Mariusz Warzecha

This paper presents the results of experimental studies on the mechanical and tribological properties of samples produced using the fused filament fabrication method. These studies aim to identify a potential material for a water-lubricated sliding bearing that will be manufactured using 3D printing. Printed specimens fabricated from four different materials were analyzed for surface profile, mechanical properties via the instrumented indentation method, and tribological behavior using a pin-on-disc setup. Although increased hardness is generally associated with improved resistance to wear, the material that exhibited the lowest wear in the pin-on-disc tests was characterized by the lowest hardness among all investigated materials. The findings suggest that other aspects, including wear mechanisms, wear products, and tribolayer development, may also exert a substantial influence.

This paper investigates the effect of ground end coils on axial stiffness, as well as the magnitude and direction of transverse reactions occurring during axial compression of a coil spring. As shown, conventional relationships for calculating axial stiffness can significantly overestimate its value, especially for springs with a small number of active coils. Transverse reaction forces during axial compression of a spring can reach high values. The paper shows that these forces can exceed more than 30% of the axial force caused by the compression of the spring. There are no relations in the available literature to estimate the effect of spring geometry on the value and direction of the transverse reaction generated during axial compression of the spring. On the basis of experimental studies of axial compression of springs, a numerical model with high accuracy was developed - the average difference between the experimental results and the results of the numerical model was 2.7%. The model took into account friction between coils, large deformations and carefully studied material parameters. Using the developed numerical model, a total of 245 numerical analyses were carried out, based on which new relationships were developed to accurately calculate axial stiffness, lateral reaction force and its angle. The new relationship for calculating axial stiffness shows better agreement with the results of numerical analyses than all the relationships found in the literature to date. The average difference between the results of this relation and the results of the numerical analyses carried out did not exceed 2%. A new relation has been proposed for determining the value of the transverse reaction occurring in axial compression of springs. This relation also shows high agreement with the results of numerical analyses. In addition, a new relation has been proposed to determine the direction of the transverse reaction force.

Accurate modelling of energy dissipation during body collisions is essential for improving the reliability of multibody dynamics simulations.Most published contact force models represent energy loss through a damping force, which introduces hysteresis in the contact response.The dissipated energy is governed by a hysteresis damping factor, typically calculated using a constant coefficient of restitution and the initial collision velocity.Although different models propose various formulations for this factor, they all assume the coefficient of restitution to be constant—despite experimental evidence showing its dependence on impact velocity.To address this limitation, an improved contact force model is proposed.It replaces the constant coefficient of restitution with a velocity-dependent function, allowing the model to capture variations in energy dissipation across different impact velocities.The formulation is compatible with both simple two-body collisions and more complex cases involving zero initial relative velocity.The proposed model was implemented in Python and evaluated against models chosen from the literature in simulations involving three to six beads arranged in collinear chains.Initial impact velocities of 0.1, 1, and 3 m/s were considered.Equivalent scenarios were also simulated using Finite Element Method (FEM) models, serving as a reference.Normalised root mean square deviation (RMSD) was used to quantify velocity prediction accuracy.The analysis shows that the proposed model yields substantial improvements, with error reductions up to 33% for six-bead systems at 3 m/s.This approach may benefit not only multibody dynamics, but also granular media simulation, wear prediction, and robotics involving repeated contacts.

Simulating multibody systems presents many challenges. Project Chrono, a specialised library, has beendeveloped to support engineers tackling these challenges. To offer reliable results, such tools requirecomplex validation. This study aims to analyse and validate the low-level behaviour of contact force modelsimplemented in the module chrono::core, part of the Project Chrono library. To accomplish this, impactsoccurring in systems consisting of 4 to 6 spheres were used. The velocity of the sphere initiating the impactranged from 0.1 to 3 m/s. The post-impact velocity was used as the main comparison quantity. The referencedata for comparison were obtained from FEM analysis performed in Code Aster. The comparison resulted ingraphs showing the percentage velocity errors for all the systems investigated. These plots showed significanterrors, reaching 22.75% for some cases. At the same time, the average error for all spheres in the mentionedcase was equal to 1.68%. This led to the conclusion that a proper definition of model parameters can lead tosatisfactory results on a global model scale. The study also described potential sources of errors and proposeddirections for further development.

