Experimental analysis of the forming behavior of ash wood veneer with nonwoven backings

Abstract

In the present study, the forming behavior of veneer with nonwoven backings was analyzed. The paper contributes to the lack of data on numerical predictions of the formability of veneers for the manufacturing of automotive trim parts. Tensile and shear tests were carried out at normal climate conditions and after water immersion to obtain material parameters for a transverse isotropic material description. The Tsai Wu failure criterion was applied to the estimation of strength under different stress combinations. Analysis of the directional deep drawing capacity of the veneer laminate was done by the Nakajima test. Stress states from biaxial to uniaxial were induced into the material depending on the geometry of the sample. Strains were evaluated locally until material failure using the digital image correlation method. Major strain was defined in the direction perpendicular to the grain. Increasing major strain was found from biaxial to uniaxial stress states. Highest strain limits were found for wet veneers tested with heated forming tools. Cracks occurred in the early wood zone for all geometries and propagated in the direction parallel to the grain. Generally, the Nakajima test is suitable for the evaluation of the formability of veneer laminate sheets. The presented data and, in general, the suggested experimental program can be used for the development and validation of veneer laminate material models for forming simulations.Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Modelling Inhomogeneity of Veneer Laminates with a Finite Element Mapping Method Based on Arbitrary Grayscale Images

“…Under a prescribed displacement from the boundary condition, the LW zones took higher stresses due to higher stiffness ( Figure 11 a). The results in the transverse direction showed the characteristic strain distribution with higher strain concentration in the EW zones, which was observed as well in reference [ 14 ] ( Figure 11 b). Failure occurred in one EW zone as expected.…”

“…Immersion was done at room temperature for one hour until constant mass was reached. The procedure in detail and a full characterization of the material is depicted in reference [14]. Tensile tests were carried out with a standard testing device (Inspekt 10, Hegewald & Peschke, Nossen, Germany).…”

“…There was only a small range specified for because the EW zone is acting like a predetermined failure zone and thus EW strength coincides with the global strength. Poisson’s ratio was kept constant for both EW and LW according to measurements of reference [ 14 ], whereas was adjusted automatically keeping the symmetry condition of the stiffness tensor: …”

“…Constituent damage parameters according to Equations (9)- (14) were defined as variables with ranges specified based on the preliminary, experimental observations (see Section 2.1.2). That way, LW was assumed to have higher Youngs´s moduli , higher strength or , and lower ultimate The simulation of the tensile test was realized by fixing the bottom edge nodes and applying a prescribed translational displacement to the upper edge nodes.…”

“…There was only a small range specified for Y T,EW because the EW zone is acting like a predetermined failure zone and thus EW strength coincides with the global strength. Poisson's ratio ν 12 was kept constant for both EW and LW according to measurements of reference [14], whereas ν 21 was adjusted automatically keeping the symmetry condition of the stiffness tensor: Element erosion was triggered once the effective strain of 0.6 was reached. Within the optimization setup, the d-optimal algorithm was chosen to find optimal combinations of the continuous parameters.…”