High Slip Research Articles

Micro-mechanisms of anisotropic deformation in the presence of notch in commercially pure Titanium: An in-situ study with CPFEM simulations

This study investigates the impact of notch severity and initial texture on the micro-mechanisms during low strain deformation in commercially pure Titanium, exploiting in-situ electron back scatter diffraction (EBSD) experiments and crystal plasticity finite element model (CPFEM). In-situ tests were performed at different strain steps of un-notched and notched samples of transverse direction (TD) and rolling direction (RD) orientations. CPFEM, based on initial EBSD microstructures, predicted profuse prismatic slip traces and early activation of prismatic slip in notched sample, with RD orientation exhibiting higher activity. Further, CPFEM results revealed early activation of high CRSS slip systems as well as evidence of early twin activity at notch tip due to severely localized plastic deformation and steep strain gradient, as observed by GND maps causing higher stress at grain boundaries. At the notch tip, digital images correlation (DIC) at microscale indicated strain localization at 45∘ and 90∘ to the tensile axis for TD and RD orientations, respectively. Furthermore, 2.5D and 3D CPFEM confirmed distinct strain patterns at notch tip: TD orientation exhibited combined basal and prismatic slip influences, while RD orientation displayed dominant prismatic slip systems at localized strain. The model also successfully predicted anisotropic surface roughness, contributing to early necking in RD orientation.

Clinical and Radiological Predictors of Slower and Non-Improvement Following Surgical Treatment of L4-5 Degenerative Spondylolisthesis: Preliminary Results.

Retrospective cohort. To identify the predictors of slower and non-improvement following surgical treatment of L4-5 degenerative lumbar spondylolisthesis (DLS). There is limited evidence regarding clinical and radiological predictors of slower and non-improvement following surgery for L4-5 DLS. Patients who underwent minimally invasive decompression or fusion for L4-5 DLS and had a minimum of 1-year follow-up were included. Outcome measures were: (1) minimal clinically important difference (MCID), (2) patient acceptable symptom state (PASS), and (3) global rating change (GRC). Clinical variables analyzed for predictors were age, gender, body mass index (BMI), surgery type, comorbidities, anxiety, depression, smoking, osteoporosis, and preoperative patient reported outcome measures (PROMs) (Oswestry Disability Index, ODI; Visual Analog Scale, VAS back and leg; 12-Item Short Form Survey Physical Component Score, SF-12 PCS). Radiological variables analyzed were slip percentage, translational and angular motion, facet diastasis/cyst/orientation, laterolisthesis, disc height, scoliosis, main and fractional curve Cobb angles, and spinopelvic parameters. 233 patients (37% decompression, 63% fusion) were included. At <3 months, high pelvic tilt (PT) (OR 0.92, P 0.02) and depression (OR 0.28, P 0.02) were predictors of MCID non-achievement and GRC non-betterment, respectively. Neither retained significance at >6 months and hence, were identified as predictors of slower improvement. At >6 months, low preoperative VAS leg (OR 1.26, P 0.01) and high facet orientation (OR 0.95, P 0.03) were predictors of MCID non-achievement, high L4-5 slip percentage (OR 0.86, P 0.03) and L5-S1 angular motion (OR 0.78, P 0.01) were predictors of GRC non-betterment, and high preoperative ODI (OR 0.96, P 0.04) was a predictor of PASS non-achievement. High PT and depression were predictors of slower improvement and low preoperative leg pain, high disability, high facet orientation, high slip percentage, and L5-S1 angular motion were predictors of non-improvement. However, these are preliminary findings and further studies with homogeneous cohorts are required to establish these findings.

