Institute Of Mechanics,Chinese Academy of Sciences
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Simultaneous improvement of strength and ductility in a P-doped CrCoNi medium-entropy alloy
No full textA newly developed P-doped CrCoNi medium-entropy alloy (MEA) provides both higher yield strength and larger uniform elongation than the conventional CrCoNi MEA, even superior tensile ductility to the otherelement-doped CrCoNi MEAs at similar yield strength levels. P segregation at grain boundaries (GBs) and dissolution inside grain interiors, together with the related lower stacking fault energy (SFE) are found in the P-doped CrCoNi MEA. Higher hetero-deformation-induced (HDI) hardening rate is observed in the Pdoped CrCoNi MEA due to the grain -to -grain plastic deformation and the dynamic structural refinement by high-density stacking fault-walls (SFWs). The enhanced yield strength in the P-doped CoCrNi MEA can be attributed to the strong substitutional solid -solution strengthening by severer lattice distortion and the GB strengthening by phosphorus segregation at GBs. During the tensile deformation, the multiple SFW frames inundated with massive multi-orientational tiny planar stacking faults (SFs) between them, rather than deformation twins, are observed to induce dynamic structural refinement for forming parallelepiped domains in the P-doped CoCrNi MEA, due to the lower SFE and even lower atomically-local SFE. These nano-sized domains with domain boundary spacing at tens of nanometers can block dislocation movement for strengthening on one hand, and can accumulate defects in the interiors of domains for exceptionally high hardening rate on the other hand. (c) 2024 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology
A nonparametric point-by-point method to measure time-dependent frequency in wavelength modulation spectroscopy
No full textA nonparametric point-by-point (NPP) method is presented for high-accuracy measurement of the timedependent frequency (laser frequency) in tunable laser absorption spectroscopy, crucial for ensuring ultimate measurement accuracy. In wavelength modulation spectroscopy in particular, the parametric methods in current use for time-dependent frequency measurement are insufficiently accurate and are difficult to apply to complex modulation scenarios. Based on a multi-scale viewpoint, point-by-point measurement of the frequency is realized by linear superposition of the frequency information mapped from the interferometric signal on a unit scale and on a local scale. Validation experiments indicate that the measurement accuracy of the proposed NPP method is three times that of the existing parametric methods, while effectively immunizing against non-ideal tuning effects. Additionally, the NPP method is suitable for use with arbitrarily complex modulations such as square wave modulation, for which parametric methods are inapplicable
A Trans-scale Shear-lag Model for Characterizing the Size Effect and Viscoelasticity of Staggered Shells
No full textNatural biomaterials with staggered structures exhibit remarkable mechanical properties owing to their unique microstructure. The microstructural arrangement can induce size-dependent and viscoelastic responses within the material. This study proposes a strain gradient viscoelastic shear-lag model to elucidate the intricate interplay between the strain gradient and viscoelastic effect in staggered shells. Our model clarifies the role of both effects, as experimentally observed, in governing the mechanical properties of these biomaterials. A detailed characterization of the size-dependent responses is conducted through the utilization of a microstructural characterization parameter alongside viscoelastic constitutive models. Then, the effective modulus of the staggered shell is defined and its formula is derived through the Laplace transform. Compared to classical models and even the strain gradient elastic model, the strain gradient viscoelastic model offers calculated moduli that are more consistent with experimental data. Moreover, the strengthening-softening effect of staggered structures is predicted using the strain gradient viscoelastic model and critical energy principle. This study contributes significantly to our understanding of the mechanical behavior of structural materials. Additionally, it provides insights for the design of advanced bionic materials with tailored properties
The Effect of Relative Humidity on Creep Behavior of Cement Paste Microprism
