Deformation Range Research Articles

Experimental and numerical study of the compressive fatigue behavior of a Ti6Al4V mapped rhombioidal dodecahedral structure fabricated by electron beam melting

Triple-periodicarrayed porous structures are regarded as the most promising materials for the fabrication of medical bone implants. The fatigue properties of cellular structures are critical for their long-term use in dynamic biological skeletal environments. In this study, the rhomboidal dodecahedral cell structure of a Ti6Al4V alloy prepared by electron beam melting with different mapping ratios in one coordinate direction was homogenized. Based on this, the compressive fatigue behavior and fatigue failure mechanism under high cyclic loading were studied. To improve the fatigue performance and reduce the influence of residual stress, the microstructure was post-treated by cryogenization and characterized to analyze the evolution mechanism. The fatigue test results of the entire cell structure showed that failure was asynergy between fatigue damage and the ratchet effect. A change in the mapping ratio significantly affected the homogenization mechanical performance, which resulted in the fatigue properties. Based on the test results and numerical simulations, the cross-sectional elastic properties and local maximum stress of struts with different structural mapping ratios were expressed analytically. The fatigue life of the strut with the maximum local stress in the range of elastic deformation and that of the homogeneous block under the preset loading limit of the system were both modeled with appropriate material constants. The high-cycle fatigue life model was established to assist the fatigue behavior prediction of lattice structures.

Numerical modeling of stresses and deformation in the Zagros–Iranian Plateau region

Abstract. The Zagros orogenic system resulted due to collision of the Arabian plate with the Eurasian plate. The region is characterized by ocean–continent subduction and continent–continent collision, and the convergence velocity shows variations from east to west. Therefore, this region shows the complex tectonic stress and a wide range of diffuse or localized deformation between both plates. The in situ stress and GPS data are very limited and sparsely distributed in this region; therefore, we performed a numerical simulation of the stresses causing deformation in the Zagros–Iran region. The deviatoric stresses resulting from the variations in lithospheric density and thickness and those from shear tractions at the base of the lithosphere due to mantle convection were computed using thin-sheet approximation. Stresses associated with both sources can explain various surface observations of strain rates, SHmax, and plate velocities, thus suggesting a good coupling between lithosphere and mantle in most parts of Zagros and Iran. As the magnitude of stresses due to shear tractions from density-driven mantle convection is higher than those from lithospheric density and topography variations in the Zagros–Iranian Plateau region, mantle convection appears to be the dominant driver of deformation in this area. However, the deformation in the east of Iran is caused primarily by lithospheric stresses. The plate velocity of the Arabian plate is found to vary along the Zagros belt from the north–northeast in the southeast of Zagros to the northwest in northwestern Zagros, similarly to observed GPS velocity vectors. The output of this study can be used in seismic hazards estimations.

Update on the Diagnosis and Management of Early-onset Scoliosis.

In this article, we review the most recent advancements in the approaches to EOS diagnosis and assessment, surgical indications and options, and basic science innovation in the space of early-onset scoliosis research. Early-onset scoliosis (EOS) covers a diverse, heterogeneous range of spinal and chest wall deformities that affect children under 10 years old. Recent efforts have sought to examine the validity and reliability of a recently developed classification system to better standardize the presentation of EOS. There has also been focused attention on developing safer, informative, and readily available imaging and clinical assessment tools, from reduced micro-dose radiographs, quantitative dynamic MRIs, and pulmonary function tests. Basic science innovation in EOS has centered on developing large animal models capable of replicating scoliotic deformity to better evaluate corrective technologies. And given the increased variety in approaches to managing EOS in recent years, there exist few clear guidelines around surgical indications across EOS etiologies. Despite this, over the past two decades, there has been a considerable shift in the spinal implant landscape toward growth-friendly instrumentation, particularly the utilization of MCGR implants. With the advent of new biological and basic science treatments and therapies extending survivorship for disease etiologies associated with EOS, the treatment for EOS has steadily evolved in recent years. With this has come a rising volume and variation in management options for EOS, as well as the need for multidisciplinary and creative approaches to treating patients with these complex and heterogeneous disorders.

Investigation the Effect of MR Fluid Composition on Properties at Low Strain Ranges.

