He, Xiaocong
Zhang, Yue
Xing, Baoying
Gu, Fengshou
Ball, Andrew
The mechanical properties of extensible die clinched joints in titanium sheet materials were investigated in this paper. Tensile-shear tests were carried out to characterize the mechanical properties of different clinched joints made of the similar titanium sheets and the dissimilar metal sheets combinations. The normal hypothesis tests were performed to examine the rationality of the test data. The load-bearing capacity, energy absorption and failure modes of different titanium sheets clinched joints were studied. Results showed that almost all titanium sheets clinched joints failed in the neck fracture mode. Results also showed that the load-bearing capacity and energy absorption of clinch joints with titanium as upper sheets are higher than that of the clinched joints with titanium as lower sheets. (C) 2015 Elsevier Ltd. All rights reserved.
Acoustic emission analysis is an effective diagnostic method in modern tribo-monitoring. Many experimental studies have been conducted to investigate the relationship between AE parameters and wear and friction. This paper develops a theoretical model to correlate acoustic emissions to sliding friction based on elastic asperity contact of materials. It is found that sliding speed, load supported by asperities, the number of asperity contact and surface topographic characteristics influence the energy of AE signal. With the help of this model it is possible to estimate the contact load supported by asperities from AE measurement, which is a critical parameter to evaluate lubrication conditions in engineering applications. The establishment of this model will provide a theoretical basis for future studies on the motioning and prognostics of tribological process using AE technology. (c) 2009 Elsevier B.V. All rights reserved.
He, Xiaocong
Xing, Baoying
Zeng, Kai
Gu, Fengshou
Ball, Andrew
Self-piercing riveting (SPR) is a new high-speed mechanical fastening technique which is suitable for point-joining dissimilar sheet materials, as well as coated and pre-painted sheet materials. With an increasing application of SPR in different industrial fields, the demand for a better understanding of the knowledge of static and dynamic characteristics of the SPR joints is required. In this paper, the SPR process has been numerically simulated using the commercial finite element software LS-Dyna. For validating the numerical simulation of the SPR process, experimental tests on specimens made of aluminium alloy have been carried out. The online window monitoring technique was introduced in the tests for evaluating the quality of SPR joints. Good agreements between the simulations and the tests have been found, both with respect to the force-travel (time) curves as well as the deformed shape on the cross-section of the SPR joint. Monotonic tensile tests were carried out to measure the ultimate tensile strengths of the bonded joints, SPR joints and SPR-bonded hybrid joints. Deformation and failure of the joints under monotonic tensile loading were studied. The normal hypothesis tests were performed to examine the rationality of the test data. This work was also aimed at evaluating experimentally and comparing the strength and energy absorption of the bonded joints, SPR joints and SPR-bonded hybrid joints.
Li, Guoxing
Gu, Fengshou
Wang, Tie
Yang, Tiantian
Ball, Andrew
To understand the effects of vibration of cylinder liners on engine combustion performance, tribological behaviour and vibro-acoustic radiations, this study investigates the dynamic responses of cylinder liners by finite-element modelling and experimental validation. The finite-element model is established in this study to predict the dynamic responses of cylinder liners to two significant sources: combustion shock and piston side thrust. It takes into account both the characteristics of structural modes and nonlinearities of assembly constraints when selecting adequate elements for efficient computation of the responses under both the highly nonlinear combustion pressure excitations and subsequent piston slap impacts. The predictions are then evaluated against experimental results under different engine operating conditions. To suppressing noise in measured signals, continuous wavelet analysis is employed to process the complicated responses for characterizing key response events and their frequency ranges. The results show agreeable correspondences between the numerical predictions and measured vibration signals, paving the way for investigating its effect on the combustion and lubrication processes.
Li, Guoxing
Gu, Fengshou
Wang, Tie
Lu, Xingchen
Zhang, Li
Zhang, Chunfeng
Ball, Andrew
The friction pair of piston rings and cylinder liner is one of the most important friction couplings in an internal combustion engine. It influences engine efficiency and service life. Under the excitation of piston slaps, the dynamic deformation of cylinder liner is close to the surface roughness magnitudes, which can affect the friction and lubrication performance between the piston rings and cylinder assemblies. To investigate the potential influences of structural deformations to tribological behaviours of cylinder assemblies, the dynamic deformation of the inner surface due to pistons slaps is obtained by dynamic simulations, and then coupled into an improved lubrication model. Different from the traditional lubrication model which takes the pressure stress factor and shear stress factor to be constant, the model proposed in this paper calculated these factors in real time using numerical integration to achieve a more realistic simulation. Based on the improved piston rings and cylinder liner lubrication model, the minimum oil film thickness and friction force curves are obtained for an entire work cycle. It shows that the friction force obtained from the improved model manifests clear oscillations in each stoke, which is different from the smoothed profiles predicted traditionally. Moreover, the average amplitude of the friction forces also shows clear reduction.
The cytoplasmic Ca-2+ concentration ((Ca-2+)-i) was continuously monitored in single glucagon-producing alpha-2-cells isolated from the mouse pancreas and later identified by immunostaining. Up to 60% of the alpha-2-cells exhibited spontaneous (Ca-2+)-i oscillations (frequency 0.1-0.3/min) in a medium containing 3 mM glucose. In originating from a basal level of 60-100 nM, reaching peak values of 300-400 nM and promptly disappearing after blocking voltage-dependent Ca-2+ channels with methoxyverapamil, the oscillations resembled those in insulin-releasing beta-cells stimulated by glucose. The oscillatory activity was suppressed when combining elevation of glucose to 20 mM with the addition of 2-2000 ng/ml insulin. Whereas 10 mM of L-arginine or L-glycine transformed the oscillations into sustained elevation of (Ca-2+)-i, there was no response to 1 mM tolbutamide or 0.1-1 mM gamma-aminobutyric acid. The observations that alpha-2-cells differ from islet cells secreting insulin and somatostatin in responding to adrenaline with mobilisation of intracellular calcium can be used for their rapid identification. It is suggested that the oscillations reflect periodic entry of Ca-2+ due to variations of the membrane potential.
