Jo vuodesta 1968 Rakenteiden Mekaniikka -lehden aiheina ovat olleet kiinteiden ja virtaavien aineiden teoreettinen, laskennallinen ja kokeellinen mekaniikka sekä näihin liittyvä matematiikka ja sovellukset. Esimerkkeinä voidaan mainita rakenteiden staattinen ja dynaaminen lujuusanalyysi, monikappaledynamiikka, virtausmekaniikka, rakenteen ja virtauksen vuorovaikutus, rakenteiden ja koneiden suunnittelu ja mitoitus, rakenteiden optimointi, rakenteiden toimivuus ääritilanteissa, älykkäät koneet ja rakenteet, värähtelymekaniikka, kontaktimekaniikka, roottoridynamiikka, murtumismekaniikka ja väsyminen, termomekaniikka, maa- ja kallioperän mekaniikka, rakenteiden materiaalitekniikka, uudet materiaalit, dynaamisten systeemien optimaalinen säätö, elementtimenetelmät ja -analyysi, biomekaniikka, mikromekaniikka, mekaniikan teolliset ja lääketieteelliset sovellutukset sekä mekaniikan ja lujuusopin opetus. Vertaisarvioitujen tieteellisten artikkelien lisäksi lehti julkaisee myös kirjallisuuskatsauksia, lyhyitä kommenttikirjoituksia lehdessä julkaistuista artikkeleista ja lyhyitä raportteja lehden aihealueisiin liittyvistä, mielenkiintoisista teknisistä menetelmistä tai ratkaisuista. Näiden kirjoitusten pituus on rajattu kuuteen sivuun.
Improving quality of torsional analysis of prismatic beams by using an interpolated warping function
This paper examines the torsion of beams with undeformable cross-sections. A novel approach is proposed, in which an interpolated warping function is defined as a continuously differentiable function across the entire cross-sectional area. This formulation enables methods that require the warping value to be accessible as a continuous function at any point within the section. The approach facilitates deformation analysis within the framework of three-dimensional elasticity, employing continuum-based beam elements governed by general continuum mechanics material laws. The primary objective of this study is to establish a general method for determining warping functions for complex cross-sections, intended for future applications in the absolute nodal coordinate formulation. The approach does not replace earlier methods, which have proven highly efficient and even suitable for hand calculations. Instead, it provides a general-purpose framework that can yield improved accuracy in certain cases. Whereas traditional treatments distinguished primarily between open and closed profiles, the present formulation emphasizes the importance of recognizing the nature of each profile and selecting interpolation methods accordingly.
Copyright (c) 2026 Simo Nikula, Aki Mikkola, Marko Matikainen, Timo Björk https://creativecommons.org/licenses/by/4.0
Honey Badger Algorithm for optimizing truss structures with discrete design variables
An optimization strategy utilizing the Honey Badger Algorithm (HBA) is formulated in this article for the optimal design of truss structures with discrete variables under multi-load scenarios. HBA is implemented to optimize fundamental design criteria that involve the cross-sectional areas of the truss members. Structural evaluations are conducted by analyzing different cross-sectional configurations, with the primary objective of minimizing the total mass of the structure while satisfying stress and displacement constraints. The HBA is used as a metaheuristic optimizer to explore the design domain and converge towards optimal configurations. This approach is applied to several benchmark examples, including planar and spatial trusses, and the results are compared with existing studies to assess the algorithm's performance. The optimization outcomes confirm the effectiveness and robustness of HBA in solving constrained structural optimization problems, as well as its ability to achieve rapid convergence toward high-quality solutions
Copyright (c) 2026 Ouadie El Mrimar, Zakaria El Haddad, Bousselham Samoudi, Othmane Bendaou https://creativecommons.org/licenses/by/4.0
Copyright (c) 2025 Jarkko Niiranen https://creativecommons.org/licenses/by/4.0
Asymmetric constant-stress arch shape in tied-arch bridges
This study focuses on the asymmetric, momentless, constant-stress form of the arch in tied-arch bridges. The most common asymmetric shape of arch bridges is caused by variations in the heights of the abutments that support them. In recent years, a number of arch bridges with asymmetrical arches have been constructed, creating distinctive and intriguing aesthetics. This article proposes a methodology for optimally designing an asymmetric arch. The use of inclined parallel hangers is demonstrated to facilitate the creation of a pleasing, moment-free, constant stress tied-arch shape. The method used to calculate the shape of a tied-arch under constant stress is verified by finite element analysis. The primary objective of this paper is to demonstrate that an asymmetrical shape can be a structurally viable option without incurring excessive additional costs.
