Factor Kf Research Articles

The Radius Size Variation Effects on Fatigue Strength of AA6061-T6 and AA6061-O Alloys

This research ensured the effects of radius variation on fatigue – life of AA6061-T6 and annealed alloy, AA6061-O. Five different sizes of radius (1, 2, 4, 8, and 16) mm were studied using Neuber notch factor (Kf) instead of the theoretical stress concentration factor (Kt). The numerical modeling was adopted using ANSYS Workbench 15 to evaluate the radius size effectiveness on strain and stress distribution, while the experimental procedure carried out to determine the strain-life constants for analytical calculations. The results show that the reduction in the radius leads to increase stress, while the strain remains close to each other with the variations of radius for both alloys. The decrement in stress and strain values for annealed specimens were observed in comparison with base alloy. The transition life (NT) was decreased whenever the radius decreased in both alloys. The fatigue life of annealed specimens increased for all values of radius compared to the specimens without annealed. The comparison of the fatigue life between the experimental and numerical results shows that the experimental results have more than those obtained by numerical estimation and this indicated the validity of the numerical approach.

New proposal to express notch stress approach results by equivalent SCFs

For the fatigue design of welded structures, such as jacket substructures for offshore wind energy turbines, the structural stress approach is state of the art. Standards and guidelines also allow the application of the notch stress approach for complex welded components, weld roots, or to consider the advantages of the real weld geometry if measured or after grinding within the fatigue design. Since the theoretical background as well as the application of both approaches differs widely, it is not possible to directly integrate the fatigue notch factor Kf according to the notch stress approach into the design formalism of the welded structures based on the structural stress approach. Therefore, this paper derives a methodology to transform the elastic fatigue notch factor Kf into an equivalent stress concentration factor. By applying the introduced concept design engineers are able to selectively combine the advantages of both approaches without adapting the approved software tools to perform the fatigue design of complete welded structures.Furthermore, the presented concept of the equivalent stress concentration factor is an effective tool to perform a direct comparison of the relative fatigue resistance according to both approaches – structural stress approach and notch stress approach – on structural stress concentration level rather than on the level of damages or lifetime. This opportunity of comparison is applied on a tubular X-joint of a jacket substructure. The computed stress concentration factors are in good accordance between both approaches which is similar to the lifetime based results given in literature for application of both approaches on tubular K- and Y-joints.

Study on Application of Fatigue Strength Reduction Factor and Stress Concentration Factor in Fatigue Analysis of Screw Threads

Taking the reactor pressure vessel as an example, the theoretical relationship of fatigue strength reduction factor (Kf) and stress concentration factor( Kt ), the reasonable values of Kf and Kt, the principles of equivalency of Kf and Kt in engineering project and the methods and techniques of how to use Kf and Kt in fatigue analysis are presented. An example of fatigue analysis for screw threads of reactor pressure vessel (RPV) stud with certain Kf is given. Consequently, definitions and differences of Kf and Kt are classified. Opinions on the application of Kf to high strength alloy stud are given, which can be used as a reference to the stud selection and the structure design in the engineering application.

Effects of κ-carrageenan on the structure and rheological properties of fish gelatin

Fish gelatin (FG) and κ-carrageenan (KC) were mixed to simulate the physicochemical properties of porcine gelatin (PG). The effects of the mixing ratio between FG and KC on the interaction, structure, and rheological properties of FG were investigated. The maximum associative interaction occurred at the critical mixing ratio of KC:FG (w/w) at 4:96, where the median particle size (D50) of the FG-KC coacervates was 1168 ± 175 nm, and the zeta potential was −3.8 ± 0.8 mV. Interestingly, the rheological properties of the mixed gel (KC:FG at 4:96) matched those of PG, including the melting temperature (Tm), gelling temperature (Tg), dynamic consistency factor (Kf), and instantaneous compliance (J0). The relationship between structure and physicochemical properties was proposed as a schematic model. The associative interaction between FG and KC was critical for FG's modification and could be applied to improve FG's rheological properties towards PG.

