**7. Conclusions and forecast**

104 Metal Forming – Process, Tools, Design

schematically.

between adhesive thickness, surface roughness Rmax and bond strength is shown according to [8]. It is recommended that the adhesive thickness is equal to the surface roughness Rmax. A smaller thickness avoids a complete coating. To achieve improvements in damping behavior the surface roughness and the thickness of the adhesive layer has to be reduced.

Numerical die-bending results of side length L = 40 mm are shown in Figure 10. Now, the strain distribution of the upper and lower fiber of both layers are shown and compared with the plastomechanical preliminary design. Computation according to [25] offer a k-factor of k��� � ��, which fits quite good for the maximum strain, calculated with a numerical method in the midst of the bending. The real positions of the neutral axis are shown

**Figure 19.** Numerical results of elongations of the external fibers (bending axis at distance t = 40 mm)

Thee founded results to influence the forming behavior, are further tested with simulation of v-die-bending. With a punch radius of r = 8,5 mm, a side length of L = 40 mm and a constant thickness of the sandwich s = 1,4 mm, the five typical constellations for different

**6. Optimization of vibration damping sandwich sheets** 

Inaccuracies of preliminary design are ascribed to the [25]:

• Negligence of elastic behavior of the cover sheets

• Linearization of the material properties • Linearization of the elongation distribution

• Constant strain over bending angle

• Constant thickness during and after the bending process

**6.2. Forming tendencies of multilayer sandwich sheets** 

**6.1. Comparison of numerical and plastomechanical calculations** 

At the Chair of Forming Technologies at the University of Siegen vibrations damping composite sheets were investigated regarding their forming limits.

During forming, failure modes like delamination, displacement and buckling of the cover sheets occur. The mechanical properties of the metal layers are determined by uniaxial tensile tests. Tensile shear tests are carried out under variation of the shear velocity. The numerical calculations are calibrated with the tensile shear test. To verify the adhesive description, maximal tension and displacement in normal direction will be proved.

Forming of Sandwich Sheets Considering Changing Damping Properties 107

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A plastomechanical preliminary design has been developed for sandwich sheets with a viscoelastic and shear transmitting interlayer. Especially displacement and delamination are described with preliminary design and verified with numerical calculations. But this plastomechanical preliminary design shows improvable deliverables. Especially the inaccuracies of the strain distribution over thickness and bending angle should be improved. Therefore many experimental forming tests with different materials are planned.

Instead of symmetrical sandwiches, significant improvements can be achieved by e.g. reducing the thickness of the outer metal layer. With increasing the number of sheets the total thickness of the composite can be achieved. On the other hand thin inner layers tend to buckling. The buckling tendency should be investigated further.
