Mathematical modelling and experimental investigation on sun and solar drying of white mulberry

The drying kinetics of white mulberry was investigated in a solar dryer with forced convection and under open sun with natural convection. The constant rate period is absent from the drying curve. The drying process took place in the falling rate period. The drying data were fitted to the different mathematical models. The performance of these models was investigated by comparing the determination of coefficient (R), reduced chi-square (χ ²) and root mean square error (RMSE) between the observed and predicted moisture ratios. Among these models, the drying model developed by Logarithmic model showed good agreement with the data obtained from the experiments in the solar dryer with forced convection drying mode. The Verma et al. model has shown a better fit to the experimental mulberries data for open sun drying with natural convection mode than the other models. The effective moisture diffusivity values were estimated from Fick’s diffusional model. These values were 3.56×10⁻⁹ m²/s for solar drying and 2.40×10⁻⁹ m²/s for open sun drying.     

Effects on mechanical properties in electron beam welding of TC4 alloy by laser shock processing

The surface of TC4 titanium alloy welding line by electron beam welding (EBW) was processed by high power Q-switched and repetition-rate Nd: glass laser. Effects of laser power and spot diameter on residual stress and microhardness of the TC4 alloy welding line by laser shock processing (LSP) have been analyzed. Results show that residual stresses almost do not change as laser power is 45.9 J, spot diameter is ϕ9 mm; While laser power is 45.9 J, spot diameter less than ϕ3 mm, the distribution of residual stress in welding line occurs obvious variation, which residual stress increase obviously with spot diameter decrease. When power density is bigger than 1.8 × 10¹⁰ W/cm², residual stresses of electron beam welding line occur change by LSP, which improve obviously residual stress distribution; while laser power is bigger than 1.2 × 10¹⁰ W/cm², the surface micro-hardness of electron beam welding line occurs change by LSP, which improve obviously micro-hardness distribution. Mechanical properties of TC4 titanium alloy welding line will be improved by LSP, which provides experimental foundation for further controlling the distributions of residual stress and micro-hardness during laser shock processing. __________ Translated from Journal of Jiangsu University (Natural Science), 2006, 27(3): 207–210 [译自: 江苏大学学报 (自然科学版)]     

Tribology of confined Fomblin-Z perfluoropolyalkylethers: molecular weight dependence and comparison between unfunctionalized and telechelic chains

The dynamic shear properties of molecularly-thin films of unfunctionalized and end-functionalized (telechelic) Fomblin-Z perfluoropolyalkylether (PFPAE) melts with number-average molecular weight M _n≈ 3000−4000 g,mol^-1 have been studied at shear rates of 10^-2−10⁵ s^-1 at normal pressures of 1 and 3 MPa. The shear responses are compared to measurements on end-functionalized polymers of the same chemical composition but lower molecular weight, M _n≈ 2000 g,mol^-1. The predominantly elastic response and high shear moduli of the confined film of unfunctionalized polymer, Fomblin Z03, suggest that it forms a structure likely to solidify already at low pressure. Its lubricating properties are less favorable than the ones found for hydroxyl- (DOL) and piperonyl-terminated Fomblin-Z (AM2001, AM3001), where associated molecules form a structure less prone to solidification under confinement. The thickness of the compressed films of the end-functionalized polymers increased more strongly with molecular weight than as M _n ^0.5 . The shear moduli were found to be larger, the higher the molecular weight, indicating slower relaxations. At a normal pressure of 3 MPa, these films solidified and displayed stick–slip as seen already at 1 MPa in the Z03 film. The limiting shear stress of the unfunctionalized Z03, σ > 3 MPa, exceeded by an order of magnitude the limiting shear stress of all of the end-functionalized polymers. The limiting shear stress of the hydroxyl-terminated polymer was larger than that of the piperonyl-terminated polymer. This revised version was published online in August 2006 with corrections to the Cover Date.     

