Textile Materials – Fabrics (8): Basic mechanical properties of fabrics
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1. Tensile properties of fabric
1. Tensile performance index of fabric
Breaking strength: The breaking strength index unit of fabric is commonly N/5cm, which is the breaking strength of fabric with a width of 5cm.
Work of rupture: The work done by the external force on the fabric when the fabric is stretched to break under the action of external force.
There are also elongation at break, specific work at break, etc.
2. Factors affecting the tensile properties of fabrics
(1) Fiber properties: Different fiber types have different tensile breaking properties of fabrics. Even for the same type of fiber, when its properties are slightly different, the tensile breaking properties of the fabric will also change accordingly.
(2) Linear density and structure of spinning yarn
Under the same conditions of fabric structure and density, the strength of fabrics woven with yarns with larger linear density is higher than those with smaller linear density.
(3) Warp and weft density and fabric structure
If the warp density remains unchanged and only the weft density increases, the weft strength of the fabric will increase, while the warp strength will tend to decrease; if the weft density remains unchanged and only the warp density increases, not only the warp strength of the fabric will increase, but the weft strength will also increase. trend. There are many types of fabric weaves. As far as the three original weaves of woven fabrics are concerned, when other conditions are the same, the elongation at break of plain weave is greater than that of twill weave, and twill weave is greater than satin weave.
(4) Machine tension
The machine tension of the fabric during the weaving process will affect the strength of the spinning yarn and the structure of the fabric, thereby affecting the strength of the fabric. The tension on the upper machine is large, that is, the load of the spinning yarn is large. If multiple sheddings are performed under a large load, the warp strength will suffer a great loss, thus reducing the strength of the fabric.
(5) Test conditions
2. Tear performance of fabric
The phenomenon of the fabric edge being torn apart under a concentrated load is called tearing, also known as tearing.
1. Factors affecting the tearing strength of fabric
(1) Intrinsic factors affecting the tearing strength of fabrics
Spinning yarn properties: The tearing strength of the fabric and the size of the stress triangle area are closely related to the strength of the spinning yarn. The tearing strength of the fabric is approximately proportional to the yarn strength. The greater the elongation at break of the spinning yarn, the smaller the friction coefficient, the larger the stress triangle area, and the more spinning yarns are stressed at the same time, so the tearing strength is greater.
Fabric structure: Different fabric structures have different interlacing points of warp and weft yarns, and the degree of relative movement of spinning yarns is also different. Generally, the tearing strength of plain weave fabric is small, the tearing strength of square weave fabric is large, the tearing strength of satin weave and twill weave is between the two, and the tearing strength of satin weave is greater than the twill weave.
Fabric shrinkage: The influence of fabric shrinkage on fabric tearing strength has two aspects: on the one hand, when the weaving shrinkage increases, the fabric elongation increases, the stress triangle increases, and the number of stressed yarns increases, so that The tearing strength increases; on the other hand, when the weaving shrinkage increases, the bending degree of the spinning yarn increases, which increases the mutual extrusion and friction between the spinning yarns, and the stress triangle becomes smaller, which also reduces the single-slit tearing strength. reduce. But the former is the dominant factor.
The warp and weft density of the fabric: Under the same conditions of spinning yarn diameter, fabrics with low warp and weft density have greater tearing strength. For fabrics with larger warp and weft density, the stress triangle becomes smaller, the number of stressed yarns is less, and the tearing strength is reduced.
Fabric finishing: After the fabric is finished with resin, the general wearing properties of the fabric can be improved, but the tearing strength of the fabric will be reduced.
(2) Effect of test conditions on fabric tearing strength
Influence of sample size: In the trapezoidal tear test, the stress triangle is related to the length of the broken yarn at the incision. The longer the length, the larger the stress triangle area, and the greater the number of stressed yarns. , the tearing strength is also greater.
The influence of tearing speed: Usually the trapezoidal tearing strength increases with the increase of tearing speed (because it is stretching); the single seam tearing strength decreases with the increase of tearing speed (because it is a shear triangle zone).
