Peak force as function of the embedded length in pull-out and microbond tests: effect of specimen geometry

We have derived the equations which explicitly express the peak force, F _max, and the apparent interfacial shear strength, τ _app, measured in the pull-out and microbond tests, as functions of the embedded length. Three types of test geometries were considered: (1) a fiber embedded in a cylindrical block of the matrix material; (2) microbond test with spherical matrix droplets; and (3) pull-out test in which the matrix droplet had the shape of a hemisphere. Our equations include the local interfacial shear strength (IFSS), τ _d, and the frictional interfacial stress, τ _f, as parameters; the effect of specimen geometry appeared in the form of dependency of the effective fiber volume fraction on the embedded length. The values of τ _d and τ _f were determined by fitting our theoretical curves to experimental F _max (l _e) plots by using the least squares method. Our analysis showed how the local IFSS and the frictional interfacial stress affected the measured F _max and τ _app values. In particular, it was revealed that intervals of embedded lengths could exist in which frictional interfacial stress had no effect on F _max and τ _app, even if the τ _f value was high. We also derived an equation relating the scatter in the interfacial strength parameters (τ _d and τ _f) to the scatter in τ _app, which is experimentally measurable, and proposed a procedure to determine the standard deviations of τ _d and τ _f from experimental pull-out and/or microbond test data.     

Process–structure–property relationships for nugget and heat affected zone regions of AA2524–T351 friction stir welds

Abstract

The effects of weld tool rotational speed ω, welding speed v and z-axis force F_Z during friction stir welding of the aluminium alloy 2524-T351 on the resulting process response variables, nugget microstructure, nugget tensile properties and heat affected zone hardness variations were investigated. For the range of conditions examined, the results indicate that ω has the dominant effect on nugget properties and structure, that optimum nugget tensile properties can be obtained by increasing ω to obtain a peak temperature that is just below the incipient local melting temperature, and that excessive values of ω result in low nugget ductility because of localised embrittlement near the weld crown. The study has also shown that the peak weld temperature is inversely related to the measured torque T ₀. The T ₀–ω relationship appears to be a useful guide for weld modification, as it is indicative of conditions leading to overheating in the nugget region.     

New repulsive potential functions with angle distributions for local path planning

This paper presents new repulsive potential functions (RPFs) for point robot path planning. In this scheme, the RPF for path planning has a different magnitude at each direction of a RPF based on the angle between a goal and an obstacle, unlike a conventional RPF in which the same magnitude at each direction is obtained. In doing so, the RPF attempts to overcome some of the typical problems that may arise with the conventional RPF. In particular, this paper presents a set of analyses for designing potential functions to avoid local minima for a number of representative scenarios. Specifically, the following cases are addressed: (i) a non-reachable goal problem (a case in which the potential of the goal is overwhelmed by the potential of an obstacle), (ii) an obstacle collision problem (a case in which the potential of the obstacle is overwhelmed by the potential of the goal) and (iii) a narrow passage problem (a case in which the potential of the goal is overwhelmed by the potential of two obstacles). The proposed RPF scheme eliminates the non-feasible area for the three cases by the help of an angle-varying magnitude between a goal and an obstacle. The example results show that the proposed RPF scheme can effectively construct a path-planning system with the capability of reaching a goal and avoiding obstacles despite possible local minima.     

A Location Management Scheme Supporting Route Optimization for Mobile Hosts

Using the Internet as a foundation for wirelessnetworking, there is currently a great deal of interestin providing IP networking support for mobile hosts. Asa result of IPs reliance on the entire Internet address for host identification, most proposalsdepend on a default route through the mobile host's homeaddress, which makes for unnecessarily long routes. Thispaper introduces two concepts, localregion and patron service, based on thelocality features of host moving and calling patterns.It then shows how these concepts work together torealize a location management scheme for achievingoptimal routing for most traffic while restricting costlylocation propagation. The proposed scheme wasimplemented using a network simulator and evaluated fromrouting effectiveness point of view, as compared withits location overhead.     

Local path planning using a new artificial potential function composition and its analytical design guidelines

This paper presents a new framework for path planning based on artificial potential functions (APFs). In this scheme, the APFs for path planning have a multiplicative and additive composition between APFs for goal destination and APFs for obstacle avoidance, unlike conventional composition where the APF for obstacle avoidance is added to the APF for goal destination. In particular, this paper presents a set of analytical guidelines for designing potential functions to avoid local minima for a number of representative scenarios based on the proposed framework for path planning. Specifically the following cases are addressed: (i) a non-reachable goal problem (a case in which the potential of the goal is overwhelmed by the potential of an obstacle), (ii) an obstacle collision problem (a case in which the potential of the obstacle is overwhelmed by the potential of the goal) and (iii) a narrow passage problem (a case in which the potential of the goal is overwhelmed by the potential of two obstacles). The example results for each case show that the proposed scheme can effectively construct a path-planning system with the capability of reaching a goal and avoiding obstacles despite possible local minima.     