Assessment of the sulfide corrosion fatigue strength for a multi-pass welded A106 Gr B steel pipe below the low SSCC limit

In the area of heavy construction, welding processes are vital in the production and maintenance of pipelines and power plants. Welding processes happen to produce residual stresses and change the metal structure as a result of the large nonlinear thermal loading that is created by a moving heat source. The fusion welding process generates formidable welding residual stresses and metallurgical change, which increase the crack driving force and reduce the resistance to the brittle fracture as well as the environmental fracture. This is a serious problem with many alloys as well as the A106 Gr B steel pipe. This pipe that is used in petrochemical and heavy chemical plants either degrades due to corrosive environments, e.g., chlorides and sulfides, and/or become damaged during service due to the various corrosion damage mechanisms. Thus, in this study, after numerically and experimentally analyzing the welding residual stress of a multi-pass welded A106 Gr B steel pipe, the sulfide stress corrosion cracking (SSCC) characteristics were assessed in a 3.5 wt.% NaCl solution that was saturated with H₂S gas at room temperature on the basis of NACE TM 0177-90. The specimens used are of two kinds: un-notched and notched. Then, the sulfide corrosion fatigue (SCF) strength for the un-notched specimen was assessed below the low SSCC limit that was previously obtained from the SSCC tests for the notched specimen. From the results, in terms of the SSCC and SCF, all the specimens failed at the heat-affected zone, where a high welding residual stress is distributed. It was found that the low SSCC limit of un-notched specimens (σ_{SSCCun-notched}) was 46% (230 MPa) of the ultimate tensile strength (σ_U=502 MPa) of a multi-pass welded A106 Gr B steel pipe, and the notched specimens (σ_SSCCnotched) had 40% (200 MPa) of the ultimate tensile strength. Thus, it was determined that σ_{SSCCun-notched} was 13% lower than σ_SSCCnotched. Further, the sulfide corrosion fatigue limit (σ_{SCFun-notched}) was 32% (160 MPa) of the ultimate tensile strength of welded specimens. This σ_{SCF un-notched} was 20% lower than σ_SSCCnotched.     

An analysis of the signal-to-noise ratio of a current amplifier

The signal-to-noise ratio of the current amplifier that includes a differenting delay line (50 ns) and an RC integrator is analyzed. The amplifier is intended for use in conjunction with charge-, curret-, or voltage-pulse detectors, including those with large capacitances or low ohmic resistances. The amplifier and detector can be connected with a long (in this work, up to 100 m) radio-frequency cable. The root-mean-square intrinsic noise charge of the amplifier is 2.8×10³ e ⁻ when the input is nonloaded and 13.7×10³ e ⁻ when a 20-meterlong 3 cable is connected to the input. If the charge produced by the detector is constant and the pulse duration decreases, then both the signal-to-noise ratio and the equipment speed performance can be increased.     

Fatigue design of various type spot welded lap joints using the maximum stress

Recently, a new issue in designing spot welded structures such as automobile and train car bodies is to predict an economical fatigue design criterion. One of the most typical and traditional methods is to use a ΔP—N_f curve. However, since the fatigue data on the ΔP—N_f curve vary according to the welding conditions, materials, geometry of joint and fatigue loading conditions, it is necessary to perform the additional fatigue tests for determining a new fatigue design criterion of spot-welded lap joint having specific dimension and geometry. In this study, the stress distributions around spot welds of various spot welded lap joints such as in-plane bending type (IB type), tension shear type (TS type) and cross tension type (CT type) were numerically analyzed. Using these results, the ΔP—N_f curves previously obtained from the fatigue tests for each type were rearranged into the Δσ -N _f relations with the maximum stresses at the nugget edge of the spot weld.     

Microwave drying and moisture diffusivity of white mulberry: experimental and mathematical modeling

The literature surveyed revealed that drying kinetics of white mulberry under microwave treatment has not been investigated. In present study, both experimental study and mathematical modeling on microwave drying of white mulberry was performed. The microwave drying process which reduced the moisture content of mulberry from 3.76 to 0.25 (g water/g dry matter) was carried out at 90, 180, 360, 600, and 800 W in a modified microwave drying set-up. The effects of microwave drying technique on the moisture ratio and drying rate of white mulberry were investigated experimentally. Both the effects of microwave power level (under the range of 90–800W) and initial sample weight (50–150g) were studied. No constant rate period was observed. Mathematical modeling of thin layer drying kinetics of white mulberry under microwave treatment was also investigated by fitting the experimental drying data to eight thin layer drying models. Among the models proposed, Midilli et al. model precisely represented the microwave drying behavior of white mulberry with the coefficient of determination higher than 0.999 and mean square of deviation (χ²) and root mean square error (RMSE) lower than 1.1×10⁻⁴ and 8.9×10⁻³, respectively for all the microwave drying conditions studied. The effective moisture diffusivity (D_eff) of white mulberry varied from 0.45×10⁻⁸ to 3.25×10⁻⁸ m²s⁻¹. Both the drying constant (k) and D_eff increased with the increase of microwave power level.     