The paper presents the results of eight magnetorheological (MR) fluids of different compositions. Magnetite and carbonyl iron were used as magnetic particles. MR fluids based on glycerin and OKS 352 oil were produced using stabilizers in the form of oleic acid and Aerosil 200 (Evonik Resource Efficiency GmbH, Hanau, Germany) silica; additives such as graphite and yellow dextrin were also used. The aim of the study was to determine the properties of various combinations of components on the dynamic properties of MR fluids, i.e., properties characterizing the fluid within the range of low deformations, as well as to investigate the effect of different compositions on structural yield stress and flow stress prepared MR fluids at different magnetic field induction values.

THE INFLUENCE OF THE ANTHROPOGENIC FACTOR ON THE BLACK SEA COAST WITHIN THE ODESSA REGION

Problem Statement & Purpose. The city of Odessa is the center of a large industrial and port agglomeration on the northwestern coast of the Black Sea between Cape Karabush and Sanzheyskiy Cape. Until the foundation of the seaport and the city, the Black Sea shores and estuaries almost always existed in a natural state, except for local small areas located in temporary fishing, military, wandering sites. But from the end of the 18th century, the first buildings and transformations of natural slopes began, which began to significantly change the surrounding nature of the coast and coastal land, because «the history of the development of Odessa is the history of the fight against abrasion landslides». These and many other authors (A. M. Drannikov, G. M. Zub, E. E. Kitran, N. A. Khrennikov, I. Ya. Yatsko and others) testified about the general appearance, morphology and dynamics of natural coastal landslides in the period up to the end of the 40s of the XX century. It is the consequences ofanthropogenic influence and their consideration, analysis and current situation on the Odessa coast of the Black Sea that is the purpose of this work. Data & Methods. The actual materials of this work were obtained by the authors over the course of decades in the area between Capes Lanzheron and Bugovo on the Odessa coast. Buildings to protect the coast from destruction were instrumentally studied. Two leading groups of coastal marine research were used as the main ones: route-expeditionary and stationary. Their office processing included the use of cartographic, graphical modeling, mathematical statistics, geographical comparison, water and sieve analysis, geomorphological leveling, etc. For comparisons, the materials of Yu. D. Shuisky, I. P. Zelinskiy, D. Ya. Bertman, A. R. Shuvalov, A. V. Kisselis. Results. The increase in anthropogenic pressure on the natural system of the Black Sea coast within the Odessa area forced us to carry out additional studies of the Odessa coastal defense complex. It is located between the Langeron Cape in the north and the southern flank of Bolshoy Fontan Cape, for about 12.5 km. The named complex changed the coast very much, there was a strong influence of anthropomorphogenesis. At the same time, designers and builders were guided by a more perfect natural scheme of sediment distribution in the sphere of action of the North-West along the coastal sediment flow. The artificial transformation of the Odessa coast has led to the emergence of several types of anthropogenic landforms instead of natural ones. Coastal protection and other structures are represented by surface, intra-slope and underwater, longitudinal and transverse, positive and negative, sedimentary, concrete, reinforced concrete, metal, high, low for various purposes, etc. They correspond to a special classification. The effectiveness of the introduction of hydraulic structures is ensured by their functionality. The main property is the ability to extinguish and disperse the energy of sea waves with a loss of 10 to 60%. The structures lead to the loading of the shear tongue, the diversion of groundwater, the prevention of abrasion of the subslopes from storm impact, and they have a recreational and ecological purpose. Wave action on artificial sandy beaches, on their significant vertical and horizontal deformations, is accompanied by sediment loss. Wave processing of sediments provides the development of an equilibrium profile that occurs in different stages: initial transformation of the shape, formation of sand sizes, very fast transformation during the first 1–3 years and slow changes during subsequent repair backfilling. At the same time, the range of deformations is large, very close to natural, despite the surrounding structures.