Dynamic Constitutive Model for Reactive Powder Concrete with Standard Curing

In view of the disadvantages of steam curing of reactive powder concrete (RPC), RPC with standard curing (SCRPC) is proposed. SC-RPC is an ultra-high strength concrete material prepared with high strength cement, silica fume, and gypsum by standard curing. In this study, quasi-static and impact compression tests were performed to investigate the mechanical properties of SC-RPC. The results show that steel fiber and the strain rate significantly affect the compression performance. Nevertheless, the Holmquist–Johnson–Cook (HJC) constitutive model is mainly used to analyze the dynamic response of brittle materials, such as common concrete, under shock and impact. Therefore, based on the quasi-staticand impact compression tests and the HJC constitutive model for concrete, by analyzing the steel fiber strengthening effect under quasi-static uniaxial compression, strain rate hardening, and the damage softening effect under SHPB impact compression, the steel fiber strengthening factor Kf , dynamic increase factor DIF, and revised damage variable D are introduced, and a modified HJC constitutive model for RPC with standard curing is proposed.

Fatigue behavior of 590MPa Tensile Strength galvanneal coated sheet steel laser welded blanks

The use of Laser Welded Blanks (LWBs) with different grade/gauge combinations in automotive body structures is well established; however, the acceptance of LWBs in fatigue critical chassis and underbody components has been slower because of lack of reliable models for durability assessment of laser welded joints (LWJ). Most prior fatigue studies of LWBs are carried out in tension - tension loading mode, making it difficult to relate it to the cyclic deformation and fatigue behaviors of the substrate steel grade. In contrast, in this study, LWJ is conceptualized as a "notch" to estimate the local stresses from the strain - life data of the parent grade and the fatigue notch concentration factor (Kf) is estimated from the nominal stress values of LWJ. The method is illustrated with strain controlled fatigue data for 1.4 mm galvanneal coated 590 MPa steel and fully reversed, fatigue data for homogeneous and heterogeneous LWB combinations. The results indicate that for both homogeneous and heterogeneous LWJ configurations, Kf increases with fatigue life, but tends to saturate at life levels greater than about million cycles. Considering 105 cycles to failure as an example, Kf is estimated as 1.07 for the homogeneous and 1.25 for the heterogeneous combinations.

Quantitative Correlation of 7B04 Aluminum Alloys Pitting Corrosion Morphology Characteristics with Stress Concentration Factor

The accelerated pitting corrosion test of 7B04 aluminum alloy specimen was carried out according to the spectrum which simulated airport environment, and the corresponding pitting corrosion damage was obtained and was defined through three parameters A and B and C which respectively denoted the corrosion pit surface length and width and corrosion pit depth. The ratio between three parameters could determine the morphology characteristics of corrosion pits. On this basis the stress concentration factor of typical corrosion pit morphology under certain load conditions was quantitatively analyzed. The research shows that the corrosion pits gradually incline to be ellipse in surface and moderate in depth, and most value of B/A and C/A lies in 1 between 4 and few maximum exceeds 4; The stress concentration factor Kf of corrosion pits is obviously affected by the its morphology, the value of Kf increases with corrosion pits depth increasement under certain corrosion pits surface geometry. Also, the value of Kf decreases with surface width increasement under certain corrosion pits depth. The research conclusion can set theory basis for corrosion fatigue life analysis of aircraft aluminum alloy structure.

Using ESEM to analyze the microscopic property of basalt fiber reinforced asphalt concrete

The basalt fiber staggered distribution in the asphalt concrete matrix and the bonding situation between asphalt are analyzed by images collected using field emission environmental scanning electron microscope (ESEM) test equipment. The results show that bonding of the fiber and the asphalt binder is very good and there is a strong binding force of chemical bonding connections between the two; the lipophilicity of basalt fiber is very good, the wrapped cover ability of asphalt for fiber is very strong; basalt fiber forms the local space network structure in the asphalt concrete matrix, effectively overcome the relative slip between the particles, connect the damaged parts into a whole; basalt fiber across internal micropores, and the internal defects in material can be remedied. At the same time, crack resistance mechanism of the fiber to internal micro cracks is qualitatively explained according to the magnitude of the stress intensity factor Kf.