A study on properties of corrosion fracture surfaces of GFRP in synthetic sea water

In this paper we investigate the stress corrosion cracking (SCC) mechanism and the properties of the corrosion fracture surface of glass fiber reinforced plastics (GFRP) produced by hand lay-up (HLU) in synthetic sea water. The test material is a GFRP with vinylester type epoxy acrylate resin (an unsaturated polyester) as the matrix and chopped strand mat (CSM) type E-glass fiber as the reinforcement. The slow strain rate test (SSRT) was perormed on dry and wet specimens in air and sea water. Here the pH concentration of synthetic sea water was controlled to 6.0, 8.2 and 10.0, and the strain rates varied from 1×10⁻⁴ (sec⁻¹) to 1×10⁻⁷ (sec⁻¹). The results confirm the fact that in wet specimens tested at a particular strain rate, evidence of SCC such as co-planar, mirror and hackle zone appear. Moreover, stress corrosion of GFRP in sea water was characterised by flat fracture surfaces with only small amounts of fiber pull-out.     

Low-temperature creep behavior of ultrafine-grained 5083 Al alloy processed by equal-channel angular pressing

Low temperature creep behavior of ECAPed Al 5083 alloy with grain sizes of approximately 300 nm was investigated at temperatures of 498, 523 and 548 K. The value of the stress exponent was found to be 3.5 at a low stress level and increased to 5.0 at a high stress level. At the low stress level, the creep curve exhibits typical class II behavior due to the accumulated strain during the ECAP process, even though the creep is controlled by solute-drag processes with a stress exponent of 3.5. The average value of Q obtained from the analysis of the data is close to that for dislocation pipe diffusion. Therefore, on the basis of the activation energy in a temperature range of 498K to 548K at low and high stress level, the creep deformation is controlled by dislocation glide and climb processes, respectively, and the rate-controlling diffusion step might be dislocation pipe diffusion.     

Numerical determination of the elastic compliance of roller bearings using the hertz theory

Analytical determination of the elastic compliance of roller bearings using the Hertz theory is presented. It is revealed that this parameter depends on the external load q and is varied from 15 × 10⁻⁶ up to 35 × 10⁻⁶ mm²/N for the wide range of q variation.     

Turbulence modeling of natural convection in enclosures: A review

In this paper a review of recent developments of turbulence models for natural convection in enclosures is presented. The emphasis is placed on the effect of the treatments of Reynolds stress and turbulent heat flux on the stability and accuracy of the solution for natural convection in enclosures. The turbulence models considered in the preset study are the two-layer k − ɛ model, the shear stress transport (SST) model, the elliptic-relaxation (V2-f) model and the elliptic-blending second-moment closure (EBM). Three different treatments of the turbulent heat flux are the generalized gradient diffusion hypothesis (GGDH), the algebraic flux model (AFM) and the differential flux model (DFM). The mathematical formulation of the above turbulence models and their solution method are presented. Evaluation of turbulence models are performed for turbulent natural convection in a 1:5 rectangular cavity ( Ra= 4.3×10¹⁰) and in a square cavity with conducting top and bottom walls ( Ra= 9 1.58×10⁹) and the Rayleigh-Benard convection ( Ra = 2 × 10⁶ ∼ Ra = 10⁹). The relative performances of turbulence models are examined and their successes and shortcomings are addressed.     

Pulsed interferometric calorimetry

The possibility of using semiconductor single crystals (Si, GaP, etc.) as calorimeters for pulsed heat flux measurements is discussed. The method of laser interferometric thermometry in the reflected light at a wavelength of 1.15 μm makes it possible to detect changes δθ≈2×10⁻⁵ K in the temperature of a 1-mm-thick Si single crystal. The sensitivity of a calorimeter with laser readout is sufficient for detection of the absorbed energy δE≈15 μJ/cm² and is independent of the Si plate thickness. The method for selecting the working point in the resonance curve for achieving maximum sensitivity in detection of pulse fluxes is discussed.     

CsI(Tl)-calorimeter calibration with positive-kaon decay products

The CsI(Tl) calorimeter was calibrated in the KEK-E246 experiment withK _μ2-andK _π2-positivekaon decays. The following calorimeter parameters were obtained: an energy resolution (σ) of 4.1% forE=242.5 MeV, a π⁰ invariant-mass resolution (σ) of 5.6%, and an angular resolution (σ) of 3.1^o.     

