The stress and fatigue testing is to grasp.
An important part of quality.
It is directly related to fiber quality grading and terminal applications, such as clothing, home textiles, automotive interior decorations and many other uses.
Any textile has to undergo repeated changes in strength and stress. Therefore, testing the fatigue degree of textiles is particularly important.
Fiber fatigue in India
The core of
The engineering fiber materials and engineering textile structures need to undergo varying stresses at different intensities during use.
If the stress is very small, the alternating loading and unloading will usually result in stress concentration, thus greatly reducing the strength of the fabric.
Because of the cumulative wear, with the increase of the number of stress cycles, the strength of fiber resistance to external force will gradually decrease.
When the alternating stress is far less than the limit of strength under static load, damage may occur, which we call fatigue damage.
Fatigue damage has a major impact on the quality and market prospects of products, such as fabric, home furnishings, automotive interior materials, and conveyor belts in the application of industrial textiles.
For high stability multifilament yarns, the strength of fatigue resistance has a direct impact on the processing performance.
We can see its effect in weaving and sizing and twisting of multifilament yarns.
The final stability is closely related to fatigue properties of single fiber and filament.
With the continuous application of a large number of new fibers to garment fabrics and other industries, textile experts all over the world have shown great interest in the study of fatigue properties of fibers, and the textile fiber industry in India is one of the countries in the world that carried out early and in-depth testing of fiber fatigue.
The India industry believes that the textile fibers themselves do not have much elastic interval. Therefore, it is the main method to obtain the fatigue test results by finding the direct effect of periodic load causing damage.
In 1993, India textile expert Ann Nanji Ed La and others proposed that under the cyclic loading, the wear and fatigue failure caused by tensile compressive stress and bending stress should have three criteria: 1. fatigue failure, 2. mechanical property loss, 3. appearance damage. Anandjiwala
Fatigue failure usually occurs when the cumulative damage caused by cyclic fatigue reaches the limit, and the yarn stress exceeds the allowable stress. Failure of mechanical properties is that before the fatigue life and consequences of mechanical loss (usually tensile strength) produce, the yarn stress reaches the known value of cyclic fatigue. The appearance damage is based on the fine structure of the yarn, and the qualitative data are obtained according to the influence mode and influence degree of fatigue damage, so that the fatigue resistance of different kinds of fibers can be concluded and compared.
This may be the core of India textile fatigue research.
The birth of various cyclic tensile loading methods
The conditions of fiber breakage can be measured by various methods.
In order to facilitate classification, they are generally divided into the normal breaking load range of cyclic tensile loading (0%~50%); deflection, fiber stress overrun, surface friction caused by the forward and backward swing of rollers measured; and double shaft roller rotation.
In 1963, cyclic tensile loading technology was first applied to fiber fatigue measurement by Indian Buss (Booth) and Hearle.
The sample is extracted with two clips, one of which is used for displacement cycle.
The defect of this method is that the stress relaxation is aggravated due to incomplete recovery of specimens, and most of the specimens are no longer subjected to tension loading in each stress cycle.
Only when the tensile strength exceeds the allowable range will the fiber be broken.
In order to overcome fiber breakage, India researchers have adopted a cumulative tension cycle technology.
At the end of each tension cycle, this technique inhibits stress relaxation and adds fixed tension to the next cycle to help restore the stress of the sample.
This method makes fiber easier to observe in circulation.
In 1970 and 1971, he and other testing technicians identified them as one of the main detection methods in their experimental instruments and regarded them as guidelines.
Since then, this method has begun to spread in the textile industry of India.
The first step is to clamp the fibers with two sets of clamps, one of which is connected to the vibrator in 0-10kHz frequency and 3 millimeters at 50kHz frequency.
The upper clamp is connected to the piezoelectric sensor, and the single arm bridge is bonded to the cantilever beam.
By means of this method, the electronic signals are analyzed from the periodic load and the average load of fiber proportioning.
In 1974, another expert in India also used the bending fracture test technology, and one end of the sample was fixed on the shaft clamp of the suspension vibrator, so the fiber was flexed in the amplitude of about 2 millimeters.