Biosensor-assisted selection of optimal parameters for designing molecularly imprinted polymers selective to phosmet insecticide

Molecularly imprinted polymers (MIPs) for phosmet insecticide were synthesized by batch polymerization. The affinity of functional monomers to phosmet was tested using an original method involving an electrochemical biosensor based on acetylcholinesterase inhibition. It was demonstrated that association of phosmet with appropriate functional monomers resulted in a decrease of enzyme inhibition. Using this method, it was shown that N,N-methylenebis(acrylamide) displayed the highest interactions with phosmet using DMSO as solvent. These results were in good accordance with those obtained by conventional computational modeling. Molecularly imprinted polymers (MIPs) and non-imprinted polymers (NIPs) were synthesized and adsorption isotherms were studied to describe their interaction with phosmet. Freundlich isotherm was able to fit phosmet adsorption on MIPs with good agreement (R2 = 0.9). The pre-exponential factor KF determined for MIPs was 1.439mg(1−N)g−1LN, more that 10 times higher than for NIPs (0.125mg(1−N)g−1. LN), indicating an increase of binding sites number and average affinity.

Empirical Approach to Understanding the Fatigue Behavior of Metals Made Using Additive Manufacturing

High-cycle fatigue measurements were performed on alloys prepared by powder-bed fusion additive manufacturing techniques. Selective laser melted (SLM) nickel-based superalloy 625 and electron beam melted (EBM) Ti-6Al-4V specimens were prepared as round fatigue specimens and tested with as-built surfaces at stress ratios of −1, 0.1 and 0.5. Data collected at R = −1 were used to construct Goodman diagrams that correspond closely to measured experimental data collected at R > 0. A second way to interpret the HCF data is based on the influence of surface roughness on fatigue, and approximate the surface feature size as a notch. On this basis, the data were interpreted using the fatigue notch factor kf and average stress models relating kf and stress concentration factor Kt. The depth and root radius of surface features associated with fatigue crack initiation were used to estimate a Kt of 2.8 for SLM 625. For Ti-6Al-4V, a direct estimate of Kt from HCF data was not possible, but approximate values of kf based on HCF data and Kt from crack initiation site geometry are found to explain other published EBM Ti-6Al-4V.

(Invited) Power Loss Reduction in Perforated-Channel HFET Switches

The key factors affecting the efficiency of power electronic systems are the conduction and switching losses in semiconductor power switches. For field-effect transistor switches, the conduction power loss is proportional to the product of the squared current, ION , flowing through the switch in the on-state and the switching loss is proportional to the squared maximum switch voltage, VMAX, the effective device output capacitance, COUT , and the switching frequency, fSW . Therefore, the RONCOUT product is an important figure of merit of a FET-type switch determining the overall power efficiency. Our proposed and implemented Perforated Channel (PC) FET design 1 allowed us to significantly reduce RON , but not COUT. We now propose and demonstrate the improved PC-HFET design that allows us to reduce both RON and COUT . This design reduces the power losses and significantly improves the efficiency of power electronics systems. In the PC-HFET, the portions of the channel under the gate are removed and the remaining channel forms a dash-line of islands WG1 wide with WGG spacing between them. The channel “filling factor” in PC-HFET is kF = WG1/(WG1+WGG ). Compared to conventional HFET with the same total width W, the total channel width and, hence, the device gate capacitance, of the PC-HFET is kF times smaller. However, our analytical estimates, numerical simulations (using the 3D simulation in Synopsys Sentaurus device simulator), and experimental data all show the on-resistance of the PC-HFET can be only 10-15% higher than that of the conventional HFET of the same width. This is achieved due to a strong current spreading effect in the source-to-gate and, especially, in a larger gate-to-drain spacing. The gate capacitance of PC-HFET reduces proportionally to the kF factor as proven by our simulations and experimental data presented in [1]. However our 3D simulations show that the CGD scaling in PC-HFET at high drain voltage is nearly the same as that for conventional HFET. To reduce this capacitance, we proposed the PC-HFET device design with the holes extending into the gate-drain spacing. Our simulations show that the hole extension allows for nearly the same CGD reduction as the gate metal removal over the holes. We used the obtained RON and CGD data to calculate the power loss in AlGaN/GaN PC-HFET and showed that the PC-HFET design filling factor kF = 0.25 reduces the total conversion loss in the power switch by more than a factor of 2. [1] G. Simin, M. Islam, M. Gaevski, J. Deng, R. Gaska, and M. Shur, “Low RC-constant Perforated-Channel HFET”, IEEE El. Dev. Letters, V. 35, pp.449-451, 2014 Figure 1

