Mode II modeling of adhesive materials degraded by fatigue loading using cohesive zone elements

Proceedings of the Institution of Mechanical Engineers, Part G:

Monteiro

Carbas

et al. 2020

Due to their inherent advantages, the use of adhesive joints is widely increasing in advanced industrial sectors such as automotive and aircraft structures, where the lightweight components play a significant role in the efficiency of the products. These structural adhesively bonded connections mostly experience cyclic stress conditions during their service life. One of the most critical fatigue loading conditions for adhesive joints is the tensile cyclic loading. To design against tensile fatigue conditions recently a cohesive zone modelling (CZM) technique combined with a degradation approach was proposed in the literature. However, to apply this degradation method on cohesive elements, the total fatigue life of the joints should be known before the analysis. The aim of the current work is to improve this degradation approach to calculate the fatigue life automatically. To achieve this, a combination of Paris law and degradation model were considered in a numerical procedure. Using the Paris law and the experimental results obtained out of the fatigue crack propagation tests of DCB (double cantilever beam) specimens, the tensile fatigue life of each integration point (IP) during the analysis is estimated automatically. The model was validated and calibrated by experimental data.

Section: Numerical Toolmentioning

confidence: 99%

Section: Numerical Toolmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Tensile fatigue life prediction of adhesively bonded structures based on CZM technique and a modified degradation approach

Proceedings of the Institution of Mechanical Engineers, Part G:

Monteiro

Carbas

et al. 2020

“…9 Fracture mechanics-based methods have been experimentally and numerically considered by several authors. [10][11][12][13][14][15][16][17][18] In these works, the influence of different geometrical and loading parameters has been analysed on fatigue crack growth of adhesive materials. Ajdani et al 15 presented a new test method to measure the fracture energy of brittle and semibrittle adhesive joints subjected to mixed mode loading conditions.…”

Section: Introductionmentioning

confidence: 99%

The influence of mode mixity and adhesive system on the fatigue life of adhesive joints

Sousa

Fatigue Fract Eng Mat Struct

Goyal³

et al. 2020

In real applications, adhesive joints are commonly subjected to fatigue and mixed mode loading conditions. The aim of the current work is to experimentally analyse the influence of mode mixity on the fatigue strength of joints with an epoxy‐based adhesive. Different adhesive systems (acrylic and epoxies) were considered for pure mode I fatigue loading conditions. To achieve this, Arcan joints with an epoxy adhesive were manufactured and tested at different mode mixities. Based on stiffness degradation, monitored during the tests, damage evolution was calculated for different loading conditions and for all the tested adhesives. Finally, fatigue envelopes were constructed for different fatigue life regimes. Results show that a shear loading component reduces both the static strength and fatigue life of the joints. A small reduction rate of the stiffness was found throughout the most part of the life until a sudden drop was observed, indicating a smooth damage evolution.

“…24 Costa et al, 25 recently developed a statistical fatigue degradation relation for joints subjected to pure mode I cyclic loading conditions. The method was further developed for pure mode II 26 and then extended to mixed mode 27 conditions. Based on the Costa et al method, the degradation of the cohesive properties is a function of the current number of load cycles, the total fatigue life of the joint, the value of the cohesive parameter at its initial condition and a fitting parameter which should be set to fit the experimental data with the numerical results.…”

Section: Introductionmentioning

confidence: 99%

A modified degradation technique for fatigue life assessment of adhesive materials subjected to cyclic shear loads

Proceedings of the Institution of Mechanical Engineers, Part C:

Monteiro

Carbas

et al. 2020

Understanding the fatigue response of adhesive joints under cyclic shear stress is important to avoid fatigue failure of the bonded structures. Recently, a cohesive zone modelling (CZM) technique was developed where the cohesive properties of the elements were degraded by a proposed empirical relation. However, based on this degradation approach, the fatigue life of the joints should be known before running the analysis. The aim of the current study is to improve the numerical method in which the fatigue life of the joints will be automatically estimated during the analysis. To achieve this, the concepts of fracture mechanics are considered by using the Paris’ law combined with the degradation model. A user material subroutine is developed to conduct the numerical calculations based on the concepts of CZM. End notched flexure (ENF) tests were carried out to evaluate the numerical data. Based on the results, it was found that the modified approach, in which the total fatigue life is obtained automatically, can be employed for fatigue life assessment of adhesive joints subjected to cyclic shear stresses.