In 1983, engineers in India developed a device that can generate cyclic friction in any structure under a controlled temperature and a specific chemical environment, thereby exerting constant axial tensile load on filament, yarn or fabric stripe.
This effect enables fiber materials to simulate stress stretching, bending and wear endurance while processing.
In 1993, according to the three standards of fatigue failure, wear rate and appearance damage, India researchers studied the fatigue properties of high stability yarn (Warp) by using a network detector called Sulzer-Ruti.
Since then, another expert in India, James Lyons, has developed a new test method, that is, using two upper and lower stoppers to hang up the fibers, and the bottom clamps are supported by two handles.
The slightly lower handle runs through the adjustable slider in the vertical swing, which is one of the constant displacement test methods -- the amplitude of the torsion fatigue test.
Since then, other India fiber test experts have used flexural fatigue tests in fiber samples to study the reverse deformation of positive and negative substitution.
The most frequently used method is to make the fiber with a length of 10 cm under torsion under constant pulling force to determine whether the fiber is broken.
Thus, India experts invented a shaft rotation detection technology.
That is, fiber is rotated by variable torsion deformation.
Fiber fatigue monitoring data are provided in the combination of torsion and tensile mode.
Since then, they have designed a set of equipment specially for compression type twisted fiber test.
This mode of action makes it easy to observe the fatigue of both ends of fibers and produces buckles under compressive axial loads.
They have developed a bending fracture testing technology successively.
This not only improves the accuracy of the test of abrasion resistance and fatigue resistance caused by the cyclic stretching of yarns, but also expands the distribution of stress fatigue produced by cyclic bending of fibers.
Two axis rotation detection technology
Of all the fatigue tests, the most effective test is the biaxial test.
It can effectively combine cyclic bending and torsion to obtain corresponding results.
At present, this method is similar to the fracture in actual use because of the breakage of fibers after multiple splitting.
Therefore, in the observation of textile yarn processing, biaxial rotation technology is more popular.
Biaxial rotation means that the fibers rotate axially in the bending configuration.
But India experts did not stop. In 1980, an expert named Carlisle proposed several methods for testing equipment.
One way is that the coarse fibers of a single filament can easily be twisted and clamped so that the ends of the fibers can be knobs together.
This method leads to anticipated changes in stress stretching and compression, but is not suitable for filaments with diameters of 10 microns.
Free biaxial rotation technology
The expected changes in stress stretching and compression are not suitable for filament diameters of 10 microns.
The other method is that the author overcomes the disadvantages of the first method. On the basis of this, a small curvature radius force is applied to make the fiber pass through the roller shaft or metal wire through a certain tension, so that one end of the fiber is torsional and bears the load to produce stress stretching.
Roll driving technology with unidirectional driving
In 1979, India expert Carl and Halle further studied.
The outstanding feature of the test method is that the ends of the fiber samples are clamped by two clamps in the 90 degree direction.
The fiber is forced, bending on the roller, moving axially through one of the clamp shaft under its hanging tension, and placing the fiber under constant tension.
The clamp has no influence on the net twist at the same speed and direction.
This test result is related to the roll that is controlled by compression and elongation during rotation.
This fatigue effect eventually leads to fiber breakage, thus obtaining data.
In 1979, he and other experts re developed a set of more advanced equipment.
Fiber tension is easier to control and is controlled by rollers connected to a cantilever fixed on a phase measuring device.
Then another technology came out in India, which follows similar inspection principles but is parallel to the clamp shaft.
The combined effect of stress stretching is that it allows fibers to bend around 8 degrees of curvature around the roll, and the fiber length varies between 700-1700.
In the system, the end of the fiber sample is connected to the two clamp shaft.
In addition, another new tension system has been successfully invented. The roller installed on the online polarized beam can move freely along the stainless steel shaft on the bearing.
In this way, the tension can be tested simply by increasing gravity.
However, this method enables the roller to rotate and compress the fibers, which will cause fiber damage.
Factors affecting the formation of fracture data
Since the method of measuring fiber breakage is different, the data obtained from the test are different from each other. This is logical, and the circular data obtained is the most widely used method to reflect fiber fracture.