Li, Guoxing
Gu, Fengshou
Wang, Tie
You, Jianjun
Ball, Andrew
The paper presents a study of the relationship between the combustion behavior and vibration response of internal combustion (IC) engines fueled with biodiesel based on finite element modelling along with experimental evaluation. An improved finite element (FE) model is established and validated to predict the dynamic responses of cylinder liners with respect to two main sources: combustion shock and piston side thrust. Based on the validated FE model, the response characteristics of the cylinder liner in an IC engine fueled with biodiesel and its causal relationship with excitation sources have been predicted. Due to the lower calorific value of biodiesel, a greater amount of fuel is injected into the combustion chamber to maintain power outputs, which results in a prolonged combustion duration and subsequent higher overall vibration levels, compared with that of diesel. The advanced ignition of biodiesel is the main cause to the compound effect on the coupling of piston side-thrust force, thereby resulting in a nonlinear increase in the root mean square (RMS) of local vibration response close to the combustion top dead center (TDC). These key findings provides insight understandings for not only biodiesel combustion diagnostics but also more accurate diagnostics of fossil diesel based on nonintrusive vibrations.
Gu, Fengshou
Yesilyurt, Isa
Li, Yuhua
Harris, Georgina
Ball, Andrew
In order to discriminate small changes for early fault diagnosis of rotating machines, condition monitoring demands that the measurement of instantaneous angular speed (IAS) of the machines be as accurate as possible. This paper develops the theoretical basis and practical implementation of IAS data acquisition and IAS estimation when noise influence is included. IAS data is modelled as a frequency modulated signal of which the signal-to-noise ratio can be improved by using a high-resolution encoder. From this signal model and analysis, optimal configurations for IAS data collection are addressed for high accuracy IAS measurement. Simultaneously, a method based on analytic signal concept and fast Fourier transform is also developed for efficient and accurate estimation of IAS. Finally, a fault diagnosis is carried out on an electric induction motor driving system using IAS measurement. The diagnosis results show that using a high-resolution encoder and a long data stream can achieve noise reduction by more than 10 dB in the frequency range of interest, validating the model and algorithm developed. Moreover, the results demonstrate that IAS measurement outperforms conventional vibration in diagnosis of incipient faults of motor rotor bar defects and shaft misalignment. (c) 2005 Elsevier Ltd. All rights reserved.
Feature selection method has become the focus of research in the area of engineering data processing where there exists a large amount of high-dimensional data from the high-frequency acquisition system. For high-dimensional data processing; engineers often resort to feature extraction methods and statistical theories to convert the original features into new features. However; the converted data always lose the engineering meaning of the original features and the choice and use of conversion methods are challenging. In this paper; a hybrid feature selection model is presented to select the most significant input features from all potentially relevant features. The algorithm combines a filter model with a wrapper model. In the filter model; four variable ranking methods are used to pre-rank the candidate features. These four methods including Pearson correlation coefficient; Relief algorithm; Fisher score and Class separability; measure features from various angles; which leads to different ranking results. Therefore; a weighted voting scheme is introduced to re-rank features based on the degree of significance of the four methods on the classification error rate of Radial Basis Function (RBF) classifier. In wrapper model; a Binary Search (BS) method and a Sequential Backward Search (SBS) method are utilized to minimize the number of relevant features when promising to keep the classification error rate of RBF classifier below a given threshold. To demonstrate the potential of applying the method to large-scale engineering data processing; a case study is conducted.
Farage, Peter
Ball, Andrew
McGenity, Terry J.
Whitby, Corinne
Pretty, Jules
The use of fire in land management has come under increasing scrutiny with regard to its potential effects on sustainability and climate change. Moorlands in the United Kingdom have traditionally used rotational burning of the heather (Calluna vulgaris) to improve the grazing and habitat, especially for grouse (Lagopus lagopus scoticus). However, these ecosystems overlie carbon-rich soils and concerns have been raised about the merits of this practice. In order to assess the impact of rotational burning on carbon balance, an investigation was undertaken on a grouse moor in the Yorkshire Dales, UK. This showed that the quantity of carbon stored above ground in heather biomass ranged from 600 to 1325 g C/m(2) (typical for UK upland heaths). However, the national UK carbon inventory assumes 200 g C/m(2), thereby appearing to underestimate considerably the importance of these habitats for carbon storage above ground. Analysis of 2 burns in subsequent years showed that 16 +/- 4% and 24 +/- 5% (+/- s.e.) of the above-ground material was consumed in the fires, resulting in the direct release of 103 +/- 22 and 201 +/- 62 g/m(2) of carbon, respectively. Indirect carbon losses, which other studies have shown to be primarily due to erosion, were estimated to release another 5-21 g C/m(2). year. The significance of other major greenhouse gas fluxes was assessed for the whole system using published parameters and models. We show that, over the burning cycle of 15-20 years, losses of carbon from burning are < 10% of the total losses of carbon from the system, implying that careful burning management at this site does not have a major detrimental effect on the carbon budget, which for this moor lies within the range of an annual net loss of 34 g C/m(2). year to a net uptake of 146 g C/m(2) year.