Papers by A. Młyniec
ABSTRACT The performance of many mechanical structures highly depends on weather conditions in re... more ABSTRACT The performance of many mechanical structures highly depends on weather conditions in region of operation. One of the main limiting factors of their performance in cold regions is the icing process. Icing of structures can be a reason of mechanical and electrical failures and can be dangerous for people working closely to, for instance, rotating wind turbine blades. To prevent de-icing process an inspection system informing about the possibility of collecting ice on surface of operating structures is of particular interest. The following work considers a numerical modeling approach and experimental investigations of the ice detection and de-icing process. The proposed numerical model is based on the cohesive-zone approach used to simulate the delamination at the ice/aluminum interface. Model parameters are specified in terms of fracture energy as a function normal and shear deformation at the interface. A linear elastic traction separation law prior to damage and progressive degradation of the material stiffness after failure is assumed. The ice detection and removal is accomplished by ultrasonic waves excited by the piezoelectric transducers. The experimental results for aluminum plate with ice layers are presented. The results confirmed possibility of icing identification by means of piezoelectric transducers, although ice removal effectiveness depends on the thickness of ice layers. Finally, a proposal of a new deicing adaptive system is given.
articles by A. Młyniec
In this article, we present the constitutive models taking into account the stability of liquid s... more In this article, we present the constitutive models taking into account the stability of liquid silicone rubber's. We propose the phenomenological large strain viscoelastic material model and the enhanced chemomechanical model. The phenomenological model is calibrated to the experimental investigations probing the thermomechanical behavior of liquid silicone rubber's, while the chemomechanical model uses kinetic theory, to calculate the changes of mechanical properties in time. The proposed chemomechanical model employs: chemical reaction kinetics, statistical mechanics and microstructural based Bergstr{\"{o}}m-Boyce material model. Viscoelastic material property changes resulting from e.g. the variation of crosslink density are computed using the Arrhenius equation. The material model is validated by comparison with results of compression tests of specimens aged in 125 and 175 °C non-loaded and under stress of 0.48 MPa. We achieve 96{\%} compliance for investigated temperature and pressure range. The good agreement with the experimental data, demonstrates that chemomechanical modeling framework provides a useful tool for the prediction of the stability of liquid silicone rubbers and the lifetime of vibration isolators.
Aim: The aim of this study was to create a multiscale model of the Achilles tendon from molecular... more Aim: The aim of this study was to create a multiscale model of the Achilles tendon from molecular to macro scale. Materials and Methods : Using molecular dynamics we have built a collagen molecule model in the molecular scale. Scaling up we created a coarse-grained model of a collagen nanofibril, which was used for the calibration of a Mooney-Rivlin hyperelastic tendon material model. Results: We obtained Young moduli values of a collagen molecule for small (8.44 GPa) and large strains (63.29 GPa), as well as for the collagen nanofibrils (7.64 GPa). All obtained moduli were in good agreement with existing experimental data. The calibrated material model used in finite element analysis predicted accurately the sites of tendon failure. Conclusion: This study derives information directly from the molecular scale, and can be used for predicting tendon mechanical properties both in physiological and pathological conditions.
The following paper describes investigations on the impact of harsh environment on shear and tens... more The following paper describes investigations on the impact of harsh environment on shear and tensile strength of multi-material adhesive joints. The samples were made from carbon fiber – epoxy composites, aluminum and two types of advanced steels: abrasion resistant and high-strength. In order to assess the suitability of structural bonding for this sort of applications, it was decided to test two different epoxy-based adhesives, designed for moderate and elevated operating temperatures. The harmful conditions were simulated by means of humidity-temperature cycling tests, according to the SAE standard. The obtained results revealed that even moderately harsh humidity-temperature loads can cause debonding of the joints, even if no external forces are applied. In order to gain insight into this phenomenon, a series of finite element analyses was performed, simulating the exposure of the samples to the chosen environmental conditions. Based on these studies, the temperature expansion coefficient was identified as the crucial factor for the performance of the joints made from dissimilar materials. The results of the described experiments, confirmed by numerical calculations, constitute a guideline for multi-material structural design, supporting this constantly growing branch of modern engineering with a relevant input.