The Saddleback Deformity in Teleost Fish: Identification of a Unique Global Hotspot in Eastern Australia

The saddleback deformity, an abnormality of the dorsal fin and profile, lacking one to all of the dorsal spines, accompanied by shape, number and position abnormalities of associated pterygiophores, has been reported in teleosts under culture conditions and in the wild in many locations throughout the world, including North and South America, Asia, Australia, Europe, India and the Middle East. A unique global hotspot for saddleback deformities in wild teleosts is the southeast Queensland Australia coastal region between 26° S and 28° S. At this location the incidence of saddleback has been relatively stable but very high at about 10% of individual teleosts taken in the associated fishery since 1997. Opinions on causation have focused on two possibilities, a developmental defect associated with water pollution or a physical injury. The range of skeletal deformities is vastly different in cultured teleosts compared with those occurring in the wild. There is now mounting evidence that physical injury is causing saddleback in teleosts in southeast Queensland Australia. Such injury could be caused by predatory behaviour of piscivorous fish or birds, parasites, or escapement or release from fishing nets and other fishing gear. Population mortality rates associated with saddleback in southeast Queensland are unknown, but expected to be high. The high level of occurrence of saddleback in teleosts in southeast Queensland Australia together with the good understanding of their fisheries biology (age and growth rates, reproductive biology, habitat dependence) and stock assessments of the associated fisheries provide excellent opportunities for further research which would add to the scientific understanding of the saddleback deformity in teleosts throughout the world. A recommendation from this review is that support should be sought by research providers (universities and Government research agencies) from routine annual funding offers from the Australian and Queensland Governments to achieve an increase in the scientific understanding of the saddleback deformity.

Fatigue life and failure mechanism of nylon 66 cord/rubber composites under wide temperature range

This work simulates the real harsh service conditions of Fiber-reinforced polymer composites (FRPC), and the dynamic adhesion and failure mechanism of nylon 66 (PA66)-reinforced natural rubber (NR) composites under large deformation and wide temperature range are deeply studied by comprehensive analysis of the interfacial adhesion evolution, microstructure and failure damage location of the composites, interfacial heating rate, and modulus ratio of PA66/NR. The failure mechanism of PA66/NR composites is interfacial debonding at −20 °C, 25 °C and 80 °C, whereas that at 120 °C is matrix cracks. Interestingly, at −20 °C, the crack expansion at the interface is slow, and the samples show two-stage damage during fatigue, resulting in the highest fatigue life. At 80 °C, the interface heating rate and modulus ratio of the PA66/NR composites is the lowest, and thus the fatigue life is higher than that at 25 °C and 120 °C. Keywords: fiber reinforced polymer composites, fatigue life, failure mechanism.

Design of a variable-diameter wheel with a novel distributed compliant mechanism

Compliant variable-diameter mechanisms enable adaptation of variable-diameter wheels to both road and soft terrain. Conventional compliant variable-diameter mechanisms, in which every wheel-foot is an independent load-bearing structure, rely heavily on rigid-body mechanisms. To overcome the structure restriction and improve their performances, we introduce a novel compliant mechanism in which circumferentially distributed leaf springs or combination springs with large deformation range are used as flexible components. The springs constitute the closed outer ring and the overall load-bearing structure in the wheel. A novel screw transmission mechanism was designed to achieve motions with two degrees of freedom. Based on the geometric relationships, a dimensional design method for the mechanism is proposed. The chained beam-constraint-model and integration methods are introduced to obtain the spring deflections and maximum hub rotation angle. These methods can be used for further design of the transmission mechanism. The wheel design is then verified experimentally. The results indicate that the required design targets were achieved. Thus, the proposed mechanism diversifies the structure type and design of compliant mechanisms and expands the applicability of variable-diameter wheels in mobile platforms.

Analysis of surface deformation characteristics in pipe jacking construction based on the theory of a stratum cross-correlation conditional random field

For the surface deformation problem caused by pipe jacking construction, a conditional random field (CRF) method based on Co-Kriging theory is used to establish a stochastic simulation method for soil parameters in a finite element model, considering the constraint effect of borehole data and the influence of the correlation of adjacent strata. Combined with the pipe jacking case, the statistical laws of soil parameters and surface deformation laws are analyzed and compared with the unconditional random field (URF) method to verify the reliability and applicability of the proposed method. The research results show that the stochastic simulation method can effectively characterize the spatial variability and autocorrelation of stratigraphic parameters and obtain the surface deformation law and deformation range caused by pipe jacking construction. The parameters generated by the proposed method have a higher correlation and smaller stochastic range. When using the method to analyze engineering problems, the stochastic curves obtained from the analysis are more concentrated, and the discrete range is smaller.

