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Secondary Bonding
The issue of secondary bonding between polyester and epoxy substrates has been an area of concern for some time. Comparative in-house tests have abounded, but without quantative results they can only demonstrate modes of failure and give a ‘feel’ for the force required at break. ISO 527 was modified to accommodate a tensile double lap joint. Four types of specimen were tested to show that polyester tabbing has the same strength when bonding polyester or epoxy substrates.
Secondary Bonding Lap Joint Test Results
| Failure Load | Apparent Shear Strength | Failure Mode* | |
|---|---|---|---|
| A | 42.45 KN (9,540 lbf) | 5.66 MPa (820 psi) | Interlaminar Shear** |
| B | 48.47 KN (10,900 lbf) | 6.46 MPa (937 psi) | Interlaminar Shear |
| C | 46.50 KN (10,450 lbf) | 6.20 MPa (899 psi) | Interlaminar Shear |
| D | 47.08 KN (10,580 lbf) | 6.28 MPa (911 psi) | Interlaminar Shear |
* Interlaminar failure occurred with the CSM layer of tabbing laminates
** One specimen showed adhesive failure between the tabbing and substrate.
A – Polyester peel plied substrate, polyester tabbing
B – Polyester sanded substrate (80 grit), polyester tabbing
C – Epoxy peel plied substrate, polyester tabbing
D – Epoxy sanded substrate (80 grit), polyester tabbing
This data is provided as an aid to materials selection only. No express or implied warranty is made regarding the accuracy of the information contained herein.