Abstract
For detailed stress distribution analysis of bondlines, non-linear finite element analysis (FEA) is necessary. Depending on the load case in relation to shear and tension/compression adhesives show a different behaviour of the yield point [1], which is e.g. included in the Mahnken and Schlimmer [2] model. State of the art for biaxial tested adhesive material-characteristics is the use of bonded tubular butt joints under variable torsion and tension loads. Important for the quality of the determined material values is the alignment of both tubes. The quality is significantly improved, if both tubes are aligned perfectly coaxial. Also, the bondline has to be free of voids. In previous work [3], Wölper investigated the effects of coaxial and angle deviations for the results of material characteristics using FEA. A slight deviation has a strong negative impact to the results. Particularly for thin film-adhesives with elevated curing temperatures, the change of viscosity of the adhesive and the thermal expansion of the tubes must be considered. Previous investigations regarding the manufacturing of the specimens showed shortfalls in joining and curing them. Due to voids, geometric deviations or poorly-bonded tubes, no reliable results were achieved yet. Therefore, a new assembly-device is developed and tested. The results show well joined tubes without a significant angle deviation and with an average of 40 µm in coaxial deviation. The thickness of the bondline can be adjusted and is constant over the whole diameter. The new joining-device enables the testing of tubular butt joints to determine biaxial material values of thin higher-temperature-cured film-adhesives. The device is patented to DE 102017114538.9.
Highlights
The results show well joined tubes without a significant angle deviation and with an average of 40 μm in coaxial deviation
The new joining-device enables the testing of tubular butt joints to determine biaxial material values of thin higher-temperature-cured film-adhesives
In order to use the potentials of carbon-fibre-reinforced-polymer (CFRP) as a light weight structure material, CFRP material characteristics are important
Summary
In order to use the potentials of carbon-fibre-reinforced-polymer (CFRP) as a light weight structure material, CFRP material characteristics are important. Film adhesives with elevated curing temperatures like Hysol® EA9695 [6] typically cure above 120 °C This causes a problem through thermal expansion during the cure process. By clamping only one tube and guiding the other, consolidation force is applied by an additional weight on the guided adherend to provide the sufficient pressure to the adhesive. With a weight on top of the tubes, a consolidation force is applied to the bondline to prevent any voids and air inclusions. Calculation of design parameters The calculation of core and sealing diameters uses the simplified analytical equation for thermal expansion of solid materials l = l0 · α · T (1). To calculate the different diameters of the sealing element and the core, Eq 1 has to be transformed and inserted by following variables (Table 1). Measurements reveal the point of lowest viscosity of 1000 Pa s is at 90 °C [12] for EA 9695
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