Copyright (c) 2025 Esko Järvenpää, Anssi Laaksonen https://creativecommons.org/licenses/by/4.0
Phase field method for brittle fracture implemented with polygonal finite elements
The aim of this article is to model fracture propagation in brittle materials, such as rocks and concrete, with the phase field approach. The hybrid formulation of the phase field theory is adopted because it enables using an ad-hoc, or a problem specific, crack driving force, here of Mohr–Coulomb type, to correctly model brittle materials under compression or shear. Hybrid formulations are variationally inconsistent because the crack driving force is not the same as the one used in the underlying energy functional. They are, however, thermodynamically consistent, and computationally cheap since they allow to use a linear balance of momentum equation within the robust staggered scheme to solve the coupled system for the phase field and the displacement field. The phase field method is implemented with 2D polygonal finite elements based on the Wachspress interpolation functions. As numerical examples, typical test cases of notched samples under mode I and II loadings are simulated. Finally, a slope stability problem is solved as an engineering application.
Suomen mekaniikkapäivien 2024 erikoisnumero
Copyright (c) 2025 Timo Saksala, Mahmood Jabareen , Reijo Kouhia https://creativecommons.org/licenses/by/4.0
Indentation hardness of 3D-printed metals
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.
Copyright (c) 2025 Gia Khanh Pham, Ruth Domes, Ümit Mavis, Johannes Ernstberger, Christian Seidel, Constanze Eulenkamp, Christine Hausner-Henzel, Anh Son Nguyen, Gia Vu Pham https://creativecommons.org/licenses/by/4.0
Analysis of flow behavior of bioinks outside the 3D-printing nozzles
The major challenge in extrusion-based bioprinting for medical application is printability, which largely depends on the flow behavior of bioinks just outside the nozzle. This flow behavior is influenced by several factors, including nozzle dimensions, bioink density, bioink viscosity, surface tension of the bioink-air interface, and the desired printing speed and structure. Accurately predicting the flow behavior of bioinks outside the nozzle in advance can reduce the costs associated with experimental testing. In this work, Volume of Fluid (VOF) method under Finite Volume method (FVM) framework is used to study the flow behavior outside a single nozzle. Computational Fluid Dynamics (CFD) simulations are conducted to analyze the behavior of bioinks outside the printing nozzles and flow behaviors are compared with literature. Initial simulations are performed using water due to its well characterized rheological and physical properties, and its widespread use as a reference medium in bioink formulations. The effect of all process parameters on the flow outside the nozzle was analyzed using water as the working fluid. By applying two non-dimensional numbers, Reynolds number and Weber number, flow demarcation regimes are established for water. Furthermore, simulations are performed for boinks to predict their printability. The model predictions for the qualitative flow behavior of bioinks at different temperatures matches well with experimental data from the literature.
Copyright (c) 2025 Ashish Pawar, Ashvin Chaudhari, Eero Immonen https://creativecommons.org/licenses/by/4.0
Transient thermal stress FE-analysis method development
This research paper addresses the challenges of thermomechanically loaded components in four-stroke medium-speed engines, focusing on exhaust pipe failures due to low-cycle thermal fatigue. Wärtsilä's shift towards 100 % renewable energy has altered engine operating conditions, leading to new challenges in exhaust components subjected to fluctuating thermal conditions. The study focuses on the transient method's ability to detect phenomena during heating and cooling in stress and temperature histories, optimizing the transient analysis definitions and providing some principles for design modifications in thermal stress problems. A case study of nodular cast iron exhaust manifold is used as an example. Traditional methods using cyclic steady-state temperatures have been found insufficient, prompting the development of a more accurate transient method that uses measured temperatures during the engine's thermal cycle. The paper compares conventional steady state heat transfer analysis and two transient heat transfer analyses for defining thermal boundary conditions. The temperatures in the first transient analysis are defined accurately from the measurements, leading to more realistic results and long calculation time. The second transient analysis is improved to offer a balanced method between accurate thermal boundary definitions and shorter calculation time. The transient method reveals higher stress amplitudes in previously low-stress zones, identifying the actual critical points on the exhaust pipe.
