The role of deformation history on stress relaxation and stress memory of filled rubber

Abstract

Although the magnitudes of inelastic and viscoelastic effects in filled rubbers are small relative to that of the elastic response, these effects are nevertheless critical in applications such as gaskets, seals and dampers. This study investigates the role of deformation history on relaxation of rubber through time-dependent experiments following a range of deformation histories. Two grades of carbon-black filled EPDM were subjected to uniaxial tensile deformation followed by stress-relaxation or stress memory at fixed deformation. Stress relaxation was found to be highly dependent on strain levels following a single loading. When an additional load-unload cycle was added to the history, the rubbers relaxed an approximately constant fraction of stress after a given time, provided that the strain at stress relaxation was smaller than the historical maximum. This fraction was independent of both the applied strain and of the maximum strain, and suggests that the relaxation process is independent of scragging procedures used to control the modulus. Stress memory observed following load-unload cycles was also approximately independent of strain history.

Rotational Cone Tribometer (RCT) for Approaching the Tribological Behavior of Hard and Soft Sealing Materials Under Dynamic Line Contact

“…Moreover, the “running‐in” phase observed in the measured friction moment (M Z ) lasted for approximately 90 s, which also correlates with the initial phase in stress relaxation where there is a significant loss in vertical force, which subsequently is a function of the compressive strain . Thus, during “running‐in” phase, in addition to the effect of restructuring of the contact zone, viscoelastic behavior also has an influence.…”

Fractional derivative modeling of time-varying viscosity materials considering initial loading ramp in real experiments

“…The process that links these two apparently different approaches began with the work of Gemant [5], who suggested that fractional-order time differentials be used to describe the frequency-dependent moduli of viscoelastic material [6]. Because of the long history dependence or the so-called memory effects, a fractional operator is found to be a powerful tool for modeling viscoelastic behaviors, particularly for building time-dependent constitutive models, where the strain or stress response is highly dependent on previous loading and deformation history [7, 8]. In turn, Blair et al [9] proposed a fractional element, namely Scott–Blair (SB) element, which is considered the simplest and most basic model using fractional derivative [7].…”

SBR, NBR, NR ve EPDM Sentetik Kauçuk Türlerinin Normalize Edilmiş Gerilme Gevşemesi Davranışları

“…Literatürde, kauçuğun bu inelastik davranışını modellemek için ilk bilimsel çalışma 1944 yılında Tobolsky [4] tarafından yapılmıştır. Kauçuk kompozitlerin performansı üzerinde gerilme gevşemesi bu kadar etkili olmasına rağmen günümüzde bu konuda pek fazla çalışma mevcut değildir [5]. Yapılan çalışmalarda farklı dolgu maddeleri ilave edilerek kompozit malzemeler üretilmiş ve gerilme gevşemesi testleri gerçekleştirilmiştir.…”