High friction stress and weak grain-refinement strengthening effect induced by severe lattice distortion in ZrTiNb medium entropy alloys

In this work, we have studied the grain-refinement strengthening effect of body-centered cubic Zr50Ti35Nb15 medium entropy alloy. The results suggest that the yield strength increases as grain size decreases from 530 μm to 0.51 μm, reaching the maximum value of 651 MPa, and still having decent ductility. Moreover, it is found that the alloys exhibit a high Hall–Petch intercept of 564 MPa and a low Hall–Petch slope, which means strong lattice friction stress and weak grain-refinement strengthening. The high lattice friction stress originates from the obstruction of dislocation motion caused by atomic size and modulus misfit. Dislocation interaction and multiplication in grain interior is difficult due to the high dislocation slip resistance, leading to a weak dislocation pile-up capability at grain boundary. Instead, dislocations nucleation and emission become the dominant deformation process since low shear modulus promotes dislocation source activation.

Geochemical characteristics of hot springs in active fault zones within the northern Sichuan-Yunnan block: Geochemical evidence for tectonic activity

The geochemistry of the fluids is spatially closely related to faults and earthquakes that have been detected in the northern Sichuan-Yunnan (SC-YN) block. However, the processes and factors that control hydrothermal fluid circulation on a regional scale remain challenging. The geochemical circulation of the hot springs integrated with geological and geophysical data revealed the processes and controlling factors of the relationship between fluid circulation and tectonic activity. Our results showed that the hydrochemical type of the hot springs at the intersection of the Yushu-Ganzi fault (YS-GZF), Xianshuihe fault (XSHF) and Yunongxi fault (YNXF), Jinshajiang fault (JSJF) and Batang fault (BTF) as well as Ganzi-Litang fault (GZ-LTF) is composed of Na-HCO3 and Na-HCO3·Cl. It demonstrated higher reservoir temperature and circulation depth (5 − 7 km). The helium isotope (0.22 − 2.36 Ra) of the gas indicated that the mantle helium composition was up to 5 − 30 %. These hot springs may undergo water–rock-gas exchange reactions with deep fluids. Considering geological and geophysical background as well as previous studies, the geochemical characteristics of the hot spring at the intersections of faults in the north of the SC-YN block are thought to be controlled by the deep-driven upwelling lower crustal flows, mixing with shallow hot spring water and the temporal and spatial heterogeneity of the high strain fields, slip rates, and permeability of the fault intersections. Whereas, the transport of fluids in hot springs of fault may increase pore fluid pressure, and reduce the effective stress at the intersection of the fault zones, which can promote fault sliding and provoke seismic events as well as fault movements. It could result in the enhancement of regional tectonic activity. This study provides an important basis for seismic prediction with hot spring hydrochemistry stations.

Resolving the slip-rate inconsistency of the northern Dead Sea fault.

Reported fault slip rates, a key quantity for earthquake hazard and risk analyses, have been inconsistent for the northern Dead Sea fault (DSF). Studies of offset geological and archeological structures suggest a slip rate of 4 to 6 millimeters per year, consistent with the southern DSF, whereas geodetic slip-rate estimates are only 2 to 3 millimeters per year. To resolve this inconsistency and overcome limited access to the northern DSF in Syria, we here use burst-overlap interferometric time-series analysis of satellite radar images to provide an independent slip-rate estimate of ~2.8 millimeters per year. We also show that the high geologic slip rate could, by chance, be inflated by earthquake clustering and suggest that the slip-rate decrease from the southern to northern DSF can be explained by splay faults and diffuse offshore deformation. These results suggest a microplate west of the northern DSF and a lower earthquake hazard for that part of the fault.

Characterization of seismicity from different glacial bed types: machine learning classification of laboratory stick-slip acoustic emissions

Abstract Subglacial seismicity presents the opportunity to monitor inaccessible glacial beds at the epicentral location and time. Glaciers can be underlain by rock or till, a first order control on bed mechanics. Velocity-weakening, necessary for unstable slip, has been shown for each bed type, but is much stronger and evolves over more than an order of magnitude longer distances for till beds. Utilizing a de-stiffened double direct shear apparatus, we found conditions for instability at freezing temperatures and high slip rates for both bed types. During stick–slip stress-drops, we recorded acoustic emissions with piezoelectric transducers frozen into the ice. The two populations of event waveforms appear visually similar and overlap in their statistical features. We implemented a suite of supervised machine learning algorithms to classify the bed type of recorded waveforms and spectra, with prediction accuracy between 65–80%. The Random Forest Classifier is interpretable, showing the importance of initial oscillation peaks and higher frequency energy. Till beds have generally higher friction and resulting stress-drops, with more impulsive first arrivals and more high frequency content compared to rock emissions, but rock beds can produce many till-like events. Seismic signatures could enhance interpretation of bed conditions and mechanics from subglacial seismicity.

