•Simple Damage Energy Criterium for life prediction in multiaxial fatigue.•Through frequency domain a multiaxial stress state can be reduced.•Auto and cross power spectra are the fundamental ...mathematical functions to do this.•Comparison between theoretical predictions and experimental data.
In this paper, a new, simple Damage Energy Criterium for life prediction in multiaxial fatigue, developed in the frequency domain, is described and verified. The first aim of this paper is to demonstrate that through a correct use of the energetic approach, developed in the frequency domain, it is possible to achieve an accurate result. The proposed theoretical procedure finds its conceptual foundation in the fact that the energy criterion cannot be directly applied to usual stress state in the time domain; however, with a simple passage it is possible to accurately reduce a multiaxial stress state to an equivalent uniaxial one. For this reason, this work will be characterized by analytical content and by substantial mathematical demonstrations. At the end, in order to verify the method and consolidate the general procedure, some experimental tests are used to corroborate the validity of this criterion. This proposal shows drastically simpler technique than any other proposed in current literature.
•We developed a new criterion for the frequency domain life estimation.•We consider mechanical components under random loading.•We proposed an original procedure to evaluate fatigue damage.•The idea ...is to divide the single PSD into frequency bands.•The method was validated by numerical comparison with the reference ones.
The evaluation of the fatigue behavior of mechanical systems and components subjected to random loads is increasingly being addressed to the frequency domain environment both in terms of dynamic analysis and in terms of results post-processing.
The procedure set out in the paper (bands method) is formulated without assumptions about the shape of the Power Spectral Density (PSD) function to be analyzed, in order to obtain a criterion that can be applied to any typology of the related random process. The basic idea of the proposed approach is that each PSD function can be divided into frequency bands, for each of them a Rayleigh distribution could be associated and that the aforementioned distributions could be opportunely combined to obtain the actual damage. The method is theoretically developed and numerically validated on a particular subset of PSD functions by comparing the results obtained with those carried out by the time domain damage evaluation reference method and a frequency domain direct approach (Dirlik’s method).
With regard to the time domain reference criterion the stress time histories are generated by the indirect method (a previously defined authors’ method), the cycles spectra are obtained by Rain Flow Counting, (RFC) and the damage is evaluated by Palmgren–Miner’s rule.
•A frequency domain approach for the evaluation of fatigue life in case of Sine-Sweep test is proposed.•The proposed method is compared with classical time domain approach supplying accurate results ...in terms of fatigue damage.•The proposed method can solve multiaxial stress state reducing it into an equivalent uniaxial stress.•The computational time needed with the proposed method for the evaluation of fatigue damage is 16 time lower if compared to time domain method.
The 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.
•We analyse multiaxial fatigue.•We compare time domain classical criteria with their translation into frequency domain.•We demonstrate the goodness of the frequency domain approach also in multiaxial ...stress state conditions.
Fatigue analysis of mechanical components subjected to random loads has been recently upgraded through several developments of calculation procedures, with the scope to support the designer within the loading condition numerical simulation. Under such scenario, the frequency domain approach is characterized by interesting features, which support its adoption in alternative or in conjunction with the classic time-domain approach, especially when the frequency domain is applied for the individuation of the component critical locations. The major goal of this paper consists of an overview about the strength and weaknesses of frequency approach with respect to the time domain one by comparing the reference time domain methods with their frequency domain translation. A significant test case development will be shown, representing a classic automotive one (chassis validation). Promising results of the frequency method application will be presented, encouraging its adoption on large scale.
•We developed a design procedure for Roller Coaster supporting structures.•The stiffness matrix betweenconnection points and rail and supporting structures is obtained.•The procedure was validated on ...an industrial test case.
In this paper a procedure for the design of the structures of a generic roller coaster (RC) is described. This activity is part of a partnership that the authors are entertaining with one of the major European amusement park industries. The full procedure, developed on theoretical bases and under simplified hypotheses, aims to make designers able to properly and quickly size the complete structure (for complete structure authors mean rails and support structures). In the present paper the design of the support structures is presented. The data, needed by this procedure, are: the rail track tridimensional geometry and the time histories of contact forces between vehicles and rails. The procedure has been subsequently verified by applying it to an existing RC in order to test all its capabilities and foresee future development and improvement, aiming to insert it in a consolidated general procedure, ever growing and expanding.
