Objectives: To evaluate the effect of Poisson coefficient (ν) / E-modulus (E) ratio and adhesive thickness (μm) on the concentration of the principal stress components (SC) and the length of stress-affected interface area in µTBS specimens.
Methods: One quarter, axisymmetric models of non-trimmed micro-specimens (4.5x0.5mm) were created with appropriate mesh refinement at the adhesive and free-edge area with adhesive layer sandwiched between two similar adherents. A 15 MPa load was applied at the outer edge, while roller boundary conditions were applied along the adhesive midplane mid-width. Double coinciding nodes with glue contact were applied at the interface. Finite element calculations were performed within the elastic deformation range. Material properties, ν/E ratio between adhesive and adherents, stress-concentration factor and length of stress-affected area for each principal stress component are described in the table below:
|
Adhesive |
Adherent |
ν/E adhes/adher |
axial |
radial |
circumferential |
shear |
|||||||
|
ν |
E |
Thick |
ν |
E |
SC |
μm |
SC |
μm |
SC |
μm |
SC |
μm |
|
|
0.25
|
3
|
10 |
0.3
|
18
|
5
|
0.26 |
12.5 |
0.13 |
43.5 |
0.03 |
18.75 |
-0.23 |
25 |
|
25 |
0.29 |
25 |
0.12 |
50 |
0.04 |
25 |
-0.21 |
50 |
|||||
|
50 |
0.58 |
50 |
0.10 |
150 |
0.12 |
50 |
-0.29 |
125 |
|||||
|
100 |
0.75 |
93.75 |
0.04 |
250 |
0.17 |
125 |
-0.32 |
262.5 |
|||||
|
0.3 |
9 |
25 |
0.3 |
9 |
1 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
|
0.2 |
6 |
||||||||||||
|
0.25
|
3
|
25 |
0.3 |
9 |
2.5 |
0.07 |
50 |
-0.12 |
50 |
-0.02 |
25 |
-0.10 |
50 |
|
15 |
4.16 |
0.25 |
-0.12 |
0.0. |
-0.18 |
||||||||
|
21 |
5.83 |
0.41 |
-0.10 |
0.07 |
-0.24 |
||||||||
|
24 |
6.66 |
0.47 |
-0.09 |
0.09 |
-0.26 |
||||||||
|
30 |
8.33 |
0.57 |
-0.07 |
0.12 |
-0.30 |
||||||||
Results: The larger the adhesive thickness and ν/E ratio, the higher the stress concentration at the free-edge. The length of the stress-affected area at the free-edge was greatly influenced by the adhesive thickness.
Conclusion: Edge debonding in μTBS specimens is expected with thick adhesive layers, which can contribute to lower or more variable bond strengths.