Developing a High Ductility Mg Alloy Via Non-basal Slips and Intergranular Coordination Induced by Li and Er Addition

Developing a High Ductility Mg Alloy Via Non-basal Slips and Intergranular Coordination Induced by Li and Er Addition

Application of machine learning to assess the influence of microstructure on twin nucleation in Mg alloys

Twin nucleation in textured Mg alloys was studied by means of electron back-scattered diffraction in samples deformed in tension along different orientations in more than 3000 grains. In addition, 28 relevant parameters, categorized in four different groups (loading condition, grain shape, apparent Schmid factors, and grain boundary features) were also recorded for each grain. This information was used to train supervised machine learning classification models to analyze the influence of the microstructural features on the nucleation of extension twins in Mg alloys. It was found twin nucleation is favored in larger grains and in grains with high twinning Schmid factors, but also that twins may form in the grains with very low or even negative Schmid factors for twinning if they have at least one smaller neighboring grain and another one (or the same) that is more rigid. Moreover, twinning of small grains with high twinning Schmid factors is favored if they have low basal slip Schmid factors and have at least one neighboring grain with a high basal slip Schmid factor that will deform easily. These results reveal the role of many-body relationships, such as differences in stiffness and size between a given grain and its neighbors, to assess extension twin nucleation in grains unfavorably oriented for twinning.

Spondylolisthesis in children younger than 10 years: Who will progress to a high grade slip?

Spondylolisthesis in children younger than 10 years: Who will progress to a high grade slip?

Electroosmotic flow and heat transfer characteristics of a class of biofluids in microchannels at high Zeta potential

Peristalsis is an important dynamic phenomenon in the field of biomedical research, and has great application prospects in microscale fluids. In recent years, this biomimetic (peristaltic) phenomenon has gained widespread attention due to its large-scale applications in various medical and industrial fields, such as radiation therapy, peristaltic blood pumps, and drug delivery systems. In this study, the electroosmotic flow and heat transfer characteristics are investigated under high wall Zeta potential and slip boundary conditions for a certain type of biological fluid that satisfies the Newtonian fluid model. Fluid flows under the joint action of external electric field, magnetic field, and Joule heating. Firstly, without using the Debye-Hückel linear approximation, the numerical solutions are given by using the Chebyshev spectral method for the nonlinear Poisson-Boltzmann equation, the fourth-order differential equation satisfied by the stream function, and the thermal energy equation. The results are compared with those obtained by using the Debye-Hückel linear approximation to demonstrate the effectiveness of the numerical method used in this study. Secondly, the effects of wall Zeta potential, Hartmann number &lt;inline-formula&gt;&lt;tex-math id="M11"&gt;\begin{document}$H$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M11.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M11.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, electroosmotic parameter &lt;inline-formula&gt;&lt;tex-math id="M12"&gt;\begin{document}$m$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M12.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M12.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, slip parameter &lt;inline-formula&gt;&lt;tex-math id="M13"&gt;\begin{document}$\beta $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M13.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M13.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; are discussed on the flow characteristics, peristaltic pumping, and trapping phenomena under electromagnetic environments, and the influence of Joule heating parameter &lt;inline-formula&gt;&lt;tex-math id="M14"&gt;\begin{document}$\gamma $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M14.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M14.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; and Brinkman number &lt;inline-formula&gt;&lt;tex-math id="M15"&gt;\begin{document}$Br$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M15.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M15.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; is explored on heat transfer characteristics. The results show that 1) wall Zeta potential plays an important role in controlling the velocity of fluid peristaltic flow; 2) the increase of electroosmotic parameter &lt;inline-formula&gt;&lt;tex-math id="M16"&gt;\begin{document}$m$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M16.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M16.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; and slip parameter &lt;inline-formula&gt;&lt;tex-math id="M17"&gt;\begin{document}$\beta $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M17.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M17.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; increases the flow velocity in the central region of the channel, while the increase of Hartmann number &lt;inline-formula&gt;&lt;tex-math id="M18"&gt;\begin{document}$H$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M18.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M18.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; hinders the flow of fluid; 3) these flow behaviors exhibit opposite trends near the channel walls; 4) the number of streamlines captured by peristaltic transport decreases with Hartmann number &lt;inline-formula&gt;&lt;tex-math id="M19"&gt;\begin{document}$H$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M19.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M19.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; and electroosmotic parameter &lt;inline-formula&gt;&lt;tex-math id="M20"&gt;\begin{document}$m$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M20.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M20.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; increasing; 5) the increase of Joule heating parameter &lt;inline-formula&gt;&lt;tex-math id="M21"&gt;\begin{document}$\gamma $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M21.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M21.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; and Brinkman number &lt;inline-formula&gt;&lt;tex-math id="M22"&gt;\begin{document}$Br$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M22.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231685_M22.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; leads temperature to rise.

