The micromechanics of fiber pull-out

doi:10.1016/0022-5096(96)00019-1

Journal of the Mechanics and Physics of Solids

Volume 44, Issue 7, July 1996, Pages 1147-1159, 1161-1177

https://doi.org/10.1016/0022-5096(96)00019-1 Get rights and content

Abstract

Results of experimental and modeling studies on the micromechanics of fiber pull-out are reported. For the experiment an optical glass fiber coated with a layer of acrylate or gold-palladium alloy is embedded in an epoxy matrix and then pulled out at various speeds. The fiber has a diameter of 125 or 200 μm. While the fiber is pulled out, the coating is left embedded in the epoxy matrix, producing frictional sliding between the contact surfaces of the glass fiber and the coating. As the thin and long fiber is pulled out, the trace of pull-force versus displacement shows several distinct stages corresponding to different pull-out processes. In the debonding process of the glass-acrylate interface, stable crack growth was observed prior to unstable sliding. The stable crack growth behavior is believed mainly to be caused by the fact that the interface fracture toughness is strongly mode dependent and the mode mixity of the debonding crack varies towards tougher mode as the crack advances. After the interface is completely debonded, the trace of pull-force versus displacement shows stick-slip oscillations about a constant mean full force. Through the use of photoelasticity it is found that the unstable stick-slip sliding of the glass-acrylate interface is caused by the propagation of a highly concentrated active sliding zone, a dislocation, along the interface. When a thin gold-palladium coating is introduced at the interface to produce debonding and sliding along the glass-gold-palladium interface, the initial stable crack growth is not observed and the interface dislocation emission is suppressed. The interface fracture toughness and the frictional sliding resistance are found to depend on the thickness of the coating; the interface fracture toughness is higher for thicker gold-palladium coatings, while the frictional sliding resistance is higher for thinner gold-palladium coatings. The sliding at the glass-gold-palladium interface also shows a stick-slip behavior under certain conditions. However, unlike the stick-slip process accompanying dislocation emission observed in the sliding process of glass-acrylate interface, the stick-slip is generated, while the entire contact interface slides simultaneously, by rate-dependent softening and hardening of the frictional interface. It is demonstrated that significant features of this type of stick-slip process can be predicted using a phenomenological friction law with an internal state variable.

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The pull-out load corresponding to point C (in this case, Pf) represents the total frictional force resisted by the system [13,30]. In the dynamic stage, a constant (β = 0.0), a slip hardening (β > 0.0), or a slip softening (β < 0.0) can be observed [29,31–35]. Slip hardening occurs when the frictional stress between the fiber and the mortar increases due to the shape of fibers, embedded length, and the abrasion effect [21,32].
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Fig. 2 shows the single fiber pull-out test treated in the previous paper [33,34] whose ISSF will be compared to Fig. 1. The micro-bond test in Fig. 1 can be used more conveniently than the pull-out test in Fig. 2 where large matrix region should be prepared by molding during the cure procedure [2,35]. This is the reason why most of the previous experiments employed the micro-bond test instead of the pull-out test [3].
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Despite these many efforts at capturing failure behavior in soft composites, progress in understanding the mechanisms of material failure has been greatly inhibited by the difficulty of experimentally visualizing the multiscale structural changes during and leading up to failure, a point repeatedly recognized by prior researchers of fibrous systems (Koh et al., 2013; Li, 2016; Peña, 2011). Non-destructive methods such as Raman spectroscopy (Melanitis et al., 1993) and photoelasticity (Tsai and Kim, 1996) have been used to understand the stress state around single fibers embedded in a matrix during uniaxial loading and fiber pullout, respectively. Fiber networks have been studied experimentally (Bircher et al., 2019; Koh et al., 2013; Yang et al., 2015) using X-Ray scattering (Yang et al., 2015), optical microscopy, electron microscopy (Bircher et al., 2019; Koh et al., 2013), and light scattering (Sacks, 2003) during stretching to relate fiber reorientation to strain stiffening and damage evolution.
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The micromechanics of fiber pull-out

Abstract

J. Mech. Phys. Solids

Mater. Sci. Engng

J. Mech. Phys. Solids

J. Mech. Phys. Solids

Scripta Metall.

J. Mech. Phys. Solids

Wear

Int. J. Solids Structures

Polymer

The debonding and pull-out of ductile wires from a brittle matrix

J. Mater. Sci.

Harvard University Report Mech-119

Modeling of rock friction, 1, experimental results and constitutive equations

J. Geophys. Res.

The axial force needed to overcome frictional resistance on a circular fiber as it slides through a hole in an elastic material

Eur. J. of Mech., A/Solids