Experimental Finite Element Method Research Articles

G-Lattices: A Novel Lattice Structure and Its Generative Synthesis Under Additive Manufacturing Constraints

Abstract This paper introduces a novel strut-based lattice structure that is called G-Lattices and a method for their generative synthesis. Given additive manufacturing (AM), user and geometrical constraints, G-Lattices can automatically be generated via a particle tracing algorithm, which places/moves particles in a lattice unit cell. As a proof of concept, several G-Lattices are manufactured through an AM machine. Additionally, the proposed G-Lattice synthesis method is customized for the models under vertical loading, which are validated through finite element method experiments and have greater strength over volume ratios compared to conventional lattice structures.

Probabilistic and stochastic analysis of the effective properties for the particle reinforced elastomers

The main issue in this paper is determination of the effective properties of the reinforced elastomers in terms of uncertainty of the reinforcing particles ratio or the applied strain rate. We discuss in this context various concepts for calculation of those properties like general, cluster-dependent as well as strain-dependent models and also different probabilistic strategies – thanks to analytical, simulation and the tenth order perturbation-based approaches. This is done to determine the most optimal strategy in terms of a time and computer power consumption and to compare an accuracy of the basic probabilistic characteristics determination, especially in the perspective of further usage in the Finite Element Method experiments with real and the homogenized elastomers. Numerical experiments provided for the elastomers reinforced with the carbon black and silica using the computer algebra system MAPLE show a perfect agreement of all those techniques for general models, a lack of analytical solution for the power-law breakdown theory and the very good agreement of the first two probabilistic moments determined according to the nonlinear concepts. Finally, we discuss also the stochastic aging of the reinforced elastomers in terms of the linear increase of the strain rate with the coefficients defined uniquely as the Gaussian random variables with the given first two probabilistic characteristics.

Influence of intermediate deformation rates in softwoods characterized with fracture resistance R-curves

Fracture resistance curves of Norway spruce were evaluated over a range of crosshead speeds between 0.05 and 200 mm/min using compact tension specimens. The fracture resistance curves were determined via J-integral K R versus Δa (crack extension) using hybrid experimental–finite element method with stepwise quasi-static and transient dynamic analysis. Coupling experiments and high-speed camera with a rate of 0.5–135 frames/s capture enabled determination of crack kinetics and velocities. Digital image correlation method was employed to evaluate strain distribution maps of the fracture process zone. Deformation measurements suggested strong strain localization and significant influence of the loading rate. The most distinct strain map was evaluated for the loading rate of 200 mm/min, suggesting inertial effects. Rising fracture resistance develops for smaller crack lengths (0.15–0.20 a/w) for all loading rates, with an increase of up to 20–50% compared to initiation values. Fracture resistance R-curves were evaluated for single individual specimens as well as for averaged load–deformation responses, which hide strong localisations in single responses. Influence of deformation rate on the shape and magnitude of fracture resistance curves is significant. Inertial effects in transient dynamic response give rise to twofold higher fracture resistance of softwoods compared to quasi-static resistance.