Nowadays, in the field of transmissions, one of the most important objectives is to realize gears with high efficiency so as to reduce power losses, operating temperatures, noise and wear.
The target ...of this work is to analyze spur gear efficiency through two different approaches for friction coefficient calculation along the line of action in order to evaluate the possible differences.
The first method analyzed considers a mean friction coefficient that follows Niemann's equation, the second method considers a local value for the friction coefficient following Hai Xu studies.
For this purpose the efficiency variation versus the addendum modification of the pinion is taken into consideration for each of the following: operating conditions, transmission ratio and sum of addendum modification coefficient variations.
Moreover, using the results of the first part of the paper, some of the more used methods for gear teeth optimization, in terms of the apportion of the addendum modification coefficient, are investigated in depth and compared in terms of efficiency so as to find out the best behaviour about: load capacity, safety against wear, noise and vibration.
► We analyzed spur gear efficiency. ► We used two different approaches for friction coefficient calculation. ► We considered Niemann's equation and Hai Xu studies. ► We investigated some of the more used methods for gear teeth optimization. ► We considered load capacity, safety against wear, noise and vibration.
Abstract The introduction of fused deposition modelling in the industrial sector to produce functional components in thermoplastic materials, such as PLA, requires knowledge of the performance limits ...of such elements during the design phase. Predicting the breaking load resistance of notched specimens is essential to evaluate the mechanical performance of components manufactured using this technology. This study compares different methodologies based on the critical distance criterion (TCD) for predicting the static breaking strength of printed notched specimens made with Fused Filament Fabrication (FFF) technology using PLA material. Specimens with different topologies of V-notches were printed according to a standardized configuration. Various analysis techniques were applied to determine the breaking strength of each specimen. By comparing the results obtained with experimental data to assess their accuracy and reliability, it has been demonstrated that these methodologies, coupled with the concept of equivalent elastic material (EMC), can be useful for predicting static breaking load.
Abstract The evaluation of fatigue damage of structural components within dynamic systems subjected to random loads is typically addressed using multibody models wherein one or more components are ...modeled as flexible using the modal approach. While incorporating flexible elements allows for consideration of their influence on the overall dynamic behavior of the system, certain components are intentionally designed to function as rigid bodies. Consequently, in this case the incorporation of flexible elements within multibody models merely leads to complex and time-consuming analysis. Hence, it would be more pragmatic to realize rigid body multibody models, with components characterized solely by their inertial properties, and subsequently extract the dynamic forces applied to the components to be verified. The assessment of stress can then be carried out by exploiting the principle of superposition of effects in the time domain. In this context, the objective of the present study is to develop this methodology in the frequency domain. This approach not only capitalizes on the simplicity of rigid multibody models but also harnesses the computational capabilities of the frequency-domain method for evaluating fatigue damage in components subjected to random loading conditions. This work, therefore, provides a rapid, effective, and robust method for verifying and designing rigid mechanical components integrated into dynamic systems subjected to random loads.
In the present paper, a new approach to combine load conditions expressed by power spectral density functions and to synthesize them into an equivalent one was presented. This method is based on the ...concept of fatigue damage spectrum and on the system dynamics. It was developed to design or verify operative durability tests (i.e., tracks), able to test payloads transported by vehicles, which could be alternative to laboratory ones, defined by the norm. By analyzing the acceleration spectrum of the norm and the acceleration measurements (all expressed in terms of power spectral density functions) acquired on the designed tracks during an experimental activity conducted on a wheeled transport vehicle, it was possible to verify the goodness of the proposed approach.
Abstract Additive manufacturing (AM) technology has experienced significant growth in recent years, opening new prospects across various sectors, from biomedicine to aerospace. Among these, the Fused ...Filament Fabrication (FFF) additive manufacturing technology, which deposits material layer by layer, enables the integration of piezoelectric material during the printing process, thereby allowing for the creation of sensors within thermoplastic components. Such sensors have the potential to monitor and detect various internal physical parameters within the component at locations inaccessible to traditional sensors. In this field, scientific research is continuously advancing, primarily aimed at developing sensors with high performance. In this context, the objective of this study is to assess the measurement properties, both static and dynamic, of sensors produced using this technology and to evaluate the influence on the static and dynamic behavior of the component caused by the incorporation of these sensors within the component itself.
