Abstract
ABSTRACT Adhesive bonding is increasingly used in numerous industrial branches (aeronautics, space, etc.) for the many advantages this technique features. The quality of the adhesive bonds depends on diversified factors, and bonding defects within the joints are common. These defects may take the shape of pores, of various sizes, which are a possible threat to the good mechanical strength of the joints. These pores may create unwanted stress concentrations, and they are susceptible to locally weaken the adhesive joints. As they are created during the bonding process, the hypothesis that the bonding and curing conditions should influence their properties is well-founded. In order to validate this assertion, adhesively bonded samples were made, for different adhesives and different curing cycles. In particular, the influence of the peak temperature reached during the curing cycle was studied. The pores in the joints were then observed and studied using X-ray microtomography. The performances of the segmentation technique developed for the data processing were studied beforehand on synthetic data, in order to identify the limitations of the suggested methodology and to quantify the uncertainty on the computed quantities. It was found that a higher curing temperature may induce noticeable pore growth phenomena (mainly dilation and coalescence). In particular, this growth seems to be predominant halfway-through the thickness of the joints, resulting in an observable decrease in the effective section.
Highlights
Structural bonding has known a surge in use and popularity in the past two decades, for several reasons: (i) this technique allows engineers to design lighter and more energy-saving structures, (ii) it is well-suited to multimaterials assemblies, (iii) it paved the road to mechanical assemblies using materials incompatible with traditional techniques, and (iv) bonded structures feature fairly interesting stress distribution properties
It is possible to carry out various considerations on these datasets, whether geometrical or microstructural
The surfaces of the substrates are not perfectly parallel to one another. This is most certainly caused by the machining of the substrates, the mechanical treatment applied to the bonding surfaces and more generally an imperfect bonding process
Summary
Structural bonding has known a surge in use and popularity in the past two decades, for several reasons: (i) this technique allows engineers to design lighter and more energy-saving structures, (ii) it is well-suited to multimaterials assemblies, (iii) it paved the road to mechanical assemblies using materials incompatible with traditional techniques (welding, bolting, riveting, etc.), and (iv) bonded structures feature fairly interesting stress distribution properties. Due to the numerous elements impacting the quality of the joint, bonded structures are highly sensitive to defects which may occur during the bonding process Among these commonplace defects that cannot be avoided in standard bonding conditions, one may reference the creation of pores throughout the mixing, bonding, and curing steps. These pores could possibly be a significant disturbance to the good mechanical resistance of the bond, as (i) they decrease the cross-section of the joint, (ii) the continuum and the stability of the adhesive are challenged and put at risk, (iii) they may induce unwanted stress concentrations, and (iv) they may lead to predisposed crack propagation paths within the material. As these voids within the material are created during the bonding and the curing of the adhesive, it is fair to hypothesise that the bonding conditions and the curing conditions should have an influence on their characteristics (mainly number, volume fraction, and size)
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