Main features of textile structures
- Resilience and Flexibility
The ability of a material to recover its original shape and size after removal of strain which caused the deformation is known as resilience. Textile structures are visco-elastic in nature and due to this unique feature of visco-elasticity they are resilient and flexible. Unlike traditional engineering materials (TEMs), textile structures are highly resilient and they can spring back to their original state after being crushed or wrinkled. Resilience is also termed as memory. Resilience is a vivid characteristic of most textile structures and it can be expressed as:
Resilience can also be defined as a measure of elastic reversibility. The creep and relaxation properties of both textile fibers and fabrics are directly related to resilience. Primary creep that is recoverable deformation is a function of delayed elasticity which is also an important factor in resilience. While, the secondary creep that is permanent deformation is a measure of elastic irreversibility.
Advantage of resilience
Being resilient, textile structures offer moderate resistance to deforming force and spring back on removal of strain while producing only shallow wrinkles which finally disappear. In case of textile structures like fabrics for clothing the rates of strain and retraction are usually low but the cyclic deformation is significant. Meanwhile, clothing is not worn continuously and there is a definite rest period between cyclic deformations or between series of cycles. Therefore, the secondary creep is not too much important and baggy knees and wrinkled sleeves do occur but they can be removed by proper deformation at high temperatures and moisture contents. Therefore in case of clothing resilience controls secondary creep or delayed recovery, feel and the appearance of the fabric. Whereas, In case of textile structures like fabrics for upholstery applications the rate of strain is slow and takes place under dead load therefore the secondary creep is more important. In case of textile structures like pile fabrics for carpet application, the structure undergoes two kinds of stresses the impact stress which is caused by the walking on it and the constant stress caused of long duration due to furniture. The impact stress requires rapid recovery that is achieved due to the feature of resilience.
Textile structures have good formability as compared to TEM’s. The formability of a textile structure i.e. a fabric can be defined as the maximum compression a fabric can take up in the plane in a certain direction before it buckles. The formability can be expressed as the product of an anisotropy ratio and the square of the fabric thickness. The formability of a fabric determines its tailor ability and the crease pattern. The formability is dependent on fabric direction, and the integrated formability is related to the product of buckling load and shear angle.
Advantage of formability
In case of garment manufacturing formability is the key feature for raw material. Formability is actually a term used by the tailor to express ease of making up the garment. Due to their good formability textile structures can be tailored in to various shapes very easily. Unlike TEM’s textile structures can be bent, twisted, cut into different shapes and patterns with much less energy. For example woven fabrics can undergo large strains even at low stresses due to the straightening of the crimped constituent yarns within the fabric and can be deformed into shapes. This feature makes textile structures the premier and only candidate for clothing needs of humans.
Viscoelastic materials exhibit both viscous and elastic characteristics when they undergo deformation. They resist shear flow and strain linearly when stress is applied. They have a time dependent or frequency dependent stress and strain relationship. The slope of stress vs. strain plot depends on strain rate. Elastic materials undergo strain when stretched and quickly return to their original state when the stress is removed. While, viscoelastic materials have both of these properties. They have a unique equilibrium structure and ultimately recover fully after removal of a momentary load. Textile structures have this unique feature of viscoelasticity. After being squeezed they return to their original shape when given enough time for recovery.
Advantage of viscoelasticity
Unlike purely elastic materials, textile structures own a viscoelastic feature and have an elastic component as well as a viscous component. Elastic materials do not dissipate energy on removal of applied load. Conversely, textile structures being viscoelastic loses energy. Hysteresis is always observed in the stress strain curve. The area of the loop is equal to the energy lost during the loading cycle. In reality, viscoelasticity is a molecular rearrangement. In case of textile structures like yarns or fabric this phenomenon can be explained by the fact that when a stress is applied to them, the unit cells or fibers in the structure will slip and rearrange themselves. This movement or rearrangement is called creep. A back stress will be created in the structure. When the magnitude of the back stress and applied stress becomes equal then the structure will no longer creeps. On the removal of applied stress the accumulated back stresses will cause the fibers to return to their original arrangement with loss in the energy. Therefore, this behavior makes textile structures a potential candidate for application where energy dissipation is required at a certain level like, energy dissipation during an impact event.
4. Porosity and Breathability
Most of the textile structures like yarns and fabrics are highly porous and breathable materials. For example every piece of woven fabric is an integration of warp yarns and weft yarns through intersection. The extent of this intersection is largely dependent on the friction between fibers and yarns together with fibre entanglement, while the distance between two parallel adjacent yarns determines the porosity of a fabric structure. The existence of such a discrete porous structure is a key feature of textile structures which distinguishes them from a continuum engineering structure such as a metal sheet.
Advantage of porosity and breathability
Porosity and breathability of textile structures as clothing material have a dominant influence on the performance characteristics of a material, particularly in controlling transport of fluids. The suitability of a particular fabric structure for clothing applications depends on its ability to maintain the thermal equilibrium of the wearer together with resistance to transmission of heat and moisture. The fiber type and the fabric structure both influence the moisture transmission characteristics of the fabric. Though, the fibers do not transmit an appreciable amount of moisture. The moisture transmission through the fabric occurs only through the void spaces or pores within the fabric that is the portion unoccupied by fibers and is purely a structural feature. Therefore, higher air permeability of textile structures or porosity is advantageous in applications where better moisture transmission is aimed.
5. Thermophysiological properties and Moisture management
Thermo-physiological comfort includes properties related to moisture and thermal management. It is the garment’s ability to keep the wearer dry and to regulate body temperature during a change in the environmental temperature or humidity and during physical activity therefore contributing to the thermal equilibrium of the body. Thermo-physiological comfort mainly lies in moisture management of the textile structure of clothing material, which often refers to the transport of both moisture vapor and liquid away from the body. Moisture management of textile structures is mainly influenced by the thermal properties of those structures. Natural textile fibers like cotton, wool, and silk provide unique moisture management properties which are directly related to their structures and provide comfort. Comfort can be defined as a pleasant state of psychological, physiological and physical harmony between a human being and the environment. That is why instead of the some promising properties of most of the synthetic textile structures they are not preferred for clothing application because of their hydrophobic nature which provides less comfort to the wearer compared to the natural fabrics. For a person engaged in normal routine indoor activity the metabolic heat generated (which increases six times with 14 times more perspiration during sporting activity) should be dissipated readily through the clothing as sweat. Therefore an important feature of any textile structure is how it transports the sweat water out of the body surface in order to make the wearer feel comfortable.
Advantage of Thermophysiological properties and moisture management
Textile structure as clothing material plays a vital role in thermo-regulatory process as it alters heat loss from the skin and also changes the moisture loss from skin. In the case of clothing, temperature is not a vital factor, both because of the thermo-stating effect of the human body and the inability of humans to remain alive except within a limited range of temperatures. However, moisture content is a very important factor. When the external climatic conditions outmatch the body requirements some specific textile material can be used to provide the optimum body demands for better comfort feelings due to their unique structure. Therefore, the type of garment and the climate for which it is intended to use must be taken into consideration.