•Effect of hot isostatic pressing (HIP) on multiaxial fatigue of AM Ti-6Al-4V.•Build orientation effect on multiaxial fatigue of AM Ti-6Al-4V.•Surface roughness effect on multiaxial fatigue of AM ...Ti-6Al-4V.•Damage mechanism and effect of defects in multiaxial fatigue of AM Ti-6Al-4V.
Additive manufacturing (AM) technology has gained significant attention in recent years due to several important advantages. However, design of critical load carrying parts using this technique is still at its infancy, partly due to the inferior performance and lack of sufficient understanding of cyclic deformation and fatigue behaviors of AM metals as compared to their wrought counterparts. Similar to most other components in different industries, AM parts typically undergo cyclic loadings through their service life; therefore, fatigue performance is a key performance criterion. In addition, due to common presence of multiaxial stress states at fatigue critical locations, multiaxial fatigue is of special interest. In this study, thin-walled tubular specimens made of Ti-6Al-4V alloy fabricated with powder bed fusion (PBF) process were used to investigate their cyclic deformation and fatigue behaviors. The main focus of this study was on the effect of hot isostatic pressing (HIP) on fatigue performance under uniaxial, torsion, combined in-phase, and 90° out-of-phase axial-torsion loads. To study build orientation effect, both vertically built and diagonally built (at 45°) specimens were included. However, no substantial difference on the fatigue behavior of vertical and 45° built specimens was observed. Although the majority of specimens had a machined surface, some torsional tests with as-built surface were also included to evaluate surface roughness effect. It was found that even after HIP treatment, the rough surface is the dominant factor in shortening the fatigue life. In addition, to evaluate the effectiveness of the HIP treatment, torsion fatigue performance of the HIPed specimens were compared to torsion fatigue performance of annealed AM specimens, as well as to the multiaxial fatigue behavior of the conventional wrought material. Fatigue failure mechanism of the HIPed material was shear, similar to the wrought material, and fatigue performance was found to be similar to the wrought alloy. Fatigue test results were correlated well using a shear-based critical plane parameter approach, also similar to the wrought material. Comparison of multiaxial fatigue data in this study and a similar previous study by the authors indicates that fabrication machine-to-machine and the associated build parameter differences can result in substantial differences in the observed defect size and population, resulting in different failure mechanisms and subsequently different fatigue performance.
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.
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.
•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.
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.
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, Letnik:
294
Journal Article
Recenzirano
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.
Display omitted
•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.
Bayesian linear regression for surface roughness prediction Kong, Dongdong; Zhu, Junjiang; Duan, Chaoqun ...
Mechanical systems and signal processing,
August 2020, 2020-08-00, 20200801, 2020-08-01, Letnik:
142, Številka:
C
Journal Article
Recenzirano
Odprti dostop
•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.
•Pressure exerts a negligible effect on most TIMs when pressure exceeds 0.3 MPa.•Surface roughness exerts little effect the performance of PCMs and LMPAs.•PCMs and LMPAs show good performance at low ...pressure.•Thermal pads and carbon-based materials can hinder heat transfer when surface is smooth.
Using thermal interface materials (TIMs) is generally considered an effective way to reduce thermal contact resistance. In this paper, effects of surface roughness, temperature and pressure on TIMs’ performance are investigated. A variety of TIMs including thermal pads, carbon-based materials, phase change materials (PCMs) and low-melting-point alloys (LMPAs) are experimentally studied, and their performance is compared with the case without using any TIM. Results indicate that, when pressure is below 0.3 MPa, the interface thermal resistance (ITR) decreases when the pressure increases, but such a trend is not obvious when pressure exceeds 0.3 MPa. The increase of surface roughness causes the ITR of thermal pads and carbon-based materials to increase, but does not affect the performance of PCMs and LMPAs. Interface thermal resistance of carbon-based materials decreases a little as temperature increases and that of thermal pads is not affected by temperature in test range. The ITR of PCMs and LMPAs sharply decreases when temperature exceeds phase change point. When surface roughness is 0.8 μm, thermal contact resistance of aluminum is 189 mm2·K·W−1 at 0.2 MPa and 153 mm2·K·W−1 at 0.4 MPa, but the ITR of thermal pads is 136–395 mm2·K·W−1 at 0.3 MPa and the ITR of one carbon-based material is 165 mm2·K·W−1 at 0.5 MPa.
This paper describes the development of artificial neural network (ANN) models and multi-response optimization technique to predict and select the best cutting parameters of wire electro-discharge ...machining (WEDM) process. To predict the performance characteristics namely material removal rate and surface roughness, artificial neural network models were developed using back-propagation algorithms. Inconel 718 was selected as work material to conduct experiments. A brass wire of 0.25
mm diameter was applied as tool electrode to cut the specimen. Experiments were planned as per Taguchi's L9 orthogonal array. Experiments were performed under different cutting conditions of pulse on time, delay time, wire feed speed, and ignition current. The responses were optimized concurrently using multi-response signal-to-noise (MRSN) ratio in addition to Taguchi's parametric design approach. Analysis of variance (ANOVA) was employed to identify the level of importance of the machining parameters on the multiple performance characteristics. Finally, experimental confirmations were carried out to identify the effectiveness of this proposed method. A good improvement was obtained.
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