Lighweight vehicle construction is desirable nowadays, from the point of view of economic considerations and environmental issues. A reduction of vehicle mass may be achieved, in principle, by choosing from a spectrum of lighter materials. The trend is to an increased usage of higher strength steels, already having more than 50 % market penetration. The very-special strength properties of these steels do bring with them some extraordinary production and joining issues that bonding is able to solve: Spotwelding of these steels is more difficult, uses higher currents and pressures that lead to faster electrode degradation. Since hybrid bonded/welded joints allow a reduction in weldcount, this alone somewhat relieves indirectly these problems. Even more critical for these newer steels, is that the heat-affected-zones of the welds suffer embrittlement which the much more evenly-stressed bonded joint would circumvent entirely. For longterm dynamic loading this is an especially important consideration. The already better long-term dynamic joint integrity of bonded joints, in the case of softer steels, is clearly superior by orders of magnitude when applied to high strength steels. The dynamic impact performance of bonded joints, for temperatures of practical importance, are very good. In addition the extra sealing offered by the adhesive also improves the corrosion protection. Since higher strength steels show a natural weakness regarding stress corrosion, bonding takes on an even more important role for these steels. Ageing tests, conducted over a broad range, together with practical experience in structurally-bonded automobiles support this. Modern high strength steels present a main thrust towards reducing vehicles mass. Bonded technology improves the efficient usage of these materials and is thus of central importance in vehicle constructions. Future improvements in adhesives will continue to secure a key role for this joining technology; the results presented here of newer generation adhesives already illustrate this. It has been possible recently to improve the toughness of adhesives, resulting in a new generation of structural adhesives. Application of these adhesives leads to clear improvements; especially the dynamic joint integrity from a temperature range of ca. 80 deg C to even as low as - 40 deg C. One notices a reduction in the strength of the joint with a reduction in yield point, but the new generation adhesive clearly improves on the older type. Quasi-static joint strength remains at a constant, high level with the samples only failing after the yield point of the metal.
The same structural strength in spite of thinner sheets
Dieselbe strukturelle Festigkeit trotz dünner Bleche
Adhäsion - Kleben & Dichten ; 53 , 3, Extra: Adhesives & Sealants ; 14-18
2009
5 Seiten, 6 Bilder, 1 Tabelle
Article (Journal)
German
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