Copyright (c) 2025 Sami Kreivi, Janne Kemppainen, Teemu Kuivaniemi, Antti-Jussi Vuotikka, Tero Frondelius https://creativecommons.org/licenses/by/4.0
Computer vision framework for crack detection and estimation of air leakage through the straight-through cracks in buildings envelopes
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.
Copyright (c) 2025 Maliheh Jahabakhsh, Andrea Ferrantelli https://creativecommons.org/licenses/by/4.0
Simulation of hydrogen-induced failure in high strength steel
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.
chemo-mechanical and fracture mechanics-based failure model
Copyright (c) 2025 Stefan Lampenscherf, Gia Khanh Pham https://creativecommons.org/licenses/by/4.0
A metamodel-based design optimization scheme for minimizing energy consumption of unconditioned residential buildings considering passive features
The demand for appliances and equipment has risen as a result of emerging technologies and increasing economic growth. The outcome is high level of energy consumption worldwide, particularly in structure and infrastructure sectors. Among these sectors, residential construction stands out as one of the primary energy consumers for infrastructure development. Thus, to construct buildings that use net-zero or nearly-zero energy, architects and engineers must prioritise energy-efficient planning and implementation. This paper aims to develop a scheme to minimize the energy consumption of an unconditioned residential building based on design optimization of passive architectural design variables. Here, a parametric model is developed by using four passive architectural design variables: orientation, window-to-wall ratio, shading depth and shading angle, This generates a large number of options for the analysis of the building's energy consumption. A metamodel-based design optimisation strategy has been implemented for a single-family, single-storey, unconditioned residential building in Guwahati City, India, with the objective to minimize energy use. The results from the case study showed that by optimizing the above-mentioned passive design strategies, the energy consumption of the considered building is lower by 52% as compared to the reference design.
Copyright (c) 2025 Shrutismita Talukdar, Subhrajit Dutta https://creativecommons.org/licenses/by/4.0
On the derivation of constant-coefficient partial differential equations for elastic shells
Here the problem of formulating a representative model problem of shell theory is considered. We study two ways to obtain a constant-coefficient expression for the strain energy density function of a linearly elastic shell. The first formulation has already been given in the context of the analysis of boundary layers in thin shells, while the other is introduced here. It appears that the essential difference between the formulations is that the constant-coefficient expressions for the strains given here depend on four geometric parameters instead of the two parameters of curvature needed by the earlier derivation. The source of this discrepancy is investigated and shown to be related to the properties of the metric tensors that are attainable by means of different parametrizations of a given surface.
Copyright (c) 2025 Mika Malinen https://creativecommons.org/licenses/by/4.0
Thermal convection in a Brinkman porous medium saturated with couple-stress nanofluid: a Galerkin weighted residual approach for different conducting boundaries
The thermal instability of a couple-stress nanofluid saturated by a porous media is studied in this article. For the porous medium, the Darcy–Brinkman model is used. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. Three cases of free-free, rigid-rigid and rigid-free boundaries are considered. For this problem, oscillatory convection is ruled out. By using the one-term Galerkin method and normal mode analysis, we solve the eigenvalue problem with Rayleigh number as an eigenvalue. The effects of Darcy number, couple-stress parameter, porosity parameter, modified diffusivity ratio, Lewis number and concentration Rayleigh number are examined analytically and graphically for stationary convection.
Copyright (c) 2025 Vinod Kumar, Pushap Lata Sharma, Deepak Bains https://creativecommons.org/licenses/by/4.0
Copyright (c) 2024 Jarkko Niiranen https://creativecommons.org/licenses/by/4.0
Kunniapuheenjohtaja Matti Rannan muistoa kunnioittaen
Copyright (c) 2024 Raimo von Hertzen, Eero-Matti Salonen https://creativecommons.org/licenses/by/4.0
Design of a non-linear wire-rope tuned mass damper – linearized model-based approach
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.
Copyright (c) 2025 Samuli Rytömaa, Sampo Laine, Raine Viitala https://creativecommons.org/licenses/by/4.0
Finite element methods for elastic contact: penalty and Nitsche
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.
