Towards Tough Thermoplastic Adhesive Tape by Microstructuring the Tape Using Tailored Defects

Abstract

This paper presents a strategy towards achieving thermoplastic adhesive tapes with high toughness by microstructuring conventional tapes using tailored defects. Toughened tape was manufactured using two layers of a conventional tape where the bondline between the two adhesive layers was microstructured by embedding tailored defects with specific size and gap between them using PTFE film. Mode I toughness of the toughened tape was characterized experimentally. A high-fidelity finite element model was implemented to describe the toughening mechanisms using double cantilever beam simulations and end notch flexural tests. The model considers for the plasticity of the adhesive layer, the decohesion at the adherend-adhesive and adhesive-adhesive interfaces and progressive damage inside the adhesive layer. The adhesive-adhesive interface with the tailored defects inside the adhesive layer enables crack migration between adherend-adhesive interfaces, crack propagation at adhesive-adhesive interface, backward crack propagation under the defect, and plastic deformation of the adhesive ligament. The maximum toughness improvement of the tape with tailored defects of equal width and gap between two successive defects of 2 mm reached 278% and 147% for mode I and II, respectively, compared to conventional tape.

Keywords: adhesive joints; damage mechanics; fracture toughness; modeling; thermoplastic adhesive tapes.

Figure 1

Manufacturing toughened thermoplastic tapes and bonding DCB samples.

Figure 2

Experimental double cantilever beam test set up.

Figure 3

Two-dimensional models: (a) double cantilever beam (DCB), (b) end notch flexural (ENF) tests for bonded joints with thermoplastic adhesive tapes incorporating tailored defects, and (c) the cohesive interfaces and tailored defect details with tape’s stress–strain response.

Figure 4

Determining interfacial strength for cohesive elements $\#1$.

Figure 5

Mesh sensitivity analysis for double cantilever beam (DCB) tests on toughened thermoplastic adhesive tape with 2 mm sacrificial defect and 5 mm gap: (a) load-displacement (P-$\delta$) response; (b) fracture toughness, $G_I$-crack length, $a_I$ response (R-curve); and (c) meshes with different element sizes. the red lines in c represent the defects.

Figure 6

Proposed model prediction and experimental results for double cantilever bean test on: (a,b) conventional tapes, (c,d) toughened tape with 2 mm sacrificial defect and 5 mm gap, and (e) corresponding damage mode at 3 mm displacement for the toughened tape. In (e) the red lines represents the defect position and the blue arrows represent the crack propagation path.

Figure 7

Double cantilever beam (DCB) simulation crack width, c and gap between two successive cracks, g effects on, (a,c) load-displacement; and (b,d) R-curve, respectively.

Figure 8

End notch flexural (ENF) simulation crack width, c, and gap between two successive cracks, g, effects on, (a,c) load-displacement; and (b,d) R-curve, respectively.

Figure 9

Toughening mechanisms in thermoplastic adhesive tapes with 2 mm crack length and 5 mm gap between cracks: (a) load-displacement curves for double cantilever beam (DCB) simulation; and crack propagation in (b) conventional tape and (c) toughened tape.

Figure 10

Experimental evolution of toughening mechanisms in thermoplastic adhesive tapes with 2 mm crack length and 5 mm gap between cracks: (a) load-displacement curves for DCB test; and crack propagation in (b) conventional tape, and (c) toughened tape.

Figure 11

Toughening mechanisms in thermoplastic adhesive tapes with 2 mm defect length and 5 mm gap between defects: (a) load-displacement curves for end notch flexural (ENF) simulation; and crack propagation in (b) conventional, and (c) toughened tape.

Figure 12

Toughened thermoplastic adhesive tapes microstructure effects on mode I and II toughness with respect to the defect length c at a gap between successive defects g = 5 mm in (a) and g at c = 2 mm in (b). The analysis in the figure was extracted from the FE simulation.