Optimal design of tapered roller bearings for maximum rating life under combined loads

Using the relationships of the ISO 281 standard, this paper optimizes the internal dimensions of tapered roller bearings for maximum rating life. The bearing system addressed contains two identical bearings subjected to an arbitrary combination of centred radial and axial forces. It is shown that the basic rating life increases more than quadratically with the roller infill and the aspect ratio of the rollers, increases with the sixth power of the pitch diameter of the roller set and decreases with the third power of the applied radial force. Further, for any given ratio of axial to radial force, an optimal contact angle exists which maximizes the rating life of the bearing pair, irrespective of the actual bearing size and ratio of roller diameter to pitch diameter. The optimization procedure can either be used to design custom-made bearings or to select from manufacturers\u2019 catalogues the bearing with the best contact angle for any assigned loading condition

Heuristic structural optimization of two-dimensional filling materials with square-triangular supercells

Cellular filling materials are a commonplace in additively manufactured parts to lower the structural weight without detriment to the mechanical properties. This technical note undergoes the heuristic optimization of a 2D metamaterial with repetitive supercells derived from a square frame divided by median and diagonal lines into eight triangles. The inherent quadriaxiality of this layout is ideally suited to resist multiaxial stress fields, while enabling size refinement to match the local scale of the component. A step-by-step procedure is developed which optimizes the thickness of the beams along the principal axes of the cell (sidewise and diagonal) according to a fully stressed design concept. Preliminary Finite Element models, including either bar or beam elements, confirm the theoretical results for a case study. Extension of the optimal approach to 3D geometries is envisioned using a cubic cell which incorporates the present 2D grid on each face of the cube

Experimental investigation and model validation of the shear strength of hybrid interfaces up to complete failure

The paper experimentally investigates hybrid interfaces pressurereinforced and bonded with anaerobic adhesive. While their static strength has been deeply investigated, their behavior up to complete failure lacks of a constitutive model. This work aims to assess the applicability of a simple model involving a cohesive law and a pure 10 friction law, in order to describe the interface behavior up to complete failure under different contact pressure levels. A systematic experimental campaign investigates the shear strength of cylindrical specimens butt-bonded and pressure reinforced over an annular surface. The tests involve two anaerobic adhesives and 15 four pressure levels. The experimental torque-rotation curves confirm that the strain energy up to complete failure is given by a cohesive term and a pure friction term, both of them linearly dependent upon the contact pressure

SISTEMA DI CARATTERIZZAZIONE PER FLUIDI MAGNETOREOLOGICI: EFFETTO DELLA PRESSIONE IN MODALITA’ SCORRIMENTO

Il presente lavoro descrive l’ apparecchiatura sperimentale per la caratterizzazione di fluidi magnetoreologici (MR) in modalità scorrimento, sottoposti a pressione. Lavori di letteratura riportano indicazioni sull’effetto della pressione sui fluidi MR a taglio, ma oiché molti dispositivi commerciali lavorano in modalità scorrimento è interessante investigare questo aspetto. La progettazione del sistema è sviluppata in tre fasi: progetto del sistema meccanico, progetto del circuito magnetico, progetto della campagna sperimentale. L’attrezzatura effettua la misura della tensione di snervamento apparente del fluido MR in funzione di pressione, campo magnetico e velocità del fluido. Il circuito magnetico, progettato con un software FEM è stato verificato con un gaussmetro, evidenziando un ottimo accordo numerico-sperimentale. Il sistema sviluppato si pone come strumento per valutare se la pressione del fluido MR possa essere usata come strumento per potenziare gli attuali sistemi semiattivi basati su fluidi MR, come smorzatori e dissipatori lineari

Enhanced properties of magnetorheological fluids: Effect of pressure

Magnetorheological fluids are extensively used in the industrial world to produce dissipative systems in an easily adjustable or even self-adaptive way. Sometimes their intrinsic rheological properties fail to meet system requirements in terms of available forces or yield stress for a given design space. In technical literature, previous works show a dependency of the shear strength of magnetorheological fluids on the internal pressure of the fluid, called squeeze strengthen effect. This work aims at the experimental validation of the behaviour of the magnetorheological fluids in both flow and shear modes under a given compressive state. Two specific ad hoc experimental test rigs are used for the campaign. The systems are designed in order to apply the magnetic field and the pressure at the same time and the tests are carried out following a design of experiment method. The magnetic parts of the system are designed with the help of a magnetic finite element simulation software, then the experiments are performed and the results are collected. The output is analysed through an analysis of variance approach, a statistical procedure that shows the influence of multiple variables on the system outputs. The outcome of the experimental tests confirms the beneficial effect of the pressure in both flow and shear modes, with performances up to three times compared with the datasheet values, where no pressure is considered

