Using a cohesive damage model to predict the tensile behaviour of CFRP single-strap repairs

Abstract

This work addresses both experimental and numerical analyses regarding the tensile behaviour of CFRP single-strap repairs. Two fundamental geometrical parameters were studied: overlap length and patch thickness. The numerical model used ABAQUS Ò software and a developed cohesive mixed-mode damage model adequate for ductile adhesives, and implemented within interface finite elements. Stress analyses and strength predictions were carried out. Experimental and numerical comparisons were performed on failure modes, failure load and equivalent stiffness of the repair. Good correlation was found between experimental and numerical results, showing that the proposed model can be successfully applied to bonded joints or repairs.

Modelling adhesive joints with cohesive zone models: effect of the cohesive law shape of the adhesive layer

“…The stiffness matrix, K, contains the adhesive stiffness parameters. A suitable approximation for thin adhesive where a is a non-dimensional parameter, related to a specific material, that establishes the rate of damage evolution with dn,s layers is provided with Knn ¼ E, Kss ¼ G, Kns ¼ 0 [21,40]. For all of the three CZM shapes, initiation of damage was evaluated by the (for a¼ 0 a triangular law is attained).…”

“…Since the energy required for crack growth is averaged over the damaged area, results are mesh independent provided that a minimum refinement is used, more specifically if a minimum of three to four elements are undergoing the softening process at the damage front [21,44]. Fig.…”

“…These results are consistent with previous observations for these types of adhesives is identical up to Pm , whilst the predictions mainly differ in the value of Pm. These figures were chosen because they represent the [21,24]. Thus, the large plastic flow of the adhesive at a constant level of stresses after attaining the peak strength is captured by minimum and maximum values of LO for the Araldite s 2015, the FE simulations, by using damage definitions that correspond to a constant level of stresses at the end of the elastic region.…”

“…It is thus recommend adjusting the shape of the CZM laws to conform to the behaviour of the thin material strip or interface they are simulating. Developed CZM include triangular [17], linear-parabolic [18], polynomial [19], exponential [20] and trapezoidal laws [21]. Thus, CZM can also be adapted to simulate ductile adhesive layers, whose behaviour can be approximated with trapezoidal laws [14].…”

Strength prediction of single- and double-lap joints by standard and extended finite element modelling

“…The cohesive elements should be placed along the paths where damage is prone to occur, which can be difficult to identify. However, in bonded assemblies damage growth is restricted to well defined planes, i.e., at the interfaces between the adhesive and the adherends, or cohesively in the adhesive, which allows surpassing this limitation [22,23]. A broad variety of works were published that prove the feasibility of this technique to model bonded assemblies, with promising results.…”