Design of PDMS/CNT flexible pressure sensor based on double structure with the regulation of electrical properties

Introducing microstructure on the surface or porous structure inside of dielectric layer can improve the sensitivity and monitoring range of the flexible pressure sensor. However, developing pressure sensors with high sensitivity in the high-pressure range is challenging because of the trade-off between sensitivity and linearity of pressure. Here, we report a design approach based on the collaboration of double structure and electrical characteristics that can improve sensor sensitivity at high pressure. The surface microstructural and internal porous structure of the dielectric layer provide a more comprehensive deformation range for the sensor from a mechanical perspective. The effects of the conductive carbon nanotube (CNT) content between two structures on the overall electromechanical characteristics of the sensor were studied. This collaborative (structure and component) design can effectively increase the monitoring range of the sensor and accomplish “gear shifting” of the sensitivity by the non-uniform distribution of CNT in the structure. The optimized capacitive pressure sensor exhibits outstanding sensitivity over a wide monitoring range (1.17 kPa−1 in the 0−100 kPa, 0.49 kPa−1 in the 100−350 kPa, and 0.23 kPa−1 in the 350−1000 kPa), and fast response capability (30 ms). The pressure sensor has excellent integrated sensing performance in rubber wheels' static/dynamic pressure monitoring, demonstrating application potential in high-pressure fields.

The Structural, Mechanical, Half-Metallic, and Magnetic Properties of Quaternary Heusler Alloy CrFeVAl: A First-Principles Study

Heusler alloys are promising spintronic materials. For spintronics, it is essential to explore magnetic materials with high spin polarization and high Curie temperature. Theoretical methods based on first-principles calculations have been extensively used for studies of materials because these methods can reduce material costs. Hence, a quaternary Heusler alloy, CrFeVAl, in which one Fe atom in the Fe2VAl crystal structure is replaced with Cr atom, was investigated by first-principles calculations using the CASTEP package. The results showed that the CrFeVAl alloy is a type-2 stable compound with a LiMgPdSn-type structure, having an equilibrium lattice constant of 5.842 Å. An investigation of its mechanical properties showed that the alloy is similar to Fe2VAl and that it is an anisotropic brittle material. Notably, the inclusion of Cr was found to effectively reduce the brittleness compared to that of Fe2VAl. In addition, its Debye temperature was calculated to be 368.3 K, which is lower than that of the Fe2VAl alloy. Electronic structure calculations indicated that CrFeVAl is an excellent half-metallic ferromagnetic material, with a spin polarization of 100%. Examination of the electronic structure further showed that the magnetism in CrFeVAl originates mainly from the spin contribution of the d electrons of the transition metal atoms in the alloy and the hybridisation between their d orbitals. The deformation range of the alloy under stress was between −2.7 and 2.0%, demonstrating that the alloy can maintain excellent half-metallic behaviour. Therefore, we believe that CrFeVAl can be employed as a new spintronic material.

Toxicity of Heavy Metals and Detergent Inducing Morphological Deformities and Survival Rate of Chironomous Circumdatus

In Chironomidae larvae, the potential effects of heavy metals and detergent can be seen as a result of morphological deformities in larval mentum, mandibles, oral cavity, and in different body regions. In this experiment, the objectives were to examine (I) The potential effects of heavy metals forming morphological deformities in Chironomidae larvae. (II) The survival rate of Chironomidae larvae in exposure to detergent and heavy metals. (III) To establish a dose-response relationship between toxicant and chironomid larvae. Consecutive developmental stages of larvae from egg to fourth instar were chronically exposed to the four sublethal concentrations of lead (0, 5, 50, 200 µg/g), copper (0, 1, 10, 100 µg/g), and detergent (0, 100, 200, 300 mg/g). Tetraphyll flakes were given as food. This experiment reveals the assessment of toxicity by the sublethal concentration of copper (Cu), Lead (Pb), and detergent induce low to high range of mouthpart and body deformities and survival rates in different instars of Chironomous circumdatus larvae during chronic exposure tests over several generations. According to the consecutive observations, it was found that the deformation frequency of oral region and body were high in detergent medium while lead and copper showed comparatively less deformation rate and high survival. In both lead and copper media, the survival rate shows a declining pattern and deformation frequency increased on increasing the dose.

