This paper covers the essential aspects of modeling surface roughness for microwave applications based on underlying physics. After a short summary of the relevant field theoretical fundamentals, ...surface roughness metrology and commonly used roughness parameters are described. Existing models and their limitations are discussed before the recently proposed Gradient Model is introduced. To this purpose, the modeling approach, the derivation from Maxwell's equations, model predictions, and their experimental verification are shown. Reasonable choices for effective material parameters reflecting the electromagnetic effects of surface roughness as well as a corresponding surface impedance concept are derived. Both concepts allow for easy application of the Gradient Model with 3-D field solvers or analytical models. The obtained simulation results illustrate roughness impact on loss and phase delay in typical transmission lines. Comparison to measurement results up to 100 GHz shows that the Gradient Model accurately predicts these quantities for rough conductor surfaces. As it is not limited to transmission lines only, it significantly improves the design process for arbitrary microwave applications with 3-D field solvers for this frequency range.
Selective Laser Melting (SLM) and Electron Beam Melting (EBM) are powder bed fusion processing which allows to build-up parts by successive addition of layers using 3D-CAD models. Among the ...advantages, are the high degree of freedom for part design and the small loss of material, which explain the increase of Ti-6Al-4V parts obtained by these processes. However, Ti-6Al-4V parts produced by SLM and EBM contain defects (surface roughness, porosity, tensile residual stresses) which decrease significantly the High Cycle Fatigue (HCF) life. In order to minimize the porosity and tensile residual stresses, post-processing treatments like Hot Isostatic Pressing (HIP) and Stress Relieving are often conducted. But the modification of the surface roughness by machining is very costly and not always possible, especially for parts with complex design. The aim of this work is to evaluate the effect of the surface roughness and microstructure of Ti-6Al-4V parts produced by SLM and EBM on the HCF life. Five sets of specimens were tested in tension-compression (R=-1; f=120Hz): Hot-Rolled (reference); SLM HIP machined; SLM HIP As-Built; EBM HIP machined; EBM HIP As-Built. For each condition, microstructure characterization, observation of the fracture surface of broken specimens and surface analysis were carried out respectively by Optical Microscope (OM), Scanning Electron Microscope (SEM) and 3D optical profilometer. Results of fatigue testing show a significant decrease of the HCF life mainly due to the surface roughness. Along with experimental testing, numerical simulations using FEM were conducted using the surface scans obtained by profilometry. Based on extreme values statistics of the crossland equivalent stress averaged on a critical distance, a methodology is proposed to take into account the effect of the surface roughness on the HCF life.
Rainfall changes the geometric undulations of wind-driven sea surface, thereby altering the traditional relationship between wind vector and backscattering coefficient, which poses some challenges ...for microwave remote sensing measurement and inversion. This paper proposes a new sea-spectrum model based on the wind-driven Apel spectrum combining some correction factors of rain-generated ring waves, rain-induced damping, and rain-induced roughness. Then this new spectrum is used to compute the backscattering coefficients using two-scale method (TSM) with approximate cutoff wavenumber in Ku-band. Comparison with the observational data of HY-2B scatterometer indicates that the simulated results after rainfall correction are more consistent with satellite observation. Simulation error for vertical polarization decreases from 2.574 to 1.9200 dB, while the error for horizontal polarization decreases from 3.2965 to 2.8153 dB. In addition, the comparison with the empirical GMF models also confirmed the accuracy and reliability of the new spectrum of rain-impacted sea surface.
•We have for the first time, discussed the effect of Ra thoroughly on the evolution of the non-dimensional droplet spreading diameter β for droplet impacting.•We extended previous work on βmax to ...accommodate Ra effect and the derived empirical correlations of βmax as a function of Ra show good agreement with both the present and previous experimental data.•The transition from spreading to splashing empirically fitted as a function of the surface roughness, which also shows reasonably good agreement with all the public literature data.