Influência de probióticos na prevalência parasitária e níveis de glicose e cortisol em tilápia do Nilo

A adição de probióticos em rações visa atuar como um bioestimulante da flora intestinal das tilápias. A fase de alevinagem em tanques-rede utiliza grande densidade de peixes, o que pode potencializar os efeitos de estresse. Os probióticos surgem como uma alternativa para a mitigação ou prevenção de danos. O objetivo deste trabalho foi avaliar a influência dos probióticos Bacillus cereus var. Toyoi e Bacillus subtilis C-3201 na prevalência parasitária e verificar o estado de saúde por meio do perfil bioquímico de glicose e cortisol e do fator de condição de Fulton (Kf) para atuar como indicador quantitativo do bem-estar de tilápia do Nilo da linhagem GIFT cultivada em tanques-rede. Foram utilizados 1800 juvenis de tilápia do Nilo distribuídos em 20 tanques-rede de 0,5 m x 0,5 m x 0,7 m instalados em tanques com baixa renovação de água. O grupo de peixes sem a adição de probióticos (T1) recebeu apenas dieta basal. Os probióticos liofilizados foram incluídos na ração utilizando 2 % de óleo vegetal na mesma proporção utilizada em todos os grupos experimentais. Na ração basal foram adicionados níveis de 0,5 % B. cereus (T2), 0,5 % de B. subtilis (T3), 0,25 % de B. cereus + 0,25 % B. subtilis (T4). As dietas com adição de B. cereus e/ou B. subtilis não foram eficientes no controle da infestação ectoparasitária por monogenóides e trichodinídeos. Houve maior (p

Effect of small scale notches on the very high cycle fatigue of AISI 310 stainless steel

ABSTRACTFatigue behaviour of AISI 310 stainless steel has been investigated up to very high cycles. The fatigue crack initiation sites were found at the surface of the material. Persistent slip bands developed at the surface of the specimens led to the crack initiation. At lower stress levels, shallow persistent slip bands were found at the surface of the specimens, and the fatigue limit was obtained.Notched specimens showed lower fatigue lives. Notched specimens with higher stress concentration factor (Kt) showed higher fatigue strength reduction factor (Kf). It was found that shallow notches of depth ~100 µm may reduce the fatigue life substantially.

Fatigue properties of vibration‐welded postindustrial waste nylon with glass fibers at room and elevated temperatures

The effect of temperature on the tensile and fatigue strength of vibration‐welded and unwelded postindustrial waste nylon 6 reinforced with 30 wt% glass fiber (PIWGF) was experimentally examined, and the results were compared to those obtained from a 30 wt% glass fiber reinforced prime nylon 6 compound (PAGF) from a previous study. Fatigue tests were performed under sinusoidal constant amplitude tension‐tension load at a stress ratio of R = 0.1 and within the frequency range of 2–10 Hz at temperatures from 24 to 120°C. Stress levels from just under the tensile strength down to the run‐out point at 5 million cycles were used. It was found that increasing temperature led to a significant decrease in both tensile strength and fatigue life. For PIWGF, there was ∼20% strength reduction under both static tensile and cyclic loading as compared to PAGF. For both welded and unwelded PIWGF, the endurance ratio; i.e., the ratio of fatigue strength to static tensile strength, was ∼45% regardless of the temperature. The fatigue notch factor (Kf) was between 1.4 and 1.8 for all test temperatures examined. POLYM. ENG. SCI., 55:799–806, 2015. © 2014 Society of Plastics Engineers