Fracture resistance of simulated heat affected zone areas in HSLA structural steel

Abstract

The fracture toughness of some areas in the multi-pass heat affected zone (HAZ) of a high strength low alloy (HSLA) structural steel was analysed in a straightforward way using precracked, cylindrical specimens tested on a conventional tensile machine. The specimens were made from samples with a simulated HAZ microstructure; however, the size of the samples was restricted by the limitations of the Gleeble machine. The brittleness of the samples was an indication of the detrimental effect of welding on their toughness. The specimens were not large enough for a direct K_Ic measurement over a wide testing temperature range; it was necessary to modify the results. The low fracture toughness and the substantial shift of fracture transition temperatures suggest that welding of the investigated steel could be a delicate procedure.     

Frequency Hopping Code Division Multiple Access for Wireless Local Access

In this paper, the suitability of Slow FrequencyHopping Code Division Multiple Access (SFHCDMA) isevaluated for wireless local access applications.Investigations of the wireless channel indicate that frequency hopping mitigates the poorpropagation characteristics associated with low mobilitycommon to fixed wireless applications. Employingstatistical analysis and simulation models, it is shownthat the frequency hopped channel displays inherentfrequency diversity. Consequently, an FH architecture isresilient to the effects of intersymbol interferencearising from significant time dispersion frequently experienced in the wireless channel.Furthermore, interference diversity of SFH-CDMA resultsin a robust air interface technique. With simulationtechniques it is demonstrated that SFH-CDMA can support the medium rate service bearers (approximately1 Mbps) required for wireless local access, whilstproviding high capacity.     

Corrosion of porous iron electrodes containing metal additives in alkaline batteries

Abstract

Major problems currently associated with alkaline porous iron electrodes include the high rate of selfdischarge and the low utilisation efficiency of the active iron. The corrosion rates of porous iron electrodes electrodeposited with lead, mercury, silver, copper, or sulphur were analysed by the open circuit potential decay, cathodic potentiostatic polarisation, and gasometric methods. It was found that incorporation of elemental sulphur and copper produced the lowest corrosion rates.     

Convection driven melting of anisotropic metals

Abstract

This paper numerically explores melting of a pure substance with the thermal conductivity of the solid phase, assumed to be anisotropic. A two-phase test case for such situations is deduced from the standard one-phase Gobin–Le Quéré melting benchmark. The solution is presented for Prandtl number 0·02, Stefan number 0·01 and Rayleigh number 2·5 × 10⁴ which are specific for metals. Three cases are compared in terms of the terminal interface boundary position and average liquid fraction as a function of time for isotropic case and two distinctly oriented principal directions of the thermal conductivity tensor. The calculations have been performed by using the one-domain enthalpy formulation with artificial melting interval and the recently developed explicit local radial basis function collocation method (LRBFCM) which belongs to the entirely new generation of meshless methods. The results are not sensitive to the increased thermal conductivity of the solid phase in the direction parallel with the heated boundary but sensitive with the increase of the thermal conductivity of the solid phase in the direction perpendicular to the heated boundary.     

Non-destructive characterization and quality control of intact strawberries based on NIR spectral data

External and internal quality parameters of strawberries (Fragaria x ananassa Duch.) were studied at harvest and during postharvest refrigerated storage using a handheld micro-electro-mechanical system (MEMS) near-infrared spectrophotometer. A total of 189 strawberry punnets were used to develop calibration models using various spectral signal pretreatments and linear and non-linear regression algorithms; the sampling unit for both NIRS analysis and reference methods comprised 5 strawberries from each punnet. Modified partial least squares analysis confirmed the feasibility of NIRS for predicting color-related external quality parameters (L^∗, a^∗ and C^∗) as well as firmness, soluble solid content and titratable acidity. For other tested parameters (b^∗, h^∗ and pH), the results suggested that NIRS prediction was not feasible. However, the application of a LOCAL algorithm considerably improved the ability of models to predict all the internal quality parameters studied. Use of the LOCAL algorithm proved valuable in minimizing the error in NIRS models for predicting complex internal quality parameters, mainly those related to texture and acidity. Subsequently, the ability of NIR technology to classify individual strawberries as a function of variety was tested using partial least squares discriminant analysis (PLS-DA), which yielded percentages of correctly classified samples (ratio of correctly classified samples to total samples) ranging from 57% for the Camarosa variety to 78% for Antilla Fnm.