Institute Of Mechanics,Chinese Academy of Sciences
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Effects of specimen size and hot isostatic pressing on high-cycle and very-high-cycle fatigue of additively manufactured Ti6Al4V
No full textThis study investigates the effects of specimen size and hot isostatic pressing (HIP) on the high-cycle fatigue (HCF) and very-high-cycle fatigue (VHCF) performance of additively manufactured (AMed) Ti6Al4V. Three groups of specimens were designed and fabricated. Two of them had control volumes of 50 mm3 and 8294 mm3, respectively, and the third group consisted of 50 mm3 subjected to HIP treatment. The results indicate that fatigue performance demonstrates a notable size effect as the control volume increases, with smaller specimens exhibiting higher fatigue strength. However, this size effect gradually diminishes with increasing failure cycles. For the HIP-treated specimens, crack initiation is no longer dominated by void defects but occurs due to alpha-phase grain cleavage. For the two groups without HIP treatment, a statistical analysis of crack initiation defects reveals that, in both HCF and VHCF states, the fatigue cracks in larger specimens always originate from internal defects. The average defect sizes are 109 mu m for large sized specimen group and 54 mu m for small sized specimen group. By using the probabilistic control volume model, the fatigue strength of large specimens was predicted based on the fatigue data of small specimens, and the prediction was consistent with the experimental data
Deterioration mechanism of adhesion properties of FRP-soil interface induced by moisture
No full textThe deterioration of fiber-reinforced polymer (FRP)-soil interfacial adhesion due to water intrusion has been a core issue in geotechnical engineering, but its microscopic mechanism remains unclear. In this study, molecular dynamics (MD) simulation method is employed to reveal the microscopic deterioration mechanism of water on adhesion properties of epoxy-quartz (i.e., FRP-soil subsystem) interface, the structural and dynamic characteristics of interlayer water film. The steered molecular dynamics pulling simulation and the modified Bell's model are used to evaluate the adhesion energy of epoxy-quartz interface in dry and wet cases. The simulation results show that (1) the interfacial water film weakens adhesion strength of epoxy-quartz interface, playing a dual role in "interface isolation" and "lubrication", aggravating the interfacial debonding. (2) The work of adhesion, maximum pulling force, potential of mean force, and adhesion energy of dry system are significantly higher than those of wet system. (3) The interlayer water film has a distinct layered structure: bound, free, and sparse water layers, which have different angle orientations and density distributions. (4) The diffusion coefficient increases with the rising thickness of free water layer, which may trigger a capillary-seepage effect and aggravate interface deterioration. This study provides atomic-scale insights into moisture-induced FRP-soil interface failure mechanism
Experimental Investigation of a Liquid Metal Mini-Channel Cooling System Coupled with Liquid Carbon Dioxide (CO2) Throttling Refrigeration
No full textVisible light-responsive hydrogels for cellular dynamics and spatiotemporal viscoelastic regulation
No full textViscoelastic heterogeneity of matrices plays a pivotal role in cancer cell spreading, migration, and metastasis. However, the creation of viscoelastic platforms with spatial-temporal regulation is hindered by cytotoxicity and short regulation durations. Our research presents a dual mechanism for stress relaxation regulation- both intrinsic and responsive- by incorporating Schiff base bonds and a visible light-responsive thiuram disulfide (TDS) moiety into the hydrogel. Modifying base bonds facilitates a broad spectrum of intrinsic stress relaxation times. At the same time, incorporating the visible light-responsive TDS moiety endows the hydrogel with responsive viscoelastic properties. These properties are characterized by minimal cytotoxicity, spatial-temporal controllability, dose dependency, and reversibility. Utilizing this platform, we demonstrate that ovarian cancer cells exhibit contrasting behaviors in contraction and spreading when subjected to dynamic stress relaxation changes over various time periods. Additionally, we observed a "memory effect" in the cell's response to alterations in stress relaxation time. We can spatially direct cell migration through viscoelastic heterogeneity, achieved via photopatterning substrates and laser spots. This innovative approach provides a means to regulate the viscoelasticity of hydrogels across a wide range of timescales, thereby opening avenues for more advanced studies into how cells interpret and respond to spatiotemporal viscoelastic signals
On the preprocessing of physics-informed neural networks: How to better utilize data in fluid mechanics
No full textPhysics-Informed Neural Networks (PINNs) serve as a flexible alternative for tackling forward and inverse problems in differential equations, displaying impressive advancements in diverse areas of applied mathematics. Despite integrating both data and underlying physics to enrich the neural network's understanding, concerns regarding the effectiveness and practicality of PINNs persist. Over the past few years, extensive efforts in the current literature have been made to enhance this evolving method, by drawing inspiration from both machine learning algorithms and numerical methods. Despite notable progressions in PINNs algorithms, the important and fundamental field of data preprocessing remain unexplored, limiting the applications of PINNs especially in solving inverse problems. Therefore in this paper, a concise yet potent data preprocessing method focusing on data normalization was proposed. By applying a linear transformation to both the data and corresponding equations concurrently, the normalized PINNs approach was evaluated on the task of reconstructing flow fields in four turbulent cases. The results illustrate that by adhering to the data preprocessing procedure, PINNs can robustly achieve higher prediction accuracy for all flow quantities under different hyperparameter setups, without incurring extra computational cost, distinctly improving the utilization of limited training data. Though mainly verified in NavierStokes (NS) equations, this method holds potential for application to various other equations