Performance of the adhesively joined composite structures frequently depends on their stiffness s... more Performance of the adhesively joined composite structures frequently depends on their stiffness since excessive deformation can alter their functionality. In this article, we present the structurally based constitutive model which takes into account the influence of the post-curing as well as thermolysis process on stiffness of epoxy adhesives. We propose the chemomechanical model considering the autocatalytic post-curing process and thermolysis, which dominates in the first phase of the degradation process at elevated temperatures. The proposed model employs reaction kinetics of curing and ther- molysis of epoxy, statistical mechanics as well as non-linear large strain constitutive material model which incorporates influence of chemical reactions. Presented model is calibrated to the results of experimental investigations probing the influence of the aging cycles according to the SAE/USCAR standard on stiffness of the epoxy adhesives. The material model is validated by comparison with results of single lap shear tests after HumidityeTemperature aging in class I and V.We achieve 98.3{\%} compliance for investigated aging cycles. Proposed model takes into account not only aging effects but elevated temperatures as well. Thus it can be used for prediction of the mechanical behavior of heavy loaded epoxy adhesive joints working in engine compartment. The consistency of the experimental results with model predictions, proves that our chemomechanical model constitutes a useful tool for the prediction of the durability and lifetime of adhesively joined structures.
In this manuscript we investigate the influence of loading rate and fibril length on viscoelastic... more In this manuscript we investigate the influence of loading rate and fibril length on viscoelastic and failure behavior of collagen nanofibrils. The computational experiments were performed using three-dimensional shape-based Coarse-Grained models of collagen nanofibrils, with parameters derived from atomistic simulations. The atomistic computational tensile and shear experiments were performed using Molecular Dynamics and extended AMBER force field for aqueous and non-aqueous environments. The Coarse-Grained interactions were defined by both intermolecular and intramolecular potentials which describe non-bonded and bonded interactions respectively. Computational studies revealed that the hydrogen bond network impacts both viscoelastic behavior and failure of collagen nanofibrils. Greater fibril length results in brittle cracking while higher loading rates result in ductile behavior, due to the unwinding and sliding of the fibril. The proposed Coarse-Grained model can be used in further studies incorporating the effects of ageing, such as collagen degradation and glycation.
The Achilles tendon (AT) consists of fibers originating from the soleus muscle (SOL), which lies ... more The Achilles tendon (AT) consists of fibers originating from the soleus muscle (SOL), which lies deep, and the medial (GM) and lateral (GL) heads of the gastroc-nemius muscle, which lie superficial. As the fibers descend toward the insertion of the AT, the individual subtendons twist around each other. The aim of this study was to investigate the twisted structure of the AT and its individual subtendons. Specimens of the AT, with preserved calcaneal bone and a fragment of the triceps surae muscle, were obtained from 53 fresh-frozen, male cadavers (n=106 lower limbs). The angle of torsion of each of the AT's subtendons was measured using a specially designed and 3D-printed tool. The mean distance between the most distal fibers of the triceps surae muscle and the superior border of the calcaneal bone was 60.77±14.15 mm. The largest component of the AT at the level of its insertion into the calcaneal bone is the subtendon from the GL (44.43{\%}), followed by the subtendon from SOL (27.89{\%}), and the subtendon from GM (27.68{\%}). The fibers originating from the GM rotate on average 28.17±15.15°, while the fibers originating from the GL and SOL twist 135.98±33.58° and 128.58±29.63°, respectively. The torsion of superficial fib-ers (GM) comprising the AT is significantly lower than that of deeper fibers (GL and SOL). The cross-sectional area of the AT is smaller at the level of the musculo-tendinous junction than at the level of its insertion. This study illustrates the three types of the AT with differently twisting subtendons, as well as a generalized model of the AT. Types of AT torsion may potentially alter the biomechanical properties of the tendon, thus possibly influencing the pathophysiologic mechanisms leading to the development of various tendinopathies.
inproceedings by A. Młyniec
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Papers by A. Młyniec
articles by A. Młyniec
inproceedings by A. Młyniec