Effects of ultrasonic surface rolling process on tribological behavior of 4Cr13 stainless steel

Ultrasonic surface rolling (USR) process is a novel surface strengthening technique based on the tool head's high-frequency impact on the workpiece. USR can cause severe plastic deformation on the superficial surface of metal material, and greatly improving the mechanical properties of the material. This paper elucidates the effects of USR passes on the surface roughness, sample height, microstructure, microhardness, residual stress, and tribological properties of 4Cr13 stainless steel. The results revealed that multiple USR treatments refined the near-surface layer grain of the sample. Compared with untreated sample, USR treatments significantly improved the surface roughness and microhardness of the samples. Obvious compressive residual stress and plastic deformed with a maximum value of about -723 MPa and a depth of about 229 μm were also introduced into the sample surface. Under a dry friction environment, the samples that underwent the USR treatments exhibited significantly enhanced wear resistance, and six rolling passes were found to be the most suitable treatment.

Controlling Conditions of the One-Dimensional Consolidation Test on Peat Soil

This paper studies the changes in the loss on ignition (LOI), total nitrogen content (TN), and strain in a one-dimensional consolidation test on peat soil. The effects of small-range fluctuations in the ambient temperature and changes in the sample height on the consolidation process of peat soil are proposed and verify the inhibitory effect of thymol on the decomposition of organic matter. The results show that when the ambient temperature fluctuates in a small range, the consolidation rate is significantly affected. Under a low load, the ambient temperature increases by 1–2 °C, and the consolidation rate can be increased by up to 10 times. This study presents the changes in loss on ignition (LOI) and total nitrogen content (TN) during consolidation, which proves that soaking the samples with a thymol solution can effectively control the decomposition of organic matter in peat soil. The strain of peat soil at a height of 30 mm is greater than or equal to that of other height samples, while that of mucky soil is 20 mm. Therefore, 30mm is the recommended sample height for peat soil for the one-dimensional consolidation test.

Gravity-induced phase phenomena in plate-rod colloidal mixtures

Gravity can affect colloidal suspensions since for micrometer-sized particles gravitational and thermal energies can be comparable over vertical length scales of a few millimeters. In mixtures, each species possesses a different buoyant mass, which can make experimental results counter-intuitive and difficult to interpret. Here, we revisit from a theoretical perspective iconic sedimentation-diffusion-equilibrium experiments on colloidal plate-rod mixtures by van der Kooij and Lekkerkerker. We reproduce their findings, including the observation of five different mesophases in a single cuvette. Using sedimentation path theory, we incorporate gravity into a microscopic theory for the bulk of a plate-rod mixture. We also show how to disentangle the effects of gravity from sedimentation experiments to obtain the bulk behavior and make predictions that can be experimentally tested. These include changes in the sequence by altering the sample height. We demonstrate that both buoyant mass ratio and sample height form control parameters to study bulk phase behavior.

Aplikasi Size Effect Law Pada Beton Marine dengan Pola Bukaan Tarik

AbstrakPengembangan infrastruktur di bidang maritim adalah salah satu strategi untuk mengembangkan perekonomian. Beton marine banyak digunakan sebagai material struktur pada pembangunan infrastruktur di bidang maritim tersebut. Beton marine harus menggunakan beton high performance concrete (HPC). Dengan berkembangnya teknologi beton HPC pengoptimalan efisiensi komponen struktur menjadi lebih signifikan.Pada perencanaan pelaksanaan pembangunan khususnya pada tahap analisa struktur, jarang sekali direncanakan kekuatan terhadap mekanika fraktur yang seharusnya juga didesain agar keruntuhan secara fraktur bisa diatasi. penelitian ini mengkaji aplikasi size effect law pada beton HPC pada balok dengan berbagai ukuran yang sudah ditentukan (small, medium dan high) untuk memperoleh nilai energy fraktur (Gf). Hasil penelitian ini dapat berkontribusi dalam penerapam metode untuk mendapatkan nilai parameter dari kinerja fraktur. selain itu, data parameter dapat digunakan dalam mengkalibrasi analisa numerik elemen struktur berbasis fraktur energi agar dapat dipastikan kinerja struktur yang sesungguhnya.Hasil pengujian menunjukkan energi fraktur pada benda uji set II (rasio takik terhadap tinggi sample = 1/6) lebih besar 8,4% dari benda uji set I (rasio takik terhadap tinggi sample = 1/3). Factor geometri dan kemiringan pada garis regresi (A) menurun selaras dengan menurunnya rasio takik. Dari angka keruntuhan nilai berada pada range 0,1 < < 10 yang menandakan material didesain harus dengan kriteria nonlinear fracture mechanic.Kata-kata Kunci: Beton marine, mekanika fraktur, size effect law, nonlinear fracture mechanics AbstractInfrastructure development in the maritime sector is one strategy for developing the economy. Marine concrete is widely used as a structural material in infrastructure development in the maritime sector. Marine concrete must use high performance concrete (HPC). With the development of HPC concrete technology, optimization of the efficiency of structural components has become more significant.In the construction implementation planning, especially at the structural analysis stage, it is rare to plan the strength of the fracture mechanics which should also be designed so that fracture collapse can be overcome. This study examines the application of size effect law on HPC concrete on beam of various predetermined sizes (small, medium and high) to obtain the fracture energy value (Gf). The results of this study can contribute to the application of the method to obtain parameter values of fracture performance. In addition, parameter data can be used in calibrating the numerical analysis of energy fracture based structural elements in order to ascertain the actual performance of the structure.The results showed that fracture energy in specimen set II (ratio of notches to depth = 1/6) was 8.4% greater than specimen set I (ratio of notches to sample height = 1/3). The geometric factor and slope of the regression line (A) decreased in line with the decreasing notch ratio. From the brittleness number, the value of β is in the range 0.1 <β <10 which indicates that the material should designed with nonlinear fracture mechanic criteria.Key words: marine concrete, fracture mechanics, size effect law, nonlinear fracture mechanics