No full textDespite decades of extensive studies, the mechanism of concrete creep remains a subject of debate, mainly due to the complex nature of cement microstructure. This complexity is further amplified by the interplay between water and the cement microstructure. The present study aimed to better understand the creep mechanism through creep tests on microprisms of cement paste at hygral equilibrium. First, microprisms with dimensions of 150 mm x 150 mm x 300 mm were prepared by precision cutting from a cement paste specimen with a water-to-cement ratio of 0.4. Subsequently, uniaxial compression and creep tests were carried out on these microprisms in a chamber with controlled relative humidity (RH). To mitigate the impact of plasticity and damage, the applied peak load was set to generate a stress level that was approximately 40% of the compressive strength. Moreover, an analytical coefficient phi was formulated to account for the foundation effect on microprism creep, agreeing with the numerical analysis employing the finite element method. Our findings showed that the microscale creep compliance varied when the RH level was changed from 90% to 11%. Furthermore, logarithmic and power-law models were both applied to simulate creep curves. Lastly, the modeled creep behaviors were compared with those obtained by microindentation experiments in previous studies
The Effect of Relative Humidity on Creep Behavior of Cement Paste Microprism
No full textDespite decades of extensive studies, the mechanism of concrete creep remains a subject of debate, mainly due to the complex nature of cement microstructure. This complexity is further amplified by the interplay between water and the cement microstructure. The present study aimed to better understand the creep mechanism through creep tests on microprisms of cement paste at hygral equilibrium. First, microprisms with dimensions of 150 mm x 150 mm x 300 mm were prepared by precision cutting from a cement paste specimen with a water-to-cement ratio of 0.4. Subsequently, uniaxial compression and creep tests were carried out on these microprisms in a chamber with controlled relative humidity (RH). To mitigate the impact of plasticity and damage, the applied peak load was set to generate a stress level that was approximately 40% of the compressive strength. Moreover, an analytical coefficient phi was formulated to account for the foundation effect on microprism creep, agreeing with the numerical analysis employing the finite element method. Our findings showed that the microscale creep compliance varied when the RH level was changed from 90% to 11%. Furthermore, logarithmic and power-law models were both applied to simulate creep curves. Lastly, the modeled creep behaviors were compared with those obtained by microindentation experiments in previous studies
Overestimation of pore volume in high-TOC shales by low-temperature nitrogen adsorption: Phenomenon and cause analysis
No full textMarine shales exhibit pore structures spanning multiple scales, from nanometers to micrometers, necessitating a combination of various methods for comprehensive characterization. Helium expansion (HE) and lowtemperature nitrogen adsorption (LTNA) are commonly used in the industry. In this study, an anomalous phenomenon is observed that a considerable number of samples exhibit pore volume (PV) characterized by LTNA exceed that characterized by HE, which should be larger. The causes of these anomalies are not fully understood. A comparative study of the characterization results from these two methods is conducted on shale samples from the Wufeng and Longmaxi Formations in Well R8 in southern Sichuan Basin. First, the influence of sample size and sample weight on the LTNA-characterized PV is clarified to further confirm the objective existence of the anomalies. Subsequently, by comparing results from the two methods for samples with the same particle size, it is revealed that a strong correlation exists between the relative difference in the characterized PVs and the organic matter content. For high-TOC (Total Organic Content) shales, the LTNA-characterized PV approached or even exceeded that characterized by HE. Through the analysis of linear thermal expansion coefficients, the obtained result of organic matter falls within the range from previous researches, indicating that the skeleton of organic matter undergoes more significant shrinkage than inorganic minerals at liquid nitrogen temperature. This should be the primary reason for the overestimation of PVs characterized by LTNA in high-TOC shales. The findings can help refine characterization techniques, and enhance the accuracy of reservoir evaluations
Aerodynamic control of evaporative self-assembly in colloidal droplets