Effect of temperature on fatigue strength of vibration welded and unwelded glass reinforced nylon 6

The effect of temperature on the tensile and fatigue strength of vibration welded and unwelded 30wt% glass fiber reinforced nylon 6 (PA6GF) was experimentally examined. Fatigue tests were performed under sinusoidal constant amplitude tension–tension load at a stress ratio of R=0.1 and within the frequency range of 2–10Hz. Stress levels from just under the tensile strength down to the run-out point, at 5 million cycles, were used. It was found that increasing temperature led to a significant decrease in both tensile strength and fatigue life. However, it was also noted that for both welded and unwelded PA6GF, the endurance ratio, i.e., the ratio of fatigue strength to static tensile strength, was approximately 45% regardless of the temperature. The fatigue notch factor (Kf) lies between 1.5 and 1.75 regardless of test temperature.

Proposal for a stress modification factor for the fatigue design of flange thickness transitions in welded girders

Thickness steps or transitions are often used in flanges of bridge girders in order to adapt the bending resistance of the cross-sections to variable bending moment distributions. The sudden change of the stiffness distribution within the cross-section at these details causes additional local forces and stresses, which cannot be properly taken into account by classical beam-theoretical calculations, and which lead to a deterioration of the fatigue performance of the welded details at and around the transition. A modification of nominal stresses – e.g. by the use of an appropriate stress concentration factor kf – is therefore required in order to obtain safe joint designs with respect to fatigue.The stress-raising effects at flange thickness transitions are of a similar nature as the ones caused by plate or angular misalignments, for which kf-factors are provided in the literature. However, the specific configuration of flanges in – often quite deep – bridge girders causes additional (beneficial or detrimental) effects that have not been sufficiently studied before, and which are currently not correctly considered in common design practice.This paper discusses the characteristic local load-carrying behaviour and stress distribution in flange thickness transitions of welded I-section bridge girders, which were studied by numerical, experimental and analytical means. The paper furthermore introduces a new, accurate and mechanically coherent analytical formulation of kf-factors for the modification of nominal longitudinal stresses in bridge girder flanges; these new kf-factors could be used for practical fatigue design verifications. The possibility of including further amendments to the proposed formulation in order to take into account for the effects of additional unintentional misalignment or dimensional tolerances at the butt weld were also discussed. Finally, an outlook is given on the need to also consider additional stress concentration factors for shear in the fillet welds in the areas surrounding a thickness transition.

Production of medical radioisotope 153Sm in the Tehran Research Reactor (TRR) through theoretical calculations and practical tests

The feasibility of producing 2000–3000mCi 153Sm by irradiation of 152Sm in 5MW TRR was studied via TRR core simulation. In this study the cross-section of 152Sm (n,γ) 153Sm reaction from ENDF/B library was used. The effective activation cross section for production of 153Sm is obtained using the neutron spectra in different irradiation channel of the core. The activity of the simulated samples is calculated using the obtained fluxes and cross sections. Then samples were prepared and irradiated under different conditions and fluxes. The final production’s specific activity was measured by the standard dose calibrator ISOMED 1010. By comparison of the theoretical calculations and actual measurements, an empirical correction factor (Kf) was obtained, which is helpful in production procedure of the 153Sm radioisotope. The optimal weight of the samples and irradiation time was studied according to the flux calculations based on the location of the sample and saturated activity calculation. In order to test the proposed conditions, samples were prepared and were irradiated under the proposed conditions. According to the compared results with the initial irradiation condition, the new proposed sample which weighed 4mg of Sm2O3 is acceptable for the labeling, therefore this study led to nearly 60% decrease in the amount of material used in the production process.

