Janis Sliseris

Virtual characterization of MDF fiber network

A virtual design method for medium density fiberboards (MDF) is proposed with the aim to optimize the fiber orientation and lay-up of MDF. The new method estimates the stiffness and strength by using microstructure models of the MDF fiber network. The virtual design is used to improve the manufacturing technology of MDF plates with multilayer oriented fiber structure. Experimental investigations of the mechanical behavior of MDF microstructure for various fiber geometries, glue content and distribution are complicated, time consuming and expensive. On the other side, virtual microstructure design allows to develop a new wood fiber based material with less experimental work. Microstructure models help to better understand the non-linear damage mechanical behavior of a wood fiber network depending on fiber geometrical parameters. Such parameters as crack distribution and fiber deformation on micro-scale level are complicated to experimentally measure, but possible to model using computer simulations. The virtual design tool requires less empirical data. The model takes into account information on average wood fiber orientation, fiber diameter, fiber length and mechanical properties of wood fiber cell wall and glue. The numerical method for strength and stiffness analysis of MDF microstructure was calibrated using standard MDF with non-oriented fibers. It turned out that this method gives precise results for MDF with oriented fibers and even with multilayer structure. The proposed virtual microstructure design tool can significantly improve and speed-up the optimization manufacturing technology of MDF and other wood fiber based composites.

Curvature analysis for asymmetrical multi-layer composite

Curvature analysis for asymmetrical multi-layer composite One possibility to reduce material consumption in bent construction is flat plate replacement with curved or saddle shaped plate (shell). This solution is beneficial in case of plywood sheet, provided that curved or saddle shaped plates are made in widely used multilevel plywood presses with parallel shelves. Curvature is gained by using layers with required physical properties, geometric dimensions, orientation, creating structurally asymmetrical material, relative to mid-surface. While it is conditioning in different moisture-temperature conditions, it gains projected shape.

Numerical Simulation and Experimental Verification of Hollow and Foam-Filled Flax-Fabric-Reinforced Epoxy Tubular Energy Absorbers Subjected to Crashing

Numerical methods for simulating hollow and foam-filled flax-fabric-reinforced epoxy tubular energy absorbers subjected to lateral crashing are presented. The crashing characteristics, such as the progressive failure, load–displacement response, absorbed energy, peak load, and failure modes, of the tubes were simulated and calculated numerically. A 3D nonlinear finite-element model that allows for the plasticity of materials using an isotropic hardening model with strain rate dependence and failure is proposed. An explicit finite-element solver is used to address the lateral crashing of the tubes considering large displacements and strains, plasticity, and damage. The experimental nonlinear crashing load vs. displacement data are successfully described by using the finite-element model proposed. The simulated peak loads and absorbed energy of the tubes are also in good agreement with experimental results.