Genetic algorithm-based parameter inversion and pipeline subsidence prediction

To invert mine subsidence parameters and predict the timing of associated risk to underground pipelines passing through mining areas with incoherent subsidence information, this study proposes a model based on combining the advantages of interferometric synthetic aperture radar (InSAR) technology, the probability integral method (PIM), segmented Knothe time function, and genetic algorithm. Firstly, InSAR technology is used to analyze a time series of surface deformation in a mining area, circle the range of large-gradient deformation, and distinguish the subsidence edge from the subsidence center. In the case of the subsidence edge (small-scale deformation), InSAR results are retained, whereas in the case of the subsidence center (large-scale deformation), subsidence parameters, such as the subsidence coefficient and influence radius, are obtained via the genetic algorithm. The subsidence of the working face in the mining area is determined by combining InSAR information and the PIM parameter inversion-based basin model. This allows us to obtain continuous surface subsidence information, study surface subsidence trends over time, and predict future pipeline subsidence. The researchers subsequently test the efficacy of this model in the Qinchi mining area in Shanxi Province, China. Sentinel-1A images were used as the data source, combine the PIM and segmentation time function, and use the genetic algorithm to obtain the subsidence mining parameters. The inversion results show that the subsidence coefficient is 0.5917 (with an error of 2%), and the main influence angle tangent value is 1.927 (with an error of 2.18%), indicating high inversion accuracy. Based on this model, the study predict that subsidence in the Qinchi mining area will threaten the structural integrity and operation of the intersecting pipeline by November 2025.

Strain-sensitive mechanoluminescence with high stability and self-recovery toward stretchable strain sensor

Due to its unique strain-light response, non-contact measurement and visualization characteristics, strain-sensitive mechanoluminescent (ML) materials are expected to replace traditional strain gauges as a new generation of strain sensing materials. The strain sensing technology has high requirements for the multi-parameter response characteristics, stability and sensing working range of sensing materials. In this work, a composite flexible strain sensing ML device composed of La4GeO8 doped with lanthanide rare earth ions Ln3+ and polydimethylsiloxane (PDMS) is proposed. The ML of the device can produce good linear response to stress, strain and loading rate under tensile action. The minimum strain response threshold is less than 2% of the relative strain, and the sensing range can reach 100% of the relative strain in the full elastic deformation range. In addition, the ML intensity of La4GeO8: Ln3+@PDMS has the characteristic of self-recovery, and its self-recovery is related to the maximum strain of loading and the placing time. The wavelength (visible-near infrared) and color adjustable ML can be achieved by adjusting the type and doping concentration of rare earth ions. Moreover, the device has high thermal stability and water resistance, indicating that it is also adaptable to extremely harsh environments. The results show that La4GeO8: Ln3+@PDMS can be used as a strain-sensing-material with multi-dimensional mechanical parameter response, and has potential application prospects in the field of flexible tensile strain sensors.

Highly stretchable, self-healable and adhesive, thermal responsive conductive hydrogel loading nanocellulose complex for a flexible sensor

Currently, with the widespread concerns of smart soft sensors in wearable electronics, human health detection and electronic skin, flexible conductive hydrogels have been extensively studied. However, it remains a great challenge to develop hydrogels that have both satisfactory mechanical performance with stretchable and compressible and high conductive. Herein, based on synergistic dynamic hydrogen and metal coordination bonds, polyvinyl alcohol (PVA)/poly (2-hydroxyethyl methacrylate) (PHEMA) hydrogels doped with polypyrrole decorated cellulose nanofibers (CNFs@PPy) are developed via free radical polymerization. The loading versatile CNFs@PPy highlighted the complex hydrogels super-stretchability (approximately 2600 % elongation) and excellent toughness (2.74 MJ/m3) properties to tensile deformation, strong compressive strength (1.96 MPa), fast temperature responsiveness and outstanding strain sensing capability (GF = 3.13). Moreover, the PHEMA/PVA/CNFs@PPy hydrogels possessed rapid self-healing and powerful adhesive abilities to various interfaces without extra assistance, as well as distinguished fatigue resistance performance. Such advantages make the nanocomposite hydrogel displayed high stability and repeatable to both pressure and strain in a wide range of deformations, enabling a promising candidate in the fields of motion monitoring and healthcare management.

