Chiminelli et al 2019a - Revision history

Materiales.Compuestos at 19:14, 30 October 2022

2022-10-30T19:14:42Z

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Scipediacontent at 11:51, 7 May 2022

2022-05-07T11:51:33Z

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Scipediacontent: Scipediacontent moved page Draft Content 350992336 to Chiminelli et al 2019a

2022-03-31T19:00:52Z

Scipediacontent moved page Draft Content 350992336 to Chiminelli et al 2019a

Scipediacontent: Created page with "== Abstract == Adhesive joints are characterized by non-uniform distribution of stresses and strains along the bond-lines, with maximum values near the ends of the overlaps...."

2022-03-31T19:00:50Z

Created page with "== Abstract == Adhesive joints are characterized by non-uniform distribution of stresses and strains along the bond-lines, with maximum values near the ends of the overlaps...."

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== Abstract ==

Adhesive joints are characterized by non-uniform distribution of stresses and strains along the bond-lines, with maximum values near the ends of the overlaps. This phenomenon can cause the premature failure of the joints, being specially critical when brittle or semi-brittle structural adhesives are considered. This has motivated the research in the field of ‘functionally graded adhesive’ (FGA) or ‘multiple-adhesive’ joints, which reduce the phenomena described through a combination of rigid and brittle adhesives with more flexible and ductile ones. In this way, these strategies allow to notably increase the joints maximum load capacity.
In this field, this article presents the work carried out by ITAINNOVA within the project SAFEJOINT. Specifically, the potential of the techniques based on ‘banded’ gradings as approximations of the continuum gradings is analysed. The study is focused in aluminium-composite single lap shear (SLS) joints with epoxy adhesives.
The work done covers both the numerical optimisation of the joints and the fabrication and testing of samples in order to verify experimentally the potential for improvement of the technique comparing with mono-adhesive joints. Finally, an example of application of the technology is presented.

== Full document ==
<pdf>Media:Draft_Content_350992336native-articles-240.pdf</pdf>

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 [[Image:Chiminelli_et_al_2019a-image19-c.png|600px]]
-'''Figure 16.''' Load vs. Displacement curves obtained from the bending tests. The red curves correspond to the test of the aluminium frame alone (S1). The curves in blue correspond to the demonstrator (S2, aluminium structure + the composite panel). The green curves correspond to the composite panel bonded with the flexible adhesive.
+<div class="center" style="width: auto; margin-left: auto; margin-right: auto;">
-</div>
+<span style="text-align: center; font-size: 75%;">'''Figure 16.''' Load vs. Displacement curves obtained from the bending tests. The red curves correspond to the test of the aluminium frame alone (S1). The curves in blue correspond to the demonstrator (S2, aluminium structure + the composite panel). The green curves correspond to the composite panel bonded with the flexible adhesive.
 The main parameters that can be obtained from these curves (in this case, the stiffness and the maximum load) are resumed in Table 1.

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 Taking into account this, the structure defined is shown in Figure 11. The ensemble is composed by a sandwich composite panel (2 mm glass fibre composite skins and a 25 mm PET core) bonded to an aluminium external frame (section with variable thicknesses between 2 mm and 6 mm). In this case, the grading has been designed specifically for the load cases of interest through a set o simulations of the full component and using sub-modelling techniques to analyse in detail different geometric and material parameters.
 <div class="center" style="width: auto; margin-left: auto; margin-right: auto;">
 <span style="text-align: center; font-size: 75%;">'''Figure 11.''' Demonstrator selected as application example.</span></div>
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-  [[Image:Chiminelli_et_al_2019a-image15.png|600px]] </div>
+  [[Image:Chiminelli_et_al_2019a_3037_chiminelli_fig12.png|600px]] </div>
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-  [[Image:Chiminelli_et_al_2019a-image16-c.png|312px]] </div>
+  [[Image:Chiminelli_et_al_2019a_9626_chiminelli_fig13.png|312px]] </div>
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 The results are plotted for each actuator (F1 and F2) separately in Figure 16.
 [[Image:Chiminelli_et_al_2019a-image19-c.png|600px]]
 '''Figure 16.''' Load vs. Displacement curves obtained from the bending tests. The red curves correspond to the test of the aluminium frame alone (S1). The curves in blue correspond to the demonstrator (S2, aluminium structure + the composite panel). The green curves correspond to the composite panel bonded with the flexible adhesive.
 The main parameters that can be obtained from these curves (in this case, the stiffness and the maximum load) are resumed in Table 1.
-[[Image:Chiminelli_et_al_2019a-image20.png|600px]]
+<div class="center" style="width: auto; margin-left: auto; margin-right: auto;">
 It can be seen that the difference in terms of stiffness between the demonstrator (with the FGA) and the aluminium frame is approx. 123%. Moreover, the demonstrator presents also a significantly higher stiffness comparing with the panel bonded with the flexible adhesive (53% higher).

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 <div class="center" style="width: auto; margin-left: auto; margin-right: auto;">
-  [[Image:Chiminelli_et_al_2019a-image13.png|534px]] </div>
+  [[Image:Chiminelli_et_al_2019a_2240_chiminelli_fig10.png|534px]] </div>
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 As mentioned, the grading strategy proposed is based on mixtures of two base structural adhesives: a relatively brittle one and a more flexible one. This allows adhesives with intermediate mechanical properties to be created. Then, the joints can be optimized seeking not only the best geometric parameters but also the best mechanical properties distribution. In order to be able to mix two adhesives to generate a new adhesive with tailored properties, the materials must i) be chemically compatible, ii) have enough different mechanical properties to produce significant improvement in the joints responses, and iii) be able to be polymerized using a common curing cycle (both the adhesives and their mixtures). The adhesives chosen for the study were the Scotch-Weld EPX Epoxy DP490 (brittle) and the DP190 (more flexible) from the same series (sold by 3M). Both adhesives and some mixtures created using them (50% DP490–50% DP190 and 70% DP490–30% DP190) were characterized through tensile tests. The test specimens were manufactured according to [9] with standard dimensions. Static tensile tests were conducted using a MTS Universal Testing Machine with a load cell of 100 kN at a constant cross head speed of 1.0mm/min. All tests were conducted at room temperature. The mechanical behaviour obtained in terms of the true stress and true strain for the base adhesives and different mixture ratios is plotted in Fig. 1. This graph shows how the mixture of the two adhesives effectively generates materials with resultant intermediate mechanical properties.
-[[Image:Chiminelli_et_al_2019a-image5.png|600px]]
+[[Image:Chiminelli_et_al_2019a_1374_chiminelli_fig1.png|600px]]
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