Mechanical behaviour of thick structural adhesives in wind turbine blades under multi-axial loading

Testing mechanical performance of adhesively bonded composite joints in engineering applications: an overview

“…The thickness of adhesive bondlines in large wind turbine rotor blades (WTRBs) can reach or exceed 20-30 mm in several areas to compensate for manufacturing tolerances. [282][283][284][285] Two-component paste adhesives are used for such joints, and due to the common fabrication procedures, the resulted bondlines contain a significant number of fabrication defects (voids). It is expected, however, that with modern technologies for mixing and dosing the void content can be significantly reduced.…”

“…[285] difficult to scale down the thickness of the bondline and derive realistic scaled joints for the down-scaled blade. [289] Adhesive bondline thickness of wind turbine blades is much larger, [10,310] hence, the problem of down-scaling for experimental investigations becomes more pronounced. Such scaling problem was identified very early by Hart-Smith [16] who recognized that the behavior of typical long-overlap structural bonded joints is frequently very different from equivalent short-overlap test specimens.…”

“…[321] design process. Thus, for better understanding of the damage process and the failure patterns observed in thick bonded joints, more knowledge is required on the multi-axial behavior of the bulk adhesive itself, [282] while attention should be paid to the residual strains developing in the adhesive bulk due to the exothermic curing as was mentioned earlier in this document. Thick bondlines can lead to higher exothermic peak producing higher residual strains.…”

Costs of repair of wind turbine blades: Influence of technology aspects

“…The thickness of adhesive can be of the order up to 30 mm for the blade of 70 m and above. 42,43 Assuming m = 0.5, one can estimate that the post-repair lifetime (time until next repair) decreases by 7%, if the total section area of voids is increased from 40 to 4 mm and by 25% if m = 2.…”

“…If the S–N curve of the polymer material is given as N = aσ − m , where N —lifetime (amount of cycles to failure) a and m —parameters of the material, then the lifetime of the layer with given voids is Near a spherical void, the stress reaches 3 times of remote applied stress. Assuming that the damage in voided material starts not in arbitrary place, but in the vicinity of void, in the point of highest stress, the lifetime of a layer with void is reduced by The thickness of adhesive can be of the order up to 30 mm for the blade of 70 m and above 42,43 . Assuming m = 0.5, one can estimate that the post‐repair lifetime (time until next repair) decreases by 7%, if the total section area of voids is increased from 40 to 4 mm and by 25% if m = 2.…”