Design of shape memory alloy sandwich actuators: an analytical and numerical modelling approach

Shape memory alloy (SMA)-based actuator composites are characterised by a high force output which is activated by a temperature increase. In this work we exploit this property to design sandwich structures with SMA-matrix composite actuator skins capable of exhibiting a reversible, tailored flexural response. A theoretical model which predicts the resultant deflection and flexural moment produced as a result of selectively actuating one of the system skins was developed and confirmed using a multi-step Finite Element (FE) analysis which takes into account the fabrication pathway through which these systems may be manufactured. The model correlates the geometric parameters and material properties of the various components making up the system and provides a quantitative description of the role which each variable plays in determining the overall sandwich actuator performance. This is necessary for the future production and implementation of such systems in real-life applications

Fatigue life prediction of notched components: a comparison between the theory of critical distance and the classical stress-gradient approach

Abstract Fatigue life prediction for machine components is a key factor in the industrial world and several methods can be traced in technical literature to estimate life of notched components. The paper correlates the classical stress-gradient approach, here after called support factor (SF) method, proposed by Siebel, Neuber and Petersen with the modern theory of critical distance (TCD) approach by Tanaka and Taylor. On the one hand, the main asset of the SF method is that it relies only on the knowledge of the maximum stress and stress gradient in the hot spot. By contrast, the TCD needs the calculation of the stress distribution for a finite depth inside the material. On the other hand, the main drawback of the SF method is that the material parameter ρ* is available only for a limited collection of materials and moreover the experimental procedure to retrieve this parameter is not clearly defined in the technical literature. In order to overcome this limitation, the paper investigates the correlation between the material parameter ρ* and the critical distance L of the TCD by relying on a specific stress function. A comparison between the SF method and the TCD is then performed by considering three different benchmark geometries: a general V-notch in a plate, a pressure vessel and an industrial oleo-hydraulic distributor. Effective stresses are analytically retrieved and compared using both methods for the first two benchmarks and with the help of an elastic finite element analysis for the last one. The resus appear good in terms of fatigue life prediction, especially for the industrial case study

Modellazione efficiente agli elementi finiti per l\u2019analisi a collasso di strutture incollate complesse

Il lavoro verifica l\u2019applicabilit\ue0 di un modello semplificato agli elementi finiti per l\u2019analisi a collasso post elastico di strutture incollate complesse in parete sottile. Al fine di superare le limitazioni dei modelli di letteratura come l\u2019uso di elementi speciali, il lavoro sfrutta un modello ridotto gi\ue0 presentato dagli autori in campo elastico. Tale modello \ue8 basato sulla rappresentazione degli aderendi mediante elementi semistrutturali (piastre o gusci) e dell\u2019adesivo per mezzo di speciali elementi coesivi. La continuit\ue0 strutturale tra aderendi e adesivo \ue8 ottenuta mediante vincoli interni (tied mesh) che accomunano i gradi di libert\ue0 dei nodi mutuamente affacciati di aderendi ed adesivo. La struttura analizzata \ue8 un simulacro di incollaggio industriale e produce nella strato adesivo una sollecitazione complessa, analizzabile solo con modelli numerici. Si considera una struttura tubolare in parete sottile a sezione quadrata, fatta di due spezzoni posti testa a testa e incollati con fazzoletti di lamiera sui quattro lati. La struttura \ue8 sottoposta a flessione a tre punti fino al cedimento e la zona incollata posta disassata rispetto al punto di applicazione del carico riceve una sollecitazione indiretta. I risultati dell\u2019analisi FEM, confrontati direttamente con le curve sperimentali forza-spostamento, evidenziano una buona accuratezza del metodo, in termini di rigidezza, forza massima e comportamento post elastico della struttura, accompagnati da ridotte dimensioni del modello e tempi di calcolo molto contenuti. Grazie a questi vantaggi, la procedura si presta ad effettuare l\u2019analisi di strutture incollate complesse, altrimenti ingestibili se affrontate con una modellazione agli elementi finiti tradizionale