experimental analysis of tooth root strains in a sun gear of the final drive for an off highway axle

Abstract The force acting on gear teeth can be influenced by several factors such as profile modifications, stiffness variations during meshing, inversion of the sliding direction at the pitch line, tip-to-root interferences, gears and shaft deflections and bearings clearances. Moreover, in planetary gear sets the load can be shared unevenly among the planet gears due to manufacturing inaccuracies of the system. An accurate evaluation of the real load-time history experienced by the teeth is not straightforward and is affected by strong approximations even when advanced simulation software packages are used to create the theoretical model. Therefore, experimental analysis of the behavior of gears under in-service load still constitutes a major step in the development of new transmission systems. In this work, three strain gauges were applied at different positions along the tooth root width of the sun gear mounted in the final drive of an off-highway axle. Strain measurements where then performed during a bench test of the complete axle and the signal was acquired by means of a telemetry system. Finally, the acquired data were used to assess the accuracy of software calculations and to identify the causes of overloads

Estimates of climate system properties incorporating recent climate change

Historical time series of surface temperature and ocean heat content changes are commonly used metrics to diagnose climate change and estimate properties of the climate system. We show that recent trends, namely the slowing of surface temperature rise at the beginning of the 21st century and the acceleration of heat stored in the deep ocean, have a substantial impact on these estimates. Using the Massachusetts Institute of Technology Earth System Model (MESM), we vary three model parameters that influence the behavior of the climate system: effective climate sensitivity (ECS), the effective ocean diffusivity of heat anomalies by all mixing processes (Kv), and the net anthropogenic aerosol forcing scaling factor. Each model run is compared to observed changes in decadal mean surface temperature anomalies and the trend in global mean ocean heat content change to derive a joint probability distribution function for the model parameters. Marginal distributions for individual parameters are found by integrating over the other two parameters. To investigate how the inclusion of recent temperature changes affects our estimates, we systematically include additional data by choosing periods that end in 1990, 2000, and 2010. We find that estimates of ECS increase in response to rising global surface temperatures when data beyond 1990 are included, but due to the slowdown of surface temperature rise in the early 21st century, estimates when using data up to 2000 are greater than when data up to 2010 are used. We also show that estimates of Kv increase in response to the acceleration of heat stored in the ocean as data beyond 1990 are included. Further, we highlight how including spatial patterns of surface temperature change modifies the estimates. We show that including latitudinal structure in the climate change signal impacts properties with spatial dependence, namely the aerosol forcing pattern, more than properties defined for the global mean, climate sensitivity, and ocean diffusivity.</p

Nanostructure and nanomechanics of stomatopod cuticle

PhDChinese Scholarship CouncilChinese Scholarship CouncilChinese Scholarship CouncilCrustacean cuticle has attracted extensive attention for biomimetic purposes due to its outstanding mechanical properties including high toughness and stiffness. The mantis shrimp (stomatopod) telson is an extreme example, structurally optimized for dynamic loading at high impact forces. Alpha-chitin fibrillar building blocks play a key role in determining the overall mechanical properties due to its hierarchical design across all length scales. Synchrotron X-ray diffraction combined with in-situ mechanical testing was employed to investigate the structural and mechanical responses in telson cuticle at different hierarchical levels. The stomatopod tergite was used as a reference to learn how the structural and mechanical design will be correlated to the morphological changes in telson. In the thesis, we developed a novel three dimensional fibre orientation reconstruction method using mathematical models. The method was used to determine the orientation and intensity distributions of both the in-plane and out-of-plane mineralised chitin fibres from the two dimensional synchrotron X-ray diffraction scans collected from telson and tergite samples. Subsequently, in-situ tensile tests were performed on tergite cuticle to study the deformation and reorientation mechanisms of chitin fibres in the Bouligand layers comprising the bulk of the tergite, by tracing the variation of lattice spacing of the (002) peaks (along fibril direction) and (110) peaks (perpendicular to the fibril) found in the X-ray diffraction spectrum of α-Chitin. Finally, in-situ four-point bending tests were conducted to study how morphological changes contribute to the nanomechanical properties of telson across the entire tissue 4 cross-section. Pre-strains were identified in the cuticle in static states, and vary according to the morphological position. Under loading, fibrils near physiological impact site deformed more than those in adjacent region, demonstrating different roles in energy dissipation in telson. These above findings provide useful guidelines for designing synthetic composite materials that resist repetitive impact loading

Beyond equilibrium climate sensitivity

ISSN:1752-0908ISSN:1752-089

Stili umoristici, benessere soggettivo, percezione di salute e stile di vita

Introduzione: Martin, nel 2003, propone un nuovo approccio allo studio delle differenze individuali nell\u2019uso dell\u2019umorismo che tiene conto della multidimensionalit\ue0 di questo costrutto. L\u2019HSQ misura quattro stili umoristici: affiliativo, auto-accrescitivo, aggressivo e auto-denigrativo, che hanno diversi effetti sulla salute generale percepita (Greven, 2008) e sul benessere soggettivo (Bilge & Saltuk; 2007). L\u2019obiettivo di questo studio \ue8 quello di valutare il ruolo predittivo degli stili umoristici sul benessere, sulla percezione del proprio stato psico-fisico e su alcuni comportamenti di salute. Metodi: 281 soggetti (53,7% femmine; et\ue0 media 37,44 anni, d.s.=14,47) hanno compilato: HSQ-20 italiano; PANAS; Satisfaction With Life Scale. Inoltre sono stati rilevati: BMI, fumo di sigaretta, esercizio fisico, percezione di salute fisica e mentale. Risultati: Tenendo sotto controllo et\ue0, genere e livello educativo, il frequente ricorso agli stili umoristici adattivi e lo scarso utilizzo di quelli disadattivi predicono un buon grado di benessere percepito (R2=0,30, p&lt;0,0001); un elevato utilizzo di umorismo auto-accrescitivo e un limitato uso di quello auto-denigrativo predicono una buona salute mentale (R2=0,14, p&lt;0,0001); la salute fisica \ue8 influenzata da alto umorismo affiliativo e auto-accrescitivo e basso umorismo auto-denigrativo (R2=0,05, p=0,001); scarso umorismo affiliativo e scarso umorismo aggressivo sono associati a un pi\uf9 elevato BMI (R2=0,30, p=0,002); infine un elevato umorismo affiliativo \ue8 associato ad un maggior esercizio fisico (R2=0,02, p=0,01). Nessuno degli stili umoristici risulta predittivo del fumo. Discussione: I risultati delle analisi sembrano confermare il modello di Martin (2003), secondo il quale il benessere e la salute dipendono non solo dalla preferenza per stili umoristici adattivi, ma anche dall\u2019evitamento di quelli disadattivi. Tale aspetto deve pertanto essere preso in considerazione nel programmare interventi che abbiano come finalit\ue0 promuovere il benessere e gli stili di vita salutari attraverso l\u2019uso dell\u2019umorismo