MULTI AXIAL FATIGUE DESIGN OF LASER WELDED PLASTIC PARTS

摘要

Complex plastic structures need to be joined in case of function integration or to simplify manufacturing. As joining technology for plastic a lot of different processes are available and well evaluated. The "designer" can choose a joining technique depending on the parts which have to be joined. One such joining technique is the laser welding process. The laser works without contact to the parts' surfaces, produces laser welded joints with excellent weld line qualities and with a high degree of automation and reproducibility. Often the laser welding process is used for joining the housing of electrical components and microcomputers in different fields of application. These housings protect the electrical devices from environmental and mechanical loadings. It is a great challenge to design these parts reliably and to consider all possible effects on service life. Methods for the design of such parts are very complex in use and need a lot of different input data. Material data concerning static and cyclic loading and especially multiaxial loading are often not available. In this paper a method currently being developed is presented for the fatigue design of multi axial loaded laser welded plastic parts. This method uses a local concept to determine the stresses in the weld line. To this end, a fictitious notch radius is modelled and analysed via the finite element method in order to determine the local strain energy density in the weld line for a number of loading scenarios. Experimental multi axial fatigue tests of a tubular laser welded test specimen (MultiWeldTester) made of Polypropylene serve as material data input for the concept. The loading conditions are tension and torsion as well as in phase multiaxial tension-torsion (Figure 2, left). The validation load case is internal pressure, again using the MultiWeldTester as a specimen.