Spatial Relationships Between Coseismic Slip, Aseismic Afterslip, and On‐Fault Aftershock Density in Continental Earthquakes

AbstractDamaging aftershock sequences often exhibit considerable spatio‐temporal complexity. The stress changes associated with coseismic slip and aseismic afterslip are commonly proposed to drive aftershock sequences, but few systematic studies exist and do not always support strong, universal driving relationships. To investigate the roles that these two sources of stress changes may play in driving aftershocks, we assess the spatio‐temporal relationships between coseismic slip, afterslip, and on‐fault (within 5 km) aftershock density following seven Mw6.0–7.6 continental‐settings earthquakes, using available high‐quality slip models and regional seismic data. From previous empirical work and frictional considerations, near the mainshock we expect coseismic slip and afterslip to be anti‐correlated, and aftershocks to occur where coseismic slip is low/zero, near high slip gradients, and/or to migrate with afterslip. However, we find that spatial relationships between afterslip and coseismic slip, and between afterslip and aftershock density differ between earthquakes. Aftershock density correlates with coseismic slip following five of the earthquakes, and with total cumulative slip (coseismic slip + afterslip) following six: indicating that on‐fault aftershock distributions may be approximated by total slip (at current resolutions). Additionally, we find that the gradients of coseismic slip and afterslip (proxies for new stress concentrations) do not clearly correlate with aftershock distributions and that the choice of spatial domain over which relationships are tested can affect results significantly. A possible explanation of these results is that fault zones contain considerable fine‐scale structural and frictional heterogeneity. Nonetheless, the empirical evidence for frequently assumed relationships between coseismic slip, afterslip and on‐fault aftershocks is mixed.

Research on Micro Gap Flow Field Characteristics of Cylindrical Gas Film Seals Based on Experimental and Numerical Simulation