A fatigue perspective on damage accumulating in lithium-ion batteries under dynamic cycling
No full textLithium-ion batteries (LIBs) are playing an increasingly pivotal role in nowadays clean energy society. Similar to the fatigue behavior of solids and structures, the performance of LIBs also degrades under repeated usage, exhibiting a capacity decay during cyclic service. Battery fatigue seriously threats safety operation of the energy- using system, demanding a profound understanding on the cycle-life of LIBs. In order to quantify fatigue damage in LIBs, we construct an empirical fatigue map based on large-scale experiments at various constant charging and discharging rates. In combination with the empirical relationship between charging-rate C, discharging-rate D, and resultant cycle-life N, we formulate a damage function fi due to any cycling number ni at a constant charging- rate Ci and discharging-rate Di: fi = ni/Ni, where Ni is the cylcle-life of the battery at Ci and Di. The damage f in batteries under dynamic cycling profiles is assumed to be linear accumulated and follows the Palmgren-Miner rule, f = & sum; ifi. A failure state, with f = 1, can be conveniently assessed for batteries subjected to arbitrary dynamics cycling profiles. Experimental validation of the fatigue map and damage function exhibits a mean percentage of no more than 7.0 % and 2.1 %, respectively. The method reported here enables us to extend safety analysis from material scale to battery scale, and is therefore meaningful for cycle-life evaluation of LIBs, as desired in energy storage systems consisting of many cells
Attenuation of Richtmyer-Meshkov instability growth of fluid layer via double shock
No full textSuppression of the hydrodynamic instabilities involved in the inertial confinement fusion has attracted much attention but remains a challenge. In this work, we report the first theoretical analysis and experimental validation on attenuating the instability growth of a shock-accelerated fluid layer through a second shock impact. An analytical model is established to predict linear growth rates of the perturbations at two interfaces of the layer by considering both the effects of interface coupling and reverberating waves. Theoretically, there are nine possibilities for simultaneously attenuating the instability growths of perturbations at the two interfaces. Accordingly, shock-tube experiments are specially designed and conducted, and nine possibilities are all realized by experiments, which verifies the reliability of the analytical model and also demonstrates the feasibility of attenuating the instability growth of a fluid layer via double shock
Recent Developments and Future Directions in Flow Visualization: Experiments and Techniques
No full textFlow visualization has long been a critical tool for understanding complex fluid dynamics in both natural and engineered systems ..
Self-organization of multiple shear bands in CoCrNi chemically complex medium entropy alloys
No full textComplex concentrated alloys (CCAs), also known as medium/high entropy alloys (M/HEAs), possess a multitude of outstanding properties attributing to their distinctive chemically disordered structure, which endows them with broad application prospects in many engineering fields. As a fundamental and ubiquitous non-equilibrium phenomenon, shear localization has received significant attention during past several decades. However, the collective behavior of multiple shear bands in CCAs or M/HEAs has not been comprehensively elucidated. Here, we tackle this problem in CoCrNi medium entropy alloy by thick-walled cylinders technology. Via the experimental design, the specimens subjected to diverse deformations were effectively "frozen", thereby facilitating the acquisition of the self-organization characteristics of multiple shear bands in distinct evolution stages. A notable scaling law of multiple shear band spacing was identified. To uncover the underlying physical mechanism of the scaling law, a multiple shear band energy dissipation evolution dynamics model was formulated. Subsequently, a competing map of shear band nucleation and growth was established. It is found that the coordinated propagation of stacking faults and twins may trigger the transformation from the face-centered cubic structure to the hexagonal close-packed structure and even amorphization in late stage of shear band growth. The amorphization regions possess a high probability of serving as nucleation sites with a propensity for void formation. Eventually, with the progression of void evolution, fracture occurs
Long-term settlement of deepsea pipelines on a soft clayey seabed: Poro-elasto-viscoplastic modeling
No full textThe long-term settlement of subsea pipelines on a clayey seabed is crucial for the on-bottom stability of the pipelines, especially in deep waters. In this study, a poro-elasto-viscoplastic finite element analysis is performed for predicting long-term settlement of subsea pipelines by incorporating a rheological constitutive model. A method for identifying the creep-settlement (Sc) from the total-embedment (Sk) is proposed on the basis of the obtained linear relationship between the secondary consolidation coefficient (C alpha e) of the clayey soil and the total-embedment (Sk) of the pipe. The identifying method is validated with the existing theoretical solutions and experimental data. Parametric study is then performed to investigate the key influential parameters for long-term settlement of subsea pipeline. A non-dimensional parameter Gc is introduced to quantitatively characterize the soil rheology effect on pipeline settlement. The relationship between the proportion of creep-settlement in the total-embedment (Sc/Sk) and Gc is eventually established for identifying whether the proportion of creep-settlement in the total-embedment is remarkable