No full textThe evaporation of colloidal droplets on solid surfaces frequently results in the undesirable "coffee ring effect", a well-known phenomenon that has attracted significant attention across various fields, including inkjet printing, micro/nano fabrication, and coatings, due to its adverse implications. Although several control strategies, such as heating, exist to mitigate the coffee ring effect, to develop a simple, efficient, and non-contact universal approach still remains a significant challenge. In this study, we present an innovative approach to enhance the interfacial evaporation of droplets by implementing actively controlled airflow. This airflow generates intense internal motion within the droplet, promoting a more uniform dispersion of colloidal particles. Simultaneously, it significantly increases the evaporation rate at the liquid-air interface, facilitating the capture of colloidal particles and their arrangement into well-organized crystal structures. In contrast to conventional methods, this approach does not necessitate any alterations to the substrate or liquid, thereby demonstrating broader applicability. We are optimistic that this advancement will positively influence the fabrication of high-quality, highperformance printed electronics
Safety assessment of explosion fragment projection in a wind field
No full textRisk assessment plays a crucial role in the arrangement design of storage vessels with flammable fuels or explosible chemicals. Underestimating the safety distance between vessels may lead to a domino catastrophe caused by scattered fragments from an unexpected explosion: an individual explosion resulting in a chain of explosions. In this work, we proposed a general mathematical model to study the fragment trajectory after explosion, with a focus on how the trajectory is affected by wind. Considering the wind effect in the proposed model, we predicted the fragment trajectory and probability distribution by solving the equations of motion for a projectile in the quadratic-resistant medium. Our results show that the maximum projection distance of the fragment varies linearly with the wind speed and increases nonlinearly with the explosion energy. Also, the derived probability distribution of scattering fragments aids in estimating safety distances between vessels with explosive fuel, providing a guideline for the risk assessment for vessel arrangement
Fatigue Short Crack Growth Prediction of Additively Manufactured Alloy Based on Ensemble Learning
No full textIn situ fatigue crack propagation experiment was conducted on laser cladding with coaxial powder feeding (LCPF) K477 under various stress ratios and temperatures. Multiple crack initiation sites were observed by using in situ scanning electron microscopy (SEM). The fatigue short crack growth rate was measured, and the impacts of temperature and stress ratio on this growth rate were analyzed. Based on these experiments, the experimental data were expanded, and three ensemble learning algorithms, that is, random forest (RF), extreme gradient boosting (XGBoost), and light gradient boosting machine (LightGBM), were employed to establish a fatigue short crack growth rate model controlled by multiple parameters. It is indicated that the RF model performs the best, achieving a coefficient of determination (R2) of up to 0.88. The fatigue life predicted by the machine learning (ML) method agrees well with the experimental one
Mechano-gated iontronic piezomemristor for temporal-tactile neuromorphic plasticity
No full textIn bioneuronal systems, the synergistic interaction between mechanosensitive piezo channels and neuronal synapses can convert and transmit pressure signals into complex temporal plastic pulses with excitatory and inhibitory features. However, existing artificial tactile neuromorphic systems struggle to replicate the elaborate temporal plasticity observed between excitatory and inhibitory features in biological systems, which is critical for the biomimetic processing and memorizing of tactile information. Here we demonstrate a mechano-gated iontronic piezomemristor with programmable temporal-tactile plasticity. This system utilizes a bicontinuous phase-transition heterogel as a stiffness-governed iontronic mechanogate to achieve bidirectional piezoresistive signals, resulting in wide-span dynamic tactile sensing. By micro-integrating the mechanogate with an oscillatory iontronic memristor, it exhibits stiffness-induced bipolarized excitatory and inhibitory neuromorphics, thereby enabling the activation of temporal-tactile memory and learning functions (e.g., Bienenstock-Cooper-Munro and Hebbian learning rules). Owing to dynamic covalent bond network and iontronic features, reconfigurable tactile plasticity can be achieved. Importantly, bridging to bioneuronal interfaces, these systems possess the capacity to construct a biohybrid perception-actuation circuit. We anticipate that such temporal plastic piezomemristor devices for abiotic-biotic interfaces can serve as promising hardware systems for interfacing dynamic tactile behaviors into diverse neuromodulations