Abstract
This paper explores the uniaxial tensile creep response of acrylic-based pressure-sensitive adhesive (PSA), which exhibits a unique multi-phase creep response that does not have the classical steady-state region due to multiple transitions caused by several competing mechanisms: (i) cavity nucleation and growth in the interior of the adhesive material of the PSA system, as well as at the interfaces between the PSA and the substrate; (ii) fibrillation of the bulk adhesive, and (iii) interfacial mechanical locking between the adhesive and the bonding substrate. This results in multiple regimes of strain hardening and strain softening, evidenced by multiple regions of steady-state creep, separated by strong transitions in the creep rates. This complex, multi-phase, nonlinear creep response cannot be described by conventional creep constitutive models commonly used for polymers in commercial finite element codes. Accordingly, based on the empirical uniaxial tensile creep response and the mechanisms behind it, a new mechanistic model was proposed. This is capable of quantitatively capturing the characteristic features of the multiphase creep response of single-layered PSA joints as a function of viscoelastic bulk properties and free energy of the PSA material, substrate surface roughness, and interfacial surface energy between the adhesive and substrate. This is the first paper to present the modeling approach for capturing unique multi-phase creep behavior of PSA joint under tensile loading.
Highlights
This study examines the creep response of pressure-sensitive adhesive (PSA)-bonded joints to tensile loading, because such joints creep more severely under tensile loads than under shear loads
He noticed that the static shear strength and holding time of the sample can be calculated from the master curve of the dynamic shear test, but the method cannot be applied to a highly viscous polymer [5]
The hydrostatic stress release rate decreases as the size of the cavities increases and the amount of hydrostatic stress preserved in the bulk of PSA decreases
Summary
Many studies on the tack, peel, shear, and shear creep properties of PSA bonded assemblies have been performed in recent decades. Fujita et al studied the effects of miscibility and viscosity on the shear creep resistance of PSAs based on natural rubber. They concluded that the holding time (which is the required time for the PSA tape under shear load to completely debond from the adherend) tended to decrease as the tackifier content increased [1]. Poh and Kwo investigated the effects of adhesive (coating) thickness on shear performance of Standard Malaysian Rubber (SMR)-based PSA They concluded that the shear strength increased as the adhesive thickness increased [4]. Zosel studied the correlation between the shear strength and the mechanical properties of PSA by measuring the deformation behavior in a static and dynamic shear test. Sancho-Querol et al explored a new formula with blended ECH resin that enable PSAs exhibiting excellent creep, high tack, high peel strength, and lap-shear strength at room temperature [11]
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