A Prediction Model for Additive Manufacturing of Inconel 718 Superalloy

Inconel 718 is a nickel-based superalloy and an excellent candidate for the aerospace, oil, and gas industries due to its high strength and corrosion resistance properties. The machining of IN718 is very challenging; therefore, the application of additive manufacturing (AM) technology is an effective approach to overcoming these difficulties and for the fabrication of complex geometries that cannot be manufactured by the traditional techniques. Selective laser melting (SLM), which is a laser powder bed fusion method, can be applied for the fabrication of IN718 samples with high accuracy. However, the process parameters have a high impact on the properties of the manufactured samples. In this study, a prediction model is developed for obtaining the optimal process parameters, including laser power, hatch spacing, and scanning speed, in the SLM process of the IN718 alloy. For this purpose, artificial neural network (ANN) modeling with various algorithms is employed to estimate the process outputs, namely, sample height and surface hardness. The modeling results fit perfectly with the experimental output, and this consequently proves the benefit of ANN modeling for predicting the optimal process parameters.

Measuring the residual stress and stress-corrosion cracking susceptibility of additively manufactured 316L by ASTM G36-94

Residual stress is a contributor to stress-corrosion cracking (SCC) and a common byproduct of additive manufacturing (AM). Here the relationship between residual stress and SCC susceptibility in laser powder bed fusion AM 316L stainless steel was studied through immersion in saturated boiling magnesium chloride per ASTM G36-94. The residual stress was varied by changing the sample height for the as-built condition and additionally by heat treatments at 600, 800, and 1200 °C to control, and in some cases reduce, residual stress. In general, all samples in the as-built condition showed susceptibility to SCC with the thinner, lower residual stress samples showing shallower cracks and crack propagation occurring perpendicular to melt tracks due to local residual stress fields. The heat-treated samples showed a reduction in residual stress for the 800 and 1200 °C samples. Both were free of cracks after &gt;300 hours of immersion in MgCl2, while the 600 °C sample showed similar cracking to their as-built counterpart. Geometrically necessary dislocation (GND) density analysis indicates that the dislocation density may play a major role in the SCC susceptibility.

Stratigraphy of stable isotope ratios and leaf structure within an African rainforest canopy with implications for primate isotope ecology

The canopy effect describes vertical variation in the isotope ratios of carbon (δ13C), oxygen (δ18O) and partially nitrogen (δ15N) within plants throughout a closed canopy forest, and may facilitate the study of canopy feeding niches in arboreal primates. However, the nuanced relationship between leaf height, sunlight exposure and the resulting variation in isotope ratios and leaf mass per area (LMA) has not been documented for an African rainforest. Here, we present δ13C, δ18O and δ15N values of leaves (n = 321) systematically collected from 58 primate food plants throughout the canopy (0.3 to 42 m) in Côte d’Ivoire, West Africa. Besides leaf sample height and light availability, we measured leaf nitrogen and carbon content (%N, %C), as well as LMA (n = 214) to address the plants’ vertical resource allocations. We found significant variation in δ13C, δ18O and δ15N, as well as LMA in response to height in combination with light availability and tree species, with low canopy leaves depleted in 13C, 18O and 15N and slightly higher in %N compared to higher canopy strata. While this vertical isotopic variation was not well reflected in the δ13C and δ15N of arboreal primates from this forest, it did correspond well to primate δ18O values.

