Drag reduction (DR) agents are used at very low concentrations to accelerate significantly the flow in oil pipeline conduits, oil well operations, flood water disposal, fire fighting, field ...irrigation, transport of suspensions and slurries, sewer systems, water heating and cooling systems, airplane tank filling, marine systems, and biomedical systems including blood flow. DR agents are typically high molecular mass polymers; this review discusses a mechanism explaining how DR occurs using such agents. All pertinent experimental findings are challenged with that mechanism and all are shown to support it. In industrial applications DR agents undergo mechanical degradation in turbulent flow. An equation predicting the degradation as a function of time is presented and successfully confronted with experimental data. Experimental methods of determination of DR are outlined. Finally a connection between DR and flocculation is discussed.
Materials are often characterized in terms of their toughness, though more than one definition of toughness exists. Likely the most widely recognized means of defining material toughness, denoted ...here as τ, is by the area under the stress strain curve from a tensile test. Another important feature describing the nature of materials is that property known as brittleness, which has for a long time been much less quantitatively understood. Using a quantitative definition of brittleness provided in 2006, we demonstrate the existence of a quantitative relationship between τ and brittleness B, valid for polymers with a very wide range of chemical structures and properties, for some polymer-based composites, and also for steel and aluminum. We provide an equation relating toughness to brittleness, while for polymers we mark the determining influence of chemical structures on the properties B and τ.
•We prove the existence of a relationship between brittleness B and tensile toughness τ of polymers.•Aluminum and steel fit on the same diagram.•We provide an equation relating τ to B.
The main functions of thin-walled structures-widely used in several industries-are to reduce the weight of the finished product and to increase the rigidity of the structure. A popular method for ...machining such components, often with complex shapes, is using milling. However, milling involves undesirable phenomena. One of them is the occurrence of vibrations caused by the operation of moving parts. Vibrations strongly affect surface quality and also have a significant impact on tool wear. Cutting parameters, machining strategies and tools used in milling constitute some of the factors that influence the occurrence of vibrations. An additional difficulty in milling thin-walled structures is the reduced rigidity of the workpiece-which also affects vibration during machining. We have compared the vibration signal for different approaches to machining thin-walled components with vertical walls made of Ti6Al4V titanium alloy and Inconel 625 nickel alloy. A general-purpose cutting tool for machining any type of material was used along with tools for high-performance machining and high-speed machining adapted for titanium and nickel alloys. A comparison of results was made for a constant material removal rate. The Short-Time Fourier Transform (STFT) method provided the acceleration vibration spectrograms for individual samples.
Insufficient attention to tribology of materials, including friction, scratchability, and wear, causes severe financial losses in industry. Despite this situation persisting for decades, scratch ...resistance is still not sufficiently understood. This applies even more to sliding wear, which is multiple scratching along the same groove. We have employed molecular dynamics computer simulations to study sliding wear of amorphous polymeric materials. Our simulations pertain to a coarse-grain model of high-density polyethylene. The obtained results include analysis of penetration depth, residual depth, segment displacement as a function of time, and recovery percentage for a range of indenter diameters and force magnitudes. Effects of each of these parameters on the tribological properties are evaluated, providing useful information that can enable tailoring materials for specific applications.
Glass transition temperature
T
g
values characterize pure polymers, polymer blends, copolymers, as well as matrices in polymer-based composites.
T
g
s as function of composition reflect miscibility ...(or lack of it) and determine all properties. We present a new equation for the dependence of
T
g
on composition in blends as well as in copolymers. We compare results obtained from earlier equations (Fox, Gordon–Taylor, Kwei) and those from the new equation with experimental data.
