1,721,002 research outputs found
Finite elements procedure for evaluating temperature distribution in polyurethane-coated wheels
No full textPolymeric materials find extensive applications across various engineering sectors. Among these, a particularly critical application for these materials is in the field of roller coasters. The wheels are typically made with an aluminum hub and a dense polyurethane coating, which, being in contact with the track, endures dynamic loads at high speeds. Due to the viscoelastic behavior typical of polymeric materials, these loads induce overheating of the coating leading to rapid degradation of the wheel. This results in machine downtime and a significant waste of time and money. In this manuscript, a methodology for finite element thermal-structural analysis has been developed. This method allows for the rapid evaluation of temperatures reached during operational cycles if compared to classical coupled-field thermal-structural analysis. The proposed methodology proves to be useful in selecting the appropriate type of wheels during the design phase requiring short computational time. The study first involved the development of the methodology, followed by validation through a comparison of analysis results with data obtained from experimental tests conducted by the manufacturer
Spectral analysis of sine-sweep vibration: A fatigue damage estimation method
No full textThe use of frequency methods for the estimation of fatigue life of mechanical components has almost supplanted the use of classical time domain methods due to their effectiveness about results and efficiency. Most of spectral methods are developed for random applications while other excitations, such as sine-sweep, are devoid of ad hoc methods. Given the countless advantages of spectral methods, this activity proposes a frequency domain method for fatigue life estimation for sine-sweep excitation. The proposed approach, tested on a simple structure, showed it can achieve the same results of a classical time domain approach but with a remarkable computational efficiency
Dynamic experimental and numerical analysis of loads for a horizontal axis micro wind turbine
No full textThe optimal use of micro wind energy conversion systems is not only a matter of efficiency, but it also involves a number of issues related to the technology and the dimensions of the system in relation with the environment. The growing request of micro wind energy technology for urban areas is nowadays stimulating the research on several subjects. Structural safety is crucial, in order to prevent damages in case of gusts. Noise and vibration assessment and minimization is another relevant issue too, especially for horizontal axis machines with higher efficiency and larger rotational speed. On these grounds, in this work a horizontal axis wind turbine having 2 m of rotor diameter is studied experimentally and numerically. Experimental tests have been performed with steady and unsteady wind conditions and accelerations have been collected, at meaningful operating conditions of the wind turbine, and consequently analyzed. The analysis of the experimental spectra is compared against numerical simulations performed with the aeroelastic code Fatigue, Aerodynamics, Structures and Turbulence (FAST) and this allows to interpret the complex load structure to which the wind turbine is subjected. In particular, evidence of the blade-passing phenomenon is collected: due to the small size of the system, the tower and blades undergo an interesting mechanical interplay
Analytical procedure for the optimization of plastic gear tooth root
No full textThe increasing diffusion of plastic gears in many industrial sectors makes it necessary to have a better knowledge of the bending strength properties of teeth in order to ensure an adequate design process. However, technological development has not gone hand in hand with the standard development necessary to carry out an optimized design process. To date, the specific standards for plastic gears refer mainly to design and calculation methods for the metal gears. So, the possible optimization strategy for the tooth root geometrical profile is also driven by the typical metal production processes. This paper presents an innovative approach, supported by an analytical procedure, to design optimized plastic gear wheels. The results obtained by the analytical approach is compared to the standardized one to highlight similarities and discrepancies. The goodness of the proposed results is verified also through finite element numerical analysis. The goal of the paper is to provide the designer with an analytical approach useful to optimize the root geometry design of plastic gears for lower root bending stress
Non-stationarity index in vibration fatigue: Theoretical and experimental research
No full textRandom vibrations induce damage in structures, especially when they are operating close to their natural frequencies. The stationarity of the input excitation is one of the fundamental assumptions required for frequency-domain fatigue-damage theory. However, for real applications, excitation is frequently non-stationary and the identification of this non-stationarity is not easy. This study researches run-tests to identify the index of non-stationarity. Further, using excitation signals with different rates of amplitude-modulated non-stationarity, the index of non-stationarity is experimentally and theoretically researched with regards to the fatigue life. The experimental research was performed on a flexible structure that was excited close to a natural frequency. The experimental fatigue life is compared to the theoretical fatigue life under the stationarity assumption. The analysis of the experimental results reveals a close relation between the identified non-stationarity in the excitation signal and the fatigue life of the structure. It was found that amplitude-modulated non-stationary excitation results in a significantly shorter fatigue life if compared to a similar level of stationary excitation
Fatigue damage assessment in wide-band uniaxial random loadings by PSD decomposition: outcomes from recent research
No full textSpectral decomposition of a PSD into narrow frequency bands has been suggested as a promising way for estimating the fatigue damage of uniaxial wide-band random loadings. The basic idea has been formulated in some recent publications, which also proposed different combination rules to sum up the damage of each narrow frequency band. The purpose of this technical note is to clarify the analogies, relationships and differences among the approaches developed in such publications
A novel method for the evaluation of driving simulator performances
No full textThe use of driving-simulator is increasing wide-spreading in the whole automotive
sector. The adoption of driving simulator indeed allows evaluating the design choices directly
during the design stage thought the man-machine interaction, where man" means the driver
while machine" means the mathematical model of the car traduced to the driver thought a
dierent machine: the driving simulator. In this research activity a questionnaire was developed
to evaluate the performances of a driving simulator focusing on two main aspects. The rst one
regards the ability of the driving simulator to accurately reproduce the driving feelings without
inducing motion sickness sensations. The second instead regards the ability of the driver to
objectively judge the vehicle performances throughout a set of parameters. All these aspects
were rstly numerically investigated implementing different models showing different dynamics
characteristics and successively veried by experimental test at the driving simulator. The
drivers scores, about both the accuracy of the mathematical model and the driving simulator,
were analysed in order to understand if their feelings match the real behaviour imposed to the
ca
A contribute to the development of a design procedure for space-born sandwich panels with CFRP skins and an aluminum core
No full textComposite sandwich panels have a vast heritage and are commonly employed
in various fields. The space industry is not an exception and often space structures and experiments use this type of panels. This paper represents an effort toward the development of a design procedure for space-born sandwich panels. The here-presented work has been performed on a real test case: the structural sandwich panel of a scientific space mission.
In this preliminary phase, classical methodologies were used to ensure the satisfaction of the mechanical requirements and for the minimization of the panel mass and dimensions. Tools such as Finite Element (FE) were employed to help with the design. Increasingly detailed models were developed and used to design the space panels. In addition, this work describes the future roadmap of the projec
Single-process 3D-printed structures with vibration durability self-awareness
No full textThe recent advances in additive manufacturing technology allow the realization of single-process thermoplastic material extrusion (TME) 3D-printed embedded sensors, leading to the easy and inexpensive production of smart structures. While single-process TME dynamic strain sensors have already been researched, vibration durability self-awareness is more than just an additional 3D printed strain sensor and several questions need to be answered. Is the durability self-aware sensors position structure-specific? Is the fatigue life of the sensory element longer than the base structure? Does the fatigue influence the self-awareness capability? Those and several other questions are theoretically and experimentally addressed in this research. Two different fatigue identification methods are researched (i.e. the peak-response and the frequency-drop methods). It was found that the vibration durability self-aware structure printed in a single process is viable and the frequency-drop based method gives reliable fatigue estimation; the fatigue damage was correctly identified even in the case the sensory element was 3D printed in the fatigue zone and already significantly damaged. This research opens up new capabilities for self-aware TME 3D-printed structures
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