Temperature and humidity conditions: Different temperature and humidity will affect the breaking strength and elongation at break of the spinning yarn itself, and seriously affect the surface friction properties of the spinning yarn, thus affecting the tearing strength of the fabric.
2. Tear in fabric
Fabric cracking refers to the structural damage caused by the lateral slippage of the spinning yarn after the fabric is subjected to external forces during use.
There are many reasons for cracks: the fiber itself has a small friction coefficient, high straightness, high hardness and bending stiffness; the fabric has a small warp and weft density, a loose fabric structure, and few interlacing points; the warp and weft yarns have a tight structure and a completely smooth surface. , high twist, etc., as well as the machine tension during the weaving process, etc.
3. Bursting performance of fabric
Under the action of a load perpendicular to its plane, the phenomenon that the fabric rises or bulges, expands and breaks is called bursting.
Factors affecting the bursting performance of fabrics:
Weaving��The tensile breaking strength has a direct impact on the bursting strength. Generally, as the tensile strength in the warp and weft directions of the fabric increases, the bursting strength increases significantly.
The structure of the woven fabric in the warp and weft directions and the degree of difference in yarn properties have a great impact on the bursting or bursting strength of the fabric. Experiments have shown that when the elongation at break and shrinkage of warp and weft yarns are similar to the warp and weft densities, the warp and weft systems play a large role in sharing the load at the same time, so the bursting strength is greater; conversely, the warp and weft systems have a large difference. , first of all, when a system with poor elongation ability breaks, the bursting strength will be smaller.
Knitted fabrics have the characteristics of high elongation and isotropic adjustment, and have high bursting strength.
The fiber strength of nonwoven fabrics and the strength of the fixation points between fibers are the key factors that affect bursting. Secondly, fiber friction, curling and entanglement also affect bursting performance.
4. Bending properties of fabric
The ability of a fabric to resist bending deformation is called bending or bending stiffness.
Factors affecting the rigidity and flexibility of fabrics:
1. Fiber properties
The initial modulus of fiber is the decisive factor in the rigidity and flexibility of fabric. The initial modulus of the fiber is large and the fabric is rigid.
Compared with fibers with circular cross-sections, fibers with special-shaped cross-sections are more rigid. In addition, the bending stiffness of hollow fibers increases as the hollowness increases, and the stiffness of the fabric also increases. The bending and friction coefficients of the fibers also affect the bending stiffness of the fabric. The larger the value, the stiffer the fabric.
2. Spinning yarn shape
When the diameter of the spinning yarn is thicker and the twist is larger, the bending stiffness of the spinning yarn is larger and the fabric is stiffer; on the contrary, the fabric is softer.
3. Fabric geometry
The more interlacing points in a woven fabric, the shorter the floating length, the greater the tangential sliding resistance between warp and weft yarns, the smaller the possibility of relative movement between warp and weft yarns in the fabric, and the stiffer the fabric.
The longer the loop length in a knitted fabric, the fewer contact points between the spinning yarns, the smaller the tangential sliding resistance between the spinning yarns, and the softer the fabric.
In nonwoven fabrics, the more bonding points between fibers, the larger the bonding points, the greater the rigidity of the nonwoven fabric.
No matter what kind of fabric, when its thickness increases, the bending stiffness of the fabric also increases significantly.
4. Post-arrangement
Synthetic fiber fabrics are exposed to high temperatures during singeing, coloring, and heat setting. If the temperature is not handled properly, the fabric will become hard and brittle.
The rigidity and flexibility of fabrics can be changed by mechanical and chemical methods. When cotton and linen fabrics are treated with liquid ammonia, the softness of the fabric can be improved and the effect is significant. To improve the stiffness of the fabric, stiffening finishing can be performed. To improve the softness of the fabric, soft finishing can be used.
Fabric Materials – Fabrics (8): Basic Mechanical Properties of Fabrics
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