Mode II fatigue crack growth properties of adherends bonded with DP8005: End–notched flexible tests

doi:10.1016/j.ijfatigue.2018.02.026

International Journal of Fatigue

Volume 111, June 2018, Pages 333-344

https://doi.org/10.1016/j.ijfatigue.2018.02.026 Get rights and content

Highlights

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A faster destructive effect occurred under Mode II fatigue tests than that occurring in Mode I fatigue tests.
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The values of $Δ$ G_II.th for the aluminum alloy, GF/PP, and CF/EP specimens for the ENF fatigue tests were 258.7, 288.6, and 323.9 Jm⁻², respectively.
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The fracture surfaces for the aluminum alloy, GF/PP, and CF/EP specimens were cohesive dominant failures.
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$Δ$ G_II.th of adherends bonded with DP8005 under mixed−mode loading can be approximately estimated by using only the fracture toughness value.

Abstract

Using end–notched flexible (ENF) tests, this study investigates the Mode II fatigue crack growth properties of adherends bonded with a DP8005 acrylic–based adhesive. The experimental results obtained from the ENF fatigue tests were compared with the results from the double cantilever beam (DCB) fatigue tests to obtain comprehensive fracture properties for DP8005. By comparing the slopes defined by the Paris law, a faster destructive effect was observed in ENF fatigue tests compared with that observed during the DCB fatigue tests. The study demonstrates that engineers and/or designers can estimate the threshold energy release rate range using only fracture toughness under mixed–mode loading.

Introduction

A fatigue test using AS4/PEEK specimen was proposed to measure a fatigue threshold under Mode I and II loadings in 1990 [1]. Murri et al. [2] investigated the effects of the insert thickness and precracking techniques using 24-ply unidirectional specimens of glass/epoxy under Mode I and II fatigue loading. Fatigue behaviors for fiber–reinforced polymer matrix composites (FRP) were investigated under Mode II loading before the FRP subcomponents were commercialized in structural materials [3], [4], [5]. However, producing the structural materials as a single part is difficult because of different shapes of the subcomponents. Adhesive bonding is increasingly utilized to bond the similar and dissimilar subcomponents, such as FRP and light alloys. In this case, the investigations in the fatigue behavior for structural materials in adhesively bonded joints are important from a fail–safe or damage tolerance design perspective [6].

The advantages of adhesive bonding include uniform stress distribution, reduced weight, and an effective bonding between thin plates [7]. A major problem in the automotive industry is noise (or vibration), which travels through the air and solid components, such as windows and closure panels [8]. Thus, ductile rather than brittle adhesives are utilized to reduce interior vehicle noise. DP8005 is one such acrylic–based adhesive that is ductile and is one of the possible candidates for this reason.

In previous studies, double cantilever beam (DCB) [9] and end–notched flexure (ENF) [10] tests have been conducted to measure the fracture toughness of various materials under Mode I and II static loadings, including an aluminum alloy, a glass fiber–reinforced polypropylene matrix composite (GF/PP), and carbon fiber–reinforced epoxy matrix composite (CF/EP) adherends bonded with DP8005. The results indicated that the G_IC of the aluminum alloy, GF/PP, and CF/EP specimens under Mode I loading were 1071, 1438, and 1652 Jm⁻², respectively. In addition, the experimental results showed that the fracture toughness (G_IIC) values of the aluminum alloy, GF/PP, and CF/EP specimens under Mode II loading were 2398, 2474, and 2428 Jm⁻², respectively. Dominant failure modes for the three adherends were cohesive under Mode II static loading. Furthermore, Mode I fatigue crack growth properties of the adherends bonded with DP8005 were discussed using the DCB specimens [11]. The results revealed that the slope defined by the Paris law (linear region in a logarithmic plot of fatigue crack growth rates versus energy release rate range) was 2.85. The threshold release rate range ( $Δ$ G_I.th) for the aluminum alloy, GF/PP, and CF/EP specimens were 46.5, 69.3, and 72.5 Jm⁻², respectively. Additional fracture properties (interfacial failures) for the aluminum alloy specimen were observed under Mode I static and fatigue loadings, which were caused by weak bonding between the adhesive and aluminum alloy. These Mode I fatigue crack growth properties of adherends bonded with DP8005 are insufficient for engineers or designers to determine a criterion for the damage tolerance design of the structural materials because peel (tension) force is applied to the specimens under Mode I fatigue loading. Shear force is also one of the most important factors to be considered since the fatigue crack growth properties of adherends bonded with DP8005 under Mode II loading (shear force) is required for engineers or designers to understand the fracture behaviors of adherends.

Thus, this study aims to measure the Mode II fatigue crack growth properties of ENF specimens on adherends bonded with DP8005. The fatigue crack growth properties obtained from the ENF tests were compared to those of DCB tests to provide the overall fracture properties for DP8005. The Paris law (linear region) were obtained from the ENF and DCB fatigue tests to discuss the destructive effect. Fracture surfaces were observed using a microscope to clarify failure modes.

Section snippets

Materials

An aluminum alloy (5052–H34, average thickness = 3.0 mm), a GF/PP (Tepex dynalite 104–RG600(6)/47%, average thickness = 3.0 mm, Bond Laminates, Germany), and a CF/EP (F6343B–05P (0/90)₁₄, average thickness = 3.3 mm, Toray Industries Inc., Japan) were used as the adherends. A two–part acrylic–based adhesive (3M^™ Scotch–Weld^™ Structural Plastic Adhesive DP8005, Japan) was used to bond the adherends. The advantages of this adhesive include its ability to bond adherends and polyolefins and its

Load–displacement curves

Typical load–displacement (P–δ) curves for P_cst are shown in Fig. 2, in which (a), (b), and (c) were obtained from the aluminum alloy, GF/PP, and CF/EP specimens, respectively. Red and black solid lines were obtained from the minimum and maximum loads using P_cst of each specimen. Experiments were conducted with P_cst values of eight, three, and eight to determine the relation between da/dN and $Δ$ G_II for the aluminum alloy and CF/EP, and GF/PP specimens, respectively. The δ values increased with

Conclusions

Fatigue tests using the ENF specimens were performed to measure the fatigue crack growth properties of different adherends, including the aluminum alloy, GF/PP, and CF/EP specimens, which were all bonded with a DP8005 acrylic–based adhesive under Mode II loading. A faster destructive effect occurred under Mode II fatigue tests (higher n values) than that occurring in Mode I fatigue tests. Moreover, higher energies were required under Mode II fatigue tests to propagate cracks compared with that

Acknowledgements

This paper is based on results obtained from a future pioneering project commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Competing interests

The authors declare that we have no competing interests.

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Mode II fatigue crack growth properties of adherends bonded with DP8005: End–notched flexible tests

Highlights

Abstract

Introduction

Section snippets

Materials

Load–displacement curves

Conclusions

Acknowledgements

Competing interests

Int J Fatigue

Int J Fatigue

Int J Fatigue

Int J Fatigue

Compos Struct

Characterization of Mode I and Mode II delamination growth and thresholds in AS4/PEEK composites

Compos Mater: Testing Design

Fatigue in adhesively bonded joints: a review

ISRN Mater Sci

Handbook of adhesion technology