, and judge whether the gap meets the requirements;

(4) fix the fiber to be tested, and use an optical microscope to observe the fiber to be tested at a magnification of more than 400 times to determine whether the fiber to be tested has been fixed;

(5) The shear test of the micron-scale fiber to be tested is carried out on the nanomechanical testing system. The probe of the nano-indenter is compressed and loaded to the center of the fiber to be tested until the fiber to be tested is broken, and the indentation depth is 5×10 ^-4 mm. And measure the shear force F _s required to cut the fiber to be tested, the size of the probe is 0.9 to 0.95 times the gap in the middle of the base;

(6) The calculation formula of the shear strength T of the fiber to be measured is:

Among them, r _f is the radius of the fiber to be tested, and F _s is the shear force required to cut the fiber to be tested, and the measurement and fixation are observed by an optical microscope at a magnification of more than 400 times;

(7) Repeat the above steps, and take the average value of multiple measurements.

Working principle: When the probe is used to compress and load the fiber to be tested, the strain caused by the large elastic modulus of the base can be ignored, which ensures that the two surfaces of the base are always vertical during the compression load, so that the fiber to be tested is in a shear state. Fracture occurs.

Beneficial effects: Compared with the prior art, the present invention has the following remarkable features: it can test the shear strength of accurate micron-sized fibers, and can provide basic mechanical performance parameters of materials for failure criterion analysis of fibers under complex stress states.

Description of drawings

Fig. 1 is a flow chart of the present invention;

Fig. 2 is the structural representation of clamp 4 of the present invention;

Fig. 3 is the structural representation of base of the present invention;

Fig. 4 is a finite element model diagram of the present invention.

Detailed ways

In the following embodiments, the radius r _f of the fiber 1 to be tested is taken as 3.5 μm.

Table 1. Variation law of shear stress with gap width obtained by finite element simulation

Gap/mm Shear stress/MPa 0.04 608.92 0.02 606.99 0.018 675.68 0.01 710.45

(1) Finite element analysis: first use UG to establish the model of the fiber 1 to be tested, the base 2 and the probe 3 as shown in Figure 3, the tangential displacement of the fiber 1 to be tested to shear failure is 5×10 ^-4 mm, for Probe 3 imposes a direction along the tangential direction of the fiber 1 to be tested, with a displacement constraint of 5×10 ^-4 mm in size, and then solves the shear stress of the fiber 1 to be tested, and simulates the gap between the base 2 and the base 2 to be tested by changing the distance between the base 2 The influence of the shear stress of fiber 1, the results are shown in Table 1. It can be seen from Table 1 that the shear stress of the cross-section of the simulated fiber 1 to be tested increases suddenly when the gap between the base 2 is 0.018mm. It can be determined that the distance is The minimum spacing of the base 2 when the fiber 1 to be tested is in a shear state;

(2) Treatment of the base 2: the material of the base 2 must be selected from a material with a large elastic modulus, and the clamp 4 must be selected from a magnetic metal and easy to process. Here, the material of the base 2 is selected to be tungsten, and the material of the clamp 4 is steel. The amount of tungsten is large and does not react with nitric acid. Tungsten is non-magnetic and cannot be fixed on the grinding machine, while steel is magnetic and can fix the tungsten sheet on the grinding machine for processing. As shown in Figures 2 to 3, the fixture 4 is fixed on the grinding machine, and the A plane is finely ground so that its surface roughness is not greater than 0.35 μm (10% of the radius of the fiber 1 to be tested), and then the A plane of the pair of tungsten sheets The alignment is glued on the fixture 4 with super glue, and then the B of the tungsten sheet is finely ground to ensure that the surface roughness and flatness of the plane are consistent with the surface roughness and flatness of the plug gauge. The characteristic of this processing sequence is that A, The verticality of the two planes of B makes the fiber 1 to be tested in a shear state when it is pressed down, and then fix the plug gauge with the plane B tungsten sheet of the pair of tungsten sheets, and clamp the tungsten sheet with a clip, and clamp the clamped tungsten sheet The B plane of the piece is in contact with the bottom of the mosaic groove and gently press down on the tungsten piece to ensure that the B plane of the pair of tungsten pieces is on the same plane as the base 2 of the mosaic groove, and the tungsten piece is embedded in the groove with a mounting agent. Take out the mosaic block and soak it in dissolved nitric acid to melt the plug gauge in the gap, and get the base 2 with a distance of 0.018mm. The characteristic of the plug gauge is that it can react with concentrated nitric acid, while the mosaic agent and tungsten sheet do not react with nitric acid. ;

