Experimental and numerical investigation into effect of elevated temperature on fretting fatigue behavior

Fretting fatigue damage occurs in contacting parts when they are subjected to fluctuating loadings and sliding movements at the same time. This phenomenon may occur in many applications such as bearings/ shafts, bolted and riveted connections, steel cables, and steam and gas turbines. In this paper, the effect of elevated temperature on fretting fatigue life of Al7075-T6 is investigated using a new device for fretting fatigue tests with variable crank shaft mechanism. Also a finite element modeling method was used to estimate crack propagation lifetime in aluminum alloy, Al7075-T6 specimens at elevated temperature under fretting condition. In this method, shear and normal stresses that are caused by contact load are updated at each crack growth increment. Finally, a comparison between the experimental and numerical results is done in order to evaluate the FE simulation. Department of mechanical engineering, Islamic Azad University, Takestan Branch, Takestan, Iran The experimental results show that: (i) fretting fatigue life of the material increases with temperature up to 350°C by 180% for low stresses and decreases by 40% for high stresses, (ii) this fashion of variation of fretting fatigue life versus temperature is believed to be due to degradation of material properties which occurs by overaging and wear resistance increase due to oxidation of aluminum alloy. While overaging gives rise to degradation of mechanical strength of material and hence the reduction of its fretting fatigue life, surface oxidation of the specimens brings some improvement of fatigue behavior of the material. Metallurgical examination of the specimens reveals that temperature results in precipitation of impurities of al-7075-T6. The size of precipitated impurities and their distances gets bigger as temperature increases. This could be a reason for material degradation of specimens which are exposed to heating for longer time duration

Towards a digitised process-wheel for historic building repair and maintenance projects in Scotland

Purpose – With the increasing demand for high quality economical and sustainable historic building Repair and Maintenance (R&M) allied with the perennial problem of skills shortages (PM-project management and on-site practice) investment in new technologies becomes paramount for modernising training and practice. Yet, the historic R&M industry, in-particular Small–Medium sized Enterprises (SMEs) have yet to benefit from digital technologies (such as laser scanning, virtual reality (VR) and cloud-computing) which have the potential to enhance performance and productivity. Design/methodology/approach – A qualitative participatory action research approach was adopted. One demonstration project (Project A) exhibiting critical disrepair, showcasing the piloting of a five phased digitised ‘process-wheel’ intended to provide a common framework for facilitating collaboration of project stakeholders thereby aiding successful project delivery is reported. Five semi-structured interviews were conducted with industry employers to facilitate the process-wheel concept development. Findings – Implementing only Phase 1 of the digitised ‘process-wheel’ (e-Condition surveying incorporating laser scanning) resulted in an estimated 25-30% cost and time savings) when compared to conventional methods. The accrued benefits are two-fold: (1) provide a structured standardised data capturing approach that is shared in a common project repository amongst relevant stakeholders; (2) inform the application of digital technologies to attain efficiencies across various phases of the process-wheel. Originality/value – This paper has provided original and valuable information on the benefits of modernising R&M practice, highlighting the importance of continued investment in innovative processes and new technologies for historic building R&M to enhance existing practice and in form current training provision. Future work will focus on further piloting and validation of the process-wheel in its entirety on selected demonstration projects with a view of supporting the industry to digitise its workflows and going-fully digital to realise optimum process efficiencies

Geometrically nonlinear isogeometric analysis of laminated composite plates based on higher-order shear deformation theory

In this paper, we present an effectively numerical approach based on isogeometric analysis (IGA) and higher-order shear deformation theory (HSDT) for geometrically nonlinear analysis of laminated composite plates. The HSDT allows us to approximate displacement field that ensures by itself the realistic shear strain energy part without shear correction factors. IGA utilizing basis functions namely B-splines or non-uniform rational B-splines (NURBS) enables to satisfy easily the stringent continuity requirement of the HSDT model without any additional variables. The nonlinearity of the plates is formed in the total Lagrange approach based on the von-Karman strain assumptions. Numerous numerical validations for the isotropic, orthotropic, cross-ply and angle-ply laminated plates are provided to demonstrate the effectiveness of the proposed method

The geology and geochronology of Al Wahbah maar crater, Harrat Kishb, Saudi Arabia

Al Wahbah is a large (∼2.2 km diameter, ∼250 m deep) maar crater in the Harrat Kishb volcanic field in western Saudi Arabia. It cuts Proterozoic basement rocks and two Quaternary basanite lava flows, and is rimmed with an eroded tuff ring of debris from the phreatomagmatic explosion that generated the crater. A scoria cone on the northern wall of the crater was dissected by the explosion and exposes a dolerite plug that was intruded immediately prior to crater formation. The dolerite plug yields a <sup>40</sup>Ar/<sup>39</sup>Ar age of 1.147 ± 0.004 Ma. This is the best possible estimate of the time Al Wahbah crater formed. It is a few tens of thousand years younger than the age of the lower and upper basalt flows, 1.261 ± 0.021 Ma and 1.178 ± 0.007 Ma respectively. A dolerite dyke exposed within the basement in the wall of the crater is dated at 1.886 ± 0.008 Ma. This is the most precise age so far determined for the initiation of basaltic volcanism of Harrat Kishb, and confirms that it is significantly younger than the other post-rift volcanic provinces in the region. This study provides constrains the timing of humid climatic conditions in the region and suggests that the Quaternary basaltic volcanism that stretches the length of the western side of the Arabian peninsula may prove to be useful for establishing palaeoclimatic conditions