Hot Workability Investigation of an Fe-Al-Ta Alloy Using Deformation Processing Maps

Fe-Al-Ta alloys are expected to replace high-alloyed steels in steam turbine blades. However, the mechanical properties of the forged blades are still not optimal due to limited grain refinement during hot forging and the coarse-grained microstructure inherited from the as-cast precursor. It is, therefore, essential to investigate the hot deformation behavior of the alloy to identify the optimum range for the deformation parameters leading to good hot workability with significant grain refinement. The hot deformation behavior and hot workability of an Fe-25Al-1.5Ta (at.%) alloy were investigated in the present work using constitutive modeling and the concept of processing maps. Uniaxial compression tests were conducted in a strain rate range from 0.0013 s−1 to 1 s−1 and in a temperature range from 900 °C to 1100 °C, where a disordered A2 α-(Fe, Al) matrix phase along with a C14-(Fe, Al)2Ta Laves phase were confirmed by X-ray diffraction. The flow stress–strain curves showed a broad maximum followed by a slight drop in stress until a steady state was reached. The optimum processing window for the studied alloy was located at 910–1060 °C/0.0013–0.005 s−1, where the efficiency of the power dissipation (η) and strain rate sensitivity (m) reached 50% and 0.33, respectively. The material underwent a combination of dynamic recovery and dynamic recrystallization over the whole tested deformation range. No flow instabilities were predicted based on Prasad’s flow instability criterion when deformation was performed up to a true strain of 0.5 and 0.8, indicating a high degree of hot workability of the studied alloy over the entire deformation range tested. The current study reveals a well-suited parameter range for the safe and efficient deformation of Fe-Al-Ta alloys, which may contribute to the optimization of the thermomechanical processing of this alloy.

Structural mechanisms of enhanced mechanical property in ZrCu metallic glass at low temperatures

The application of traditional crystalline materials as structural materials cannot meet critical design challenges due to low-temperature brittleness. To address this issue, this study investigates the deformation behavior of Zr2Cu metallic glass (MG) model at ambient and low temperature states by molecular dynamics (MD) simulations to unravel the governing mechanisms associated with mechanical performance. Structurally representative amorphous models of the MG were developed and their evolutions under tensile loadings at ambient (300 K) and low temperatures (250 K, 200 K, 150 K, 100 K, 50 K) were captured. Notably, significant variations in maximum stress and corresponding strains characterized the stress-strain behavior as elastic-plastic properties increased with decreasing temperatures. Stress activations of the atomic mass were rapidly incipient at the ambient condition, but largely constrained at low temperatures by which the density variations of activated zones and the emerging strain of first shear transformation zones (STZ's) established a negative correlation with temperature as inferred by the wider strain range of deformation. Disparities in strain thresholds accounted for the higher free volume content at the ambient state, but as temperatures declined, fine structural differences stimulated the formation of densely-packed structures in the amorphous model at low temperatures by the spontaneous annihilation of excessive free volumes. Consequently, the higher growth rates of the average atomic potential energy and the retarded emergence of high-potential-energy atomic mass suggest that at low temperatures, there is a higher resistance to shear band nucleation and higher barrier for atomic migration. As a result, the generation of free volumes, formation of STZs and shear bands were retarded, leading to the enhanced ductility. Thus, at low temperatures, unique tuning mechanisms of structural performance were evolved in the amorphous model that suitably enhanced the constitutive properties of Zr2Cu MG.