Coupled Effect of Filler Content and Countersurface Roughness on PTFE Nanocomposite Wear Resistance

In tests of PTFE with 2.9% volume content alpha-phase alumina nanoparticles (40 or 80 nm) in sliding reciprocation against polished steel, wear rates of ~10⁻⁷ mm³/Nm were measured which is four orders-of-magnitude lower than unfilled PTFE and two orders-of-magnitude lower than with microparticles (0.5 or 20 μm) of more conventional filler size. This was similar to that previously reported in unidirectional sliding, and did not vary greatly with stroke of reciprocation. For a microfilled PTFE, the wear rate gradually increased towards that of unfilled PTFE as filler content was reduced, whereas nanofilled PTFE maintained relatively constant ~10⁻⁷ mm³/Nm to filler contents as low as 0.18% before reverting towards the rapid wear rate of unfilled PTFE. Lightly filled nanocomposites depend upon low countersurface roughness to maintain such low wear rate, and with increasing roughness the wear rate was found to transition at a critical value to a wear rate of ~10⁻⁵ mm³/Nm. Nanocomposites with higher filler contents were able to retain the low wear rates against rougher countersurfaces, as the critical roughness at which this wear resistance was lost tended to increase with the square of the filler content. Upon encountering extremely high countersurface roughness in the range R _a = 6–8 μm, nanocomposites at each filler content eventually increased in wear rate to ~10⁻⁴ mm³/Nm. The steel countersurface did not appear to play an important role in the extreme wear resistance of these alumina nanofilled PTFE composites, as comparable performance was also displayed against alumina countersurfaces.     

Multichannel wire gas electron multipliers with 1- and 3-mm gaps

The operation of multichannel wire gas electron multipliers (MWGEMs) with gaps between electrodes δ = 1 and 3 mm, when the chamber is filled with commercial neon under a 0.4- and 1.0-atm (abs.) pressure and irradiated with α and β particles, is studied. The following maximal proportional electron multiplication coefficients are obtained: 6 × 10³ (α, irradiation, δ = 3 mm, 1 atm, and 20% streamers), 1.2 × 10⁴ (β⁻, 3 mm, 1 atm, and 50% streamers), 6 × 10³ (α, 3 mm, 0.4 atm, and 20% streamers), and 10⁵ (β⁻, 3 mm, 0.4 atm, and 50% streamers). The maximal proportional electron multiplication coefficients are obtained in the MWGEM and its anode (induction) gap in the sequential electron multiplication mode: 1.08 × 10⁵ (β⁻, 1 mm, 0.4 atm, 50% streamers), 2 × 10⁶ (β⁻, 3 mm, 0.4 atm, 20% streamers), and 1.12 × 10⁵ (α, 3 mm, 0.4 atm, 50% streamers).     

Reciprocating Sliding Friction and Wear Property of Fe<Subscript>3</Subscript>Si Based Alloys Containing Cu in Water Lubrication

Fe₃Si, Fe₃Si alloys containing Cu were fabricated by arc melting followed by hot-pressing. The friction and wear behaviors of Fe₃Si based alloys with and without Cu addition against Si₃N₄ ball in water-lubrication were investigated. The friction coefficient and the wear rates of Fe₃Si based alloys decreased as the load increased. The wear rate of Fe₃Si was higher than that of AISI 304. The addition of Cu can significantly improve the friction and wear properties of Fe₃Si based alloys and substantially reduce the wear rates of Si₃N₄ ball. The wear rate of Fe₃Si–10%Cu was 2.56 × 10⁻⁶ mm³ N⁻¹ m⁻¹ at load of 20 N and decreased to 1.64 × 10⁻⁶ mm³ N⁻¹ m⁻¹ at load of 90 N. The wear rate of Si₃N₄ ball against Fe₃Si–10%Cu was 1.41 × 10⁻⁶ mm³ N⁻¹ m⁻¹, while the wear rate of Si₃N₄ ball against AISI 304 was 5.20 × 10⁻⁶ mm³ N⁻¹ m⁻¹ at load of 90 N. The wear mechanism was dominated by micro-ploughing. The combination of mechanical action (i.e., shear, smear and transference of Cu) and tribochemical reaction of Si₃N₄ with water was responsible for the improved tribological behavior of Fe₃Si alloys containing Cu under high loads.     