Međudjelovanje četiri-razinskog atoma u impulsnom svojstvenom stanju s jednomodnim poljem

We study the interaction between a four-level atom (ladder type) in a momentum eigenstate with a single mode cavity field in the presence of non-linearities of both the field and the intensity-dependent coupling. The constants of motion and the wave function for the atomic system have been obtained. Special attention is given to discuss some statistical aspects of the considered atomic system such as momentum increment, momentum diffusion and high-order squeezing. The influence of the Kerr-like medium and the intensity dependent coupling on the momentum increment and the high-order squeezing are investigated numerically. It is found that addition of these parameters has an important effect on both the momentum increment and the squeezing phenomenon.Proučavamo međudjelovanje četiri-razinskog atoma (poput ljestvi) u impulsnom svojstvenom stanju s jednomodnim poljem u rezonatoru, uz nelinearnosti polja i vezanja ovisnog o intenzitetu. Izveli smo stalnice gibanja valne funkcije atomskog sustava. Posebnu smo pažnju posvetili raspravi o statističkim odlikama razmatranog atomskog sustava, kao što su povećanje i difuzija impulsa i zbijanje višeg reda. Numerički smo istražili utjecaj Kerrovog sredstva i vezanja ovisnog o intenzitetu na povećanje impulsa i zbijanje višeg reda. Našli smo da dodavanje tih parametara ima snažan učinak na povećanje impulsa i pojavu zbijanja

Međudjelovanje četiri-razinskog atoma u impulsnom svojstvenom stanju s jednomodnim poljem

We study the interaction between a four-level atom (ladder type) in a momentum eigenstate with a single mode cavity field in the presence of non-linearities of both the field and the intensity-dependent coupling. The constants of motion and the wave function for the atomic system have been obtained. Special attention is given to discuss some statistical aspects of the considered atomic system such as momentum increment, momentum diffusion and high-order squeezing. The influence of the Kerr-like medium and the intensity dependent coupling on the momentum increment and the high-order squeezing are investigated numerically. It is found that addition of these parameters has an important effect on both the momentum increment and the squeezing phenomenon.Proučavamo međudjelovanje četiri-razinskog atoma (poput ljestvi) u impulsnom svojstvenom stanju s jednomodnim poljem u rezonatoru, uz nelinearnosti polja i vezanja ovisnog o intenzitetu. Izveli smo stalnice gibanja valne funkcije atomskog sustava. Posebnu smo pažnju posvetili raspravi o statističkim odlikama razmatranog atomskog sustava, kao što su povećanje i difuzija impulsa i zbijanje višeg reda. Numerički smo istražili utjecaj Kerrovog sredstva i vezanja ovisnog o intenzitetu na povećanje impulsa i zbijanje višeg reda. Našli smo da dodavanje tih parametara ima snažan učinak na povećanje impulsa i pojavu zbijanja

Acute effects of cigarette smoking in habitual smokers, a focus on endothelial function

AbstractBackgroundThe chronic effect of cigarette (cig.) smoking is well established. The acute effect of smoking abolishes the concept, argued by heavy smokers, to decrease the number of smoked cigarettes instead of quitting.AimTo detect the acute effects of cigarette smoking and the duration of these effects.Patients and methodsThirty four smokers (age 21–35years) were studied at 3 occasions; 9h after the last cig. smoking, 5min after one cig. smoking and 30min after 3 cig. smoking within 30min. They were subjected to measurement of both ventricular functions using standard and tissue Doppler imaging (TDI), aortic distensibility, stiffness and endothelial function assessment by endothelium-dependent flow-mediated dilatation (FMD) and maximum vasodilatation.ResultsAfter one cigarette smoking, we found a statistically significant effect on blood pressure, Heart Rate, FMD percent, Dilation Ratio, aortic distensibility (P=0.007), and aortic stiffness index (ASI) (P=0.01). Furthermore the LV diastolic function was significantly impaired after smoking. Despite disappearance of acute effect of 3 cig. smoking within 30min on blood pressure, Heart Rate and aortic distensibility, a significant difference was still found as regards FMD percent and dilation ratio denoting the extension of the endothelial dysfunction for more than 30min after the last cigarette.ConclusionMany acute changes occur following one cigarette smoking even in habitual smokers. Persistence of endothelial dysfunction parameters after smoking indicates the failure of circulation adaptation in response to such offense that might contribute to the precipitation of acute events in vulnerable patients