Pull-off tests

The principle of the EN ISO 4624 2003 pull-off test requires a dolly to be glued or soldered to the composite panel. An increasing pull-off force is then applied to the dolly until the coating detaches from the substrate. The adhesive strength of the bond is calculated from the maximum force applied and the size of the detached area. If failure occurs elsewhere than between substrate and metallization, it is essential to add a reference to the fracture pattern as a supplement to the measured value. 

Porous coatings such as those that prevail in MID technology when conductors are applied by thermal spraying, for example, can allow the adhesive applied to fix the dolly to the sample to penetrate through the coating to the substrate and falsify the result of measurement. It is also necessary to ensure that the substrate is adequately secured. A twist test is an alternative if compliance with this require- 

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Specification for electroplated coatings of 65/35 tin/nickel alloy Method for the evaluation of results of accelerated corrosion tests on metallic coatings Methods of test for paints Cross-cut test Pull-off test for adhesion Resistance to artificial weathering (enclosed carbon arc) and Addendum No. 1 Resistance to continuous salt spray Notes for guidance on the conduct of natural weathering test... 

This section describes some of the most common exposure tests or ageing procedures applied to antifouling systems. The ageing processes are normally succeeded by adhesion or pull off tests described in section 5.1. 

Blister Box Test, according to ASTM D 4585 (ISO 6270). This test evaluates the water resistance of a coat by condensation of water vapour. The panel surface with the coating system is exposed to 40°C, saturated water vapour, at an angle of 15° to the horizontal. The reverse side of the panel is exposed to room temperature. At each inspection blisters and rust are evaluated according to ASTM D 714 (ISO 4628-2) and ASTM D 610 (ISO 4628-3) respectively. Cracking is evaluated according to ISO 4628-4. When the test is stopped, adhesion is evaluated according to ASTM D 3359, tape test (ISO 2409) or ASTM D 4541 (ISO 4624), pull-off test. 

Figure 12. Top hat stiffener pull-off test set-up (a) mode I, (b) mixed mode I/II.

Transverse pull-off tests induce mainly mode 1 loading, provided the base panel is sufficiently rigid. Finite element analyses have been performed to look at this geometry in more detail, and will be reported elsewhere, but here a simple analytical beam theory expression is used to predict the pull-off failure load [21] ... 

The results from 12 pull-off tests on QX/epoxy specimens with implanted defects are shown in Figure 15. Both measured and predicted values are shown. Different criteria may be used to compare top hat pull-off and fracture test values. These include various acoustic emission parameters (first acoustic events, first events above a certain amplitude), visual or image analysis parameters or values on the load-displacement plots. Several criteria have been examined, here non-linear values are shown (Gic = 240 J/m, the lower, dashed line). 

In the following sections, we describe the ability to ran tests sensitive to values of Q that are characteristic of processes confined to the interfacial region. First, the sample preparation and experimental procedure are described for two types of tests a straight pull-off test and a cyclic interfacial fatigue test. Then, the results of these tests are presented with data for the forces required for fracture of the samples, as well as the calculations for Q related to the cycHc fatigue test We conclude with a discussion of the significance of the results that have been obtained for our model system. 

These graphs are compiled from pull-off tests for 130 nm TMPC layers with no PEO layer present. 

Fig. 23.6 (a) Tack curve for a pull-off test involving two TMPC layers in the absence of PEO. The layers were heated to 80 °C while in contact and cooled to room temperature before pull-off (b) Image of the elastomer side of the sample, showing the contact area after completion of the experiment. 

Fig. 23.9 Maximum tensile loads as a function of the PEO layer thickness, for a series of pull-off tests where the samples had been heated to 80°C while in contact.

The pull-off test for measuring adhesion is described in ISO4624. Adhesion is assessed by measuring the minimum tensile stress necessary to detach or to rupture the coating in a direction perpendicular to the substrate. The result gives the minimum tensile stress required to break the weakest interface (adhesive failure) or the weakest compound (cohesive failure) of the test assembly. Mixed adhesive-cohesive failure may also occur. 

Secure adhesion of the CP film on a substrate is another important mechanical property for long-term function of a bioimplant device. Pull-off tests (ASTM standard procedure D-4541-95) and other ASTM adhesion and hardness assays may provide valuable information on the adherence of CP films to metal substrates [1,137]. 

Stud or butt tests representing pull-off tests used for the measiuements of the adhesion characteristics between an ink/paint coating and the substrate. An adhesive is applied to the paint coating, and a metallic stud made of aluminum is glued onto the surface by the adhesive applied to the paint coating. Subsequently, the pull force is utilized perpendicular to the substrate surface with a constant rate. This measurement provides an excellent measurement of adhesion for systems, for example, for polymer-metal interfaces [98]. Figure 8.14 schematically illustrates the puU-off test schematically [99]. 

A possible design strategy for avoiding strip end debonding is the limitation of the FRP force in the EBFR at the position of the last crack (Rg. 4.14).The existing force in the EBFR should be smaller than the force that can be anchored in a pull-off test (Rg. 4.15). The formulations for this force include typically the elastic modulus, Et, thickness, u, and width, bt, of the... 

Pull-off test and corresponding strain and shear stress on the basis of a biiinear bond shear stress-siip reiation. 

Adhesion is defined as the physical attraction or joining of two substances, especially the macroscopically observable attraction of dissirmlcir substances. There cire many techniques to study adhesion, namely pull-off tests, interfacial fracture tests, blister tests, mapping of interfacial properties, probe modification, and scratch tests. 

In the tests shown in Fig. 14.5, only the film is deformed. More rarely, the underlying substrate is also deformed, for example during pull-off, stretching or bending shown in Fig. 14.6, and this causes detachment of the film, but now the force is different from that found for rigid substrates. For example, in the pull-off test of Fig. 14.6(a), the substrate deformation dominates the failure process and decreases the adhesion force enormously Let us now deal with aU the above tests in more detail. 

Little information exists on the effects of surface pretreatment on bond strength and durability, and there is a general absence of appropriate test methods to assess such effects on adhesion. The pull-off test(68) is, perhaps, currently the most suitable the slant-shear test, as described in BS 6319(69), is of limited use in assessing adhesion because the interfaces are not subjected to tensile forces. 

Tests to measure the bond which can be obtained with the concrete of the structure to be strengthened are best carried out on the structure itself. A possibility is to utilise a pull-off test as developed for the non-destructive testing of concrete(21). A circular steel probe is bonded to the concrete surface and specially designed portable apparatus is then used to pull off the probe, along with a bonded mass of concrete, by applying a direct tensile force. Any defects in bond would be revealed by the occurrence of failures at the adhesive-concrete interface. 

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