Experimental investigation on multiaxial ratchetting behaviour and fatigue life of silicone seal adhesive bonding butt-joints

https://doi.org/10.1016/j.ijadhadh.2020.102700Get rights and content

Abstract

The multiaxial fatigue experiments were conducted on the silicone seal adhesive bonding hollow cylinder butt-joints under the stress-controlled mode at laboratory ambient temperature. The effect of loading path, equivalent stress amplitude, equivalent mean stress and cycle time on the multiaxial ratchetting behaviors and fatigue life were discussed. The experimental results showed that the effects of non-proportional loading path on the ratchetting strain were greater than that of the proportional loading path. Moreover, the effects of the normal stress on the ratchetting strain were relatively larger than that of the equivalent shear stress under the multiaxial loading paths. In addition, the ratchetting strain increases and fatigue life decreases with the increase of equivalent stress amplitude and mean stress, and the decreasing cycle time. The effects of cycle time on the multiaxial ratchetting strain and fatigue life under the elliptic loading path were insignificant for the silicone seal adhesive bonding butt-joints.

Introduction

Adhesively bonded joints as a mechanical assembly technology have been extensively employed in many industrial applications such as automotive, aerospace, construction, microelectronic, etc. as alternatives to traditional mechanical joints [1]. In practical use, the adhesive materials and the adhesively bonded joints are subjected to repeated multiaxial loadings, which will lead to the fatigue failure and destruction. Ratchetting evolution is a method to analyze the process of fatigue failure of materials or structural components undergoing a cyclic stressing with non-zero mean stress [2]. The multiaxial ratchetting behaviors and fatigue life of adhesive bonding joints has attracted much interest in the field of design. Therefore, a deep understanding of the multiaxial ratchetting behaviors and the fatigue life of adhesively bonded joints has become a serious issue for the safety evaluation.

In its applications, the fatigue strength is generally considered to be the most important in respect to long-term service life. Hence, the effects of fatigue strength and fatigue life of the adhesively bonded joints have been extensively investigated. Schneider et al. [3] studied the dependence of fatigue strength on stress amplitude and temperature of the scarf joints bounded by a commercial single component hot curing toughened epoxy adhesive. It was found that the fatigue strength of the scarf joints decreased with the increase of stress amplitude and temperature, and the temperature played a leading role in the failure of the scarf joints. Boutar et al. [4] investigated the effect of surface roughness and adhesive thickness on the fatigue life of the single lap joints bounded by an one-component polyurethane adhesive. It was found that the single lap joints had the maximum fatigue life when the surface roughness was 0.6 μm and the adhesive thickness was 1 mm. Jen et al. [5] found in their experimental study that the fatigue strength of the adhesively bonded scarf specimen increases significantly with the increase of scarf angles of the specimens. In addition to experimental research, numerical simulation method is also used to study fatigue damage of a adhesively bonded joints. Khoramishad et al. [6] developed a numerical damage model that is only related to the adhesive system and not to joint configuration, and adopted a bi-linear traction–separation description of a cohesive zone model to simulate the progressive damage of the adhesively bonded joints under cyclic loading. Two kinds of single lap joints (single lap joints and laminated doublers in bending) were numerically simulated. The simulated fatigue life, back-face strain and predicted damage growth are consistent with the experimental fatigue response.

Ratchetting refers to the accumulation of plastic strain caused by cyclic plasticity under cyclic stress [7]. The multiaxial ratchetting behaviors and fatigue life of adhesive bonding joints has attracted much interest in the field of design. Ratchetting effects produce not only undesirably deformations but also fatigue damage [8]. The ratchetting behaviors have been investigated mainly focus on metal materials in the past [[9], [10], [11]]. In recently years, the ratchetting behaviors of some non-metallic materials have attracted more attention for its engineering applications, and some research work has been carried out to the fatigue performance and fatigue life of non-metallic materials [[12], [13], [14]]. The ratchetting strain of non-metallic materials is mainly affected by the applied mean stress, stress amplitude and stress rate, and increases with the increase of mean stress, stress amplitude and the decrease of stress rate [15,16]. The non-metallic materials had a strong memory for loading history, prior stress cycling with higher stress level restrains the ratchetting strain in subsequent cycling with lower stress level [17,18]. Time-dependence is also an important property of non-metallic ratchetting.Kang et al. [19] investigated the ratchetting behaviors of the polyester resin and glass fiber reinforced polyester resin matrix composites by the cyclic tests with different loading conditions including some time-related factors. The results demonstrated that the time-dependent ratchetting of the polyester resin and its composites mainly stems from the viscosity of the polyester resin, while the addition of glass fiber into the resin matrix improved the resistance of the composites to the ratchetting deformation and lowered the time-dependence of the ratchetting. The uniaxial fatigue failure behaviors for a variety of non-metallic materials and adhesively bonded joints have been extensively investigated in the last decades. However, only a few research works have been carried out to consider the multiaxial ratchetting evolution and fatigue life of the adhesively bonded butt-joints.

In this study, the multiaxial fatigue experiments were conducted on the hollow cylindrical butt-joints specimen by the stress-controlled using four loading paths (proportional path, rhombic path, circular path and elliptical path). The strain response curve and the stress-strain component curve of fatigue experiments under different loading paths and different loading conditions were analyzed. Furthermore, the effects of equivalent stress amplitude, equivalent mean stress and cycle time on the ratchetting strain and the fatigue life of the silicone seal adhesively bonded butt-joints were discussed in details, and the comparison of the effects of various factors on ratchetting strain and fatigue life was conducted.

Section snippets

Materials and specimens

The adhesive used in the experiments is a commercially available silicone sealant, DB527; provided by Wuhan Double Bond Kaim Co., Ltd. The hollow cylindrical made of T6061 aluminum alloy was used as the butt-joints adherend. The preparation processes of the specimen are as follows [20].

The adherend was machined to specimen dimensions. To ensure a uniform surface roughness for each specimen, the bonding surfaces of specimen were polished by 360# abrasive paper prior to bonding. And then, the

Effects of loading path on multiaxial ratchetting behaviors and fatigue life

In order to illustrate the effect of loading path on the multiaxial ratchetting behaviors and fatigue life of the adhesively bonded butt-joints, a series of multiaxial fatigue experiments were carried out with same equivalent stress amplitude, cycle time and equivalent mean stress (0.318mpa, 4s and 0.424mpa) and different loading paths (i.e. proportional loading path, rhombic loading path, circular loading path and elliptical loading path).

The normal strain-equivalent shear strain curves of the

Conclusions

The effects of loading path, equivalent stress amplitude, equivalent mean stress and cycle time on the equivalent ratchetting strain and fatigue life of the silicone seal adhesive bonding butt-joints were discussed. The multiaxial fatigue experiments have been carried out under stress-controlled mode using the hollow cylindrical butt-joints specimens. The experimental results demonstrated that the ratchetting behaviors appeared in all four loading paths with the number of cycles increase, and

Acknowledgements

This work was supported by National Natural Science Foundation of China (No. 10972200, No. 50805147), and Natural Science Foundation of Henan Province (No. 182300410175).

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  • Evaluation of multiaxial fatigue life prediction approach for adhesively bonded hollow cylinder butt-joints

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    Besides, the effects of stress amplitude, mean stress and cycle time on the fatigue life of the adhesively bonded joints were experimentally investigated. Details of specimen preparation and experimental data processing can be found from our previous studies [2]. Loading conditions of each loading path are listed in Table 1, 2 and 3, respectively.

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