This paper reports an experimental investigation on the impact dynamics of droplets (water, decane, ethanol, and tetradecane) onto a flat stainless steel surface, using high-speed microphotography and with a particular interest in the effect of surface roughness on the impact dynamics. Results show that the impacting water droplet spreads on the surface in the form of a rim-bounded lamella and the rim contracts back after reaching the maximum spreading, while this contraction motion is absent for the fuel liquids. With the increase of Weber number (We) and surface roughness, splashing, evidenced by the ejection of secondary droplets, is favored. The droplet spreading, which is characterized by a normalized diameter β, is accelerated with increasing We, while the surface roughness and Ohnesorge number (Oh) tend to slow down the spreading process. Furthermore, the maximum normalized spreading diameter, βmax, depends primarily on the (We/Oh) and the increase in the surface roughness slightly reduces βmax. The transition from spreading to splashing is enhanced with increasing We or Ra or both. An empirical correlation of βmax as a function of the surface roughness was derived based on the present experimental data. In addition, the transition from spreading to splashing can be represented by a critical (We/Oh)1/2, which was fitted as a function of the surface roughness. All the proposed empirical correlations show good agreement with literature data and are believed to be of importance for the spray/wall interaction modelling.
What affects the biocompatibility of polymers? Jurak, Małgorzata; Wiącek, Agnieszka Ewa; Ładniak, Agata ...
Advances in colloid and interface science,
August 2021, 2021-08-00, 20210801, Volume:
294
Journal Article
Peer reviewed
In recent decades synthetic polymers have gained increasing popularity, and nowadays they are an integral part of people’s daily lives. In addition, owing to their competitive advantage and being ...susceptible to modification, polymers have stimulated the fast development of innovative technologies in many areas of science. Biopolymers are of particular interest in various branches of medicine, such as implantology of bones, cartilage and skin tissues as well as blood vessels. Biomaterials with such specific applications must have appropriate mechanical and strength characteristics and above all they must be compatible with the surrounding tissues, human blood and its components, i.e. exhibit high hemo- and biocompatibility, low or no thrombo- and carcinogenicity, foreign body response (host response), appropriate osteoconduction, osteoinduction and mineralization. For biocompatibility improvement many surface treatment techniques have been utilized leading to fabricate the polymer biomaterials of required properties, also at nanoscale. This review paper discusses the most important physicochemical and biological factors that affect the biocompatibility, thus the reaction of the living organism after insertion of the polymer-based biomaterials, i.e. surface modification and/or degradation, surface composition (functional groups and charge), size and shapes, hydrophilic-hydrophobic character, wettability and surface free energy, topography (roughness, stiffness), crystalline and amorphous structure, nanostructure, cell adhesion and proliferation, cellular uptake. Particularly, the application of polysaccharides (chitosan, cellulose, starch) in the tissue engineering is emphasized.
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•The review outlines a general scheme for creating bio- and hemocompatible polymer materials.•Biomaterials of proper mechanical characteristics and of positive host-response are required.•Biocompatibility is determined by the graft surface physicochemical properties.•Properly selected surface features of polymer provide the conditions for the tissue repair.•Knowledge of processes inducing the host response is a way to find the suitable implant.
Abstract Most effective method to find the roughness parameters in rarefied gas flow is to calculate them from aerodynamic measurements, solving the inverse problem. The value of the main roughness ...parameter obtained from the solution of inverse problem is substantially higher (at least 1,25–1,5 times) than similar value of the same parameter measured from the profile diagrams. Thus, the effect of surface roughness in aerodynamic values of rough surface in rarefied gas flow is always significantly underestimated. First main reason of it is the low precision of roughness parameter measurements from the profile diagrams, and the second is based on usual lack of taking into account aerodynamic shadowing effect.
Abstract
The work develops a localized hypersonic cross-flow transition criterion considering the influence of cross-flow intensity and surface roughness. A cross-flow extension of hypersonic ...modified γ-Re
θ
transition model based on Chant2.0 computing platform is implemented. The extended transition model is used to predict the cross-flow transition on the elliptic cone (HIFiRE-5) in multiple states, and the predicted results are in good accordance with the experimental results.
•A method of extracting effective features for monitoring surface roughness is presented.•KPCA_IRBF is re-derivated according to the derivation of PCA.•A new kind of BLR model abbreviated as ...Standard_SBLR is firstly proposed.•KPCA_IRBF helps to improve the prediction accuracy and ameliorate the CI of BLR.•Under the support of KPCA_IRBF, Standard_SBLR shows superior predictive performance.
