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Fracture mechanics applied to the determination of adhesion strength between epoxies and hydraulic mortars
The determination of adhesion strength between polymers and mortars always creates problems. The use of traditional tests like direct tension, flexure or shear, normally doesn`t make possible the correct determination of the adhesion strength. If the adhesive is good and the mortar surfaces are well prepared, the failure is in the mortar. With this kind of failures it is possible to say that adhesion strength is higher than the failure stress. But is not possible to give a numerical value of adhesion strength. A test based on fracture mechanics makes easier the determination of adhesion strength. The use of a notched specimen concentrates the stresses in the polymer/mortar joint and adhesive failures are more frequent. With adhesive failures, it is possible the determination of the numerical value of the adhesion strength. The specimen used was a double cantilever beam (DCB), because with this one the crack has a greater length for propagation. The polymer used was an epoxy. The mortar was a standard mortar. With these two materials, the failures were in the mortar, during tension tests. However the DCB tests lead to mixed failures with predominant failure in the adhesive. The determination of fracture energy (Gf) of the bonded specimens needs the knowledge o the crack length. This parameter changes during the test and is not easy to determine. For this purpose it was used three methods: acoustic emission, extensometer in the middle of the crack way and compliance. The compliance method seems to be the most promisius. Another problem was the deviation of the cracks outside their expected path, parallel to the greater dimension of the specimens. To avoid the problem the specimens were reinforced externally with steel plates. With this reinforcement, the failures followed their entire expected path. In the last phase of this study it was tried to avoid the work of bonding steel plates. DCB specimens with variable section were tested with good results.
Fracture mechanics applied to the determination of adhesion strength between epoxies and hydraulic mortars
The determination of adhesion strength between polymers and mortars always creates problems. The use of traditional tests like direct tension, flexure or shear, normally doesn`t make possible the correct determination of the adhesion strength. If the adhesive is good and the mortar surfaces are well prepared, the failure is in the mortar. With this kind of failures it is possible to say that adhesion strength is higher than the failure stress. But is not possible to give a numerical value of adhesion strength. A test based on fracture mechanics makes easier the determination of adhesion strength. The use of a notched specimen concentrates the stresses in the polymer/mortar joint and adhesive failures are more frequent. With adhesive failures, it is possible the determination of the numerical value of the adhesion strength. The specimen used was a double cantilever beam (DCB), because with this one the crack has a greater length for propagation. The polymer used was an epoxy. The mortar was a standard mortar. With these two materials, the failures were in the mortar, during tension tests. However the DCB tests lead to mixed failures with predominant failure in the adhesive. The determination of fracture energy (Gf) of the bonded specimens needs the knowledge o the crack length. This parameter changes during the test and is not easy to determine. For this purpose it was used three methods: acoustic emission, extensometer in the middle of the crack way and compliance. The compliance method seems to be the most promisius. Another problem was the deviation of the cracks outside their expected path, parallel to the greater dimension of the specimens. To avoid the problem the specimens were reinforced externally with steel plates. With this reinforcement, the failures followed their entire expected path. In the last phase of this study it was tried to avoid the work of bonding steel plates. DCB specimens with variable section were tested with good results.
Fracture mechanics applied to the determination of adhesion strength between epoxies and hydraulic mortars
Aguiar, J. L. Barroso de (Autor:in)
01.01.2001
Aufsatz (Konferenz)
Elektronische Ressource
Englisch
DDC:
690
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