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Finite Element Analysis of Adhesive Bondlines Using Spring Elements

Project Description

Apply the adhesive bondline modeling technique outlined in “Software Tools for Analysis of Bonded Joints” by Farhad Tahmasebi.

Technical Approach

The technique outlined by Farhad Tahmasebi to model an adhesive bondline utilizes the combination of spring and rigid bar elements. This technique was applied to the ASTM D 1002 lap-shear coupon test for a bonded steel assembly. To validate the modeling technique, a model using solid brick elements to simulate the adhesive bondline was also generated. The longitudinal deflection (displacement in the x-direction), shear and peel stresses were compared to investigate the results.

Schematic of ASTM D1002 lap-shear test (Applied load = 1,000 lbs)

Discussion

The materials used and their properties to model the assemblies are presented in Table 1.0. Table 2.0 gives a summary of the modeling assumptions. The two (2) analysis approaches have advantages and disadvantages which are outlined in Table 3.0. The models were generated such that there was an identical number of nodes. Also, since the technique utilized to model the spring elements allow extraction of results along the centerline of the bond, the adhesive solid element model required three (3) elements through the thickness of the bondline to extract data at the centerline. In summary, solid elements would be best suited for a detailed sub-structural analysis. The spring element method is best suited for the analysis of thin bondlines (less than 0.03 inches) and large models where it is necessary to simulate the adhesive bondline.

Adhesive spring element model
Elements: 1,405, Nodes: 1,144
Adhesive solid element model
Elements: 1,100, Nodes: 1,144


Results

The deflection, shear and peel stresses gave very good correlation between the two modeling techniques. The plots below show that the spring adhesive model gives a smoother stress distribution compared with the solid adhesive model.

Delta(x) (spring model) = 0.0075 inches Delta(x) (solid model) = 0.0076 inches