This paper presents a new method for generating nonlinear helical spring geometries based on a rigorous mathematical formulation. The model was developed for two scenarios for modifying a spring with a stepped helix angle: for a fixed helix angle of the active coils and for a fixed overall height of the spring. It allows the development of compression spring geometries with non-linear load-deflection curves, while maintaining predetermined values of selected geometrical parameters such as the number of passive and active coils and the total height or helix angle of the linear segment of the active coils. Based on the proposed models, Python scripts were developed that can be implemented in any CAD software offering scripting capabilities or equipped with Application Programming Interfaces. Examples of scripts that use the developed model to generate the geometry of selected springs are presented. FEM analyses of quasi-static compression tests carried out for these spring models have shown that, using the proposed tools, springs with a wide range of variation in static load-deflection curves can be obtained, including progressive springs with a high degree of nonlinearity in the characteristics. The obtained load-deflection curves can be described with a high degree of accuracy by power function. The proposed method can find applications in both machine design and spring manufacturing.

This paper presents the results of an experimental analysis of the distribution of transverse stiffness of cylindrical compression helical springs with selected values of geometric parameters. The influence of the number of active coils and the design of the end coils on the transverse stiffness distribution was investigated. Experimental tests were carried out for 18 sets of spring samples that differed in the number of active coils, end-coil design and spring index, and three measurements were taken per sample, at two values of static axial deflection. The transverse stiffness in the radial directions were tested at every 30° angle. A total of 1,296 measurements were taken, from which the transverse stiffness distributions were determined. It was shown that depending on the direction of deflection, the differences between the highest and lowest value of transverse stiffness of a given spring can exceed 25%. The experimental results were compared with the results of the formulas for transverse stiffness available in the literature. It was shown that in the case of springs with a small number of active coils, discrepancies between the average transverse stiffness of a given spring and the transverse stiffness calculated based on literature relations can reach several tens of percent. Analysis of the results of the tests carried out allowed conclusions to be drawn, making it possible to estimate the suitability of a given computational model for determining the transverse stiffness of a spring with given geometrical parameters.

During measurements, the crankshafts of marine engines are usually supported on a set of rigid prisms. Such prisms maintain a constant height position, cause different values of reaction forces and, consequently, may cause elastic deformations of the crankshafts. Thus, the measurements of the dimensions and geometry of the crankshaft may be distorted. This article proposes a measuring system developed to support the crankshaft with a set of flexible supports. These supports implemented the given reaction forces, which ensured the elimination of the crankshaft deformations, regardless of the possible deviations, i.e., in the coaxiality of the main crankshaft journals. The values of these forces were calculated using the finite element method (FEM). These calculations showed that in order to eliminate the crankshaft deformations, the values of the reaction forces must change not only on individual supports, but also with the change of the shaft rotation angle during the measurement. The numerical experiments showed that the application of flexible supports results in uniform contact reaction forces on adjacent main journal supports. This uniformity occurs regardless of the quality of the crankshaft geometry. Thus, the necessity to use a set of flexible supports for measuring marine engine crankshafts was confirmed. The research also showed that the values of the reaction forces ensuring the elimination of shaft deflections under the assumption of nodal support can be treated as corresponding to the resultant reaction forces realized by the prismatic heads.

The reliability and safety of bolted joints is one of the crucial engineering problems during design of mechanical structures. In this paper, finite element method was used to investigate an asymmetrical, seven-bolted joint. The modelling takes into account the phenomenon of friction and the mechanics of contact between the joined elements. The bolts were preloaded using two different approaches: single and multi-pass. The damage of a bolt was simulated by its removal from the model. The conducted research showed influence of the number of preloading passes and its order on the forces acting in bolts both before and after damage. The obtained results were validated by experimental tests and presented as force diagrams for all investigated cases.