The sequence of such processing is characterized in that the verticality of the two planes A and B can be guaranteed so that the fiber 1 to be tested is in a shear state when it is pressed down, and acetone can react with the main component of superglue α-cyanoacrylate ethyl ester to make The tungsten piece falls off from the fixture 4, the plug gauge can react with nitric acid, but the tungsten piece and the mounting agent do not react with nitric acid, ensuring the successful dissolution of the plug gauge in the gap, different gaps can be controlled by plug gauges of different thickness;

(3) Use an optical microscope to observe the distance at a multiple of not less than 400, determine the actual distance of the gap, compare it with 0.018mm, and judge whether there is little difference;

(4) Use tweezers to carefully pick up a single fiber 1 to be tested across the gap, and stick one end of the fiber 1 to be tested on the base 2 with hot-melt adhesive, then straighten the fiber 1 to be tested, and use a hot-melt Fix the other end with glue, and evenly fix the fiber 1 to be tested at a certain distance in the lateral direction of the base 2; use an optical microscope to observe the fiber 1 to be tested at a magnification of not less than 400 times, and determine whether the fiber 1 to be tested is fixed;

(5) The prepared shear sample of the fiber 1 to be tested is compressed and loaded on the nanoindenter using a probe 3 with a size slightly smaller than 180 μm. At this time, the fiber 1 to be tested is in a shear state and will pass the nanomechanical test. The shear test of the fiber 1 to be tested is carried out by the system, and the shear force required to cut the fiber 1 to be tested is measured;

(6) According to the formula Calculate the shear strength of the fiber 1 to be tested, where r _f is the fiber radius, and F _s is the shear force required to cut the fiber.

Table 2 is the test data and fiber shear strength obtained from the fiber shear test using the method of the above example. The fibers are uniformly fixed at a certain distance in the transverse direction of the tungsten sheet and numbered in sequence from left to right, respectively T300- S-1, T300-S-2, T300-S-3, T300-S-4, T300-S-5, it can be seen from the table that the fiber shear strength of T300 fiber is 675.42MPa, and the standard deviation is 122.30 MPa; the shear strength of T700 fiber is 942.94MPa, and the standard deviation is 153.62MPa.

Table 2 fiber shear strength test data

Numbering Shear force/N Shear strength/MPa T300-S-1 0.0642 834.52 T300-S-2 0.0413 536.85 T300-S-3 0.0485 630.44 T300-S-4 0.0467 607.05 T300-S-5 0.0591 768.23 average value 0.0520 675.42 standard deviation 0.0094 122.30

Claims (10)

1. a kind of micron order fiber cutting strength test method, it is characterised in that comprise the steps of:

(1) finite element analysis determines the proper range of pedestal (2) spacing that fiber is under shearing condition；

(2) pedestal (2) for fixing fiber to be measured (1) is pre-processed；

(3) size of pedestal (2) intermediate space is measured；

(4) fixed fiber (1) to be measured；

(5) probe (3) loads the central compression of fiber to be measured (1), and measures the shearing force F needed for cutting fiber_s；

(6) calculation formula of the shear strength T of fiber (1) to be measured are as follows:

Wherein, r_fFor fiber to be measured (1) radius, F_sFor the shearing force needed for cutting fiber to be measured (1).

2. a kind of micron order fiber cutting strength test method according to claim 1, it is characterised in that: the step (1) when finite element analysis, pedestal (2) spacing size is altered in steps until the shear stress of fiber cross section becomes larger suddenly.

3. a kind of micron order fiber cutting strength test method according to claim 1, it is characterised in that: the step (2) plane for pasting fiber on pedestal (2) will guarantee that two planes in parallel, sheared are vertical.

4. a kind of micron order fiber cutting strength test method according to claim 3, it is characterised in that: the plane Surface roughness is less than the 10% of fiber radius.

5. a kind of micron order fiber cutting strength test method according to claim 3, it is characterised in that: the pedestal (2) material not reacted with acid by high elastic modulus and is made.

6. a kind of micron order fiber cutting strength test method according to claim 1, it is characterised in that: the step (2) diameter of fiber (1) to be measured is 1~900 μm in.

7. a kind of micron order fiber cutting strength test method according to claim 1, it is characterised in that: the step (3) pedestal (2) intermediate space is less than or equal to 5 times of fiber to be measured (1) radius in.

8. a kind of micron order fiber cutting strength test method according to claim 1, it is characterised in that: the step (5) middle probe (3) indentation is until fiber to be measured (1) is broken.

9. a kind of micron order fiber cutting strength test method according to claim 1, it is characterised in that: the step (5) size of middle probe (3) is 0.9~0.95 times of pedestal (2) intermediate space.

10. a kind of micron order fiber cutting strength test method according to claim 1, it is characterised in that: the measurement It is observed under 400 times or more amplification factors with fixed by optical microscopy.