Estimation of Notch Sensitivity and Size Effect on Fatigue Resistance

This paper addresses the problem of high cycle fatigue resistance associated to notches and the role of short crack propagation in the fatigue notch sensitivity quantified by the notch factor kf. An integrated fracture mechanics approach is proposed to estimate the fatigue notch sensitivity, by including the effect of both blunt and sharp notches.Whether fatigue strength at a given life is controlled by crack initiation (very blunt notches, kf = kt), by microstructuraly short cracks (blunt notches, kf <kt), or by mechanically short crack propagation (sharp notches, kf <<kt), depends on the stress concentration kt, the notch length D and the material threshold to crack initiation ΔσeR, to short crack propagation ΔKth and to long crack propagation ΔKthR.The approach includes the prediction of the fatigue crack propagation threshold for short cracks, previously developed to analyze the short crack behavior in metallic materials with or without blunt notches, and is integrated adding the influence of sharp notches and accounting for the controlling parameters. It estimates the fatigue resistance of the component by comparing the threshold for fatigue crack propagation as a function of crack length, ΔKth, with the applied ΔK for the given configuration. Estimations for results reported in published bibliography are presented.The proposed fracture mechanics approach allows accounting for the effects of notch acuity, notch size and intrinsic material fatigue properties on fatigue notch sensitivity. It opens the door to a new simple method for predicting fatigue notch sensitivity and fatigue strength of components with geometric concentrators by using parameters that can be easily measured or estimated, without the necessity of any fitting parameter.

On the performance of circular concrete-filled high strength steel columns under axial loading

This work presents a numerical study to investigate the performance of circular high-strength steel tubes filled with concrete (CFT) under monotonic axial loading. A model is developed to implement the material constitutive relationships and non-linearity. Calibration against previous experimental data shows good agreement. A parametric study is then conducted using the model and compared with codes provisions. Strength and ductility of confined concrete are of primary concern. Variables considered are yield stress of steel tube and column diameter. The assessment of column performance is based on axial load carrying capacities and enhancements of both strength and ductility due to confinement. Two parameters namely strength enhancement factor (Kf) and ductility index (μ) are clearly defined and introduced for assessment. Results indicate that both concrete strength and ductility of CFT columns are enhanced but to different extents. The ductile behaviors are significantly evident. The increase in yield stress of steel tube has a minimal effect on concrete strength but pronounced effect on concrete ductility. However, reduction in ductility is associated with using high-tensile steel of Grade 70. The overall findings indicate that the use of high-strength tube in CFT columns is not promising. This finding may seriously be considered in seismic design.

Durability of asphalt mixture in different corrosion solution

The corrosion to asphalt mixture under different kinds of corrosion solution, such as pH=2 solution, pH=12 solution, pH = 12 solution and 10% Na2SO4 solution, was studied. The performance attenuation of asphalt mixture was analyzed under the normal environment and the freeze-thaw environment, and the analysis was given on the sensitivity of the test results to the evaluation index. The experimental results show that the performance of asphalt mixture is attenuated faster under the acidic solution, alkaline solution and sulfate solution. Corrosion factor Kc, freeze-thaw corrosion factor Kf, and freeze-thaw effect factor Kfc are proposed to evaluate asphalt mixture resistance to corrosion in different kinds of corrosion solution. The values of Kc and Kfc decrease with the increasing of corrosion time. The change rule of Kf show that the rate of corrosion is decreased by the action of freeze-thaw in acidic solution and in alkaline solution, but is increased by the action of freeze-thaw in sulfate solution. The microscopic analysis indicates that acid solution reacts with aggregate of asphalt mixture, alkaline solution reacts with asphalt cement of asphalt mixture, the surface tension of sulfate solution and crystallization of sulfate are the main reasons which weak the performance of asphalt mixture.