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.

Failure and deformation behavior of veneer laminates of ring porous wood species vary with the individual arrangement of early- and latewood zones over a veneer sheet. Therefore, a method is presented, where local failure and damage modes are considered for finite element models with respect to forming simulations, during the development process of automotive interior trim parts. Within the mapping tool Envyo, a routine has been realized for the discretization of early- and latewood zones from ash wood veneer surfaces to finite element meshes. The routine performs the following steps: reading a grayscale image of known size and generation of a point cloud based on the number of pixels; transformation and scaling of the generated point cloud to align with a target finite element mesh; nearest neighbor search and transfer of grayscale values to the target mesh element centroids; assigning part and therefore material properties to the target elements based on the mapped grayscale value and user-defined grayscale ranges. Due to the absence of measurement data for early- and latewood, optimization was used to identify locally varying material constants. A set of material input parameters for early- and latewood was created, calibrating the force-displacement response of tensile test simulations to corresponding experimental curves. The numerical results gave a very good agreement to the failure behavior of tensile tests in the loading directions longitudinal and transverse to the fiber orientation. Furthermore, in a stochastic analysis the characteristic distribution of tensile strength and ultimate strain could be verified for the suggested procedure. The introduced modelling approach can be applied for the discrete implementation of inhomogeneity to numerical simulations.

In automotive manufacturing, laminated veneer sheets are formed to have 3D geometries for the production of trim parts with wood surfaces. Nowadays, investigation of the formability requires extensive tests with prototype tools, due to the brittle, anisotropic and inhomogeneous material behaviors. The present paper provides numerical methods for the simulation of the forming process of veneers with non-woven backings. Therefore, a conventional forming process of an interior trim part surface is carried out experimentally and numerically, using veneer samples with different individual textures originating from the characteristic growth ring structure. Gray scale images of these samples are mapped to finite element models to account for the wood-specific structure. The forming simulation process comprises two steps, where a gravity simulation depicts the initial position of the blank sheets and the closing of the tool induces the material deformation. The virtual forming of the digital twins accurately reproduces the wrinkling behavior observed in experimental studies. Based on the proposed methods, the design process of manufacturing wood trim parts based on tedious prototype tooling can be replaced by a fully virtual forming process taking into account the individual growth-related properties of the veneer structure.

In dieser Arbeit wurde ein Prüfverfahren angewendet, das statische, zyklische Belastung von Klebstofffugen infolge Quellen und Schwinden des Holzes simuliert und plastische Verformungen im niedrigen Lastbereich aufzeigt. Es wurde das elastische Verhalten von Zugscher‐Prüfkörpern, welche aus Buchenholz verklebt mit drei verschiedenen Holz‐Klebstoff arten (MUF, PRF, PUR) hergestellt wurden, unter zyklischer Zug‐ und Druck‐Belastung untersucht und die Verlust‐ und Speicherenergie ausgewertet. Alle getesteten Verkle bungen wiesen bereits bei sehr niedrigem Lastniveau von 3 MPa viskose Anteile auf, die mit höherer Last zunahmen. Für die PRF‐Verklebung wurde bei der Laststufe von 7 MPa ein elastischeres Verhalten beobachtet als für die übrigen Ver klebungen. Die für die PUR‐Verklebung erfasste ansteigende Verlustenergie deutet auf eine Aufweichung der Klebstofffuge hin.