To improve the prediction accuracy of surface roughness in milling process, this paper provides an unique feature extraction method and comprehensively analyzes four types of Bayesian linear regression (BLR) model (Standard_BLR, Gaussian_BLR, Standard_SBLR and Gaussian_SBLR). Among them, Standard_SBLR is firstly proposed. Vibration information of the workpiece, fixture and spindle is adopted as the monitoring signal. The unique feature extraction method consists of three stages: extraction of time-domain features from the vibration signals, dimension-reduction by principal component analysis (PCA) and dimension-increment by the integrated radial basis function based kernel principal component analysis (KPCA_IRBF). The BLR models can provide both the predicted value and the corresponding confidence interval (CI). Two types of milling experiment (down milling and up milling) are conducted to reveal the influence of dimension-increment process of KPCA_IRBF on the predictive performance of the BLR models. Experimental results show that when combined with KPCA_IRBF, Standard_SBLR has the best predictive performance among the four BLR models. This also shows that KPCA_IRBF is highly effective in improving the prediction accuracy and compressing the CI of Standard_SBLR. To further prove the superiority of Standard_SBLR, other powerful machine learning methods such as partial least squares regression (PLS), artificial neural network (ANN) and support vector machine (SVM) are also utilized to realize surface roughness prediction under the support of KPCA_IRBF. This paper lays the foundation for accurate monitoring of surface roughness in real industrial settings.
A comprehensive understanding of the combined effects of surface roughness and wettability on the dynamics of the trapping process is lacking. This can be primarily attributed to the contradictory ...experimental and numerical results regarding the impact of wettability on the capillary trapping efficiency. The discrepancy is presumably caused by the surface roughness of the inner pore‐solid interface. Herein, we present a comparative μ‐CT study of the static fluid‐fluid pattern in porous media with smooth (glass beads) and rough surfaces (natural sands). For the first time, a global optimization method was applied to map the characteristic geometrical and morphological properties of natural sands to 2‐D micromodels that exhibit different degrees of surface roughness. A realistic wetting model that describes the apparent contact angle of the rough surface as a function surface morphology and the intrinsic contact angle was also proposed. The dynamics of the trapping processes were studied via visualization micromodel experiments. Our results revealed that sand and glass beads displayed opposite trends in terms of the contact angle dependence between 5° and 115°. Sand depicted a nonmonotonous functional contact angle dependency, that is, a transition from maximal trapping to no trapping, followed by an increase to medium trapping. In contrast, glass beads showed a sharp transition from no trapping to maximal trapping. Since both porous media exhibit similar morphological properties (similar Minkowski functions: porosity, surface density, mean curvature density, Euler number density), we deduce that this difference in behavior is caused by the difference in surface roughness that allows complete wetting and hence precursor thick‐film flow for natural sands. Experimental results on micromodels verified this hypothesis.
Key Points
Wettability, surface roughness, and pore space structure have an impact on trapping efficiency
Porous media with rough surface, as natural sands and glass‐ceramic micromodels, were studied
Wettability‐controlled crossover from snap‐off to by‐pass trapping and spontaneous precursor thick‐film flow were observed
The effect of surface roughness and polishing orientation on fatigue life is investigated. Fully reversed bending fatigue tests are conducted on ASTM A1008 specimens having surface roughness ...asperities ranging from mirror finish (Ra = 0.05 μm) to coarse (Ra = 1.5 μm). Two polishing directions (i.e., orientations) are examined. For the range of roughness values tested, the results suggest that polishing orientation has a strong influence on fatigue life. Specifically, within the range of surface roughness values tested, fatigue life was found to be relatively insensitive to surface roughness asperities when the roughness orientation was parallel to the direction of surface stress but sensitive to surface roughness asperities when the orientation crossed the direction of surface stress. Results are generalized using the concept of fracture fatigue entropy (FFE). It is shown that, unlike fatigue life, FFE is independent of polishing orientation, a noteworthy result. To explain the behavior of FFE in relation to surface roughness asperities, a fatigue thermodynamics theory is presented that hypothesizes that all specimens of the same material fail at equivalent entropy levels.
Highlights
The influence of surface roughness on fatigue life is investigated.
Extensive fully reversed bending fatigue tests are performed.
Surface roughness lay has a pronounced influence on fatigue life.
Fracture fatigue entropy (FFE) is sensitive to the roughness regardless of its lay.
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