Experimental Investigation and Finite Element Modelling of the Influence of Hydrostatic Pressure on Adhesive Joint Failure

Abstract

Structural adhesives have been increasingly used in automotive industries in conjunction with lightweight structural components to maximize weight reduction in modern car design. They are used to bond various kind of lightweight materials such as FRP composites or metallic alloys and provide a good distribution of force across joining area without damaging the substrates. For automotive applications, bonded components have been often used in complex loading environments which brings failure prediction of adhesive joints a key of success for this technology. As polymer-based materials, hydrostatic pressure can have a major impact on adhesive joint failure in addition to temperature and strain rate. Its influence can be investigated using a specific test fixture known as a modified-Arcan fixture. This article presents the characterization of epoxy-based adhesive using a series of modified-Arcan tests to apply different loading taking in account effect of hydrostatic pressure onto adhesive joints. A high-order exponential Drucker-Prager failure criterion is chosen to interpret the yield and failure surface. Finally, the non-linear behaviour of adhesive is identified via 0° and 90° Arcan tests which correspond respectively to tri-axial and shear modes and the validation of this behaviour is carried out by mix-mode 60° and 120° Arcan tests. The simulation shows a good agreement only with the result in direction 60° while in direction 120° the divergence is obvious due to the different in damage mechanism of this mode.

Finite Element Implementation of the Exponential Drucker–Prager Plasticity Model for Adhesive Joints

“…The exponential version of this criterion shows a good prediction of polymer base material behavior [6]. Despite the development of yield functions in previous works [7], the flow function for plastic deformation is limited to a linear function, resulting in a non-associated flow when using the exponential Drucker-Prager yield criterion. With this type of flow, the simulations are prone to diverge when subjected to a serious tri-axial load in tension or negative hydrostatic pressure, which is a critical load case for adhesives [8].…”

“…Table 3: Summary of identified parameters for the adhesive [7] σ eff = σ y + q 1 − e −cε p eq + Hε p eq σ y (MPa) q (MPa) c H(MPa)…”

Test for the deep: magnetic loading characterization of elastomers under extreme hydrostatic pressures

“…Yet when the load cell is positioned inside the pressure chamber, it is subjected to hydrostatic pressure, making its calibration unreliable [31][32][33]. The other problems like deflection of adhesion [31,34], strain measuring [24][25][26]35] and pressure keeping [17][18][19][20]35] also exist. To avoid the influence of hydrostatic pressure on the load cell, efforts have been made to place it outside the pressure chamber.…”

Effect of the Stress State on the Adhesive Strength of an Epoxy-Bonded Assembly

“…The limit characteristics of adhesive assemblies are generally determined from the results of mechanical testing, which can be aimed either at the physical laboratory simulation of the behavior of specific assembly components under expected operating conditions or at obtaining empirical information for identification of failure criteria and models used in design and verification calculations. The latter aim can be effectively achieved by using modification of Arcan specimens [21][22][23][24][25][26][27][28][29][30][31], which enable the cleavage stress to shear stress ratio to be varied in a wide range. The test results can offer fracture loci determining the limit states of adhesive assemblies as dependent on the stress state and thermomechanical loading conditions [30][31][32].…”

“…The latter aim can be effectively achieved by using modification of Arcan specimens [21][22][23][24][25][26][27][28][29][30][31], which enable the cleavage stress to shear stress ratio to be varied in a wide range. The test results can offer fracture loci determining the limit states of adhesive assemblies as dependent on the stress state and thermomechanical loading conditions [30][31][32]. However, it is noted herewith that, in order to obtain correct results, it is necessary to decrease or take into account the effect of stress concentration at the specimen edges [25][26][27][28].…”