Flexible support cylindrical gas film seals (CGFSs) adapt well to rotor whirling and have a good gas lubrication effect during thermal deformation. However, when a CGFS operates under the “three high” (high interface slip speed, high-pressure differential, and high ambient temperature) operating conditions, the complex deformation of the support structure is a crucial factor affecting the stability of the CGFS. A thorough and systematic analysis of the micro gap flow field characteristics of flexible support CGFSs is a fundamental problem when we study the deformation of the support structure under multiple physical field conditions. This study uses a cylindrical gas film high-speed rotor test rig to study and compare the sealing characteristics of experiments and numerical simulations and then optimizes and verifies the accuracy and effectiveness of the simulation model. A cross-scale gas film grid model is used to analyze the flow field characteristics and seal ability of different groove models and compare the mechanical characteristics and sealing performance. We also analyze the gas film pressure distribution in micro gaps and explore the impact of dynamic pressure groove microstructure on flow field characteristics. Results show that micro gaps are the primary conditions for generating hydrodynamic effects, and high rotational speed, high-pressure differential, and large eccentricity have a significant effect on improving hydrodynamic effects and enhancing gas film stability. However, an increase in these parameters can cause an increase in leakage rate. A single flow channel makes it easier to improve the hydrodynamic effect, gas film load-bearing ability, and gas film stability while reducing leakage rate. The analyses in this study supplement and improve the theory of the flow field characteristics of cylindrical annular micro gaps and provide a theoretical basis for exploring the relation between the support structural parameters of the CGFS and the mechanical characteristics of the micro gap flow field. This study provides important guidance to the establishment of a quantitative design theory of supporting structures.

Combustion of liquid ammonia and diesel in a compression ignition engine operated in high-pressure dual fuel mode

This study investigates the characteristics of a compression ignition engine fuelled by ammonia and diesel in high-pressure dual fuel mode. The study focuses on the effect of injection strategies on engine performance and important emissions like NH3, NO/NO2 and N2O. The engine was operated with fixed intake air conditions and at an engine speed of 1500 rpm for all operating points, and liquid ammonia was directly injected at 180 bar using a GDI injector. The ammonia energy shares tested were 40 %, 50 % and 60 %. Various combustion modes were achieved by fixing the diesel injection timing at −15 CAD aTDC and varying the ammonia injection timing between -80 and 2.5 CAD aTDC. Injecting ammonia early (-80/-60 CAD aTDC) led to premixed-type combustion with very high ammonia slip (65 %). Delaying the ammonia injection to -30 CAD aTDC, i.e. 15 CAD before the diesel injection, yielded a very long ignition delay due to the strong influence of the ammonia injection on the diesel injection, resulting in premixed combustion of ammonia and diesel. Injecting ammonia simultaneously or after diesel did not affect the diesel ignition, yielding stable combustion where the ammonia burned during the mixing-controlled phase. Temporally overlapping injections of ammonia and diesel resulted in the highest combustion efficiency, lowest ammonia slip, highest NOx emissions, and lowest N2O emissions, i.e., the optimal cases found. For temporally overlapping ammonia and diesel injections, extending the ammonia injection to after the end of diesel injection was found to increase ammonia slip compared to injecting ammonia before diesel, due to the limited time for liquid ammonia to vaporise, mix and combust in the expansion stroke. The NOx and N2O emissions were found to have opposite trends, where the highest NOx and lowest N2O concentrations were achieved for the operating points with the highest combustion efficiency. Delaying the combustion phasing improved the combustion efficiency for the 40 % and 50 % ammonia energy share cases, while for the 60 % cases, it deteriorated, which can be explained by the injection of ammonia after the end of diesel injection for the 60 % ammonia energy share cases.

Study on the physicochemical properties of Chinese PVA fibers: Toward low-cost cement-based composites

Engineered Cementitious Composites (ECC) reinforced by Japanese Polyvinyl Alcohol (PVA) fiber showed excellent tensile ductility, which attracted much attention in the field of civil engineering in recent years, but the application was still limited by cost. There were quite a few kinds of low-priced PVA fibers in China, with a tremendous difference in physical and chemical properties. In this paper, a variety of typical PVA fibers produced in different regions in China were compared with the products imported from Japan to analyze the performance differences, especially the dispersion and enhancement effect in fiber reinforced cement matrix composites. Combining with the physical and chemical characteristics of each fiber, the relationship between the characteristics of fibers and the properties of composites was summarized. The experimental results illustrated the strength and interface characteristics of PVA fibers were the dominating influencing factors to the bending and tensile properties of PVA-ECC, while hardly affected the compressive strength. Insufficient intrinsic strength of fibers significantly decreased bending resistance and tensile strength. Excessive oil agent treated PVA fibers performed lower interfacial reaction with the cement matrix, meanwhile original PVA fiber with high hydrophilicity was not conducive to the dispersion and bridging function. The appropriate interface treatment approach could guarantee the fibers to achieve the sliding pull out bridge connection, and also meet the high slip strengthening effect, leading to the multi-seam cracking and strain hardening characteristics of ECC material. This work provided the preparation of low-cost cement-based composites, guiding the selection of fiber raw materials in ECC.