Copyright (c) 2025 Tom Gustafsson, Rolf Stenberg https://creativecommons.org/licenses/by/4.0
Model of material movement on the working surface of a vibrating machine
This article presents studies related to the calculation of the peculiarities of the movement of bulk material on the working surface of a vibrating machine – for example, on a sowing surface – in terms of the intensity of the potential force field acting on the material being processed. This approach makes it possible to adjust its design to the selected technological process at the design stage of the vibrating machine, which further makes it possible to minimize energy consumption for vibration processing of bulk raw materials without reducing the quality of its preparation.
Copyright (c) 2024 V Zaselskiy, S Shved, Dmytro Popolov, I Zaselskiy https://creativecommons.org/licenses/by/4.0
A 2D mesoscale model for concrete fracture under dynamic loading
In this paper, we present a 2D mesomechanical model for describing concrete fracture behavior under dynamic loading. The aggregate-mortar mesostructure of concrete is explicitly described, while the interfacial transition zone is represented as a weak zone of finite elements around the aggregates. Concrete failure is described by a damage-viscoplasticity model based on the Drucker–Prager yield criterion and the Rankine criterion as the tensile cut-off. For the viscoplastic part of the model, the consistency approach is adopted. In the damage model, separate scalar damage variables are applied for tensile and compressive stress regimes. Uniaxial compression and tension tests are simulated as the numerical examples. The model holds some promise because it reproduces the experimental failure modes in tension and compression, and in dynamic Brazilian disc test, and predicts a realistic compressive-to-tensile strength ratio as well as the strain-rate sensitivity effect for concrete.
Copyright (c) 2025 Timo Saksala, Sulata Dhakal, Reijo Kouhia https://creativecommons.org/licenses/by/4.0
The article discusses the principles of arch design as they apply to snow vaults and presents different types such as parabolic, catenary, circular and constant stress. The parabolic momentless arch requires a constant vertical load throughout the span, resulting in a decreasing snow thickness from the crown to the base. In contrast, the catenary arch is formed by an inverted hanging chain, maintaining a uniform snow thickness throughout the structure, governed by a hyperbolic cosine function. The shape of the constant stress standalone arch is determined by the unit weight and the compressive stress, described by a logarithmic cosine function. In comparing snow arches, the article asserts the superiority of the constant stress form over the catenary and parabolic forms, highlighting its ability to span greater distances. Despite its advantages, the constant stress form has not yet found application in the construction of snow vaults. In addition, snow vaults are subject to significant deformation and require regular checks and recalculations throughout their life to ensure structural integrity.
Copyright (c) 2024 Esko Järvenpää, Antti H. Niemi, Matti-Esko Järvenpää https://creativecommons.org/licenses/by/4.0
Application of a numerical method in analyzing the operation of single-stage scissor lifts
Scissor lifts are special devices for transporting or lifting with a wide range of applications. By extending or retracting the hydraulic cylinder arranged in the scissor frame, the system can raise or lower the platform to the designated height. This study was conducted to analyze the relationship between the configuration of the cylinder and the movement of the platform in single-stage scissor lifts. By applying a numerical method and assigning parameters for the cylinder arrangement, the displacement of the platform and the forces in the cylinder can be easily calculated. The results obtained from the calculation process show the practicality of the proposed method in determining the optimal configuration for designing single-stage scissor lift systems.
Copyright (c) 2024 Tuan Dang https://creativecommons.org/licenses/by/4.0
Estimating quantiles in acceptance criteria for structural components
The probabilistic foundations of methods to control the characteristic properties of structural materials, expressed as p-quantiles, are discussed. We argue that the acceptance criteria in the quality control should be based on quantile estimators complying with the definition of the quantile. We introduce the distribution-free concept of definition-based quantile estimator. For normal distribution, an application of different types of estimators, as well as some attribute methods and mixed methods presently used, are illustrated by operating characteristic curves. We recommend the prediction method by which the subjective limit values of the mixed methods are eliminated, information from the sample will be used more effectively than in the attribute methods, and the questions about the proper confidence level or a “known” variation coefficient need not be considered. However, the direct application of the prediction method results in stricter quality control than that presently used. Therefore, we recommend adopting p’ > p in such a way that if the predicted p’-quantile estimate is equal to or higher than the lower lilmit L, the required value of the p-quantile, the lot is accepted in the quality control. If the present quality level is appropriate, the value of p’ can be chosen in such a way that the present level is maintained. If not, necessary modifications are possible simply by adjusting p’.
