Rakenteiden Mekaniikka

Alkusanat

Jarkko Niiranen — Mon, 23 Jun 2025 00:00:00 +0300

Design of a non-linear wire-rope tuned mass damper – linearized model-based approach

Samuli Rytömaa, Sampo Laine, Raine Viitala — Mon, 23 Jun 2025 00:00:00 +0300

Wire rope springs are used in tuned mass damper applications due to their inherent energy dissipation properties, low cost, thermal stability and mechanical robustness. The dynamics of the wire rope springs are characterized by the relative sliding of the strands inside the wire ropes. Damping of the wire rope consists of the friction loss between the wire strands and structural damping under mechanical deformations. Moreover, the relative sliding alters the effective stiffness of the structure. These properties are non-linear and depend on the vibration amplitude. Modeling these non-linear dynamics has proven difficult, and no clear standard approach for design exist. In this paper, an amplitude based linearization framework is used to model the system dynamics for wire rope based tuned mass damper. The vibration suppression performance of the wire-rope tuned mass damper is compared to a linear tuned mass damper with similar mass ratio. The performance of the two dampers are compared for a system with multiple degrees of freedom, and the possible mistuning of the dampers is also considered. The results show that wire rope based tune mass damper, in comparison to a conventional linear tuned-mass damper, can suppress vibrations with a wider frequency band and under varying natural frequencies.

Finite element methods for elastic contact: penalty and Nitsche

Tom Gustafsson, Rolf Stenberg — Mon, 23 Jun 2025 00:00:00 +0300

We consider two methods for treating elastic contact problems with the finite element method; the penalty method and Nitsche's method. For the penalty method, we discuss how the penalty parameter should be chosen. Both the theoretical analysis and numerical examples show that an optimal convergence rate cannot be achieved. The method is contrasted to that of Nitsche's method which is optimally convergent. We also give the derivation of Nitsche's method by a very simple consistency correction of the penalty method.

Simulation of hydrogen-induced failure in high strength steel

Stefan Lampenscherf, Gia Khanh Pham — Mon, 23 Jun 2025 00:00:00 +0300

We present a coupled chemo-mechanical and fracture mechanics-based model capable of predicting the onset of hydrogen-induced macroscopic crack growth as a function of material, loading and environmental variables. The model is implemented using the commercial multi-physics simulation package COMSOL and solved as a coupled deformation–diffusion problem to define a fracture criterion as a function of residual and externally applied loads and hydrogen concentration. The local hydrogen-induced material damage is approximated by a parametric dependency of local fracture resistance on hydrogen concentration. As an example, we demonstrate the ductile-brittle transition of the failure pattern of a double-notch specimen under tension w/o and w/ hydrogen loading.

Computer vision framework for crack detection and estimation of air leakage through the straight-through cracks in buildings envelopes

Maliheh Jahanbakhsh, Andrea Ferrantelli — Mon, 23 Jun 2025 00:00:00 +0300

Over time, buildings inevitably experience physical and functional deterioration. Regular and accurate inspections are essential to ensure safety and functionality, helping to avoid hazardous and uncomfortable conditions. Cracks, a common indicator of structural distress, also facilitate air infiltration due to pressure differences between the interior and exterior. The precise and efficient detection of cracks, along with the estimation of air infiltration through these cracks, is therefore critical for civil engineering applications that aim to reduce energy consumption and enhance indoor air quality. This paper introduces a novel image processing framework for automatic detection of cracks in building envelopes, coupled with the measurement of indoor and outdoor air parameters, which could be used to assess crack size and to estimate air infiltration rates by using heat transfer and fluid mechanics formulas. A computer vision-based system for automatic crack detection is first developed by using the Python OpenCV library through binarization, Otsu's thresholding and Canny operator; geometric quantification of the cracks is then obtained via skeletonization, and the resulting morphological characteristics of the cracks are finally used to estimate airflow by using common fluid mechanics formulas.

Indentation hardness of 3D-printed metals

Mon, 23 Jun 2025 00:00:00 +0300

Additive manufacturing is typically used for rapid prototyping and the production of small to medium quantities of complex parts. The quality of 3D-printed metallic parts depends on the printing process parameters and material behaviour. In order to characterize the mechanical properties of materials, the nearly non-destructive micro-indentation hardness testing of additively manufactured steel and aluminium alloy using Laser Powder Bed Fusion technology was investigated in this study. The micro-hardness and modulus of elasticity of hot work tool steel AISI H13 (1.2344) were evaluated to study the influence of printing parameters, such as laser power and laser scanning speed. While no pile-up or sink-in effects were detected in the steel samples, the pile-up effect was observed during the hardness measurement of the aluminum alloy AlMg1Si AA-6061. Since the pile-up effect leads to an overestimation of the measured hardness, a correction factor was applied to account for this deviation, resulting in an adjusted value approximately 7% lower than the initially measured hardness for the aluminum alloy. In addition, the statistical reliability of the measured hardness properties of the 3D-printed metals was evaluated using the Weibull distribution. It was demonstrated that the indentation test is highly suitable for analyzing small additively manufactured samples with relatively little effort while delivering high statistical reliability and providing meaningful insights into the mechanical properties of the materials, such as micro-hardness and indentation modulus.