Tribophysical phenomena on sliding surfaces of polyester composites evaluated by spectroscopic and thermal analysis

Polyethylene terephthalate/polytetrafluoroethylene (PET/PTFE) composites were slid under different temperatures or contact pressures and surfaces are scanned with Raman spectroscopy to examine orientation and crystallisation effects induced by frictional stresses and flash temperatures. Characteristic absorption bands at 996 cm⁻¹ and 857 cm⁻¹ or 2,908 cm⁻¹ and 2,960 cm⁻¹ are used for quantification of amorphous, crystalline and rigid-amorphous phases after sliding. With almost an identical amount of total trans conformation either obtained after sliding at high temperatures or normal loads, the orientation of the molecular backbone is mainly concentrated in the formation of a crystalline phase during sliding at high temperatures. When sliding under high normal loads, orientation is concentrated in the rigid-amorphous phase with a stress-induced transition from rigid-amorphous phase into crystalline phase above 25 MPa, yielding a reduced slope in a wear rate versus normal load plot. Visual and thermal analysis of the wear debris shows that degradation under low normal loads is attributed to wear of the amorphous phase with long resident times of debris in the sliding interface. The formation of a load-carrying transfer film is attributed to a post-polymerisation reaction of the wear debris at low contact pressures.     

Creep characterization of type 316LN and HT-9 stainless steels by the K-R creep damage model

The Kachanov and Rabotnov (K-R) creep damage model was interpreted and applied to type 316LN and HT-9 stainless steels. Seven creep constants of the model,A, B. k, m, λ, γ, andq were determined for type 316LN stainless steel. In order to quantify a damage parameter, the cavity was interruptedly traced during creep for measuring cavity area to be reflected into the damage equation. For type 316LN stainless steel, λ=ε _R /ε* and λ _f =ε/ε _R were 3.1 and increased with creep strain. The creep curve with λ=3.1 depicted well the experimental data to the full lifetime and its damage curve showed a good agreement whenr=24. However for the HT-9 stainless steel, the values of A and A/ were different as λ=6.2 and λ _f =8.5, and their K-R creep curves did not agree with the experimental data. This mismatch in the HT-9 steel was due to the ductile fracture by softening of materials rather than the brittle fracture by cavity growth. The differences of the values in the above steels were attributed to creep ductilities at the secondary and the tertiary creep stages.     

Tribological characteristics of polycrystalline Magnéli-type titanium dioxides

The results presented in this paper have clarified experimentally, that titania-based Magnéli-phases (Ti₄O₇/Ti₅O₉ and Ti₆O₁₁) with (121)-shear planes exhibit more anti-wear properties than lubricious (low-frictional) properties. The results for dry sliding indicate that the coefficients of friction lie in the range of 0.1–0.6 depending on sliding speed and ambient temperature. The COF decreased with increasing temperature (T= 22–800°C) and increasing sliding speed (υ= 1−6 m/s). The dry sliding wear rate was lowest for the Al₂O₃ at 1 m/s at 800°C with values of 1.7 × 10−8 and 6.4 × 10−8 mm³/N m, comparable to boundary/mixed lubrication, associated with a high dry frictional power loss of 30 W/mm². The running-in wear length and, more important, the wear rate decreased under oscillating sliding tests with increasing relative humidity. The contact pressure for high-/low-wear transition increased under oscillating sliding tests with increasing relative humidity. At room temperature and a relative humidity of 100% the steady-state wear rate under dry oscillating sliding for the couple Al₂O₃/Ti₄O₇–Ti₅O₉ was lower than 2 × 10−7 mm³/N m and therefore inferior to the resolution of the continuous wear measurement sensor. TEM of wear tracks from oscillating sliding revealed at room temperature a work-hardening as mechanism to explain the running-in behavior and the high wear resistance. The hydroxylation of titania surfaces favours the high-/low-wear transition. This revised version was published online in August 2006 with corrections to the Cover Date.     

Epoxy, ZnO, and PTFE nanocomposite: friction and wear optimization

To lower the friction coefficient and increase the wear resistance of epoxy, nanoparticles of zinc oxide and polytetrafluoroethylene (PTFE) were added in small volume percents to an epoxy matrix. Tribological testing of the samples in this study was completed on a linear reciprocating tribometer with a 250 N normal load and a 50.8 mm/s sliding speed. Several samples were made and tested following a modified Simplex Method optimization procedure in order to find a volume percent for optimized wear resistance and friction coefficient. The sample with the optimum wear rate consisted of 1 volume percent of zinc oxide nanoparticles and 14.5 volume percent of PTFE nanoparticles. It had a wear rate of k = 1.79 × 10⁻⁷ mm³/Nm; 400× more wear resistant than neat epoxy. The sample with the optimum friction coefficient consisted of 3.5 volume percent of zinc oxide nanoparticles and 14.5 volume percent of PTFE nanoparticles and had a friction coefficient of μ = 0.113, which is almost a 7× decrease in friction coefficient from neat epoxy.