Copyright (c) 2024 Matti Pajari, Lasse Makkonen https://creativecommons.org/licenses/by/4.0
Evaluation of machine learning techniques for capacity prediction of cold-formed steel beams subjected to bending
Stiffened Cold-Formed Steel (CFS) sections often exhibit intricate nonlinear behaviors attributable to factors such as flexure effects and excessive slenderness. Traditional design methodologies, including the direct stiffness method, may inadequately capture these subtleties, potentially resulting in conservative or suboptimal designs. This study aimed to evaluate the performance of various machine learning algorithms, including simple and ensemble models, to predict the bending capacity of stiffened and unstiffened cold-formed beams in pure bending. A parametric study was conducted based on verified finite element analysis, and the machine learning algorithms were utilized to develop a unified capacity prediction method. The performance of six classical machine learning algorithms and four ensemble models were compared. The findings demonstrate that ensemble models, including AdaBoost, Gradient Boosting, Random Forest, and Extra Trees, outperform simple machine learning models in predicting the bending capacity of CFS beams. Moreover, introducing the stacking ensemble technique, using six different base models selectively, resulted in better performance than the individual baseline models. The approach addressed the nonlinearity pattern in the dataset caused by the flexure effect and excessive slenderness. The study suggests that adopting the proposed numerical and machine learning techniques could be a reliable method for predicting the structural behaviour and conducting cost-effective design of CFS beams, compared to the traditional analytical methods.
Copyright (c) 2024 Ayman Hamdallah, Antti H. Niemi, Ahmed Abdullah https://creativecommons.org/licenses/by/4.0
Extension of paperboard modelling with Föppl–von Karman terms for improved stress state under suction pressure
A practical method for solving the bending stiffness of a thin orthotropic plate based on measured deflection and known loading was studied. The target application was paperboard manufacturing and related process control. Here, finite element (FE) method was used to create virtual paperboard and its deflection data. The accuracy of the linear Kirchhoff plate model used in the practical method was tested against the FE model with known load and material properties. It was found that in the case of significant deflections, the linear Kirchoff model was not accurate. The non-linear Föppl--von Kàrmàn model takes into account the occurring membrane stresses and extends on the Kirchhoff model, allowing for larger deflection. The non-linear Föppl--von Kàrmàn model was found to successfully describe the simulated situation and could be used to better solve for the paperboard's bending stiffness values over two axes.
Copyright (c) 2024 Mikko Salo, Jarno, Matti Vilkko, Mikko Kanerva https://creativecommons.org/licenses/by/4.0
Numerical investigation of box shape effects on soil direct shear test
The direct shear test is a fundamental method in geotechnical engineering that provides crucial soil shear strength parameters, including cohesion (c) and the angle of internal friction (ϕ). These parameters play a pivotal role in structural design, slope stability assessment, and soil stability evaluation. However, achieving a uniform normal stress distribution within the shear box remains a challenging task, which can result in inaccuracies in test results. This study investigates the impact of shear box shape, specifically comparing circular and square configurations, on the outcomes of the direct shear test. The findings reveal that the choice of lower or upper box movement has a minimal effect on test results. Moreover, circular boxes demonstrate superior normal stress distribution, leading to reduced variations in comparison to square boxes. Wall friction effects lead to lower shear capacity measurements, with circular boxes yielding higher shear levels when contrasted with square boxes. Additionally, the soil along the sides and corners of the specimen experiences diminished shear stress due to reduced normal stress. This research contributes significantly to our comprehension of how shear box shape influences the determination of shear strength parameters in direct shear tests, ultimately enhancing the reliability of geotechnical engineering assessments.
Copyright (c) 2024 Rashid Hajivand Dastgerdi, Arif Khan , Kamran Kazemi, Michal Kowalski, Agnieszka Malinowska https://creativecommons.org/licenses/by/4.0
Tekninen selvitys: Kommentteja aiempiin teknisiin selvityksiin
Copyright (c) 2024 Markku Heinisuo https://creativecommons.org/licenses/by/4.0
Copyright (c) 2024 Matti Kangaspuoskari, Hannu Koivurova, Antti Niemi https://creativecommons.org/licenses/by/4.0
Copyright (c) 2024 Reijo Kouhia https://creativecommons.org/licenses/by/4.0