Compressional Resilience is the property of the material body by virtue of which material withstands the sudden shocks of energy without undergoing permanent deformation.
𝑅 = (𝐸𝑛𝑒𝑟𝑔𝑦 𝑜𝑓 𝑅𝑒𝑡𝑟𝑎𝑐𝑡𝑖𝑜𝑛) / (𝐸𝑛𝑒𝑟𝑔𝑦 𝑜𝑓 𝐷𝑒𝑓𝑜𝑟𝑚𝑎𝑡𝑖𝑜𝑛)
The deformation here may be of tensile, compressional shear or a complex combination of various types of strains, retraction, here it is used to refer to release of strain.
Resilience is the primary property of fabrics. The example of suit clears the idea of resilience.
The extent to which the suit keeps its shape and drape, the absence of bulges at the knees and elbows and the disappearance of wrinkles which are formed during daily use after hanging overnight will characterize the fabric as to the extent of its resilience.
Using a clenched fist test wherein a sample is repeatedly crushed in the hand suggests their parameters of judgment.
- Flow the fabric piles or folds under compression in order to be resilient it must offer a certain moderate resilience to the closing of the fist. If it yields too easily it may be classified as limp or dead; if it resists too much it will appear to be boardy, stiff or harsh.
- How the fabric behaves upon sudden opening of the fist. A resilient material will spring back rapidly into a fairy open state, demonstrating a certain springiness loftiness or liveliness. If it recovers slowly it will be characterized as limp or slow.
- How the fabric appears after repeated compression when flattened out on the table. If a fabric is resilient, it will show only the presence of indistinct shallow wrinkles, which will disappear completely in a few minutes. This last property is also referred to as crushproofness.
Hamburger defined elasticity and resilience. The ability of a material to return spontaneously to its former size, shape or attitude after being strained whereas resilience connotes the amount of strain energy present in a stressed system.
It emphasizes the quality of softness and at the same time the ability to recover from large deflections where the time factor is important.
The end-use requisites as retention of shape, retention of drape, wrinkle resistance, hand (softness, stiffness, hardness, limpness, liveliness, boardiness, springiness, roughness, smoothness) and retention of thickness and bulk are all dependent upon the resilience of the structure.
The compressional resilience is an important parameter for evaluation of blankets, wearing apparel. When warmth is a factor, permanency of pile fabrics including carpets and bulk fibre utilization in mattresses, cushions and like.
The compressional resilience refers the ability of a fabric to maintain an original thickness, may be used as one criterion of warmth.
Measuring Compressional Resilience
The specimen is placed on the anvil without tension.
The foot is lowered upon the specimen by means of the rack and pinion and the pressure is gradually increased.
When the pressure reaches 0.1 PSI, the thickness is recorded. Similar simultaneous observations are made at seven other pressures up to 2.0 PSI.
The pressure is then gradually reduced and observations are made at the same pressure during unloading, the upper dial indicating the spring elongation given by curve B at various pressures.
The observations are made in rapid succession.
Thickness: Thickness of the specimen when the pressure is increased to 1 PSI.
Compressibility: Ratio of the rate of decrease in thickness with the pressure of one PSI to the standard thickness.
Compressional Resilience: Work recovered from the specimen when the pressure is decreased from 2.0PSI to 0.1 PSI expressed as % of the work done on the specimen when the pressure is increased from 0.1 to 2.0 PSI.
Rees used three criteria namely
1. Overall specific volume. (Volume occupied by a specific weight of fibre)
2. The compressibility of the fibre mass.
3. The ability of the fibre mass to recover from compression. Specific volume or filling capacity is quantitatively defined as the ratio of the overall volume under particular pressure to the weight of the fibres.
Compressibility is defined as the % reduction in volume of the fibre mass resulting from a specified increase in the applied pressure.
The amount of the fibre mass to recover from compression is expressed as the amount of energy returned by the material on the removal of load expressed as a percentage of the energy expended in compressing the material between the same limits of pressure.
Compressional Resilience Properties of Textile Fibres
Fibres in a yarn spiral around one another, as individual fibre will have roughly the shape of an open spiral spring when twisted into a yarn.
If the spiral spring is stretched it may elongate either by uncoiling or by twisting about the axis of the fibre forming the spring.
If the fibre surfaces are to be separated from one another, the fibre should uncoil rather than twist when the yarn is stretched, or as the fibres uncoil they also unpack thus freeing their surfaces, whereas if a fibre merely twists about its own axis any elongation of the yarn will only tend to pack the fibres more closely together.
Using engineering concepts and example of cylindrical wire; if the wire is easily bent, but resists the torsion about its own axis, the spring will uncoil on stretching but if the material resists bending whilst it twist easily about its own axis.
The spring will coil up on stretching. If n is the modulus of torsional rigidity and E is young’s modulus then spring will unbend and uncoil when (1/n2/E) is negative and it will coil up when this expression is negative.
All ordinary materials (steel, glass etc.) have a positive value and they all coil on stretching. The (1/n-2/E) data for fibres shows that only wool fiber has a negative value and therefore tend to uncoil rather than tighten up stretching.
Wool fibre shows a negative value because of its directional effect. All other fibres show positive values. The grater the positive value, greater the tendency to produce tightly packed smooth yarns.
Cotton will give the least tightly packed yarns, viscose or possibly silk the most. The experimental analysis shows that sponge rubber to have the highest compressibility (Softness) in conjunction with resilience.
The wool blanket is the next upon washing; it maintains its compressibility while reducing 25% of its resilience. The cotton, wool and cellulose acetate have the highest compressibility under the designated conditions of loading, compressibility must be governed by the fibre configuration and also the state of aggregate of the fibres in the bulk mass.
The fact that uncrimped synthetic or regenerated fibres are “Slick” and uniform probably explains in part why filting together more easily and closed initially produce a less lofty mass and subsequently are compressed to the lesser extent when subjected to compressional force.
The results of the observations show that wool has the highest resilience of all fibres while the viscose staple fibres the lowest. The cellulose acetate falls next to wool in ranking followed by cotton.
Summarizing the results for compressibility and resilience shows that wool is best in both. Other fibres viz. nylon, silk are almost good as in resilience but have much less compressibility. Compressional resilience is the only property, which relates to the thermal insulation property of blankets.
This is because relationship exists between thickness resilience and thermal insulation and all wool blankets having high compressional resilience probably will retain its original thickness and hence its thermal insulation more nearly than would a blanket made from cotton or rayon.