Fatigue damage accumulation of cold expanded hole in aluminum alloys subjected to block loading

Fatigue damage accumulation of cold expanded hole in aluminum alloys used in land transportation components was investigated. Tests were carried out using pre-cracked SENT specimens and inserting an expanded hole at the crack tip. The degree of the cold expansion was chosen equal to 4.3%. Tests were performed in two and four block loading under constant amplitude. Two sequences were compared.The increasing and the decreasing magnitude were compared. The experimental results were compared to the damage calculated by the Miner's rule and a new simple fatigue damage indicator. This comparison shows that the ‘model of the damage stress’, which take into account of the loading history, yields a good estimation of the experimental results. Moreover, the error is minimized in comparison to the Miner's model.     

Toward hydrogen enriched natural gas “HCNG” fuel on the algerian road

The Algerian transport sector is still largely dependent on petroleum. Pollution emitted by this sector is constantly increasing with the expansion of the automobile fleet. Thus, there is a pressing need for use of cleaner and economically viable alternative fuels. Therefore, the use of Hydrogen enriched Compressed Natural Gas (HCNG) is expected to play a significant role to reach this target. When hydrogen and natural gas are used together in an internal combustion engine, large benefits are possible. Algeria has significant resources and potential to introduce this new fuel. The development of HCNG as a transportation fuel allows an entry point for hydrogen in the transportation sector. The aim of this paper is to discuss strategic ways to introduce HCNG as road fuel, in Algeria. Two fundamental strategic elements were designed to introduce the Hydrogen Enriched Natural Gas as a transportation fuel. These are, the development of compressed natural gas as a road fuel, and the completion of the MedHySol project. The MedHySol project includes the production and the distribution of solar produced hydrogen, and involves the project HySolThane intended for the development of HCNG fuel road with 8% vol of Hydrogen in Natural Gas.     

Fatigue life prediction under variable loading based on a new damage model

To examine the performance of nonlinear models proposed in the estimation of fatigue damage and fatigue life of components under random loading, a batch of specimens made of 6082 T 6 aluminium alloy has been studied and some of the results are reported in the present paper. The paper describes an algorithm and suggests a fatigue cumulative damage model, especially when random loading is considered. This paper contains the results of mono-axial random load fatigue tests with different mean and amplitude values performed on 6082 T 6 aluminium alloy specimens. Cycles were counted with rainflow algorithm and damage was cumulated with a new model proposed in this paper and with the Palmgren–Miner model. The proposed model has been formulated to take into account the damage evolution at different load levels and it allows the effect of the loading sequence to be included by means of a recurrence formula derived for multilevel loading, considering complex load sequences. It is concluded that a ‘damaged stress interaction damage rule’ proposed here allows a better fatigue damage prediction than the widely used Palmgren–Miner rule, and a formula derived in random fatigue could be used to predict the fatigue damage and fatigue lifetime very easily. The results obtained by the model are compared with the experimental results and those calculated by the most fatigue damage model used in fatigue (Miner’s model). The comparison shows that the proposed model, presents a good estimation of the experimental results. Moreover, the error is minimized in comparison to the Miner’s model.     

Charge-extraction technique for studying the surface states in MOSdevices

A method called the charge-extraction technique is proposed for studying the surface states in MOS devices. This new technique utilizes the substrate current arising from the non-steady-state emission of carries from the surface states instead of that arising from their steady-state recombination, as utilized in the charge-pumping method. This is achieved by confining the amplitude of the gate-voltage signal to such a magnitude that the surface region of the device does not cross the depletion limits. A new theoretical model is developed for the present case which predicts the occurrence of a maximum value of the substrate current at a certain optimum frequency of the applied gate-voltage signal. Experimental measurements have been found quite in conformity with the theoretical model. It is found that the maximum substrate current and the corresponding optimum frequency, obtained in this way, can serve as more handy and precise parameters for the determination of the surface states     

Gammatone filterbank and symbiotic combination of amplitude and phase-based spectra for robust speaker verification under noisy conditions and compression artifacts

Multimedia Tools and Applications - The main novelty of this work resides in incorporating a Gammatone filter-bank as a substitute of the Mel filter-bank in the extraction pipeline of the Product...     

Tensile Properties and Fusion Zone Hardening for GMAW and MIEA Welds of a 7075-T651 Aluminum Alloy

Tensile and hardness values for 7075-T651 aluminum alloy in the as welded and post weld heat treated conditions（solubilization and artificial aging-T6）,obtained using GMAW and modified indirect electric arc（MIEA）welding processes are presented.Results showed that the base material along rolling direction exhibited a tensile strength of around 600 MPa and elongation of 11%.For the as welded condition,tensile strength was 260 MPa and elongation percent of 3%.This behavior was attributed to brittleness induced by the microstructural characteristics of the welded alloys,as well as high porosity.Hardness profiles along the welds were obtained and different welded zones were identified.A soft zone（＊100 HV0.1） in the heat affected zone for GMAW and MIEA was observed,the minimum hardness corresponding to weld metal（＊85 and ＊96 HV0.1for GMAW and MIEA,respectively）.The high dilution between filler and base metal during welding in MIEA allows to the Zn and Cu to flow from the base metal into the weld metal,inducing hardening by solution and subsequent artificial aging.In this regard,the hardness of the weld metal for MIEA increases by 56%,while the tensile strength reaches a value close to 400 MPa.For GMAW,non-favorable hardening effect was observed for the weld metal after solution and artificial aging.     