A comprehensive assessment for the structural change of waxy crude oils induced by pour point depressant beneficiation

In the petroleum industry, the solid paraffins that precipitate out from a waxy crude oil complicate the low-temperature flow characteristics, causing major difficulties in pipeline transportation. Pour point depressants (PPDs) are often utilized to improve the flow characteristics of crude oils by modifying the morphology and structure of wax crystals, becoming a great technical and economic interest. The improving mechanism of PPDs on the structure of gelled waxy crude oil can be attributed to the nucleation, co-crystallization, and adsorption effect to the precipitated wax crystals, preventing the waxy structure from growing further and forming a volume spanning network. Many previous works about the PPDs’ effect have merely focused on the pour point, apparent viscosity, and yield strength depressing ability, while other structural properties have rarely been comprehensively evaluated. The objective of this study is to comprehensively reveal the change of the wax particle structure in oils benefitted with PPDs. The structure of gelled oils doped with PPDs was found to become less elastic and more susceptible to shear perturbation with a lower linear deformation range of 0.42% and a longer relaxed time scale of 3000 s. Large amplitude oscillatory shear (LAOS) tests show that the nonlinear viscoelastic behaviors can be weakened by PPDs, whereas the third harmonic value obtained by Fourier-transform analysis increases after adding PPDs, indicating that the sensitivity to applied load are strengthened. Meanwhile, the value of yield strain increases to about 8.7%, and the irreversible plastic deformation zone becomes relatively broader (brittleness index I increases to 70.9), which mean a more ductile fracture induced by PPDs would occur when yielding. Although the additive PPDs weaken the structural strength and the non-Newtonian characteristics (kinetic index of n1 increases to 0.8), the characteristic of thixotropy is obviously strengthened, and the doped crude oils exhibit a faster structural breakdown process after yielding. All these novel changes for structural features explored in this paper provide theoretical guidance into understanding the practical engineering problems of accelerated process for the pipeline restart flow benefitted with PPDs.

On the automated characterisation of inclusion-induced damage in 16MnCrS5 case-hardening steel

Manganese sulphide inclusions are commonly found in steels and known to facilitate the formation of deformation-induced damage sites in the form of voids during cold forming. These damage sites either exist as cracks, splitting the inclusion in two parts, or as delamination, separating the inclusion from the surrounding steel matrix. Both negatively influence the longevity of components, especially under cyclic loading. The analysis of damage is inherently scale-bridging, ranging from deteriorated global mechanical properties of the finished part, over the damage behaviour of individual inclusions, to the local description of individual voids. In this work, we set out to devise an analysis approach gathering information on all these scales. To this end, we conducted in-situ tensile tests while acquiring high resolution SEM panoramic images and analysed them with two neural networks, trained for this work, to detect damage sites with respect to the inclusions at which they nucleated. We find that the main damage mechanism during tensile deformation parallel to the length of inclusions is cracking and that damage evolution is equally influenced by void nucleation and void growth in the observed range of deformation. By focussing on the damaging behaviour of different inclusions, we show that the position of inclusions in the microstructure influences the resulting damage evolution and that the vicinity of pearlite bands leads to decreased damage formation.

Advection-enhanced heat and mass transport from neutrally suspended droplet in simple shear flow

Advection-enhanced heat and mass transport from a single droplet neutrally suspended in a simple shear flow has been studied using high-fidelity numerical simulation. The capillary number ranges from 0.01 to 0.5, which encompasses the entire range of small deformation, large deformation, and breakup of the droplets. The Reynolds number is from 0.01 to 1, including regions of both weak and strong advection. The temperature and mass concentration are modeled as the concentration of a passive scalar released at the droplet surface. Two Schmidt numbers, 10 and 100, are considered, for which flow advection plays a role in the transport of passive scalar. For unbroken droplets, the interaction between the carrier fluid and the suspended droplet leads to several different flows around the droplet. The fluid motions together with scalar diffusion constitute a coupled transport mechanism for passive scalar. The dependence of scalar release rate on Reynolds and Peclet numbers can be roughly described by the correlation for a rigid sphere. For broken droplets, the basic flow features around the droplet during the process of elongation and breakup are similar to those of an unbroken droplet. The variation of the scalar release rate can be decomposed into several stages, corresponding to the process of droplet elongation and breakup. The variation of the scalar release rate exhibits a high correlation with the capillary, Reynolds, and Peclet numbers. This suggests that it is feasible to develop an empirical model that incorporates the effects of the number and size distributions of child droplets after breakup.