Titanium and nickel alloys are used in the creation of components exposed to harsh and variable operating conditions. Such components include thin-walled structures with a variety of shapes created ...using milling. The driving factors behind the use of thin-walled components include the desire to reduce the weight of the structures and reduce the costs, which can sometimes be achieved by reducing the machining time. This situation necessitates, among other things, the use of new machining methods and/or better machining parameters. The available tools, geometrically designed for different strategies, allow working with similar and improved cutting parameters (increased cutting speeds or higher feed rates) without jeopardizing the necessary quality of finished products. This approach causes undesirable phenomena, such as the appearance of vibrations during machining, which adversely affect the surface quality including the surface roughness. A search is underway for cutting parameters that will minimize the vibration while meeting the quality requirements. Therefore, researching and evaluating the impact of cutting conditions are justified and common in scientific studies. In our work, we have focused on the quality characteristics of horizontal thin-walled structures from Ti6Al4V titanium alloys obtained in the milling process. Our experiments were conducted under controlled cutting conditions at a constant value of the material removal rate (2.03 cm3⁄min), while an increased value of the cut layer was used and tested for use in finishing machining. We used three different cutting tools, namely, one for general purpose machining, one for high-performance machining, and one for high-speed machining. Two strategies were adopted: adaptive face milling and adaptive cylindrical milling. The output quantities included the results of acceleration vibration amplitudes, and selected surface topography parameters of waviness (Wa and Wz) and roughness (Ra and Rz). The lowest values of the pertinent quantities were found for a sample machined with a high-performance tool using adaptive face milling. Surfaces typical of chatter vibrations were seen for all samples.
Knowledge of the glass transition temperatures (Tgs) as function of composition reflects miscibility (or lack of it) and is decisive for virtually all properties of polymer-based materials. In this ...article, we analyze single blend-average and effective Tgs of miscible polymer blends in full concentration ranges. Shortcomings of the extant equations are discussed to support the need for an alternative. Focusing on the deviation from a linear relationship, defined as ΔTg = Tg - φ₁Tg,₁ - φ₂Tg,₂ (where φi and Tg,i are, respectively, the weight fraction and the Tg of the i-th component), a recently proposed equation for the blend Tg as a function of composition is tested extensively. This equation is simple; a quadratic polynomial centered around 2φ₁ - 1 = 0 is defined to represent deviations from linearity, and up to three parameters are used. The number of parameters needed to describe the experimental data, along with their magnitude and sign, provide a measure of the system complexity. For most binary polymer systems tested, the results obtained with the new equation are better than those attained from existing Tg equations. The key parameter of the equation a₀ is related to parameters commonly used to represent intersegmental interactions and miscibility in binary polymer blends.
In this study, we studied the physical and mechanical properties of polymer composite with wastes that incorporating boron. The polymer composites were produced with epoxy based resin and wastes as ...mineral additive. The wastes were added to mixtures in different ratio by replacing the resin from 0 to 66% by weight. Slump-flow and viscosity tests are carried out on fresh samples after mixing. Composites were cured in air condition and they were de-molded after 24 hours. They gain ultimate strength after 7 days. Therefore, tests for characteristics were performed on 7 aged specimens. On the polymer composite samples, compressive strength, flexural strength, wear resistance, water absorption and density tests were performed. As a result, addition of the wastes that including boron increased the compressive strength of polymer composites; however, it made the composites more brittle material with low flexural strength.
Hindered amine light stabilizers (HALSs) and nano ZnO were used to stabilize polypropylene (PP) film-based formulations that were exposed to ultraviolet (UV) light for different lengths of time, ...simulating the harsh outdoor weather of Dallas, Texas, USA. UV doses applied in our laboratory are 121 times larger than the UV dose provided by the sunlight in Texas. 15 different compositions were studied. Tensile behavior, UV transmittance, thermal stability (by thermogravimetric analysis) and dynamic friction of the so exposed PP-based films were determined. Scanning electron micrographs of fracture surfaces were obtained. Nano-ZnO-containing stabilizers impart strong UV resistance to our films. The combination of HALSs and nano-ZnO stabilizers makes the PP films harder-which is important for some PP applications, such as toy manufacturing.
Brittleness of materials—whether it occurs naturally or with aging—affects significantly performance and manifests itself in various properties. In the past, brittleness was defined qualitatively, ...but now a definition of brittleness for viscoelastic materials exists, enabling analysis of all types of polymer-based materials. The quantity brittleness,
B
, has been evaluated for neat thermoplastics, but here composites and metal alloys are also assessed. The physical significance of brittleness is connected to the dimensional stability of materials. The connections of brittleness to tensile elongation and to fatigue are explored while its relationship to surface properties—specifically wear by repetitive scratching—is examined more closely. The economic impact of wear results in monetary loss associated with failure and reduced service life of plastic parts—thus its connection to brittleness finds use across a broad spectrum of industrial applications which utilize plastics for manufacturing, processing, etc. We also demonstrate a correspondence between impact strength (Charpy or Izod) and brittleness of polymers. It is shown that the assumption hardness is equivalent to brittleness is inaccurate; this fact has important implications for interpreting the results of mechanical testing of viscoelastic materials.
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