Fatigue life estimation after crack repair in 6005 A-T6 aluminium alloy using the cold expansion hole technique

In this paper, the hole drilling (HD) and the cold expansion (CE) processes, which were used as a technique for crack repair, were investigated in order to estimate the beneficial effects on fatigue crack initiation (FCI). The FCI life is defined as the number of cycles to initiate a new crack of 0.2 mm on the surface of the specimen. Three hole radii and three degrees of cold expansion (DCE%) values were tested after a crack propagation period. Crack retardation after the CE process was observed. This phenomenon is due to two mechanisms: retardation owing to both geometric and mechanical effects, which is produced by the stress concentration at the drilled hole, and the large strain‐induced compressive residual stresses around the hole. In this report, the influence of the loading conditions was studied. For high values of the stress intensity factor range ΔK_ρ around the hole (based on the pseudo crack length a + ρ), the number of cycles corresponding to crack initiation N_i is low. At the edge of the hole, the maximum stress range can be approximated by the following formula: Δσ_max = 2ΔK_ρ /√πρ , where ρ is the hole radius and ΔK_ρ is the related stress intensity factor range.The FCI life extension, defined by the number of cycles corresponding to crack re‐initiation N_i , is related to the relative maximum stress range ratio R_σ = [(Δσ_max )/(Δσ_max )_th ] where (Δσ_max )_th is the value of the threshold maximum stress range obtained when N_i = 2 × 10⁶ cycles. The relationship between N_i and R_σ may be written as a power function.     

A shelf-space-dependent wholesale price when manufacturer and retailer brands compete

We propose a game-theoretic model involving the manufacturer of a national brand and a retailer selling her private label along with the national brand. The retailer can use either a differentiation strategy or an imitation strategy for offering her store brand. We consider two cases: the benchmark case, where both players have symmetric information and play a Nash game, and the incentive case, where the national brand’s manufacturer, acting as a leader, offers an incentive to the retailer in order to benefit from a larger proportion of the shelf space, which ultimately increases her own profit. By comparing both situations, we attempt to derive the conditions under which it is profitable for the manufacturer to implement such an incentive strategy and investigate if the results are idiosyncratic to the PL concept. These conditions are fourfold, and include the private label’s image, the price competition between the national brand and the private label, the transfer price level and the shelf-space allocated to the national brand in the benchmark case.     

Analysis of the distribution of thermal residual stresses in bonded composite repair of metallic aircraft structures

In this study, the distribution of the thermal residual stresses due to the adhesive curing in bonded composite repair is analysed using the finite element method. The computation of these stresses comprises all components of the structures: cracked plate, composite patch and adhesive layer. In addition, the influence of these residual stresses on the repair performance is highlighted by analysing their effect on the stress intensity factor at the crack tip. The obtained results show that the normal thermal stresses in the plate and the patch are important and the shear stresses are less significant. The level of the adhesive thermal stresses is relatively high. The presence of the thermal stresses increases the stress intensity factor at the crack tip, what reduce the repair performance.     

Robust regression fusion of GMM-UBM and GMM-SVM normalized scores using G729 bit-stream for speaker recognition over IP

A novel approach, based on robust regression with normalized score fusion (namely Normalized Scores following Robust Regression Fusion: NSRRF), is proposed for enhancement of speaker recognition over IP networks, which can be used both in Network Speaker Recognition (NSR) and Distributed Speaker Recognition (DSR) systems. In this framework, it is basically assumed that the speech must be encoded by G729 coder in client side, and then, transmitted at a server side, where the ASR systems are located. The Universal Background Gaussian Mixture Model (GMM-UBM) and Gaussian Supervector (GMM-SVM) with normalized scores are used for speaker recognition. In this work, Mel Frequency Cepstral Coefficient (MFCC) and Linear Prediction Cepstral Coefficient (LPCC), both of these features are derived from Line Spectral Pairs (LSP) extracted from G729 bit-stream over IP, constitute the features vectors. Experimental results, conducted with the LIA SpkDet system based on the ALIZE platform3 using ARADIGITS database, have shown in first that the proposed method using features extracted directly from G729 bit-stream reduces significantly the error rate and outperforms the baseline system in ASR over IP based on the resynthesized (reconstructed) speech obtained from the G729 decoder. In addition, the obtained results show that the proposed approach, based on scores normalization following robust regression fusion technique, achieves the best result and outperform the conventional ASR over IP network.