Quantification of deformation response at cyclic compression of polymer fibrous systems Snezana B. Stankovic n University of Belgrade, Faculty of Technology and Metallurgy, Textile Engineering Department, Karnegijeva 4,11120 Belgrade, Serbia article info Article history: Received 7 January 2014 Accepted 8 February 2014 Available online 15 February 2014 Keywords: Polymers Fiber Cyclic compression Elastic deformation Viscoelasticity Secondary creep abstract The difficulty in qualitative evaluation of deformation properties of polymer fibrous assemblies lies in the fact that these materials differ from materials such as wood, concrete, steel, etc., as a consequence of the manifestation of non-linear and plastic deformation. In this work, an attempt was made to quantify repeated compression performance of textile fibrous structures by using the concept of energy. Particular attention was paid to the nonelastic deformation of polymer fibrous systems under compression. Starting from the fact that the compression curve governs the energy-absorption characteristics of materials subjected to repeated stress, deformation components were determined by calculating the energy- absorbing properties and specific parameters – the irreversible compression work of all-cycle compres- sion and the compression work of viscoelastic deformation of all-cycle compression. These parameters made it possible to estimate the compression hysteresis and then calculate the share of deformation components at lateral compression of polymer fibrous systems. & 2014 Elsevier B.V. All rights reserved. 1. Introduction Nature and man-made polymer fibers are widely applied materials in practice and they are available with a great range of mechanical properties. Fibrous polymer structures exhibit non- linear deformations, substantial plastic flow and no apparent rupture. Fibers can be easily assembled in a number of different two- or three-dimensional structures using highly automated techniques such as stitching, weaving, braiding and knitting. From the aspect of suitability for a particular use, an engineer- ing material needs to be evaluated by answering two questions: To what extent the material resist the deforming force that will be applied? and to what extent will the material recover when the deforming force is removed [1]? Therefore, the mechanical beha- vior of fiber assemblies is of great interest in many fields of engineering such as fiber reinforced composites, paper, and textiles manufacturing. Lateral compressional behavior of fibrous assemblies is one of the most important properties of textile materials used for garment or insulating materials. It is also of considerable practical interest in composite structure, where the compatibility of the lateral compression and recovery behavior of the fiber (or fiber assembly) and matrix has a strong influence on the ultimate properties of the composite. In addition, the cyclic compressional loading behavior of fibrous assemblies is an impor- tant consideration in the design of industrial products made of these materials. Polymer fibrous material is considered to be an imperfectly elastic body, since it exhibits a strain lag or hysteresis upon the removal of stress. This hysteresis loss is due to an inter-fiber friction and viscoelastic nature of the fibers and their assemblies at a mesoscopic level within the fabric. So, the deformation resulting from the compression of a fabric may be divided into two components, one taking place immediately (elastic deformation), another one over a period of time (delayed deformation) further subdivided into recoverable (viscoelastic, primary creep) and irrecoverable (plastic, secondary creep) [2]. Some physical con- cepts involve the determination of the compression properties of the material by using simple “end-point” deformation (thickness at the start, at maximum load and at the end of the cycle). However, the fact is that between the initial and final points of cyclic compressional loading any number of lines may exist, each one indicating certain load-deformation behavior. Therefore, for this study the idea was to determine the deformation response of polymer fibrous assemblies by utilizing the concept of energy. It should be noted that the determination of elastic deformation components of polymer fibrous assembly in terms of energy (or work done) has been introduced since 1940s of the 20th century [3]. The authors determined the resilience as the amount of energy returned by the sample upon the removal of compres- sion load expressed as the percentage of the energy stored up as Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/matlet Materials Letters http://dx.doi.org/10.1016/j.matlet.2014.02.020 0167-577X & 2014 Elsevier B.V. All rights reserved. n Tel.: þ381 11 33 03 857; fax: þ380 11 33 70 387. E-mail address: stankovic@tmf.bg.ac.rs Materials Letters 122 (2014) 162–165