From this, we can see that the main factors that affect fatigue life are the following:
1. the toughness of the fiber itself.
The study found that the stronger the toughness formed in fiber processing, the longer the fiber life, while the polypropylene fiber was more resilience than nylon and polyester.
Later, it was also said that the thickness of the cell wall of cotton fiber had a significant effect on its life span.
2. the influence of environmental temperature.
With the increase of temperature, the fatigue life of nylon shows a downward trend.
Other studies have come to the same conclusion that the fatigue life of polyester and single nylon filament decreases with increasing temperature.
3. the influence of relative humidity.
By changing the relative humidity, India technical experts found that different humidity could affect the fatigue life of polyester and nylon wires.
However, the fatigue temperature of polyester filament is stable at every level of humidity, while the fatigue life of nylon filament increases with the increase of humidity from 50% to 100% in cyclic fatigue. The temperature increases from 0 to 200 degrees, and the fatigue life shows a downward trend.
The influence of 4.pH value.
In 1977, he proved that the pH value (0~14) of nylon fiber was in the range of 6.6 pH, and the conclusion was that if the pH value was between 0~2, the fatigue life of nylon increased obviously.
In fact, as early as in 1952, an expert in the carbonation parameter of 46 wool samples after the study concluded: carbonized fibers than the processed fibers in flexural fatigue resistance is smaller.
5. mercerizing mercerizing.
Due to the improvement of fiber processing technology and the removal of many weak elements in the controlled fiber, the length of the flexural fatigue life of the fiber is also affected by the mercerizing process.
Experiments show that the processing technology can shorten and prolong the fiber life.
6. the effect of resin.
Some resins will be added to the fiber.
According to India expert research, resin processing will significantly reduce the fatigue life of cotton fibers.
7. the effect of water.
Studies have shown that moisture has a crucial effect on pH value and affects fatigue properties of nylon filament, cotton fiber, polyester and nylon single filament, but the degree of influence is different.
However, India experts believe that the life of unprocessed cotton fibers in water is significantly longer than that in air.
Although the life of mercerized fiber is the same as that of water, it is still more than two times higher than that of untreated cotton.
However, the fatigue life of polyester and nylon filament immersed in seawater is shorter than that in distilled water.
The life of cotton fiber in air is longer than that in wet condition.
Application of fatigue technology research in textile industry
The conventional test method of fatigue performance in India is cyclic loading test under certain stress / tension.
This method can be reflected in the daily production application.
In textile processing, tensile fatigue produces warp breakage.
This mechanical deflection factor has great influence on textile wear, and its flexural fatigue life is closely related to wear.
For example, the wear of carpet is mainly caused by flexural fatigue.
Tires are also subjected to periodic stress and unequal stress, stress relaxation and stress compression under different humidity and temperature conditions. Therefore, the tire fatigue resistance is particularly important in tire performance, because the reinforcement performance of tire is a major factor in the structural load of motor vehicles.
Laundry and sizing also play a decisive role in fatigue. These processes can change the insulation and permeability of clothing.
The stress and tension fatigue produced by the conveyor belt deteriorates in the high modulus interlayer, resulting in fatigue damage occurring in the pull after the ship's haulage and docking.
Fatigue damage will also deteriorate in textile machinery, including distortion, interweaving, intertwining or entanglement of fibers.
Local deformation is usually caused by stress stretching, bending, lateral pressure, shear force and non bending.
The fatigue damage performance of multifilament in deformation and distortion operation, under repeated stress of different stress, the fatigue property of fiber is very important for the application of many end products, such as clothing, home furnishings, automobile decoration materials and other industrial fabrics.
The tensile fatigue properties of yarns with high stability under periodic tensile and damage can also be detected by other methods. The yardstick of yarns also includes fracture, damage rate, visual appearance and so on.
The fatigue testing technology of India has a certain reference value. Several of the fatigue influencing factors commonly exist in various fields of textile fibers, so it is of great significance for us to study how to improve the testing technology and product quality of fibers.