A terramechanics model for high slip angle and skid with prediction of wheel-soil interaction geometry

Previously developed terramechanics models of wheel-soil interaction forces do not cover the full span of possible wheel states, including large slip angles and ratios. This paper synthesizes a model that covers the full range of slip and skid ratios and slip angles by building on classic terramechanics and soil failure models. The need for wheel and soil specific tuning is reduced through use of a closed-form model of soil flow around the wheel to determine the wheel-soil contact geometry. The terramechanics model is validated both with and without the soil flow model on two wheels in sand for slip ratios from −1 to 0.9 and slip angles from 0° to 60°, showing good prediction of tractive forces, sidewall forces, and sinkage over a wide variety of states. The data from these experiments is also presented, as the only open source data set to cover both a high range of slip angles and slip ratios.

Achieving strength-ductility synergy in a laser-powder bed fused near-α titanium alloy through well-crafted heat treatments

The design of a two-step heat treatment (solutionizing and aging) protocol for laser-powder bed fused Ti-6Al-2Sn-4Zr-2Mo (L-PBF-Ti-6242) and its effect on microstructure and mechanical properties are studied. The heat treatment is designed considering the kinetics of α’ to β transformation and nanotwin annihilation with an emphasis on preserving the unique, ultrafine, and hierarchical microstructure. The solutionizing temperature of 900 °C for 10 and 20 min is selected based on the α’ to β transformation percentage. The aging temperatures of 300 °C and 350 °C for 12–72 h are chosen considering the kinetics of nanotwin annihilation. A total of 15 conditions are evaluated from these solutionizing and aging parameters including as-built, only solutionized, solutionized-aged, and direct aging. The as-built microstructure has the highest strength and lowest ductility due to the ultrafine acicular α’ martensite and dense dislocation network. The solutionized microstructure has α/α’and β phases with different dislocation densities. This condition results in the lowest strength and highest ductility, governed by the presence of the bcc phase (β), and high mean effective slip length in the α/α’ phase. The aging process (following the solutionizing step) results in changes in dislocation substructure in the α/α’ phase which leads to an increase in strength, controlled by a reduction in mean effective slip length. The formulated two-step heat treatment leads to the best strength-ductility synergy in this study.

Push-pull locomotion: Increasing travel velocity in loose regolith via induced wheel slip

Push–pull locomotion is an effective mobility mode for traversing loose lunar regolith and climbing sandy slopes. A rover with an active suspension can generate thrust from a set of anchored wheels by adjusting its wheelbase while driving the remaining wheels. This paper explores the relationship between the velocities of the rotational and translational suspension elements. Using a kinematic slip greater than 30%–40%, inchworming surpasses both the travel velocity and power efficiency of normal driving on slopes between 10°–20°. On a 20°slope, inchworming improves travel reduction from 98% to 85% and reduces normalized power consumption by a factor of eight. Experiments with NASA’s upcoming Volatiles Investigating Polar Exploration Rover show that increasing kinematic slip increases its travel velocity in a sink tank by 35%. Models using granular resistive force theory indicate that wheels driving at higher slip can generate greater tractive force and thus reduce the load on the anchored wheels. Otherwise, at lower driving slip, the load capacity of anchored wheels may be exceeded and result in oscillatory overall travel. These experiments suggest that there is further room to improve wheeled locomotion by intentionally inducing wheel slip, especially in articulated suspensions.

