By removing oxide layers , the surfaces are cleaned in a way that is suitable for adhesive bonding.
In addition, the parameters used especially in the cleanLASER process for processing light metals especially aluminum and magnesium in a single process step not only lead to cleaning, but also to modification of the component surface. This makes it possible to achieve extremely high corrosion stability and thus a long-term adhesive pre-treatment. Many years of experience as well as optimized laser systems are the basis for a durable connection. Do you have any questions?
We want to be happy to assist you. Three different grades of emery paper, P50, P80 and P were used for the different surface roughness values and the flat plate without abraded surface was considered as a one grade. Figure 1 shows the surface roughness pattern used for both aluminum and mild steel adherend. Two roughness parameters: the average surface roughness R a and the maximum surface roughness maximum height of profile, R z were used to evaluate the surface quality of the specimens.
Surface roughness values, R a and R z were measured using a profilometer Mitutoyo-SJ, Japan for both abraded and non abraded samples. The cut-off length 4 mm was selected for the measurement and the profilometer measuring range was 0. The surface roughness measurements were performed in different areas, along two different directions longitudinal and transverse. The measured surface roughness values, R a and R z of aluminium and mild steel adherend are given in table 4 and 5 , respectively. Surface roughness tester Hommelwerke Model T was used to measure the 2D surface roughness profile of both aluminium and mild steel adherends.
ISO M1 filter was used with a transverse length of 4. The wetting characteristic of all types of the adherend surface different surface roughness was determined using a contact angle.
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In order to measure the contact angle, a 1 ml drop of epoxy resin Araldite r was deposited on the adherend surface with a disposable micro-syringe. A minimum of three contact angle tests was recorded in different surface area to obtain an average result and also cross verification of surface uniformity.
The complete instrument set-up for contact angle measurement is shown in Fig. A single strap joint geometry was used for the experiment fig. The bonding surface area was cleaned with acetone before the application of the adhesive. The adhesive was applied on the adherend surface and spread over it with a spatula. The adherends were then bonded by applying constant pressure on the specimen upto 48 hrs. The joints were cured at room temperature for 48 hrs.
The adhesive thickness was 0.
The single strap specimens were tested using an universal testing machine Fine Spavy Associates and Engineering Pvt. Five specimens were tested for each condition at room temperature. The gripping length was kept at 30 mm at both ends, while the gripping width was over the whoe width of the specimen. Load-displacement values were recorded. As it can be seen from fig. However, a negligible increment was observed at lower surface roughness range i. This high increment in contact angle with the surface roughness values P and P80 in both adherend type lead to lower wettability which make a barrier for adhesive spreading on the surface Barsellino et al.
It means, the adhesive does not penetrate well completely into asperities and consequently, the interface between liquid and solid is not continuous over the overlap area. This reduces the effective bond area and leads to interfacial failure instead of cohesive failure of adhesive as noticed by Hitchcock et al.
Table 6 and 7 shows the shear strength with respect to surface roughness value of aluminium and mild steel adherends. Aluminium adherend having surface roughness value of 1. From Table 6 it can be seen that the shear strength increases with increasing surface roughness of the aluminium adherend compared to the non abraded adherend surface. A high surface roughness of the adherend material was not proven to provide significant improve in terms of shear strength of the joints.
The same trend of shear strength joints with respect to adherend surface roughness was observed for the mild steel adherend bonded joints table. A continuous increase in shear strength was observed up to a maximum surface roughness of 3. Figure 8 shows the shear strength with respect to the adherend surface roughness of both adherend bonded joints. It is clearly seen that both the alumimum and mild steel adherend joints follow the same shear strength trend with only the difference in the magnitude of strength.
Both the adherend joints showed an increase in shear strength with an increase in surface roughness and then decrement in strength. These results are in agreement with previous research Tezcan et al. Increase of bonding area, mechanical interlocking between surface modification and micro-columns of the adherends are the possible reasons for the improvement in strength at initial level.
Howecer, but at the higher surface roughness this is not valid. From the contact angle study, it was found that higher contact angle at the higher surface roughness as compared to P adherend surface which lead to lower wettability. This might be the reason for lower shear strength at high roughness value even though the bonding area is higher. A maximum shear strength can be obtained over the optimum surface roughness value for a particular adherend-adhesive bonded joints.
However, a simple correlation with the surface roughness is not sufficient to predict the joint performance, as there are other parameters responsible for the increment in strength Spagiari and Dragoni, The failure mode of the specimens was visually examined after testing and can be seen in fig. Upon visual examination, all the joints prepared by different surface treatments have shown dominantly interface failure.
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This is in the same line of findings by Hitchcock et al. They concluded that an increasing surface roughness usually reduce the wettability of the surfaces. This phenomenon might be the reason for interfacial failure in both adhered type bonded joints. A Scanning Electron Microscopy SEM analysis was carried out with the joints having a higher failure load in order to better understand the failure mechanism. Figure 10 and 11 show a typical SEM micrograph resulting from a mild steel adherend and aluminium adherend joints with mechanical abrasion by P emery paper.
From the SEM images, shear yielding bands can be observed, which indicate plastic deformation particularly evident from the fig.
The adhesive remains on the lower adherend surface, as shown in fig. The fracture surface of aluminium adhered joints specimen, fig. Both joints specimen show evidence of adhesive ductility, regions of cohesive failure and also interface failure mode.
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In this work, the effect of adherend surface roughness on adhesive bond strength was investigated. Single strap joints with different adherends i. There is an optimum surface roughness for maximum strength in both aluminum and steel adherend joints. Examination of fractured surfaces SEM after testing showed an evidence of adhesive deformation for the joints at higher failure load.
The strength variations with respect to the surface roughness follow the same trend initially increases and then decreases with roughness as a function of material. However, a large difference in magnitude of the shear strength between aluminium and mild steel adherend joints was observed. It implies that there is a strong dependence of adherend material on the adhesive bond strength along with the surface roughness factor.
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Contact angle increases continuously with an increasing surface roughness compared to the non-abraded specimen. The shear strength of all treated surface joints is higher than the non abraded adherend joints, despite the higher contact angle lower wettability. It implies that these increments in shear strength are not supported by contact angle wettability phenomenon.
The above results indicate that the shear strength associated with the different adherend surface roughness cannot be explained only by increased roughness characteristics, such as mechanical interlocking, surface texture and increased bonding area. An understanding of the chemical bond characteristics between the adhesive and adherend material before an application is also essential.
Even though surface roughness is an important parameter for joints strength, the proper selection of adherend-adhesive material combination should not be ignored for maximum performance of adhesive bonded joints. Azari, S.