Particle Flow Simulation of Failure Characteristics of Deep Rock Influenced by Sample Height-to-Width Ratios and Initial Stress Level under True-Triaxial Unloading

The micromechanism of the effects of different height/width ratios (H/W) and initial stress levels on unloading characteristics of deep rock was investigated based on PFC3D true-triaxial unloading simulation. The results show that the increase of H/W will increase the movement speed of rock particles and intensify the acoustic emission (AE) activity inside the rock. With the increase of H/W, the failure mode of rock changes from splitting failure to tensile-shear failure. With increasing initial stress level, the particle velocity and overall fragmentation degree of rock increase. However, the increase of lateral stress will limit the coalescence of microfractures and weaken AE activity in the rock. Under unloading condition, the bonds between particles generally crack along the unloading direction, and the tensile effect is more pronounced under the condition of low initial stress level and high H/W. Under unloading condition, the variable energy of rock increases with increasing H/W and initial stress level, and the kinetic energy of rock particles increases with increasing H/W. The increase of initial stress level will increase the kinetic energy of rock particles when H/W is high.

Rock strength and time dependent deformation of borehole breakouts in the ICDP Outokumpu deep borehole

&lt;p&gt;While the mechanical properties of plate boundaries are relatively well known and characterized by earthquake occurrence, intraplate regions are still largely &lt;em&gt;&amp;#8220;terra incognita&amp;#8221;&lt;/em&gt;, especially in cratonic shields where only seldom and very few data related to the state of the stress field are available. The only way to detect such data and understand the geological and physical processes responsible for the present stress field in an intraplate area is to carry out in-situ measurements of stress-induced deformation in a borehole over time. We had a unique and extraordinary opportunity to measure and investigate the time-dependent deformation in an aseismic area directly in-situ inside the 2500 m Outokumpu open borehole in eastern Finland. The stress data acquired in 2006 and 2011 have been analysed and show that a slow but continued deformation of the upper part of the Earth&amp;#8216;s crust, albeit unexpected, is still ongoing. The continuous formation and development of stress-induced borehole enlargements in a tectonically very stable and almost aseismic area is unforeseen and raises questions of global importance. For this, two complementary approaches were conducted: identification of breakout zones and rock physics measurements on selected drill cores. We compared the two datasets to study the changes of breakout geometry and to quantify the growth of the breakouts in this time span from differences in width, length and depth. For the second method, UCS experiments were conducted providing unconfined compressive strength on specimens collected from above, middle and below breakout zones, and rough estimates of the static Young&amp;#8217;s modulus based on the initial length and axial travel of the load frame. The sample height-diameter (H:D) ratio of available drill cores was less than required in testing standards (ASTM D7012, 2014, ISRM 1999). The relatively small grain size of drill cores allowed drilling of smaller-diameter subcores that in most cases fulfilled or exceeded the minimum H:D ratio (1.7&lt;H:D&lt;2.3). We realized that also along the same lithology some zones are affected by enlargements and other remain undamaged. Therefore, we performed the geomechanical analyses on specimens from the same lithology but not affected by failures. Fifty-one uniaxial compressive tests were conducted on specimens belonging to four main rock types at different depths: biotite gneiss, diopside tremolite skarn, micaschist and serpentinite. Results from geomechanical test show UCS values range from 27 to 245 MPa with an average of 102 MPa and a standard deviation of 42, while the elastic Youngs modulus range from 3 to 20 GPa with an average of 7.3 GPa and a standard deviation of 2.8. Most samples collected within breakout zones have UCS values from 40 to 170 MPa and H:D ratio from 1.8 to 2.0, less that required by the standards. The samples outside of the breakout zones show UCS values from 27 to 186 MPa, and H:D ratio from 1.7 to 2.3. The hypothesis for testing was that borehole breakouts were formed in weaker rocks. Our results does not confirm this hypothesis, but the observed time-dependent deformation in Outokumpu borehole is interesting and calls for further studies.&lt;/p&gt;

Associations Between Motor Competence, Moderate-to-Vigorous Physical Activity, and Body Mass Index Among Preschoolers Over 1 Year

Background: To examine the associations between motor competence (MC), moderate to vigorous physical activity (MVPA), and body mass index (BMI) changes over 1 year in preschoolers. Methods: Fifty-four preschoolers (24 girls; 42.4%) aged 4–5 years old from the metropolitan area of Porto, Portugal comprised the sample. Height, body mass, and BMI were calculated. MC was assessed according to the Movement Assessment Battery for Children-2. MVPA was measured by accelerometry. For each participant, changes in MVPA, MC, and BMI over a year were computed. Different levels of MC were calculated; and then data were analyzed. Results: The MVPA increased over time in all levels of MC in the follow-up. The BMI decreased over time for all levels in follow-up (P = .001). The preschoolers classified as at a high level of MC were more likely to spend more time in MVPA (in minutes) than their counterparts with low MC in follow-up. Multiple linear regression analyses, adjusted by sex and age, were fit to predict Δ% MC by Δ% MVPA and Δ% BMI. The Δ% MC was positively associated with Δ% MVPA. Conclusion: Increases in MC were positively associated with MVPA. Higher performance in MC increases due to time spent in MVPA. Improvement of MC in young children has potentially relevant policy implications related to MVPA and public health.