Effect of Surface Coating Condition on High‐friction Organic Zinc‐rich Paints for HSFB Joints

AbstractWith the development of paints, high‐friction organic zinc‐rich paints with slip coefficients more than 0.45 have been advanced, making it possible to obtain more sophisticated and higher quality high strength bolted friction joints. Moreover, comparing to the inorganic zinc‐rich paints used at present, organic zinc‐rich paints are more appropriate for using in situ construction. However, since the application conditions of organic coatings have not been specified, it is recommended that a slip test should be carried out separately for each surface preparation to confirm the slip coefficient. In this study, slip tests were carried out on high strength bolted friction joint specimens to investigate the influence of high‐friction organic zinc rich paint film thickness and surface preparation on the slip coefficient. Furthermore, based on the experimental results, a surface preparation that can consistently produce a high slip coefficient is proposed.

Principal slip zone in kaolinite gouge: A seismic slip indicator?

Some fault gouges (e.g., kaolinite) exhibit velocity-strengthening behavior and slide stably at low, subseismic slip rates (e.g., 1–10 μm/s), accompanied by the preferential development of foliation rather than a principal slip zone or a discrete narrow band of large shear strain. However, a remarkable observation from experimental gouges sheared at seismic slip rates (>0.1 m/s) is that all the gouges show a well-developed principal slip zone, irrespective of their frictional behaviors (velocity weakening or velocity strengthening) at subseismic slip rates. These observations imply that in some gouges, a principal slip zone develops only at seismic slip rates and can be used as a seismic slip indicator. To test this idea, we conducted shear tests on dry kaolinite powder and wet kaolinite paste at low (0.1–100 μm/s), intermediate (∼1 mm/s), and high (1 m/s) slip rates and at a normal stress of 3 MPa. The dry powder specimen recovered after the experiments showed a principal slip zone at all slip rates. In contrast, the paste specimens showed a principal slip zone only at the seismic slip rate. They display foliation and R-shears at low and intermediate slip rates, indicating the occurrence of distributed shear. The microstructure of the wet paste at the seismic slip rate is similar to that reported from a natural kaolinite-rich seismic slip zone. Considering the experimental results, the structures of the experimental and natural seismic slip zones, and the unlikely fault slip under dry conditions, we suggest that kaolinite gouges with principal slip zone(s) can be a seismic slip indicator. Further studies may be extended to other gouge materials showing similar velocity strengthening and stable sliding at subseismic slip rates to determine whether the same conclusion can be drawn.

Performance and emission characteristics of an ammonia/diesel dual-fuel marine engine

This study explores the challenges and possibilities of using ammonia (NH3) as a carbon-free fuel for marine propulsion in a Wärtsilä ammonia/diesel dual-fuel engine using a reactivity-controlled compression ignition (RCCI) concept. The main issues in ammonia RCCI engines are high ammonia slip and high emissions of nitrogen oxides and nitrous oxide. A joint experimental and computational investigation was conducted to understand the combustion process, pollutant and greenhouse gas (GHG) formation mechanisms, and the effects of injector configuration and injection timing on engine performance. A comparative assessment between the ammonia/diesel RCCI engine and a baseline natural gas/diesel RCCI engine showed that, upon replacing premixed natural gas with ammonia and maintaining the same energy share of diesel (8.5% of the total energy from diesel), the engine yielded considerably poor combustion efficiency. Increasing diesel usage to 24% share of the total energy allowed a successful engine operation, cutting GHG by 70%. However, higher diesel usage increased CO and CO2 emissions. N2O emission was attributed to the slow premixed ammonia/air flame propagation and near-wall flame quenching. The primary sources of NO emissions in ammonia/diesel RCCI engines were identified as fuel-NOx from premixed ammonia oxidation and thermal NOx in the diesel flame region. A recommendation was put forth for enhancing the operating conditions and injection strategies of ammonia RCCI engines. The proposed operation and injection strategy results in a 45% reduction in CO emission, a 60% reduction in total GHG emissions, and, notably, an 89% decrease in CO2 emissions compared to the LNG/diesel engine.